Modal analysis of close modes using perturbative sensitivity approach

Problems of very close modes often arise in engineering practice due to structural symmetries or large-scale repetitive structures with little damping, and accurate determination of the modal parameters of such modes is very important in response and stability calculations, such as those of large flexible aerospace structures. Conventional modal analysis techniques can be used to extract accurate modal parameters when the two modes of interest are moderately close. They become inapplicable, however, when two very close modes exist. In this paper, a new method for the estimation of modal parameters of very close modes is presented. By perturbing the structure using mass or stiffness modifications, the proposed method separates the two very close modes so that they can be accurately analysed. Then the modal sensitivities are determined from which the required modal parameters of the two very close modes of the test structure can be accurately estimated. The proposed method has been applied to numerically simulated receptance data of a plane structure as well as practically measured receptance data of a plate-like structure. Analysis results have demonstrated the practicality of the proposed method.

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