HyperMesh Basic Training - oss.jishulink.comoss.jishulink.com/caenet/forums/upload/2008/04/05/200883098418000.… · HyperMesh is a high performance finite element pre- and post-processor

HyperMesh Basic Training

Volume 1

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Copyright © 2003 Altair Engineering, Inc., All rights reserved.

Altair® HyperMesh® Basic Training

Trademark Acknowledgments: Altair HyperMesh is a registered trademark of Altair Engineering, Inc. All other trademarks and registered trademarks are the property of their respective owners. Comments concerning the training material may be made to [email protected]. HM_day1_60_rev1.doc

Altair Engineering Introduction to HyperMesh i

Table of Contents

Day 1

Preface .................................................................................................................................1

Chapter 1: Introduction to HyperMesh.............................................................3

The HyperMesh Window ...........................................................................................................4

Graphics Area.......................................................................................................................4

Header Bar ...........................................................................................................................5

Main Menu............................................................................................................................5

Using the Mouse ...................................................................................................................5

Macro Menu..........................................................................................................................6

Exercise 1.1: Opening a Database File.................................................................................7

Permanent Menu ..................................................................................................................8

Toggles and switches..........................................................................................................10

Exercise 1.2: Displaying Elements and Geometry...............................................................10

Using the model browser to control model display ...............................................................12

Secondary Menu.................................................................................................................15

Menu Items.........................................................................................................................15

Exercise 1.3: Translating Elements ....................................................................................19

Standard and Performance Graphics ..................................................................................24

Macro Menu........................................................................................................................25

The Default Macro Menu.....................................................................................................27

The Files Panel ........................................................................................................................30

The Collectors Panel...............................................................................................................31

Exercise 1.4: Using the Card Panel ....................................................................................32

Default HyperMesh Files.........................................................................................................35

Table of Contents

Introduction to HyperMesh Altair Engineering ii

Chapter 2: Creating an FEA Model.................................................................37

Creating, Solving, and Analyzing an FEA Model................................................................... 37

Exercise 2.1: Retrieving a HyperMesh Database ............................................................... 38

Exercise 2.2: Creating Material Collectors.......................................................................... 38

Exercise 2.3: Creating and Editing Component Collectors.................................................. 39

Exercise 2.4: Creating 2-D Elements with the Spline Panel ................................................ 41

Exercise 2.5: Creating 3-D Elements with the Line Drag Panel........................................... 44

Exercise 2.6: Cleaning up the Model.................................................................................. 45

Exercise 2.7: Creating Load Collectors .............................................................................. 46

Exercise 2.8: Applying Constraints to the Model................................................................. 47

Exercise 2.9: Creating Forces............................................................................................ 49

Exercise 2.10: Creating Load Steps................................................................................... 52

Exercise 2.11: Using the OptiStruct Solver......................................................................... 53

Post-processing the Results.................................................................................................. 55

Exercise 2.12: Viewing a Deformed Shape ........................................................................ 57

Exercise 2.13: Viewing a Contour Plot ............................................................................... 58

Chapter 3: Geometry Clean Up and Tetrameshing .......................................59

Geometry Cleanup.................................................................................................................. 60

Exercise 3.1: Importing and observing the model ............................................................... 62

Exercise 3.2: Cleaning up geometry................................................................................... 65

Exercise 3.3: Surface Meshing .......................................................................................... 72

Exercise 3.4: Checking the Element Quality and Tetrameshing.......................................... 77

Exercise 3.5: Cleaning up and verifying the model ............................................................. 79

Altair Engineering Introduction to HyperMesh 1

Preface

Who should attend

This course is designed for students who have not used HyperMesh and wish to develop skills for analyzing FEA models. This course covers these topics: managing the HyperMesh interface, working with FEA models, Geometry cleanup, and surface meshing.

Each section also includes “hands-on” exercises to help you become comfortable with the new techniques presented here.

Manual notations

This manual uses the following notations.

• courier for text that you type in

• bold italic for panel names, button names, and sub-panel names.

Information that is of importance or warning messages will appear in a note box.

� This is an example of a note box. Important information appears here.

! This is an example of a warning box. Critical information appears here.

For more help

Should you desire additional help with material in this course, see the back of the title page of this manual for contact information.

Comments about this manual may be directed to [email protected].

Preface

Introduction to HyperMesh Altair Engineering 2


Chapter 1: Introduction to HyperMesh

HyperMesh is a high performance finite element pre- and post-processor that allows you to build finite element and finite difference models, view their results, and perform data analysis. In addition, you can use Altair’s OS/FEA linear solver to quickly validate component level and product performance and improve product design.

HyperMesh is a Computer Aided Engineering (CAE) tool as described in the diagram below:

The CAE Process

CAE process flow



The HyperMesh Window The HyperMesh window consists of five main areas: the graphics area, the Macro Menu, the header bar, the main menu, and the Permanent Menu. You can access a secondary menu by using the keyboard function keys.

PermanentmenuHeader bar

Graphics area

Main menu Page buttons

Macro menu

HyperMesh main screen

Graphics Area

The graphics area displays geometry, models, and plots.

Chapter 1: Introduction to Hyper Mesh


Header Bar

The header bar displays the current panel title and model status information. Messages also appear on the header bar temporarily overriding the title and status information.

Main Menu

From the Main Menu you can select one of seven functions organized by Page. Each Page contains various tools to assist you in performing that function.

Page Function

Geom Line creation and geometry editing functions

1D 1-D element creation and editing functions

2D 2-D surface and element creation and editing functions

3D 3-D surface and element creation and editing functions

BCs Boundary conditions, system, and load creation functions

Tool Model editing, utility, model checking, and informational functions

Post Post-processing and xy plotting functions

Using the Mouse

The mouse attached to your system is integral to HyperMesh and can be used in almost every aspect of user input. A two- or three-button mouse may be used with HyperMesh.

The mouse buttons have these functions.

Left mouse button Performs selection operations.

Right mouse button Deselects entities in the graphics area. Aborts graphics operations.



Middle mouse button In the rotate (r) and arc dynamic motion (a) modes, selects a new center of rotation when you pick a node in the model.

CTRL + left mouse button Dynamically rotates the model

CTRL + middle mouse button Zooms into an area of the model

CTRL + right mouse button Pans the model

Users can also use CTRL plus C and CTRL plus V to cut and paste text and numeric information.

Macro Menu

The Macro Menu allows you to customize the standard interface to include function buttons, radio options, and text that has HyperMesh-supplied and user-defined macros associated with it. The menu is located, by default on the right side of the screen area, above the Permanent Menu.

A macro file controls the display and available operations of the Macro Menu. Attributes that you can change include:

• The page on which to display the menu

• Text to be displayed on the control

• Location and size of the menu

• Help message to be displayed on the menu bar

• Macro to call, with optional arguments to pass

� See the Macro Menu section in the On-line Help for more information about creating and customizing the Macro Menu.



Exercise 1.1: Opening a Database File

Retrieve a HyperMesh database file

1. From any page, select the files panel.

2. Click the radio button to select the hm file sub-panel.

The radio button indicates that the files/hm file sub-panel is active.

3. Click the green retrieve … button to bring up the windows style file browser.

4. Locate the file called bumper.hm , then click the Open button in the file browser.

The bumper.hm file should be located in your working directory for this class. Alternately, it can be found in the HyperWorks installation under altair/tutorials/hm/training

5. Click return to exit the files panel.

bumper.hm



Permanent Menu

The Permanent Menu allows you to manipulate the view of the model, control which collectors are displayed in the graphics area, set global modeling parameters, and edit solver-specific data.

Standard Graphics Mode

Performance Graphic Mode

The Permanent Menu viewing functions listed below can be accessed by clicking on the desired function on the Permanent Menu or using the keyboard hot keys, designated by the same letters and the plus and minus sign on the menu. You can also use the arrow keys on the keyboard to rotate the model.

z (zoom) Magnify the view of a specific portion of a model, indicated by drawing a circle around it, in the graphics area.

p (plot) Replot or refresh the graphics area.

←←←← ↑↑↑↑ →→→→ ↓↓↓↓ Incrementally rotate the model about the screen x and y axes by the angle specified in the options/modeling menu sub-panel.

Incrementally rotate the model counter-clockwise and clockwise around the screen z axis.

w (window manager) Position and scale xy plots and title windows.

f (fill) Maximize the view of the displayed collectors in the graphics area.

r (rotate) Dynamically rotate the model about the screen x and y axes. With the middle mouse button, pick a node or point to be the rotation center. (Picking a rotation center cannot be done during animation processes or while viewing a mesh.)



s (slide zoom) Dynamically zoom in and out the model by moving the mouse towards and away from you.

c (center) Translate the model, or pan the model, by selecting a new center.

t (true view) Select model views by using local vectors or by entering the absolute view angles.

a (arc rotate) Dynamically rotate the model by clicking and dragging. With the middle mouse button, pick a node or point to be the rotation center. (Picking a rotation center cannot be done during animation processes or while viewing a mesh.)

