Optistruct Optimization 90 Vol1 Manual

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OptiStruct Optimization Concept Design and Structural Optimization Volume I

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I HyperWorks 9.0

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Table of Contents

OptiStruct Optimization Concept Design and Structural Optimization

Volume I

Chapter 1: Introduction to OptiStruct ................................................................... 1

Chapter 2: Topology Optimization ...................................................................... 15

Chapter 3: Topography Optimization................................................................ 121

HyperWorks 9.0 II


III HyperWorks 9.0


Chapter 1

Introduction to OptiStruct

What is OptiStruct? Altair OptiStruct is a finite element and multi-body dynamics software which can be used to design and optimize structures and mechanical systems. OptiStruct uses the analysis capabilities of RADIOSS and MotionSolve to compute responses for optimization.

Structural Design and Optimization

Structural design tools include topology, topography, and free-size optimization. Sizing, shape and free shape optimization are available for structural optimization.

In the formulation of design and optimization problems, the following responses can be applied as the objective or as constraints: compliance, frequency, volume, mass, moment of inertia, center of gravity, displacement, velocity, acceleration, buckling factor, stress, strain, composite failure, force, synthetic response, and external (user defined) functions. Static, inertia relief, nonlinear gap, normal modes, buckling, and frequency response solutions can be included in a multi-disciplinary optimization setup.

Topology, topography, size, and shape optimization can be combined in a general problem formulation.


Chapter 1: Introduction to OptiStruct

HyperWorks 9.0 OptiStruct Optimization 1

Copyright © 2008 Altair Engineering, Inc. All rights reserved. Altair Proprietary and Confidential Information

A World Class Suite of CAE Tools

HyperMeshHyperViewHyperGraphHyperFormMotionView

WHAT IS ALTAIR HYPERWORKS?

MotionSolveOptiStructHyperStudyHyperViewPlayerHyperWebAltair HyperWorks

HyperViewHyperMesh

HyperGraph

HyperForm

MotionView MotionSolveOptiStruct

HyperStudy

HyperView PlayerHyperWeb


What is OptiStruct

• An Optimizer with a Finite Element and Multi-body dynamics solver integrated

• Used for the design, analysis and optimization of structures and mechanical systems

• OptiStruct Structural Optimization solutions:• Topology

• Topography

• Shape and Size

• Free Size and Free Shape



2 OptiStruct Optimization HyperWorks 9.0


Optimization Definitions:

• Topology: is a mathematical technique that optimized the material distribution for a structure within a given package space

• Free Size: is a mathematical technique that produces an optimized thicknessdistribution per element for a 2D structure.

• Topography: Topography optimization is an advanced form of shape optimization in which a design region for a given part is defined and a pattern of shape variable-based reinforcements within that region is generated using OptiStruct .

• Shape: is an automated way to modify the structure shape based on a predefined shape variables to find the optimal shape.

• Size: is an automated way to modify the structure parameters (Thickness, 1D properties, material properties, etc…) to find the optimal shape.

• Free Shape: is an automated way to modify the structure shape based on set of nodes that can move totally free on the boundary to find the optimal shape.


Optimization Terminology:

• Design Variables: System parameters that are varied to optimize system performance.

• Design Space: selected parts which are designable during optimization process. For example, material in the design space of a topologyoptimization

• Response: Measurement of system performance.

• Objective Function: Any response function of the system to be optimized. The response is a function of the design variables. Ex. Mass, Stress, Displacement, Moment of Inertia, Frequency, Center of Gravity, Buckling factor, and etc.

• Constraint Functions: Bounds on response functions of the system that need to be satisfied for the design to be acceptable.

• Feasible Design: One that satisfies all the constraints.

• Infeasible Design: One that violates one or more constraint functions.

• Optimum Design: Set of design variables along with the minimized (or maximized) objective function that satisfy all the constraints.





Structural Optimization Concepts

The Optimization Problem Statement:

• Objective (What do I want?)

min f(x) also min [max f(x)]

• Design Variables (What can I change?)

XiL � Xi � Xi

U i =1,2,3,…N

• Design Constraints (What performance targets must be met?)

gj(x) � 0 j = 1, 2, 3, …, M

Note: The functions f(x), gi(x), can be linear, non-linear, implicit or explicit, and are continuous

Example: Explicit y(x) = x2 – 2xImplicit y3 – y2x + yx - � x = 0


Optimization Problem Example

• A cantilever beam is modeled with 1D beam elements and loaded with force F=2400 N. Width and height of cross-section are optimized to minimize weight such that stresses do not exceed yield. Further the height h should not be larger than twice the width b.






• Objective• Weight: min m(b,h)

• Design Variables• Width: bL < b < bU, 20 < b < 40

• Height: hL < h < hU, 30 < h < 90

• Design Region: All beam elements

• Design Constraints:

σσσσ (b,h) ≤ σmax, with σmax = 160 MPa

τ (b,h) ≤ τmax, with τmax = 60 MPa

h ≤≤≤≤ 2*b



Mathematical Design Space

Beam width, b (mm)

Bea

m h

eigh

t, h

(mm

)





Interpreting the Results

• Objective• Did we reach our objective?

• How much did the objective improve?

• Design Variables• Values of variables for the improved design

• Constraints• Did we violate any constraints?


Interpreting the resultsWhat can go wrong?

• Local minimum vs. global minimum

• Solution might not be available with the given objective, constraints and design variables – over constrained

• Efficiency of Optimization

• Relation between constraints and design variables wrt their numbers

• Unconstrained Optimization Problem

• Optimization problem setup is not appropriate

• Issues related to FEA modeling

• Stress constraints on nodes connected to rigids





How Structural Optimization Cuts Development Time

• Most of the product cost is determined at the concept design stage

• Problem:minimum knowledge, but maximum freedom

• Need: effective concept design tools to minimize downstream “re-design” costs and time-to-market


Structural DesignAltair-Bus

CAD model withgeneric elements

System Level Requirements(Loads analysis and packaging)

Parametric Shape VectorsFinite Element

Modeling

Package Space and Loads

Size and Shape Optimization

Altair OptiStruct®

Final Design

Optimization in Practice: Altair Bus





OptiStruct vs. HyperStudy: When to Use Which Tool?


OptiStruct Features: Input decks• Nastran Style ASCII Input Format

• Elements

• 3D Shell: TRIA3/6, QUAD4/8

• 3D Solid: TETRA4, TETRA10, PENTA6, PENTA15, PYRA5, PYRA13, HEXA8, HEX20

• 1-D Elastic: ROD, TUBE, BAR, BEAM, ELAS1, ELAS2, BUSH

• 1-D Rigid: RROD,RBAR,RBE2, RBE3

• Concentrated Mass : CONM, CMASS

• CWELD, CVISC, CDAMP, CGAP (Non-Linear gap element), CGAPG (node-patch nonlinear gap element)

• Composite Material Properties (PCOMP(G))

• Load Types

• Forces, Pressures, Moments, Enforced Displacements, Thermal Loads, Radial Loads, Gravity Loads, Distributed Loads on 1D

• Dynamic loads





OptiStruct Features: Results• Output

• Displacements, Rotations, Velocity, Acceleration

• Stresses – Von mises, Normal, Shear, Principal, Grid Point, Corner stress

• Strains – Von mises, Normal, Shear, Principal

• Element Strain Energy and Strain Energy Density

• Element Densities – Topology optimization

• Shape Changes – Shape/Topography optimization

• Element Thickness – Size/Free-Size optimization

• SPC (Reaction-) Forces, MPC Force, Grid Point Forces, Element Forces

• Sensitivity Analysis output

• Output Result Formats

• HyperMesh Binary Format (Default) (.res)

• Altair H3D format (Default) (HyperView and HyperViewPlayer)

• OptiStruct ASCII Format

• NASTRAN Punch file Format (.pch)

• NASTRAN OP2 Format (.op2)

• PATRAN ASCII Format


OptiStruct Features: Optimization Responses

• Compliance, strain energy (COMP) – Total and Regional• Weighted Compliance (WCOMP)• Natural Frequency (FREQ)• Inverse of Weighted Eigenvalues (WFREQ)• Combination of Weighted Compliance and Weighted Inverse Eigenvalues (COMB)• Mass (MASS), Volume (VOLUME) – Total and Regional• Mass Fraction (MASSFRAC), Volume Fraction (VOLFRAC) – Total and Regional, only used

in topology optimization• Nodal Displacements (DISP)• Stress (STRESS)• Buckling Mode (LAMA)• Center of Gravity (COG)• Force (FORCE)• Mass Moments of Inertia (INERTIA)• Strain (STRAIN)• Composite stress, strain, failure (CSTRESS, CSTRAIN, CFAILURE)• Frequency response displacements, velocity, acceleration (FRDISP, FRVELO, FRACCL)• Frequency response stress (FRSTRE), strain (FRSTRA)• Frequency response force (FRFORC)





OptiStruct Input - optimization

• I/O Option Section

• Case Control Section

• Define Load Cases (Sub Cases, Load Steps)

• Definition of Objective and Constraint Reference

• Bulk Data Section

• Optimization Problem

� Design Variables

� Responses

� Constraints

• Optimization parameters (DOPTPRM)

• Finite Element Model


Response Definition

• DRESP1

• Simple response definition

• Mass, mass fraction, volume, volume fraction, compliance, frequency, displacement, stress, strain, force, composite responses, weighted compliance, weighted frequency, and compliance index, frequency response analysis responses

• DRESP2

• Response definition using a user defined function

• Defines responses as function of design variables, grid location, table entries, responses, and generic properties

Example: Average displacement of two nodes:

• DRESP3

• Response definition using a user defined external function

• External function may be written in C (C++) or Fortran

2),(

2121

xxxxF

+= Where x1, x2 are nodal displacements





Constraint and Objective definition

• DCONSTR

• Defines Responses as optimization constraints.

• Relates response to lower and/or upper bound

• DCONADD

• Adds constraints under same id

• DESSUB, DESGLB

• Load case dependent, and independent reference in Case Control Section

• DESOBJ

• Load case dependent, and independent reference in Case Control Section

• Min/max


Constraint and Objective Definition: Load Case Reference

Objective and design constraints need to be defined load case dependent if the response is a reaction to a load

• Load case dependent

• Compliance, frequency, displacement, stress, strain, force, composite responses

• Functions using these responses w/o load case assignment

• Load case in-dependent (global)

• Mass, mass fraction, volume, volume fraction, center of gravity,moments of inertia, weighted compliance, weighted frequency, compliance index

• Functions using these responses

• Functions using compliance, frequency, displacement, stress, strain, force, composite responses with load case assignment





Optimization Tools:

• DEQATN

• Defines an equation

• Linked to DVPREL2, DRESP2 for user defined property or response.

• DTABLE

• Defines constants used in DEQATN

• Linked to DVPREL2, DRESP2

• DSCREEN

• Constraint screening definition

• DOPTPRM

• Optimization parameter definitions

• Max number of iterations, minimum member size control, moving limits, tolerances


Optimization Setup in HyperMesh

• Optimization Panel (Analysis page)

• Optimization problem set up

• OptiStruct Panel (Analysis page)

• Launch OptiStruct solution

• OSSmooth Panel (Post page)

• Generate geometry from topology results





Optimization Setup module in HyperMesh

• Definition of Design Variables

• Definition of Responses, Constraints and Objective

• Definition of Equations

• Optimization Control, Constraint Screening







Chapter 2

Topology Optimization

Setting up Topology Optimizations Topology optimization generates an optimized material distribution for a set of loads and constraints within a given design space. The design space can be defined using shell or solid elements, or both. The classical topology optimization set up solving the minimum compliance problem, as well as the dual formulation with multiple constraints are available. Constraints on von Mises stress and buckling factor are available with limitations. Manufacturing constraints can be imposed using a minimum member size constraint, draw direction constraints, extrusion constraints, symmetry planes, pattern grouping, and pattern repetition. A conceptual design can be imported in a CAD system using an iso-surface generated with OSSmooth, which is part of the OptiStruct package.

Free-size optimization is available for shell design spaces. The shell thickness or composite ply-thickness of each element is the design variable.


Chapter 2: Topology Optimization



Optimization Disciplines

Topology optimization

Method to find the optimum material distribution in a given design space

Topography optimization

Method to evaluate the optimum stiffening pattern on a thin part

TopologyTopography


Fundamental Procedure of Topology Optimization

“old” design

design proposal





Design Variables Topology Optimization

Density = 1

Density = 0 E/E0

ρ/ρ0

(ρ/ρ0)p

1

1

Density MethodVery robust

Penalty FactorMore discrete design proposals

What does OptiStruct change?


OptiStruct Input: Topology Optimization

DTPL card – Design Variable definition for topology optimization

• Shells - Property with base and total thickness defines topology design space

• Solids – Properties define topology design space

• Composites (PCOMP) - Properties define topology design space

• Rod, Bar, Weld , Bush- Properties define topology design space

• Stress constraints bounds

• Manufacturing constraints definition

HyperMesh Topology panel:





Topology optimization on PCOMP

• Increase/decrease the thickness of given ply angle

• Ability to optimize the angle as well by creating “phantom” ply

Optimized PCOMP

0

• mat option on DTPL

• Ply � ply based PCOMP (default)

• Homo � homogenized PSHELL

PCOMP

45

- 4590

0

X

y z

0


Exercise 2.1 : Design Concept for a Structural C-clip

• Import geometry into HyperMesh

• Define material and element properties

• Mesh the model

• Apply constraints and loads (boundary conditions)

• Run baseline analysis; check results

• Set up the optimization problem:

• Define the design space

• Create responses for volume and nodal displacements

• Set design constraints on the displacement responses

• Define the objective function

lbub ddddVol ≥∧≤∈ 21)min(





OSSmooth: Geometry Extraction of Optimization Results

• A Geometry creation tool for Topology/Topography/Shape Optimized models

• Supports different output formats (IGES, STL, H3Detc.)

• Advanced geometry smoothing options for smoother surfaces

• Surface reduction option to reduce the size of IGES and STL files

• Integrated into HyperMesh and is easy to use

IGESIGES


Optimization Example: Engine Mount Bracket

Six load cases:

• start

• backwards

• into pothole

• out of pothole

• attachment loads

• engine transport

Optimization Problem:

• Minimize mass

• Maintain stiffness, strength

Courtesy Volkswagen AG, WolfsburgCourtesy Volkswagen AG, Wolfsburg





Shape OptimizationShape OptimizationSizing OptimizationSizing Optimization


Topology OptimizationTopology Optimization

Preliminary Preliminary DesignDesign

Design Design SpaceSpaceLoadsLoads

Final Final DesignDesign

Topology OptimizationTopology OptimizationGeometry RecoveryGeometry Recovery

Engine Mount Bracket: Optimization Design Process



Engine Mount Bracket: Results

Topology ResultsInitial Design Concept





Mass: 730g (-20%)Same stiffness, strength


Engine Mount Bracket: Comparison

Original Design Optimized Design


Courtesy TECOSIM GmbH, RuesselsheimCourtesy TECOSIM GmbH, Ruesselsheim

Topology Optimization Example: Radiator Bracket

• Original bracket failed

• Reduce stress in bracket

• Single load case






Topology Optimization results




Interpretation of OSSmooth results in CAD







OriginalDesign

OptimizedDesign


Max. v. Mises Stress Max. Displ. Mass


• Task: Stiffening of a bulk head using ribs

• 2 load cases

• Hydrostatic load (fuel)

• Take-off

Pressure load on blue part

• Clamped perimeter

• 2 man holesDesign space

Topology Optimization Example: Bulkhead Stiffeners





Stiffening

• Optimization between sheet thickness and rib hight


Topology Results


Max. Deflection:85%

Original layout Optimized design

Max. Deflection:100%






Exercise 2.2 : Design Concept for an Automotive Control Arm

• Define three different load cases

• Define responses for volume and nodal displacements

• Set design constraints on nodal displacements for each load case

• Define the objective function: min(vol)


Exercise 2.3 : Increasing Natural freq. of an Auto Splash Shield

• Setup the normal modes analysis in HyperMesh

• Run the analysis and post-process in HyperView

• Define the optimization problem

• Run the optimization and post-process

• Setup the final modes analysis in HyperMesh

• Run the analysis and post-process in HyperView





Exercise 2.4: Sym. and Draw Dir. Constraints in a Top. Opt.

