About Modal Contribution

When performing Evaluate FRF or Evaluate Transmissibility, you can use the Modal Contribution option to determine the individual normal mode frequencies that contribute most to the overall amplitude and phase at selected input frequencies. The software generates a response function for each input frequency and output node or element you select. The results are displayed in a polar plot.

Selecting input frequencies

You can select input frequencies for the modal contribution evaluation by:

• Selecting points on a plotted function. For example, suppose you have a previously generated response function that has peaks where you want to evaluate the FRF.

• Selecting from a list of the normal mode frequencies.

• Combining the above two methods. For example, you can compare the contribution of a previously generated response function to a normal mode frequency.

Displaying maximum contributors

Use the Generate Maximum Contributors Only option to limit the points in the modal contribution results to only the largest-contributing modes. You can specify how many modes to include in the Number of Contributors box.

For example, if the number is 5 (the default number), the generated response function will contain six points: a mode 0 point that represents the total amplitude from all the modes (all the modes in your solution results—not just the sum of the largest contributors) and five points for the five modes that contribute the most to the response.

Polar plot display

The contributions of the selected input frequencies are displayed in a polar plot, which displays the complex numbers in a circular grid representing amplitude and phase angle. Each arrow on the polar plot represents a normal mode frequency (the X value is the mode ID) and output node or element on the model.

In the following example, the arrows have been marked using Probing Mode, which lets you more easily read the mode ID, the magnitude, and phase angle.

Arrows are displayed in different colors and formats (such as a dashed line) for each output node or element at each input frequency. In the next example, the solid red arrows represent modal frequencies at one output node on the model and the dashed blue lines represent the modal frequencies at a second output node.

Note:

One of the solid red arrows represents the total amplitude.

How do I

Evaluate FRF or Transmissibility

Learn more

FRF and Transmissibility

Quick links

Command reference

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About Modal Contribution, Simcenter 3D 2021.1 Series

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