+ - Zoom in and out about the center of the screen by the factor specified in the options/modeling menu sub-panel.

b Go back to the previous view.

view Display the model in several basic views and save and restore different views of your model.

These Permanent Menu items allow you to access panels that set global parameters, customize the interface, and control the screen display.

Menu Item Function and sub-panels

Defines parameters for viewing and model handling:

modeling Specify geometry and model tolerances and display settings.

graphics Specifying settings for standard and performance graphics modes.

menu config Specify settings for panel and graphic label font sizes. Also specifies and activates the Macro Menu.

colors Specify settings for background color, panel colors, axis colors and geometry cleanup colors.

page names Allows you to change page names.

postscript Specify postscript print options.

options

Spaceball Specify sensitivity settings for the spaceball.



Menu Item Function and sub-panels

card Edits solver specific data in card format.

global Defines global parameters that are accessed by several different panels.

help Accesses HyperMesh on-line documentation.

disp Controls which collectors are displayed in the graphics area.

View the HyperMesh model structure as a tree like display of components and assemblies

vis Controls display options. Available when performance graphics mode is active.

Toggles and switches

These icons for toggles and switches appear on some panels and sub-panels.

Toggle: Alternates between two options.

Switch: Presents a pop-up (floating) menu with several options to choose from.

Exercise 1.2: Displaying Elements and Geometry

In this exercise, turn on and off the display of elements and geometry by using the display panel on the Permanent Menu .

� Check boxes displaying a check are active; check boxes without a check are inactive.

Change the screen display

1. From the Permanent Menu , select the disp panel.



2. Click the switch to the left of comps . See figure below.

A pop-up menu appears with a list of the collector types whose display you can turn on and off. The mouse cursor appears at the center of the pop-up menu.

When you move the mouse cursor out of the pop-up menu, the pop-up menu closes.

3. Select comps from the pop-up menu to specify components are to be displayed.

Once you select comps , the pop-up menu closes.

4. Click the toggle to the left of elems to obtain geoms as the active component collector to the geoms entity type. See picture above for the location of the toggle.

A list displays of the component collectors containing geometry. There is a check in the check box preceding the component collector mid1_and_lines to indicate that the geometry in the mid1_and_lines component collector is currently displayed in the graphics area.

5. Right click the check box preceding the component collector mid1_and_lines, or right click the text, mid1_and_lines.

The check box preceding mid1_and_lines no longer has a white check mark in it (inactive). The display of geometry (lines) in the mid1_and_lines component collector is off.

6. From the Permanent Menu , click p to refresh the graphics area.

7. Click the toggle to elems to set the active component collector entity type to elements.

A list of component collectors that contain elements is displayed. There is a check mark in the check box preceding the component collectors, end1, end2, mid1_and_lines and mid2.

switch

toggle



8. Right click the check boxes preceding the component collectors end1 and mid1_and_lines or right click the text, end1 and mid1_and_lines.

The check boxes preceding end1 and mid1_and_lines have no white check marks in them. The display of elements in the end1 and mid1_and_lines component collectors is off.

9. From the Permanent Menu click p to refresh the graphics area.

10. In the graphics area, click on a blue element near the element’s handle. The handle is the dot in the center of the element (element centroid).

The check box preceding end2 has no white check mark in it. The display of elements in the end2 component collector is off.

11. Left click the check box preceding the component collector end2 or click the text, end2.

The check box preceding end2 has a white check mark in it. The display of elements in the end2component collector is on.

12. Click all .

All of the elements in all of the component collectors display.

The check boxes preceding the component collector’s names have check marks.

13. Click return to exit the display panel.

Using the model browser to control model display

An alternate way to control the display attributes of the model is through the model browser. The model hierarchy displays in a tree-like structure. Component display attributes such as color, display style (performance graphics mode), name, and current component can be set using a pop up menu activated by right clicking in the model browser.

1. To activate the model browser from the Permanent Menu click the tree

icon, .



This launches the model browser in a new window. This window can be resized and repositioned independently of the HyperMesh window.

2. Click the radio button next to Elems at the bottom of the model browser.

3. Click the check box corresponding to a component to toggle the display of the elements in that component on and off.

4. Left click the mid1_and_lines component name.

The blue highlight around the component name indicates it has been selected.

5. Click the right mouse button.

A pop-up menu appears with a series of choices applicable to the selected component.

6. Select the Make current option.

The name mid1_and_lines now displays with bold italic letters indicating this component is the current, active component.

Components and available menu choices



The menu choices available for the components include making the component the current component, changing the color, changing the display style (when in performance graphics mode) and renaming or deleting the component.

Some of the choices in the pop up menu are disabled, as they do not apply to specific components. These include changing between standard and performance graphics, creating new assemblies or components, or changing the name display mode. To use these options, right click within the model browser window, but not on a specific component name.

7. Create a new assembly by right clicking outside of the list of components and selecting Create new assembly from the pop-up menu. If desired, the name can be changed.

Assemblies are functional groupings of components used to organize a model. Within the model browser, components can be added to an assembly by dragging and dropping them into the assembly.

8. Drag the end1 , end2 mid1_and_lines and mid2 components into the new assembly. When dragging, release the mouse when the assembly name is highlighted.

The display of the entire assembly is now controlled with a single mouse click in the checkbox corresponding to the assembly. Also, by clicking the small minus sign where the assembly branches from the model tree, you can collapse the assembly component list.

9. Select the performance graphics mode by right clicking outside of the component list, and then, under Change graphics mode , selecting performance .

In performance graphics mode , the display style for the components can be controlled by clicking the icon representing the current style and toggling through the choices. The style can also be controlled using the Change style menu for the specific component.

10. Close the model browser by clicking the small X in the upper right corner of the model browser window.



Secondary Menu

Access the secondary menu by pressing the function keys, F1 through F12, and SHIFT F1 through SHIFT F12. Secondary functions temporarily interrupt main panel functions while leaving all settings and selections intact. When the secondary function completes, the initial main panel function resumes.

� Keyboard templates are available to identify the panel that each function key accesses. The function keys may be reassigned to different panels by using the build menu panel on the Tool page.

Menu Items

Panels can contain sub-panels or tools. These tools appear as function buttons, toggles, switches, entity selectors, direction selectors, data entry fields, input fields, and pop-up menus. The tools on each panel allow you to specify settings and enter information needed to perform the panel’s function.

Panels in HyperMesh work from left to right. The left side of the panel contains the information gathering tools for the operation and on the right side of the panel are the action buttons to carry out the operation.

From the Tool page, select the translate panel to view the menu items described in this section.

Translate panel

Entity Selector

The entity selector allows you to choose which type of entity is to be modified when a function is performed. The entity selector may or may not have a switch; some panels perform a function on only one type of entity. The entity selector button is yellow; when it is surrounded by a blue box, the collector is active and ready for you to select or pick the entities to be processed.

Entity selector Direction selector



Direction Selector

The direction selector allows you to define a plane or vector by using the global x, y, or z axis; or a base point; or by selecting a vector; or by selecting nodes in the database. Click the switch to obtain the pop-up menu of available directions.

Switch Form of plane definition

Base Edit button Reset button

Direction selector Direction selector pop-up menu

x-, y-, and z-axis These options allow you to specify a direction along any one of the global axes.

N1, N2, N3 This option allows you to create a user-defined direction. Selecting two nodes, N1 and N2, allows you to define a vector direction with base point at N1 toward N2. Selecting three nodes, N1, N2, and N3, allows you to define a plane with base point at N1 (unless otherwise specified). The vector is normal to the plane and its direction is determined by the right hand rule.

Setting vector direction using right hand rule



vector Allows you to use a pre-existing vector entity (something you can create using the vector panel) to define a direction.

base Defines the base of the direction vector, that place along the infinite line that defines the direction, where you want the plane to be defined. Think of a flat mirror defining a plane perpendicular to a ruler. You can move the mirror along the ruler, while maintaining the same orientation, and the base node defines where you are along the length of the ruler.

edit Click this button to enter the Node Vector Edit panel in the direction selector (see below). In this panel, you can define or edit the coordinates of N1, N2, and N3 and/or the base node by editing the coordinate values for these nodes.

reset Clears the node selections.

� In the on-line help, the direction selector is referred to as the “plane and vector collector.”



