# Tet Meshing a Solid

When performing a simple tet mesh, try using Patran’s AutoTet mesher (it’s actually pretty good).

Two different ways to mesh a model are presented:

1) Import or create a solid object, and simply mesh it using the AutoTet mesher (EASIEST).

2) Mesh the exterior surface of the model with tri shell elements, equivalence the nodes to produce a completely closed volume, next autotet mesh the interior of the enclosed volume by selecting the tri elements (more control).

Method 2 – Using the AutoTet mesher to create a solid mesh from an enclosed boundary of tri elements
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1) Create a triangular mesh on the outer boundary of the desired solid mesh.

2) Ensure the outer boundary mesh is a true enclosed volume by equivalencing all common nodes on the boundary edges of the tri mesh with the following commands:

• Elements-> Equivalence/List/Tolerance Cube
– in “Nodes to Equivalence” enter all node points in the boundary tri mesh, and click “Apply”

• As a quick check: Elements-> Verify/Element/Boundaries and select “Free Edges” to make sure the mesh is tied together and entirely enclosed.

If there are “cracks” in the boundary mesh, there will be a yellow line along the crack. If nothing, then the mesh is entirely enclosed.

3) Before filling in the boundary tri elements with tet4 elements, the user must make sure the normals of the elements are pointing in a outward direction for the solid piece. To check the normals, do the following:

• Geometry->/Edit/Surface/Reverse

– Select all the surfaces used to create the tri mesh, and click the “Draw Normal Vectors” button.

An arrow will appear at the center of each surface showing the normal direction.  If there are any surfaces with the normals pointing inward,  each surface must be individually selected using the “Surface List” box and click the “Apply” button to reverse those surfaces. Continue with this procedure until all the surfaces have outward pointing normals. Since the elements you created earlier are associated with these surfaces, their normals will also be modified automatically.

4) The AutoTet mesher must be provided with a list of the tri element ids so it can mesh the inside of the boundary with tet4 elements.

• Elements-> Create/Mesh/Solid
– Select “TetMesh” option
– Select “Tet4” for Element Topology
– For the “Input List”, specify all the tri element ids. To select all these tri elements using the mouse, click on the Tri element filter button (located in a small toolbar panel above the main viewport) and then proceed to highlight all the desired boundary tri elements.
– Click “Apply” and the AutoTet Mesher will fill in the boundary with Tet4 elements.

Once finished, the boundary tri elements can be deleted.