Research On Lift Model And Control Strategy Of Fin Stabilizer System At Zero/Low Speed

When the ship sails on the sea, it will move in six degree of freedom for the disturbance of ocean wave,sea breeze,ocean current. The rolling movement is the most serious under the same ocean disturbance. Rolling movement has a serious effect on working order of the equipment in the ship, the cosiness of passenger and the security of goods on the ship. Fin stabilizers are the most successful and most widely used active equipments for ship anti-roll.90 percent of roll motion can be eliminated by using fin stabilizers. As the work principle of fin stabilizer, it can effectively reduce the rolling movement when the ship sails at a high speed and it can not reduce the rolling movement when the ship sails at a low speed or zero speed. Among existing equipments, only the effectiveness of ship anti-roll tank is not affected by the speed of ship. But the volume of tank is usually too large. Ship anti-roll tank can work well when disturbance resonance frequency is close to that of ship. If the resonance frequency doesn't match, the roll motion of ship might be strengthened. In order to reduce ship roll movement at all speed, some ships adopt ship anti-roll tank and fin stabilizer together. Though it can get good perfection, it is not a economical method. In this dissertation we dedicate to research a fin stabilizer system with three kinds of working method which are zero speed,low speed and high speed working method. Fin stabilizer system at high speed has been well developed. We will mainly research on zero and low speed fin stabilizer system.The dissertation is based on project supported by national science foundation of China:Research on lift theory of ship bionic roll stabilization at zero speed(50575048) and Research on antiroll of underwater vehicle near surface based on Transmutative Fin (50879012). It mainly researches on the working mode of zero and low speed fin stabilizer,the lift model of zero and low speed fin stabilizer and the control strategy of zero and low speed fin stabilizer system.The working mode and the fixing fashion of zero and low speed fin stabilizer are firstly expatiate. Then four kinds of zero and low speed fin stabilizer system which are zero speed fin stabilizer system with Weis-Fogh mechanism, zero speed fin stabilizer system with lengthways movement, zero speed fin Stabilizer system with transmutative fin and low speed fin Stabilizer system with lengthways movement.The key factor in designing of zero and low speed fin stabilizer system is to analyse and get the lift model of fin at zero and low speed. We will mainly research on zero speed fin stabilizer system with lengthways movement, zero speed fin Stabilizer system with transmutative fin and low speed fin stabilizer with lengthways movement for their predominance. We analyse the lift generated on the fin in ideal hydro environment and nonideal hydro environment. We get the lift model in ideal environment with conformal representation theory,movement transform theory and Blasius theorem. As glutinosity of the hydro in nonideal hydro environment, it will generate vortices on fins when fins move in nonideal hydro environment. The vortices will generate press distinction on two sides of the fin and it is one parts of lift generate on the fin. We ignore the thickness of fin for the complexity of vortices and adopt a applied method to analyse the lift generated by vortices.The model of ship rolling movement is variational for the change of sail and loading of the ship. All the three kinds of lift model are nonlinear. So the zero and low speed fin stabilizer system are a serious variational and nonlinear system. As SVM(support vector machine) has a good identification ability, we adopt a inverse control method based on SVM to solve the nonlinearity and time varying of zero and low speed fin stabilizer system. The identification of SVM is without feedback-error, So the identification of SVM to zero and low speed fin stabilizer system maybe has some insufficient and it will affect the stability and the stationarity of the system. SVM also need some time to identify the system when the system has a sudden change. We adopt a compound control strategy based on SVM and GAFC(fuzzy controller based on genetic algorithm) for the under-control of the system that is induced by the sudden change of the system and under-identification of SVM. The fuzzy controller will make the system has a good stability and the stationarity when SVM is identifying zero and low speed fin stabilizer system. Define a coordination factor, To adjust the proportion of the two kinds of control strategies and to determine whether to identify the system once again or the identification is sufficient based on the coordination factor. This control structure can make the system has a good stability characteristic and static accuracy.To construct zero and low speed fin stabilizer system with the lift model that we get and design controller with complex control strategy that we introduce. Simulation results show that all the fin stabilizer system get a good reduction of ship rolling angle and it prove the efficiency of zero and low speed fin stabilizer system. As zero fin stabilizer's lift capacity is not very large,the anti-roll effect will decrease when the oceanic condition become more serious.As low speed fin stabilizer has a large lift capacity,the anti-roll effect of low speed fin stabilizer system is not severely affected by the oceanic condition.