• Set up the FE model in HyperMesh

• Define the symmetry and draw direction control parameters for optimization

• Submit the check job to OptiStruct

• Post-process the results


Topology Optimization with stress Constraints

• Global von mises stress constraints

• Apply to entire model including non design space

• Stress constraints for a partial domain of the structure are not allowed

• The reason is that it often creates an ill-posed optimization problem as elimination of the partial domain would remove all stress constraints

• Local stresses are still high

• This is for general stress level control

• Local stress should be taken care of by using shape/size

Stress < 50 Stress < 30






• Common problem formulation when stress constraints are included

• Not recommended formulation

Minimize (total / regional) volume/ mass

with stress constraints (displacement or frequency constraints can be combined)

Minimize compliance

with stress constraints + volume fraction

If the volume constraint is active, it prevents satisfaction of stress constraints !!


Compliance Design : Load case 1 repeated 3 times






Stress Design: Load case 1 repeated 3 times



Stress vs. Compliance Design







• Set up in HyperMesh

• Stress responses thru DRESP1 are for Size/Shape/Topology


Exercise 2.5 : Topology Optimization of a Hook with Stress Constraints

• Create design variable for topology optimization

• Create von mises stress constraints on DTPL card

• Create response

• Create the objective function: min(vol)


4 loading cases





• What are Manufacturing Constraints?

• Additional input for the optimization problem

• OptiStruct tries to meet manufacturing constraints

• Why are they so important?

• Make it much easier to interpret optimization results

• Use of standard profiles/manufacturing tools/processes

• Optimized structures are of no value if nobody can manufacture them

• Implemented manufacturing constraints

• Maximum member size

• Minimum member size

• Draw direction constraint

• Pattern repetition

• Pattern grouping

• Extrusion constraint

Topology Optimization using Manufacturing Constraints


Topology Optimization using Manufacturing Constraints

Manufacturing constraints for topology optimization helps generate practical design concepts

• Minimum member size control specifies the smallest dimension to be retained in topology design. Controls checker board effect and discreteness.

• Maximum member size control specifies the largest dimension allowed in the topology design. It prevents large formation of large members and large material concentrations are forced to more discrete forms.

• Pattern grouping / repetition can be applied to enforce a repeating pattern or symmetrical design even if the loads applied on the structure are unsymmetrical or non-repeating.

• Draw direction / extrusion constraints can be applied to obtain design suitable for casting or machining operations by preventing undercut or die-lock cavities.





Manufacturing Constraints: Minimum Member Size Control

• Input: approximate minimum diameter d in two dimensions

• Works in 2D and 3D

• Controls the size of small structural features

• Controls “checkerboarding”

• Easier interpretation of the resulting layout

• Higher computation cost

d = 60

d = 90

Without min member size

• Difficult to manufacture due to micro structures

• Results are mesh dependent


• Definition of maximum allowable structural member size

• Eliminates material concentrations

• Mesh considerations

• Shell and solid elements

• Tetrahedral and hexhedral

• Min member > 3 X mesh size

• Max member > 2 X min size

Manufacturing Constraints: Maximum Member Size Control

Without Maximum Member size

Without Maximum Member size

WithMaximum Member size

WithMaximum Member size





Cyclic Repetition

• Symmetry definitions

• Cyclic repetition of design features within a single domain

• User enters # of wedges

• Application: Cyclic structures with non symmetrical loadcases

Manufacturing Constraints: Pattern Repetition


Pattern RepetitionApplication example: Airplane Wing Ribs

• Goal: same topology on every rib

• Scaling factor to account for different sizes of design space





Pattern Repetition

Without pattern repetition With pattern repetition

Application example: Airplane Wing Ribs


Draw Direction Constraint

• Define global casting direction

• Eliminates undercuts in design proposal

• Reduces interpretation effort

• Important if part shall be manufactured by

• Casting

• Injection molding

• Milling

• Draw type options

• Single

• Split





Example: Determine Optimum Stiffeners in Torsion Loaded U-Profile


Initial Structure

Optimization ModelO

ptim

izat

ion

Res

ults

Without Draw Direction

With Draw Direction



Example: Optimum Rib Pattern of a Control Arm

With Draw DirectionWithout Draw Direction





Extrusion Constraint

Manufacturing control for constant cross sections

Package space

Design proposal without extrusion constraint

Design proposal with extrusion constraints


Combination of Manufacturing Constraints

Any combination of manufacturing constraints is possible

PatternGroupingPattern

Grouping

PatternRepetition

PatternRepetition

DrawDirection

DrawDirection

MemberSize

MemberSize

ExtrusionConstraintExtrusionConstraint

Pattern Grouping (Symmetry)

Draw Direction

Symmetry

Draw Direction+





Applications of Topology Optimization

Determination of Optimum Rib Patterns for Reinforcement

• Non design space represents general geometry concept

• Design space defines areas where ribs shall be introduced

• Manufacturing constraints crucial

• Draw direction

• Minimum & maximum member size


Exercise 2.6: Topology Optimization with Extrusion Constraints

• The use of HyperMesh to setup extrusion constraints

• The set up the design optimization problem –responses, objective and constraints

• An examination of the results





Common Topology Optimization Problems

• Minimize (weighted / total / regional) compliance

with constrained (total / regional) volume / mass fraction

• Minimize (total / regional) volume/ mass fraction

with constrained displacements

• Maximize (weighted) frequency


• Minimize (total / regional) volume / mass fraction

with constrained frequencies

• Minimize combined compliance and frequencies


• Minimize (total / regional) volume/ mass fraction

with stress constraints


Additional Optimization Considerations

Constraint Screening (DSCREEN)

• Screening - specify normalized threshold value• Temporarily ignores constraints which are less than the normalized threshold

value during optimization

• Regionalization - specify maximum number of constraints to be retained for a given region

• Considers user specified number of most violated constraints for each load case and region id.

• Essential in situations where there are many constraints• E.g. Stress constraints for shape/size optimization.

• If too many constrained responses are screened, it may take considerably longer to reach a converged solution or, in the worst case, it may not be able to converge on a solution if the number of retained responses is less than the number of active constraints for the given problem.





Free-Size Optimization



• Topology optimization

• Design space = Total – Base Thickness

• Design variable – Density

• Poor bending representation of semi-dense elements

• Truss-like design concepts, no shear panels

• Free size optimization

• Design variables - Thickness of each element

• Accurate bending representation

• Expandable to composites

• Shear panels possible if they represent the best conceptBase

thicknessTotal thickness

Thickness






1,00

1,50

2,00

2,50

3,00

3,50

4,00

4,50

5,00

5,50

1 1,5 2 2,5 3 3,5 4 4,5 5

Maximum dispacement

Op

timu

m m

ass

Truss Concept

Plate Concept

Topology

Free-Size � Concept by topology and Free-Size� Followed by sizing with buckling and stress constraints in sizing



• The solution will be “discrete” when it needs to be so as the optimum design





Free-Size Optimization on PCOMP

• Composite Free-Size Optimization

• Each Ply within Each Element has Thickness Design Variable (PCOMP)

• Stiffness Effected by Laminate Family and Element Thickness in Optimization

T = Ply4 (nom)45

PCOMP

sym

T = Lower T = Upper

T = Ply3 (nom)90

T = Ply2 (nom)-45

T = Ply1 (nom)0

T = Ply4 (opti)45

PCOMP

sym

T = Ply3 (opti)90

T = Ply2 (opti)-45

T = Ply1 (opti)0 T_0

T_Total

Laminate Family

[T_0/T_Total, T_+-45/T_Total, T_90/T_Total]

After Optimization


Exercise 2.7 : Free-Size nonlinear gap optimization on Airplane wing rib

• Create design variable for Free-Size optimization

• Define optimization responses, objective and constraints

• Run the same model with topology optimization

• Compare the results




Design Concept for a Structural C-clip Using the topology optimization technique yields a new design and optimal material distribution. Topology optimization is performed on a concept design, resulting in a design that is lighter in most cases, and also performs better than the concept design. Topology optimization allows designers to start with a design that already has the advantage of improved material distribution and is ready for fine tuning with shape or size optimization.

In this exercise, topology optimization is performed on a model to create a new boundary for the structure and to remove any unnecessary material. The optimization normalizes each element according to its density and lets you remove elements with low density. The resulting structure is lighter and satisfies all constraints.

The optimization problem for this exercise is stated as:

Objective: Minimize volume fraction.

Constraints: Translation in the y-axis for node A < 0.07mm.

Translation in the y-axis at node B > -0.07mm.

Design variables: The density of each element in the design space.

In this exercise, you will:

• Set up the model in HyperMesh

• Define loads

• Analyze the model

• Set up the optimization

• View the results




Step 1: Launch HM and set the RADIOSS OptiStruct User Profile

1. Launch HyperMesh.

(A User Profiles… GUI will appear.)

2. Choose OptiStruct) in the User Profile dialog.

3. Click OK.

This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models in Bulk Data Format for RADIOSS and OptiStruct.

Step 2: Open the File called cclip.hm

1. From the pull-down menu, File >> Open….

An Open file… browser window pops up.

2. Pick the cclip.hm file.

3. Click Open

The cclip.hm database is loaded into the current HyperMesh session, replacing any existing data. The database only contains geometric data.

Step 3: Create materials and properties and assigning them to components

Because components need to reference a material, the materials collectors should be created first.

1. Click Model Browser tab on the Tab menu

2. Right click inside the Model Browser , Create >> Material

(When in this popup do not hit the Enter Key on the keyboard until you are completely done.)

3. For Name: enter, Steel.

4. Pick MAT1 as Card image.

5. Click on Create/Edit.

6. The MAT1 card image pops up.

7. For E, enter the value 2.1E5.

8. For Nu, enter the value 0.3.

9. For RHO, enter the value 7.85E-9.




10. Click return

11. Right click inside the Model Browser, Create >> Property

12. For Name: enter prop_shell.

13. Pick PSHELL as Card image.

14. Select Steel as the Material.


16. The PSHELL card image pops up.

17. Activate the thickness field for the shell component by clicking [T]. This allows you to edit this field. 1.0 is shown and is the default. Leave it at this value.

18. Click return to exit the panel.

19. From pull down menu, Collectors >> Edit >> Components.

20. Click on comps, check the box comp_shell and click select

21. Toggle no property to property =

22. Double click on property = and select prop_shell

23. Click on update

24. Click return.

Step 4: Create load collectors

Next we will create two load collectors (constraints and forces) and assign each a color. Follow these steps for each load collector.

1. Right click inside the Model Browser, Create >> LoadCollector.


2. For Name: enter, Constraints.

3. Leave Card image: option to None

4. Select a suitable color.

5. Click on Create

6. Similarly create a LoadCollector called Forces




Step 5: Create constraints

For the three nodes in the following figure that show constraints, we need to create these constraints and assign them to the spc load collector as outlined in the following steps.

1. From Model Browser expand LoadCollectors, right click on constraints >> Make Current

2. Go to Analysis page and click on constraints panel.

3. Select nodes and corresponding dofs and click on create to create constraints as shown below.

Mesh showing the boundary conditions applied on the c-clip

4. Click Return.




Step 6: Create forces

In this step, we load the structure with two opposing forces of 100.0 N at the opposite tips of the opening of the c-clip.

1. From Model Browser under expand LoadCollectors, right click on Forces >> Make Current

2. Go to Anlysis page, click on forces panel.

3. To create the force at the top of the opening, click on the node at the top of the opening (A) of the c-clip as in the figure below.

4. Click magnitude=, enter 100.0 and press Enter.

5. Set the switch below to y-axis.

6. Click create.

An arrow, pointing up, should appear at the node on the screen

7. Similarly to create the force at the bottom of the opening, left mouse click on the node at the bottom of the opening (B) of the c-clip.

8. Click magnitude=, enter -100.0 and press Enter.

9. Verify the y-axis is selected

10. Click create

An arrow, pointing down, should appear at the node on the screen

11. To provide a separation between the arrows, select uniform size=, type 7, and press Enter.


Opposing forces created at the opening of the c-clip.




Step 7: Create Load Cases

The last step in establishing boundary conditions is the creation of a subcase.

1. Go to Analysis page, click on loadsteps panel.

2. Click name=, type opposing forces, and press Enter.

3. Check the box preceding SPC.

An entry field appears to the right of SPC

4. Click on the entry field and select constraints from the list of load collectors.

5. Check the box preceding Load and select forces from the list of load collectors.

6. Select type as linear static.

7. Click Create.


Step 8: Run the Analysis

A linear static analysis of this c-clip is performed prior to the definition of the optimization process. An analysis identifies the responses of the structure before optimization to ensure that constraints defined for the optimization are reasonable.

1. Go to Analysis page enter the RADIOSS panel.

2. Click save as… following the input file: field.

A Save file… browser window pops up.

3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, cclip.fem, in the File name: field.

The .fem filename extension is the recommended extension for Bulk Data Format input decks.

4. Click Save.

Note the name and location of the cclip.fem file displays in the input file: field.

5. Set the export options: toggle to all.

6. Click the run options: switch and select analysis.

7. Set the memory options: toggle to memory default.

8. Click Radioss.

9. Close the DOS window after you see the message: Process completed successfully




Post Processing Analysis Results

Step 9: View displacement contour

1. From the Radioss Panel, click on HyperView.

HyperView launches with the cclip.h3d file which contains the model and the results.

2. Close the message popup window.

3. From pull down menu click on Graphics >>Contour.

4. Choose Displacement as the Result type and the pull down menu below Displacement as “Y”.

5. Click Apply.

This should show the contour of “Y” component of displacements.

Get the contour value for the nodes where the force was applied.

6. From pull down menu click on File >> Exit quit HyperView.

7. Click No on save popup window.

8. Click return to exit from the Radioss panel.




Optimization Setup The preliminary finite element model, consisting of shell elements, element properties, material properties, and loads and boundary conditions has been defined. Now a topology optimization will be performed with the goal of minimizing the amount of material to be used. When reducing material in an existing mesh with the same loads and boundary conditions, it follows for the model to be less stiff and more prone to deform. Therefore, the optimization process needs to be constrained with a displacement so that a balance between material and overall stiffness is achieved.

