Research On Lift Mechanism And System Model Of Fin Stabilizer At Zero Speed

Anti-roll tank is main anti-roll system to reduce ship roll when ship is at zero speed or low speed. But anti-roll capacity of anti-roll tank is limit, and anti-roll tank got the best anti-roll effectiveness when its resonance frequency is similar as ship roll frequency, it will increase ship roll in some frequency. Traditional fin stabilizer only can reduce ship roll when ship speed is medium or high, it is decided by its anti-roll theory. Lift generated from traditional fin stabilizer is proportional to the square of velocity of ship, so lift is increased when ship speed is high. A new kind of anti-roll technology which fin stabilizer is used to reduce ship roll at zero speed came out as anti-roll technology developed, anti-roll theory is still developing now.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).Main research area is about rotating way and lift model of fin stabilizer when ship is at zero speed .First anti-roll systems are introduced, then anti-roll theory of fin stabilizer at zero speed is narrated. Four types of fin stabilizer at zero speed is proposed as single fin stabilizer pitching at zero speed, single fin stabilizers rolling at zero speed, single fin stabilizer pitch and heave at zero speed and double-wing fin stabilizers flapping at zero speed, and their working process are analyzed.Researching on lift model of fin stabilizer at zero speed is a key problem to decide whether fin stabilizer can be used to reduce ship roll at zero speed. Two different types of single fin stabilizer's working principles and their lift models have been studied. Lift model of single fin stabilizers rolling at zero speed was built based on potential theory of single Weis-Fogh mechanism, and lift model proposed can basically give the changing of lift on fin stabilizer as fin stabilizer is rotating. Lift model of single fin stabilizers pitching at zero speed was built based on tail fin swaying theory of fish, force on fin is divided three part: normal force, added mass force and influence force of vortex and their simple model is built. Numerical simulation of single pitching fin stabilizer is done by using a CFD software (Fluent), the lift curve of fin stabilizer got from Fluent is compared with the simulation curve from lift model, the lift model can simulate the force generated from fin stabilizer basically as fin stabilizer rotates.Lift model of double-wing fin stabilizer flapping at zero speed was built base on hydrodynamic theory of Weis-Fogh mechanism. Some parameters were assumed in potential theory, lift model built based on potential theory can not reflect real lift on fin stabilizer. So lift model base on vortex theory was built. Lift model base on vortex theory can simulate lift better than lift model base on potential theory.Finally, ship-single fin stabilizer and ship-double-wing fin stabilizer models were built. Ship-single fin stabilizer model and ship-double-wing fin stabilizers were used to simulate ship roll base on real ship parameters under different sea conditions, single fin stabilizer at zero speed can reduce ship roll well under low sea condition and anti-roll effectiveness is more than 55% from simulation results, the anti-roll effectiveness of double-wing fin stabilizers was about 50%.