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Module 02: Preprocessing

Introduction to ANSYS Mechanical

17.0 Release

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Module 02 Topics

Geometry
Contact
Coordinate Systems
Named Selections
Object Generator
Selection Information

Workshop 02.1: 2D Gear and Rack Analysis
Workshop 02.2: Named Selections
Workshop 02.3: Object Generator 1
Workshop 02.4: Object Generator 2
Appendix 02.1: Named Selections Worksheet

This module covers basic preprocessing topics that are common to all mechanical analysis disciplines:

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02.01 Geometry

The Geometry branch contains the part(s) that make up the model.

In Mechanical, there are three types of bodies which can be analyzed:

Solid bodies are 3D or 2D volumes or areas
Surface bodies are only areas
Line bodies are only curves/lines
Each is explained next . . .

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02.01 Geometry

Solid bodies are geometrically and spatially 3D or 2D:

3D solids are meshed by default with higher-order tetrahedral or hexahedral solid elements with quadratic shape functions.
Each node in a 3D element has three translational degrees of freedom (DOF) for structural or one temperature DOF for thermal.

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02.01 Geometry�

2D solids are meshed by default with higher order triangular or quadrilateral solid elements with quadratic shape functions.

The “2D” switch must be set on the Project page prior to importing geometry.

Each node in a 2D element has two translational degrees of freedom (UX and UY) for structural or one temperature DOF for thermal.
2D solids are used to represent three types of 3D geometry, “Axisymmetric”, “Plane stress” and “Plane strain”.

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02.01 Geometry

Surface bodies are geometrically 2D but spatially 3D:

Surface bodies represent structures which are thin in one dimension (through the thickness). Thickness is not modeled but supplied as an input value.
Surface bodies are meshed with shell elements having six DOF (UX, UY, UZ, ROTX, ROTY, ROTZ).

Line bodies are geometrically 1D but spatially 3D:

Line bodies represent structures which are thin in two dimensions. The cross-section is not modeled, it is mapped on to the line body.
Line bodies are modeled with beam elements having six DOF (UX, UY, UZ, ROTX, ROTY, ROTZ).

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02.01 Geometry

In general, bodies and parts are the same. In DesignModeler or SpaceClaim however, multiple bodies may be grouped into multibody parts.

Multibody parts share common boundaries so nodes are shared at that interface.

No contact is needed in these situations.

Example:

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02.01 Geometry

To assign material properties to a part, highlight it and select from the available properties in the “Assignment” field:

The only materials appearing in the list will be materials added using the “Engineering Data” application (see chapter 2).
The user can also access Engineering Data directly for creating, editing or importing new materials.

For surface bodies a thickness needs to be supplied as well (thickness can also be imported).

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02.01 Geometry

A summary of all parts along with assigned materials, mesh statistics, etc.

Select “Geometry” branch and toggle the “Worksheet” icon.
Toggle between graphics or worksheet via tabs at bottom

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02.02 Contact

When multiple parts are present, contact elements define the relationship between parts.

Are parts bonded together, sliding, transferring heat, etc.?

Without contact or spot welds, parts will not interact with each other.

Contact elements can be visualized as a “skin” covering the regions where contact will occur.

Contact is covered in more depth in Module 6: “Connections and Remote Boundary Conditions.”

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02.03 Coordinate Systems

The Coordinate Systems branch initially contains only the global Cartesian system:

User coordinate systems can be Cartesian or cylindrical and can be renamed.
User coordinate systems can be added and used for mesh controls, point masses, directional loads, results, etc.
An icon in the Graphics Option toolbar allows all coordinate systems to be viewed simultaneously.

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02.03 Coordinate Systems

Coordinate Systems are defined by selecting “Coordinate System” icon from the Context toolbar.

Associative coordinate systems can be defined by selecting geometry (surfaces, edges, etc.). Associative CS update their origin to match geometry updates.

Non-associative coordinate systems are defined by entering its location in global coordinates.

The location and orientation can then be further modified using the various transforms from the context toolbar.

Translate

Rotate

Flip

Move Up/Down

Delete

Transforms

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02.04 Named Selections

Named Selections are groups of geometric or finite element entities:

Named selections can be created either by selecting the desired items and clicking the “Named Selection” icon in the context toolbar or RMB > Named Selection OR using the named selection worksheet (shown later).

Named selections must be composed of “like” entities (all surfaces or all edges, all nodes, etc.).

RMB

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02.04 Named Selections

A new criteria selection can be based on an initial selection:

Make an initial selection followed by a RMB > “Create Named Selection”.
Note, initial selection must be a single entity.

RMB >

Selection here will create the first row of the worksheet.

Convert to nodal named selection immediately.