Input Fields

Input fields are used to enter text or numerical values. A description of the type of input precedes the field.

Input field

For a numeric input field, you can double click the input field and use the HyperMesh calculator to enter the value.

Calculator

Pop-up Menus

Pop-up menus display when there are several options from which to choose.

The extended entity selection menu allows you to specify alternate methods for selecting entities of the current data type. To use the extended entity selection menu, click the yellow data type button of the entity selector. The menu automatically closes after you have made your selection.

Extended entity selection menu for elements



Another example of a pop-up menu is the view menu, which allows you to specify five different model views or select from ten pre-set views. HyperMesh immediately processes the selection you have made and then waits for you to make more selections. This pop-up menu remains on the screen until you move the mouse cursor outside the menu.

The View Menu

Function Buttons

The color of the menu button corresponds to its purpose:

green Carries out a function or a command.

red Exits a panel or aborts a command.

Exercise 1.3: Translating Elements

In this exercise, use the view menu to select a new view of the model and the translate panel to translate elements along a vector. These techniques are used on several HyperMesh panels.

Accessing the translate panel

1. From the Main Menu click the radio button next to Tool to go to the Tool page.

2. Click translate button to go to the translate panel..



Displaying the model in a different view

1. From the Permanent Menu , click view .

The view pop-up menu displays.

2. Click top in the pop-up menu.

3. Move the mouse cursor out of the pop-up menu.

The view menu automatically closes.

Selecting the elements to translate

1. Click the entity selector switch, located in the upper left part of the menu panel under Translate.

A pop-up menu displays listing all the entity types you can modify with the translate panel. The mouse cursor is located at the center of the pop-up menu.

2. Select elems to specify “elements” as the entity type you want to translate.

After you select elems , the pop-up menu automatically closes. The yellow entity selector button displays “elems ” and the button has a blue border to indicate it is active.

3. Click elems .

The extended entity selection menu displays. The mouse cursor is located in the center of the pop-up menu.

4. Click by collector , indicating you want to select the elements by “component” collector.

After you select by collector , a list of component collectors displays.

In the graphics area, pick an orange element. Selecting this element also selects the component collector that contains the element, in this case end1 .



The picked element is momentarily highlighted white. The check box preceding end1 has a white check mark in it.

5. Click select .

This selects all the elements in the component collector, end1 , as the elements to be modified when you use the translate function.

The translate panel displays again and all of the elements in the component collector, end1 , display in white in the graphics area.

Specifying a direction to translate the selected elements

1. Click the direction selector switch.

A menu displays with a list of plane and vector options for translating the selected entities. The mouse cursor is located at the center of the pop-up menu.

2. Click N1,N2, N3 to select the three node method.

After you select N1, N2, N3, the pop-up menu automatically closes.

3. Click N1.

The N1 button has a blue border to indicate that it is active. The selected elements in the graphics area display in gray because the entity selector is not active.

4. In the graphics area, click a node.

A green circle appears in the graphics area at the node that was picked. The N1 button no longer has a blue border, but the N2 button does. N2 is currently active.

5. In the graphics area, click any node.

A blue circle displays in the graphics area at the node that you specified. The N2 button no longer has a blue border, but the N3 button does. N3 is currently active, but in this case, a node for N3 will not be specified.

� Selecting just 2 nodes defines a vector for the direction of translation. Selecting a third node defines a plane and the direction of translation would be the vector normal to that plane.



6. In the graphics area, right click the blue circle to deselect the node N2.

The blue node N2 is not displayed in the graphics area. The N2 button has a blue border.

7. In the graphics area, click on a different node.

A blue circle is displayed in the graphics area at the node that you specified.

Measuring a portion of the bumper

1. Press the function key, F4, on the keyboard to interrupt the translate panel and access the distance panel.

The distance panel displays. The N1 button in the distance panel has a blue border to indicate that it is active.

2. Click edit .

The Node Vector Edit panel displays.

3. Pick a node in the graphics area for N1.

The x, y, z coordinates can be edited for N1.

4. Pick another node for N2.

The x, y, z coordinates can be edited for N2.

5. Click return to exit the Node Vector Edit panel.

The distance panel displays. The absolute distance between N1 and N2 automatically displays in the input field following distance = .

6. To exit the distance panel, click return .

The translate panel re-displays. The elements and the nodes for N1 and N2 selected prior to using the distance panel are still selected.



Specifying a distance to translate the selected elements

1. Double-click magnitude = .

The calculator pop-up menu displays.

2. Click 5 and 0, in that order, in the calculator menu.

3. Click exit in the calculator menu.

The calculator pop-up menu closes. The value that you entered (50.0) in the calculator menu displays in the data field following magnitude = .

Translating the selected elements

1. Click translate + .

The highlighted elements translate 50 units in the positive N1-N2 vector direction with N1 being the vector’s base node and the vector passing through N2.

2. From the Permanent Menu click f.

The model is sized to fit the screen.

3. From the Permanent Menu use rotate, r, or arc rotate, a, to rotate the model.

Observe how it changes.

4. Click translate - .

The highlighted elements are translated 50 units in the negative N1-N2 vector direction. The elements are in their original position.

5. Click reset on the direction selector.

The N1 button has a blue border indicating it is active.

6. Try translating the selected elements in the positive X-axis direction by defining a plane using N1, N2, N3.



7. To exit the translate panel, click return .

Standard and Performance Graphics

HyperMesh has two graphics engines: standard and performance. The differences between the two graphics engines are summarized below:

HyperMesh feature Standard Graphics Performance Graphics

vis panel Not available. The vis panel, controlling element display characteristics, accessible from the Permanent Menu is active only when the performance graphics engine is selected.

pick handles All geometry and elements have pick handles.

Geometry and element pick handles can be displayed in the graphics area by making active the appropriate options in the options/modeling sub-panel.

There are pick handles for 1-D elements only.

Element pick handles for 1-D elements can be displayed in the graphics area by activating the appropriate option in the options/modeling sub-panel.

Picking nodes in the graphics area

Click on the desired node. Click on the desired node or press and hold down the left mouse button. Drag the mouse cursor anywhere along an element until it is highlighted, and then move the mouse cursor close to the desired node of the highlighted element.

Picking geometry and elements in the graphics area

Press and hold down the left mouse button and drag the mouse cursor near a pick handle until the line, surface, or element is highlighted.

1-D elements are selected the same way as in standard graphics mode. For any other type of entity, press and hold down the left mouse button and drag the mouse cursor anywhere along the line, surface, or element until it is highlighted.

Model display attributes

View model only in wireframe. In the hidden line , contour , vector plot , deformed , transient , and replay panel, view model in wireframe or hidden line.

View model anytime in wireframe, hidden line, hidden line with mesh lines, hidden line with feature lines, and/or transparent.

AVI and H3D file creation

Not available. Can create AVI and H3D files.



When the performance graphics engine is active, there are five element display attributes from which to choose. The attributes are assigned in the vis panel:

wireframe Element edges are displayed with

lines.

hidden line Elements are displayed as filled

polygons.

hidden line with mesh lines Elements are displayed as filled

polygons with the element edges drawn in mesh line color.

hidden line with feature lines Elements are displayed as filled

polygons with the “feature” edges drawn in mesh line color.

transparent Elements are displayed as

transparent, filled polygons.

Macro Menu

The Macro Menu allows you to customize the standard interface to include function buttons, radio options, and text that have Altair-supplied and user-defined macros associated with them. The menu is located on the right side of the screen area, above the Permanent Menu .

A macro file controls the display and available operations of the Macro Menu . Attributes you can change include:

• The layout of the buttons on the macro page. You can create multiple macro pages allowing you to group macros by type of operation.

• Text to be displayed on the macro button

• Location and size of the macro button

• Help message to be displayed on the menu bar

• Macro to call, with optional arguments to pass

Macros may contain any valid command file commands, and are enclosed by the *beginmacro() and *endmacro() commands. Macros can accept variable arguments, passed to them from a control, by using the arguments $1, $2, etc. to specify where the arguments should be substituted. The *callmacro()



command allows you to call a macro from within another one, which allows you to create groups of standard reusable macros.

When HyperMesh starts, if there is a macro file named hm.mac in the current HOME (UNIX only), or the application base directory, then it automatically runs to define the attributes and contents of the Macro Menu . You may also run a macro file after HyperMesh starts, or toggle the display of the Macro Menu from the options/menu config panel.

� While macros offer a great deal of flexibility, you must remember that once a macro executes, there is no way to cancel the execution or reject the results. A macro may not be called recursively.



