WB-Mech_120_Ch03_Analysis

3-1ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

May 5, 2009Inventory #002593

Workbench - Mechanical Introduction 12.0

Chapter 3

General Preprocessing




Training ManualChapter Overview• In this chapter, using features without the use of the Wizards will be

covered• Topics:

A. GeometryB. ContactC. Workshop 3-1, “Contact Control”D. MeshingE. Named SelectionsF. Coordinate SystemsG. Workshop 3-2, “Meshing Control”

• The capabilities described in this section are generally applicable to the ANSYS DesignSpace Entra licenses and above and are noted in the lower-left hand tables




Training ManualIntroduction• In the previous chapter, the Mechanical GUI was introduced through the use

of the Mechanical Wizards• In this chapter, navigating through the GUI without the Wizards will be

covered




Training Manual… Introduction• The Outline Tree is the main way of setting up an analysis– The Context Toolbar, Details View, and Graphics Window update,

depending on which Outline Tree branch is selected– Use of the Outline Tree will be emphasized in this chapter

Use of the Outline Tree is the means by which users navigate through the Simulation GUI.




Training ManualA. Geometry Branch• The Geometry branch lists the part(s)

that make up the model. • In Simulation, there are three types of

bodies which can be analyzed:– Solid bodies are general 3D or 2D

volumes/areas/parts– Surface bodies are only areas– Line bodies are only curves– Each is explained next . . .




Training Manual… Types of Bodies• Solid bodies are geometrically and spatially 3D or 2D:

– 3D solids are meshed with higher-order tetrahedral or hexahedral solid elements with quadratic shape functions.

– 2D solids are meshed with higher order triangle or quadrilateral solid elements with quadratic shape functions

• The “2D” switch must be set on the Project page prior to import• Geometry type cannot be changed from 2D to 3D (or vice versa) after import

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

3D Solids 2D SolidsAxisymmetric cross section




Training Manual… Types of Bodies• Surface bodies are geometrically 2D but spatially 3D:

– Surface bodies represent structures which are thin in one dimension (through-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.– Line bodies are modeled with linear beam elements having six DOF (UX, UY, UZ,

ROTX, ROTY, ROTZ).

Line BodySurface Body




Training Manual… 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




Training Manual… Material Properties• To assign material properties to a body

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 previous chapter).

• For surface bodies a thickness needs to be supplied as well.




Training Manual… Geometry Worksheet

• A summary of bodies and assigned materials is available– Select “Geometry” branch and then the “Worksheet” tab




Training ManualB. Contact• When multiple parts are present, a means of defining the relationship

between parts is needed.– Contact regions define how parts interact with each other.

• Without contact or spot welds, parts will not interact with each other:– In structural analyses, contact and spot welds prevent parts from penetrating

through each other and provide a means of load transfer between parts.– In thermal analyses, contact and spot welds allow for heat transfer across parts.– Multibody parts do not require contact or spot welds.

BA

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

Load




Training Manual… Solid Body Contact• When an assembly is imported contact

surfaces are automatically detected and created:– The proximity of surfaces is used to

detect contact. Tolerance for contact detection is available in the “Connections” branch details.

• Contact is also used for 2D geometry. Contact “surfaces” are represented by edges.

• Certain license levels allow surface to edge, edge to edge and mixed solid/surface contact.

• Note, automatic contact should always be checked and verified before proceeding with an analysis.




Training Manual… Solid Body Contact– Contact elements provide the relationship between parts.– Each part maintains a separate mesh. This means that one small part will not

drive mesh density of the entire assembly and/or the user can make parts of interest have a finer mesh than other parts

Note the non-matching mesh at the interface between parts.Mix of hexahedral elements contacting tetrahedral elements is possible.




Training Manual… Solid Body Contact• When a contact region is highlighted in the connections branch, parts are made

translucent for easier viewing.– Selecting a contact region makes non participating bodies translucent.– Contact surfaces are color coded for easy identification.




Training Manual… Solid Body Contact• “Go To” utilities allow a more detailed investigation of contact definitions:

– Corresponding bodies in tree– Bodies without contact– Contact regions for selected bodies– Contacts common to selected bodies

– Contacts can be quickly renamed to match part names

RMB




Training Manual… Solid Body Contact• To manually define a contact pair insert a manual contact region and select

and apply “contact” and “target” surfaces.

RMB




Training Manual… Advanced Solid Body Contact• For ANSYS Professional licenses and above, advanced contact options are

available:– Auto detection dimension and slider– Asymmetric contact– Contact results tool– More contact formulations available– Pinball control




Training Manual… Advanced Solid Body Contact• The Pinball region represents a contact detection zone:

– Contact calculation/detection occurs when contact gap is within the pinball radius.

– The pinball radius dimension may be entered to ensure that bonded contact is established for a large clearance or gap.

