Ansys Meshing

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Transcript of Ansys Meshing

Module 10

Meshing

Meshing

Overview Recall that meshing is a three-step procedure: Define element attributes

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Specify mesh controls Generate the mesh

In this chapter, we will expand on each of these steps and also discuss additional meshing options.

Topics covered:A. Multiple Element Attributes B. Controlling Mesh Density C. Changing a Mesh D. Mapped Meshing E. Hex-to-Tet Meshing F. Mesh Extrusion G. Sweep Meshing H. Workshop

January 30, 2001 Inventory #001441 10-2

Meshing

A. Multiple Element Attributes

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

As we discussed earlier, every element has the following attributes associated with it: Element type (TYPE) Real constants (REAL) Material properties (MAT)

Most FEA models have multiple attributes. For example, the silo shown here has two element types, three real constant sets, and two materials.TYPE 1 = shell TYPE 2 = beam

MAT 1 = concrete MAT 2 = steel

REAL 1 = 3/8 thickness REAL 2 = beam properties REAL 3 = 1/8 thickness

January 30, 2001 Inventory #001441 10-3

Meshing

...Multiple Element Attributes

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Whenever you have multiple TYPEs, REALs and MATs, you need to make sure that each element is assigned the proper attributes. There are three ways to do this: Assign attributes to the solid model entities before meshing Activate a global setting of MAT, TYPE, and REAL before meshing Modify element attributes after meshing

If no assignments are made, ANSYS uses default settings of MAT=1, TYPE=1, and REAL=1 for all elements in the model. Note, the current active TYPE, REAL, and MAT dictates mesh operation.

January 30, 2001 Inventory #001441 10-4

Meshing

...Multiple Element AttributesAssigning Attributes to the Solid Model 1. Define all necessary element types, materials, and real constant sets. 2. Then use the Element Attributes section of the MeshTool (Preprocessor > MeshTool): Choose entity type and press the SET button. Pick the entities to which you want to assign attributes. Set the appropriate attributes in the subsequent dialog box.

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Or select the desired entities and use the VATT, AATT, LATT, or KATT command. 3. When you mesh an entity, its attributes are automatically transferred to the elements.

January 30, 2001 Inventory #001441 10-5

Meshing

...Multiple Element AttributesUsing Global Attribute Settings 1. Define all necessary element types, materials, and real constant sets. 2. Then use the Element Attributes section of the MeshTool (Preprocessor > MeshTool): Choose Global and press the SET button.

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Activate the desired combination of attributes in the Meshing Attributes dialog box. We refer to these as the active TYPE, REAL, and MAT settings.

Or use the TYPE, REAL, and MAT commands. 3. Mesh only those entities to which the above settings apply.

January 30, 2001 Inventory #001441 10-6

Meshing

...Multiple Element AttributesModifying Element Attributes

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

1. Define all necessary element types, materials, and real constant sets. 2. Activate the desired combination of TYPE, REAL, and MAT settings: Preprocessor > -Attributes- Define > Default Attribs... Or use the TYPE, REAL, and MAT commands

3. Modify the attributes of only those elements to which the above settings apply: Issue EMODIF,PICK or choose Preprocessor > Move/Modify > -ElementsModify Attrib Then pick the desired elements

4. In the subsequent dialog box, set attributes to All to current.

January 30, 2001 Inventory #001441 10-7

Meshing

...Multiple Element AttributesSome points to keep in mind: You can verify element attributes by activating attribute numbering: Utility Menu > PlotCtrls > Numbering Or /PNUM,attr,ON, where attr may be TYPE, MAT, or REAL

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Element attributes assigned directly to solid model entities will override the default attribute pointers. By assigning attributes to solid model entities, you can avoid having to reset attributes in the middle of meshing operations. This is advantageous because ANSYS meshing algorithms are most efficient when meshing all entities at once. Clearing a solid model entity of its mesh will not delete attribute assignments.

January 30, 2001 Inventory #001441 10-8

Meshing

...Multiple Element Attributes Demo: Resume ribgeom.db

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

List element types, real constants, and materials. One of each has been defined. Bring up MeshTool, choose area attributes, and press Set Pick the single area, show the Area Attributes dialog box, and press OK. (There is only one set of attributes, but this illustrates the general procedure.)