The Default Macro Menu

The Macro Menu is located on the right side of the graphics region. It divides into three areas: macro, display, and page. Each area has multiple options. The Disp Macro Menu is shown to the right.

The Page selection buttons are at the bottom of the Macro Menu just above quit. The six preset buttons are QA, Mesh, User1 , off , Disp , and Geom . Each page contains different Tools and macros.

The Tools buttons allow you to perform functions quickly that would normally take several steps. Each page has its own set of tools.

On the Geom page there are three tools:

Isolate surf Allows you to isolate either an inner or an outer surface layer from a 3-D model. This macro works only on the surfaces attached to the selected surface. The other layer and thickness are then placed in a temp directory and masked.

Washer Scale a circular line 1.5 times and then trim that new line into the surface. This will allow for a better mesh quality around circular holes.

Adj circ pts Places three additional fixed points on an inner line, and then projects those points to a concentric line. This allows you to create a higher quality mesh.

On the QA page there are twelve tools to help you clean up a pre-existing mesh quickly. There are eight tools to isolate any elements that fail certain element check criteria. The macro displays only those elements that fail. The values of these criteria can be changed in the hm.mac file but are preset to:

Length < 5.0

Jacobian < 0.5

Warpage > 20.0

Aspect Ratio > 5.0



Max Angle Quad > 150.0

Max Angle Tria > 140.0

Min Angle Quad < 20.0

Min Angle Tria < 10.0

You can then use the next four macros to quickly modify any elements that fail the element checks.

Find attached Finds all of the elements attached to the displayed elements.

Remesh Allows you to remesh the selected elements plus one, two, or three attached layers of elements. Remesh uses the current size, does not break connectivity, and uses the mixed element type.

Smooth Allows you to apply the smoothing algorithm to the selected elements plus one, two, or three attached element layers.

Find between Finds the elements that are shared between two components

On the Mesh page there are six macros.

Elems by surf Allows you to delete elements associated to a selected surface.

Remesh Functions as on the Mesh page.

Smooth Functions as on the Mesh page.

Split warped Processes the entire model and splits all quad elements with a warpage greater than 20 into trias along the diagonal of the quad.

The Disp Macro Menu has several macros for light source and specularity and these Display: buttons. They allow you to modify the graphics display in several ways.

Geom Allows you to turn off or on all of the geometry in the model.

Elems Allows you to turn off or on all of the elements in the model.

Shrink Allows you to shrink the elements in the model by 20%.



Gfx Allows you to display the model either in performance or standard graphics mode.

Vis opts Allows you to select the topology visualization mode for displaying the model. Four modes are available:

0 Standard mode, the mode most commonly used.

1 Component color, the model is always displayed with the edges the same color as the associated component, even in the automesh panel.

2 Topology mode, the surface edges are displayed according to connectivity, as in the geom cleanup panel.

3 Shaded mode, allows you to view the model in shaded mode regardless of which panel you are currently using.

Surf Line Allows you to place surface lines on your model. You can place one, two, three, or no lines on each surface.

Only comps Turns off every type of collector except component collectors.

Mask lines Masks all of the lines in the model that are displayed.

Temp nodes Removes all of the displayed temporary nodes.

Macros off Allows you to turn off the Macro Menu.



The Files Panel

The files panel contains the following functions:

hm file Saves and retrieves HyperMesh binary database files.

There are no restrictions placed on HyperMesh database file extension names other than those imposed by the operating system.

It is not possible to retrieve a HyperMesh database file into another HyperMesh database file.

import Loads CAD generated geometry or finite element model information.

It is possible to import a CAD generated geometry or a finite element model information file into a HyperMesh database file.

The HyperMesh path name for import translators is /altair/hm/6.0/bin/feinput/ . By default, this path is specified in the translator = field on this sub-panel.

export Translates CAD geometry or finite element information for specific analysis codes.

The path name for templates is /altair/templates/6.0/feoutput/ . By default, this path is specified in the template = field on this sub-panel.

command Executes a HyperMesh command file.

template Specifies the template file used to format the HyperMesh database for a specific analysis code.

The path name for templates is /altair/templates/ 6.0/feoutput/ . By default, this path is specified in the template file = field on this sub-panel.



results Specifies the results file.

With the exception of Altair OptiStruct files, results files need to be translated to “HyperMesh language” before they can be viewed in HyperMesh. Translate a results file by using the appropriate translator in the /altair/translators/6.0/ directory.

� To reset the default path for import, export, or template, delete the entire path name, leave the panel, and then return to the panel.

The Collectors Panel The collectors panel allows you to create, review, and edit collectors and card images or dictionaries. Collectors store and organize data such as geometry, elements, element properties, element materials, loads, systems, and vectors. HyperMesh has six types of collectors:

component Holds only element, line, and surface data.

NOTE: Elements, lines, and surfaces cannot exist unless a component collector exists. If you do not create a component collector first, HyperMesh automatically creates one, auto1 , for the entities produced.

property Holds only property information about the elements in the component collectors.

material Holds only material information about the elements in the component collectors.

load Holds only load data such as forces, pressures, and constraints.

NOTE: Loads cannot exist unless a load collector exists. If you do not create a load collector first, HyperMesh automatically creates one, auto1 , for the loads produced.

system Holds only coordinate systems.

vector Holds only vectors.



beam section Holds beam section data.

In the collectors panel, collector card images or dictionaries can be selected when a template is referenced in the files/template sub-panel or in the global panel. Card images and dictionaries store attributes according to the template referenced. When the HyperMesh database is exported, the attributes in the card images or dictionaries are exported to the bulk data file.

Exercise 1.4: Using the Card Panel

In this exercise, practice using the card panel to review the bumper model’s attributes. It is important to know that the bumper model was created with the abaqus/standard.3d template loaded in HyperMesh. To review the model’s attributes, load this template.

Loading the template

1. From any menu page select files .

2. Select the template sub-panel.

3. Double-click template file = .

4. Select abaqus/ .

5. Select standard.3d .

6. To exit the files panel, click return .



Reviewing an element

1. From the Permanent Menu click card .

2. Click the entity selector switch and select elems or double-click an element in the model to change the entity selector to elems .

3. In the graphics area, pick a green-colored element.

4. Click edit .

A card image of the element pops up. The card image identifies that the selected element is an Abaqus S4 type element and is in the component collector named mid2 . The element’s ID displays. This information is formated in the analysis bulk data file as it appears in the card image.

5. To exit the card image, click return .

Reviewing a component collector

1. Set the entity type to comps .

2. Click comps .

3. Click end1 .

4. Click select .

5. Click edit .

A card image of the component collector end1 pops up. The card image indicates the elements in this collector have a thickness of 2 units and are made of a material named steel. This information is formatted in the analysis bulk data file as it appears in the card image.

6. To exit the card image, click return .



Reviewing and editing a material collector

1. Set the entity type to mats .

2. Click mats .

3. Click steel .

4. Click select .

5. Click edit .

A card image displays of the material collector steel. The card image identifies that steel is isotropic and elastic. It also shows the values for E and NU. This information is formatted in the analysis bulk data file as it appears in the card image.

6. Click the input field under NU and change the value to 0.28 .

7. To exit the card image and to accept the change made to steel , click return .

8. To exit the card panel, click return .



Default HyperMesh Files HyperMesh includes or automatically creates several default files. These include:

hm.cfg configuration file

command.cmf command file

hmmenu.set user interface settings

[feinput translator name].hmx unsupported FE data file

[feinput translator name].msg import file messages

hm.cfg

The hm.cfg file is a default configuration file that is read on start-up. The hm.cfg file controls many aspects of how HyperMesh runs at your particular site. You can edit the commands in the hm.cfg file to your own preferences. For more information about the hm.cfg file, please see the HyperMesh on-line help, User’s Guide, The HyperMesh Configuration File and the hardcopy Altair HyperWorks Installation Guide.

command.cmf

The command.cmf file is a standard ASCII file that HyperMesh reads and writes. Command files allow you to retrieve a work session in case of a system crash or program a series of procedures. You can use a command file in applications that contain repetitive steps or you can create demonstrations.

All commands executed by the HyperMesh command processor are written to this file. This file is automatically created in the directory in which you started HyperMesh. If the file already exists, new commands are appended to the existing file.

For more information about the command.cmf file, please see the HyperMesh on-line help, User’s Guide, Commands.



hmmenu.set

The hmmenu.set file is a binary file that HyperMesh updates when you exit HyperMesh. Your personal hmmenu.set file stores many global parameters and is located in the directory from which you started HyperMesh. If the file already exists, it is overwritten after you run a new session. The most recent global parameter values in the current HyperMesh session are written to this file when you exit. The next time you start HyperMesh, it has the values recorded in the hmmenu.set file. If the file does not exist when HyperMesh is invoked, the global parameter values are default values.

