ABSTRACT:

This paper presents a numerical investigation of the influence of raised invar edges on wet drop tests pressures. The aim of this study is to evaluate the capabilities of the CFD software OpenFOAM (Ref. [6]) to deal with fluid structure impact problems in the context of sloshing inside membrane tanks. More precisely, the objective is to simulate water drop tests for a smooth wedge on one hand and a wedge equipped with invar edges (like these which equip the Cargo Containment System NO96 produced by GTT) on the other hand, both falling into calm water without inclination. The obtained numerical results are then compared to Wagner's solution for the smooth wedge and to experimental measurements for the wedge with edges presented in (Ref. [2]). Numerical simulations are in very good agreement with Wagner's solution and experimental results (Ref. [2]) showing the OpenFOAM capability to deal with fluid structure impact problems in the context of sloshing inside membrane tanks. The agreement between numerical and experimental results confirms also that raised invar edges tend to enhance the magnitude of sloshing pressures. This confirmation emphasizes the importance of considering the physics of invar edge effects in defining the design pressure to be used in assessing the integrity of membrane LNG tanks.

1 – INTRODUCTION

In order to manage the risk of failure due to sloshing, adequate assessment of sloshing loads and structural capacities are required. The state of the art of sloshing model tests has improved a lot these last few years, by including more physics such as reproduction of realistic irregular 6 degrees of freedom motion for the tank, introduction of a special ullage gas mixture in order to respect the LNG gas/fluid ratio density in the model tank. But some physical phenomena are still not reproduced in actual sloshing model tests.

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