Problems with Mesh in Multiphysics

[Anonymous]

Hey,

I'm having some problems when I'm doing the Mesh in Multiphysics 2012. All parts works fine, except one. The mesh results says that the part is "not watertight". Does anyone know how I can solve this problem?

Thank you,

Sara

[PipePakPat]

There are three types of geometries that can be imported into the Mechanical or Multiphysics software:

• 3D Solid
• Surface
• DXF or IGES Wireframe

For 3D solid models, the model must import without problems interpreting the geometry data.  If problems exist, these parts may appear with a bold red outline on the part icon in the model tree.  One can then right-click on CAD Mesh Options and choose to view "Feature Matching" to determine if any multimatched or unmatched features exist in the model.  If non-zero values exist, then slide the mesh size to the largest value and choose "Apply".  If the both numbers don't approach zero, then slide the adjustment to the smallest value and choose "Apply".  After trying these upper and lower bounds, try to find the value closest to 100% that would allow zero for multimatched and unmatched features.  This fine tuning can allow a model which has imported with discrepancies to mesh successfully.  These settings apply on a per part basis.

If there is no bold red outline on a per part basis and/or the feature matching indicates zero for both multimatched and unmatched features, then then next step will be to use a different surface mesh size.  This can be accomplished by accessing the 3D Mesh Settings option and adjusting the slider to a finer position (perhaps 80% instead of the default value of 100%), then re-meshing the model.

So let's now learn more about the message you received while trying to mesh your model, which indicated the model may not be watertight.  This message will appear when the program has first created the surface mesh on the model, then second, attempts to differentiate the "inside" of the surface mesh and the "outside" of the surface mesh.  This differentiation can only occur if the surface mesh encloses a volume. 

If a surface model is meshed using the "Solid" meshing option, then this same error will be produced.  When meshing a surface model, the "Plate/Shell" meshing option should be used instead of "Solid" which skips the watertight check and subsequent solid meshing phase.  It should be noted that surface models/parts will always have the bold red outline, described above, on the part icon in the model tree.  This is as expected.

The last option relates to the import of DXF or IGES planar wireframe geometry, which can then be used to generate a 2D mesh of that bounded plane.  Since this meshing method does not include the watertightness solid meshing check, further explanation will be deferred.  This reference is only included for completeness.

Please let me know if you have further questions.

[John_Holtz]

Hi Sara,

You can also try the things mentioned on this page in the Help: "Help > Autodesk Simulation > Mesh Models > Mesh Overview > Meshing CAD Solid Models > Watertight Problems in Meshes"