Use the Modal Solver (
) to perform either parameter stepping (also called frequency response) or time stepping (also called transient response) using a reduced model. The model reduction uses precomputed eigenvalues and eigenvectors. This solver is automatically used when a
Time Dependent, Modal or
Frequency Domain, Modal study is added to the model.
Use the Defined by study step list to specify if the settings are synchronized with the corresponding study step, or select
User defined to specify all settings locally.
Use the Study type list to select the basic study type. Select:
For a Frequency Domain, Modal study, use the
Parameter values field to enter a vector of parameter values that define the parameter value span for the frequency-domain simulation. Click the
Range button (
) to define a range of parameter values using the
Range dialog box.
An alternative to specifying parameter values directly in the Parameters values field is to specify them in a text file. You can use the
Load parameter values field and the
Browse button to specify such a text file. Click the
Read File button to read the specified file. The read values appear in the
Parameters values field.
Use the Parameter list type list to control how to interpret the parameter values entered in the
Parameter values field. Select:
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Frequency (the default setting) to use the parameter values without modification.
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Fraction to multiply the parameter values by the absolute value of the largest eigenvalue in the reduced model divided by two.
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Spread to treat the parameter values as an interval around each eigenvalue in the reduced model. That is, the absolute value of each eigenvalue is multiplied by the parameter values and the resulting parameter value vectors are concatenated into one.
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Use the Linearity list to specify the type of linear behavior. Select:
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Linear to use a linear solver with the same linearization point for both residual and Jacobian computation, which corresponds to one step in Newton’s method.
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Linear perturbation (the default setting) to use a linear solver that computes the Jacobian in the same way as the Linear option but uses a zero solution when computing the residual. It is useful for small-signal analysis and similar applications where the variations around a linearization point are of interest.
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For a Time Dependent, Modal study, select a
Time unit from the list. Then use the
Times field to enter a vector of times that define the time span for the simulation. Click the
Range button (
) to define time values. Output from a simulation includes the times given in this field and the corresponding solutions.
Use the Relative tolerance field to enter a positive number (default value: 0.01). Depending on the selection in the
Study type list in the
General section, the tolerance means one of the following:
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When a Frequency Domain, Modal study is selected, the Relative tolerance is used as a termination tolerance for iterative linear system solvers and for error checking (if enabled) for direct linear system solvers.
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When a Time Dependent, Modal study is selected, the Relative tolerance is used by the solver in each time step to control the relative error. The absolute tolerance settings below work in the same way as for the time-dependent solver, but internally the full length absolute tolerance vector is transferred to the modes by the same transformation (projection) as is used to transform the problem to reduced form (the eigenmodes).
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For the maximum time step, select an option from the Maximum step constraint list. By default, the solver chooses a maximum time step automatically. Select
Constant as the maximum step constraint for manual specification of a fixed maximum time step in the
Maximum step field. A constant maximum step constraint is a positive scalar value, which can be an expression that evaluates to a numerical value before entering the solver. The expression can include global parameters. Select
Expression as the maximum step constraint for more general expressions of the allowed maximum time step. These expressions are evaluated while solving and can, for instance, depend on the time parameter itself.
Use the Solution list to specify a solver configuration to be used when constructing the reduced model.
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The Use list is available for solution sequences with additional stored solutions. When available, select an option to specify a solution containing the modes to be used in the reduced model.
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Use the Eigenpairs list to specify which of the eigenpairs present in the solution to include when constructing the reduced model. The default setting is
All and the solver uses all available eigenpairs. Select
Manual to enter a space-separated list of
Eigenpair numbers in the field.
Use the Damping ratios field to enter either a scalar value or a space-separated list with values. The total number of entered values must be one or equal to the number of eigenpairs in the reduced model. If one number is entered, that value becomes the damping ratio for all eigenpairs. If the field is empty (the default), no damping is applied by the solver.
A frequency-domain problem solved by the Modal Solver is assumed to be a linearization about a solution. You can specify such a solution (a linearization point) with the
Prescribed by list. Select:
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Initial expression to use the expressions specified on the Initial Values nodes under a specific physics interface as a linearization point.
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Solution to use a solution as a linearization point. Then, when Solution is selected from the Prescribed by list, specify which solution to use . Select:
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Zero to use a linearization point that is identically equal to zero.
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Select the Store linearization point and deviation in output check box to store the used linearization point in the output.
If Reduced matrices is selected, click to select the check boxes corresponding to matrices and vectors that should be stored in the output. The following matrices and vectors can be exported for all modal solvers:
Stiffness matrix,
Damping matrix,
Damping ratio matrix,
Mass matrix,
Projection matrix,
Load vector,
Input matrix,
Output matrix,
Output bias, and
Input feedback matrix. For Time Dependent, Modal studies the following can also be exported:
Time derivative input matrix,
Second time derivative input matrix,
Initial value vector,
Initial derivative vector,
Initial value input matrix,
Initial value time derivative input matrix,
Stiffness matrix times ud, and state-space matrices (
Mc,
MA,
MB,
Null,
D,
C,
ud, and
x0). For Frequency Domain, Modal studies the following can also be exported:
Mass matrix times particular solution,
Damping matrix times particular solution, and
All load vectors.
Use the Load factor field to enter a globally available scalar-valued expression (default: 1). The solver uses this expression to multiply the residual. The purpose is to facilitate the use of simple nonconstant Dirichlet boundary conditions (for frequency response) and simple nonconstant Neumann boundary conditions (for transient response).
Click the Add button (
) to add a constant and then define its name in the
Constant name column and its value (a numerical value or parameter expression) in the
Constant value column. By default, any defined parameters are first added as the constant names, but you can change the names to define other constants. Click
Delete (
) to remove the selected constant from the list.
Select the Keep warnings in stored log check box if you want the warnings to remain in the log for troubleshooting or other use.