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Chapter 1

Introduction

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Training Manual

Introduction to ANSYS 7.1 - Part 1

Table of Contents

8. Loading1. Introduction

2. FEA and ANSYS

3. ANSYS Basics

4. General Analysis Procedure

5. Creating the Solid Model

6. Creating the Finite Element Model

7. Defining the Material

9. Solution

10. Structural Analysis

11. Thermal Analysis

12. Coupled-field Analysis

13. Postprocessing

14. Short Topics

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Chapter 2

FEA and ANSYS

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Chapter 2 - FEA and ANSYS

What is FEA?

Finite Element Analysisis a way to simulate loading conditions ona design and determine the designs response to thoseconditions.

The design is modeled using discrete building blocks calledelements.

Each element has exact equations

that describe how it responds to acertain load.

The sum of the response of allelements in the model gives thetotal response of the design.

The elements have a finite numberof unknowns, hence the namefinite elements.

Historical Note

The finite element method ofstructural analysis was createdby academic and industrialresearchers during the 1950sand 1960s.

The underlying theory is over100 years old, and was the basisfor pen-and-paper calculationsin the evaluation of suspensionbridges and steam boilers.

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...What is FEA?

The finite element model, which has a finitenumber of unknowns,can only approximatethe response of the physical system, whichhas infiniteunknowns.

So the question arises: How good is the approximation?

Unfortunately, there is no easyanswer to this question. It dependsentirely on what you are simulating

and the tools you use for thesimulation. We will, however,attempt to give you guidelinesthroughout this training course.

Physical System F.E. Model

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...What is FEA?

Why is FEA needed?

To reduce the amount of prototype testing

Computer simulation allows multiple what-if scenarios to be testedquickly and effectively.

To simulate designs that are not suitable for prototype testing

Example: Surgical implants, such as an artificial knee

The bottom line:

Cost savings

Time savings reduce time to market!

Create more reliable, better-quality designs

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About ANSYS

ANSYS is a complete FEA software package used by engineersworldwide in virtually all fields of engineering:

Structural

Thermal Fluid (CFD, Acoustics, and other fluid analyses)

Low- and High-Frequency Electromagnetics

A partial list of industries in which ANSYS is used:

Aerospace

Automotive

Biomedical

Bridges & Buildings

Electronics & Appliances

Heavy Equipment & Machinery

MEMS - Micro Electromechanical Systems

Sporting Goods

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About ANSYS

Structural analysis is used to determine deformations, strains,stresses, and reaction forces.

Static analysis

Used for static loadingconditions.

Nonlinear behavior suchas large deflections, largestrain, contact, plasticity,hyperelasticity, and creepcan be simulated.

Compression of a Hyperelastic Seal

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About ANSYS

Dynamic analysis

Includes mass and dampingeffects.

Modal analysis calculates natural

frequencies and mode shapes. Harmonic analysis determines a

structures response tosinusoidal loads of knownamplitude and frequency.

Transient Dynamic analysisdetermines a structuresresponse to time-varying loadsand can include nonlinearbehavior.

Other structural capabilities Spectrum analysis

Random vibrations

Eigenvalue buckling

Substructuring, submodeling

Mode Shape Animation

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About ANSYS

Explicit Dynamics with ANSYS/LS-DYNA

Intended for very large deformation simulations where inertia forcesare dominant.

Used to simulate impact, crushing, rapid forming, etc.

Impact Analysis of a Vehicle Crash Test

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About ANSYS

Thermal analysis is used to determine the temperaturedistribution in an object. Other quantities of interest includeamount of heat lost or gained, thermal gradients, and thermal flux.

All three primary heat transfer modes can be simulated:conduction, convection, radiation.

Steady-State Time-dependent effects are

ignored.

Transient To determine temperatures, etc.as a function of time.

Allows phase change (melting orfreezing) to be simulated.

Transient Temperature of aWarming Clothes Iron

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About ANSYS

Electromagnetic analysis is used to calculate magnetic fields inelectromagnetic devices.

Static and low-frequency electromagnetics

To simulate devices operating with DC power sources, low-frequencyAC, or low-frequency transient signals.

Example: solenoid actuators,

motors, transformers Quantities of interest include

magnetic flux density, fieldintensity, magnetic forces andtorques, impedance, inductance,

eddy currents, power loss, andflux leakage.

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About ANSYS

High-frequency electromagnetics

To simulate devices with propagating electromagnetic waves.

Example: microwave and RF passive components, waveguides,coaxial connectors

Quantities of interest include S-parameters, Q-factor, Return loss,dielectric and conducting losses, and electric and magnetic fields.

Electric field (EFSUM) in a coaxial cable

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About ANSYS

Electrostatics

To calculate the electric field from voltage or charge excitation.

Example: High voltage devices, micro-electromechanical systems(MEMS), transmission lines

Typical quantities of interest are electric field strength andcapacitance.

Current Conduction

To calculate current in a conductor from an applied voltage

Circuit Coupling

To couple electric circuits with electromagnetic devices

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About ANSYS

Types of electromagnetic analysis:

Static analysis calculates magnetic fields due to direct current (DC) orpermanent magnets.

Harmonic analysis calculates magnetic fields due to alternatingcurrent (AC).

Transient analysis is used for time-varying magnetic fields.

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About ANSYS

Computational Fluid Dynamics(CFD)

To determine the flowdistributions and temperatures in

a fluid. ANSYS/FLOTRAN can simulate

laminar and turbulent flow,compressible and incompressibleflow, and multiple species.

Applications: aerospace,electronic packaging, automotivedesign

Typical quantities of interest arevelocities, pressures,temperatures, and film

coefficients.

Velocity of Fluid in a Duct Pressure Distributionon a Football

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About ANSYS

Acoustics

To simulate the interaction between a fluid medium and the surroundingsolid.

Example: speakers, automobile interiors, sonars

Typical quantities of interest are pressure distribution, displacements,and natural frequencies.

Contained-Fluid Analysis

To simulate the effects of a contained, non-flowing fluid and calculatehydrostatic pressures due to sloshing.

Example: oil tankers, other liquid containers

Heat and Mass Transport

A one-dimensional element is used to calculate the heat generated bymass transport between two points, such as in a pipe.

