CHARACTERISTICS AND APPEARANCE CONDITION OF FLUID RESONANCE IN A NARROW GAP BETWEEN MODULES OF VERY LARGE FLOATING STRUCTURE

Abstract

This study presents an appearance condition of resonant phenomena in a narrow gap between two modules of very large floating structure under waves. We apply a theoretical method for an estimation of natural frequency of fluid in a U-tube with different diameters to a theoretical development for the appearance condition. A natural frequency of fluid in the gap which is composed of a geometrical condition of floating structure, a gap width, a length of module, a draft and a water depth, is derived by energy conservation around a module on the side of incident wave. Then, the appearance condition is derived by substituting a dispersion relation of incident wave into the natural frequency of fluid in the gap as kl tanh kh=1 (k: incident wave number, l: geometrical condition of floating structure, h: water depth). A laboratory experiment is also conducted in order to understand characteristics of fluid resonance in the gap, and the validity of the appearance condition is verified by the arrangement of experimental results using kl tanh kh and l/λ(λ: wave length).