Dealing with Geometry

Mishal

Greetings All

This may be a very broad question.

For work purposes I generally get models from the drafting team which is done in NX. I usefully fix up the geometry for FEA purposes which is then done in Strand7 (the other engineers use NX for analysis). With regards to the fixing up of the geometry, much of it is done in the modelling environment (NX) however there are many tools on Strand7 to fix up geometry such as grafting edges to faces, performing intersections and so forth.

When dealing with Mecway, the meshing packages do not have much in terms of fixing geometry. How do you guys normally do this? I am assuming that a lot of work is going into your modelling environment to get the geometry up to scratch? Or is there other packages that are used to fix up geometry?

JohnM

Mishal, you make me feel spoiled - we export to STEP from Solidworks or Inventor, and most of the time they simply mesh (especially in Gmsh). If we want to simplify the geometry, this is usually done in those CAD packages as well (sometimes in FreeCAD or SpaceClaim, but this is "last resort"). It might be worth discussing best practice with the design teams on how things are created!

Mishal

JohnM, thanks for your response. Are you guys generally using brick meshes or surface meshes? I am not sure about Solidworks and Inventor, but FreeCAD cannot create a midsurface from a 3D model. The fixing up of my models usually pertains to developing geometry that is midsurfaced.

prop_design

I have been using Rhino 5 to manually create midsurface and solid models. I import step files into Netgen and create midsurface and solid meshes using tet elements with midside nodes. I have never been able to figure out gmsh. The built in Mecway meshing has given me a lot of problems compared to Netgen. I am going to switch to MoI v4 soon. I don't like Rhino much and wouldn't recommend it to anyone. MoI is also very affordable. Since I make the models myself, I've never had to clean anything up. I don't think Rhino or MoI would be very good at trying to fix a model that already had problems. My models are very simple blade models. So it's not hard to create a midplane. If you have really complex geometry, that you need to clean up, I don't know what to recommend.

Sergio

You could try to teach to you CAD team to design with FEA in mind, leaving small features as small radius, chamfers and holes to the end of the model, so is easy then to export a simplified model for FEA without need to further simplification or defeaturing. Very often for sheet metal parts the desiger choose to model the face that is in contact with other parts, so in case of need to increase thikness the basic surface doesn't change; but still you can use this surface using shell offset in FEA, so no need to create a midsurface.

Mishal

Thanks for the comments guy!