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Chapter 3

ANSYS Basics

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Output

Window

Icon Toolbar Menu

Abbreviation Toolbar Menu

Utility Menu

Graphics AreaMain Menu

Input Line

Chapter 3 The GUI

Layout

Current Settings

Raise/Hidden Icon

User Prompt Info

Command Window Icon

Model ControlToolbar

C G

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Chapter 3 The GUI

Main Menu

Tree structure format.

Contains the main functions required for ananalysis.

Use scroll bar to gain access to long treestructures.

Colors used to show tree level.

scroll bar

Chapter 3 The GUI

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Chapter 3 The GUI

Main Menu

Tree structure behavior sub branch preserved

Before collapsing Preprocessor Branch After expanding Preprocessor Branch

The tree structure is the same before

and after the Preprocessor branch ofMain Menu is collapsed

Select to collapse

Preprocessor Branch

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Chapter 3 The GUI

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Chapter 3 The GUI

Abbreviation Toolbar Menu

Contains abbreviations-- short-cuts to commonly usedcommands and functions.

A few predefined abbreviations are available, but you can add

your own. Requires knowledge of ANSYS commands.

A powerful feature which you can use to create your own buttonmenu system!

Chapter 3 The GUI

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Chapter 3 The GUI

Icon Toolbar Menu

Contains iconsof commonly used functions.

Can be customized by the user (i.e adding icons, additional

toolbars)

Pan-Zoom-Rotate

New Analysis

Open ANSYS File

Save Analysis

ANSYS Help

Image Capture

Report Generator

Chapter 3 The GUI

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Chapter 3 The GUI

.Icon Toolbar Menu

Jobname definition when using Open ANSYS File Icon:

the ANSYS jobname will be changed to the prefix of the database file being resumed.

Open ANSYS

File

When opening the blades.db database(using the Open ANSYS File Icon), the

jobname will be changed to blades.

The Open ANSYS File Icon can be used to open either ANSYS

Database or ANSYS Command file types

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Chapter 3 The GUI

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Chapter 3 The GUI

Input Window

Allows you to enter commands. (Most GUI functions actuallysend commands to ANSYS. If you know these commands, youcan type them in the Input Window).

As a command is typed, the format of the command isdynamically displayed.

Click on theX to returnthe input tothe toolbar.

Clicking on the ANSYSCommand Window Iconmoves the input line to aseparate commandwindow, which can bemoved around the screen.

Chapter 3 The GUI

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Chapter 3 The GUI

Utility Menu

Contains utilities that are generally available throughout theANSYS session: graphics, on-line help, select logic, file controls,etc.

Conventions used in Utility Menu:

indicates a dialog box

+ indicates graphical picking

> indicates a submenu

(blank) indicates an action

Chapter 3 The GUI

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Chapter 3 The GUI

Current Settings

The current element attributes settings, and currently activecoordinate system are displayed at the bottom on the GUI.

Element Attributes Active Coordinate System

Chapter 3 The GUI

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C apte 3 e GU

User prompt info

Instructions to the user are displayed in the lower left hand area ofthe GUI. The user will be given user prompt info for operationssuch as picking operations.

User Prompt Info

Chapter 3 The GUI

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Preferences

The Preferences dialog (Main Menu >Preferences) allows you to filter outmenu choices that are not applicable tothe current analysis.

For example, if you are doing a thermalanalysis, you can choose to filter outother disciplines, thereby reducing thenumber of menu items available in the

GUI: Only thermal element types will be shown

in the element type selection dialog.

Only thermal loads will be shown.

Etc.

Chapter 3 - Interactive Mode

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Graphics and Picking

A Dynamic Mode setting is alsoavailable using Pan-Zoom-Rotate .

The same mouse button assignmentsapply.

On 3-D graphics devices, you can alsodynamically orient the light source.Useful for different light source shadingeffects.

When using 3-D driver


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Training ManualGraphics and Picking

Other functions in the Pan-Zoom-Rotate dialog box:

Preset views

Zoom-in on specific regions ofthe model

Pan, zoom, or rotate indiscrete increments (asspecified by the Rate slider)

Rotation is about thescreen X, Y, Z coordinates.

Fit the plot to the window

Reset everything to default

The majority of these optionsare available in the ModelControl Toolbar.

Front +Z view, from (0,0,1)

Back -Z view (0,0,-1)

Top +Y view (0,1,0)

Bot -Y view (0,-1,0)

Right +X view (1,0,0)Left -X view (-1,0,0)

Iso Isometric (1,1,1)

Obliq Oblique (1,2,3)

WP Working plane view

Zoom By picking center of asquare

Box Zoom By picking twocorners of a box

Win Zoom Same as Box Zoom,

but box is proportionalto window.

Back Up Unzoom to previouszoom.


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Training ManualThe Database and Files

Save and Resume

Since the database is stored in the computers memory (RAM), itis good practice to saveit to disk frequently so that you can

restore the information in the event of a computer crash or powerfailure.

The SAVE operation copies the database from memory to a file

called the database file(or db filefor short). The easiest way to do a save is to click on Toolbar > SAVE_DB

Or use:

Utility Menu > File > Save as Jobname.db

Utility Menu > File > Save as SAVE command


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Training ManualThe Database and Files

To restore the database from the db file back into memory, use theRESUME operation.

Toolbar > RESUME_DB

Or use:

Utility Menu > File > Resume Jobname.db

Utility Menu > File > Resume from

RESUME command

The default file name for SAVE and RESUME isjobname.db, butyou can choose a different name by using the Save as orResume from functions.


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Training ManualExiting ANSYS

Three ways to exit ANSYS:

Toolbar > QUIT

Utility Menu > File > Exit

Use the /EXIT command in the Input Window

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Chapter 4

General Analysis Procedure

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Chapter 4 - General Analysis Procedure

O i

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Training ManualOverview

Preprocessing

Solution

Postprocessing

PreliminaryDecisions

Every analysis involves four main steps:

Preliminary Decisions

Which analysis type?

What to model? Which element type?

Preprocessing

Define Material

Create or import the model geometry Mesh the geometry

Solution

Apply loads

Solve

Postprocessing

Review results

Check the validity of the solution

Chapter 4 - A. Preliminary Decisions

Whi h l i t ?

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Training ManualWhich analysis type?

