Nonlinear Motion of an Air-Cushion Vehicle over Waves

Abstract

The nonlinear behavior of an air-cushion vehicle (ACV) during coupled pitch and heave motion over a sinusoidal wave is studied. The vehicle is of the plenum-chamber type with a transverse stability skirt, which is a contributor to the nonlinearily. Further nonlinearity results from the contact of the flexible skirt with the surface. The airflow is considered incompressible, and water compliance is neglected. Numerical computations have been made for the craft response in head seas as a function of encounter frequency for a set of Froude numbers and skirt configurations. The motion is found to be highly damped, and strongly dependent on the depth of the stability skirt, though not on its longitudinal position. Weak peaks in the response curves are displayed, their strength and location being a function of the wave height. The effect of skirt contact forces is found to be negligible on the craft motion. The predicted pressure fluctuations can be large and, at sufficiently high frequencies, result in subatmospheric pressures in the cushion.