Should the participation factors reported in the mode coefficient table after a spectrum analysis always be positive?


March 17, 2023 at 9:00 amFAQParticipant
No. The sign has an equal probability of being positive and negative. The participation factor is used to determine how much of the mass of a certain mode is moving in the same direction as the excitation. The excitation direction is defined in a spectrum analysis with the SED command. The participation factor formula given in Theory Manual is the mode shape transposed times the mass matrix times a vector of ones that are associated with the direction of excitation. The negative of a mode shape is a valid solution, so the participation factor can be negative. The effective mass of a mode is its participation factor squared.

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