The analysis type usually belongs to one of the followingdisciplines:

Structural Motion of solid bodies, pressure on solid bodies, orcontact of solid bodies

Thermal Applied heat, high temperatures, or changes intemperature

Electromagnetic Devices subjected to electric currents (AC or DC),electromagnetic waves, and voltage or charge

excitationFluid Motion of gases/fluids, or contained gases/fluids

Coupled-Field Combinations of any of the above

The appropriate analysis type for this model is a structural analysis!


Wh t t d l?

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Training ManualWhat to model?

What should be used to model the geometry of the spherical tank?

Axisymmetrysince the loading, material, and the boundaryconditions are symmetric. This type of model would provide themost simplified model.

Rotational symmetrysince the loading, material, and theboundary conditions are symmetric. Advantage overaxisymmetry: offers some results away from applied boundaryconditions.

Full 3D modelis an option, but would not be an efficient choicecompared to the axisymmetric and quarter symmetry models. Ifmodel results are significantly influenced by symmetricboundary conditions, this may be the only option.

An axisymmetric and a one-quarter symmetry (i.e. rotationalsymmetry) model will be analyzed for this model!


Which Element Type?

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Training ManualWhich Element Type?

What element type should be used for the model of the sphericaltank?

Axisymmetric model:

Axisymmetric since 2-D section can be revolved to created 3D

geometry.

Linear due to small displacement assumption.

PLANE42 with KEYOPT(3) = 1

Rotational symmetry model:

Shell since radius/thickness ratio > 10

Linear due to small displacement assumption.

membrane stiffness only option since membrane stresses arerequired.

SHELL63 with KEYOPT(1) = 1

Since the meshing of this geometry will create SHELL63 elementswith shape warnings, a mid-side noded equation of the SHELL63 wasused:

SHELL93

Chapter 4 - B. Preprocessing

Create the Solid Model

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Training ManualCreate the Solid Model

A typical solid model is defined by volumes, areas, lines, andkeypoints.

Volumesare bounded by areas. They represent solid objects.

Areasare bounded by lines. They represent faces of solid objects, or

planar or shell objects.

Linesare bounded by keypoints. They represent edges of objects.

Keypointsare locations in 3-D space. They represent vertices ofobjects.

Volumes Lines & KeypointsAreas


Create the Solid Model

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Training ManualCreate the Solid Model

One-quarter Symmetry ModelAxisymmetric model

What geometry should be used to model the spherical tank?


Create the FEA Model

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Training ManualCreate the FEA Model

Meshingis the process used to fill the solid model with nodesand elements, i.e, to create the FEA model.

Remember, you need nodes and elements for the finite elementsolution, not just the solid model. The solid model does NOT

participate in the finite element solution.

Solid model FEA model

meshing


Create the FEA Model

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Training ManualCreate the FEA Model

What would the mesh of the spherical tank look like?


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T i i M l

Chapter 4 C. Solution

Define Loads

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Training ManualDefine Loads

There are five categories of loads:

DOF Constraints Specified DOF values, such as displacementsin a stress analysis or temperatures in athermal analysis.

Concentrated Loads Point loads, such as forces or heat flow rates.Surface Loads Loads distributed over a surface, such as

pressures or convections.

Body Loads Volumetric or field loads, such as temperatures(causing thermal expansion) or internal heatgeneration.

Inertia Loads Loads due to structural mass or inertia, suchas gravity and rotational velocity.

Training Manual

Chapter 4 C. Solution

Define Loads

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Edge Symmetryconstraint

Edge Symmetryconstraint Tangential

Constraint*

Hydrostaticpressure

Hydrostaticpressure

TangentialConstraint*

Edge Symmetryconstraint

Define Loads

What are the loads on the spherical tank models?

* Tangential constraint used to allow comparison to Roarke closed form solution.

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Chapter 4 - D. Postprocessing

Review Results

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Postprocessing is the final step in the finite element analysisprocess.

It is imperative that you interpret your results relative to the

assumptions made during model creation and solution.

You may be required to make design decisions based on theresults, so it is a good idea not only to review the results carefully,

but also to check the validity of the solution.

ANSYS has two postprocessors:

POST1, the General Postprocessor, to review a single set of resultsover the entire model.

POST26, the Time-History Postprocessor, to review results at selectedpoints in the model over time. Mainly used for transient and nonlinearanalyses. (Not discussed in this course.)

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Chapter 4 - D. Postprocessing

Review Results

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Axisymmetric model

What are the meridional stress results in the spherical tankmodels?

One-quarter Symmetry Model

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Chapter 6 Creating the Finite Element Model

Overview

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g

Meshingis the process used to fill the solid model with nodesand elements, i.e, to create the FEA model.

Remember, you need nodes and elements for the finite elementsolution, not just the solid model. The solid model does NOT

participate in the finite element solution.

Solid model FEA model

meshing

Training Manual


Element Attributes

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There are three steps to meshing:

Define element attributes

Specify mesh controls

Generate the mesh

Element attributesare characteristics of the finite element modelthat you must establish prior to meshing. They include:

Element types Real constants

Material properties

Section properties (for BEAM44,188, and 189, SHELL181, and PRETS179)

Training Manual


Element Attributes

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Element Type

The element type is an important choice that determines thefollowing element characteristics:

Degree of Freedom (DOF) set. A thermal element type, for example,has one dof: TEMP, whereas a structural element type may have up tosix dof: UX, UY, UZ, ROTX, ROTY, ROTZ.

Element shape -- brick, tetrahedron, quadrilateral, triangle, etc.

Dimensionality -- 2-D (X-Y plane only), or 3-D. Assumed displacement shape -- linear vs. quadratic.

ANSYS has a library of over 150 element types from which youcan choose. Details on how to choose the correct element type

will be presented later. For now, lets see how to define anelement type.

Training Manual


Element Attributes

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Element category

ANSYS offers many different categories of elements. Some of thecommonly used ones are:

Line elements Shells

2-D solids

3-D solids

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Element Attributes

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Line elements:

Beamelements are used to model bolts, tubular members, C-sections,angle irons, or any long, slender members where only membrane andbending stresses are needed.

Linkelements are used to model springs, bolts, preloaded bolts, andtruss members.

Spring (combination)elements are used to model springs, bolts, orlong slender parts, or to replace complex parts by an equivalentstiffness.

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Element Attributes

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Shell elements:

Used to model thin panels or curved surfaces.

The definition of thin depends on the application, but as a generalguideline, the major dimensions of the shell structure (panel) should

be at least 10 times its thickness.

