The Time Dependent (
) study and study step are used when field variables change over time.
Selecting a Time Dependent study adds a Time Dependent study step node and sets up a solver with a
Time-Dependent Solver. Use this study for a time-dependent or transient simulation using a Time-Dependent Solver for computing the solution over time. Also see
The Relationship Between Study Steps and Solver Configurations. You do not need to consider the settings in the
Time-Dependent Solver unless the simulation does not behave as expected. For example, the simulation behaves in an unexpected way when changing the end time, in case you may need to adjust the default settings for the time stepping and the tolerances. You may also need to output more time steps and use a strict time stepping and tolerance to fully resolve fast dynamics and to avoid aliasing effects.
Select a Time/parameter list method. This option only appears if there are active least-squares objective functions defined in the model. The default is
Manual, which means that the time list defined in the
Times field is used. The other possibility is
From least-squares objective, which means that the time list defined by least-squares objectives is used. If you use the latter possibility, you specify the
Initial time instead (the default is 0).
Select a Time unit from the list (default: s) to use a time unit that is convenient for the time span of the simulation. Then specify the time interval for the output from the simulation in the
Times field using the selected time unit. You can type a monotonically increasing list of individual values, for example,
0 1 2 5 10 20; use the
range operator, for example,
range(0,0.1,1.5), which (using seconds as the time unit) gives time steps from 0 to 1.5 s with a step size of 0.1 s; or use any combinations of such input.
When plotting the results from a time-dependent simulation, you can choose to plot the solution at any of the times specified in the Output times field. You can also plot an interpolated solution at any intermediate time. The interpolation used between times is a cubic Hermite spline; that is, the interpolation uses both the solution values and their time derivatives at two points: the closest output times before and after the time for which the interpolated solution is computed.
From the Tolerance list, choose
Physics controlled (the default) to use the tolerance suggested by the physics. Choose
User controlled to override the suggested relative tolerance with a value that you enter in the
Relative tolerance field. The tolerance settings control the internal time steps taken by the solver, so selecting large time steps for the output times does not affect the accuracy in the time stepping.
Select Adaptive mesh refinement from the
Adaptive mesh refinement list to activate time-dependent mesh adaptation. Then choose the geometry in which you want to use adaptive mesh refinement from the
Adaptation in geometry list. If you want to use adaptive mesh refinement in only part of that geometry, select the geometric entities for the adaptation in the
Geometric Entity Selection for Adaptation that becomes available below this section.
Under Mesh element control, choose a method from the
Adaptation method list:
Depending on the choices for these settings, see Adaptive Mesh Refinement (Time-Dependent Adaptation) for additional settings for adaptive mesh refinement in the
Adaptive Mesh Refinement subnode under the
Time-Dependent Solver node in the generated solver configuration.
From the Geometric entity level list, choose the geometric entity on which you want to do adaptive mesh refinement:
Entire geometry (the default),
Domain,
Boundary, or
Edge (3D only). For example, selecting
Boundary can be useful if the model includes a physics interface defined on boundaries (surfaces) and you want to base the adaptation on that physics interface. For all levels except
Entire geometry, select the geometric entities to include using the
Selection list and selection tools below.
Select the Automatic remeshing check box if you want the solver to remesh automatically when the quality of the mesh becomes poor in a Time Dependent study. Select the geometry to use for the automatic remeshing from the
Remesh in geometry list. With automatic remeshing active, the solver adds an
Automatic Remeshing subnode under the
Time-Dependent Solver node. In that subnode, you specify the mesh quality expression that determines when to remesh.