COMSOL 6.3 - Stationary Solver

) to find the solution to linear and nonlinear stationary problems (also called static or steady-state problems). This solver is automatically used when a Stationary or Frequency Domain study is added to the model.

Also see About the Stationary Solver for information about Damped Newton Methods, Linear Solvers vs. Nonlinear Solvers, and Pseudo Time Stepping.


	When used under an Optimization Solver node, some of the settings below are instead available in the settings for the Optimization Solver node.

General

Use the list to specify if the settings are synchronized with the corresponding study step.

The number in the field (default: 0.001) is used for tolerance-based termination of iterative solver processes and for error checking (if enabled) for direct linear system solvers. To specify it here, you need to select from the list.


	The termination tolerance used for iterative processes is also influenced by values specified in the Tolerance factor fields present in active Fully Coupled, Segregated, and Segregated Step subnodes. See Termination Criterion for the Fully Coupled and Segregated Attribute Nodes for details.

Use the list to specify whether to use a nonlinear or linear solver. Select:

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to perform an analysis that automatically detects if the problem can be solved with a linear solver approach. If this option is selected, no other settings are required.

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to use a linear solver. When the Fully Coupled solver is used with Automatic or Constant damping (the damping is equal to 1), this option uses the same linearization point for both residual and Jacobian computation and corresponds to one step in Newton’s method. If the damping is not equal to 1 and the Termination technique allows for more than one iteration, then an iterative approach will be used; the residual will be reassembled for the updated solution, but the Jacobian will be kept fixed. Notice that if this approach converges, it will converge to the solution to the problem at hand, which can be nonlinear. When a Segregated solver is used, and the Termination criteria allows for more than one iteration, then an iterative approach will be used that is very similar to the Fully Coupled solver, where the residuals for the individual segregated steps are reassembled with the updated solution while the Jacobians are kept constant from its initial assemble using the Linearization point.

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to use a linear solver. This option computes the Jacobian in the same way as the option but include only special weak contribution terms when assembling the residual. Only terms encapsulated by the linper operator are included. This option is useful for small-signal analysis and similar applications where the variations around a linearization point are of interest.

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to use a nonlinear solver. If this option is selected, no other settings are required.

Values of Linearization Point

If or is selected, COMSOL assumes that the problem to be solved is a linearization about a solution. Specify such a solution (a linearization point) using the list. Select:

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to use the expressions specified on the nodes under a specific physics interface as a linearization point.

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to use a solution as a linearization point. Use the list to specify which solution to use if has been set to . Select:

to use a linearization point that is identically equal to zero.

Any other solution to use it as linearization point. It can be the current solution in the sequence or a solution from another sequence or a solution that was stored with the Solution Store node. You select a stored solution by changing to the name of the stored solution.

Select the checkbox to store the used linearization point. Also see Linear Solvers vs. Nonlinear Solvers.

Variables

This section is only visible when the study contains a Stationary Then Eigenfrequency study step. It can be used to specify which dependent variables are computed with the Stationary solver. The same dependent variable cannot appear in the equivalent section of the Eigenvalue Solver, control variables excepted.

Output

Select the checkbox to compute and store reaction forces in the output.

The computation of boundary flux variables involves solving a system of equations to obtain a continuous field from nodal flux values. If the checkbox is selected, this system of equations is lumped. The benefits of using this option is that it can avoid certain spurious oscillations in the computed flux field and that it is slightly faster. Lumping is not suitable in 3D for shape functions of order higher than 1.

Results While Solving

This section is not available in the following cases:

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When you add a Stationary Solver as a subnode to an Optimization node.

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In nested parametric sweeps, it is only available for the innermost sweep.

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When you use one of the following sweep study types: Function Sweep, Material Sweep, Batch Sweep, and Cluster Sweep.

To enable these settings, select from the list under . Select the checkbox to allow plotting of results while solving in the window. Then select what to plot from the 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 dataset 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 window and a window.

Use the list to select any probes to evaluate. The default is , which selects all probes for plotting and tabulation of probe data. Select to open a list with all available probes. Use the (

), (

), and (

) buttons to make the list contain the probes that you want to see results from while solving. Select to not include any probe.

Constants

In this section you can define constants that can be used as temporary constants in the solver. You can use the constants in the model or to define values for internal solver parameters. These constants overrule any previous definition (for example, from Global Definitions). The constant values are expressions and can, for example, include the range() operator, units, and global expressions. The constant name can be a new or an existing global parameter. The constant is temporary in the sense that it is only defined during the solver run. You cannot override parameters used in the following parts of the model:

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Parameter-dependent lists

Also, the Parametric and Time Dependent solvers overrule any definition of solver constants.

Constants settings for a solver node do not carry over to postprocessing.

Some examples of when it can be useful to define constants for a solver:

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When doing more advanced solver sequences, where constants need to be changed between calls (for example, in for-loops).

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When you do not want to change the global definition of a parameter or when you cannot or do not want to use a Parametric Solver feature.

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When you want to define auxiliary parameters that are part of the equations like CFLCMP or niterCMP and where the solver does not define these parameters.

Click the button (

) to add a constant and then define its name in the column and its value (a numerical value or parameter expression) in the column. By default, any defined parameters are first added as the constant names, but you can change the names to define other constants. Click (

) to remove the selected constant from the list.

Log

This section, which is initially empty, contains a log from the time stepping. It is not available when the stationary solver is a subnode to another solver. This log is stored in the Model MPH-file. Select the to keep warning messages in this log so that the information in those warnings is also available when reopening the model.

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Automotive Muffler: Application Library path

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Deformation of a Feeder Clamp: Application Library path


	The Log Window