ABSTRACT

This paper presents experimental data and numerical computations for two trimaran hull forms for high speed transportation: one with round bilge component hulls and one characterized by a hard-chine main hull. The experimental data concern residual resistance results systematically collected for a grid of configurations of both hull forms. The numerical analysis, carried out on the same grid, is aimed to the assessment of the capability of a boundary element method to comply with the physical results related to a complex marine vehicle as the trimaran which involves appreciable interference problems of the free surface pattern around the component hulls. In addition a numerical optimisation is presented which was attempted to individuate the best position of the side hulls by coupling the boundary element method with a stocastic optimisation process similar to genetic algorithms. The search of the best configuration had the objective of minimizing wave resistance in the two-dimensional space describing the side hull positions.

INTRODUCTION

Trimaran hulls have recently been subject of interest for some marine applications. In fact they have been considered as alternative to monohulls in high speed transportation and in naval applications. In fact, this solution seems to offer good enough hydrodynamic performance and consequently better economy, larger deck area and adequate stability characteristics. A recent example regards the design of a naval vessel which led to the building of a prototype and to the publications of several studies (Royal Inst. of Naval Arch. 2000). Another significant design example has also performed for a fast ferry 126 m long which has recently been built(Armstrong, 2003) For this reason, reference data about their measured hydrodynamic performance or reports about applications of numerical methods for their evaluation may be useful for people involved in the design of such vehicles.

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