Particle penetration occurred during the simulation of two-phase flow.
I am trying to simulate a two-phase flow and replicate the work of Fourtakas in 2016. To do this, I introduced the DP criterion to determine whether soil particles yield, and I fixed the particles that did not yield (set du / dt = 0). However, I found that soil particles penetration occurred during motion, causing the computation to crash：
The computation initially remains stable, but later, it seems that the entrained soil particles in motion pass through the fixed soil particles below, causing a chain reaction that leads to a collapse.
I have tried adjusting some parameters, such as changing the DDT or using higher viscosity, but it only reduces the severity and duration of the collapse. However, the soil particles still exhibit non-physical penetration and oscillation.
I would like to know if this issue can be resolved by adjusting the parameters or other measures.