"Time step too small" is shown when the current time step is less than 10% of the initial time step. You can always decrease the minimum time step to continue the calculation. After loading your problem, go to the Controls panel and select Time step Options. Change the Minimum Time Step to a very small number, or zero. Zero Minimum Time Step means that the minimum time step size is calculated automatically by the code. The variables affecting the time step are the smallest cell size, gap size, velocity, and sound speed.
For Lagrangian type parts, you need to examine the geometry of the parts to see if there are distorted cells.
For Eulerian type parts, you need to examine the velocity and sound speed of the parts to see if there are abnormal velocity or sound speeds.
If Lagrange-Lagrange interaction is
involved in the calculation, you need to check the gap size and gap type. If internal gap is
used, the time step is usually calculated from the gap size because it is the
smallest. The internal gap size decreases with the decreasing cell length and
thus causes the smaller time step size. So the best
type of gap is EXTERNAL GAP. Change the gap type to EXTERNAL and run the
For Euler calculations, following the instructions help you to prevent a small time step: