Section 9 Mesh Cleanup. Copyright © 2010 Altair Engineering, Inc. All rights reserved.Altair Proprietary and Confidential Information Mesh cleanup CAD

Section 9

Mesh Cleanup

Copyright © 2010 Altair Engineering, Inc. All rights reserved. Altair Proprietary and Confidential Information

Mesh cleanup

CAD models can have features like chamfers, fillets that are not desired.

If the CAD model is not good, it is possible to generate a mesh that has,

Holes in it (fails water tight test),

Elements overlapping/intersection,

Bad element quality.

Holes have to be filled and overlapping elements to be removed before a volume

mesh can be generated.

To generate a good tet-mesh, the tri-mesh quality should be reasonably good.

Assembly of CAD models is done by first converting them to a mesh model followed

by imprint operations. The imprint operation can result in very poor quality elements.

SimLab has tools to

Display the failed elements (element intersection and holes).

Automated and manual mesh cleanup tools.

Mesh Cleanup


Mesh error display tools

The meshing tool bar has functions that can be used to locate errors in a mesh

Free Edges

Elem Intersection

Quality Test

Free Edges

This option will display Free and non-manifold edges in the selected model

Free edge: A tri-element that does not share its edge with an adjacent tri-

element. These are coloured “Orange”

Non-manifold edge: A tri-element that shares it edge with more than 2

other tri-element. These are coloured “Yellow”

The display will add a layer of adjacent elements around the Free and Non-

Manifold edges, to improve the visibility.

Mesh Cleanup


2 elements missing in the

surface mesh

“Free Edge” command will display the free

edges in Orange and 2 layers of elements

around the free edges

Free Edge

Free Edge Display


3 elements meet along the

edge of the cube

“Free Edge” command will display the free

edges in Orange and the non-manifold edges

in yellow. In addition 2 layers of adjacent

elements are displayed

Non-manifold edge Free Edge

Non Manifold Edge Display


There is a zero area

triangle with nodes 46, 47

and 57

“Elem Intersection” shows the adjacent 3

elements are intersecting

Element Overlap


For the model in the previous page, if we check the Aspect ratio, the maximum value is

infinity. Id the display button is selected all tri-elements with aspect ratio greater than 20 will

be displayed. A layer of adjacent elements will also be displayed. Otherwise it will be hard to

see the zero area triangle.

Element Overlap


There are several tools to cleanup a mesh

Automated cleanup

Fill Hole

Fill Crack

AutoTriClean – Improves the aspect ratio of a tri-mesh

Manual cleanup

Create Element

Split

Swap

Collapse

Equivalence

Combine 2Tris to Quad

Split Quad to Tris

Mesh Cleanup Tools


• Select three nodes to create an element. On the selection of the third node, an element

is created and the element layers around it are updated.

Create Elements


This tool helps to split an element along its edge.

An error shown in this picture would cause the Element intersection. .

Select the edge to be split.

After edge splitting the nodes will be equivalenced, by default.

Split


After Split

Before Split

Split


This is used to swap an element edge to improve the mesh.

Instead of deleting and creating the elements, a swap operation is performed.

Swap


In certain instances, there will be very narrow elements which will affect

the quality of Tri elements and reflect badly in the quality check. These

elements can be collapsed to get a good quality mesh.

In these cases Collapse tool will be useful.

After collapse short edge

Collapse


Select the node which is on the element edge to be collapsed.

Select the element edge to be collapsed.

Click Apply Button.

The element will be collapsed to the node selected.

In the picture shown above, the narrow elements causes poor quality of the mesh.

When collapsed, the quality becomes better.

The quality is improved now.

Collapse


Equivalence joins two nodes within tolerance to form a single node and thereby

eliminates Free edges.

Equivalance


Select the two nodes and specify the tolerance. Then click Apply to join the nodes.

Free Edge Display


The nodes are joined and the free edge is removed.

Free Edge Display


The automated quad-meshing code might not create all quads but leave few tri elements.

This tool helps to manually convert the tris to quads.

Combine 2 Tri to Quad


• This option is used to delete (Tri/Quad) elements. Solid elements connected to the

surface element will also get deleted.

Before Deleting After Deleting

Delete Element

Documents

Section 9 Mesh Cleanup. Copyright © 2010 Altair Engineering, Inc. All rights reserved.Altair Proprietary and Confidential Information Mesh cleanup CAD