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Element Attributes

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2-D Solid elements:

Used to model a cross-section of solid objects.

Must be modeled in the global Cartesian X-Y plane.

All loads are in the X-Y plane, and the response (displacements) are

also in the X-Y plane. Element behavior may be one of the following:

plane stress

plane strain

generalized plain strain

axisymmetric

axisymmetric harmonic

Y

XZ

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Element Attributes

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Plane stressassumes zero stress inthe Z direction.

Valid for components in which the Zdimension is smaller than the X and Y

dimensions. Z-strain is non-zero.

Optional thickness (Z direction)allowed.

Used for structures such as flat platessubjected to in-plane loading, or thindisks under pressure or centrifugalloading.

Y

XZ

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Plane strainassumes zero strain in the Zdirection.

Valid for components in which the Z dimension ismuch larger than the X and Y dimensions.

Z-stress is non-zero. Used for long, constant cross-section structures

such as structural beams.

YX

Z

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Axisymmetryassumes that the 3-D model anditsloading can be generated by revolving a 2-Dsection 360 about the Y axis.

Axis of symmetry must coincide with the global Y

axis. Negative X coordinates are not permitted.

Y direction is axial, X direction is radial, and Zdirection is circumferential (hoop) direction.

Hoop displacement is zero; hoop strains andstresses are usually very significant.

Used for pressure vessels, straight pipes, shafts,etc.

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Element Attributes

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3-D Solid elements: Used for structures which, because of geometry, materials, loading, or

detail of required results, cannot be modeled with simpler elements.

Also used when the model geometry is transferred from a 3-D CAD

system, and a large amount of time and effort is required to convert itto a 2-D or shell form.

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Element Attributes

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To define an element type: Main Menu > Preprocessor >

Element Type > Add/Edit/Delete

[Add] to add new element type

Choose the desired type(such as SOLID92) and pressOK

[Options] to specify additional

element options Or use the ET command:

et,1,solid92

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Element Attributes

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To define real constants: Main Menu > Preprocessor > Real

Constants

[Add] to add a new real constant

set. If multiple element types have

been defined, choose the elementtype for which you are specifyingreal constants.

Then enter the real constantvalues.

Or use the R family of commands.

Different element types requiredifferent real constants. Check theElements Manual, available on-line,for details.

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Element Attributes

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To define section properties: Main Menu > Preprocessor > Sections

Ability to Import Sections

Beam, Shell and Pretension sections can

be created. Or use the SECxxx family of commands.

Different element types require different

section properties. See the ElementsManualfor details.

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Element Attributes

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Material Properties

Every analysis requires somematerial property input: Youngsmodulus EX for structural elements, thermal conductivity KXX for

thermal elements, etc.

Refer to Chapter 7 for details on the two ways to define materialproperties.

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Multiple Element Attributes

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Most FEA models have multiple attributes. For example, the silo shownhere has two element types, three real constant sets, and two materials.

MAT 1 = concreteMAT 2 = steel

REAL 1 = 3/8 thicknessREAL 2 = beam propertiesREAL 3 = 1/8 thickness

TYPE 1 = shellTYPE 2 = beam

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Assigning Attributes to the Solid Model

1. Define all necessary element types, materials, andreal constant sets.

2. Then use the Element Attributes section of theMeshTool (Main Menu > Preprocessor > MeshTool):

Choose entity type and press the SET button.

Pick the entities to which you want to assignattributes.

Set the appropriate attributes in the subsequentdialog box.

Or select the desired entities and use the VATT,AATT, LATT, or KATT command.

3. When you mesh an entity, its attributes areautomatically transferred to the elements.

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Using Global Attribute Settings

1. Define all necessary element types,materials, real constant sets and sectionnumbers

2. Then use the Element Attributes sectionof the MeshTool (Main Menu > Preprocessor> MeshTool):

Choose Global and press the SET button.

Activate the desired combination of attributesin the Meshing Attributes dialog box. Werefer to these as the activeTYPE, REAL, MATand SECNUM settings.

Or use the TYPE, REAL, MAT and SECNUMcommands.

3. Mesh only those entities to which the abovesettings apply.

IIIITraining Manual


Controlling Mesh Density

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ANSYS provides many tools to control mesh density, both on aglobal and local level:

Global controls

SmartSizing

Global element sizing

Default sizing

Local controls

Keypoint sizing

Line sizing

Area sizing

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SmartSizing

Determines element sizes by assigning divisions on all lines,taking into account curvature of the line, its proximity to holes and

other features, and element order.

SmartSizing is off by default, but is recommended for freemeshing. It does not affect mapped meshing. (Free meshing vs.mapped meshing will be discussed later.)

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To use SmartSizing: Bring up the MeshTool (Main Menu > Preprocessor >

Meshing > MeshTool), turn on SmartSizing, and set thedesired size level.

Or use SMRT,level Size level ranges from 1 (very fine) to 10 (very

coarse). Defaults to 6.

Then mesh all volumes (or all areas) at once, rather thanone-by-one.

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Examples of different SmartSizelevels are shown here for atetrahedron mesh.

Advanced SmartSize controls, such

as mesh expansion and transitionfactors, are available on the SMRTcommand or:

Main Menu > Preprocessor > Meshing >Size Cntrls > SmartSize > Adv Opts

You can turn off SmartSizing usingthe MeshTool or by issuing smrt,off.

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Global Element Sizing

Allows you to specify a maximum element edge lengthfor the entire model (or number of divisions per line): ESIZE,SIZE

or Main Menu > Preprocessor > Meshing > MeshTool; thenselect Size Controls, Global ,and [Set]

or Main Menu > Preprocessor > Meshing > Size Cntrls >ManualSize > Global > Size

Can be used by itself or in conjunction with

SmartSizing. Using ESIZE by itself (SmartSizing off) will

result in a uniform element size throughout thevolume (or area) being meshed.

With SmartSizing on, ESIZE acts as a guide,

but the specified size may be overridden toaccommodate line curvature or proximity tofeatures.

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Default Sizing

If you dont specify any controls, ANSYS uses default sizing, whichassigns minimum and maximum line divisions, aspect ratio, etc. based

on element order.

Meant for mapped meshing, but is also used for free meshing ifSmartSizing is off.

