The research on interactions between water waves and floating structures with narrow gaps plays an important role in revealing the mechanism of hydrodynamic resonance in very large floating structures and side-by-side offloading ships. To investigate free-surface oscillations in two narrow gaps between three identical fixed rectangular boxes, a two-dimensional viscous flow numerical wave tank based on a constrained interpolation profile method is established. A tangent of hyperbola for interface capturing method is employed to capture the free surface, whereas a virtual particle method is used to treat the floating body surface. An internal wave maker is used for generating the incident waves. The computational results of wave height in narrow gaps are found in good coincidence with available experimental data, especially for the resonant frequencies. At the fundamental frequencies, the resonant wave heights both in both gaps are more than four times that of the incident wave height, whereas at the second resonant frequencies, they are about three times that of the incident wave height. In addition, the wave forces on the floating bodies are calculated. The fundamental frequencies of wave forces on the upstream body and downstream body are generally consistent with the fluid resonance frequencies in narrow gaps, whereas the frequency response of wave forces on the middle body happens at the second resonant frequency in the gap between the upstream body and the middle one.

INTRODUCTION

For an effective utilization of ocean space, very large floating structures (VLFS) are a good and potential solution, and they have triggered extensive investigations in last two decades, such as offshore airports, floating bridges, floating piers, disaster footholds, and so forth (Ohmatsu, 2005; Suzuki, 2005; Wang and Tay, 2011). In general, VLFS are composed of a number of modules that introduce narrow gaps between multimodules arranged side by side (Iwata et al., 2007). Besides, side-by-side offloading, such as a floating liquefied natural gas (FLNG) facility to an LNG carrier, drilling vessels, or offshore wind turbines, also forms a very narrow gap in offshore operations. The characteristic scales of the gaps are very small in comparison with the typical dimensions of those floating modules. The fluid resonance in the narrow gaps tuned by the incident wave induces large-amplitude wave run-up in the gaps and leads to a significant increase of wave forces on the adjacent modules, which can pose a serious threat to engineering safety. Therefore, it is of practical importance to investigate the resonance influence because of these gaps.

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