Research On System Design And Control Strategy Of Advanced U-tube Tank Stabilizer

Anti-rolling tank is one of the most widely used stabilizing equipments which can provide good stabilization at any vessel speed. The added advantages of anti-rolling tank are being low cost, simple mechanism and effectiveness at reducing heeling. Passively-controlled U-tube tanks consist of two separate tanks connected by a water conduit at the base and an optional air conduit in the roof. The stabilizing moment provided by tank depends on the energy of ship rolling. The valves or baffles in the conduits are used to keep the fluid flow in the tank a phase lag of 90 degree after the ship rolling, which can provide effective ship stabilization.The paper is based on the item"Control Engineering of Ship"setup among the school 211 key construction projects. Theoretical problems of passively-controlled U-tube tanks are mainly investigated in the paper. System configuration method and control strategy of the tank stabilizer are intensively studied and analyzed.Firstly, the principle of the fluid motion in the tank is discussed. The forces and moments exerted by the tank system on all six degrees of freedom of the ship are considered. The modeling method of ship motion with tank stabilizers which is on the ship rolling freedom is introduced. On the basis of mathematical model of ship motion with one tank, the model of ship motion with two tanks in different constructions is established. The performance of single-tank stabilizers and double-tank stabilizers is investigated.The system configuration method is deeply researched. There is randomness, nonlinear element as well as uncertainty existing in ship motion system, which can deteriorate the performance of the anti-rolling tanks designed under linear assumption. As the nonlinear elements and uncertain problems in ship motion considered, structural parameter design method of tank stabilizers is proposed as a modern control design problem. The selection and optimization of passive mechanical components of single-tank system and double-tank system can be achieved by solving the robust performance optimization problem. Simulation results show that, under nonlinear conditions, the tank stabilizers designed in novel method is more effective than that designed in traditional method. The results also show that the double-tank system extends effectively-stabilizing frequency compared with single-tank system.An intermittent control strategy, where the valves fixed in the air conduit of tank are either open or closed, is studied in the paper. Base on the deduction of compressible gas equation of state, the strategy that switching valve can effectively extend the periods of tank liquid oscillation is proved theoretically. Passive PD control strategy is proposed to overcome the phase lag between optimum phase and actual phase arose by water inertia. Simulation results show that the novel control strategy can maintain the desired phase relationship between the liquid movement and ship rolling. Then the effectiveness of tank stabilizers is improved.In contrast to the intermittent method, the continuous control strategy which involves various intermediate valve opening to modify the fluid flow is researched. Based on the compressible gas state equation and the equation of fluid motion, influence between valve opening and tank-fluid-oscillation parameters is investigated. Discrete-time linear auto-regressive model of the fluid oscillation under different valve opening is formed by system parameter identification technology. The CARIMA model of ship rolling under the control of tank fluid oscillation is established. Based on the theory of generalized predictive control, the valve opening is involved to control the fluid flow in the tank, which can make the tank stabilizer more frequency adaptive. The simulation results showed that the mentioned control strategy is found to be effective under different ship sailing condition.