– Pinball radius is displayed as a sphere in the graphics window.– Status: near field, far field, closed/sliding, closed/sticking.




Training Manual… Surface Body Contact

• Shell contact includes edge-to-face or edge-to-edge contact:– Shell contact is not turned on by default.– User can turn on detection of face-to-edge

or edge-to-edge contact.– Priority can be set to prevent multiple contact

regions from being formed in a given regionby setting priority.




Training Manual… Spot Weld• Spot welds provide a means of connecting assemblies at discrete points:

– Spot weld is defined in the CAD software. Currently, only DesignModeler and Unigraphics define spot welds supported by Mechanical.

Spot weld pairs




Training Manual… Contact Worksheet• The “Worksheet” tab of the “Connections” branch provides a summary of

various contact and spot weld definitions:




Training Manual

• Workshop 3.1 – Contact Control• Goal:– Investigate several types of contact behavior.

C. Workshop 3.1 – Contact Control




Training ManualD. Meshing• The nodes and elements representing the geometry model make up the

mesh:– A “default” mesh is automatically generated during initiation of the solution.– The user can “generate” the mesh prior to solving to verify mesh control

settings.– A finer mesh produces more precise answers but also increases CPU time and

memory requirements.




Training Manual… Global Meshing Controls• Physics Based Meshing allows the user to specify the

mesh based on the physics to be solved. Choosing the physics type will set controls such as:– Solid element mid-side nodes– Element shape checking– Transitioning

• Physics preferences can be:– Mechanical– Electromagnetics– CFD– Explicit

• Setting the physics preference pre-configures the Advanced meshing defaults discussed on subsequent pages.

• Note: only Mechanical meshing preferences are discussed in this course.




Training Manual… Global Meshing Controls• Basic meshing controls are available under the “Defaults” group in the

“Mesh” branch– The user has control with a single slider bar

• “Relevance” setting between –100 and +100

- Relevance = coarse mesh

+ Relevance = fine mesh




Training Manual… Global Meshing Controls

• Advanced global controls: – Relevance Center: sets the mid point of the

“Relevance” slider control.– Element Size: defines element size used for

the entire model.– Shape Checking:

• Standard Mechanical – linear stress, modal and thermal analyses.

• Aggressive Mechanical – large deformations and material nonlinearities.

• Solid Element Midside Nodes:– Program Controlled (default), Dropped or

Kept.

Element A Element B

Kept Dropped




Training Manual… Global Meshing Controls• Straight Sided Elements : – Displayed when solids are present in the

model or enclosures from DesignModeler are present. Must be used for Electromagnetic simulations.

• Initial Size seed: – Controls the initial seeding of the mesh size

for each part. (Explained in more detail on next slide)

• Smoothing : – Attempts to improve element quality by

moving nodes. Number of smoothing iterations can be controlled (Low, Medium, High).

• Transition : – Controls the rate at which adjacent elements

will grow (Smooth, Fast)




Training Manual… Global Meshing Controls• Initial Size Seed:

– Active Assembly (default) : • Initial mesh sizing will be determined by the active set (unsuppressed) of parts.

– Full Assembly: • Initial mesh will not be affected by the suppressed/unsuppressed state of parts.

– Part: • Initial seeding based on each part’s size independently. Mesh will not change due to part

suppression. Generally gives finer mesh. Mesh may not be uniform through out the assembly.

Part-Based Mesh SeedingNodes: 44,013(Mesh seeding is based on parts, so less uniform between parts)

Assembly-Based Mesh SeedingNodes: 15,670(Mesh seeding is more uniform between parts)




Training Manual… Local Meshing Controls• Local Mesh Controls can be applied to either a Geometry Selection or a

Named Selection. These are available only when the mesh branch is highlighted. Available controls include : – Method Control– Sizing Control– Contact Sizing Control– Refinement Control– Mapped Face Meshing (EMAG and cyclic, not covered)– Inflation Control– Pinch Control– Gap Tool (EMAG only, not covered)




Training Manual… Local Meshing Controls : Method (continued)

• Method Control : Provides the user with options as to how solid bodies are meshed: (Valid only for bodies).

• Automatic (default): – Body will be swept if possible. Otherwise, the

“Patch Conforming” mesher under “Tetrahedrons” is used.

• Continued . . .




Training Manual

• Tetrahedrons: – An all Tetrahedron mesh is generated.

• Patch Conforming: – Expansion Factor controls the internal growth

rate of the tetrahedrons.

• Patch Independent Meshing:– Faces and their boundaries may or may not be

respected during meshing operations.– The exception is when a boundary condition is

applied to a surface, its boundaries are respected.

– See next page for Patch Independent options.

