In this paper a comparison between model basin experiments and results of linear diffraction computations on side-by-side moored LNG carriers is presented. The computations are based on a variation of the damping lid method in diffraction codes to suppress non-realistic high wave elevations between two floating objects in close proximity. The damping lid method was originally formulated by Chen (2005). In the original method damping is added to the free surface between the vessels. In this paper, an alternative approach is used, in which damping is also applied to the free-surface inside the vessels, instead of the traditional rigid-lid approach. This method reduces the grid dependency and provides a better comparison with model tests results.

INTRODUCTION

Liquefied Natural Gas (LNG) is becoming a more important source of energy. LNG carriers can be used to transport the cargo from the offshore production platform to the shore or from terminal to terminal. Offshore floating LNG systems become a more and more economic viable solution. Due to the cryogenic nature of the LNG the offloading is not yet done with floating hoses. Loading arms with a short reach are currently used on jetties. The short reach of those loading arms requires the LNG carrier to moor side-by-side to the LNG terminal or production platform during offloading operations. The economics of a terminal or production platform are directly related to its availability; the percentage of time the approach of the LNG carrier, berthing, on- or offloading and sail away can take place successfully. A thorough understanding of the hydrodynamics of the two floating bodies in close proximity is necessary to identify if criteria of successful operation can be met. Linear diffraction analysis, based on potential theory, can be used to calculate vessel response in waves. Discrepancies are observed in results of diffraction analysis of two floating bodies in close proximity.

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