THE EFFECT OF MODAL COUPLING IN RANDOM VIBRATION ANALYSIS

When modal analysis techniques are used to determine spectral densities of the responses of distributed-parameter linear mechanical structures subjected to stationary random excitation, a summation of all modal spectral densities (both direct- and cross-) should be performed. A very common textbook recommendation is that the modal cross-spectral densities may be neglected if certain conditions are satisfied. In this paper that recommendation will be discussed. Using a simple example the influence of modal cross-spectral densities on the spectral densities of some responses of a simply supported beam will be investigated. Response standard deviations will be determined and the importance of the modal cross-spectral densities in some frequency ranges, covering also resonance frequencies of the beam, will be demonstrated. Special interest is devoted to extreme values of some response processes.

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