Parametric Optimisation of SWATH Hull Forms by Systematic Use of CFD Methods

The paper presents some hydrodynamic studies performed during the preliminary phase of an ambitious research project aimed to the design of modern, efficient and 'environment friendly' SWATH ships. The work deals with the parametric optimisation of SWATH hull forms with special regards to wave resistance and generated wave patterns characteristics. A simple suitable parametric definition of lower hulls surfaces has been devised in such a way to be easily employed for the automated generation of a series of hull forms, within the frame of a computer assisted optimisation procedure based on CFD technology. The geometry generation module allows for the change of a set of hull geometrical parameters, assumed as free variables of the optimisation problem, while respecting a number of design constraints, such as the total displacement and local details of the hull surface. The CFD analysis of each hull configuration has been performed through a linear free surface potential flow code, based on Rankine source panel method. The best candidate solutions are finally checked with a general thin boundary layer integral method, to prevent them from any undesired flow separations. The shape of the two final optimised hull forms, corresponding to two different design speeds, are critically discussed against a conventional (reference) design by comparing predicted wave resistance and wave patterns. Based on this analysis, interesting considerations about wave cancellation effects, main responsible for the achieved resistance reductions, are drawn. Finally guidelines and indications for the hydrodynamic design of optimal SWATH hull forms are also provided in the conclusions, analysing also the behaviour of the wave resistance coefficients curves over a wide speed range.