Air cushion vehicle response to waves in the surf zone

Heave motion of an air-cushion vehicle in response to wave encounters as it transitions through the surf zone is presented. Wave transformation from deep waters to the beach is described using the model of Dally et al. (1985) and the shallow-water SWAN model. The vehicle considered is a surface effect ship (SES) that maintains an air cushion between its two side hulls and the deck hull. The airflow is considered to be incompressible. In view of the shallow draft of the vehicle, the evolving wave field that the vehicle encounters is considered as forcing the heave motion. Numerical computations are presented for the transformation of a regular wave over the beach slope and of an offshore JONSWAP spectrum and the vehicle response in transitioning at speed U in head seas. The heave motion is described as function of time and frequency in a coordinate system moving with the transitioning vehicle. Advancing the state of predictions of vehicle response in the surf zone facilitates the structural design process for the vehicle.