Mode pairing and shape correlation methods

In the model update solution process, to pair reference and work normal modes automatically or manually, use Mode Pairing Control. You cannot combine the pairing methods: use the same method to pair all modes.

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.

You can pair modes automatically, by using the:

• 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. A MAC value is 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 paired reference and a work mode shapes is greater than the minimum value you specify. X-Ortho magnitude lies between zero and one: one indicates perfectly matching mode shapes, and zero indicates perfectly orthogonal mode shapes

Reference modes are always used as masters for pairing in the Model Update solution process.

In the Model Update group, you can set the shape correlation method as MAC or X-Ortho when the pairing method is set to Manual. It is not possible to change the shape correlation method for the MAC or X-Ortho pairing method because the shape correlation method is identically set.

Mode Tracking

During optimization, the software re-computes modes at each step and pairs the modes according to the selected pairing method. When you set the pairing method to Manual, the pairing process ignores the mode shapes. Instead, the solver uses the mode tracking to determine the new frequency of a mode based on its previous natural frequency and on the frequency sensitivities: \lambda_t = \lambda_0 + \sum_{i=1}^N{(DV_i - 1.0) \frac{\partial \lambda_0}{\partial DV_i}}

Where DV_i is design variables.

Where do I find it?

Application	Pre/Post
Prerequisite	An active Model Update solution process
Simulation Navigator	Right-click the Mode Pairing node→Edit

How do I

Modify the mode pairing and shape correlation method

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Mode pairing and shape correlation methods, Simcenter 3D 2021.1 Series

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