Using Modal Expansion to expand measurements to a FEM

Modal Expansion noise and vibration solution allows you to expand vibration measurements from less detailed measurement points to a more detailed FEM mesh. You can then use the expanded modal information to perform other analyses using the FEM.

Vibration measurements may be displacements, velocities, or accelerations and may include both displacements and rotations. You can map the entire set of measurement data to a FEM or select only portions to be expanded to the structural mesh.

Vibration measurements are typically made at only selected points on a structure. A structural FEM mesh can be very detailed, so Modal Expansion allows greater use of measurement data in your simulations with a more complete description of the component's structural behavior. Vibration measurements may be displacements, velocities, or accelerations and may include displacements and rotations. You can map the entire set of measurement data to a structural model or select only portions to be expanded to the FEM.

• Add previously solved FEM mode shapes (Mode Set).

• Import and map vibration measurement points to related nodes in the Mode Set representation of the FEM mesh in the Model and Load Pre-processing Mesh Mapping.

• Create new Simcenter 3D Modal Expansion solution.

• Use the vibration measurements file and mapping table from Step 2 as input parameters in Modal Expansion.

• Solve the Modal Participation Factors (MPFs) between the vibration measurements and the mode shapes, and then use the MPFs to expand the solution onto the full FEM mesh.

Measurements at a few locations	Modal expansion of measurements to finite element mesh

Modal Expansion options

Modal Expansion has options to control the measurement data processing.

• Single value decomposition (SVDs): You can apply SVDs during the expansion to remove less meaningful data. If the measured vibrations are fewer than the number of available mode shapes, the SVD method will compute the best fit solution for the modal expansion.

• Skip Missing DOFs: When you are making test measurements, you might measure in one direction, such as in the Z-direction, and not in the X- and Y-directions. You can then filter the measurements to skip the missing X- and Y-direction displacements (or rotations, if applicable).

Subcases and sets

Modal Expansion supports one subcase per solution. With a Modal Expansion Subcase:

• You can apply a Reduced Vibration Set that combines the input vibration data and the mapping from the mode set to the FEM geometry.The FEM geometry can include nodes, 1D, 2D, and 3D PLOTELs.

• If the mapping table does not exist, it is assumed that there is already a correct one-to-one correspondence between the vibration data and the FEM.

Input file types

Valid input measurement file types are:

• Simcenter Nastran OP2 (.op2) files

• Simcenter Nastran SC_H5 (*.sc_h5) files.

• Simcenter Nastran universal (.unv) files.

• Simcenter Testlab (.lms) files.

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

Generating modal model results for a mode set

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)

Mapping measured or computed modes to a mesh

Expanding mode shapes to a mesh workflow

Quick links

Command reference

Pre/Post video examples

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Related Topics

Assembly FEM

Using Modal Expansion to expand measurements to a FEM, Simcenter 3D 2021.1 Series

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