•

•

As a default, the double dogleg nonlinear solver is selected when a stationary study is generated and Contact nodes are present in the model. For the majority of contact problems this solver has more stable convergence properties than the Newton solver, which is the generally used default solver for other problems. Using the same settings, the Double dogleg solver tends to be somewhat slower than the Newton solver on problems where both solvers converge. It is however often possible to take larger load steps when using the double dogleg solver. For some problems, the Newton solver can still be the better choice, so if you experience problems using the default settings, try to switch solver.

•

It is important to scale the contact degrees of freedom manually. The convergence check relies on the scaling of the degrees of freedom, but since contact pressures and friction forces often are zero over parts of the simulation, you should not rely on automatic scaling. When the solver sequence is first created, both contact pressure and friction forces are given a manual scaling which is relevant for typical metal-to-metal contact. You should in most cases change this to values appropriate for your application. The variable scaling is accessed under Dependent Variables in the solver sequence. Set the scale for each variable to a value which is representative for the expected result. Too large values may give a too early convergence, while too small values may lead to an excessive number of iterations.

•

For some contact problems, it is necessary to let the parametric solver use a more defensive strategy when going to the next parameter step. This can be controlled by setting the value of Predictor in the Parametric feature to Constant.

•

When using the augmented Lagrangian method, at least one lumped step will be generated in the segregated solver for each Contact node. The number of lumped steps will be increased even more if you select the Group contact variables in solver per pair check box in the Advanced section of the settings for the Contact node. This split of variables into different lumped steps does not influence the solution as such; you can equally well group the contact variables in a single lumped step. Each lumped step will however generate an individual curve in the convergence plot, making it easier to pinpoint the source of convergence problems.

•

•