The forces in the structure are applied on the outer nodes of the opening of the clip, making those two nodes critical locations in the mesh. We applied a displacement constraint on the nodes so that they would not displace more than 0.07 in the y-axis.

Step 10: Create the topology design variables

1. Go to Analysis page, click on optimization panel.

2. Click topology to access the topology panel

3. Make sure the create subpanel is selected using the radio buttons on the left-hand side of the panel.

4. Click DESVAR=, type d_shell, and press Enter.

5. Click props and choose prop_shell from the list of props and click on select.

6. Choose type: PSHELL

7. Verify that the base thickness is 0.0.

A value of 0.0 implies that the thickness at a specific element can go to zero, and therefore becomes a void.

8. Click Create.


Step 11: Create a volume response

1. Enter the responses panel.

2. Click response=, enter volfrac

3. Change response type: to volumefrac

4. Click create

Step 12: Create a displacement response




To create a displacement as a response, you will need to supply a meaningful name for the response, set the response type to displacement, select the node for the response, and select the type of displacement (dof).

1. While already on the response panel, click response= and type upperdis

2. Change the response type: to static displacement

3. Click the node labeled A (upper opening of c-clip) as shown in the figure to select it.

4. Choose dof2 for the node.

5. Click create.

6. Click response= and type lowerdis

7. The response type: should still be static displacement.

8. Click the node labeled B (lower opening of the c-clip) as shown in the figure.

9. Select dof2 and create the response


Step 13: Create constraints on displacement responses

In this step we set the upper and lower bound constraint criteria for this analysis.




1. Click on dconstraints panel

2. Click constraint= and enter c_upper.

3. Check the box for upper bound only.

4. Click upper bound= and enter 0.07.

5. Select response= and set it to upperdis.

6. Click loadsteps.

7. Check the box next to opposing forces.

8. Click select.

9. Click create.

10. Click constraint= and enter c_lower.

11. Uncheck the box for upper bound.

12. Check the box for lower bound only.

13. Click lower bound= and enter -0.07.

14. Select response= and set it to lowerdis.

15. Click create.


Step 14: Defining the objective function

1. Click objective

2. The switch on the left should be set to min

3. Click response= and select volfrac.

4. Click create.

5. Click return twice to exit the panel.

Step 15: Run the Optimization problem

1. Go to Analysis page, click on OptiStruct

2. Click save as…, enter cclip_complete.fem as the file name, and click Save.

3. Click the run options: switch and select optimization.

4. Click OptiStruct to run the optimization.

The message … Process completed successfully appears in the window at the completion of the job. OptiStruct also reports error messages if any exist. The file




cclip_complete.out can be opened in a text editor to find details regarding any errors. This file is written to the same directory as the .fem file.

5. Close the DOS window.

The default files that get written to your run directory include:

cclip_complete.res HyperMesh binary results file.

cclip_complete.h3d HyperView binary results file.

cclip_complete.HM.comp.cmf

HyperMesh command file used to organize elements into components based on their density result values. This file is only used with OptiStruct topology optimization runs.

cclip_complete.out OptiStruct output file containing specific information on the file setup, the setup of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors that are flagged from processing the cclip_complete.fem file.

cclip_complete.sh Shape file for the final iteration. It contains the material density, void size parameters and void orientation angle for each element in the analysis. This file may be used to restart a run.

cclip_complete.hgdata HyperGraph file containing data for the objective function, percent constraint violations, and constraint for each iteration.

cclip_complete.oss OSSmooth file with a default density threshold of 0.3. The user may edit the parameters in the file to obtain the desired results.

cclip_complete_hist.mvw Contains the iteration history of the objective, constraints, and the design variables. It can be used to plot curves in HyperGraph, HyperView, and MotionView.

cclip_complete.stat Contains information about the CPU time used for the complete run and also the break up of the CPU time for reading the input deck, assembly, analysis, convergence, etc.




Post Processing Optimization Results

OptiStruct provides density information for all iterations, and also gives displacement and von Mises stress results for your linear static analysis. This section describes how to view those results in HyperView.

Step 16: View an iso value plot of element densities

This plot provides the information about the element density. Iso Value retains all of the elements at and above a certain density threshold. Pick the density threshold providing the structure that suits your needs.

1. On OptiStruct panel, click the HyperView button.

This will launch HyperView and load the cclip_complete_des.h3d file.

2. Click Close to close the message popup window.

3. In the bottom portion of the GUI, click in the area circled below to activate the Load Case and Simulation Selection dialog.

Select Design under the Load Case section and the last iteration listed under Simulation and click OK.

4. From pull down menu click on Graphics >> Iso Value.

5. Choose Element Densities as the Result type

6. Set the Current Value: to 0.3

7. Click Apply.




Iso value plot of element densities

8. Move the slider below Current value: to change the density threshold.

You will see the iso value in the graphics window update interactively when you scroll to a new value. Use this tool to get a better look at the material layout and the load paths from OptiStruct.

Step 17: Compare a static contour between the Original and Optimized material layout

1. In HyperView, click on the Next Page arrow toolbar button to go to page 2.

2. This will bring up the cclip_complete_s1.h3d file, which contains the static subcase results for the first and last iteration steps

3. In the bottom portion of the GUI, click in the area circled below to activate the Load Case and Simulation Selection dialog.

4. Select Iteration 28 under Simulation and click OK




5. From pull down menu click on Graphics >> Contour,

6. Choose Element Stresses (2D & 3D) as Result type: and select vonMises.

7. From pull down menu click on Graphics >> Iso Value.

8. Choose Result type: as Element Densities.

9. Choose Averaging Method: as Simple.

10. Click Apply.

11. From the pull-down menu, File >> Exit to quit HyperView.

12. Click No on save popup window.

13. Close HyperMesh widow too, click quit on the popup window.

The regions with high element densities indicate where material is needed and regions with low element densities are areas with scope for mass reduction.




Design Concept for an Automotive Control Arm This exercise uses OptiStruct's topology optimization functionality to create a design concept for an automotive control arm required to meet performance specifications. The finite element mesh containing designable (blue) and non-designable regions (yellow) is shown in the figure below. Part specifications constrain the resultant displacement of the point where loading is applied for three load cases to 0.05mm, 0.02mm, and 0.04mm, respectively. The optimal design would use as little material as possible.

Finite element mesh containing designable (blue) and non-designable (yellow) material. A finite element model representing the designable and non-designable material (shown in figure) is imported into HyperMesh. Appropriate properties, boundary conditions, loads, and optimization parameters are defined and the OptiStruct software is used to determine the optimal material distribution. The results (the material layout) are viewed as contours of a normalized density value ranging from 0.0 to 1.0 in the design space. Isosurfaces are also used to view the density results. Areas that need reinforcement will tend towards a density of 1.0. The optimization problem for this tutorial is stated as:

Objective: Minimize volume.

SUBCASE 1 - The resultant displacement of the point where loading is applied must be less than 0.05mm.


Constraints:


Design variables: Microstructural void sizes and orientations in the design space.

The following exercises are included: • Setting up the FE model in HyperMesh • Setting up the optimization in HyperMesh • Submitting the job • Viewing the results in HyperView




Setting Up the FE Model in HyperMesh

Step 1: Launch HM, set the RADIOSS OptiStruct User Profile and retrieve the file carm.hm


2. Choose OptiStruct in the User Profile dialog and click OK.

This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models in Bulk Data Format for RADIOSS and OptiStruct. The User Profiles… GUI can also be accessed from the Preferences pull-down menu on the toolbar. Select the optimization panel on the Analysis page

3. From the pull-down menu, File >> Open….


4. Pick the carm.hm file.

5. Click Open

Step 2: Create materials and properties and assigning them to the proper components

1. Click Model on the Tab menu

2. Right click inside the Model Browser Create >> Material.

3. For Name: enter, Steel.

4. Select MAT1 as Card image:.


6. The MAT1 card image pops up.

7. For E, enter the value 2.1E5.

8. For Nu, enter the value 0.3.

9. Click return

10. Right click inside the Model Browser window again Create >> Property.

11. In the Name: field type design_prop.

12. Scroll down to select PSOLID as Card image:.

13. Select Steel as the Material.

14. Click on Create.




15. Create another similar PSOLID property called nondesign_prop and assign it the Steel material.

16. From pull down menu, Collectors >> Assign >> Components Property

17. Click on comps, check the box nondesign then click select

18. Click on property = and select nondesign_prop

19. Click on assign

20. Repeat steps 17 – 20 to assign design_prop to the design component.

21. Click return.

Step 3: Create load collectors

Next we will create four load collectors (SPC, Brake, Corner and Pothole) and assign each a color. Follow these steps for each load collector.

1. Right click inside the Model Browser Create >> LoadCollector.

2. For Name: enter, SPC.


3. Leave Card image: field to None

4. Select a suitable color.

5. Click on Create

6. Similarly create the LoadCollectors called Brake, Corner and Pothole.

Step 4: Apply constraints

We need to create constraints and assign them to the SPC load collector as outlined in the following steps.

1. From Model Browser expand LoadCollectors, right click on SPC, and click on Make Current.

2. Go to Analysis page on main menu and click on constraints panel.


4. Select the node at one end of the bushing (see the figure below) by clicking on it in the graphics window.




5. Constrain dof1, dof2, and dof3.

6. Make sure dofs 1, 2, and 3 are checked and dofs 4, 5, and 6 are unchecked.

Dofs with a check will be constrained while dofs without a check will be free.

Dofs 1, 2, and 3 are x, y, and z translation degrees of freedom.

Dofs 4, 5, and 6 are x, y, and z rotational degrees of freedom.

7. Click create.

A constraint is created. A constraint symbol (triangle) appears in the graphics window at the selected node. The number 123 is written beside the constraint symbol, indicating that dof1, dof2 and dof3 are constrained.

Constraining dof1, dof2 and dof3 at one end of the bushing.

8. Select the node at the other end of the bushing (see the following figure) by clicking on it in the graphics window.

9. Constrain dof2 and dof3.

10. Make sure dofs 2 and 3 are checked.

11. Click create.

A constraint is created. A constraint symbol (triangle) appears in the graphics window at the selected node. The number 23 is written beside the constraint symbol, indicating that dof2 and dof3 are constrained.




Constraining dof2 and dof3 at the other end of the bushing.

12. Click nodes >> by id.

13. Enter the value 3239 and press Enter.

This selects node ID 3239 (see the next figure).

14. Constrain only dof3.

15. Click create.

A constraint is created. A constraint symbol (triangle) appears in the graphics window at the selected node. The number 3 is written beside the constraint symbol, indicating that dof3 is constrained.




Constraining dof3 on node ID 3239.


Step 5: Apply forces for Brake, Corner and Pothole loadcases

1. On Model Browser tab under expand LoadCollectors, right click on Brake, and click on Make Current

2. Go to Anlysis page, click on forces panel.


4. Enter the node number 2699 and press Enter.


6. Set the switch below to x-axis.

7. Click create.

An arrow, pointing the x direction, should appear at the node on the screen.

8. For better visualization of the arrows, select uniform size=, type 100, and press Enter.

9. On Model Browser tab under expand LoadCollectors, right click on Corner, and click on Make Current





11. Enter the node number 2699 and press Enter.


13. Set the switch below to y-axis.

14. Click create.

An arrow, pointing in the Y direction, should appear at the node on the screen.

15. On Model Browser tab under expand LoadCollectors, right click on Pothole, and click on Make Current


17. Type the node number 2699 and press Enter.


19. Set the switch below to z-axis.

20. Click create.

An arrow, pointing in the Z direction, should appear at the node on the screen.


Three separate forces in load collectors: Brake, Corner, and Pothole with the component "design" turned off using the display panel.




Step 6: Create Brake, Corner & Pothole Loadcases

The last step in establishing boundary conditions is the creation of a subcase.

1. Go to Analysis page enter the loadsteps panel.

2. Click name=, enter Brake, and press Enter.

3. Select type as linear static.


5. An entry field appears to the right of SPC

6. Click on the entry field and select SPC from the list of load collectors.

7. Check the box preceding Load and select Brake from the list of load collectors.

8. Click Create

9. Similarly create the Load Cases Corner [by selecting the load collectors Corner and SPC] and Pothole [by selecting the load collectors Pothole and SPC]

10. Click return to go back to the Analysis page.

Setting Up the Optimization in HyperMesh

Step 7: Define the topology design variables

1. Go to Analysis page click on optimization panel.

2. Click on topology.


4. Click DESVAR=, enter design_prop, and press Enter.

5. Click props and choose design_prop from the list of props and click on select.

6. Choose type: PSOLID

7. Click Create.

A topology design space definition, design_prop, has been created. All elements organized in this design property collector are now included in the design space.

8. Click return to go back to the optimization panel.




Step 8: Create a volume and displacement response

1. click on responses panel.

2. Click response = and enter vol.

3. Click on the response type switch and select volume from the pop-up menu.

4. Ensure the regional selection is set to total (this is the default).

5. Click create.

A response, vol, is defined for the total volume of the model.

6. Click response = and enter disp1.

7. Click on the response type switch and select static displacement from the pop-up menu.

8. Click nodes >> by ID.

9. Enter, 2699 and press Enter.

The node where the three forces are applied is selected.

10. Select the total disp form the radio options.

This is the vector sum of the x, y, and z translations.

11. Click create.

A response, disp1, is defined for the total displacement of node 2699.

12. Click return to exit panel.

Step 9: Define the objective

1. Click on objective panel


3. Click response= and select Vol.

4. Click create

5. Click return to exit the optimization panel

Step 10: Create constraints on displacement responses


1. Enter the dconstraints panel

2. Click constraint= and enter Constr_BRAKE




3. Check the box for upper bound only

4. Click upper bound= and enter 0.05

5. Select response= and set it to disp1

6. Click loadsteps

7. Check the box next to Brake

8. Click select

9. Click create

10. Click constraint= and enter Constr_Corner



13. With the disp1 response selected, click loadsteps

14. Check the box next to Corner

15. Click select

16. Click create

17. Click constraint= and enter Constr_Pothole



20. With the disp1 response still selected , click loadsteps

21. Check the box next to Pothole

22. Click select

23. Click create


Submitting the Job

Step 11: Check the Optimization problem

A check run may be performed in which OptiStruct will estimate the amount of RAM and disk space required to run the model. During the check run, OptiStruct will also scan the deck checking that all the necessary information required to perform an analysis or optimization is present and also that this information is not conflicting.

1. From the Analysis page enter the OptiStruct panel.

2. Click save as… following the input file: field





3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, carm_check.fem, in the File name: field.

The .fem filename extension is the suggested extension for OptiStruct input decks.

4. Click Save.

Note the name and location of the carm_check.fem file displays in the input file: field.


6. Click the run options: switch and select check.


8. Click OptiStruct.

This launches the OptiStruct check run.

Once the processing is complete (indicated in the UNIX or MSDOS window which pops up), view the file carm_check.out. This is the OptiStruct output file containing specific information on the file setup, optimization problem setup, RAM and disk space requirement for the run. Review this file for possible warnings and errors.

