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.

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.

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 check 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.

When plotting the results from a time-dependent simulation, you can choose to plot the solution at any of the times specified in the 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.

Select the Plot check box to allow plotting of results while solving. Then select what to plot from the Plot group and Update at lists. The software plots the dataset of the selected plot group as soon as the results become available either at the times specified by the output times (from the Times field) or at a set of internal times defined by the solver. Select Times stored in output (the default) or Time steps taken by solver from the Update at list.

Use the Probes list to select any probes to evaluate. The default is All, which selects all probes for plotting and tabulation of probe data. Select Manual to open a list with all available probes. Use the Move Up (), Move Down (), Delete (), and Add () buttons to make the list contain the probes that you want to see results from while solving. Select None to not evaluate any probe. For the probes, you also select Times stored in output or Time steps taken by solver (the default) from the associated Update at list at the bottom of the section.

Select the Adaptive mesh refinement check box 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.

See Adaptive Mesh Refinement 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, make a selection of the geometric entities to include using the Selection list and selection tools below.

This section contains some optional extensions of the study. The options are mutually exclusive and only one of the check boxes can be selected. See Auxiliary Sweep for its settings. Auxiliary sweeps are not available when the Time/parameter list method in the Study Settings section is set to From least-squares objective.

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.