how to pinpoint trouble areas on mesh

I've been trying to run a relatively simple geometry I made from NX6 (exported as IGES file). It appears that the geometry has a few areas that confuse the mesh generator; there are areas where the mesh is REALLY concentrated and others where the mesh is ultra sparse. Then, when I run the solver, I get the following error: "Warning:RANS Flow failed
Solver singularity: DILUPBiCG: Solving for epsilon: solution singularity. I'd assume this was from a few trouble areas in the mesh. Is there any way to pinpoint the trouble areas and then, how can I fix them in Symscape? Thanks for your help.

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Geometry Clean Up, Mesh Control, and Mesh Diagnostics

If you have the option I suggest you use STEP export rather than IGES. IGES typically comes across as surfaces that need to be stitched in Caedium which can then introduce sliver faces and tolerance level edge lengths. Whereas STEP typically preserves solids more precisely without any further clean up. For more on geometry exchange try "Geometry Exchange."

The default meshing parameters in Caedium try to ensure that each geometry edge has at least one mesh edge associated with it and then a relatively smooth mesh size transition to other areas of the geometry. Where you see very small mesh elements there is likely a very small edge or sliver face. You have a couple of options to remove small features if you don't want to resolve them:

  • Use the Face/Edge->Join tools on the Geometry Tool Palette to join the faces/edges to larger neighbors
  • Use a Boolean operation such as Booleans->Subtract to remove the feature and then patch the missing region with either the Face->Fill or Face->Loft tools

To better resolve areas of importance you need to strategically use the Conditions->Accuracy tool from the Physics Tool Palette, to impose constrains for the mesh size and growth rate on edges/faces/volumes. For more details try the tutorial tip "Accuracy Tool." Also you can see the effect of the Accuracy tool in the tutorial "Incompressible Flow Through a Pipe into a Box."

Often it is worth concentrating on just the surface mesh, rather than making a change and generating the volume mesh - which can take a while. In this case if you just use the Scalar Field->A (area) on the Results Palette you should be able to review Accuracy changes much more quickly. For more details on viewing just the mesh try "View a Mesh."

There are a selection of mesh quality metrics under Scalar Fields in the Results Tool Palette that you might also review:

  • E Ratio - ratio of min mesh edge length / max mesh edge length
  • Vol Ratio - ratio of actual volume / ideal volume based on longest mesh element edge length

To narrow the focus of the color map you can use the threshold sliders on the Legend Control and also set the range of the color map manually by changing its properties. To display the properties in the Properties Panel right-click the Color Map text. For details try "Color Map."

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