6. Quad

6.1. Why do my loops fail for cylindrical surfaces?

The solution, then, is to resolve all surfaces, so that the surface does not loop back on itself. For instance, if you track the U or V lines for any surface, the normal angle of this path to the surface should not change in angle by more than 180 degrees. Ideally, the maximum case would be 120 degrees.

From ICEM CFD 4.2 onwards, you can modify surfaces with an option "Geometry > Surface > Modify > Split folded surfaces". This option will split all cylindical surfaces at a defined angle of curvature. After splitting these surfaces, and creating loops off these surfaces, they should mesh in Quad.

[ top ]

6.2. What is the difference between quad meshes that I get from Tetra and then converting into quad as opposed to the quad mesh that I get from QUAD?

You need to see some pictures before we do the comparison.

Below is the picture where a FRAME has been meshed in QUAD allowing some triangles here and there but mostly quads in the mesh. A size of 5 was given all over on the curves. So, you can say that edge length of every quad would be 5 or so,

Below is the mesh which was meshed using Tetra surface meshing (included in Tetra license). The size is same as 5 but obviously it would lead to a much finer mesh than above. I think more than 2.5 times of above. (if you split one quad, you get two right-angled triangles. Then since, the diagonal would be of more than 5 distance, it has to be split further.

Following was meshed after converting triangles generated in [2] into quads. Every triangle would give 3 quads. So, the mesh size would go quite a lot,

Based on these, here are the real comparisons:

Quad mesh from Quad:

• + point:
  • Mesh with alignments where-ever possible,
  • Decent size of the mesh,
  • Excellent quality,
  • If fails to create the mesh in a portion, parameters could be changed to get the mesh there,
• - point:
  • It's difficult to get at times a complete quad mesh without any triangles. You might have to do a few steps to get that. Normally packages take triangles and thus it's advisable to allow a few triangles in the mesh,
  • Few minutes of extra work of creating loops,

Quad mesh from Tetra:

• + point:
  • All quads without any triangles,
  • Very easy to create i.e. requires minimum steps,
• - point:
  • Bad quality and thus would require series of actions (smoothing, editing etc) on mesh,
  • Huge mesh size (more than 4 times than of Quad mesher) for same kind of setup,
  • Has a danger of failure in conversion and that time there may not be any possible workaround. The process is pretty much automated.