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 second law must be solved.
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When there are time dependencies in a 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. This is also an efficient way of establishing correct initial conditions if there are static loads, or if some load should start at a non-zero value.
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 implicit 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
A structural dynamics problem can also be solved using explicit time-stepping, so-called explicit dynamics. COMSOL Multiphysics supports several explicit methods where the Verlet method is of main interest for structural mechanics. This is the default solver when using the Explicit Dynamics study step to set up a structural problem.
In the COMSOL Multiphysics Reference Manual:
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Time-Dependent Solver
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Studies and Solvers
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Explicit Dynamics
See Performing an Explicit Dynamics Analysis for more details solve a time-domain analysis using explicit time-stepping.
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Bracket — Transient Analysis: Application Library path Structural_Mechanics_Module/Tutorials/bracket_transient.
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Bracket — Explicit Dynamics: Application Library path Structural_Mechanics_Module/Tutorials/bracket_explicit
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Stress Relaxation of a Viscoelastic Tube: Application Library path Structural_Mechanics_Module/Material_Models/viscoelastic_tube.