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

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

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

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

Copyright © 2010 Altair Engineering, Inc. All rights reserved.Altair Proprietary and Confidential Information There is a zero area triangle with nodes 46, 47 and 57 “Elem Intersection” shows the adjacent 3 elements are intersecting Element Overlap

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

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

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

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

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

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

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

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

Copyright © 2010 Altair Engineering, Inc. All rights reserved.Altair Proprietary and Confidential Information Equivalence joins two nodes within tolerance to form a single node and thereby eliminates Free edges. Equivalance

Copyright © 2010 Altair Engineering, Inc. All rights reserved.Altair Proprietary and Confidential Information Select the two nodes and specify the tolerance. Then click Apply to join the nodes. Free Edge Display

Copyright © 2010 Altair Engineering, Inc. All rights reserved.Altair Proprietary and Confidential Information The nodes are joined and the free edge is removed. Free Edge Display

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

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