I am having issues with DPM convergence. I am using a steady-state uncoupled dpm model and I have created a UDF for a report definition which calculates the standard deviation of particles about the centre of a channel as they pass through a plane. the normal residuals (continuity and velocity) converge but the standard deviation of particles oscillates. I have run the calculation with a lower tolerance for convergence and I have reduced the mesh size significantly but the standard deviation output still oscillates.
The oscillation is smaller when the grid size is smaller but its not feasible to make the mesh smaller again.
I have also checked my boundary conditions and initial conditions and they seem to be fine.
Could someone offer advice on what else might be the problem.