… Local Meshing Controls : Method (continued)




Training Manual

• Patch Independent Options: – Maximum Element Size: size of the initial element subdivision– Approx Number of Elements: desired number of elements in model (can

be overridden by other mesh controls).– Define defeaturing Tolerance – Filters out edges based on size and angle.

If set to “Yes”, a Defeaturing Tolerance field appears where a numerical value is to be entered.

• Note: defeaturing can cause a mesh to “ignore”, and therefore mesh over, small features. The Simulation documentation contains a full description and examples.

• Continued . . .





Training Manual

• Curvature and Proximity Refinement = Yes:– Define by: maximum element size or approximate number of elements. – Defeaturing Tolerance (yes): adds tolerance controls to defeature edges.– Curvature and Proximity: automatically refines mesh based on curvature and proximity of

features.– Num Cells across Gap – Specifies the number of cells desired in narrow gaps. Refinement is

limited by the Min Size Limit. – Span Angle – Mesh will subdivide in curved regions till the individual elements span the

specified angle. Limited by Min Size Limit.





Training Manual

• Hex Dominant : Creates a free hex dominant mesh. Useful for meshing bodies that cannot be swept. Recommended for meshing bodies with large interior volumes. (only available with ANSYS Structural licenses and above)

• The hex-dominant meshing algorithm creates a quad-dominant surface mesh first, then pyramid and tetrahedral elements are filled in as needed.

• “Control Messages” will appear to warn user if volume may not be suitable for hex-dominant meshing

Solid Model with Hex dominant mesh :

Tetrahedrons – 443 (9%)

Hexahedron – 2801(62%)

Wedge – 124 (2%)

Pyramid – 1107 (24%)





Training Manual

• Sweep : – Sweep-mesh (hex and possible wedge) elements, otherwise tetrahedra.– RMB on mesh branch to “Show Sweepable Bodies”.– Type : Number of Divisions or Element Size in the sweep direction.– Sweep Bias Type : Bias spacing in sweep direction.– Src/Trg Selection :

• Automatic, manual source or manual source and target.• Automatic Thin Model – One hex or wedge through the thickness. Can choose

between Solid Shell (SOLSH190) element and a Solid element (Solid185)• Manual Thin Model – Allows user to pick a source face.

The solid body in the middle is swept-meshed whereas other volumes are meshed with tetrahedral elements.





Training Manual… Local Meshing Controls• Sizing:

– “Element Size” specifies average element edge length or number of divisions (choices depend on geometry selection).

– “Soft” control may be overridden by other mesh controls. “Hard” may not.

– Mesh biasing is available.– Available options above depend on which

entities are scoped:

• Sphere of Influence sizing, see next page.

Entity Element Size # of Elem. Division Sphere of InfluenceBodies x xFaces x xEdges x x xVertices x

Face Sizing Applied to a part.




Training Manual… Local Mesh Controls

• Sphere of Influence:– Center is located using local coordinate system.– All scoped entities within the sphere are affected by size settings.

“Sphere of Influence” (shown in red) has been defined. Elements lying in that sphere for that scoped entity will have a given average element size.

Scoped to 2 surfacesScoped to single vertex




Training Manual… Local Mesh Controls• Contact Sizing: generates similar-sized elements on

contact faces for face/face or face/edge contact region.– “Element Size” or “Relevance” can be specified.– Choose “Contact Sizing” from the “Mesh Control” menu and

specify the contact region.– Or drag and drop a Contact Region object onto the “Mesh”

object.

In this example, the contact region between the two parts has a Contact Sizing Type Relevance is specified. Note that the mesh is now consistent at the contact region.




Training Manual… Local Mesh Controls

• Element refinement divides existing mesh– An ‘initial’ mesh is created with global and local size controls first, then element

refinement is performed at the specified location(s).– Refinement range is 1 to 3 (minimum to maximum). Refinement splits the edges of

the elements in the ‘initial’ mesh in half. Refinement level controls the number of iterations this is performed.

For example shown, the left side has refinement level of 2 whereas the right side is left untouched with default mesh settings.




Training Manual… Local Mesh Controls• Mapped Face Meshing: generates structured meshes on

surfaces:– In example below, mapped face meshing on the

outer face provides a more uniform mesh pattern.

– If surface cannot be mapped mesh for any reason, meshing will continue and this will be shown in Outline Tree with icon:

• Mapped quad or tri mesh also available for surface bodies




Training Manual… Local Mesh Controls• Inflation Control: useful for adding layers of elements along specific

boundarys.

Note: Inflation is more often used in CFD and EMAG applications but may be useful for capturing stress concentrations etc. in structural applications.




Training Manual… Local Mesh Controls• Pinch: allows the removal of small features by “pinching”

out small edges and vertices (only).– Master: geometry that retains the original geometry profile.– Slave: geometry that changes to move toward the master.– Can be automatic (Mesh level) or local (add Pinch branch).




