Influence of the mode shape change from vacuum to fluid on the dynamic behavior of two submerged partially overlapped plates

Purpose In this article, a numerical method to evaluate the influence of the mode shape change from vacuum to fluid on the dynamic behavior of submerged structures is proposed. Design/methodology/approach The changed (real mode shape in fluid) and unchanged mode shapes (mode shapes in vacuum) are projected to fluid-structure interfaces, respectively. By making the interfaces vibrate in a harmonic motion with the projected mode shape, the added mass and added damping are calculated through the modal work approach. Different from the changed mode shape, an added mass updating mechanism needs to be applied to the unchanged mode shape case. By comparing the results with changed and unchanged mode shapes, the influence of mode shape change can be obtained. This method is applied to the in-phase and out-of-phase T(0,1) modes of two partially overlapped identical plates in still water. Findings Results show quite different influences on the in-phase and out-of-phase modes, which is attributed to the different influences of mode shape change on the flow field. The study also indicates that using the mode shape in fluid is essential for simulating the added damping accurately when applying the one-way fluid–structure interaction method. Originality/value The numerical method proposed in this article can also be applied to evaluate the influence of mode shape changes from vacuum to fluid of other submerged structures.