In Autodyn 2D, I'm trying to model a shock wave going through a 1000x1000 micrometer box of air (atm pressure). In the center is a circle 500 micrometer diameter representing a bubble of vacuum at about 1 mTorr. I've set up a 2 microsecond square wave shock wave of 1 GPa starting from the left hand side. The mesh is 600x600. The basic expected outcome is to see how a shock wave is dissipated when it encounters a bubble of vacuum in the air. I have the material "Air" set up with the Equation of State (EOS) as "Shock" with appropriate c and s values.
I've tried Lagrange, ALE, and always received errors of a degenerate cell occurring at the boundary of the vacuum bubble although I have tried changing the erosion models.
Lately with Lagrange, I also receive time step error (being too small), and I have tweaked it to no avail.
While trying to make a shock wave with a TNT explosion using Euler, I ended up with an overflowing cell (also at the boundary of the bubble).
Any suggestions for possible fixes would be most helpful.