Fictitious masses are used to improve the accuracy and efficiency of modal-based structural analyses that involve substructure synthesis, local excitation, and local structural changes. New formulations, which allow easy applications in various subsequent analyses, are given for two categories of fictitious masses: regular and very large. Regular masses are of the order of entire substructures, whereas very large ones are several orders of magnitude larger. The regular fictitious masses are added to selected coordinates of the finite element model for normal-mode analysis, and then removed in a way that produces modes with local deformations near the selected points, in addition to the nominal natural vibration modes.
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