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COMSOL mainly uses implicit solutions. However, an explicit solver is available that uses the Runge-Kutta method. I tried it for small solid mechanics problems and it works, but you have to manually select a stable time step. You can select the explicit solver for a time dependent step by selecting “Time Explicit Solver” from “Solver Settings” in the “Solver Configurations” node.

Nagi Elabbasi
Veryst Engineering

hey nagi,

Thank you very much. Is that in comsol Direct solvers are explicit and nondirect solvers Implicit?
I am worling in time dependent and the defualt is direct!!

No! Direct solvers and iterative solvers (the other option) are both used primarily for implicit solutions. They differ in the way they solve a system of equations of the form Ax=b. Implicit vs. explicit solution is a different issue. What is commonly called explicit solution or explicit method, at least in solid mechanics, is really explicit solution with lumped mass formulation. This involves no matrix solution at all. My previous post shows how to activate the explicit solver in COMSOL. In the “Time Explicit Solver” options you should set “Linear solver” to “Lumped”. Then you’ll see the “Direct” node shaded out.

Nagi Elabbasi
Veryst Engineering

Nagi,

Thank you very very much for your hint. I will check comsol document for more details. your help is really appreciated.

Best regdars.