Experimental analysis of the wet flexural mode response of an NPL 6A hydroelastic segmented model

Abstract

This paper investigates the effects of stiffness and mass distribution on the longitudinal flexural natural frequency response of an NPL 6A segmented monohull model in still water at zero speed. Experimental tests were undertaken in order to establish the parameters that affect the whipping frequency at model-scale so as to replicate the vibratory response of a full-scale vessel subject to slamming. The model was cut into two halves at the longitudinal centre of buoyancy and connected by a backbone beam with an elastic hinge joining the two segments. Wet vibration tests conducted on the model showed significant influences on the flexural natural frequency response through variations in stiffness and ballast mass distribution. The whipping frequency was predicted with a two degree of freedom theoretical model using an added mass approximation to provide good correlation with measured experimental data. Damping ratios of the wet transient response are also presented with respect to variations in the condition of the void separating the two model halves.