Is the optimization problem set up correctly? See Optimization Problem Parameters section of the carm_check.out file.

The objective function? See Optimization Problem Parameters section of the carm_check.out file.

The constraints? See Optimization Problem Parameters section of the carm_check.out file.

What is the recommended amount of RAM for an In-Core solution? See Memory Estimation Information section of the carm_check.out file.

Is there enough disk space to run the optimization? See Disk Space Estimation Information section of the carm_check.out file.

Step 12: Run the Optimization problem


2. Click save as…, enter carm_complete.fem as the file name, and click Save.



The message …Processing complete appears in the window at the completion of the job. OptiStruct also reports error messages if any exist. The file carm_complete.out




can be opened in a text editor to find details regarding any errors. This file is written to the same directory as the .fem file.

5. Close the DOS window or shell and click return.

The default files written to the directory are:

carm_complete.hgdata HyperGraph file containing data for the objective function, percent constraint violations, and constraint for each iteration.

carm_complete.his_data OptiStruct history file containing iteration number, objective function values and percent of constraint violation for each iteration.

carm_complete.HM.comp.cmf

HyperMesh command file used to organize elements into components based on their density result values. This file is only used with OptiStruct topology optimization runs.

carm_complete.HM.ent.cmf

HyperMesh command file used to organize elements into entity sets based on their density result values. This file is only used with OptiStruct topology optimization runs.

carm_complete.html HTML report of the optimization, giving a summary of the problem formulation and the results from the final iteration.

carm_complete.oss OSSmooth file with a default density threshold of 0.3. The user may edit the parameters in the file to obtain the desired results.

carm_complete.out OptiStruct output file containing specific information on the file setup, the setup of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors that are flagged from processing the cclip_complete.fem file.

carm_complete.res HyperMesh binary results file.

carm_complete.sh Shape file for the final iteration. It contains the material density, void size parameters and void orientation angle for each element in the analysis. The .sh file may be used to restart a run and, if necessary, run OSSmooth files for topology optimization.

cclip_complete.stat Summary of analysis process, providing CPU information for each step during analysis process.




Viewing the Results and Post-processing

Element density results are output to the carm_complete_des.h3d file from OptiStruct for all iterations. In addition, Displacement and Stress results are output for each subcase for the first and last iterations by default into carm_complete_s#.h3d files, where # specifies the sub case ID. This section describes how to view those results in HyperView.

Step 13: View the deformed structure

1. Once you see the message Process completed successfully in the command window, click the green HyperView button.

HyperView is launched and the results are loaded. A message window appears to inform about the successful loading of the model and result files into HyperView. Notice that all three .h3d files get loaded, each in a different page of HyperView.

2. Click Close to close the message window.

It is helpful to view the deformed shape of a model to determine if the boundary conditions are defined correctly, and also to find out if the model is deforming as expected. The analysis results are available in pages 2, 3, and 4. The first page contains the optimization results.

3. Click the Next Page toolbar button to move to the second page.

The second page has the results from the carm_complete_s1.h3d file. Note that the name of the page is displayed as Subcase 1 – Brake to indicate that the results correspond to subcase 1.

4. Select Linear Static as the animation mode .

5. Click the Contour toolbar button .

6. Select the first pull-down menu below Result type: and select Displacement [v].

7. Select the second pull-down menu and select Mag.

8. Click Apply to display the displacement contour.

9. Click the Deformed toolbar button .

10. Set Result type: to Displacement (v), Scale: to model units, and Type: to Uniform.

11. Enter 1000 for value:.

This means that the maximum displacement will be 1000 Model units and all other displacements will be proportional.




12. Below the Undeformed shape: section, click on the pull-down menu next to Show and select Wireframe.

13. Click Apply.

A deformed plot of your model with displacement contour should be visible, overlaid on the original undeformed mesh.

14. Click the linear static icon to animate the model .

A deformed animation for the first subcase (brake) should be displayed. Notice that the

icon changes to indicate that the model is being animated.

In what direction is the load applied for the first subcase?

Which nodes have degrees of freedom constrained?

Does the deformed shape look correct for the boundary conditions applied to the mesh?

15. At the bottom of the GUI, click on the name Static Analysis or Iteration 0,

, to activate the Load Case and Simulation Selection dialog.

16. Select the 19th iteration by double-clicking on Iteration 19.

The contour now shows the displacement results for Subcase 1 (brake) and iteration 18 which corresponds to the end of the optimization iterations.

17. Click the linear static icon again to stop the animation.

18. Click on the Next Page icon to move to the third page.

The third page which has results loaded from carm_complete_s2.h3d file, is displayed. Note that the name of the page is displayed as Subcase 2 – corner to indicate that the results correspond to subcase 2.

19. Repeat steps 2 to 15 to display the displacement contours and deformed shape of the model for the second subcase.

In what direction is the load applied for the second subcase?

Which nodes have degrees of freedom constrained?

Does the deformed shape look correct for the boundary conditions applied to the mesh?

20. Similarly, review the displacements and deformation for subcase 3 (pothole).

Step 14: Review contour plot of the density results

The optimization iteration results (Element Densities) are loaded in the first page.




1. Click the Previous Page icon until the name of the page is displayed as Design History, indicating that the results correspond to optimization iterations.

2. Click the Contour toolbar button.

3. Note the Result type: is Element Densities [s] this should be the only results type in the “file_name”_des.h3d file.

4. The second pull-down menu shows Density.

5. In the Averaging method: filed select Simple.

6. Click Apply to display the density contour.

Note the contour is all blue this is because your results are on the first design step or Iteration 0.

7. At the bottom of the GUI, click on the name Design or Iteration 0 to activate the Load Case and Simulation Selection dialog.

8. Select the last iteration by double clicking on the last Iteration #.

Each element of the model is assigned a legend color, indicating the density of each element for the selected iteration.

Have most of your elements converged to a density close to 1 or 0?

If there are many elements with intermediate densities, the DISCRETE parameter may need to be adjusted. The DISCRETE parameter (set in the opti control panel on the optimization panel) can be used to push elements with intermediate densities towards 1 or 0 so that a more discrete structure is given.

In this model, refining the mesh should provide a more discrete solution; however, for the purposes of this tutorial, the current mesh and results are sufficient.

Regions that need reinforcement tend towards a density of 1.0. Areas that do not need reinforcement tend towards a density of 0.0.

Is the max= field showing 1.0e+00?

In this case, it is.

If it is not, the optimization has not progressed far enough. Allow more iterations and/or decrease the OBJTOL parameter (also set in the opti control panel).

If adjusting the discrete parameter, refining the mesh, and/or decreasing the objective tolerance does not yield a more discrete solution (none of the elements progress to a density value of 1.0), review the set up of the optimization problem. Some of the defined constraints may not be attainable for the given objective function (or vice versa).




Step 15: View an iso value plot on top of the element densities contour


1. From Graphics pull down menu click on Iso Value. and choose Element Densities as the Result type

2. Set the Current Value: to 0.15

3. Click Apply







Increasing Natural Frequencies of an Automotive Splash Shield with Ribs A preliminary design of ribs for an automotive splash shield will be generated in this exercise. The objective is to increase the natural frequency of the first normal mode using topology to identify locations for ribs in the designable region (shown in red).

Finite element mesh containing designable (red) and non-designable (blue) material.


Objective: Maximize frequency of mode number 1.

Constraint: Upper bound constraint of 30% for the designable volume.

Design variables: Density of each element in the design space.

The following exercises are included: • Setting up the normal modes analysis in HyperMesh • Submitting the initial job • Viewing the initial results in HyperView • Setting up the optimization in HyperMesh • Submitting the optimization job • Viewing the results of the optimization in HyperView • Setting up the final normal modes analysis in HyperMesh • Submitting the job • Viewing the final results in HyperView • Comparing with initial results

The following file is needed to perform this tutorial:

sshield_opti.fem Original ASCII OptiStruct input deck.




Setting Up the Normal Modes Analysis in HyperMesh

Step 1: Launch HM, load the User Profile and retrieve a file



User Profiles… can also be accessed from the Preferences pull-down menu on the toolbar.

3. From the pull-down menu, File >> Import…. An Import… tab is added to your tab menu

4. Pick the import type: FE Model.

5. Choose the File type: OptiStruct.

6. Click on File icon button ( ).

An OptiStruct file browser will pop up.

7. Pick the sshield_opti.fem file.

8. Click Open.

9. Click Import.

The sshield_opti.fem OptiStruct input file is loaded into the current HyperMesh session.

10. Click Close to exit the Import tab menu.

Step 2: Create EIGRL load collector


2. For Name:, enter constraints

3. Click color and select a color from the palette.

4. Leave Card image: set to None.

5. Click create.

A new load collector, constraints, is created.

Next an eigenvalue load collector will be created.


7. For Name:, enter EIGRL.

8. Click color and select a different color from the palette.




9. From the Card image: choose EIGRL.

10. Click create/edit.

The EIGRL card image pops up.

11. For V2, enter the value 3000.000.

12. For ND, enter the value 2.

If a quantity in brackets does not have a value below it, it is off. To change this, click on the quantity in brackets and an entry field will appear below it. Click on the entry field, and a value can be entered.

13. Click return to save changes and exit the panel.

A real eigenvalue extraction card has been created. The first two roots between 0 and 3000Hz are to be extracted.

Step 3: Create constraints at the bolt locations

1. From Model Browser expand LoadCollectors, right click on constraints >> Make Current

.

2. Go to Analysis page click on constraints panel.


4. Click the entity selection switch and select nodes from the pop-up menu.


6. Enter the value 1075 (beside id=) and press Enter.

7. Enter the value 1076 and press Enter.

8. Constrain all dofs.




Dofs with a check will be constrained while dofs without a check will be free.

Dofs 1, 2, and 3 are x, y, and z translation degrees of freedom.

Dofs 4, 5, and 6 are x, y, and z rotational degrees of freedom.

9. Click create.

Two constraints are created. Constraint symbols (triangles) appear in the graphics window at the selected nodes. The number 123456 is written beside the constraint symbol, indicating that all dofs are constrained.


Step 4: Create a loadstep (also referred to as a subcase)

1. Go to Analysis page click on loadstep panel

2. Click name = and enter frequencies.

3. Click the type switch and choose normal modes from the pop-up menu.


An entry field appears to the right of SPC.

5. Click on the entry field and select constraints from the list of load collectors.

6. Check the box preceding METHOD(STRUCT).

An entry field appears to the right of METHOD.

7. Click on the entry field (=) and select eigrl from the list of load collectors.

8. Click create.

An Radioss loadstep has been created which references the constraints in the load collector spc and the eigenvalue extraction data in the load collector eigrl.


Submitting the Initial Job

Step 5: Run the Analysis

1. Go to Analysis page click on Radioss panel.

2. Click save as… following the input file: sshield_analysis.fem


The .fem file name extension is the suggested extension for Radioss input decks.




3. Click Save.

Note that the name and location of the sshield_analysis.fem file is now displayed in the input file: field.


5. Click the run options: switch and select analysis.


7. Click Radioss.

8. Close the DOS window after you see the message: Process completed successfully.

This launches the Radioss job. If the job is successful, new results files can be seen in the directory where the Radioss model file was written. The sshield_analysis.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.

The default files written to your directory are:

sshield_analysis.html HTML report of the analysis, giving a summary of the problem formulation and the analysis results.

sshield_analysis.out Radioss output file containing specific information on the file set up, the set up of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors.

sshield_analysis.res HyperMesh binary results file.

sshield_analysis.stat Summary of analysis process, providing CPU information for each step during analysis process.

sshield_analysis.h3d HyperView results file.

Viewing the Initial Results

Eigenvector results are output from Radioss for a normal modes analysis by default. This section describes how to view the results in HyperView.

Step 6: Review the first mode shapes in HyperView

1. While still in the Radioss panel, click the green HyperView button.

This button launches HyperView and loads the sshield_analysis.h3d file.




A Message Log pop-up will inform about the result files loaded into HyperView.

2. Click Close to exit the Message Log window.

3. Change the animation type from Transient to Modal .

4. From the pull-down menu, click Graphics >> Select Load Case.

A Load Case Simulation and Selection window will appear showing the first two natural frequencies between 0 and 3000Hz.

5. Click Ok to close this window.

6. Enter the Deformed toolbar button .

7. Make or verify the following settings in the Deformed panel.

Result Type: Eigen mode (v)

Scale: Model Units

Type: Uniform

Value: 10

8. Click Apply.

9. Enter the Animation Controls panel by clicking the directors chair .

10. Move the Max Frame Rate: slider between 60 and 1 to increase or decrease the animation speed.

You can also change the default values for Increment by: to refine your animation.

11. Click the Modal icon to start animation.

An animation of the mode shape should be seen for the first frequency.

12. Click the Modal icon again to stop the animation.

13. From the pull-down menu, click File >> Exit to quit HyperView.

14. Click No to save popup window..

Setting Up the Optimization in HyperMesh

Step 7: Create design variables for topology optimization

1. Go back to HyperMesh and click return to exit panel.





3. Click on topology to access panel.

4. Go to create subpanel using the radio buttons on the left-hand side of the panel.

5. Click desvar = and enter shield.

6. Click props.

7. Check the box next to design and click select.

8. Set type toggle to PSHELL.

9. Click on base thickness = and change the value to 0.300.

10. Click create.

A topology design space definition, shield, has been created. All elements organized into the design property collector are now included in the design space. The thickness of these shells can vary between 0.3 (base thickness defined above) and the maximum thickness defined by the T (thickness) field on the PSHELL card.

The object of this exercise is to determine where to locate ribs in the designable region. Therefore, a non-zero base thickness is defined, which is the original thickness of the shells. The maximum thickness, which is defined by the T field on the PSHELL card, should be the allowable depth of the rib.

Currently the T field on the PSHELL card is still set to 0.3 (the original shell thickness), this needs to be changed.


12. Click the Card Editor button on collector toolbar.

13. Set the entity selection to props using the down arrow next to the listed entity

14. Click the yellow props button and check the box next to design.

15. Click select.

16. Select the card image= and select PSHELL from the pop-up menu.

17. Click edit.

The PSHELL card image for the design component collector pops up.

18. Replace 0.300 in the T field with 1.000.





Step 8: Create responses

A detailed description of the available responses can be found in the OptiStruct User's Guide under Responses.

Two responses will be defined here: a frequency response for the objective and a volume fraction response for the constraint definition.

1. Click on responses panel.

2. Click response = and enter freq1.

3. Click on the response type: switch and select frequency from the pop-up menu.

4. Click on Mode Number: and enter 1 (this is the default value).

5. Click create.

A response, freq1, is defined for the frequency of the first mode extracted.

6. Click response = and enter volfrac.

7. Click on the response type: switch and select volumefrac from the pop-up menu.

8. Set the total/regional toggle to total.

9. Click create.

A response, volfrac, is defined for the volume fraction of the design space.


Step 9: Define the objective function

In this example, the objective is to maximize the response, 'freq1', which was defined in the previous section.

