convergence issue

Hi Alireza,

Typically a convergence test is looking at the convergence of a value relative to the Mesh size. However, you must keep in mind that when you change the grid size you must also change the time step size in order to ensure stability. The condition for this is the Courant-Friedrichs-Levy condition and is dt <= (v*sqrt(dx^-2+dy^-2+dz^-2))^-1 for 3D and dt <= (v*sqrt(dx^-2+dz^-2))^-1 for 2D.

You can either manually calculate this or simply leave the dt and number of time steps checked to auto and the software will perform the calculation for you.

Scott

Alireza,

You will also want to check the auto box for the number of time steps because if you do not then each simulation in your set will have a different simulation time. Think of it this way based on a dt of 6.67128190396304e-18 and 4000 time steps your simulation will be over a time of 26.685 ps. However, based on your settings if you half your grid spacing your dt will become 3.3356e-18 s so if your 4000 is fixed and not on auto this second simulation will be over a time span of 13.343 ps.

Scott