[feinput translator name].hmx

The [feinput translator name].hmx file is an ASCII file that HyperMesh creates when a bulk data file imported to HyperMesh contains cards and comment lines in the file that are not supported. All non-supported cards and comment lines are written to the [feinput translator name].hmx file.

[feinput translator name].msg

The [feinput translator name].msg file is an ASCII file that HyperMesh creates when a bulk data file is imported to HyperMesh. It contains the status of the FE import process, including messages, errors, and general summary information.


Chapter 2: Creating an FEA Model

Creating, Solving, and Analyzing an FEA Model In this section, build a model of a helical spring with plate and solid elements and apply boundary conditions. Next, solve the model by using Altair’s OptiStruct solver. Complete this section by using the post-processing tools to view the analysis results.

�Altair’s OptiStruct solver is a baseline linear static and Eigenvalue analysis tool that provides a basic evaluation of the structural integrity of an FEA model. For more information about OptiStruct, click help on the Permanent Menu , click help topics and select HyperWorks, then OptiStruct.

spring model

Chapter 3: Geometry Clean Up and Tetrameshing


Exercise 2.1: Retrieving a HyperMesh Database

In this exercise, retrieve a HyperMesh binary database file. If you have information stored in the current session, HyperMesh clears the current model before retrieving the file.

Retrieve the HyperMesh database file and load the template


2. Select the hm file sub-panel.

3. Double-click file = and use the file browser to select the spring0.hm file.

A confirmation box may appear warning that the current model will be deleted. Click Yes.

4. Select the template sub-panel.

5. Click load… and use the file browser to select first, the optistruct folder, and then the optistruct template.

Selecting the OptiStruct template allows you to define OptiStuct specific attributes in your HyperMesh session.


Exercise 2.2: Creating Material Collectors

The spring0.hm model has only one component collector and no material collectors. In this step, create a material collector with properties of mild steel.

1. From any menu page, select the collectors panel.

2. Select the create sub-panel.

3. Set the collector type to mats .



4. Click name = and enter steel.

5. Set creation method: to card image = .

6. Click card image = and select MAT1.

� The OptiStruct template supports three material types, MAT1, MAT2, MAT8, and MAT9. These correspond to the same NASTRAN material types. For more information, go to the OptiStruct/Data Formats section in the online help.

7. Click create/edit .

This loads the MAT1 card image for the new material, steel . If a block does not have a value, it is currently off. To turn it on, click the heading. To add a value for a block in the card image, click the data field and enter the number.

8. Click E, click the data entry field, and enter 2.0e5 .

9. Click NU, click the data entry field, and enter 0.30 .

10. Click return .

� It is not necessary to define a density value since only a static analysis is desired. Density values are required, however, for normal modes or buckling analysis.

Exercise 2.3: Creating and Editing Component Collectors

In this exercise, we create two component collectors. One will be for construction purposes only, and the other will hold the solid elements used for the analysis. By organizing the construction elements into a separate collector, it will be easier to delete them once we are finished building the model.



Create a component collector for 2-d elements The 2-d elements are used in the construction of the solid elements of the tube model.

1. Set the collector type: to comps .

2. Click name = and enter shell_elems .

3. Set the creation method: to no card image .

The elements put in this collector are for construction purposes only. Because they will not be used for analysis, it is not necessary to specify an OptiStruct component card image.

4. Click material = and select steel.

When you create a component collector, HyperMesh requires you to specify a material collector. If you do not specify one here, a “dummy” material collector with the same name as the component is created for you. To avoid having to delete the dummy material collector later, we instead create a reference to the existing steel material.

5. Click color and select a color from the pop-up menu.

6. Click create to create the component collector.

Create and edit a component collector for the solid elements

1. Click name = and enter solid_elems .

2. Set the creation method: to card image= .

3. Click card image = and select PSOLID from the pop-up menu.

4. Click material = and select steel .

5. Click color and select a color from the pop-up menu.



6. Click create to create the collector.

Since none of the fields on the PSOLID card can be edited, we will not use the create/edit option.

7. Click return to exit the collectors panel.

� Save your work as spring.ex2 .03.hm . See instructions below.

Save your work as a hm binary database

1. Click files .


3. Click save as … to bring up the file browser. The original file name should be highlighted in the File name field in the file browser. Start typing the new name to replace it.

4. Click save .


Exercise 2.4: Creating 2-D Elements with the Spline Panel

Set the current component and create the 2-D elements

1. From the global panel, click component = and select shell_elems .

2. Click return .

3. From the 2D page, select the spline panel.

4. Set the entity type to lines .



5. Click the circle edge.

6. Set the surface creation method to mesh, dele surf .

7. Click create .

The message “Lines appear planar, project to plane?” displays.

8. Click yes .

9. Click set edge to .

10. Click elem density = and enter 14 .

11. Click the displayed, preliminary density value on the circle.

The value changes to 14.

12. Select the element type sub-panel.

13. Set the element type selector to quads .

14. Click the blue element type icon in the model, in the middle of the circle.

The icon should change to a square. Alternately, you could click the green set all button.



15. Click mesh .

The plate mesh at the end of the spring should match the image below.

Plate mesh at the end of the spring

16. Click return to accept the mesh and exit the meshing panel.

17. Click return to exit the spline panel.

� Save your work as spring.ex2.04.hm .

To save your file, from any main panel click files , select the hm sub-panel. Click save as… to bring up the file browser. After the save completes, click return to continue your work.



Exercise 2.5: Creating 3-D Elements with the Line Drag Panel

In this exercise, drag the plate elements created in the previous exercise along the helical line. As you do this, you will create 3-D solid brick elements.

Set the current component and create the 3-D elements

1. From the global panel, click component = and select solid_elems .

2. Click return .

3. Turn on performance graphics mode by clicking the gfx per button from the Macro Menu .

4. On the 3D page, select the line drag panel.

5. Select the drag elems sub-panel.

6. Click elems and select displayed .

7. Click line list to make it active.

8. Pick the helical line in the graphics area.

9. Click the toggle to the use default vector option.

10. Click on drag = and enter 120 .

This indicates the number of element layers created along the line.

11. Click drag .

12. Click return to accept the mesh.



13. Click return to return to main menu.


To save your file, click files from any main panel, select the hm sub-panel. Click on text box after file = and enter the file name, then click save . After the save completes, click return to continue your work.

Exercise 2.6: Cleaning up the Model

At this point, we are done with the shell elements and geometry. We can now delete these two components from the database.

1. Press F2, or from the Tool page select the delete panel.

2. Set the entity type to comps .

3. Click comps .

4. Select the geometry and shell_elems collectors.

5. Click select .

6. Click delete entity .

7. Click return .



Exercise 2.7: Creating Load Collectors

In this section, create load collectors for the boundary conditions. We will be defining two load cases for this model, a compressive force and a lateral force. By organizing the forces into load collectors, it will be easier to define the load step combinations and create the load cases.

1. From any menu page, select the collectors panel.


3. Set the collector type to loadcols .

4. Click name = and enter constraints .

5. Set creation method to no card image .

6. Click color and select a color.

7. Click create .

8. Click name = and enter compression.

9. Click color and select a color.

10. Click create .

11. Repeat steps 8 – 10 and create another load collector named lateral .

12. Click return to exit the collectors panel.




Exercise 2.8: Applying Constraints to the Model

In this exercise, create constraints at one end of the model. These same constraints will be used in each of the load cases.

Set the current load collector and view

1. In the global panel, set load col = to constraints .

2. Click return .

3. From the Permanent Menu , select the view panel.

4. Select rear and zoom in on the end of the model at the most positive y-direction.

Remember that the zoom function can be accessed using the CTRL + middle mouse button.

5. Click return .

Create constraints

1. From the BCs page, select the constraints panel.


3. Click nodes and select on plane .

4. Pick any three nodes on the end face of the spring.

These nodes will be used to define the plane to search for other nodes (N1, N2 and N3). (See illustration on next page.)



Nodes to select from to define plane

5. Click tolerance = and enter .01 .

6. Set the toggle to the plane option.

7. Click select entities .

8. Click size = and enter 30 .

9. Activate the label constraints option by clicking the check box.

10. Activate degrees of freedom (dof) 1, 2, and 3.

For linear static analysis in OptiStruct degrees of freedom 1, 2, and 3 represent translations in the global x, y, and z directions respectively. Degrees of freedom 4, 5, and 6 represent rotations about the global x, y and z axis respectively. As these are solid elements, degrees of freedom 4, 5 and 6 do not apply.