1. Click on objective panel from within the optimization panel.

2. Click on the switch in the upper left corner of the panel, and select max from the pop-up menu.

3. Click response= and select freq1 from the list of responses.

4. Click loadstep and select the frequencies load step previously defined.

5. Click create.





Step 10: Define the constraints

A response defined as the objective cannot be constrained. In this case, you cannot constrain the response freq1.

An upper bound constraint is to be defined for the response volfrac.

1. Enter the dconstraints panel from the optimization panel.

2. Click constraint= and enter vconstr.

3. Check the box to the left of upper bound =.

4. Click upper bound = and enter the value 0.30.

5. Click response = and select volfrac from the response list.

6. Click create.

A constraint is defined on the response volfrac. The constraint is an upper bound with a value of 0.30. The constraint applies to all subcases as the volumefrac response is a global response.


Step 11: Define the objective tolerance

1. Enter the opti control panel from the optimization page.

2. Check the box next to OBJTOL.

3. Click on OBJTOL= and enter 0.001.

If the fractional change in the objective function (in this case the compliance) is below 0.001 for two consecutive iterations, OptiStruct will consider the optimization as converged and will stop.

4. Click return twice exit the panel.

Submitting the Optimization Job

Before running OptiStruct, you need to write your OptiStruct input deck, usually specified with the .fem file name extension.

Step 12: Run the OptiStruct Analysis

1. Go to Analysis page click on OptiStruct panel.






3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, sshield_optimization.fem, in the File name: field.

The .fem extension is used for OptiStruct input decks.

4. Click Save.

Note that the name and location of the sshield_optimization.fem file is now displayed in the input file: field.





This launches the OptiStruct job. If the job is successful, new results files can be seen in the directory where the OptiStruct model file was written. The sshield_optimization.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.

9. Close the DOS windows when you see the message: Process completed successfully.


Sshield_optimization.hgdata HyperGraph file containing data for the objective function, percent constraint violations and constraint for each iteration.

Sshield_optimization.hist OptiStruct history file containing iteration number, objective function values, and percent of constraint violation for each iteration.

Sshield_optimization.HM.comp.cmf HyperMesh command file used to organize elements into components based on their density result values. This file is only used with OptiStruct topology optimization runs.

Sshield_optimization.HM.ent.cmf HyperMesh command file used to organize elements into entity sets based on their density result values. This file is only used with OptiStruct topology optimization runs.




Sshield_optimization.html HTML report of the optimization, giving a summary of the problem formulation and the results from the final iteration.

Sshield_optimization.oss OSSmooth file with a default density threshold of 0.3. The user may edit the parameters in the file to obtain the desired results.

Sshield_optimization.out OptiStruct output file containing specific information on the file setup, the setup of your optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors.

Sshield_optimization.H3D HyperView binary results file.

Sshield_optimization.sh Shape file for the final iteration. It contains the material density, void size parameters and void orientation angle for each element in the analysis. The .sh file may be used to restart a run and, if necessary, to run OSSmooth files for topology optimization.

Sshield_optimization.stat Summary of analysis process, providing CPU information for each step during analysis process.

Viewing Results of the Optimization Run

Element Density and Element Thickness results are output from OptiStruct for all iterations. In addition, Eigenvector results are output for the first and last iterations by default. This section describes how to view those results in HyperView.

Step 13: View a static plot of the density results

1. While in the OptiStruct panel, click the green HyperView button.

This launches HyperView and loads the sshield_optimization_des.h3d file.

A Message Log window opens, indicating the location of the .h3d file.





3. Click on Entity Attributes and turn off the component named non-design.

4. Check the box before Auto apply mode to activate this mode.

5. Click the Mesh Lines icon to active this for the Auto apply mode.

6. Click All

7. Enter the contour panel by clicking the Contour icon on the toolbar.

8. Set the Result type: to Element Densities(s).

9. Click Apply.

10. From the pull-down menu, click Graphics >> Select Load Case to bring up the Load Case and Simulation Selection pop up GUI.

11. Choose the last Iteration # in the list.

12. Click Ok.



If there are many elements with intermediate densities, the discrete parameter may need to be adjusted. The DISCRETE parameter (set in the opti control panel on the optimization panel) can be used to push elements with intermediate densities towards 1 or 0 so that a more discrete structure is given.


Is the max = field showing 1.0e+00?

In this case, it is. If it is not, the optimization has not progressed far enough. Allow more iterations and/or decrease the OBJTOL parameter (set in the opti control panel on the optimization panel).

If adjusting the DISCRETE parameter, incorporating a checkerboard control, refining the mesh, and/or decreasing the objective tolerance does not yield a more discrete solution (none of the elements progress to a density value of 1.0), you may want to review the set up of the optimization problem. Some of the defined constraints may not be attainable for the given objective function (or visa-versa).

Where would you place your ribs?




Contour plot of element densities at iteration 12 with all components except the designable component turned off. (top view)

13. From the pull-down menu, click File >> Exit to quit HyperView.

Setting Up the Final Normal Modes Analysis in HyperMesh

Based on the topology results obtained above, a number of ribs were added to the model. This new design is available in the file sshield_newdesign.fem,

Step 14: Delete the current model

1. Return to HyperMesh and click return to exit the OptiStruct panel.

2. Select the delete panel on the Tool page.

or

Press F2 on the keyboard to jump to the delete panel.

3. Click delete model.

A message should pop-up asking you if you want to delete the current model.

4. Click Yes.

Deleting the current model clears the current HyperMesh database. Information stored in .hm files on your disk is not affected.





Step 15: Import the OptiStruct input file sshield_newdesign.fem

1. From the pull-down menu on the toolbar, File >> Import…. An Import… tab is added to your tab menu

2. Select the import type: FE Model.

3. Choose the File type: Optistruct.

4. Click on the Files icon button ( ).

5. An OptiStruct file browser will pop up.

6. Select the sshield_newdesign.fem file.

7. Click Apply.

The sshield_newdesign.fem OptiStruct input file is loaded into the current HyperMesh session. The ribs which were added are in the ribs component collector

8. Click Close to exit the Files panel.

Step 16: Run Radioss Analysis

1. Go to Analysis page, click on Radioss panel.

2. Click save as… following the input file: field


3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, sshield_newdesign.fem, in the File name: field.


4. Click Save.

5. Note that the name and location of the sshield_newdesign.fem file is now displayed in the input file: field.


7. Click on the run options: switch and select analysis.


9. Click Radioss.

Viewing the Results

This section describes how to view your results for the new design in HyperView.




Step 17: View the mode shapes

1. While in the Radioss panel, click the green HyperView button.

This button launches HyperView and loads the file sshield_newdesign.h3d.

A Message Log window opens, indicating the location of the .h3d file.


3. Set the Animation mode to Modal.

4. Enter the Select Load Case dialog from the Graphics pull-down menu.

The Load Case and Simulation Selection window appears showing the first two natural frequencies for the modified structure.

5. Click the Deformed toolbar button.

6. Make or verify the following settings in the Deformed panel.

Result Type: Eigen mode (v)

Scale: Model Units

7. Click Apply.

8. Click the Animation Modal Icon to Start/Stop the animation of the mode.

An animation of the mode shape should be seen for the first frequency.

9. Click the Animation Controls icon on the toolbar.

10. Move the MAX Frame Rate: slider bar from 60 to 1 to control the speed of the animation.

11. You can also change the Angular Increment: to refine your animation.

12. Click Modal again to stop the animation.

Comparing the Results What is the percentage increase in frequency for your first mode (sshield_analysis.fem vs. sshield_newdesign)?

We have seen that the frequency of the structure for the first mode has increased from 43.63 Hz to 84.88 Hz.

How much mass has been added to the part (check the mass of your ribs in the mass calc panel in the Tool page)?

What is the percentage increase in mass?




Symmetry and Draw Direction Constraints Applied Simultaneously in a Topology Optimization The purpose of this exercise is to demonstrate how to perform a topology optimization on an automotive control arm with the simultaneous application of symmetry and draw direction constraints. This exercise will use the same optimization problem considered in Design Concept for an Automotive Control Arm (OS-2010), except that a refined mesh will be used in order to better capture the effect of applying symmetric and draw manufacturing constraints simultaneously. The model used for this tutorial has a pre-defined refined mesh. The finite element mesh of the structural model containing the designable (blue) and the non-designable (red) regions, along with the loads and constraints applied, is shown in the following figure.

.


Objective: Minimize volume.



Constraints:


Design variables: Microstructural void sizes and orientations in the design space.

In this exercise, you will:

• Set up the FE model in HyperMesh

• Define the symmetry and draw direction control parameters for optimization

• Submit the job to OptiStruct





Setting Up the FE Model in HyperMesh

Step 1: Launch HyperMesh, Set the User Profile, and Import a File



This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models in Bulk Data Format for RADIOSS and OptiStruct. The User Profiles… GUI can also be accessed from the Preferences pull-down menu on the toolbar.

3. From the pull-down menu File >> Import….

An Import tab is added to your tab menu.

4. Set the Import type: to FE Model.

5. Choose the proper File type: RADIOSS (Bulk Data Format), OptiStruct.

6. Click on Files icon button ( ).

A Select RADIOSS (Bulk Data Format), OptiStruct file browser will pop up.

7. Select the carm_draw_symm.fem file, located in the HyperWorks installation directory under <install_directory>/tutorials/hwsolvers/optistruct/.

8. Click Open.

9. Click Import.

Define the Symmetry and Draw Direction Parameters for Optimization

Step 2: Define the Cutting Plane for the Symmetry Constraints and the Direction for the Draw Direction Constraints

1. From Analysis page, click on optimization panel.

2. Click on topology to access the panel.

3. Double click desvar = and select solid.

4. Go to pattern grouping subpanel to define the symmetry constraint and toggle the pattern type: to 1-pln sym.

The symmetry constraints in topology optimization lead to symmetric designs for solid models, regardless of the initial mesh, boundary conditions or loads. In this case, the 1-pln sym option enforces symmetry across a defined plane. A symmetric mesh is not




required, as OptiStruct will create variables that are nearly identical across the plane(s) of symmetry. The plane of symmetry is defined by specifying the anchor and the first nodes. The plane of symmetry will then be perpendicular to the vector from the anchor node to the first node, and passes through the anchor node.

5. Click anchor node, input the node id= 3241, and press ENTER.

This selects the node with the ID of 3241.

6. Click first node, input the node id= 3877 and press ENTER.

This selects the node with the ID of 3877.

7. Click the update button to update the design variables.

This completes the definition of the symmetry constraint.

8. Go to draw subpanel.

9. Toggle the draw type: to single.

The draw option single assumes that a single die will be used to cast the component and it slides in the defined draw direction. The draw direction is defined by specifying the anchor and the first nodes, with the draw direction being along the vector from the anchor node to the first node.

10. Click anchor node, input the node id= 3165, and press ENTER.

This selects the node with the ID 3165.

11. Click first node, input the node id= 3753, and press ENTER.

The anchor node, in conjunction with the first node, sets the draw direction or the direction of the movement of the die during casting.

12. Click the update button to update the design variables.


Submitting the Job to OptiStruct

Step 4: Run the Optimization Problem

This exercise takes a long time to run (elapsed time of about 52 hours on a typical work station) because of the fine mesh of solid elements. For the sake of user convenience, the results file (carm_draw_symm_des.h3d) is available from [email protected]. You can skip this section and directly load the results file in HyperView for post-processing. The following steps are given for the sake of completeness of this tutorial and as a helpful user reference.

1. Go to Analysis page click on OptiStruct panel.




2. Click save as…, enter carm_complete.fem as the file name, and click Save.

3. Click the run options: switch to optimization.

4. Make sure the memory options: toggle is set to memory default.


The message …Processing complete appears in the window at the completion of the job. OptiStruct also reports error messages if any exist. The file carm_complete.out can be opened in a text editor to find details regarding any errors. This file is written to the same directory as the .fem file.

6. Close the DOS window or shell and click return.

carm_complete.hgdata HyperGraph file containing data for the objective function, percent constraint violations, and constraint for each iteration.

carm_complete.his_data OptiStruct history file containing iteration number, objective function values, and percent of constraint violation for each iteration.

carm_complete.HM.comp.cmf HyperMesh command file used to organize elements into components based on their density result values. This file is only used with OptiStruct topology optimization runs.

carm_complete.HM.ent.cmf HyperMesh command file used to organize elements into entity sets based on their density result values. This file is only used with OptiStruct topology optimization runs.

carm_complete.html HTML report of the optimization, giving a summary of the problem formulation and the results from the final iteration.

carm_complete.oss OSSmooth file with a default density threshold of 0.3. The user may edit the parameters in the file to obtain the desired results.

carm_complete.out OptiStruct output file containing specific information on the file setup, the set up of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information.




Review this file for warnings and errors that are flagged from processing the cclip_complete.fem file.

carm_complete.res HyperMesh binary results file.

carm_complete.sh Shape file for the final iteration. It contains the material density, void size parameters, and void orientation angle for each element in the analysis. The .sh file may be used to restart a run and, if necessary, run OSSmooth files for topology optimization.

cclip_complete.stat Summary of analysis process, providing CPU information for each step during analysis process.

Post-processing Results with HyperView Element density results are output to the carm_complete_des.h3d file from OptiStruct for all iterations. In addition, Displacement and Stress results are output for each subcase for the first and last iterations by default into carm_complete_s#.h3d files, where # specifies the subcase ID. This section describes how to view those results in HyperView.

Step 5: Review Contour Plot of the Density Results

1. Once you see the message Process completed successfully in the command window, click the green HyperView button.

HyperView is launched and the results are loaded. A message window appears to inform about the successful loading of the model and result files into HyperView. Notice that all three .h3d files get loaded, each in a different page of HyperView.


It is helpful to view the deformed shape of a model to determine if the boundary conditions are defined correctly, and also to find out if the model is deforming as expected. The analysis results are available in pages 2, 3, and 4. The optimization iteration results (Element Densities) are loaded in the first page.

3. Click the Previous Page icon until the name of the page is displayed as Design History, indicating that the results correspond to optimization iterations.

4. Enter the Contour panel by clicking the icon on the toolbar.

Note the Result type: is Element Densities [s] this should be the only results type in the “file_name”_des.h3d file. The second pull-down menu shows Density.

5. In the Averaging method: field, select Simple.




6. Click Apply to display the density contour.

Note the contour is all blue this is because your results are on the first design step or Iteration 0.

7. At the bottom of the GUI, click on the name Design or Iteration 0 to activate the Load Case and Simulation Selection dialog.

8. Select the last iteration by double clicking on the last Iteration #.



If there are many elements with intermediate densities, the DISCRETE parameter may need to be adjusted. The DISCRETE parameter (set in the opti control panel on the optimization panel) can be used to push elements with intermediate densities towards 1 or 0 so that a more discrete structure is given.

In this model, refining the mesh should provide a more discrete solution; however, for the purposes of this tutorial, the current mesh and results are sufficient.


Is the max= field showing 1.0e+00?

In this case, it is.

If it is not, the optimization has not progressed far enough. Allow more iterations and/or decrease the OBJTOL parameter (also set in the opti control panel).

