ABSTRACT:

In this study, ship motions coupled with liquid sloshing are obtained using boundary element methods. Both the ship motion and sloshing problems are considered in linear regime. To couple the two problems, two different methods are applied: a combined wave Green function method and Rankine panel method based on frequency-domain formulation, and a Rankine panel method based on time-domain formulation. From this study, it can be shown that the linear analysis is acceptable with reasonable accuracy for the prediction of global motion response. Therefore, it can be used as a practical tool to prescreen the coupling effects of ship motions and sloshing.

INTRODUCTION

In ships with liquid cargos, ship motion and sloshing inside cargos react on each other. This means that ship motion and sloshing flow are not independent. So their coupling effects should be considered when any solution of ship motion and sloshing flow is needed for practical ship and/or cargo design. Especially for some ships such as liquid natural gas carriers, LNG floating production, storage and off-loading units (FPSO), sloshing effects have large influence because the size of liquid tanks are large and the natural period of sloshing flow can be close to that of ship motion. In recent years, some studies on the coupling analysis have been introduced by such as Kim(2002), Rognebakke and Faltinsen(2003), Newman(2005), Kim and Shin(2008) and Nam et al.(2009). In these studies, some researches adopted frequency-domain approaches based on linear potential theory. Some other researches considered nonlinear sloshing flow by time-domain approaches (e.g. Kim, 2002; Kim et al., 2007; Nam et al., 2009). Many of the time-domain approaches were based on a hybrid concept which couples linear ship motion and nonlinear sloshing flows. In this paper, the coupling effects of sloshing and ship motion are considered by both frequency-domain and time-domain approaches.

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