ABSTRACT

The motion of liquid cargo inside ship tanks is mainly studied because of the impact on the structural design of tank walls. Many effects such as sloshing, trapped waves, breaking waves occur inside a tank and the problems caused by these are more than simple structural issues. In this work the influence of the liquid cargo motion inside the tanks in the ship motion will be studied. Comparing potential models in frequency domain with experimental data (Rocha, TP et al, 2015) it was observed that for some filling percentages the results do not present good agreement, mainly below 15%. So, a time domain model was proposed. This time domain model uses the Numerical Offshore Tank code to integrate the involved forces. The idea is to separate the terms due to tanks in the potential model and input them as external forces in the time domain model. So it is possible to add generic damp terms due to tanks. In this work, the evolution of this method is explained as well as it is compared with experimental data. The main contribution is the development of a fast model to complement the potential analysis.

INTRODUCTION

The increasing demand for natural gas is encouraging the development of novel floating units' designs, capable of producing, processing and storing large quantities of LNG (Liquefied Natural Gas). Due the complexity of this activity, these novel designs are pointing for a solution considering huge barges necessary to support a large process plant and to contain tanks with great store capacity (Vieira et al., 2016).

In the design process of FLNG units it is necessary to evaluate the downtime for some operations as, for example, the LNG offloading. Many recent studies relies on evaluate the behavior of a FLNG operating side-by-side with a LNGC (LNG carrier). In these studies, more precise is the hydrodynamic model more confident is the downtime evaluation. An example of a downtime analysis can be founded in Nishimoto et al. (2016). In the downtime evaluation of side-by-side offloading operation it is mainly necessary to consider:

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