The Ave mar ferry, shown in Figure P10.9 (a), is a large 670-ton ferry hydrofoil built for Mediterranean ferry service. It is capable of 45 knots (52 mph) [29]. The boat's appearance, like its performance, derives from the innovative design of the narrow "wave piercing" hulls which move through the water like racing shells. Between the hulls is a third quasi hull which gives additional buoyancy in rough seas. Loaded with 900 passengers and crew, and a mix of cars, buses, and freight cars trucks, one of the boats can carry almost its own weight. The Ave mar is capable of operating in seas with waves up to 8 ft in amplitude at a speed of 40 knots as a result of an automatic stabilization control system. Stabilization is achieved by means of flaps on the main foils and the adjustment of the aft foil. The stabilization control system maintains a level flight through rough seas. Thus, a system that minimizes deviations from a constant lift force or, equivalently, that minimizes the pitch angle 8 has been designed. A block diagram of the lift control system is shown in Figure P10.9 (b).The desired response of the system to wave disturbance is a constant-level travel of the craft. Establish a set of reasonable specifications and design a compensator Gc(s) so that the performance of the system is suitable. Assume that the disturbance is due to waves with a frequency o) = 6 rad/s.