If adjusting the discrete parameter, refining the mesh, and/or decreasing the objective tolerance does not yield a more discrete solution (none of the elements progress to a density value of 1.0), review the set up of the optimization problem. Some of the defined constraints may not be attainable for the given objective function (or vice versa).

Step 6: View an Iso Value Plot on Top of the Element Densities Contour


1. From the pull down menu, Graphics >> Iso Value and pick Element Densities as the Result type.

2. Set the Current Value: enter, 0.3.

3. Click Apply.




An iso value plot is displayed in the graphics window. The parts of the model with densities greater than the specified value of 0.3 are shown in color, and the rest are transparent (shown in the figure below).




5. From the File pull-down menu, select Exit to quit HyperView.

Review Has the volume been minimized for the given constraints?

Have the displacement constraints been met?




Topology Optimization of a Hook with Stress Constraints In this exercise, a topology optimization is performed on a bracket-hook modeled with shell elements. The structural model with loads and constraints applied is shown in the figure below. The objective is to minimize the volume of the material used in the model subject to certain stress constraints. Topology optimization is performed to find the optimal material placement and reduce the volume. This optimization normalizes each element according to its density and lets you remove elements that have low density.

The structural model is loaded into HyperMesh. The constraints, loads, subcases and material properties are already defined in the model. The topology design variables and the optimization problem set up will be defined using HyperMesh, and OptiStruct will be used to determine the optimal material layout. The results will then be reviewed in HyperView.

The optimization problem is stated as:

Objective function: Minimize volume.

Constraints: Von Mises stress < 1.6 e 04.

Design Variables: The density of each element in the design space.

The following exercises are included in this tutorial:

• Setting up the optimization problem in HyperMesh

• Submitting the job to OptiStruct

• Post-processing the results in HyperView




Step 1: Launch HM and set the OptiStruct User Profile 1. Launch HyperMesh.

(A User Profiles… GUI will appear.)

2. Choose OptiStruct in the User Profile dialog.

3. Click OK.

This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models in Bulk Data Format for RADIOSS and OptiStruct.

Step 2: Import the Finite Element Model.

1. Click on the Import button on stander toolbar

An Import… tab is added to your tab menu.

2. Make sure the Import type: is set to FE Model.

3. Make sure the File type: is set to Optistruct.

4. Click the Select files… button , File: browser for hook.fem

A Select OptiStruct file browser will pop up. Browse for your file and select it.

5. Click Open

6. Click Import.

Step 3: Set a Reasonable view

1. Press the key “v” on the keyboard.

(A view menu will pop up)

2. Select Front from the list.

3. Go to Analysis page, click on forces panel.

4. Set the magnitude % = to 0.5

5. Click return.

6. Click on constraints panel.

7. Set the Size= to 1.0.

8. Click return.

9. Press the key “f” on the keyboard.




Setting up the optimization problem in HyperMesh

Step 4: Create the design variables for topology optimization


2. Click on topology panel.

3. Go to create sub panel by clicking the radio button.

4. Click on props button to access the properties.

5. Check the boxes next to Design and Base properties.

6. Click select.

7. In the desvar =, enter shells.

8. Set the component type: switch to PSHELL.

9. Click create.

10. Select the parameters subpanel.

11. Toggle “minmenb off” to mindim.

12. Click on the text field next to mindim =, enter 0.3.

13. Toggle under stress constraint: to stress.

14. Click on the text field stress=, enter 1.6e4

15. Click update.

This value is the stress constraint for the model.


Step 5: Creating the responses

1. On the optimization panel, click responses.

2. Click response =, enter volume.

3. Click on response type: switch to volume.




4. Ensure that the total/by entity toggle is set to total (this is the default).

5. Click create.

A response, volume, is defined for the Total Design Volume of the model.


Step 6: Defining the objective function

In this example, the objective is to minimize the volume response defined in the previous step.

1. Select the objective panel.

2. Make sure that the switch option is set to min.

3. Click response =, select volume.

4. Click create.

The objective function is now defined.


Step 7: Saving the HyperMesh database

1. Click the Save .hm File icon . A Save file… browser window pops up.

2. Select the directory where you would like to save the database and enter the name for the database, hook_opt.hm, in the File name: field.

3. Click save.

Submit the job to OptiStruct

Step 8: Submit the Job to OptiStruct

1. Go to Analysis page, click on OptiStruct panel.





3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, hook_opt.fem.


4. Click Save.

Note the name and location of the hook_opt.fem file displays in the input file: field.

5. Make sure the memory options: toggle to memory default.

6. Click the run options: switch to optimization.

7. Make sure the export options: toggle to all.


This launches the OptiStruct job. If the job was successful, new results files can be seen in the directory where the OptiStruct model file was written. The hook_opt.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.

9. Close the DOS windows after you see the message: Process completed successfully

Post-processing the Results in HyperView Element density results are output from OptiStruct for all of the iterations. In addition, displacement and stress results are output for each subcase for the first and last iterations by default. This section describes how to view those results in HyperView.

HyperView is a complete post-processing and visualization environment for finite element analysis (FEA), multi-body system simulation, video and engineering data.

Step 9: Viewing with an Isosurface plot of the density results:

1. While still in the OptiStruct panel, click the green HyperView button.

HyperView launches with the .h3d file already loaded.


3. Click the iso Value icon to enter the iso Value panel.

4. Select the Result type: Element densities (s).

5. At the bottom of the GUI, click in the portion circled below to activate the Load Case and Simulation Selection dialog.




6. Select the last iteration listed in the Simulation list.

7. Click OK..

8. Make sure that Show is set to above.

9. Click Apply.

10. Move the below Current value: slider to look at the element densities.

11. You can also enter a value of 0.3 in the Current value: field.

The isosurface post-processing feature is an excellent tool to use for viewing the density results from OptiStruct.

12. Click and move the slider bar (currently pointing to a value representing 0.3) for your density to change the isosurface.

You will see the isosurface in the graphics window interactively update when you change it to a new value. Use this tool to get a better look at the material layout and the load paths from OptiStruct.

13. Click Clear Iso.




Step 10: Viewing the element stress results:

1. Click the Next Page toolbar button to move to the second page.

The second page, which has results loaded from the hook_opt_s19.h3d is displayed; this contains the linear static results for the 1st subcase.

2. Click the Contour toolbar button .

3. Select the first pull-down menu below the Result type: and select Element stresses.

4. Select the second pull down menu and select vonMises.

5. At the bottom of the GUI, click in the portion circled below to select the last Iteration.

6. Click Apply.

Stress results for the 1st static sub case

Notice that there are some local regions where the stresses are still high; this is because topology stress constraints should be interpreted as global stress control or global stress target.

The functionality has some ways to filter out the artificial or local stresses caused by point loading or boundary conditions, but those artificial stresses will not be completely removed unless the geometry is changed by shape optimization.




Step 11: Querying the results of the elements with stresses higher than 1.6e4:

1. Click on the Query toolbar button .

2. Under Elements, uncheck any of the options which you do not want to see in the table and then click on Elements and choose By Contour.

3. Below value, enter >16000 and click Add.

4. Click Apply.

This would give a list of elements with the stress value above 16000; use the mask option to graphically find the elements above the stress value.

Query results table

Mask panel

5. Click the Next Page toolbar button to move to the third page.

6. Notice that the file Hook_opt_s32.h3d is already loaded with the results of the 2nd subcase.

7. Click on the Contour panel to observe the Stress results; they are within the permissible range.




8. Repeat the above steps to observe the results of the next 2 subcases which are a duplicate of the first 2.

Notes: The advantages of using stress based optimization over the classical minimize (compliance) subject to volume fraction constraint is that it eliminates the guessing of the right volume fraction. Additionally, it eliminates the need for compliance weighting bias for multiple subcases.

There might still be high local stress regions which can be improved more effectively with local shape and size optimization.




Topology Optimization with Extrusion Constraints The extrusion constraints method allows you to perform an optimization problem with extrusion constraints to obtain a constant cross section along a given path, particularly in the case of parts manufactured through an extrusion process. By using extrusion manufacturing constraints in topology optimization, constant cross-section designs can be obtained for solid models – regardless of the initial mesh, boundary conditions, or loads.

This exercise show the steps involved in defining topology optimization over a curved beam, simulating a rail, over which a vehicle is moving. Both ends of the beam are supported. A point load is applied over the length of the rail in seven independent load cases, simulating the movement of the vehicle. The rail should be manufactured through extrusion. The steps taken to define the topology design space, the extrusion-manufacturing constraints and the optimization parameters (responses, objective and constraints) using HyperMesh are shown.

In this exercise, you will perform topology optimization on a curved beam so that the extruded rail will be stiffer and have less material. The optimization problem is stated as:

Objective: Minimize weighted compliance

Constraints: Volume fraction < 0.3

Design variables:

The density of each element in the design space

The DTPL (Design Variable for Topology Optimization) card is used for this optimization.

The finite element mesh of the curved beam is shown in the following.

Finite element mesh of the curved beam showing loads and boundary conditions

The three-part process to complete an OptiStruct topology optimization with extrusion constraints includes:

• The use of HyperMesh to setup extrusion constraints

• The set up the design optimization problem – responses, objective and constraints

• An examination of the results




Setting up the model in HyperMesh

Step 1: Launch HM, set the OptiStruct User Profile and retrieve the file rail_complete.hm



This loads the user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models in Bulk Data Format for RADIOSS and OptiStruct. The User Profiles… GUI can also be accessed from the Preferences pull-down menu on the toolbar.

3. Select the optimization panel on the Analysis page

4. From the File pull-down menu on the toolbar, select Import….

An Import… tab is added to your tab menu.

5. Select the Import type: FE Model.

6. Choose the proper File type: OptiStruct.

7. Select the Files icon button.

8. A Select RADIOSS, OptiStruct (Bulk Data Format) file browser will pop up.

9. Browse for the rail_complete.fem file located in the HyperWorks installation directory under <install_directory>/tutorials/hwsolvers/optistruct/ and select it.

10. Click Open

11. Click Apply

Setting up the topology optimization with extrusion constraints

Step 2: Create the topology design variables

1. From the Analysis page enter the optimization panel.

2. Enter the topology


4. Click DESVAR=, type design_solid, and press Enter.

5. Click props and choose new_solid from the list of props and click on select.




6. Choose type: PSOLID

7. Click Create.

A topology design space definition, design_solid, has been created. All elements organized in this design property collector are now included in the design space.

8. Click return twice to go back to the main menu.

Step 3: Define extrusion problem and extrusion path

1. From the Tool page, enter the numbers panel.

2. Click nodes and select by id.

3. Enter numbers 71559,70001 and hit enter, check the display box then click on.

The numbers 71559 and 70001 should be displayed on the screen.

4. Click return.

5. From the Analysis page, enter optimization panel.

6. Click topology.

7. Make sure the extrusion subpanel is selected using the radio buttons on the left-hand side of the panel.

8. Double click desvar = and select design_solid.

9. Switch the toggle to no twist.

Extrusion constraints can be applied to domains characterized by non-twisted cross-sections or twisted cross-sections by using the NOTWIST or TWIST parameters, respectively.

10. Select the primary path by selecting node list and clicking by path.

It is necessary to define a ‘discrete’ extrusion path by entering a series of grids. The curve between these grids is then interpolated using parametric splines. The minimum amount of grids depends on the complexity of the extrusion path. Only two grids are required for a linear path, but it is recommended that at least 5-10 grids be used for more complex curves.

11. First, select node 71559 and then select node 70001.

12. Click update.

A line of nodes starting from 71559 and ending with node 70001 should be highlighted, indicating the extrusion path.

You do not have to select as many nodes to define the curve. This is an exercise to show that the nodes by path option can also be used.

13. Click return to go back to the Optimization panel.




Step 4: Create the volume fraction and weighted compliance response


2. Click response = and enter vol.

3. Click on the response type switch and select volumefrac from the pop-up menu.

4. Ensure the regional selection is set to total (this is the default).

5. Click create.

A response, vol, is defined for the total volume of the model.

6. Click response = and enter wcomp1.

7. Click on the response type switch and select weighted comp from the pop-up menu.

8. Click loadsteps and select step1, step2, step3, step4, step5, step6 and step7 from the extended entity selection menu that pops up.

9. Click return

10. Click create

A response, wcompl , is defined for the weighted compliance.


Step 5: Create constraints on volume fraction response


1. Enter the dconstraints panel

2. Click constraint= and enter constr1



5. Select response= and set it to vol

6. Click create



1. Enter the objective panel


3. Click response= and select wcompl.




4. Click create

5. Click return to exit the Optimization panel

Step 7: Export the file

1. From the File pull-down menu on the toolbar, select Export….

An Export… tab is added to your tab menu.

2. Make sure the Export type: FE Model.

3. Makes sure the File type: RADIOSS, OptiStruct (Bulk Data Format).

4. Makes sure the Template: Standard Format


6. Select the directory where you would like to write the OptiStruct model file and enter the

name for the model, rail_complete_extrusion.fem, in the File name: field.


7. Click Save

Viewing the Results and Post-processing

Step 8: Load the results file and post-process the topology results with extrusion manufacturing constraints

Solving time for this extrusion constraint problem takes about 2 hours. Rather than solving this geometry in class, we will pick up the process by loading the solution results file.

1. Launch HyperView

2. Click the open folder icon and load the file rail_complete_extrusion_des.h3d.

3. Click Apply.

4. At the bottom of the GUI, click on the name Design or Iteration 0,

, to activate the Load Case and Simulation.

5. Scroll to and select the last Iteration (e.g.: Iteration 41) and click OK.




6. Go to the Iso Value panel, and set the Result type: to Element Densities.

7. Click Apply.

8. Set Current Value: to 0.3.

9. Click Apply.




Isosurface plot of a curved beam rail layout of the topology optimization with extrusion constraints

As expected, the result with manufacturing extrusion constraints permits a constant cross section for the entire length of the model.

Step 9: View the section cut of the extrusion component

The Section Cut panel allows you to cut planar sections through a model. This is useful when you want to see details inside of a model.

1. Click on the Section Cut panel .

2. For Define plane:, select Y Axis.

3. Click Base to active it, and click on any corner at the center of the model.

4. Click Apply.

5. Move the slider bar below Y Axis to scroll though the model.

6. Under Display options: use the slider bar next to Width to change the Cross section width.




Contour plot of a section cut on x-z plane of the curved beam

As expected, the result with manufacturing extrusion constraints shows constant cross section through the length of the model.

7. Click Delete in the section cuts panel to get back to the original model.




Free-sizing Nonlinear Gap Optimization on an Airplane Wing Rib In this exercise, an existing finite element model of an aluminum wing rib model will be used to demonstrate how to do free-sizing optimization using OptiStruct. HyperView will be used to post-process the thickness pattern in the rib.

Wing rib model

There are four shell components in the model: the mounting flange, the web, the top and bottom flanges, and the lug. The web is connected to the lug by gap elements. Appropriate properties, loads, boundary conditions, and nonlinear subcases have already been defined in the model. The design region is the web and the rest of the components are non-design. Since a large portion of aerospace components are shell structures which are manufactured by machining or milling operations, free-sizing optimization is very suitable for those components. To understand the limitations of topology optimization for such applications, a nonlinear gap topology optimization will also be done on the wing rib model.

