Alpaca4d

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Turn geometry into solid elements ​

Make bricks from a solid that can be built in layers, or ten node tetrahedra from a tetrahedral mesh for any other shape.

Spot the cow, a solid of Ten Node Tetrahedra made from a closed mesh

Spot the cow: a closed mesh, filled with Ten Node Tetrahedra.

You need ​

  • The geometry: section polylines or a quad mesh for bricks, the output of a tetrahedral mesher for tetrahedra.
  • An nD material, and Assemble.

Steps ​

Bricks, for a solid in layers

  1. Make a series of meshes, one per layer, each with the same quad faces in the same order: loft each layer's polylines with Mesh Loft, or move or orient copies of one quad mesh.
  2. Wire the series, in order, into Meshes of Mesh Series to Brick. Set Closed to true for a ring that joins the last mesh back to the first.
  3. Wire its Mesh output into Mesh of SSP Brick, and the material into Material. It makes one brick per 8-vertex mesh.

Tetrahedra, for any shape

  1. Bring in what a mesher such as gmsh or TetGen writes: the corner points, and four point numbers per tetrahedron, counted from 0. List Item picks each one's corners, and Construct Mesh makes them a four-vertex mesh.
  2. Wire the meshes into Mesh of Ten Node Tetrahedron, and the material into Material. It adds the six edge nodes itself.
  3. Hold a face at every node on it, edge nodes included: take the element's Points, keep the ones on the face, and remove duplicates with Cull Duplicates before the Support.

Then wire the elements into Elements of Assemble.

Check ​

  • Model View draws the solid and, with Element edges on, as it is to start with, each element's edges.
  • Assemble's Mass, in kg, should be the solid's volume times the material's density.
  • Assemble warns when an edge node between two supported corners has no support of its own.

Good to know ​

  • Mesh Series to Brick stops with an error on a triangle, and on a brick that folds through itself: every mesh of the series has to carry its faces and vertices in the same order.
  • The number of bricks is (layers − 1) × faces, with one more layer when Closed is on. Check it before assembling.
  • Tolerance on Assemble, 0.01 m by default, has to be well below the size of the elements, or it welds their nodes together. The Femur uses 0.0001.
  • Ten Node Tetrahedra need an OpenSees newer than 3.8.0. Mesh Brep in 10_Utility makes a quad mesh of surfaces for ASD Shell, not solids.

See also ​