Common Study Step Settings
The study steps form a solver configuration that computes the solutions for the study. The study step nodes’ Settings windows contain the following sections (in addition to specific study settings for each type of study step):
The Study Steps Settings Windows’ Toolbar
On top of the study steps Settings windows, a toolbar contains the following commands:
Click Compute () or press F8 to compute the entire study.
Click Update Solution () or press F5 (when applicable) to update the current study. See Updating a Solution.
Study Settings
Include Geometric Nonlinearity Check Box
If you have a license for the Acoustics Module, MEMS Module, or Structural Mechanics Module (including any add-on modules such as the Nonlinear Structural Materials Module) and your model involves structural mechanics, then the Study Settings section includes an Include geometric nonlinearity check box.
Select the Include geometric nonlinearity check box to enable a geometrically nonlinear analysis for the study step. Some physics designs force a geometrically nonlinear analysis, in which case it is not possible to clear the Include geometric nonlinearity check box. For further details, see the theory sections for the respective physics interface in the applicable modules’ manuals.
Study Extensions
Reuse Solution from Previous Step List
This option is useful for parameters not handled with continuation. Select an option from the Reuse solution from previous step list.
No (the default for a Stationary study) to reset the solution to the initial values before each step or continuation sweep. The initial values will not be recalculated by the parametric solver for subsequent parameter values. Parameter dependence of the initial values can be accomplished by using parametric sweep.
Yes to always use the converged solution from the previous step, or the last solution from the previous continuation sweep (that is, never reset the solution).
Automatic (the default for a Frequency Domain study) to normally use the converged solution from the previous step or sweep. However, when multiple parameters are used, the solution from the first step of each parameter list is always used for the first step of the next list.
The difference between the three options is shown in Figure 20-2 for a 3 x 4 two-parameter sweep using the different choices for Reuse solution from previous step without continuation:
Figure 20-2: The difference between the three options for a two-parameter sweep without continuation.
When continuation is enabled by setting Run continuation for to one of the parameters, the converged solutions are always reused for the steps along the continuation sweep in this parameter. The setting for Reuse solution from previous step then determines how the solutions are reused between multiple continuation sweeps, if there are additional parameters to sweep over, as shown in Figure 20-3.
Figure 20-3: The difference between the three options for a two-parameter sweep with continuation.
For the Frequency Domain study, the auxiliary sweep is merged with the frequency sweep into a multiparameter sweep with the frequency as the parameter at the innermost level.
See About the Parametric Solver.
Results While Solving
Select the Plot check box to allow plotting of results while solving in the Graphics window. Then select what to plot from the Plot group list and, for time-dependent simulations, at which time steps to update the plot: the output times or the time steps taken by the solver. The software plots the data set of the selected plot group as soon as the results become available. You can also control which probes to tabulate and plot the values from. The default is to tabulate and plot the values from all probes in the Table window and a Probe Plot window.
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 include any probe.
Physics and Variables Selection
See Physics and Variables Selection for detailed information about this section. You can control and specify different cases where the physics interface to solve for is varied, or, for various analysis cases, which variables and physics features (for example, boundary conditions and sources) to use. The default is to solve for all physics interfaces that are compatible with the study type.
Values of Dependent Variables
When you have physics interfaces in a study step that you do not solve for but that provide degrees of freedom, you can specify how the COMSOL Multiphysics software handles the values of such degrees of freedom (dependent variables).
The settings in this section determine how the solver handles dependent variables that you do not solve for. This is applicable in, for example, a solver configuration where you only solve for a subset of the dependent variables in each step. You can also specify the initial values of variables that you do solve for.
By default, the COMSOL Multiphysics software determines these values heuristically depending on the physics as, for example, the specified initial values or a solution from an earlier study step. Under Initial values of variables solved for, the default value of the Settings list is Physics controlled. To specify the initial values of the dependent variables that you solve for, select User controlled from the Settings list.
The Initial values of variables solved for settings have no effect when using the eigenvalue solver.
Similarly, to specify the values of dependent variables that you do not solve for, select User controlled from the Settings list under Values of variables not solved for.
Then use the Method list to specify how to compute the initial values of variables solved for and the values of variables not solved for. Select:
Initial expression to use the expressions specified on the Initial Values nodes for the physics interface in the model.
Solution to use initial values as specified by a solution object (a solution from a study step).
Use the Study list to specify what study to use if Method has been set to Solution:
Select Zero solution to initialize all variables to zero.
Depending on the study type of the solution that you selected, you can choose different solutions from a list underneath the Study list:
For a Stationary study, from the Selection list, select Automatic (the default) to use the last (typically the only) solution, select First to use the first (typically the only) solution, select Last to use the last (typically the only) solution, select All to use all (typically just one) solutions from that study, select Manual to use a specific solution number that you specify, or select 1 to use the first (typically the only) solution. If you use a parametric continuation of the stationary study, there can be additional solutions to choose from.
