Hullform Design, Optimization and Controllability of a Small Waterplane Area Twin Hull (SWATH)

This paper focuses on hullform optimization and controllability of a SWATH (Small Waterplane Area Twin Hull) Hullform. The research covers the designing of a SWATH, determination of its resistance and RAO’s, its design validation, SWATH optimization using Adjoint CFD, designing of optimized SWATHs with their resistance prediction and RAO’s, comparative analysis between analytical and experimental results of parent SWATH, comparative analysis for Resistance and RAO’s of parent and optimized SWATHs along with analyzation of effect of changes in demihull spacing and separation ratio on the RAO’s of SWATHs. Solidworks and Rhinoceros software was used for designing the SWATHs while Maxsurf software was used for the determination of the SWATH hydrostatics, total resistance, and RAO’s. Maxsurf Resistance software utilizes the Molland method with slender body approximation for resistance prediction while Maxsurf motions software utilizes the panel method for RAO’s prediction. The RAO’s were found at a sea state 3 at zero speed by using the Pierson-Moskowitz spectrum. The optimization of the parent SWATH was done using the Adjoint CFD method in ANSYS fluent. Using the K-ε model, initial residual convergence and drag value and then the Adjoint CFD method were employed to achieve two different optimized SWATHs. One SWATH was fully optimized while the other was optimized with a little less drag reduction but was more construction friendly. The parent SWATH resistance was found to be 240 KN at 33 knots and the fully optimized SWATH has a 7.5% reduction in total resistance while construction-friendly SWATH has a 3.5% reduction in total resistance. The original and optimized SWATH’s, S/L and S/B ratios were varied and the RAO’s trends were found and discussed. The Hulls were tested for S/L ratios of 0.26, 0.31, 0.36, 0.42, and 0.48 while for S/B ratios of 3.45, 4.25, 4.95 and 6.45. For parent SWATH with different S/L ratio shows with an increase in S/L ratio, the values of pitch and heave RAO’s increases while roll RAO decrease. For an increase in the S/B ratios, the RAO’s of all three motions increase. For Fully optimized SWATH, with an increase in S/B ratios the RAO’s of pitch, roll, and heave motions decreases. The final fully optimized SWATH with passive fins was developed and its RAOs were found.