11. Click create to constrain the selected nodes.



12. Click return to exit the constraints panel.

Nodes with defined constraints


Exercise 2.9: Creating Forces

In this exercise, apply two load groups to the other end of the spring. One set of loads apply compressive forces to the spring, the other a lateral force to “unwind” the spring.

Set the current collector and view

1. In the global panel, set loadcol = to compression .

2. Click return .

3. From the Permanent Menu , select the view panel.



4. Select front , then zoom in on the end at the most negative y-direction.

5. Click the up arrow, either on the Permanent menu or using the keyboard, three times so the end face is almost horizontal.

Create the compressive forces

1. From the BCs page, select the forces panel.


3. Click nodes and select by window .

4. Draw a window around the end nodes of the model, as shown below. Make sure the window selection option is set to interior .

Window used to select entities

5. Click select entities .

6. Click nodes and select save .

We will select these same nodes to apply the lateral force. This step will save the node selection in a buffer so they can be recalled in the next steps.



7. Click the leftmost toggle to the global system option.

8. Click magnitude = and enter 100.0 .

9. Set the direction to y-axis .

10. Click the rightmost toggle to the magnitude % = option.

11. Click magnitude % = and enter 20.0 .

12. Activate the label loads option by clicking in the check box.

13. Click create .

Create the lateral forces

1. From the global panel, set the current load collector to lateral .

2. Click return .

3. Click nodes and select retrieve from the extended selection menu.

This will retrieve the selection of the nodes on the end face of the spring from the clipboard buffer.

4. Set the direction to N1, N2, N3.

This allows us to define the direction of the force as normal (perpendicular) to the end face of the spring.

5. Pick any three nodes on the end face of the spring.



6. Click create .

This defines loads normal to the end face of the spring. The new loads should appear in the color of the load collector defined for the lateral load.

Loads applied to the end of the spring

7. Click return .


Exercise 2.10: Creating Load Steps

The final process in specifying the boundary conditions is to create OptiStruct sub-cases (loadsteps in HyperMesh ). We will create two different sub-cases, one each for the compression and lateral loads. In each case, the constraints will also be active.

Create load steps for the compressive and lateral loads

1. From the BCs page, select the load steps panel.

2. Click name = and enter compression .



3. Click loadcols and select constraints and compression from the collector list by checking the appropriate boxes.

4. Click select .

5. Click create .

6. Click name = and enter lateral.

7. Click loadcols and select constraints and lateral from the collector list.

8. Click select .

9. Click create .

10. Click return to exit the load steps panel.


Exercise 2.11: Using the OptiStruct Solver

As with any finite element solver, the information defined in the HyperMesh database must be written out in a format that the chosen solver can understand. Do this by exporting the model using the export sub-panel on the files page. HyperMesh and OptiStruct handle this process in the background when using the OptiStruct panel on the BC’s page to launch the solution process.

Running the solver

1. From the BC’s page, select the OptiStruct panel.

A path and filename is specified by default in the file = field. In this case, it will use the name spring0.fem . If you desire, specify another name by entering it in the file = field, however, the file name chosen must have a .fem extension.



The memory default toggle will allow the solver to manage memory, or alternately, you can specify the amount of RAM allocated.

Under Run options , the top selector allows you to limit the run to perform an optimization (if the correct optimization parameters are defined), an analysis only run (as we will do), a check run (to verify model integrity) or a restart run.

The export toggle lets you choose between exporting the entire model, or just the components that are displayed.

Memory toggle

Run typeselectorExport

options

2. Click optistruct to launch the solver process.

This launches another window and starts the OptiStruct solver. After a few seconds this message appears: …Processing complete .

At this point, close the OptiStruct window.

OptiStruct creates several files in the HyperMesh starting directory. They are listed in the following table.

spring.res The HyperMesh binary results file.

spring.out The OptiStruct output file containing specific information on

• the file set-up,

• the set-up of your optimization problem,

• the 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 spring.fem file.

spring.oslog The OptiStruct log file containing compliance and volume calculations for each optimization iteration.



Post-processing the Results The OptiStruct analysis provides displacement and stress results for linear static runs. OptiStruct generates HyperMesh format binary results files directly. If another analysis package had been used (NASTRAN, LS-Dyna, ABAQUS, etc.) the output file from the solver would first need to be translated into a HyperMesh binary results file. This is done from a command line outside of HyperMesh, or from the solver panel.

Once generated, the results file needs to be specified on the files/results panel prior to post-processing.

The HyperMesh results translators can be executed from the UNIX command line (MS-DOS prompt in Windows) or using the solver panel on the BC’s page from within HyperMesh. In either case, the syntax is the same.

This is the syntax necessary to run all of the translators.

<HyperMesh translator> [arguments] <inputfile> <outputfile> <modelfile>

where:

<HyperMesh translator > The name of the HyperMesh translator to be executed.

<arguments > A list of arguments that modify the execution of the translator. This list is specific to each of the translators. For a list of the available arguments, type in the translator name with the -u option.

<inputfile > The file containing results from the analysis code.

<outputfile > The file that contains the results in HyperMesh format.

<modelfile > The file to be created containing the model, as found in the results database. This feature is available on some of the HyperMesh translators. To find out which translators have this feature, use the -u option.

If the input filename and output filename are not specified, the translator assumes that you want to translate the results from standard input to standard output. This is useful when the results file to be translated has been compressed



with a file compression utility. With UNIX style utilities, the compressed results file can be uncompressed, piped into the translator, and the output from the translator can be written to a file. An example of this command follows:

filepress run1.prs | hmnast > run1.res



Exercise 2.12: Viewing a Deformed Shape

The OptiStruct solver, when launched using the OptiStruct panel within HyperMesh, generates a HyperMesh binary results file and loads it into HyperMesh. If you used a different solver, the results file generated by the results translator would need to be loaded using the results sub-panel of the files panel.

1. From the Post page, select the deformed panel.

2. Click simulation = .

3. Select COMPRESSION.

4. Click model units = and enter 50 .

5. Click deform .

A deformed plot of your model overlays the undeformed mesh in the display. Does the deformed shape look correct for the boundary conditions you applied to the mesh?

6. Click linear to animate the results.

7. Click return .

8. Change the simulation to LATERAL .

9. Click deform .

A deformed plot of the lateral loading case displays. Does the deformed shape look correct for this set of loading conditions?

10. Click return .



Exercise 2.13: Viewing a Contour Plot

1. From the Post page, select the contour panel.

2. Click simulation = and select compression

3. Click data type = and select Displacements .

The list of data types available depends on which data types were requested for output. By default, OptiStruct will output displacement and stress results.

4. Click contour .

What is the maximum displacement value?

Where does your model have its maximum displacement?

Does this correlate with the boundary conditions applied to the model?

5. Click data type = and select von Mises Stress .

6. Click assign .

What is the maximum Von Mises stress value?

Where does your model have its maximum stress?

7. Click simulation = and select lateral .

8. Click assign .

What is the maximum Von Mises stress value?

Where does your model have its maximum stress?

Does this make sense for the boundary conditions?

9. Explore the other combinations and data types using the Contour panel.




Tetrahedral elements are solid finite elements with four triangular faces. Tetra elements are commonly used to model solid parts, especially if the geometry is complex.

In HyperMesh, the automatic tetrahedral mesher can fill any volume defined by a surface mesh of tria plate elements.

The tetrahedral mesher requires as input a continuous mesh enclosing a single volume. The quality of the resulting tetrahedral mesh depends on the quality of the initial surface mesh. To achieve good quality, size the elements to achieve adequate resolution of the model. Any size differences between neighboring elements needs to be gradual.

The tetrameshing process in HyperMesh

1. Import the CAD data and prepare the surfaces for meshing (geometry cleanup)

2. Generate a surface mesh of tria plate elements

3. Check quality and connectivity of the tria elements

4. Generate the tetrahedral mesh

5. Delete the original tria surface mesh

Each of these steps in the process is examined in detail in this section, with exercises to demonstrate the steps.



Geometry Cleanup Sometimes, the CAD geometry contains gaps, overlaps, and misalignments in surface vertices. The process to correct these problems is commonly referred to as geometry cleanup. From the Geom menu page, select the geometry cleanup panel to access the tools to help you prepare surface geometry for meshing.

Geometry cleanup panel

Topology display of surface edges

In topology display mode (the default viewing mode when in the geom cleanup panel), surface edges are colored according to their connectivity status with neighboring surface edges.

Red edges indicate free surface edges belonging to a single surface. Free surface edges usually result in mesh discontinuities; that is, any nodes placed along free surface edges will not necessarily be shared with elements on adjacent surfaces.

