The Free Vibration of Elastic Plates in Asymmetric Contact with Water

Slamming of thin-walled structures into liquid pools presents a complex strongly-coupled fluid-structure interaction problem, whose understanding requires knowledge of the structural response of the coupled system. For our system of interest, the free vibration of three horizontally oriented aluminum plates (.4 m wide, 1.08 m long) are studied in two cases: one with the plate surround by air and the other with the plate’s bottom surface in contact with a large pool of water. Three plate geometries and mounting schemes are studied: i) a stepped plate with thickness varying from 12.7 mm to 6.35 mm mounted with pinned supports, ii) a uniform plate with 6.35 mm thickness also with pinned supports, and iii) a uniform plate with 4.83 mm thickness simply supported at one end and clamped at the opposite end. Digital Image Correlation (DIC) is used to track the vibrational response of the plate induced by striking it with an impact hammer. Two-degree-of-freedom displacements are collected from tracking the center target's motion. Time and frequency response plots are presented for comparison between half-wet and air cases. It is found that the added mass of the water results in lower measured natural frequencies and modified mode shapes. Preliminary center point displacement records show linear damped oscillator response with the plate in air and evidence of a nonlinear oscillator response in the half-wet case. Additional results are discussed.