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02.04 Named Selections

In many detail window fields Named Selections can be referenced directly:

In the Details view, change “Scoping Method” from “Geometry Selection” to “Named Selection”
Select the “Named Selection” from the pull-down menu

A named selection toolbar provides quick access to basic controls “View > Toolbars > Named Selections”:

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02.04 Named Selections

If you’re interested, see�Appendix 02.1: Named Selections Worksheet�for additional background information

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02.05 Object Generator

The Object Generator uses an existing object in the tree as a template for replication.

Almost any tree object that supports “RMB > Duplicate” can be used as a template.

An example:

In the model shown, we have set up a�mesh size control on one of the hole�faces. We would like to have this�same control applied to all other holes.

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02.05 Object Generator

Highlight the tree object to be replicated (the Face Sizing in this case) and activate the Object Generator using the icon.

The object generator opens and indicates objects will be generated from the “Current Selection” (graphical selection) or from a previously defined named selection that we’ve called “Top Holes.”

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02.05 Object Generator

We choose to graphically highlight the remaining hole faces and add a Name Prefix (“FS_”) so the new objects can be easily identified in the tree.

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02.05 Object Generator

After generating, the new objects can be displayed graphically and they appear in the tree. The object names reflect that of the parent object along with the prefix chosen (if any).

In this example the object to be generated (the mesh size control) required only a single geometry selection, a face, to define its scope. Some objects that can be duplicated require multiple scoping selections (e.g. contacts, beam connections, etc.). We’ll look at this next.

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02.05 Object Generator

When an object in the tree that requires multiple scoping is selected, the object generator reflects this (a contact selection is shown here).

Fields for contact and target scoping are visible however there is no longer a “current selection” choice. Instead, named selections must now be chosen from the drop down fields.
A “Distance Between Centroids” range must now be set to indicate which parts of the named selections are to be paired to one another.
In addition to an optional prefix, new items can be tagged when generated.

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02.05 Object Generator

Here a bolted connection has been defined between the plates and named selections created for the holes in each plate. The range chosen is based on the distance between the plates (20 mm).

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02.05 Object Generator

Scoping the new objects:

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02.06 Selection Information

When a selection is made in the graphics window (node, vertex, face, etc.), the status bar lists basic information (e.g. line length, surface area, etc.). Additional information can be obtained by using the selection information window.

Activate (3 ways) by:

Icon
View > Windows > Selection Information
Double click the status bar selection.

Double Click

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02.06 Selection Information

The selection information window provides a summary of all selections and/or a list of individual selections (or both as shown).

Select: vertex, edge, face, body, node or xyz coordinate location.

Coordinate selection returns information on the nearest node to the coordinates.

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02.07 Workshop 02.1: 2D Gear and Rack Analysis

Goal:

Determine the torque required in the gear to produce the desired output.

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02.08 Workshop 02.2: Named Selections

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02.09 Workshop 02.3: Object Generator 1

Goal:

Become familiar with the operation of the object generator in the Mechanical application.

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02.10 Workshop 02.4: Object Generator 2

Goal:

Become familiar with the operation of the object generator in the Mechanical application.

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02.11 Appendix 02.1

Named Selections Worksheet

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02.11 Appendix 02.1: Named Selections Worksheet

Worksheet Criteria:

Insert a new named selection then change the scoping method to “Worksheet”.

Selections are created using various criteria.
Add, remove, filter, etc. to “stack” criteria for complex selections.
Generate selections after the criteria choices are complete.

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02.11 Appendix 02.1: Named Selections Worksheet

Worksheet Criteria is entered in rows and columns in the worksheet.

When a new worksheet opens the first step is to RMB to “Add Row”.
Subsequent rows can be added to the list or inserted mid list (order matters!).

As rows are added to the worksheet columns �are configured using drop down menus available �by clicking the desired cell.

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02.11 Appendix 02.1: Named Selections Worksheet

After entering the criteria (various actions, entity types, etc.) the named selection is created by clicking the “Generate” button.

Rows can be made temporarily inactive using the check box column on the left.
Following named selection generation, the details show the result.
To view the named selection toggle to the “Graphics” tab at the bottom of the worksheet.

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02.11 Appendix 02.1: Named Selections Worksheet�

It is often convenient to convert a geometric named selection into a nodal named selection in order to obtain the underlying nodes

Create a geometry named selection (face for example).
Create a second named selection using the “Worksheet”.
Convert the geometry selection to nodes.

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02.11 Appendix 02.1: Named Selections Worksheet

Worksheet Summary:

As can be seen, numerous controls are available in the worksheet. See the documentation for a complete discussion of each.
As discussed elsewhere in this course the “Convert To” action is used to change a geometry named selection (face, edge, etc.) to a nodal named selection.

When creating named selections using worksheet criteria �a set of tolerances is available if needed:

Tolerance adjustment is usually only necessary in special �circumstances like models in micro units or node selections �in dense meshes.

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