Shape optimisation of an integrated bulb-keel

Abstract

The objective of the thesis was to shape optimise an integrated bulb-keel using a numerical optimisation method and to validate how well the used methods suit this kind of problem. The algorithm used for the optimisation was a Non-dominated Sorting Genetic Algorithm, NSGAII. The optimisation was limited to the bulb part of the keel and 7 design variables were used together with 4 inequality constraints. The hydrodynamic performance of the keel was evaluated using a RANS viscous solver and the objective function used in the optimisation was the ratio of drag coefficient over lift coefficient CD/CL. The numerical CFD calculations were validated with experimental wind tunnel tests, which is a crucial part when investigating new types of numerical flow problems. The CFD calculations were also verified using a Least Square Root method in order to obtain the numerical error. The comparison between the wind tunnel results and the CFD results showed that the CL/CD-ratio was predicted very similarly for the numerical and experimental tests. The optimised keel design had a CD/CL-ratio improvement of around 4% compared to the initial keel design. Finally the keels were mounted on a hull of a 40-foot yacht and tested in a velocity prediction program (VPP) in order to get a more understandable performance indicator of the keels.