mech-intro 14.0 l03 genprep

2011 ANSYS, Inc. August 20, 20121 Release 14.0

14. 0 Release

Introduction to ANSYS

Mechanical Part 1

Lecture 3

General Preprocessing


Chapter Overview

In this chapter we cover basic preprocessing operations that are common to all

disciplines.

Topics:

A. Geometry

B. Contact

C. Remote Boundary Conditions

D. Workshop 3-1, 2D Gear and Rack Analysis

E. Coordinate Systems

F. Named Selections

G. Selection Information

H. Workshop 3-2, Contact Control


A. Geometry BranchThe 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

Each is explained next . . .


Types of BodiesSolid 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.

2D solids are meshed by default with higher order triangle or quadrilateral solid

elements with quadratic shape functions.

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

Each node has three translational degrees of freedom (DOF) for structural or one

temperature DOF for thermal.

3D Solids 2D SolidsAxisymmetric cross section


Types of BodiesSurface 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 linear 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 linear beam elements having six DOF (UX, UY, UZ,

ROTX, ROTY, ROTZ).

Line BodySurface Body


Multibody Parts

In general, bodies and parts are the same. In DesignModeler 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:

Common nodes are shared by adjacent bodies


Material PropertiesTo 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).

For surface bodies a thickness needs to be

supplied as well.


Geometry Worksheet

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


B. ContactWhen 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.

BALoad


Contact

When an assembly is imported contact surfaces are automatically detected and created:

The proximity of surfaces is used to detect contact.

Contact surfaces in 2D geometry are represented by edges.

Note, automatic contact should always be

verified before proceeding with an analysis.


ContactWhen a contact region is highlighted in the connections branch, parts are made

translucent for easier viewing.

Contact surfaces are color coded for easy identification.


ContactFor ease of viewing or selecting, Body Views can be activated:

Separate windows display the full model, contact body and target body.

Views can be synched (all windows move together).

Selecting (for contact scoping) can be done in any window.


ContactGo To utilities provide a simple way of verifying contact definitions:

Bodies without contact

Parts without contact

Contact regions for selected bodies

Contacts common to selected bodies

Corresponding bodies in tree

Contacts can be quickly renamed to match part names

RMB


ContactWhere surfaces are not automatically detected a manual contact pair can be defined.

Insert a manual contact region and select the contact and target surfaces.

RMB


Surface Body Contact

Shell contact includes edge-to-face or edge-to-edge

contact:

Automatic shell contact is not turned on by default but

can be set to detect face-to-edge or edge-to-edge

contact.

Priority can be set to prevent multiple contact regions in

a given region.

Edge to Surface Edge to Edge


Spot WeldsSpot welds provide a means of connecting assemblies at discrete points:

Spot welds are defined in the geometry. Currently, only DesignModeler and

Unigraphics can define spot welds supported by Mechanical.

Vertex pairs created in other CAD systems can be connected manually.

Spot weld pairs


Contact WorksheetThe Worksheet for the Connections branch provides a summary of various

contact and spot weld definitions:


C. Remote Boundary ConditionsAs the name implies, remote boundary conditions represent boundary

conditions whose center of action (or line of action) is not necessarily located

where the load is scoped. Instead, this may be in a remote location:

Remote Boundary Conditions consist of: remote forces, remote displacements, point

masses, bolts, springs, joints and moments.

Remote BCs use constraint equations when connecting to geometry.

Example of a remote force:

F

Constraint equations

connect force to scoped

surface.


. . . Remote Boundary Conditions

Two common features of remote boundary

conditions are the location and the optional

geometry behavior that can be defined in the

details.

Coordinates in the scope determine the origin of

action for remote BCs. Can be local or global

coordinates.

Can use geometry selection instead of coordinates.

Deformable or Rigid

This behavior determines whether the region of the

model where the load is scoped can deform or will

remain rigid (examples to follow).


. . . Remote Boundary ConditionsSeveral examples are included to illustrate the rigid/deformable option:

Example of a remote force scoped to the face shown in red:

See the Introduction to ANSYS Mechanical Part 2 training course for more coverage

on remote boundary conditions.

Deformable

Rigid


D. Workshop 3.1 2D Gear and Rack Analysis

Workshop 3.1 2D Gear and Rack Analysis Goal:

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


E. Coordinate SystemsThe 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.


Coordinate SystemsCoordinate 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


F. Named SelectionsNamed Selections are a means of grouping geometric or finite element entities

and naming the group for future reference:

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 by accessing the named selection worksheet.

Named selections can only be composed of like entities (all surfaces or all

edges, etc.)

In this course we introduce the basic concepts and techniques for creating

and using Named Selections. Coverage of advanced techniques can be

found in the Introduction to ANSYS Mechanical Part 2 course.

RMB


Defining Named Selections

By Worksheet: 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.


Defining Named Selections

Example, select a vertex at x,y,z = 97.7, 33, 0:

Using three operations (add, filter, remove), allows a

single vertex selection.

Results in 4 vertices selected

Results in 2 vertices filtered from the above set

Results in 1 vertex removed from the above set


Using Named Selections

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

Example (pressure load):

In the Details view, change Method from Geometry Selection to Named

Selection

Select the Named Selection from the pull-down menu

Mechanical will filter non-applicable types of Named Selections.


Using Named Selections

Named Selections can be used in other situations where geometry must be

picked:

Select Geometry from the Details view to enter picking mode (apply/cancel).

Choose the desired Named Selection from the drop down list.

Select Items in Group.

Then, click on Apply in the Details view.

12

3


G. 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


. . . 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.


Workshop 3.2 Contact Control Goal:

Investigate several types of contact behavior.

H. Workshop 3.2 Contact Control

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