Training Manual… Meshing Failures• If the mesher is not able to generate well-shaped elements, an error message

will be returned:

– The problematic geometry will be highlighted on the screen, and a named selection group “Problematic Geometry” will be created, so the user may review the model.




Training Manual… Meshing Failures• Meshing failures can be caused by a number of things:– Inconsistent sizing controls specified on surfaces, which would result in

the creation of poorly-shaped elements– Difficult CAD geometry, such as small slivers or twisted surfaces– Stricter shape checking (“Aggressive” setting in Mesh branch)

• Some ways to avoid meshing failures:– Specify more reasonable sizing controls on geometry– Specify smaller sizing controls to allow the mesher to create better-

shaped elements– In the CAD system, use hidden line removal plots to see sliver or

unwanted geometry and remove them– Use virtual cells to combine sliver or very small surfaces

– This option will be discussed next




Training Manual… Virtual Topology• Virtual Topology: combines surfaces and edges for

meshing control:

– “Virtual Topology” branch is added to the “Model” branch.

– A “Virtual Cell” is a group of adjacent surfaces that “acts” as a single surface.

– Interior lines of original surfaces will no longer be honored by meshing process.

– For other operations such as applying Loads and Supports, a virtual cell can be referenced as a single entity.

– Virtual cells can be generated automatically via RMB:• The “Behavior” controls the aggressiveness of the “Merge

Face Edges?” setting for auto generation.• Example . . .




Training Manual… Virtual Topology Example

• Consider the example below:

Virtual Cell




Training Manual… Virtual Topology Example• Keep in mind that the topology can change!– Example: a chamfer is added to the top surface in this virtual cell. The

interior lines are not recognized anymore.Element’s edge is shown as a solid line and the original chamfer and top surface is shown as a dotted blue line.

The chamfer representation is no longer present.

Mesh using virtual topology

Original mesh




Training ManualE. Named Selections• The Named Selection Toolbar provides functionality for grouping together

geometric entities:

– Named Selections allow users to group together vertices, edges, surfaces, or bodies.

– Named Selections can be used for defining mesh controls, applying loads and supports, etc.

– Provides an easy method to reselect groups that will be referenced often• Defining contact regions• Scoping results• Etc.

– Note, visibility and suppression are only applicable to body named selections.

Create Defined Names

Manipulate Show/Hide Supress/Unsuppress




Training Manual… Defining Named Selections• To create Named Selections:

– Select the vertices, edges, surfaces, or bodies of interest, then click on the “Create Selection Group” icon

– Enter a name in the dialog box– The new group will appear in the Named Selection Toolbar

as well as in the Outline Tree

• Note:– Only one type of entity can be in a particular

Named Selection. For example, vertices and edges cannot exist in the same Named Selection.

– Named Selection groups can be imported fromsome CAD systems (see Chapter 10)




Training Manual… 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• Simulation will filter non-applicable types of Named Selections.




Training Manual… 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– Toggle the Named Selection to select from the Toolbar– Select the applicable choice:

• “Select Items in Group”, “Add to Current Selection”, “Remove from Current Selection” – Then, click on “Apply” in the Details view

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Training ManualF. Coordinate Systems• The Coordinate Systems branch is usually not displayed by default, but

it can be added from the Model tree

– Coordinate systems can be used for mesh controls, point masses, directional loads, and results

• Initially the “Global Coordinate System” is added, based on the origin of the CAD model.

• Local Coordinate Systems can be imported from some CAD systems (see Simulation documentation)




Training Manual… Coordinate Systems• Coordinate Systems can be defined by selecting

“Coordinate System” icon from the Context toolbar.• Can be Cartesian or Cylindrical.• Toolbar becomes available after CS is defined.

• Local coordinate systems are defined either by: – Selecting geometry (Associative Coordinate System). The

coordinate system moves with the geometry. Its translation and rotation are geometry dependent.

– Specifying coordinates (Non-Associative Coordinate System). The coordinate system will remain as originally defined ie: it is independent of geometry.

Translate Rotate Flip Move Up/Down

Delete




Training Manual… Coordinate Systems• Coordinate systems can be used from pull-down menus in the Details

view in various applications (examples below) :

Sizing w/ Sphere of Influence Option

Directional ResultsPoint Masses

Directional Loads

Directional Displacements




Training Manual

• Workshop 3.2 – Mesh Control• Goal:– Use the various mesh controls to enhance

the mesh for the solenoid model.

G. Workshop 3.2 – Mesh Control

WB-Mech_120_Ch03_Analysis

Documents

general preprocessing

adjacent bodies ansys

training manual surface

contact training manual

multiple bodies

summary of bodies

areas line bodies

d solidsansys