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Heave Control System For A Surface Effect Ship : Disturbance Damping of Wave Induced Motion at Zero Vessel Speed

This master thesis will cover vertical motion damping of a Surface Effect Ship (SES) at zero vessel speed where the motion are induced due to wave propagations. The vital SES principle is the air cushion that partly lifts the vessel together with the hydrodynamic buoyancy. The air cushion is enclosed by two catamaran twin hulls and two rubber seals at the ends. The motion damping takes place on the vessel bow. This is necessary and important while the wind turbine maintenance workers boards the turbine. A heave control system (HCS) is created for performing this task. This notation is chosen since the control systems only task is to keep the control point closest possible to a constant heave (vertical) reference position. The HCS actively controls the air flow actuators to the air cushion. The air flow actuators are the lift fan (blowing air into the air cushion) and adjustable louvers (letting air out of the cushion). By closing the louver pins and gaining maximum effect from the lift fan, the vessel will increase its vertical position (upwards). The opposite effect will appear by opening the louver and ”choking” the lift fan, which results in a downwards motion. The control system is discussed, implemented and tested in simulation. A Kalman filter using a mathematical model has been implemented to reject heave measurement noise and to estimate non-measurable states. The HCS will be added to an already existing SES simulation model that does not support any active control of the air flow.