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OT? FEM comparison

Hello,

I am working at an university and we are using two different FEM-programs. ANSYS and CosmosWorks (conected with SOlidWorks). I am very interested to make a comparison with both and may be other programs. Because of this I made a test with a part where I changed the position of the supporting points. The solutions for the displacement were almost equal (less than 1% difference) but the stress was significantly different (over 60%). Now I am trying to get informations about "weak" points of both programs and their solvers. Has somebody some hints or sources or links to get an overview over these programs and compared results?

Many Thanks

M. Lotz

Reply to
Makus Lotz
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I suspect that either:

1) The element type was different (Cosmos uses 10-noded Tetrahedrons in the default, "high quality" solid mesh, and 4-noded tets in the "draft quality" solid mesh, and I'm not sure what the shell elements are like). ANSYS gives you many more choices. Which were you using?

2) The meshes were different. Mesh size and local refinement around an inside sharp corner, for example, can lead to very different stress values. Theoretically, stress is infinite at an inside corner; your stress value will grow as you refine your mesh.

Other than that, I don't have any info on how their solvers work, but I'm sure the theory and matrix manipulations are sound. I think it's more of a mesh difference situation.

Denny Trimble University of Washington (currently taking AA540, FEA :)

Reply to
Denny Trimble

Hello,

Denny Trimble schrieb:

1) I use the High Quality mesh at COSMOSWorks with tetrahedrons. Because of the mesh "problems" I made tests with COSMOS. I changed the density of the mesh in some steps and looked at the maximum stress v. mises and the resulting displacement of the whole model and four different points. Normally I would expect that stress and displacement values will converge. The displacement values converge like I expected to a value which I also reached with ANSYS. Unfortunately I can not see a convergence in the stress values. The mesh in ANSYS consists of ET187, also tetrahedron. I will also make some tests with its mesh density. Unfortunately it takes much longer to solve this model in ANSYS because it is a "selfwritten" parametric model to change supporting points.
2) That is true. I used at COSMOS two models, one with and one without local refinement. But both showed a convergence of the displacement but no convergence of the stress.

I want to test how much can I trust solutions from both programs because we want to design some parts which sould be lightweight. If we calculate the stress to high parts will have more weight, if it is too low the parts can be destroyed. Unfortunately the parts are too difficult to make only estimates with analytic calculations.

I think so too. But I found one comparison between COSMOS and DesignSpace (little ANSYS) were COSMOS showed better behaviour also in convergence...

Thank you very much!

M. Lotz Technical University of Ilmenau Germany

Reply to
Makus Lotz

Are you trying to analyze parts or assemblies?

-Ram

Reply to
Ramesh Ramalingam

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