# Smoothed particle Hydrodynamics: Resting fluid oscillations

I have a working SPH simulation in 2D. When the particles are in motion everything works fine. But once the simulation comes to a rest particles at the bottom begin to oscillate violently and eventually penetrate the boundary particles. I have tried dampening the simulation with two types of viscosity, XSPH and Artificial viscosity. They only helped slightly. Smaller time steps don't help either. Obviously pressures are building at the bottom. Is there another way to do fix this apart from viscosity and smaller timesteps?

$\frac{dr_i}{dt}=v_i+0.5\sum_j{(v_j-v_i)\frac{m_j}{\rho_j}W_{ij}}$
However, the problem you experienced is still not acceptable and probably depends on the pressure evaluation scheme (equation of state) and the time step size. Check the sound speed $c$ and the smoothing distance $h$ and estimate the order of the required time step size by
$\Delta t=\frac{h}{c}$.