A LINEARIZED POTENTIAL FLOW THEORY FOR THE 



MOTIONS OF AMPHIBIOUS AND NON AMPHIBIOUS 



AIR CUSHION VEHICLES IN A SEAWAY 



Dr. T.K. S. Murthy 



Portsmouth Polytechnic 

 Portsmouth, U.K. 



ABSTRACT 



The problem of the motions in a seaway of an ACV 

 supported by an air cushion which is bounded by 

 flexible extensions at the front and the rear and 

 by rigid hulls immersed in the water along the 

 sides is first formulated in the most general sen- 

 se just to show how impossible it is to obtain a 

 solution without some form of acceptable lineari- 

 zation. Four perturbation parameters are there- 

 fore selected relating to the cushion pressure, the 

 width of the side hulls, the amplitude of the oscil - 

 lations and the slope of the incident waves. The 

 velocity potential for the motion of the side hulls 

 is derived in the form of. an integral representa - 

 tion, but it has been found possible to derive on- 

 ly an integral equation for the potential due to the 

 motion of the air cushion. This could, however, 

 be reduced to an integral representation under 

 certain additional assumptions, such as that the 

 side hulls are slender. 



The steady motion and forced oscillation of the 

 ACV in calm water are first discussed. The ex- 

 pressions for the forces and moment show clear- 

 ly the separate effects of the air cushion and the 

 side hulls together with the interaction between 

 the two which may enable the optimization of the 

 overall configuration to be made. An investigation 

 of the free oscillation in regular waves yields 

 expressions for the response functions which may 



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