Hi,

I have spent considerable time trying to debug my code and am not able to find the bug in the code. I am essentially trying to simulate 3D elastic wave propagation in a pipe fixed on both ends and having an ultrasonic collar triggering ultrasonic impulse on a portion of the outer pipe segment. I would ideally like to use the KMV elements (similar to the spyro package). I generated a tetrahedral mesh of the pipe using GMsh and labeled the ends of the pipe using tag "1" and the collar segment as "2". Next I wrote the UFL expressions for 2nd order central difference for acceleration term and the elasticity as well as traction terms. The code runs but the displacement at certain nodes diverges to infinity and results in nonsensical results. I have tried multiple things including

1. specifying the collar load as displacement as well as traction
2. trying out KMV and CG element
3. trying out different KSP methods and preconditioners
4. Formulating the problem using semi-implicit HHT as well as second order explicit difference method
5. Ensuring the Gamma value of the tetrahedral mesh is atleast 0.2