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When modelling the dynamic response of an existing structure to predict the effects of design modifications, many types of forces are difficult to characterize, e.g., those due to unsteady flows or acoustic excitation. To model the forcing function in such cases, a method is presented which solves for an equivalent forcing function based on sound power measurements. The method assumes that the equivalent forcing function may be represented with a superposition of force distributions on a mode-by-mode basis, i.e., there is one force distribution per eigenvalue with the shape of the eigenvector. The method is applied to cases where the structure is lightly damped and has low modal density. Experimental results show that the method accurately predicts the effect of design changes on the structure's radiated sound power. The accuracy of the method is sensitive to small differences between the experimental and theoretical natural frequencies and thus it is important to match the damped natural frequencies of the physical structure as accurately as possible. |
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