Numerical Simulation of Surface Effect Ship Characteristics and Dynamics
Clark, Colton Gager
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The use of computational fluid dynamics to investigate surface ship dynamics and characteristics has been growing during recent years. With technological advancements continuing in leaps and bounds more and more complex simulations are possible. The interests of this paper concern the numerical simulations of a surface effect ship which is a specific type of air cushion vehicle. The simulation work presented here attempts to replicate the model tests involving a generic surface effect ship and demonstrate the value of numerical simulations in understanding air cushion vehicles. The model tests consist of a surface effect ship running through a range of Froude numbers in calm seas and a variety of wave cases. The numerical simulations were developed using CD-adapcos's STAR-CCM+ to model the surface effect ship characteristics and dynamics. The pressurized air cushion and flexible, dynamic seals are of the greatest importance when modeling a surface effect ship; however, some idealizations had to be made. The air cushion fans are represented as constant momentum sources while the seals are represented as shortened and rigid. Throughout the simulations drag, pitch, and heave were constantly monitored for comparison purposes with the model tests. It was found that the rigid skirt approximation accounts for a large portion of error when comparisons were made between the numerical and analytical data. Furthermore, it would be impossible to accurately represent the surface effect ship dynamics in waves with this approximation. An alternative method to modeling the skirts was investigated which would include the use of a porosity function. It was found that the porosity skirt model would allow for cushion pressure to be maintained while limiting the interaction of the rigid skirt and the free surface. The full implementation of porous skirts on the surface effect ship is a difficult challenge as numerical instabilities arise. However, implementing the porous skirt would lead to more accurate calm water simulations and the ability to model the surface effect ship in wave cases.
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