For a Time Dependent study, from the Time list, select Automatic (the default) to use the solution for the last time, select First to use the first solution, select Last to use the last solution, select All to use all solutions from that study, select Interpolated to specify a time in the text field that opens and use the interpolated solution at that time, select Manual to use a specific solution number that you specify, or select one of the output times to use the solution at that time. For all the options in the Time list (except All), one solution is used throughout the whole simulation. This solution is computed once before the simulation. When you select All, an interpolation is done internally for time-dependent simulations.
For an Eigenvalue study, from the Selection list, select Automatic (the default) to use the first eigenvalue and its associated eigensolution, select First to use the first solution, select Last to use the last solution, select All to use all solutions from that study, select Manual to use a specific solution number that you specify, or select one of the eigenvalues to use the corresponding eigensolution.
For a parametric or Frequency Domain study, from the Parameter value list, select Automatic (the default) to use the first parameter value set or frequency, select First to use the first solution, select Last to use the last solution, select All to use all solutions from that study, select Manual to use a specific solution number that you specify, or select one of the parameter value sets or frequencies to use the corresponding solution.
The All option is not available from the list under Initial values of variables solved for.
Under Store fields in output, you can specify to store the field variables that you solve only for some part of the geometry (a boundary, for example, if the solution in the domain is not of interest). You define the parts of the geometry for which to store the fields as selection nodes. From the Settings list, choose All (the default) to store all fields in all parts of the geometry where they are defined, or choose For selections to choose one or more selections that you add to the list. Click the Add button () to open an Add dialog box that contains all available selections. Select the selections that you want to add and then click OK. You can also delete selections from the list using the Delete button () and move them using the Move Up () and Move Down () buttons. See also the Field node, where you can also control what to store in the output, if the corresponding Dependent Variables uses user-defined settings.
Mesh Selection
Specify — for each geometry — which mesh to use for the study step. For each geometry listed in the Geometry column, select a mesh from the list of meshes in the Mesh column. Each list of meshes contains the meshes defined for the geometry that you find on the same row.
Adaptation and Error Estimates
These are settings for mesh adaptation and error estimates, available for stationary, eigenfrequency, eigenvalue, and frequency-domain study steps. Depending on the type of adaptation, meshing sequences for the adaptive mesh refinements, using Adapt or Size Expression nodes, and corresponding solutions are created for inspection and possible modification. Error estimates are available as variables for postprocessing (for example, freq.errtot for the total error estimate in a Frequency Domain study). The adaptive mesh refinement solutions become available in a separate Solution data set (Study 1/Adaptive Mesh Refinement Solutions 1, for example). When using that data set for postprocessing, you can choose to use any of the available adaptive mesh refinement solutions from a Parameter selection (Refinement level) list.
From the Adaptation and error estimates list, select Error estimates if you want to use error estimation and select Adaptation and error estimates if you want to use adaptive mesh refinement. In the latter case, error estimates that are used in the adaptation algorithm are also available for postprocessing. Choose None for no adaptation or error estimation.
Adapt — the Adapt node in a mesh sequence also provides mesh adaptation. It includes a selection of geometric entities, which can be useful if you want to limit the mesh adaptation to certain geometric entities (some but not all domains, for example).
The software performs adaptive mesh refinement in one geometry only. Use the Adaptation in geometry list to specify that geometry.
Use the Error estimate list to control how the error estimate is computed:
Select L2 norm of error squared to use the squared L2 norm of the error. This is the only option for Eigenvalue studies. Use the Scaling factor field to enter a space-separated list of scaling factors, one for each field variable (default: 1). The error estimate for each field variable is divided by this factor. Also, the L2 norm error estimate is based on a stability estimate for the PDE. Use the Stability estimate derivative order field to specify its order (default: 2).
Select Functional and specify a Functional type. Available functional types are Predefined and Manual. This option adapts the mesh toward improved accuracy in the expression for the functional. Select Manual to specify a globally available scalar-valued expression in the Functional field. If you select Predefined, you can choose a Solution functional (Functional when doing error estimation) from the following list:
-
Integral
-
L2 norm
-
L1 norm
-
Approximate max norm
Select Error indicator to specify an error indicator using an error expression, which you add to the Error expression table below using the Add button. Select the Active check box for the error expressions that should be part of the error indicator. Use the Move Up, Move Down, and Delete buttons as needed to rearrange and remove error expressions.
By default, the software automatically determines the order of decrease in equation residuals on basis of the shape function orders in the geometry. To specify a residual order manually, select the Residual order check box and specify a nonnegative integer in the accompanying field (available when Error estimate is L2 norm of error squared or Functional).
From the Solution selection list, select which solution that should be used to evaluate error estimates:
Select Use last (the default for all study types except Eigenvalue) to use the last solution.
Select Use first to use the first solution.
Select All (the default for Eigenvalue studies) to use all solutions from that study.
Select Manual to use a specific solution number that you specify as solution indices in the Indices field.
