Dynamic Simulation and Control of an Active Roll Reduction System Using Free-Flooding Tanks With Vacuum Pumps

Ship roll motion is often the critical factor for offshore operations due to its lack of damping mechanism. This paper demonstrates a dynamic simulation scheme of an active roll reduction system using free-flooding tanks controlled by vacuum pumps. The two tanks in the system are installed on each sides of a catamaran. The tank hatches are opened to the sea and the air chambers of both tanks are connected by an air duct. Vacuum pumps and air valve with active stabilization controller provides desired filling level for the tank. The ship is a dynamic model with single degree of freedom in roll. The hydrodynamic behavior of the ship is calculated using potential theory by SHIPX. The air chamber above is modelled as isothermal process of ideal gas. The behavior of the liquid flow in the tank is simulated by incompressible RANS solver using Volume of Fluid (VOF) model, then summarized as response function for the ship model. A simplified control plant model for the vacuum pumps is proposed where insignificant higher order behaviors are regarded as biases and noises. The stability is proved by Lapunov direct method. The performance of the entire system is evaluated in terms of roll reduction capability and power cost. The system is more suitable for roll reduction in low-speed or resting conditions.