ABSTRACT

In the present paper, the open source toolbox OpenFOAM was applied for analysis of the hydrodynamic force and motion of a floating lifeboat in regular waves. The Reynolds averaged Navier-Stokes (RANS) equations were solved and the free surface tracking was achieved by using the volume of fluid method. An overset mesh method was applied for the moving boundary of the lifeboat, in which a body-fitted mesh was generated around the lifeboat using the utility snappyHexMesh and a hexahedral background mesh was produced by the utility blockMesh. The field values were interpolated in the overlapping area between these two layers of meshes. The hydrodynamic forces and the motion of the lifeboat were calculated under the condition that the lifeboat was off-centered in the wave flume to mimic the effects of a larger mother ship. Due to the unsymmetrical condition, full six-degree of freedom (DOF) motion needs to be taken into account. The predicted hydrodynamic force and surface elevation for the fixed lifeboat, and the six DOF motion of the lifeboat were compared to the experimental data. Satisfactory agreement was achieved except the roll moment and motion, for which large discrepancies were observed.

INTRODUCTION

Lifeboat has been an important component of ocean-going vessels and oil/gas platforms. It needs to be designed to guarantee an effective and safe evacuation for the people on board. Lifeboats can either be dropped freely or lowered via wires. For a freefall lifeboat, it will experience water impact, submergence and resurfacing phases. During the impact phase, the lifeboat may be subjected to high impact loads. However, the advantage of a freefall lifeboat is that it can rapidly reach a safe position and speed suitable for an effective retreat (Ringsberg et al. 2017). The impact loadings on a wired lifeboat could be much lower, but it requires a longer time in the launch process. Essential for both types of lifeboats, after the deployment, they should be able to reach the safe position with acceptable motion amplitudes.

Some recent studies on the impact phase of free-falling lifeboats have been reported in the literature. Mørch (2008) proposed a computational fluid dynamic (CFD) approach to analyse the launching process.

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