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Negative volume and complex speed of sound termination

Negative volume and complex speed of sound termination

Negative volume and complex speed of sound termination

(OP)
Hello everyone!

I have a problem to simulate an impact onto soil ground (Material Model 5 Soild and Foam) with LS-Dyna, because I am getting negative volumes which lead to complex speed of sound in the material.

My model consists of two layer of soil (Automatic_Surface_To_Surface) and an round impactor. Does anyone have any advice how to solve this problem?

What I tried so far:

- Reduce the timestep scale factor to 0.67 --> no change
- Improve the hourglas formulation (I used type 2,3 and 5) --> same problem, but later error termination.


I am glad for any help and advices!


Greetings
Ed93

RE: Negative volume and complex speed of sound termination

If you are happy that your issue is not caused by incorrect units, material properties, constraints or loads:

- Identify the region where elements are turning inside out -> can you improve the mesh in that region to prevent the issue?

- If not, then you could look into 'adaptive re-meshing' to try to avoid this.

RE: Negative volume and complex speed of sound termination

Are you hand meshing? Negative volume (negative Jacobian) implies a nodal numbering scheme that did not follow the assumed element formulation, i.e. used left-handed vs. right-handed numbering.

RE: Negative volume and complex speed of sound termination

OP mentioned using LS-Dyna so I assumed the negative volume errors are due to excessive mesh distortion.

This would also make sense for impact studies on soft foam materials.

RE: Negative volume and complex speed of sound termination

Ah, good point.

RE: Negative volume and complex speed of sound termination

(OP)
Hey,

thanks for your answers!

Normaly negative volumes in foams are caused by massive compression. In my case the compression was not that big, so I have been looking for another reason and solved it by enlarging the mesh of the second soil. I think the problem was the contact between the two soils. The nodes where directly above each other and maybe some errors accured cause I used a nodes to surface contact. Now everything works fine, because I have now a little offset between the nodes.

Thanks again for your help and fast replies!

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