Green surface edges indicate edges shared between two adjacent surfaces. Nodes on shared edges are common to both adjacent surfaces.

Yellow lines represent “non-manifold” edges; that is, surface boundaries shared between three or more surfaces. These usually indicate a T-connection or a duplicate surface.

Dark blue broken lines represent suppressed edges. A suppressed edge is a surface boundary ignored by the automesher. The two adjacent surfaces are in effect stitched together to form a larger surface. Nodes are not seeded along suppressed edges.

Geometry cleanup tools

There are three tools, each with three or four different functions, available to cleanup the geometry.



Edges function

The edges function allows connectivity status changes between surface edges. It has four different tools: toggle , replace , (un)suppress , and equivalence .

Toggle allows you to select a surface edge and sequentially change its topology from free to shared to suppressed with a single left mouse click on the edge. Use the right mouse button to “undo” the toggle operation and change suppressed edges to shared or shared edges to free. To toggle a free edge to shared, a matching free edge must be located within the cleanup tolerance specified.

The replace function combines free edge pairs to shared edges, however, the resulting shared edge will be at the location of the line selected as the retained edge, and the line selected as the edge to move is eliminated. This function offers a greater amount of control over the toggle function.

The (un)suppress function allows you to select a series of lines to suppress or unsuppress. An extended line selection menu is available, allowing any of the line selection methods to be used. This function is useful for eliminating seams due to symmetric surface generation.

The equivalence function identifies and combines a large number of free edge pairs automatically.

Surfaces function

The surfaces function contains tools to identify and eliminate duplicate surfaces, and to automatically suppress shared surface edges, effectively creating larger surfaces based on features in the CAD model. Larger surfaces often allow the automesher freedom to create a better quality surface mesh.

Fixed points function

The automesher forces nodes at fixed points. To achieve better mesh control during automeshing, you may wish to manipulate some of the fixed points. The fixed points function contains tools to add, replace, suppress or release fixed points.



Exercise 3.1: Importing and observing the model

In this exercise, read in a HyperMesh file containing the surface geometry for a universal joint casting. The geometry of this file has been modified to demonstrate some of the problems that can occur with imported geometry, and subsequent exercises address these problems.

Retrieving the model



3. Click the retrieve… button to bring up the file browser.

4. Select the ujoint.hm file.

5. Click open.


U-joint model



Observing the model

Examine the model, rotating and zooming as necessary. To view the model in topology display mode, select the geom cleanup panel from the geom page. If desired, the surfaces can be shaded using the violet vis opts menu. The violet vis opts button displays a menu to control the display of the surfaces (shaded or wireframe), and checkboxes to turn on or off the display of the different edge types or fixed point (surface vertices).

Click the toggle at the top of the pop up window to change from wireframe to shaded .

Notice some of the edges are red, green or yellow. As this geometry represents a single, cast part, the goal of geometry cleanup is to end up with only shared (green) or suppressed (blue) edges.

Determining the element size to use

As a rule of thumb, elements should be sized such that two or three tetrahedral elements will be formed across the narrowest details of the part. The smallest details that need to be modeled for this part are the shoulder surfaces on each of the four ends of the universal joint. Knowing the length of these surface edges allows us to determine an appropriate element size for the model.

1. From the Permanent Menu click the view button.

2. Click restore4 to recall a preset view of the model.

3. Click return to exit the geom cleanup panel and return to the geom page.

4. Select the distance panel.

An alternate way to access the distance panel is to press the F4 key.

5. Select the two points function.



6. Click each of the two points representing the surface vertices on the narrow edge of the shoulder surface, as indicated in the illustration. Once the second point is selected, the distance between the points is given as 8.393 mm.

Measuring the distance between two nodes

For the surface mesher to form two elements across the width of this surface, use an element size of four mm.

Set global element size

An advantage to setting the element size from the global panel is it becomes the default mesh size. When you have larger models with multiple meshing activities, having the element size set globally will save you from recalculating the mesh density during all your meshing activities on your model.

1. From the Permanent Menu click the global button.

2. Click the element size = field and enter 4.0 for the default element size.

3. Click return to go back to the distance panel.



4. Hit the letter F key on the keyboard to fit the entire model to the display area.

Exercise 3.2: Cleaning up geometry

In this exercise, use the geometry cleanup tools in HyperMesh to 1) combine free surface edge pairs, 2) create filler surfaces, and 3) identify and eliminate duplicated surfaces.

Combine free edge pairs using the edges function

Most geometry cleanup operations require specific cleanup tolerances. The cleanup tolerance specifies the size of the largest gap to be closed by the cleanup operation. In general, cleanup tolerances should not exceed 15-20% of the mesh element size to reduce the significance of mesh distortions. A tolerance larger than 20% of the element size can lead to significant distortions when the mesh elements are generated, as shown in the image. The distorted mesh elements on the left side occurred during the replace edge function used to close a gap larger than 20% of the element size in the adjoining surfaces.

Mesh distortion caused by closing a large gap in geometry

Set the cleanup tolerance from the geom cleanup panel in the cleanup tol = field.



If a large number of free edges are present in the model, the equivalence tool can be very effective in combining the free edge pairs. Once the number of free edges is reduced, the toggle tool can be used to combine the remaining free edges, with a greater deal of control over the operation.

1. From the edges function, select the equivalence tool.

2. Click the yellow surfs entity selector.

3. From the extended entity selector pop-up window, select all surfaces.

4. Click eqivalence .

This combines into shared edges any free edge pairs within the cleanup tolerance (0.10 mm in this case).

The remaining free edges in the model were not combined because the matching edges were outside of the cleanup tolerance. Use the toggle tool to pair up the remaining free edges.

Combine the remaining free edges

1. If the surfaces are shaded, switch the display mode back to wireframe using the vis opts button. It will be easier to identify the remaining free edges in wireframe mode.

2. Select the toggle tool.

3. Select one of the long, curved red lines near the center of the part.

Once the line is selected, the error message in the header bar indicates that the maximum gap is 0.4546 mm.

4. Increase the cleanup tolerance to 0.5 .

This is still within the acceptable range for cleanup operations (up to15-20% of element size), based on an element size of 4.0 mm.



5. Select each of the long curved lines to combine the free edges.

Free edges to toggle to shared edges

Some of the remaining free edges in the model are still within the acceptable range for cleanup operations. For gaps larger than 0.5 mm, alternate methods will be used.

6. From the view panel recall view 1 using the restore1 button.

7. Using the Toggle tool, click the edges around the semi-circular surface to change the topology mode.

With careful selection of the edges in the toggle operation, a great deal of control is possible. Take care when selecting the free edge. The first edge you choose will be the retained shared edge and the edge nearest it and within the cleanup tolerance is eliminated.

Zoom in on the model if necessary.

� To increase the accuracy in selecting the lines, click and hold the left mouse button, then move it near the desired line until the line is highlighted. Release the mouse button at this point to select the highlighted line.

Also, it is often easier to select lines in performance graphics mode.



8. Recall view2 and toggle the free edge there.

Create filler surfaces

The remaining free edges in the model are the result of a gap larger than the maximum cleanup tolerance, 0.8. The geometry cleanup operations, if used, would distort the final mesh. A better solution is to create filler surfaces, then suppress the surface boundary between the original and new surface, effectively extending the original surface.

1. Recall view3 .

The gap between the free edges is 2.33 mm. Use the filler surface function on the surface edit panel to create a new surface to fill the gap, then suppress the bottom edge of the new surface.

2. Click return to exit the geom cleanup panel.

3. Go to the surface edit panel and select the filler surface tool.

Upon exiting the geom cleanup panel, the geometry is no longer displayed in topology mode. The vis opts controls on the Disp page of the Macro Menu allow you to control the display mode of the model. Four different visual modes are available to view surface geometry. The modes are:

0 The default mode. In most panels, surfaces are displayed in wireframe mode with the surface edges displayed in the component color. When in the geom cleanup, automesh or defeature panel, surface edges are displayed according to their topology status

1 Component color mode. Surface edges are always displayed in the component color.

2 Wireframe topology mode.

3 Shaded topology mode.

� Activating the shaded or wireframe topology modes from the Macro Menu overrides the violet vis opts panel within the geom cleanup , automesh or defeature panels.

4. From the Macro Menu select the disp page and click the vis opts: 2 button.



5. Select the four red lines bounding the gap.

Selecting the free edges around a gap

6. Click create to generate a new surface filling the gap.

7. Restore view 4 and create a filler surface there.

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

9. Go back to the geom cleanup panel.



10. Restore view 3 and toggle the lower surface edge of the new filler surface from shared to suppressed.

Supressing a lower edge

Fixing free edges caused by mis-matched points (vertices)

The remaining free edge in the model is due to a mismatched surface vertex. Use the replace fixed point function to combine the fixed points, and then toggle the free edge to shared.

