Mode pairing

Use Mode Pairing Control to automatically or manually pair reference and work normal modes, or use a combination of both methods.

You manually pair modes by entering the reference mode ID and work mode ID. Optionally, you can pair all the active reference modes by their sequential ID number using the Pair Modes Sequentially button. Manually paired modes override automatically paired modes.

You can pair modes automatically, by using:

• Sequential ID numbers.

• Frequency, where the difference between the frequency of the reference mode and the work mode is less than the frequency tolerance you specify.

• Modal Assurance Criteria (MAC) value, where the MAC value of a reference and a work mode shape is greater than the minimum value you specify. MAC value are between zero and one: one means that the two mode shapes are completely correlated and zero means that they are not correlated.

• X-Ortho magnitude, if the work solution contains a reduced mass matrix. The cross-orthogonality magnitude of a paired reference and a work mode shapes is greater than the minimum value you specify. The X-Ortho magnitude lies between zero and one: one indicates perfectly matching mode shapes and zero indicates perfectly orthogonal mode shapes.

To help you decide on the minimum MAC or X-Ortho value for automatic pairing, you can select any work or reference mode in the pairing viewer to display its MAC or X-Ortho values in red.

MAC numbers for a selected work mode	MAC numbers for a selected reference mode

When you pair mode sets, you can specify the master set.

• When the reference modes are the master modes, the algorithm processes each reference mode, searching for the best match from the work modes.

• When the work modes are the master modes, the algorithm processes each work mode, searching for the best match from the reference modes.

To export mode pairs to an Excel spreadsheet or a CSV file, in the Simulation Navigator, right-click the Mode Pairs [#] node, and select Export to Excel Spreadsheet or Export to CSV File.

Mode clusters

You can define clusters of repeated reference and work modes that exhibit similar mode shapes rotated around the axis of symmetry. You can identify modes to cluster by their almost identical natural frequencies, which indicates repeated modes. Side-by-side animations of the modes also help determine which modes should be grouped into which cluster. When you select this option, the pairing viewer does not trace the lines between the modes. The software re-computes the work mode shapes based on the shapes of the reference modes in each cluster, which results in a better MAC matrix.

Note:

Mode clusters are only supported for structural shape correlations.

Where do I find it?

Application	Pre/Post
Simulation Navigator	Right-click the Mode Pairing node→Edit

Look up more details

Modal Assurance Criteria (MAC)

Accounting for repeated modes

Quick links

Command reference

Pre/Post video examples

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Mode pairing, Simcenter 3D 2021.1 Series

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