Expanding mode shapes to a mesh workflow

You can use the Modal Expansion solution to map measured or computed mode shapes from an input mesh onto a reference finite element mesh in your simulation. You can then visualize the expanded modes in post-processing and use them in a hybrid structural or vibro-acoustic analysis of measured and computed results.

Before you begin:

• For the data source mesh, compute or measure the mode shapes and make sure that you have the results file in .op2 or .sc_h5 format. If the mode shapes are available in another format, you can use the Model and Load Pre-Processing solution process to convert them to an .sc_h5 file.Note: Make sure that the mode shapes to be expanded are detailed enough to represent an accurate structural behavior when mapped to the detailed mesh.Typically, you expand a mode shape from displacements if you will perform further analysis. Simcenter Nastran only supports mode shapes as displacements.

• For the detailed target mesh, create a SOL 103 Real Eigenvalue solution, select a frequency range or number of modes, and solve it.Note: Make sure that the mode set of the detailed mesh has enough detail to properly represent the mode shapes and frequency characteristics.

Modal Expansion Workflow
Step	Summary	Detailed help topic
1.	Open the Simulation file of the detailed mesh.
2.	Edit the FEM representation.	In the Simulation Navigator, right-click the FEM file and choose Edit Representation.Select Mode Set and set the mesh display options.	Replace a FEM file with a mode set or FRF set
3.	Create a Modal Expansion solution.	Set the Solver to Simcenter 3D Noise and Vibration.Set the Analysis Type to Structural.The Solution Type is automatically set to Modal Expansion.Click Create Solution.
4.	Edit or create the forcing frequencies modeling object.	Click Create Forcing Frequencies . If you do not define any frequencies, the software uses the input load or analysis frequencies of the input mode shapes.
5.	Edit or create the output requests modeling object.	Select an existing output request or click Edit or Create Modeling Object .Enable Displacement, Velocity, and/or Acceleration as output.Enable Modal Participation Factors.Note: Typically, you expand a mode shape from displacements if you will perform further analysis. Simcenter Nastran only supports mode shapes as displacements.	Modal Expansion Output Requests dialog box
6.	Set the singular value decomposition.	Set Relative Threshold for Singular Values % to filter the modal data.
7.	Edit the solution subcase.	Right-click Subcase – Modal Expansion and choose Edit.	Solution Step dialog box (Modal Expansion)
8.	Select mode shapes.	Select Mode Shapes as the Data Type.
9.	Select the data source.	In the Data Source group, select an existing input file or click Create Modeling Object to select a new one.
10.	Select the mode shapes file and mapping table file.	In the Mode Shapes dialog box, select a Mode Shapes File from the following file types:Nastran Results Files (.op2)Simcenter HDF5 Data File (.sc_h5) Note: The Mode Shapes File is associated with the FEM file that contains the coarse or measured mesh.Specify the Mapping Table from the following file types:Simcenter HDF5 Data File (.sc_h5) Test Files (.txt)Comma Separated Values (.csv)Note: The Mapping Table is associated with the FEM file that contains the detailed mesh and is typically a mode set file.	Mode Shapes dialog box (Simcenter 3D Noise and Vibration)
11.	Select the degrees of freedom to use.	Select the Degrees of Freedom to be used, and optionally set options to skip missing degrees of freedom based on a detection threshold percentage.Translation and RotationTranslationRotationSelect Skip Missing DOFs to ignore missing degrees of freedom, such as measurements that do not include some of the possible degrees of freedom, such as rotations.	Mode Shapes dialog box (Simcenter 3D Noise and Vibration)
12.	Solve the solution.	Right-click the Modal Expansion solution and choose Solve.	Solve dialog box
13.	Post-process the results with Post-Processing Scenario.	Right-click Results and choose Post-Processing Scenario.	Scenario-based post-processing

Learn more

Mapping measured or computed modes to a mesh

Expanding vibration measurements to a mesh workflow

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Expanding mode shapes to a mesh workflow, Simcenter 3D 2021.1 Series

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