Comparison with Ansys

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Comparison with Ansys

Published by James G. in general · 8 August 2023
I discovered a couple of comparison plots of Femdesigner FemforAD versus Ansys which I'm sharing here. Normally I prefer to compare results to classical calculations but others will like the reassurance of a comparison to a product that is at least 10 times the price (though their price seems to vary by the customers pocket size). Ansys offers much more than we do of course (mostly at extra cost, eg using more than 2 processer cores). It also has some nice features we want to add (eg. bolt pretension, MPC's), but others that are not so nice that you just have to live with (eg. why does an Ansys plastic analysis using the EPP model show 'impossible' peak stresses above yield - that has annoyed me for years). The meshes were similar in these tests but cannot be made exactly the same when using automatic meshing because we have different meshers.

Wide cantilever beam under gravity loading in Z-direction (Femdesigner results on left)

Hook under a pull pressure (Femdesigner results on top)
Notice Femdesigner has the 'signed' von Mises stress option. True von Mises stress is always positive. The sign is taken from the sign of the maximum Principal stress and it just tells you whether a region is compressive or tensile. Ansys uses this trick for fatigue calcs in order to adjust for positive mean stress but we found it useful for other purposes too. The trick only breaks down when the maximum Principal stress changes sign in adjacent elements which results in a local blip in the plot; in which case just use the unsigned version in the stress plot option list. However even that information is useful. We are not sure how Ansys stresses are recovered: Femdesigner carries out least-square extrapolations to the nodes from the interior Gauss point stresses, where stresses are mathematically most accurate.

Femdesigner Ltd
840 Ibis Court Centre Pk
Warrington, UK

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