EnginSoft International Conference 2011 |
Numerical and Experimental Evaluation of Structural Impact Behavior of Large Pod for Nautical Applications |
Scarselli Gennaro - Università del Salento (Italy) |
Abstract |
The marine vehicles usually exhibit one or more large pods exiting from the bottom keel: on these large pods propeller blades are mounted on shafts taking power through a transmission system composed by different rotating elements that transfer, through proper gears, the rotational speed from the engine shaft to the external shafts. In Figure 1 a typical architecture is reported showing the pod before mentioned and its location respect to the marine vehicle. During their operational life these structures suffer different problems due to the position in which they necessarily work: one of this is the exposure to impact damage. The navigation when is performed close to coast can take the external surfaces of the marine vehicle in contact with rocks. Also when the marine vehicle runs far from the coast it is possible that it crashes against a floating obstacle. The effects of these impacts depend on different technical parameters: the vehicle speed, the mutual stiffness of the structural parts crashing, the vehicle and obstacle mass and so on. The main risk that should be avoided is a serious damage to the marine vehicle primary structure in the points of attachment of the pod support structure. If not properly designed this attachment damage can open a fracture in the bottom keel causing, in the worst scenario, the complete loss of the vehicle and the transported payload. This is the main reason that has motivated ZF Marine to investigate the impact problems of these pods at first from a physical and numerical standpoint, thinking about a structural solution designed to “bear” an impact in controlled conditions and, then, from an experimental standpoint, realizing a “crash experiment” in which real pods have been moved against a fixed obstacle acquiring all the information about impact accelerations and forces in assigned points of the structure. In this paper this complex numerical and experimental activity is described in detail starting from the functional description of real structure working on the marine vehicle up to the conceived experiment. |
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