The optimization problem for this exercise is stated as:-

Objective: Minimize weighted compliance WCOMP.

Constraints: Volume fraction on the web < 0.3.

Design variables for free sizing optimization:

Thickness of each shell element in the design space.

Design variables for topology optimization:

Element density of each element in the design domain.




This exercise will use the following steps to set up free-sizing optimization and topology optimization:

• Create design variable for free-sizing optimization

• Define manufacturing constraint for free size


• Run the free-sizing nonlinear gap optimization

• Post-process the thickness distribution in the design domain

• Create topology design variables

• Define manufacturing constraint for topology

• Run the nonlinear gap topology optimization

• Post-process results using HyperView

• Review and compare results from free-size optimization and topology optimization




Step 1: Launch HM, set the RADIOSS OptiStruct User Profile and retrieve the file rib_complete.hm

1. Launch HyperMesh


3. From the pull-down menu on the toolbar, File >> Open….


4. Browse for the rib_complete.hm file.

5. Click Open

Step 2: Create design variable for free sizing optimization

1. From the Analysis page, select the optimization panel.

2. Select the free size panel.

3. Choose the create subpanel using the radio button on the left.

4. Click desvar= and enter shells.

5. Verify that type: is set to PSHELL.

6. Click props, choose the Web component and click select.

7. Click create.

This creates the design variable for free-sizing optimization.

Step 3: Create manufacturing constraints for free-sizing

1. While still in the Free Size Optimization panel, select the parameters subpanel.

2. Click desvars and select the shells design variable created previously.

3. Toggle minmemb off and for mindim =, enter 2.0.

4. Click update.

5. Click return.

Step 4: Create optimization responses, objective and constraints

1. Select the responses panel.

First, the weighted compliance response will be created.

2. For response =, input the name wcomp.




3. Click the switch for response type and go to the next page of available types by using >>, and click on weighted comp.

4. Click loadsteps and select both the Coup_Vert and Pressure loadcases.

The weighting factor should be 1.0 for both.

5. Click return.

6. Click create.

7. For response =, input the name volfrac to create the volume fraction response.

8. For response type, go to the previous page using <<, and click on volume frac.

9. Leave the type as total.

10. Click create.

11. Click return.

12. Click on the dconstraints panel to define the volume fraction constraint.

13. For constraint =, input the name vol.

14. Click response =, and select the volfrac response.

15. For upper bound =, input a value of 0.3.

16. Click create.

17. Click return.

18. Click on the objective panel to define the objective.

19. Toggle to min if not already done.

20. For response =, select the wcomp response.

21. Click create.

22. Click return twice.

The optimization parameters have now been defined.

Step 5: Run free-sizing nonlinear gap optimization

1. From the Analysis page, select the OptiStruct panel.

2. Click save as… following the input file: field. A Save file… browser window pops up.

3. Select the directory where you would like to write the optimization file and enter the name rib_freesize.fem in the File name: field.

4. Click Save.




Note the name and location of the rib_freesize.fem file shows in the input file: field.





This launches the OptiStruct job.

If the job was successful, new results files can be seen in the directory where the OptiStruct model file was written. The rib_freesize.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.


rib_freesize.hgdata HyperGraph file containing data for the objective function, percent constraint violations, and constraint for each iteration.

rib_freesize_hist.mvw This file is a HypeView session file and may be opened from the File pull-down menu in HyperView or HyperGraph. The file automatically creates individual plots for each of the results (objectives, constraints) contained in the .hist file. Each plot occupies its own page within HyperView (HyperGraph).

rib_freesize.HM.comp.cmf

This is a HyperMesh command file. When executed in HyperMesh, the .HM.comp.cmf file organizes all elements in the model into ten new components based on their element thicknesses at the final iteration. The components for this run are named 0.0-0.01, 0.01-0.02, 0.02-0.03, and so on, up to 0.09-0.1, considering the plate thickness of the Web is 0.1mm.

rib_freesize.html HTML report of the optimization, giving a summary of the problem formulation and the results from the final iteration.

rib_freesize.oss The file contains default settings for running OSSmooth after a successful optimization.

rib_freesize.out OptiStruct output file containing specific information on the file setup, the setup of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors that are flagged from




processing the rib_freesize.fem file.

rib_freesize.res HyperMesh binary results file.

rib_freesize.sh Shape file for the final iteration. The .sh file may be used to restart a run.

rib_freesize.stat Summary of analysis process, providing CPU information for each step during analysis process.

rib_freesize_des.h3d HyperView binary results file for element thickness information.

rib_freesize_s1.h3d HyperView binary results file for displacement and stress results for subcase 1.

rib_freesize_s2.h3d HyperView binary results file for displacement and stress results for subcase 2.

Post-process results using HyperView Element thickness distribution are output from OptiStruct for all iterations. In addition, Displacement and Stress results are output for each subcase for the first and last iteration by default. This section describes how to view those results in HyperView.

1. From the OptiStruct panel, click the HyperView button.

This should launch HyperView and load the .h3d file, reading the model and results.

2. Click close to close the message window.

3. Click the Entity Attributes icon on the toolbar and undisplay all of the components except Web. You can do this by activating the Auto apply mode: (Display OFF) and then clicking on the component that you want turned off in the GUI.

4. Click the Mesh:, shaded mesh option .

5. Click on the Web component to get a shaded mesh.

6. Go to the Contour panel and set the Result type: to Element Thicknesses.

7. Choose Select Load Case from the Graphics pull-down menu to open the Load Case and Simulation Selection dialog.

8. Select the last iteration listed in the Simulation list and click OK.

9. Click Top in the view controls section (in bottom right of HyperView panel) to get a top view of the Web.




10. Click Apply.

This will show the contour element thickness on the Web component.

Thickness contour from free-sizing nonlinear gap optimization, on the Web of plate thickness 0.1mm

As can be seen from the figure above, the result from free sizing optimization is a web with optimized thickness distribution that can be reduced subsequently into larger zones for simplification of the manufacturing process. Moreover, the design obtained from free sizing offers the freedom to create cavities, ribs and varying thickness simultaneously, which is not possible in topology optimization.

11. Click Files from the pull-down menu and select Exit to quit HyperView.

Step 6: Create design variables for topology optimization

1. First, save the current HyperMesh file by selecting the File pull-down menu and clicking Save as.

A Save as … browser window pops up.

2. Select the directory where you are running the optimization and enter rib_freesize.hm for the file name.

3. Click save.

4. Press F2 to get to the Delete Entities panel. This is where we will delete the design variable shells created for free-sizing optimization.

5. Toggle the entities to select designvars.




6. Click designvars, select shells and click select.

7. Click delete entity.

The message 1 entity was deleted should appear in the header bar.

8. Click return.

9. From the Analysis page, select the optimization panel.

10. Choose the topology panel.

11. Select the create subpanel.

12. For desvar = input the name shells.

13. Click props, choose the Web component, and click select.

14. Under type, choose PSHELL and leave the base thickness as 0.0.

15. Click create.

The web component has now been defined as the design component for topology optimization.

Step 7: Create manufacturing constraints for topology optimization

1. First, save the current HyperMesh file by selecting the File pull-down menu and clicking on Save as.

A Save as … browser window pops up.

2. Select the directory where you are running the optimization and enter the name rib_topology.hm for the file.

3. Click save.

4. Select the parameters subpanel using the radio buttons on the left of the Topology Optimization panel.

5. For desvars = select shells.

6. Toggle minmemb off and for mindim =, enter the value 2.0 for minimum member size control.

7. Click update.

8. Click return twice.

Step 8: Run the topology nonlinear gap optimization

The optimization responses, constraints and objective have already been defined.

1. From the Analysis page, select the OptiStruct panel.




2. Make sure the rib_topology.fem file shows in the input file: field.





This launches the OptiStruct job.

If the job was successful, new results files can be seen in the directory where the OptiStruct model file was written. The rib_topology.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.


rib_topology.hgdata HyperGraph file containing data for the objective function, percent constraint violations, and constraint for each iteration.

rib_topology.HM.comp.cmf HyperMesh command file used to organize elements into components based on their density result values.

rib_topology.HM.ent.cmf HyperMesh command file used to organize elements into entity sets based on their density result values.

rib_topology.html HTML report of the optimization, giving a summary of the problem formulation and the results from the final iteration.

rib_topology.oss OSSmooth file with a default density threshold of 0.3. The user may edit the parameters in the file to obtain the desired results.

rib_topology.out OptiStruct output file containing specific information on the file setup, the setup of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors that are flagged from processing the rib_topology.fem file.

rib_topology.res HyperMesh binary results file.

rib_topology.sh Shape file for the final iteration. It contains the material density, void size parameters, and void orientation angle for each element in the analysis. The .sh file may be used to restart a run.

rib_topology.stat Summary of analysis process, providing CPU information for each step during analysis process.

rib_topology_des.h3d HyperView binary results file for information on element density.




rib_topology_s1.h3d HyperView binary results file for displacement and stress results for subcase 1.

rib_topology_s2.h3d HyperView binary results file for displacement and stress results for subcase 2.

Post process the results using HyperView Element density results are output from OptiStruct for all iterations. In addition, displacement and stress results are output for each subcase for the first and last iteration by default. This section describes how to view those results in HyperView.


This launches HyperView and loads the .h3d file, reading the model and results.

2. Click close to close the message window.

3. Click the Entity Attributes icon on the toolbar and undisplay all of the components except the Web component. You can do that by activating the Auto apply mode: (to Display Off) and clicking on the components that you want turned off in the GUI.

4. Click the Mesh: panel shaded mesh option.

5. Click on the Web component to get a shaded mesh.

6. Go to the Contour panel and set the Result type: to Element Densities.

7. Click in the bottom right portion of the GUI to activate the Load Case and Simulation Selection dialog.


9. Click Top in the view controls to get a top view of the Web.

10. Click Apply to show the contour of element density on the Web component.




Contour of element density on the Web component from topology nonlinear gap optimization

The results from topology optimization show very discrete results as expected.

Review and compare results from free-sizing optimization and topology optimization

Results from the topology optimization show a truss type design with extensive cavities and voids, while the results from free-sizing optimization tend to come up with shear panels. While solid/void density distribution is the only choice for solid elements; for shell structures, intermediate densities can be interpreted as different thicknesses and penalizing then could result in potentially inefficient shell structures. Moreover, since a large portion of aerospace structures are shell structures, a shear panel type design is often desirable for manufacturing purposes especially for machine milled shell structures. Free-sizing optimization can prove to be very beneficial in those situations.




Chapter 3

Topography Optimization

Topography Optimization Topography optimization generates an optimized distribution of shape based reinforcements such as stamped beads in shell structures. The problem set up is simply done by defining the design region, the maximum bead depth and the draw angle. OptiStruct automatically provides the design variable creation and optimization control. Manufacturing constraints can be imposed using symmetry planes, pattern grouping, and pattern repetition.


Chapter 3: Topography Optimization



• Search for optimal distribution of beads (swages) in shell structures

• Conceptual design method


Plate under torsionPlate under torsion

Design variable generationDesign variable generation

Final contourFinal contourFinal DesignFinal Design


Molded Pressure Tank

• Thin walled tank filled with fluid to be optimized for stiffness





Three orthogonal planes of symmetry are defined

Symmetry



Results• Reinforcement pattern for pressure box

CONTOUR FINAL RESULT






Max. Deflect: 7.54mm Max. Deflect: 10.8mm Max. Deflect: 13.9 mm

• Notice that more ribs doesn’t necessarily mean more stiffness

Performance



Max. Deflection: 2.23Max. Stress: 267




Topography OptimizationMax. Deflection: 1.17Max. Stress: 196


Torsion Plate Example





OptiStruct Input: Topography Optimization

DTPG card – Design Variable definition for topography optimization

• Definition of Design Variables

• Nodal movement (shape change) on shell component

• Each iteration generates new nodal positions

• Shell, and composite properties (components) can be defined as topography design space.

• Shells

• Composites

• Pattern grouping

HyperMesh Topology panel:


Topography Optimization Setup

Bead Parameters

αα

Min.Min.Bead widthBead width

Max.Max.Bead height Bead height

Draw angle Draw angle

normal

global





symmetrysymmetryradialradialCyclicalCyclical

linearlinearplanarplanarCircularCircular


Pattern Grouping


Bounds

• Beads into one direction

• Beads into two directions

• Initial Bead fraction






Bead discreteness control

• Beadfrac response • Used as objective or constraint

• More discrete results will be achieved with lower beadfrac

More discrete results


Combining Optimization Types

• Optimization types can be combined

• Example: Topology + Topography

Topology + Topography

Topography

Topology

Shape Contour





Exercise 3.1 : Topography Optimization of a Torsion Plate

• Create design variable for topography optimization


• Run the optimization

• Post-Process the results




Topography Optimization of a Plate Under Torsion This exercise demonstrates how to perform topography optimization of a plate under torsion. A finite element model of the design space with loads and constraints applied is shown in the image below. It is assumed that the part is to be formed using a stamping process. The objective is to minimize the displacement of the node where the force is applied in the positive z-direction. Only the shape of the plate can be changed to achieve the objective, not the thickness.

Finite element model of the design space with loads and constraints.

A finite element model (shown in the above figure) is loaded into HyperMesh. The constraints, load, material properties, and subcase (loadstep) of the model are already defined. Topography design variables and optimization parameters are defined and the OptiStruct software is used to determine the optimal reinforcement patterns. The results are viewed as animations of the contours of shape changes of the design space. Finally, the use of the grouping patterns is shown; based on the shape changes suggested by OptiStruct, a possible pattern is chosen for ease of manufacturing.

The optimization problem for this tutorial is stated as:

Objective: Minimize nodal displacement at grid point where loading is applied.

Design variables:

Shape variables on the designable space.

The first exercise includes: • Setting up the problem in HyperMesh • Submitting the job • Viewing the results

In the second exercise, grouping pattern is defined to generate manufacturable patterns




Step 1: Launch HM, load the OptiStruct user profile and retrieve the model



This loads the OptiStruct user profile. It includes the appropriate template, macro menu, and import reader, paring down the functionality of HyperMesh to what is relevant for generating models in Bulk Data Format for RADIOSS and OptiStruct.


3. Open the Open file… GUI by selecting the File icon on the main menu.

4. Browse for and select the torsion_plate.hm file.

5. Click Open.

The torsion_plate.hm database is loaded into the current HyperMesh session, replacing any existing data.

Step 2: Check the thickness of the component

1. From Model Browser tab, expand the Property entities. Right click on design and select Card Edit.

A PSHELL card image panel should appear. OptiStruct stores information regarding shell thicknesses on the PSHELL card.

2. Ensure that the thickness, T, is set to the value 1.0.

3. Click return to go to the main menu.




Step 3: Define design variables for topography optimization

For topography optimization, a design space and a "bead" definition need to be defined. The following section outlines how this is done. For further information on "bead" definition, please see the reference manual section on the DTPG card.

