Time-Domain Analysis
There are two classes of problems where a stationary solution cannot be used:
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When the inertial forces no longer are negligible, the full problem as given by Newton’s first law must be solved.
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When there are time dependencies in the material model, as for creep or viscoelasticity.
The most general way of handling time-dependent problems is to use a Time Dependent study. In this type of analysis, you can incorporate any type of nonlinearity, and there are no limitations on the time dependence of the loads.
A time-domain solution can be preceded by a stationary study, if, for example, prestress effects are needed.
For a linear problem including inertia, using the mode superposition method is often much more efficient than using the standard direct method.
Solver Selection
The two classes of dynamic problems presented above have quite different properties. The inertial forces in the full structural dynamics problem contain second-order time derivatives of the displacements, whereas creep and viscoelasticity only have first-order derivatives. The physical and numerical properties of these equations differ significantly.
There are two general solvers for time-dependent problems in COMSOL Multiphysics.
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The Generalized alpha method, which is recommended for structural dynamics problems. This is the default solver if Structural Transient Behavior is set to Include inertial terms in the physics interface settings.
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The BDF method, which is recommended for first-order problems. This is the default solver if Structural Transient Behavior is set to Quasistatic in the physics interface settings.
In the COMSOL Multiphysics Reference Manual:
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Time-Dependent Solver
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Studies and Solvers