Design methods for unmanned marine vehicles

Marine robotics is increasingly adopted in many fields of the underwater world, however, as of today, can still be considered a challenging task. In this framework, the research activity carried out during the PhD period concentrated on the study of hull ways of failure, with special focus given to cylindrical and dome shape, and on the development of an autonomous self-moving buoy for underwater target localization and communication. Starting from the current solutions identified within the state-of-the-art, the work was conducted heading to create a simplified calculation system for the design and sizing of submarine hull parts under pressure and, in particular, to codify a fast and light computational procedure to check the resistance of cylinders and domes. The investigated underwater vehicle, i.e. the here presented case study, named FeelHippo, was designed and assembled by the Department of Industrial Engineering of the University of Florence. Its main hull is composed of an extruded PolyMethyl Methacrylate cylinder and two thermoformed domes, which for the productive process have peculiar geometrical features. First, the theoretical critical buckling pressure of the cylinder was calculated using classical formulas; second, the critical buckling pressure was analytically derived and used to determine the optimized size in order to calculate the lowest thickness of the vehicle central cylinder to address the buckling effect. The available domes were experimentally tested until breakage, and then the dome design pressures were obtained, introducing additional correlations to consider the thickness variation and the flange constraints. The performance of the resulting method was evaluated by means of Finite Element Method simulations and tested during dedicated experimental validation campaigns; although it would be useful to extend the tests, the obtained results were satisfying, indicating that the derived solution may constitute a valid design tool for thermoformed flanged plastic domes, commonly adopted in the underwater field. As concerns instead the developed buoy, useful for the localization of underwater targets such as autonomous vehicles, it was designed by means of topology optimization techniques too, and then it has been mechanically tested and successfully employed during experimental tests at sea.