Parametric Hull Form Variation and Assessment of Seakeeping Performance

Abstract: This Master Thesis is about the assessment of the seakeeping performance of different ships subjected to hull parametric variations. The latest version of the potential flow CFD software Shipflow in combination with a CAD platform (CAESES) have been used to carry out the evaluations. Two ships are studied: a simple one that can be mathematically defined, the Wigley hull, and the KVLCC2, a realistic oil tanker. The software is validated, comparing it to experimental results and other CFD solvers, showing a good agreement with the rest of the data; the mesh dependence studies also show only small variations between the used meshes and finer ones. Then, first the performance in calm water is evaluated for both ships by looking at the wave resistance. With the results of the original hulls as a reference, they are parametrically modified in different ways and evaluated as well to see which trends lead to an improved resistance. With the parametrization applied in the Wigley hull big changes can be appreciated, as the variation in wave resistance due to different parametric modifications ranges between -6% and 14%. For the KVLCC2, two different parametrizations are tested. The first one, focusing mainly on the bulb, produces changes that are generally smaller than for the Wigley hull, especially the ones due to bulb modifications; and the negative effects over the wave resistance due to variations affecting the general shape of the hull are larger than the positive effects. The second parametrization mimics the one used for the Wigley hull, focusing on the general forebody: the results obtained with this approach are very similar to the ones of the Wigley hull, also reaching wave resistance reductions of about a 6%. After that, the evaluation is moved to the ships in regular head waves, where the added resistance due to waves is studied; in a range of wavelengths going from 30% to a 200% of the length of the ship for the Wigley hull, while the study of the KVLCC2 is focused around the wavelength where the resistance is higher, at a 120% of the ship’s length and extending to 100% and 140%. Here the differences of the effect a same parametric variation has over the resistance in calm water and waves are assessed. The results of the Wigley hull show many interesting facts: some of the parametrically modified designs that performed worse in calm water have a consistent better behaviour at the wavelengths analysed; while the best designs in calm water exhibit both large positive and negative added resistance variations depending on the wavelength observed. The first KVLCC2 parametrization approach presents again smaller deviations in resistance, frequently even minor than in calm water; despite that, most of the parametric variations that worked well in calm water display also a reduction of added resistance in waves. On the other hand, the results obtained with the second parametrization of the KVLCC2 show the same trends and behaviour as for the Wigley hull.