Most real-world phenomena develop in time, but you might know that the system under study approaches a steady state described by a stationary solution.

For a stationary problem, select the Stationary Solver. When solving a set of time-dependent equations, for example the time-dependent coefficient form problem

the stationary solver searches for a solution where ∂u/∂t = 0. The Time-Dependent Solver and the stationary solver handle linear as well as nonlinear problems.

In some cases, you might want to study the natural harmonic oscillations of a time-dependent problem. This involves finding the eigensolutions u with the associated eigenvalues λ. The time-dependent PDE above is then transformed to the following form:

Such an analysis is particularly interesting in electromagnetics, structural mechanics, acoustics, and wave propagation. To study the eigensolutions and compute the eigenvalues (or eigenfrequencies), select the Eigenvalue Solver.

In addition to these fundamental solvers, COMSOL includes additional solvers for special applications such as an Optimization Solver (which requires the Optimization Module), a Time-Discrete Solver, an AWE Solver, and a Plug Flow Solver (which requires the Chemical Reaction Engineering Module). Some of these solvers are connected to special functionality in the add-on modules.