January 30, 2001 Inventory #001441 10-9

Meshing

B. Controlling Mesh Density

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

ANSYS provides many tools to control mesh density, both on a global and local level: Global controls SmartSizing Global element sizing Default sizing Local controls Keypoint sizing Line sizing Area sizing

January 30, 2001 Inventory #001441 10-10

Meshing

...Controlling Mesh DensitySmartSizing

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Determines element sizes by assigning divisions on all lines, taking into account curvature of the line, its proximity to holes and other features, and element order. SmartSizing is off by default, but is recommended for free meshing. It does not affect mapped meshing. (Free meshing vs. mapped meshing will be discussed later.)

January 30, 2001 Inventory #001441 10-11

Meshing

...Controlling Mesh Density To use SmartSizing: Bring up the MeshTool (Preprocessor > MeshTool), turn on SmartSizing, and set the desired size level. Or use SMRT,level Size level ranges from 1 (very fine) to 10 (very coarse). Defaults to 6. Then mesh all volumes (or all areas) at once, rather than one-by-one.

Training Manual

January 30, 2001 Inventory #001441 10-12

INTRODUCTION TO ANSYS 5.7 - Part 1

Meshing

...Controlling Mesh Density Examples of different SmartSize levels are shown here for a tetrahedron mesh.

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Advanced SmartSize controls, such as mesh expansion and transition factors, are available on the SMRT command (or Preprocessor > -Meshing- Size Cntrls > -SmartSize- Adv Opts...)You can turn off SmartSizing using the MeshTool or by issuing smrt,off.

January 30, 2001 Inventory #001441 10-13

Meshing

...Controlling Mesh DensityGlobal Element Sizing Allows you to specify a maximum element edge length for the entire model (or number of divisions per line): ESIZE,SIZE or Preprocessor > MeshTool > Size Controls - Global [Set] or Preprocessor > -Meshing- Size Cntrls > -Global- Size

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Can be used by itself or in conjunction with SmartSizing. Using ESIZE by itself (SmartSizing off) will result in a uniform element size throughout the volume (or area) being meshed. With SmartSizing on, ESIZE acts as a guide, but the specified size may be overridden to accommodate line curvature or proximity to features.

January 30, 2001 Inventory #001441 10-14

Meshing

...Controlling Mesh DensityDefault Sizing

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

If you dont specify any controls, ANSYS uses default sizing, which assigns minimum and maximum line divisions, aspect ratio, etc. based on element order. Meant for mapped meshing, but is also used for free meshing if SmartSizing is off.

You can adjust default size specifications using DESIZE or Preprocessor > -Meshing- Size Cntrls > -Global- Other.

January 30, 2001 Inventory #001441 10-15

Meshing

...Controlling Mesh DensityKeypoint Sizing Controls element size at keypoints: Preprocessor > MeshTool > Size Controls: Keypt [Set] or KESIZE command or Preprocessor > -Meshing- Size Cntrls > -Keypoints-

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Different keypoints can have different KESIZEs, giving you more control over the mesh. Useful for stress concentration regions. Specified sizes may be overridden by SmartSizing to accommodate line curvature or proximity to features.

January 30, 2001 Inventory #001441 10-16

Meshing

...Controlling Mesh DensityLine Sizing Controls element size at lines: Preprocessor > MeshTool > Size Controls: Lines [Set] or LESIZE command or Preprocessor > -Meshing- Size Cntrls > -Lines-

Training Manual

INTRODUCTION TO ANSYS 5.7 - Part 1

Yes for soft No for hard

Different lines can have different LESIZEs. Size specifications may be hard or soft. Hard sizes are always honored by the mesher, even if SmartSizing is on. They take precedence over all other size controls. Soft sizes may be overridden by SmartSizing.

You can also specify a spacing ratio ratio of last division to first. Used to bias the divisions towards one end or towards the middle.

January 30, 2001 Inventory #001441 10-17

Meshing

...Controlling Mesh DensityArea Sizing C