ABSTRACT:

In this paper, the sloshing effect on the roll motion of a two-dimensional rectangular box in regular waves is studied experimentally and numerically. First, we carry out experiments for a rectangular model with different filling ratios in a 2D flume. The roll motion is measured by a video camera, which can trace two different marks on the model very accurately. The steady-state roll motion is filtered out by a post process. It is found experimentally that the roll response shows a peak at the roll natural frequency and an abrupt change but with a small magnitude at the lowest sloshing natural frequency. The multi-modal method is applied to describe the free surface in the box and the resulting sloshing moment is estimated numerically. The roll motion of the model is calculated by using an in-house code based on the linear potential theory. It is found that the leading-order solution over predicts the roll motion at the sloshing natural frequencies compared to the experimental data. The next-order method gives an improved solution at the second sloshing natural frequency, but still over predicts at the lowest sloshing natural frequency.

INTRODUCTION

As clean energy has become an important global issue in the 21st century, the demand for natural gas has largely increased. In accordance with such a trend, natural gas starts to be exploited and explored even in deep waters, which implies the development of new production systems like LNG-FPSO. Meanwhile it is nowadays not easy to construct new LNG receiving terminals on land near shore, hence the new concept of LNG receiving terminals like LNG-FSRU is proposed and designed. In both cases of LNG-FPSO and LNG-FSRU, the structure is of floating type and it in general undergoes 6DOF motions under the action of incoming waves.

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