Innovation Intelligence ® Section 9 Mesh Cleanup

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Mesh Cleanup 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 has to be removed/resolved before a volume mesh is 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.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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 edges are coloured “Orange”. Non-manifold edge: A tri-element that shares it edge with more than 2 other tri-element. These edges are coloured “Yellow”. The display will add a layer of adjacent elements around the Free and Non- Manifold edges, to improve the visibility.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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 © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. 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 © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. There is a zero area triangle with nodes 46, 47 and 57. “Elem Intersection” shows the adjacent 3 elements are intersecting. Element Overlap

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Element Overlap For the model in the previous page, if we check the Aspect ratio, the maximum value is infinity. If 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.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Mesh Cleanup Tools There are several tools to cleanup a mesh Automated cleanup Fill Hole Fill Crack Auto QuadClean – Improves the Quad quality Fill Planar Edge Loop Split Row of Hex to Wedge Intersection Manual cleanup Create Element Split Swap Collapse Equivalence Combine 2Tris to Quad Split Quad to Tris Delete Element

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Auto Cleanup - Fill Crack Used to fill the crack and slot. Crack is defined as a closed loop of free element edges with angle between adjacent free element edges less than or equal to 30 o. Cracks with angle greater than 30 o are identified as slots.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Before Fill crack After Fill crack Auto Cleanup - Fill Crack

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Auto Cleanup - Fill Hole Used to fill holes, present in the meshed model. This can automatically find the holes in the body / face and fill it. In case of Edge, the user need to select an edge and click on “Display Connected Free Topo Edges” to view the associated loop or hole. Single face option is used to crate a single face between loops. Single Face option ON

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Auto Cleanup Auto Quad Clean : This tool is used to cleanup the quad elements based on interior angle and warp angle.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Create Elements Select three nodes to create an Tri element. On the selection of the third node, an Tri element is created and the element layers around it are updated. Similarly we can create quad, tet, wedge and hex elements.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Split 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 and the node. After edge splitting the nodes will equivalence by default, if the equivalence toggle is ON.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. After Split Before Split Split

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Swap This is used to swap an element edge to improve the mesh. Instead of deleting and creating the elements, a swap operation is performed.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. After collapse short edge Collapse 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.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Collapse Select the node which is on the element edge to be collapsed. Select the element edge to be collapsed. Click Apply Button. The elements will be collapsed to the node selected. In the picture shown below, the narrow elements causes poor quality of the mesh. When collapsed, the quality becomes better.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Equivalance Equivalence joins two nodes within tolerance to form a single node and thereby eliminates Free edges. Select the two nodes and specify the tolerance. Then click OK to join the nodes.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Select the two nodes and specify the tolerance. Then click Apply to join the nodes. The nodes are joined and the free edge is removed. Free Edge Display

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Combine 2 Tri to Quad The automated quad-meshing code might not create all quads but leave few tri elements. This tool helps to manually convert the Tris into Quads.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Split Quad to Tris The automated quad-meshing code might create quads with larger interior angle. This tool helps to manually convert the Quads into Tris.

Copyright © 2012 Altair Engineering, Inc. Proprietary and Confidential. All rights reserved. Delete Element This option is used to delete (Tri/Quad) elements. Solid elements connected to the surface element will also get deleted. Before Deleting After Deleting