Surface mesh with poor element (nearly colinear nodes)

dculp

The attached model generates the following surface mesh for quad dominant elements. Note the element in the upper left which has nearly colinear nodes along the curved boundary of the model. The same mesh results with either the internal mesher or Netgen 6. The meshers could correct this by specifying a maximum included angle between adjacent sides (e.g., all included angles less than 135 degrees). If such a quad element isn't possible at that location then it should be split into two triangular elements. (Of course I could manually adjust the meshing parameters to correct this problem but this shouldn't be necessary.)

Sergio

Have made some quick test with a quarter plate and basic mesh definition and my meshes doesn´t show such bad elements. Could you share your step file?

Sergio

Just playing with custom command in Gmesh, meshing, and deleting unused nodes, and then smooth the mesh in Mecway we can get a nice mesh. I don´t understand why Gmsh generate these extra nodes, and why in Mecway the mesh is not smoothed directly.

dculp

Attached is the step file (H1010b.stp).

Also, see my latest post (gmsh - How to change the 2D quad element size?) which uses the same step file.

Note that the problem mesh discussed here was generated by Mecway 18, not gmsh.

My intent with these 2D quad meshes is to eventually extrude in the Z direction to produce 3D hex mesh.

Sergio

This is the mesh on your step, using gmsh with custom commands to force the structured quads, now was not needed to do the mesh smooth after meshing.

dculp

Sergio --

Your custom commands work well. However, they generate additional nodes at the center of the elements. (I don't understand why these nodes were generated or what they are for since they aren't connected to anything.) These can be deleted by \Mesh tools\Delete unused nodes. Is there a custom command that will do this automatically?

The following shows the result (before deletion) where, tor simplicity, the mesh had been generated without midside nodes. The model with these additional nodes is attached.



Edit 2/12/2013 -- It seems that the additional nodes aren't generated if the elements aren't quadratic.