Hello everyone, I have some questions about FSI modelling. When using LAW51 with a LAW5 JWL material, LAW4 hydraulic JC and LAW6 with ideal gas EOS (all Eulerian), I sometimes have models abort due to a negative rho error in some element. What exactly causes this? The cutoff pressure for the LAW6 material is set to -1e-30.
On other occasions using a similar setup with a Type 18 contact between the air/explosive (slave) components and a solid part (master) being affected by the pressure wave, I noticed that some of the pressure wave seems to travel through the solid part. Even though the wave is influenced when it hits the part, some of it seems to diffuse through it. I did not use any artificial minimum time step such as DT/NODA/CST to speed up the computation in some models and it looked like the same behaviour. The contact stiffness and gap factors were defined as described in the manuals
Related to this: how does a larger time step (i.e. set by DT/NODA/CST) influence the Type 18 contact behaviour? Would a time step larger than the one controlled by DT/ALE contribute to this artificial diffusion? Also, how are the master and slave mesh sizes correlated - should they have a similar size or should/can the master size be (much) larger? Is it better to define the master entity as component, set or surface, or is there no difference?
