Slamming computation on the multihull Groupama 3

Innov’Sail 2010, 30th June – 1st July 2010 Lorient, France

Difficulties that forced the maxi Groupama 3 to withdraw from the Jules Verne Trophy between Brazil and Africa in November 2009 showed the need for a comprehensive study of the slamming phenomenon on hull bottoms in unforeseen navigation conditions. A survey in South Africa confirmed that structural damages were due to slamming stress on the rear of the windward hull, which has been underestimated. This condition appears in a swell when the multihull takes off and crashes back into the water at a boat speed of 30 to 40 knots.

The latest version of the software FINE™/Marine developed by CNRS, Ecole Centrale de Nantes and Numeca International allows the precise simulation of this type of problem. Indeed, the use of an automatic grid refinement algorithm enables the precise modelization of the impact of the hull on the water surface and the computation of the generated pressure field, which will be used by the designers to reinforce the structure of the hull.

We present in this paper the particularities of the automatic refinement method and its application to the trimaran Groupama 3 in the condition of the impact of the hull at an angle with respect to the sea.

INTRODUCTION

This paper presents the study of the impact of the bottom of a Groupama 3 float onto the sea surface. This phenomenon appears in very specific conditiions where the boat is sailing in reaching conditions against a swell front. In this case the multihull jumps on the wave. The impact on the waves at every landing induces extremely high loads to the float structure and deteriorate this structure.

The numerical modelization of slamming needs a very accurate and robust unsteady hydrodynamic flow solver able to capture the deformation of the free surface during the impact. We present in this paper a new automatic adaptive grid refinement method recently developped for the software FINE™/Marine and we apply it to the multihull Groupama 3 in an extreme condition of slamming.

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