You can adjust default size specifications using DESIZE or

Main Menu > Preprocessor > Meshing > Size Cntrls > ManualSize > Global > Other

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Keypoint Sizing

Controls element size at keypoints:

Main Menu > Preprocessor > Meshing > MeshTool; then

select Size Controls, Keypt, and [Set] or KESIZE command

or Main Menu > Preprocessor > Meshing > Size Cntrls >ManualSize > Keypoints

Different keypoints can have different KESIZEs, givingyou more control over the mesh.

Useful for stress concentration regions.

Specified sizes may be overridden by SmartSizing toaccommodate line curvature or proximity to features.

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Line Sizing

Controls element size at lines:

Main Menu > Preprocessor > Meshing > MeshTool;then select Size Controls, Lines, and [Set]

or LESIZE command or Main Menu > Preprocessor > Meshing > Size Cntrls

> ManualSize> Lines

Different lines can have different LESIZEs.

Size specifications may be hard or soft. Hard sizes are always honored by the mesher, even if

SmartSizing is on. They take precedence over all othersize controls.

Soft sizes may be overridden by SmartSizing.

You can also specify a spacing ratio ratio of lastdivision to first. Used to bias the divisions towards oneend or towards the middle.

Yes for softNo for hard

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Area Sizing

Controls element size in the interior of areas:

Main Menu > Preprocessor > Meshing > MeshTool; then

select Size Controls, Areas, and [Set] or AESIZE command

or Main Menu > Preprocessor > Meshing > Size Cntrls >ManualSize > Areas

Different areas can have different AESIZEs.

Bounding lines will use the specified size only if theyhave no LESIZE or KESIZE specified and if no

adjacent area has a smaller size.

Specified sizes may be overridden by SmartSizing toaccommodate line curvature or proximity to features.

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Mesh Order Control

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By default, ANSYS will mesh areas or volumes in ascending entitynumber.

The AORDER field on the MOPT command instructs ANSYS to mesh a

group of areas or volumes in order of ascending size. Main Menu > Preprocessor > Meshing > Mesher Opts , or

MOPT,AORDER,ON (default is OFF)

In cases where SmartSizing does not mesh as fine as needed,the MOPT, AORDER,on command generates finer meshes incritical areas for volume meshes

This option is not available when SmartSizing is on.

INIINITraining Manual


Generating the Mesh

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Generating the meshis the final step in meshing.

First save the database.

Then press [Mesh] in the MeshTool. This brings up a picker. Press [Pick All] in the pickerto indicate all entities.

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Generating the Mesh

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Demo: Resume ribgeom.db

Mesh with SMRT,6. (Not a very good mesh)

Re-mesh with SMRT,3 (good mesh)

Set ESIZE to 0.2 and re-mesh. The mesh becomes coarse even thoughSMRT is set to 3, because the smart-mesher takes ESIZE into account.Also, note that the element sizes are not uniform (because SMRT ison).

Turn off SMRT and re-mesh. Element sizes are now more uniform (but

not ideal).

Re-mesh with ESIZE set to 0.1.

Good meshes generated for this geometry with SMRT,3 or ESIZE,0.1.

INTININTIN

Training Manual


Changing a Mesh

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If a mesh is not acceptable, you can alwaysre-mesh the model by following these steps:

1. Clear the mesh.

The clearoperation is the opposite of mesh: it

removes nodes and elements. Use the [Clear] button on the MeshTool, or use

VCLEAR, ACLEAR, etc.

(If you are using the MeshTool, you may skip thisstep since the program will prompt you whether toclear or not when you execute step 3.)

2. Specify new or different mesh controls.

3. Mesh again.

INTININTINT

Training Manual


Changing a Mesh

A h hi i i fi h

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Another meshing option is to refinethemesh in specific regions.

Available for all area elements and onlytetrahedral volume elements.

Easiest way is to use the MeshTool:

First save the database.

Then choose how you want tospecify the region of refinement atnodes, elements, keypoints, lines, orareas and press the Refine button.

Pick the entities at which you wantthe mesh to be refined. (Not requiredif you choose All Elems.)

Finally, choose the level ofrefinement. Level 1 (minimal

refinement) is a good starting point.

INTINTINTINT

Training Manual


Changing a Mesh

D

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Demo: Continuing the last demo (ribgeom has been meshed with ESIZE =

0.2)

Choose refinement at Lines and press Refine

Pick the top line, then choose the default minimal refinement

INTINTINTINT

Training Manual


Mapped Meshing

Th t i hi th d f d

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There are two main meshing methods: freeandmapped.

Free Mesh

Has no element shape restrictions. The mesh does not follow any pattern.

Suitable for complex shaped areas and volumes.

Mapped Mesh

Restricts element shapes to quadrilaterals for areasand hexahedra (bricks) for volumes.

Typically has a regular pattern with obvious rows ofelements.

Suitable only for regular areas and volumes such asrectangles and bricks.

INTINTINTINT

Training Manual


Mapped Meshing

Free Mesh Mapped Mesh

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Free Mesh

+ Easy to create; no need to dividecomplex shapes into regularshapes.

Volume meshes can contain onlytetrahedra, resulting in a largenumber of elements.

Only higher-order (10-node)tetrahedral elements areacceptable, so the number ofDOF can be very high.

Mapped Mesh

+ Generally contains a lowernumber of elements.

+ Lower-order elements may beacceptable, so the number ofDOF is lower.

Areas and volumes must be

regular in shape, and meshdivisions must meet certaincriteria.

Very difficult to achieve,

especially for complex shapedvolumes.

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Mapped Meshing

Creating a Mapped Mesh

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Creating a Mapped Mesh

This is not as easy as free meshing because the areas andvolumes have to meet certain requirements:

Area must contain either 3 or 4 lines (triangle or quadrilateral). Volume must contain either 4, 5, or 6 areas (tetrahedron, triangular

prism, or hexahedron).

Element divisions on opposite sides must match.

For triangular areas or tetrahedral volumes, the number of elementdivisions must be even.

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INTINTINTINT

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Mapped Meshing

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INTINTINTINT

Training Manual


Mapped Meshing

Thus mapped meshing involves a three-step procedure:

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Thus mapped meshing involves a three step procedure: Ensure regular shapes, i.e, areas with 3 or 4 sides, or volumes with

4, 5, or 6 sides.