In the Weights field (only available when Solution selection is Manual or All), enter weights as a space-separated list of positive (relative) weights so that the error estimate is a weighted sum of the error estimates for the various solutions (eigenmodes). The default value of 1, which means that all the weight is put on the first solution (eigenmode). That is, any omitted weight components are treated as zero weight.
From the Adjoint solution error estimate list (only available when Error estimate is Functional), select an error estimate method in the adjoint solution: a recovery technique or a gradient-based method. Select PPR for Lagrange (the default) to enforce using the recovery technique when possible, and select Gradient based to use the gradient-based method.
The Save solution on every adapted mesh check box is selected per default. Clear this check box if you do not want to save solution on every adapted mesh. In that case, the last two solutions are saved (the finest one and the second finest).
Under Mesh adaptation, the following settings are available.
Use the Adaptation method list to control how to adaptively refine mesh elements. Select one of these methods:
General modification, to use the current mesh as a starting point and modify it by refinements, coarsening, topology modification, and point smoothing. Use the Allow coarsening check box to control if mesh coarsening is used. If the mesh contains anisotropic elements (for example, a boundary layer mesh), it is best to disable mesh coarsening to preserve the anisotropic structure.
Rebuild mesh, to set up a size expression describing the error and rebuild the meshing sequence using the size expression as input. Note that structured meshes, such as mapped and swept meshes, in general are not appropriately refined. This method is not supported on imported meshes. The size of the refined mesh is the minimum of the size of the original mesh (previous refined mesh) and the size defined by the refinement. Specify the Maximum coarsening factor (a value of 3 by default) to scale the refined mesh size in the regions where refinement is not needed.
Regular refinement, to make the solver refine elements in a regular pattern by bisecting all edges of an element that needs refinement.
Longest edge refinement, to make the solver refine only the longest edge of an element by recursively bisecting the longest edge of edge elements that need refinement. This method is less suitable for models with nonsimplex elements. This is the default method.
Use the Element selection list to specify how the solver should select which elements to refine. Select:
Rough global minimum to minimize the error by refining a fraction of the elements with the largest error in such a way that the total number of elements increases roughly by the factor specified in the accompanying Element growth rate field. The default value is 1.7, which means that number of elements increases by about 70%.
Fraction of worst error to refine elements whose local error indicator is larger than a given fraction of the largest local error indicator. Use the accompanying Element fraction field to specify the fraction. The default value is 0.5, which means that the fraction contains the elements with more than 50% of the largest local error.
Fraction of elements to refine a given fraction of the elements. Use the accompanying Element fraction field to specify the fraction. The default value is 0.5, which means that the solver refines about 50% of the elements.
Use the Maximum number of adaptations field to specify the maximum number of adaptive mesh refinement iterations. The default value is 5 in 1D, 2 in 2D, and 1 in 3D.
Use the Maximum number of elements field to specify the maximum number of elements in the refined mesh. If the number of elements exceeds this number, the solver stops even if it has not reached the number specified in the Maximum number of adaptations field. The default value is 10,000,000 (ten million) elements.
Study Extensions
These are extensions to the study’s main solver, such as adaptive mesh refinement and automatic remeshing. The options vary depending on the study type.
Auxiliary Sweep
Select the Auxiliary sweep check box to enable an auxiliary parameter sweep, which corresponds to a Parametric solver attribute node. For each set of parameter values, the chosen Sweep type is solved for. This is available for Stationary, Time Dependent, and Frequency Domain studies.
Select a Sweep type to specify the type of sweep to perform:
Specified combinations (the default) solves for a number of given combinations of values as given for each parameter in the list. The parameter lists are combined in the order given, that is, the first combination contains the first value in each list, the second combination contains all second values, and so on.
All combinations solves for all combinations of values; that is, all values for each parameter are combined with all values for the other parameters. Using all combinations can lead to a very large number of solutions (equal to the product of the lengths of the parameter lists).
In the table, specify the Parameter name, Parameter value list, and (optional) Parameter unit for the parametric solver. Click the Add button () to add a row to the table. When you click in the Parameter value list column to define the parameter values, click the Range button () to define a range of parameter values. The parameter unit overrides the unit of the global parameter. If no parameter unit is given, parameter values without explicit dimensions are considered dimensionless.
If you choose Specified combinations, the list of values must have equal length.
An alternative to specifying parameter names and values directly in the table is to specify them in a text file. Use the Load from File button () to browse to such a text file. The read names and values are appended to the current table. The format of the text file must be such that the parameter names appear in the first column and the values for each parameter appear row-wise with a space separating the name and values and a space separating the values.
Click the Save to File button () to save the contents of the table to a text file (or to a Microsoft Excel Workbook spreadsheet if the license includes LiveLink™ for Excel®).
Loading and saving the parameter table data using Excel include the units in the Parameter unit column. The unit column is ignored when saving and loading parameter data to *.txt, *.csv, and *.dat files.
For a Stationary or Frequency Domain study, select an option from the Run continuation for list: No parameter or one of the parameters given in the list.