Research On Modeling And Control Of Fin Stabilizer At Zero Speed

Ship swaying motions are inevitable for a storm-tossed ship.Among these motions,roll motion is the most prominent and affecting.Fin stabilizers are the most successful and most widely used active equipments for roll reduction.90 percent of roll motion can be eliminated by using fin stabilizers.Traditional fin stabilizer can reduce roll motion remarkably when the ship is sailing at high speed. If the ship is sailing at low or zero speed,traditional fin stabilizer cannot work. Among existing equipments,only the effectiveness of U-type tanks is not affected by the speed of ship.But the volume of tanks is usually too large.U-type tanks can work well when its 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 solve these problems,the concept of zero speed fin stabilizer is brought forward.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(50 575048).The development of fin stabilizer at zero speed is summarized at first,then the key technology to develop fin stabilizer at zero speed is confirmed.The principle of fin stabilizer at zero speed is analyzed,and the structure and work mode of fin stabilizer with single wing and double wings are compared.Lift model is the foundation to study fin stabilizer at zero speed.A primary lift model is set up based on hydrodynamics.The principle to produce and change the forces on fin stabilizer is studied analytically,and the lift characteristic of fin stabilizer with single wing is analyzed based on this model.The simulation results indicate that fin stabilizer at zero speed is a load with large inertia,so its servo system must have excellent performance.The lift and torque model of Weis-Fogh mechanism are acquired based on potential theory,but only the open process of Weis-Fogh mechanism is analyzed in this model.In order to solve this problem,a practical lift model of close process is set up based on numerical analysis.The open and close character of lift and torque at different speed is simulated in Matlab.The concept of rotary fin stabilizer at zero speed is brought forward to overcome the disadvantage of existing single wing fin stabilizer at zero speed.The simulation results indicate that the performance of fin stabilizer at zero speed can be enhanced remarkably by this design.Fin stabilizer at zero speed works in non-steady flow.Only some primary lift models can be gained based on academic analysis.So these lift models must be corrected by the data of experiments. Because the flow field of fin stabilizer at zero speed is much different from that of traditional fin stabilizer,the scheme of hydrodynamic experiment must be studied deeply.A scheme is brought forward based on the analysis of flow field around fin stabilizer at zero speed.Some parameters of experiment is confirmed by similarity theory.The accuracy of data is guaranteed by these analysis.Traditional fin stabilizer is driven by electro-hydraulic servo system which is hard to maintain.Application of electro-servo system on fin stabilizer at zero speed is discussed to enhance the reliability of control system.Driving motor is selected based on load characteristic of fin stabilizer at zero speed.Due to the complicated working environment and load characteristic of fin stabilizer at zero speed,the CARIMA(Controlled Auto Regressive Integrated Moving Average) model of permanent magnet synchronous motor is established to realize generalized predictive control.The input and output constrains of electro-servo system are analyzed to improve the full load performance.The simulation results indicate that generalized predictive controller can improve the dynamic performance of servo system and enhance roll reduction ability of fin stabilizer at zero speed.When the ship is sailing,fin stabilizers move at the same speed.The task of servo system is to turn fin stabilizers to a certain angle.The lift is produced by interaction between fin stabilizer and water,and the energy comes from the engine of ship.When the ship is anchored,the energy for roll reduction is completely provided by servo system.The power of servo system is usually much lower than that of engine,so existing fin stabilizer at zero speed cannot work well when the intensity of ocean wave is very high.In order to reduce the power consumption when the effectiveness of roll reduction is ensured,both servo system and roll controller are optimized.For servo system,the optimal movement rule based on energy performance index is discussed with minimum principle.The method to drive is ensured to increase the value between lift and energy consumption.The theoretic analysis indicate that maximum lift can be gained by proper drive method with minimum energy.The disadvantage of opposite lift for roll reduction can also eliminated.For roll controller,frequency spectrum of random ocean wave is analyzed and random optimal controller with quadratic performance index is designed based on the extended state equations.Performance index weight matrices are optimized with genetic algorithm to find the best matching point between energy consumption and effect of roll reduction.To enhance the robustness of controller,random optimal control in different sea levels is realized by introducing parameter online adjusting rules for weight matrices.The simulation results indicate that expected effect of roll reduction can be acquired with least energy when weight matrices are fixed with external disturbance.