Generating modal model results for a mode set

Before you can replace a component FEM file with a mode set, you must first generate the modal model results for that component.

• In the FEM file, define a mesh. In some cases, you may want to create visualization elements, such as Nastran PLOTEL elements (available as 1D, 2D, and 3D elements). You can use visualization elements to define the model's outline, or specific areas of interest, as visualization features. You can also create a group of PLOTEL elements to control the displacement output.For more information, see Visualization elements (PLOTELs) in assembly FEM files.

• In the Simulation file, compute the modal results using an appropriate solution, such as a Simcenter Nastran SOL 103 Real Eigenvalues solution.

The following workflow describes this process.

Step	Summary	Detailed help topic
1.	In a FEM file, create any desired PLOTEL elements.	Use PLOTEL elements to visualize a complex model or to select output results on nodes.Create a group of desired PLOTEL elements to use them later to control displacement output.	Visualization elements (PLOTELs) in assembly FEM filesGroups
2.	Create a Simulation file.		Create a new Simulation file
3.	In a Simulation file, create a structural or vibro-acoustic SOL103 Real Eigenvalue solution.	For example, set Solver to Simcenter Nastran, Analysis Type to Structural or Vibro-acoustic, and Solution Type to SOL103 Real Eigenvalues.	Create or modify a solution
4.	On the Case Control tab, activate Residual Vectors.	Activating Residual Vectors can result in greater accuracy, which may be useful for large models.	Reduce response errors with residual vectors
5.	Create the frequency range or number of modes.	Edit the solution to create the desired frequency range, or number of modes, for the solution.	Real Eigenvalue (Lanczos or Householder) dialog box
6.	Enable valid structural output.	In the Structural Output Requests dialog box:Click Disable All to clear all default outputs.On the Displacement page, select the Enable Displacements check box. Displacements are the only valid results of a modal model.You can also select the Group Reference check box, and on the Group tab, select the name of any desired PLOTEL group.	Requesting output for Nastran analyses
7.	Create desired structural constraints.	Constrain the model and add the constraint set to the solution.Note: If the model is unconstrained, and you set the lowest frequency to remove rigid body modes, this step is unnecessary.	Define user-defined constraints
8.	Solve the solution.	Simcenter Nastran computes the mode shapes and natural frequencies.	Solve the model
9.	Post-process the analysis results to ensure the solution results are correct.	You can display Mode Sets using standard post-processing or the post-processing scenarios.	Scenario-based post-processing
10.	Save the FEM and Simulation model.

How do I

Displaying alternate FEM representations

Replace a FEM file with a mode set or FRF set

Editing modes or functions in mode sets and FRF sets

Edit a mode set or FRF set

Learn more

Mode sets

Controlling mesh creation for mode sets

Replace a component FEM file in an assembly FEM with a mode set

Plot mode, ATV, or VATV set contours

Mode set theory and damping

Viscous and structural damping values in mode sets (Simcenter Nastran)

Using Modal Expansion to expand measurements to a FEM

Mapping measured or computed modes to a mesh

Expanding mode shapes to a mesh workflow

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Related Topics

Assembly FEM

Generating modal model results for a mode set, Simcenter 3D 2021.1 Series

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