A numerical study of the influence of the wave reflection on the hydrodynamic characteristics of a cylinder with moonpool

Abstract

We develop a new numerical model based on eigenfunction matching method and the method of images to investigate the influence of tank wall reflection on the hydrodynamic behaviors of a cylinder with moonpool, which is defined as an opening from the deck to the bottom of a floating structure or ship. The new numerical model is first validated by comparing its results to experimental data in the existing literature and WaveAnalysisMIT results and then is used to analyze the effects of different tank widths on the heave radiation and diffraction problems. When the tank is not too narrow, the results only show a significant difference from those in open water around the transverse sloshing frequencies of the tank, i.e., when the tank width is an integer times the wavelength. It is noticed that the reflection effects induce spikes of the amplitude of free-surface elevations at the center of the moonpool in the radiation problem but induce troughs in the diffraction problem. This is explained by estimating the phase of the waves in moonpool induced by the wall reflections. For the narrow tank that does not allow transverse sloshing in the given frequencies, the results deviate from those in open water in a width range of frequencies. The free-surface elevations outside the cylinder are also investigated.