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Modal Analysis

Modal analysis finds the natural modes and mode shapes (the eigenvalues and eigenvectors) of a component or structure.

These are the theoretical natural frequencies of vibration with no damping applied, and so although one can tell the shape that would be adopted in a particular mode and the frequency at which it would occur, plus the stress and strain energy distribution, it is not possible to tell the overall amplitude, as theoretically it would be infinite with no damping.

Nevertheless conducting a modal analysis is still useful as it can show you whether there are likely to be any modes within the operating range of a machine. In some cases there is a requirement for the first mode to be above a certain value.

Example - 1st Four Modes of a Rudder

When doing a modal analysis it is important to include all the sources of flexibility and all the masses and inertias as these will all tend to affect the modes.

If you also want to know the amplitudes of vibration, then a second step has to be undertaken, which is to conduct a Forced Vibration analysis, where a forcing function of some kind is specified, and a damping factor is applied. (See Vibration Analysis)

Please contact us if you wish to discuss having a model analysis done for you.

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