ABSTRACT

The hydroelastic response of an aircushion-type floating structure in waves is investigated by using the linear long wave theory and thin plate theory. The floating structure supported by aircushion is modeled as an elastic plate with finite breadth and infinite length, where the plate is sufficiently thin that the shallow draft approximation may be made(Namba and Ohkusu, 1999). The air in the aircushion is assumed incompressible ideal fluid. The thickness of the aircushion and the water depth are small enough that they may be approximated as shallow(Stoker, 1958). The amplitudes of water surface and deflection of the plate are assumed small enough that linearised theory is appropriate. The differential equation of the plate with the aircushion is derived, the characteristic equation of which is a fourth order equation in the wavenumber squared, which is solved using Ferrari's Formula. The dispersion relation implies two progressive waves, one is a shorter wave than the incident water wave in low frequencies and the other is a longer wave in high frequencies as well as a pontoon-type floating structure. Those two progressive waves suggest two kinds of refraction. The numerical results of response in waves with the model VL15 parameters show that the incident waves pass through the floating structure in most cases. Resonance of the structure is also shown.

INTRODUCTION

As a floating airport, pontoon-type VLFS(very large floating structure) and semi-submersible-type VLFS have been discussed recently. Many hydroelastic results to these VLFS subject to a train of waves have been reported. In this paper an aircushion-type floating structure is dealt with, the hydroelastic response of which in waves is investigated. The analytical method, which Ohkusu and Namba(1999) proposed for a pontoontype VLFS, is applied to the aircushion-type floating structure.

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