1. From the Analysis page click optimization to enter the panel.

2. Select the topography panel.


4. Click desvar= and type topo.

5. Click the highlighted props.

6. Check the box next to design and click select.

7. Click create to create the shape design variables for the selected component.

A topography design space definition, 'topo', has been created. All elements organized into the 'design' component collector are now included in the design space.

8. Select the bead params subpanel using the radio buttons on the left-hand side of the panel.

9. The field next to desvar = should contain the name of the newly created design space by default. If it does not, click on desvar = and select topo from the list of topographical design spaces.

10. Click minimum width= and enter 5.0.

This parameter controls the width of the beads in the model. The recommended value is between 1.5 and 2.5 times the average element width.

11. Click draw angle= and enter 60.0 (this is the default).

This parameter controls the angle of the sides of the beads. The recommended value is between 60 and 75 degrees.

12. Click draw height= and enter 4.0.

This parameter sets the maximum height of the beads to be drawn.

13. Check the box next to buffer zone.

This parameter establishes a buffer zone between elements in the design domain and elements outside the design domain.

14. Make sure the draw direction: toggle is set to normal to elements.

This parameter defines the direction in which the shape variables are created.

15. Make sure the boundary skip: switch is set to load & spc.




This tells OptiStruct to leave nodes at which loads or constraints are applied out of the design space.

16. Click update.

A "bead" definition has been created for the design space 'topo'. Based on this information, OptiStruct will automatically generate bead variable definitions throughout the design variable domain as shown on the DTPG page of the Reference Guide.

17. Select the bounds subpanel using the radio buttons on the left-hand side of the panel.

18. Ensure topo is in the field next to desvar = . If it is not, click on desvar = and select topo from the list of topographical design spaces.

19. Click on upper bound and enter 1.0 (this is the default).

Upper bound on variables controlling grid movement (Real > LB, default = 1.0). This sets the upper bound on grid movement equal to UB*HGT.

20. Click on lower bound and enter 0.0 (this is the default).

21. Click update.

The upper bound sets the upper bound on grid movement equal to UB*HGT and the lower bound sets the lower bound on grid movement equal to LB*HGT.

22. Click return to go to the optimization panel.

Step 4: Define the responses

A detailed description can be found in the online manual under Responses.

Define one response for the objective: displacement at the node where the force is applied.


2. Click response = and enter displace.

3. Click on the response type switch and select static displacement from the pop-up menu.

4. Click nodes and select by ID from the extended entity selection menu that pops up.

5. Type 2500 and hit the Enter key.

The node where the force is applied is now selected.

6. Select dof3.

dof1, dof2, and dof3 refer to translation in the X, Y, and Z directions.

dof4, dof5, and dof6 refer to rotation about the X, Y, and Z axes.




total disp is the resultant of the translational displacements in x, y, and z directions.

total rotation is the resultant of the rotational displacements in x, y, and z directions.

7. Click create.

A response, 'displace', is defined for the z-displacement of node 2500.

8. Click return to go to the optimization panel.


In this example, the objective is to minimize the displacement response defined in the previous section.

1. Enter the objective panel from the optimization panel.

2. Click the switch in the upper-left corner of the panel, and select min from the pop-up menu.

3. Click response = and select displace from the response list.

A loadstep button should appear in the panel.

4. Click on loadstep and select torsion from the subcase (loadstep) list.

5. Click create.

The objective function is now defined.

6. Click return twice to go to the main menu.

Step 6: Submitting the Job




3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, torsion_plate.fem, in the File name: field.


4. Click Save.

Note that the name and location of the torsion_plate.fem file is now displayed in the input file: field.

5. Set the export options toggle, underneath the run options switch, to all.




6. Click the run options switch, located in the center of the panel, and select optimization.

7. Set the memory toggle, located at the left-hand side of the panel, to memory default.


This launches the OptiStruct job. If the job was successful, new results files can be seen in the directory where the OptiStruct model file was written. The torsion_plate.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.


torsion_plate.grid An OptiStruct file where the perturbed grid data is written.

torsion_plate.hgdata

HyperGraph file containing data for the objective function, constraint functions, design variables, and response functions for each iteration.

torsion_plate.hist An OptiStruct output file for xy plotting containing the iteration history of the objective function, maximum constraint violation, design variables, DRESP1 type responses, and DRESP2 type responses.

torsion_plate.html HTML report of the optimization, giving a summary of the problem formulation and the results from the final iteration.

torsion_plate.oss OSSmooth file with a default density threshold of 0.3. The user may edit the parameters in the file to obtain the desired results.

torsion_plate.out The OptiStruct output file containing specific information on the file set up, the set up of the optimization problem, estimate for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. Review this file for warnings and errors that are flagged from processing the torsion_plate.fem file.

torsion_plate.res The HyperMesh binary results file.

torsion_plate_des.h3d

HyperView binary results file for information on shape changes.

torsion_plate_s1_h3d

HyperView binary results file for displacement and stress results for subcase 1.




torsion_plate.sh Shape file for the final iteration. It contains the material density, void size parameters, and void orientation angle for each element in the analysis. The .sh file may be used to restart a run and, if necessary, run OSSmooth files for topology optimization.

torsion_plate.stat Summary of analysis process, providing CPU information for each step during analysis process.

Viewing the Results Shape contour information is output from OptiStruct for all iterations. In addition, Displacement and Stress results are output for the first and last iteration by default. This section describes how to view those results in HyperView.

Step 7: View a static plot of your shape contours


This will launch HyperView and load the torsion_plate_des.h3d and torsion_plate_s1.h3d files reading the model and optimization results.


3. Click the Contour icon on the toolbar to enter the contour panel.

4. Set Result type: to Shape Change (v) and type to Mag.

5. Click in the bottom right portion of the GUI (as pictured) to activate the Load Case and Simulation Selection dialog.


A deformed plate appears.

7. Click Apply.

8. Is the max= field showing 4.0e + 00?

9. In this case, it is. If it is not, your optimization has not progressed far enough. Decrease the OBJTOL parameter (set in the opti control panel on the optimization panel). This value, 4.0e+00, comes from the draw height defined earlier.




Contour plot showing the reinforcement pattern at the last iteration (converged solution)

Step 8: View a transient animation of the shape contour changes

A transient animation of contour shapes will give a good idea of the shape changes happening through different iteration.

1. Verify that the animate mode menu is set to Transient as shown below.

2. Click the traffic light icon to start the animation.

3. Click the director’s chair icon to the Animation Controls panel.

4. With the animation running, use the slider bar below Max Frame Rate: on the left side of the panel to adjust the speed of the animation.

5. Click the traffic light icon again to stop the animation.

Step 9: View the deformed structure

The displacement and stress results from the first and last iterations (default) are given in the torsion_plate_s1.h3d file.

1. Click the forward arrow icon to go to the next page.




This page has the subcase information from the torsion_plate_s1.h3d file.

2. Verify that the animate mode menu is set to Linear Static.

For a better visual of what it happening with this model turn on mesh lines and contour the results as in the previous step.

3. Click the Deformed icon on the toolbar to enter the panel.

4. Set Result type: to Displacement(v).

5. Click in the bottom right portion of the GUI as pictured below to activate the Load Case and Simulation Selection dialog.

6. Select the first iteration – Iteration 0.

7. Click the cantilever beam icon to start the animation.

8. Click the director’s chair to go to the Animation Controls panel.

9. With the animation running, use the slider bar below Max Frame Rate: on the left side of the panel to adjust the speed of the animation.

A deformation animation of the original model is shown in the graphics window.

Does the deformed shape look correct for the boundary conditions you applied to the mesh?

10. Click the cantilever beam icon again to stop the animation.

11. Go to File on the pull-down menu and click Exit to quite HyperView.




Adding Pattern Grouping as a constraint for Manufacturability The configuration obtained in the previous example (see the contour plot showing the reinforcement pattern at the 17th iteration) might be difficult to manufacture. It does give an idea of what kinds of patterns are likely to optimize the structure (in this case -- to minimize the displacement at the selected node).

A possible pattern, suggested by the static contour plot obtained in the previous exercise, is to use channels parallel to a diagonal. In this example, we choose the diagonal emerging from the node where the load is applied.

Step 1: Add pattern grouping constraint

1. Going back to HM click return to exit the OptiStruct panel.

2. From the Analysis page click optimization to enter the panel.

3. Click topography to enter the panel.

4. Select the pattern grouping subpanel using the radio buttons on the left-hand side of the panel.

5. Click desvar = and choose topo from the list of topographical design spaces.

6. Click on the pattern type: switch and select linear.

7. Make sure the sub-type: switch is set to basic.

8. Click anchor node and select the node at the corner where the load is applied by clicking on it in the graphics window.

9. HM automatically move the blue halo around first node, select the node in the opposite corner by clicking on it in the graphics window.

10. Click update.

11. Click return twice to go to the main menu.

Step 2: Submitting the Job

1. From the Analysis page, click OptiStruct to enter the panel.



3. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, torsion_pattern.fem, in the File name: field.


4. Click Save.




Note the name and location of the torsion_pattern.fem file displays in the input file: field.

5. Set the export options toggle, underneath the run options switch, to all.

6. Click the run options switch, located in the center of the panel, and select optimization.

7. Set the memory toggle, located at the left-hand side of the panel, to memory default.


This launches the OptiStruct job. If the job was successful, new results files can be seen in the directory where the OptiStruct model file was written. The torsion_pattern.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.

View the new results as before. Also check the objective value for the zero-th and last iteration in the .out file. How does the final value for the objective compare to the final value obtained using 'none' option for pattern grouping?

Step 3: View a static plot of your shape contours

Repeat the steps in the previous exercise to view the contour plot of the shape change.

Contour plot showing the reinforcement pattern with pattern grouping constraint at the last iteration




Automatic Recognition of Bead Results from Topography Optimization of an L-bracket The objective of this exercise is to run a completed topography optimization model to post process the results and use the Auto-Bead Functionality.

The objective of Auto-bead is to offer automation of bead interpretation so that a prototype-like design could be created automatically.

L bracket layout.

The following steps are included:

• Import the the completed fem file to Hypermesh

• Submit the job

• Post processing




Step 1: Launch HM set the OptiStruct User Profile and Import the Fem file




3. From the File pull-down menu on the toolbar, select Import…. An Import… tab is added to your tab menu

4. Select the import type: FE Model.

5. Choose the File type: Optistruct.


7. An OptiStruct file browser will pop up.

8. Select the Lbkttopog_bead.fem file.

9. Click Apply.

The Lbkttopog_bead.fem OptiStruct input file is loaded into the current HyperMesh session.

10. Click Close to exit the Import tab.

Step 2: Run the OptiStruct job

1. Select the OptiStruct panel on the Analysis page.


3. A Save file… browser window pops up.

4. Select the directory where you would like to write the OptiStruct model file and enter the name for the model, Lbkttopog_bead.fem, in the File name: field.

5. The .fem extension is used for OptiStruct input decks.

6. Click Save.

7. Set the export options: toggle, underneath the run options switch, to all.

8. Click the run options: switch, located on the left of the panel, and select optimization.

9. Set the memory options: toggle, located in the center of the panel, to memory default.


This launches the OptiStruct job. If the job was successful, new results files can be seen in the directory where the OptiStruct model file was written. The lbkttopog_bead.out file is a good place to look for error messages that will help to debug the input deck if any errors are present.





Lbkttopog_bead.grid An OptiStruct file where the perturbed grid data is written.

Lbkttopog_bead.hgdata HyperGraph file containing data for the objective function, percent constraint violations and constraint for each iteration.

Lbkttopog_bead.hist OptiStruct iteration history file containing the iteration history of the objective function and of the most violated constraint. Can be used for an xy plot of the iteration history.

Lbkttopog_bead.res Hypermesh Results File

Lbkttopog_bead.oss OSSmooth file with a default density threshold of 0.3. The user may edit the parameters in the file to obtain the desired results.

Lbkttopog_bead.out OptiStruct output file containing specific information on the file setup, the setup of the optimization problem, estimates for the amount of RAM and disk space required for the run, information for each optimization iteration, and compute time information. It is highly recommended to review this file for warnings and errors that are flagged.

Lbkttopog_bead.h3d Hyper 3D binary results file.

Lbkttopog_bead.sh Shape file for the final iteration. It contains the material density, void size parameters and void orientation angle for each element in the analysis. The .sh file may be used to restart a run and, if necessary, run OSSmooth files for topology optimization.

Lbkttopog_bead.stat Summary of analysis process, providing CPU information for each step during analysis process.




Review the results using HyperView Shape contour information is output from OptiStruct for all iterations. In addition, Eigenvector results are output for the first and last iteration by default. This section describes how to view those results in HyperView.

Step 3: Review a transient animation of shape contour changes

1. Click HyperView

2. Click the Stoplight icon to start the animation.

An animation of the shape changes over the course of the optimization is displayed. If you wish to slow down the animation click the directors chair to the left of the stoplight and adjust the Max Frame Rate: slider to slow down the animation.

Step 4: Review the final mode shape

1. On the page toolbar click the Next Page icon.

2. Toggle the Select animation mode to Modal.

3. Click on the Load Case and Simulation Selection area in the lower right corner.

4. Toggle between Iteration 0 & Iteration 12 in the Load case: list.

Notice the topography optimization yields an almost 100% increase in the frequency of the first mode by reviewing the Mode 1-F value in the Simulation list. To animate the mode click the modal icon next to the directors chair that use to be a stoplight.

Step 5: Apply the optimized topography to the model

1. Go back to HM and click return to exit from Optistruct panel.

2. Click on Post page and select apply result panel.

3. Click simulation = and select DESIGN [12] from the list of simulations.

4. Click data type = and select Shape Change.

5. Choose displacements using the radio buttons on the left-hand side of the panel.

6. Click the component selection switch and select total disp.

7. Click nodes and select all from the extended entity selection switch.

8. Click mult = and enter 1.

9. Click apply.




The final nodal positions are applied to the structure. Be careful with saving the model now, the HyperMesh database has changed. This model can be used for further analyses. Results can now be viewed on the final shape.

10. Click Reject to get back the original shape and return to go back to main menu.

Step 6: Extract/Import Final (concept) geometry Using OSSmooth and Auto-Bead

1. On the Post page select OSSmooth panel

2. From file: select the OptiStruct base input file from which to extract the final geometry

3. For output: select the IGES output format of the final geometry.

The default output format is STL. Other format options are: Mview, Nastran, IGES, and H3D.

If you select IGES as the output format, select the output unit type. The default is mm (millimeters).

4. Select Load geom to load the new geometry into the current HM session.

5. Check the box next to autobead and enter a value of 0.3 in the bead threshold:

6. Leave the remesh option unchecked

Note: The ‘remesh’ option utilizes auto-meshing capability of HM to remesh the draw portion of the interpreted design into TRIA mesh.

7. Uncheck the surf reduction

8. Leave rest of the options at default settings.

9. Click OSSmooth

10. Click Yes to overwrite.

The new geometry will be automatically loaded into the existing Hypermesh file, turn off the display of all the elements to view the new concept geometry.




Topography results

Note: If the remesh option is checked on as shown in the below picture

The new mesh is loaded into the current Hypermesh session.




Documents

Optistruct Optimization 90 Vol1 Manual