ABSTRACT

The hydrodynamic characteristics of side-by-side moored multiple bodies were studied with the higher order boundary element method(HOBEM). Hydrodynamic coefficients, motion response amplitude operator(RAO) and drift force RAO for multi-bodies were calculated and compared with those of one vessel's cases. Discussion was highlighted on gap flow, shielding and amplifying effects due to existing of multiple vessels. It has been shown that unrealistic peaks were emerged at the vicinity of the gap flow resonance frequency. This exaggerated gap flow was reduced by adopting the artificial body boundary condition. It has been also shown that sheltering and amplifying effects has an insignificant effect on FLBT while other vessels are effected dramatically.

INTRODUCTION

Demand of energy has been increased steadily and the environmental pollution have been recognized as an important global issue, natural gas became the promising energy resource in the future. Since an onshore LNG(Liquefied Natural Gas) terminal has a potential danger of explosion, new concept of offshore LNG terminals have developed recently. FLBT(Floating LNG Bunkering Terminal) can receive LNG from LNG carrier, hereinafter LNGC, and unload LNG to LNG bunkering shuttles, hereinafter LNG BS, on the sea. During the LNG transfer process, LNGC and LNG BSs are located closely to FLBT and they are moored to FLBT by mooring ropes and fenders. In order to guarantee FLBT's motion stability and the structural reliability of the ship-to-ship mooring system, it is necessary to identify the deviation of hydrodynamic characteristics when four vessel are positioned closely.

Many researchers have studied in hydrodynamic interactions between multiple vessels. To name a few, Buchner and Loots (2004) studied the hydrodynamic performance of the two vessels side-by-side moored in close proximity. Several related researches predicted gap flow resonance frequencies by the analytic solution for a rectangular moon-pool, which was derived by Molin (2001). Comparison between the numerical and experimental studies of drift forces on a FPSO and a shuttle tanker floating side-by-side were performed by Hong et al.(2005). Several studies indicated that the gap flow effect is exaggerated at the vicinity of sloshing modes of the gap. Various methods have been utilized in order to reduce those unrealistic peaks. The rigid lid method has been presented by Huijsmans et al. (2001) and this method was utilized by researchers in MARIN, located in Netherlands. Zalar et al. (2007) adopted an artificial body damping in the radiation body boundary condition, which method was utilized in Hong et al.(2013).

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