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Research on Fin Stabilizers at Zero Speed and Its Electroservo System for Ship
Author: LuoYanMing
Tutor: JinHongZhang
School: Harbin Engineering University
Course: Control Theory and Control Engineering
Keywords: Antirolling at Zero Speed Fin Stabilizers WeisFogh Mechanism Electroservo System Direct Torque Control
CLC: U664.72
Type: PhD thesis
Year: 2007
Downloads: 255
Quote: 7
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Abstract
Fin stabilizers are most frequently and successfully used active antiroll equipments. The effectiveness of roll reduction can be more than 90 percent. But fin stabilizers work well only when the ship is sailing at high speed, and they cannot reduce ship roll when the ship is sailing at very low or zero speed. The main reason is that the lift on the fins depends on the velocity of flow around them. No enough lift can be produced when the ship is sailing at low speed, and the lift will disappear when the ship is in anchor. This is the main disadvantage of traditional fin stabilizers. Traditional fin stabilizers are not suitable for ships which sail at low or zero speed, so the idea of fin stabilizers at zero speed are 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), and project 211 of Harbin engineering university during the 10th fiveyear plan: experimental device of electroservo system on fin stabilizers. The main content is to explore a scheme that makes fin stabilizers produce lift at zero speed.The unsolved problem on roll reduction at zero speed is analyzed in detail based on the principle of lift produced by traditional fin stabilizers. The key problem to be solved is producing lift at zero speed. Domestic and foreign correlative references about this problem, and primary demonstration is carried on in the dissertation. The scheme of designing fin stabilizers at zero speed with WeisFogh mechanism is chosen ultimately.WeisFogh mechanism is a kind of new mechanism found by a British biologist WeisFogh through observing wasp’s clapping and flying movement. The lift produced by WeisFogh mechanism at zero speed is hydroinertial force. Three kinds of schemes to design fin stabilizers at zero speed is brought forward, including double wings flapped lengthways, single wing flapped lengthways and single wing flapped breadthwise.Fin stabilizers are substituted by rectangle flat thin wings for the convenience of primary research. The mathematics model of compound wing cascade and cascade WeisFogh mechanism are acquired based on potential theory when the ship is sailing. Then the lift and torque models of double wings fin stabilizers flapped lengthways and single wing fin stabilizers flapped breadthwise at zero speed are acquired on the basis of step by step degenerate derivation. The lift and torque models of single wing flapped lengthways scheme is obtained by thin wing and oscillating hydrofoil theory.By analyzing the lift and torque expression, we can draw a conclusion that turning angle velocity and turning angle acceleration of wing are two important factors for lift value. The moving manner of fins reflects all the two factors, so the character of lift and torque at constant speed, constant acceleration, sinusoid and cosine speed is simulated in Matlab. A method to calculate the power of electrical servo system is derived by analyzing the torque on fins, and the method will be the foundation for calculating the power of servo system. The symmetrical Joukowskishaped single wing fin stabilizer at zero speed is simulated in Fluent. The development of startup vortex, leading vortex and flows around fin stabilizer can be seen clearly. The validity of theoretic analysis is ensured by simulation results.Fin stabilizers at zero speed must be driven by servo system to move in a certain manner. The character of lift depends on the capability of servo system, especially the speediness of startup and stability of operation. Control of electromagnetic torque is the key of servo system for the disturbance of waves. Sliding mode variable structure space vector modulate direct torque control is selected for electroservo system, and different parts of servo system is modeled. Sliding mode control is introduced to eliminate the ripple produced by space vector modulate direct torque control. The stability of system is enhanced by the improvement. Finally, the control system of double wings fin stabilizers flapped lengthways at zero speed based is simulated in Matlab/Simulink. The results indicate that fin stabilizers at zero speed based on WeisFogh mechanism are effective for roll reduction, and its roll reducing efficiency is about 50%. This scheme is worthy of studying farther.

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CLC: > Transportation > Waterway transport > Marine Engineering > Ship machinery > Ship anti roll device > Fin Stabilizer ( Stabilizer )
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