Specify size and shape controls

Generate the mesh

INTRINTINTRINT

Training Manual


Mapped Meshing

Ensure regular shapes

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Ensure regular shapes

In most cases, the model geometry is such that the areas havemore than 4 sides, and volumes have more that 6 sides. Toconvert these to regular shapes, you may need to do one or bothof these operations:

Slice the areas (or volumes) into smaller, simpler shapes.

Concatenate two or more lines (or areas) to reduce the total number ofsides.

INTRINTRINTRINTR

Training Manual


Mapped Meshing

Slicing can be accomplished with the Boolean divide operation.

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Slicingcan be accomplished with the Boolean divideoperation. Remember that you can use the working plane, an area, or a line as

the slicing tool.

Sometimes, it may be easier to createa new line or a new area than tomove and orient the working plane in the correct direction.

INTRINTRINTRINTR

Training Manual


Mapped Meshing

Concatenation creates a new line (for meshing purposes) that is abi ti f t li th b d i th b f

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Concatenationcreates a new line (for meshing purposes) that is acombination of two or more lines, thereby reducing the number oflines making up the area.

Use the LCCAT command or Main Menu > Preprocessor > Meshing >Concatenate > Lines, then pick the lines to be concatenated.

For area concatenation, use ACCAT command or Main Menu >Preprocessor > Meshing > Concatenate > Areas

Concatenatingthese two linesmakes this a4-sided area

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Training Manual


Mapped Meshing

You can also imply a concatenation by simplyidentifying the three or four corners of the area In this

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p y y p yidentifying the three or four corners of the area. In thiscase, ANSYS internally generates the concatenation.

To do this, choose Quad shape and Map mesh in theMeshTool.

Then change 3/4 sided to Pick corners. Press the Mesh button, pick the area, and then pick the 3 or

4 corners that form the regular shape.

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Mapped Meshing

Notes on concatenation:It is purely a meshing operation and therefore should be the last step before

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It is purely a meshing operation and therefore should be the last step beforemeshing, after all solid modeling operations. This is because the output entityobtained from a concatenation cannot be used in any subsequent solid modelingoperation.

You can "undo" a concatenation by deleting the line or area it produced. Concatenating areas (for mapped volume meshing) is generally much more

complicated because you may also need to concatenate some lines. Lines areautomatically concatenated only when two adjacent, 4-sided areas areconcatenated.

Consider the add(Boolean) operation if the lines or areas meet at a tangent.

INTRINTRINTRINTR

Training Manual


Mapped Meshing

Specify size and shape controls Meshing Areas:

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This is the second step of the three-step mappedmeshing procedure.

Choosing the shape is simple. In the MeshTool, chooseQuad for area meshing, and Hex for volume meshing,then click on Map.

Commonly used size controls and the order in which

they are applied: Line sizing [LESIZE] is always honored.

Global element size , if specified, will be applied to unsizedlines.

Default element sizing [DESIZE] will be applied to unsized

lines only if ESIZE is not specified. (SmartSizing is not valid.)

Meshing Volumes:

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Mapped Meshing

If you specify line divisions, remember that:divisions on opposite sides must match but you only need to specify

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divisions on opposite sides must match, but you only need to specifyone side. The map mesher automatically transfers divisions to theopposite side.

if you have concatenated lines, divisions can only be applied to theoriginal (input) lines, not the composite line.

6 divisions specified on

each original line.

12 divisions will beautomatically applied tothis line (opposite tocomposite line).

How many divisions areused for the other twolines? (Upcoming demowill answer it.)

INTRINTRINTRINTR

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Mapped Meshing

Generate the mapped mesh

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Once you have ensured regular shapes and assigned theappropriate divisions, generating the mesh is easy. Just press theMesh button in the MeshTool, then press [Pick All] in the picker orchoose the desired entities.

INTRINTRINTRINTR

Training Manual


Mapped Meshing

Question: How would youslice this model for

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slice this model formapped meshing?

Answer: It may not be worth theeffort!

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Training Manual


Mapped Meshing

Demo: Resume ribfull db

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Resume ribfull.db

Bring up MeshTool and apply 6 divisions to top and right lines

Map-mesh the area using Pick corners. Notice that the left andbottom lines get only two divisions each (from DESIZE).

Now specify ESIZE,,4 (4 divisions per line) and re-mesh

Finally, clear line divisions, specify ESIZE,0.1 (size), and re-mesh

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Training Manual


Hex-to-Tet Meshing

For volume meshing, we have only seen twooptions so far:

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options so far:

Free meshing, which creates an all-tet mesh. Thisis easy to achieve but may not be desirable insome cases because of the large number of

elements and total DOF created.

Mapped meshing, which creates an all-hex mesh.This is desirable but usually very difficult toachieve.

Hex-to-tet meshingprovides a third option thatis the best of both worlds. It allows you tohave a combination of hex and tet mesheswithout compromising the integrity of the mesh.

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Training Manual


Hex-to-Tet Meshing

This option works by creating pyramid-shaped elements in the transitionregion between hex and tet regions.

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Requires the hex mesh to be available (or at least a quad mesh at the sharedarea).

The mesher first creates all tets, then combines and rearranges the tet elements

in the transition region to form pyramids. Available only for element types that support both pyramid and tet shapes, e.g:

Structural SOLID95, 186, VISCO89

Thermal SOLID90

Multiphysics SOLID62, 117, 122

SOLID95

Results are good even in the transitionregion. Element faces are compatible evenwhen transitioning from a linear hexelement to a quadratic tet element.

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INTROINTRO

Training Manual


Hex-to-Tet Meshing

Hex-to-tet meshing is valid for both quadratic-to-quadratic and linear-to-quadratic transitions. Element type must support a 9-node pyramid for the latter.

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Hex Mesh Transition Layer Tet Mesh

10-Node Tet13-Node Pyramid20-Node Hex

Quadraticto

Quadratic

8-Node Hex 9-Node Pyramid 10-Node Tet

LineartoQuadratic

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INTROINTRO

Training Manual


Hex-to-Tet Meshing

Procedure involves four steps:

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1. Create the hex mesh.

Start by map-meshing the regular-shaped volumes. (Or mesh theshared areas with quads.)

For stress analysis, use either an 8-node brick (SOLID45 or SOLID185)or a 20-node brick (SOLID95 or SOLID186).

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Training Manual


Hex-to-Tet Meshing

2. Activate an element type that supports both pyramids and tets. These are usually brick elements that can degenerate into pyramids

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y g pyand tets. Check the Elements Manual, available on-line, to find outwhich element types are valid.

Examples:

Structural SOLID95, 186, VISCO89

Thermal SOLID90


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Training Manual


Hex-to-Tet Meshing

3. Generate the tet mesh. First activate free meshing.

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Then mesh the volumes that are to be tet-meshed.

Pyramids are automatically generated at the interface.

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Training Manual


Hex-to-Tet Meshing

4. Convert degenerate tets to true 10-node tets. The tet mesh created by the transition mesher consists of degenerate

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elements 10-node tetrahedra derived from 20-node bricks, forexample.

These elements are not as efficient as true 10-node tets such as

SOLID92, which use less memory and write smaller files duringsolution.

To convert the degenerate tets into true tets:

Main Menu > Preprocessor > Meshing > Modify Mesh > Change Tets

Or use the TCHG command.

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Training Manual


Hex-to-Tet Meshing

Demo: Resume hextet.db

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Show element type list using Element Type > Add/Edit/Delete. Thereare two element types: SOLID45 & 95

Bring up MeshTool and set ESIZE,1 (size)

Map-mesh the regular shaped volume

Set element type to 2, and activate tet-meshing

Free-mesh the other volume

Convert degenerate tets to SOLID92

Show element type list. There are now three element types.

Select elements of type 2 (SOLID95 pyramids) and plot elements

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Training Manual


Mesh Extrusion

When you extrudean area into a volume, you can extrude the areaelements along with it, resulting in a meshed volume. This is called meshextrusion.

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e t us o

Advantage: Easy to create a volume mesh with all bricks (hexahedra) or acombination of bricks and prisms.

Obvious requirement: Shape of the volume must lend itself to extrusion.

Extrude

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Training Manual


Mesh Extrusion

2. Mesh the area to be extruded with MESH200 elements. Use mapped or free meshing with desired mesh density.

Main Menu > Preprocessor > Meshing > MeshTool

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Main Menu > Preprocessor > Meshing > MeshTool

3. Choose element extrusion options.

EXTOPT command or Main Menu >Preprocessor > Modeling > Operate > Extrude> Elem Ext Opts

Typical options are:

Active TYPE attribute (should be 3-Dsolid).

Number of element divisions in theextrusion direction (i.e, number ofelements through the thickness). Mustbe greater than zero; otherwise, onlythe area will be extruded, withoutelements.

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Training Manual


Mesh Extrusion

4. Extrude the area. First delete concatenated lines, if any. If concatenations are present,

ANSYS will not allow the extrusion operation

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ANSYS will not allow the extrusion operation.

Main Menu > Preprocessor > Meshing > Concatenate > Del Concats > Lines

Then extrude the area using any of the extrusion methods.

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Training Manual


Mesh Extrusion

Demo: Resume ribgeom.db

B i th El t T di l d l t PLANE82 l t t d

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Bring up the Element Types dialog, delete PLANE82 element type, andreplace it with MESH200 4-node quad

Also add SOLID45 as element type 2

Bring up MeshTool and set ESIZE,0.1

Choose free quad-meshing and mesh the area

Set extrusion options: TYPE=2, number of element divisions = 4

Rotate view to ISO

Extrude area along normal with offset = 0.4

Save the database to ribvol.db

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Training Manual


Sweep Meshing

Sweep meshing is yet another option available for volumemeshing. It is the process of meshing an existing volume bysweeping an area mesh

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sweeping an area mesh.

Similar to mesh extrusion, except that the volume already exists in

this case (from a geometry import, for example).

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Training Manual


Sweep Meshing

Advantages: Easy to create a volume mesh with all

bricks (hexahedra) or a combination

Target surface(1 area)

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bricks (hexahedra) or a combinationof bricks and prisms.

Option to tet-mesh volumes that are

not sweepable. Transitionpyramids are automaticallygenerated.

Requirements:

Topology of the volume must beconsistent in the sweep direction.Example: a block with a through hole(ok even if the hole is tapered).

Sourceand targetsurfaces must besingle areas. Concatenated areas arenot allowed for either the source orthe target.

Source surface(1 area)

Valid for sweep meshing

Not valid for sweep meshing

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Training Manual


Sweep Meshing

Procedure

Define and activate a 3-D hexahedral solid element

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type, such as structural SOLID45 or SOLID95.

Bring up MeshTool and choose Hex/Wedge and Sweep.

Choose how the source and target surfaces areidentified:

Auto Source/Target means that ANSYS will automatically

choose them based on the volumes topology. Pick Source/Target means that you will be choosing

them.

Press the SWEEP button and follow prompt

instructions from the picker. (Or use VSWEEPcommand.)

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Training Manual


Sweep Meshing

Tet-Mesh Option

A useful sweep option is to generate a tet-

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A useful sweep option is to generate a tetmesh in non-sweepable volumes.

To use this option: Make sure that the element type supports

degenerate pyramid and tetrahedronshapes. Examples:

Structural SOLID95, 186, VISCO89 Thermal SOLID90


Choose Main Menu > Preprocessor > Meshing> Mesh > Volume Sweep > Sweep Opts and

activate the tet-mesh option. (Or use theEXTOPT,VSWE command.)

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Training Manual


Sweep Meshing

Notes

To map-mesh a complex volume, you may need to slice it several

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p p , y ytimes and also do some area and line concatenations. For sweepmeshing, you typically need only a few slicing operations, and no

concatenations are needed!

You can control the source area mesh using standard meshcontrols. SmartSizing is generally not recommended since it is

meant for free meshing.

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Chapter 7

Defining the Material

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Training Manual

Chapter 7 Defining the Material

Material Model GUI

Specifying Individual Material Properties

Instead of choosing a material name, this method involves directlyif i th i d ti th h th M t i l M d l GUI

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specifying the required properties through the Material Model GUI.

To specify individualproperties:

Main Menu > Preprocessor >Material Props > Material Models

Double-click on theappropriate property to bedefined.

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Training Manual


Material Model GUI

Work through the treestructure to the materialtype to be defined.

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Then enter the individual

property values.

