Model problems

Question

Hey,

i built a model and it is a really simple crash analysis but there are some elements which are producing negativ volume and I don't know why. Additionally the crash surface isn't really in contact with the other surface.

Hope you can help me.

Best,

Max

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Altair Forum User · Answer

Hi Max,

Please check the model file attached. I made some modifications in the model.

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Altair Forum User · Answer

Hey,

thank you a lot. I did it but are there some new problems and I'm not really sure why I tried also option/DT/NODA/CST but it didn't work.

I get a little bit crazy of it, because other models are working well but not these.

Thanks for your help!

Best,

Max

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Altair Forum User · Answer

Hi Max,

The NEGATIVE VOLUME error happens when solid elements are very deformed and their characteristic length goes to 0. For large strain formulation the time step of an element goes to 0 when the element is compressed. In RADIOSS Starter input file (Runname_0000.rad), use Ismstr =2 in the solid property and  in RADIOSS Engine file (Runname_0001.rad) use the option/DT/BRICK/CST and provide Tmin value at which the solid elements will switch to small strain.This means that the solid elements using Ismstr =2 will use large strain formulation while their time step remains greater than tmin, and will then switch to small strain formulation.