Numerical investigation on the hydrodynamic performance of fast SWATHs with optimum canted struts arrangements

Giuliano Vernengo, Stefano Brizzolara (University of Genoa, Virginia Tech)

CHALLENGE - Small Waterplane Area Twin Hulls (SWATHs) are known to have superior seakeeping performance although higher resistance to equivalent catamarans or mono-hulls. To improve their resistance characteristics, unconventional hull forms are parametrically defined and optimized by CFD methods. No study has been made so far about the influence of strut shape on the hydrodynamic performance of SWATH. This study builds on previous SWATH optimization studies proposing a comprehensive, systematic investigation on the effect of strut shape.

SOLUTION - The effect of the design speed on the best shape is addressed through a multi-objective optimization targeting the minimum total resistance at two very different speeds, namely the cruise and slow transfer speeds. Optimum hull shapes are targeted for maximum resistance reduction, together with the predicted free waves patterns. The fully parametric model of the SWATH is created using curves and surface primitives of the CAESES 3D parametric CAD. To analyze the effect of the canted strut arrangement on the hydrodynamic calm water resistance performance of the proposed SWATH design, three optimization cases have been carried out, the first two being single objective optimizations. The NSGA II used in modeFRONTIER is used to drive the search towards the optimum. The last case is a multi-objective optimization aimed to minimize the total resistance in calm water of the complete hull at two different speeds.

BENEFITS - In conclusion, the struts geometry can contribute to reduce the total resistance from 19%, achievable considering only the shape of the underwater hull, up to 29%, contributing to about two thirds of the total. Furthermore, the struts canting angle has a major effect on the interference of the waves generated by the forward and the aft struts being an essential parameter in the design of efficient SWATH vessels.