by **raback** » 18 Mar 2018, 21:53

Hi Mark

The solution strategies are divided into "linear system" and "nonlinear system". The choices for MUMPS only deal with the linear system while the missing keywords are related to nonlinear system.

Nonlinear system settings are quite problem specific. One would typically start without relaxation and turning on Newton early on. Newton's convergence rate is faster than that of Picard (the other method) but the radius of convergence is smaller. Hence you might try to resolve convergence problems to some limit trying with relaxation (down to ~0.5, or maybe even 0.3) and keeping Picard on longer.

The convergence of nonlinear cases may also be aided by shorter timesteps. Only flows with Re<~100 have steady state solutions. When trying to find steady state solution for problems where it does not exist often leads to toggling between different attractors.

-Peter