Interactive design and variation of hull shapes: pros and cons of different CAD approaches

Modern paradigms to design complex engineering systems focus on interactive approaches able to simultaneously handle results from multidisciplinary applications. Keeping this in mind and considering that from a ship design perspective the definition of a hull shape is the first step of the whole design process, a reliable computer aided design model for shape representation and morphing becomes a key feature to navigate trough the design spiral. The proposed research focuses on the comparison of two different approaches to handle hull shape variations, namely the fully parametric model and a non-parametric method relying on the free form deformation technique. The comparison is developed considering both the easiness of building the shape of the reference model with its transformations laws and the resulting number of free design variables. The two methods are analyzed in the light of attainable hull shape variation in two design and modification test cases. The first is limited to the bulbous bow of a conventional hull while the second focuses on the whole surface of a fast, displacement, round-bilge hull.