Most isothermal simulations involve non-linearities, originating from the viscosity and sometimes from slipping boundary conditions. Defining the appropriate evolution scheme for these non-linearities is usually helpful for obtaining solutions, however, it is sometimes convenient to enable an automatic convergence strategy for rheology and slipping. You can do this using the Enable convergence strategy for rheology/slip option. The solver adjusts the appropriate settings in order to reach the solution. When selecting this strategy, the robustness of the calculation scheme is favored over the efficiency. This convergence strategy for rheology and slipping can be combined with the convergence strategy for non-isothermal flows.

For cases involving moving boundaries (free surfaces), the convergence strategy for rheology and slipping can be combined with an evolution strategy on moving boundaries. If the calculation appears to fail, however, you can apply these strategies sequentially instead of simultaneously.