Or use the MP command. mp,ex,1,30e6

mp,prxy,1,.3

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Training Manual


Listing Defined Materials

The Material Model GUI shows one material at a time. Multiplematerial properties can be listed by:

Utility Menu > List > Properties > All Materials

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Or, use the MPLIST command

Note, Nonlinear material properties can be listed using Utility Menu >

List Properties > Data Tables or via the TBLIST command.

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Chapter 8

Loading

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INTROD

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Training Manual

Chapter 8 - Loading

Define Loads

There are five categories of loads:

DOF Constraints Specified DOF values, such as displacementsin a stress analysis or temperatures in athermal analysis

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thermal analysis.

Concentrated Loads Point loads, such as forces or heat flow rates.

Surface Loads Loads distributed over a surface, such aspressures or convections.

Body Loads Volumetric or field loads, such as temperatures(causing thermal expansion) or internal heatgeneration.

Inertia Loads Loads due to structural mass or inertia, suchas gravity and rotational velocity.

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INTROD

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Training Manual

Chapter 8 - Loading

...Nodal Coordinate System

To rotate nodes, use this four-step procedure:

1. Select the desired nodes.

2. Activate the coordinate system (or create a local CS)i t hi h t t t t th d CSYS 1

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into which you want to rotate the nodes, e.g, CSYS,1.

3. Choose Main Menu > Preprocessor > Modeling >

Move/Modify > Rotate Node CS > To Active CS, then press[Pick All] in the picker.

Or issue NROTAT,ALL.

4. Reactivate all nodes.

Note: When you apply symmetry on anti-symmetryboundary conditions, ANSYS automatically rotates allnodes on that boundary.

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Training Manual

Chapter 8 - Loading

...Nodal Coordinate System

Demo: Resume rib.db.

Offset working plane to center of bottom circle (using average keypoint location).

Create local cylindrical CS at working plane origin

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Create local cylindrical CS at working plane origin.

Select nodes at radius = 0.35 and plot them.

Rotate all selected nodes into active system. Apply a UX displacement constraint (or an FX force) at all selected nodes. Note

the radial direction.

Now activate global Cartesian (CSYS,0).

Rotate all selected nodes into active system.

Replot, and note the new direction of the loads.

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INTROD

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Training Manual

Loading & Solution

Concentrated Forces

A force is a concentrated load (orpoint load) that you can apply ata node or keypoint.

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Point loads such as forces are

appropriate for line elementmodels such as beams, spars, andsprings.

In solid and shell models, pointloads usually cause a stresssingularity, but are acceptable ifyou ignore stresses in the vicinity.Remember, you can use selectlogic to ignore the elements inthe vicinity of the point load.

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Training Manual

Loading & Solution

...Concentrated Forces

In the 2-D quarter symmetry solid model shown at bottom left, notice that

maximum stress SMAX (23,590) is reported at the location of the force.

When the nodes and elements in the vicinity of the force are unselected,

SMAX ( 2 28 ) h b l f hi h i h

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SMAX (12,281) moves to the bottom left corner, which is anothersingularity due to the reentry corner. Reflected about x-z plane

half symmetry model

reentry corner

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Training Manual

Loading & Solution

Concentrated Forces

By unselecting nodes and elements near the bottom left corner,you get the expected stress distribution with SMAX (7,945) nearthe top hole.

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Training Manual

Loading & Solution

Concentrated Forces

Note that for axisymmetric models:

Input values of forces are based on the full 360.

O t t l ( ti f ) l b d th f ll 360

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Output values (reaction forces) are also based on the full 360.

For example, suppose a cylindrical shell of radius r has an edge load of Plb/in. To apply this load on a 2-D axisymmetric shell model (SHELL51

elements, for example), you would specify a force of 2rP.

P lb/in

r

2rP lb

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Training Manual

Loading & Solution

Verifying Loads

Verifying applied loads

Plot them by activating load symbols:

Utility Menu > PlotCtrls > Symbols

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Utility Menu > PlotCtrls > Symbols

Commands --/PBC, /PSF, /PBF

Or list them:

Utility Menu > List > Loads >

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Chapter 10

Structural Analysis

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Training Manual

Chapter 10 A. Preprocessing

Geometry

Geometry

Can either be createdwithin ANSYS or imported.

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Include details to improve results:

Goal is to sufficiently model the stiffness of the structure

Add details to avoid stress singularities (e.g. fillets)

Exclude details not in region of interest (e.g. exclude small holes)

Add details to improve boundary conditions (e.g. apply pressure to an

area rather than using concentrated load)

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Training Manual

Chapter 10 A. Preprocessing

Meshing

Element type The table below shows commonly used structural element types.

The nodal DOFs may include: UX, UY, UZ, ROTX, ROTY, and ROTZ.

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2-D Solid 3-D Solid 3-D Shell Line Elements

Linear PLANE42SOLID45SOLID185

SHELL63SHELL181

BEAM3

BEAM4

BEAM188

Quadratic PLANE82PLANE2

SOLID95

SOLID92SOLID186

SHELL93 BEAM189

Commonly used structural element types

Material properties

Minimum requirement is Youngs Modulus, EX. If Poissons Ratio is

not entered a default of 0.3 will be assumed. Setting preferences to Structural limits the Material Model GUI to

display only structural properties.

Real constants and Section properties

Primarily needed for shell and line elements.

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Chapter 10 B. Solution

Define Loads

Structural loading conditions can be:

DOF Constraints Regions of the model where displacements are known.

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Concentrated Forces External forces that can be simplified as a point load.

Pressures Surfaces where forces on an area are known.

Uniform Temperature Temperatures applied as a body force used with a reference

temperature to predict thermal strains.

Gravity Accelerations applied as inertia boundary conditions

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Training Manual


Displacement Constraints

Displacement Constraints

Used to specify where the model is fixed (zero displacement locations).

Can also be non-zero to simulate a known deflection

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Can also be non zero, to simulate a known deflection.

To apply displacement constraints : Main Menu > Solution > Define Loads > Apply

> Structural > Displacement

Choose where you want to apply theconstraint.

Pick the desired entities in thegraphics window.

Then choose the constraint direction.Value defaults to zero.

Or use the D family of commands: DK, DL,

DA, D.

Question: In which coordinate systemare UX, UY, and UZ interpreted?

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Training Manual


Concentrated Forces

To apply a force, the following information is needed:

node or keypoint number (which you can identify by picking)

force magnitude (which should be consistent with the system of unitsyou are using)

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