1. Restore view 5 .

2. Select the fixed points function and then the replace tool.



3. With the retained point: selector active, select the fixed point on the right side of the gap.

Selecting the point to retain and the point to move

4. Select the point on the left side of the gap as the point to move.

5. Click replace .

6. Return to the edges / toggle sub-panel and combine the free edges.

Eliminate duplicate surfaces

The only remaining problem with the geometry is a duplicated surface, identified by the yellow surface edges. Because there are no internal ribs in this part, the yellow edges indicate a duplicate surface. Use the surfaces function, find duplicates tool, to identify and remove the duplicate surface.

1. Go to the surfaces panel and select the find duplicates tool.

2. Click the yellow faces entity selector and select all faces.



3. Click find to highlight the duplicated surface.

4. Click delete to remove the duplicate surface.

Since all the edges now show green, the geometry cleanup operations are complete, and the part is ready to be meshed.

5. Save your work as a HyperMesh file.

� The cleanup panel within the automesh panel contains a number of tools used to prepare geometry for meshing: splitting or unsplitting surfaces; toggle edges; edge fillet removal; and functions to add, remove, and replace fixed points.

Exercise 3.3: Surface Meshing

The automatic tetrahedral mesh in HyperMesh fills a volume encased in tria plate elements with four sided tetrahedral elements. The size and quality of the resulting tetramesh is directly dependent on the surface mesh generated. In this exercise, generate a surface mesh of tria elements on the cleaned up geometry of the universal joint.

1. From the global panel, set the current component collector to trias .

2. From the options menu, select graphics and switch the graphics mode from standard to performance.

In performance graphics mode, the elements generated during the automesh process can be displayed in shaded mode. Because this is a solid part, shaded mode makes it easier to see the mesh and make adjustments if necessary.

3. Use the vis panel and set all of the component collectors to shaded with mesh lines, .

4. From the 2D page, select the automesh panel.

5. From the create mesh sub-panel, click the yellow surfs entity selector and select all surfaces from the pop up extended selection menu.



6. Check the box next to reset meshing parameters to: .

7. Switch the element type from mixed to trias .

When the tria element type is selected prior to initially meshing the surfaces, the automesher uses an advancing front meshing algorithm that tends to generate a very good quality, nearly equilateral tria plate element.

8. Click mesh to go to the secondary automesh menu.

At this point, the automesher calculates surface edge lengths and seeds nodes along the edges to meet the required element size criteria.

9. Click mesh to generate the initial mesh of tria plate elements.

10. Click return to accept the mesh.

Just over 17,000 four mm surface elements were generated. With that many surface elements, the tetra mesher would generate nearly 85,000 tetrahedral elements. Once these were converted to second order elements, the resulting model would have nearly 250,000 degrees of freedom, and would require considerable computational resources to solve.

By selectively re-meshing some of the surfaces and transitioning to a larger element size, the resulting number of tetra elements can be lowered, reducing the total degrees of freedom for this model by half.

11. From the view menu select the rear view.

12. Click the surfs selector and select surfaces by window .



13. Draw a selection window as shown in the image.

Selection window

14. Uncheck the reset meshing parameters to: option.

15. Click remesh .

This deletes the previous mesh on the selected surface and returns to the secondary automesh panel.

16. From the density sub-panel, click the element size = field and enter 8.0 .

17. Click the yellow recalc edge selector to make it active.



18. Click each of the mesh density numbers for all of surface edges except those adjoining the surfaces that are not being re-meshed.

Unmodified density on edges shared with original elements

For edges shared with surfaces that will not be remeshed, recalculating the mesh densities will cause mis-matched nodes and breaks the connectivity of the mesh. When completed the mesh should be similar to the image.

19. Click mesh at any time to generate the preview elements.



20. Once you are satisfied, click return to accept the mesh.

Completed mesh

21. Save your work as a HyperMesh file.



Exercise 3.4: Checking the Element Quality and Tetrameshing

The tetramesher uses the surface mesh to define the size of the resulting tetrahedral mesh. Misshapen or irregular tria elements, large size differences in neighboring elements, or discontinuities in the mesh can result in poor tetramesh quality or failure in mesh generation.

To check for slender tria elements, use the minimum interior angle check. For broken connectivity, use the equivalencing function to re-establish connectivity. (When the selected surfaces were remeshed in the last exercise, the connectivity with the remainder of the elements was broken. As long as the mesh density on those shared edges was not changed, the node equivalencing function will easily correct the discontinuity.)

This exercise covers checking the minimum interior angle of the elements to identify any possible problems and the node equivalencing function to correct any discontinuities. When these issues are resolved, generate a tetrahedral mesh using the automatic tetramesher.

Completing an element check

1. From the tools page, select check elems panel.

2. From the 2-D sub-panel, under trias , click min angle .

This calculates the minimum interior angle of the surface elements. The message on the header bar reports that 0 elements failed the test, and the minimum interior angle is 25º.

3. Click return to go back to the Tool page.

4. Go to the edges panel.

Reestablishing continuity

The equivalence function on the edges panel identifies and corrects any discontinuities within the plate element mesh. The equivalence function checks for two or more coincident nodes within the specified search tolerance.



1. With the comps entity selector active, pick any element in the model.

This selects the entire trias component and checks all of the elements in that component.

2. Click preview equivalence .

Temporary nodes are indicated at the edges shared between the re-meshed surfaces and the original elements.

3. Click equivalence .

The coincident nodes are eliminated, and the elements using them are re-defined to use the original nodes.

4. Click find edges .

This checks for any remaining nodes that are only associated to a single element. In this case there are none, and the message on the header bar reports that “the selected elements may enclose a volume”

5. Click return to go back to the main page menu.

At this point, the automatic tetramesher can be used to generate tetrahedral elements.

Generating the tetramesh

1. Using the global panel set the current component collector to tets .

2. From the 3D page go to the tetramesh panel.

3. With the comps selector under floatable trias active, pick any element in the model.

4. Click tetmesh to generate the tetrahedral elements.

5. Save your work.



Exercise 3.5: Cleaning up and verifying the model

The next steps in the modeling process are to clean up and verify the model. This includes deleting the surface elements and geometry, changing the tetra elements from first to second order, and a couple of quality checks for tetra elements.

Changing the element order

1. From the 1D, 2D or 3D page go to the order change panel.

2. Select the change to 2 nd sub-panel.

3. Click the yellow elements selector and select all from the pop up menu.

4. Leave the goggle option set to midside nodes at exact midpoint .

The toggle option, midside nodes projected to surface , may better represent the model geometry, but using it most likely will introduce warpage to the tria elements.

5. Click change order , then return .

Cleaning up the model

At this point, the geometry and shell elements are no longer needed. Deleting the geometry reduces the size of the HyperMesh binary file, frees up RAM, and improves performance. The shell elements, if left in the model, add excessive stiffness to the outer shell of the model, leading to inaccurate analysis results.

1. From the Tool page go to the delete panel.

2. Switch the entity type selector to comps .

3. Click the yellow comps selector to bring up a list of the components in the model.



4. Check the boxes for the new_geom and trias components, then click select.

5. Click delete entity , then return .

Renumbering the elements and nodes

Whenever elements and nodes are added, deleted, or edited, gaps in the ranges of node ids occur. Renumbering the ids consolidates the numbering scheme for nodes and elements used in the model.

1. From the Tool page go to the renumber panel.

2. Select the all sub-panel.

3. Click renumber then return .

Three additional element quality checks that apply to tetrahedral elements are available on the check elems / 3-d panel. These are the tetra collapse , volumetric skew , and tetra altitude ratio checks. For details on the calculations behind the checks, see the online help.

The remaining steps in the modeling process are:

• Load an feoutput template

• Define material and component properties

• Apply boundary conditions

• Export the model.

Summary

In this chapter, we made a model of a universal joint using tetrahedral elements. To accurately capture the details of the model when meshed, we set an appropriate element size. We used geometry cleanup tools to correct the problems associated with imported geometry. Filler surfaces closed gaps larger than the maximum cleanup tolerance. The model then was meshed with tria elements on its surface to prepare the model for tetrameshing. The last step was generating a tetramesh and doing a final element check.

Documents

HyperMesh Basic Training - oss.jishulink.comoss.jishulink.com/caenet/forums/upload/2008/04/05/200883098418000.… · HyperMesh is a high performance finite element pre- and post-processor