Research On The Application Of Dynamic Hydrodynamic Character Model Of Fins Stabilizers

Fin stabilizers system, which is one of the most widely used anti-rolling apparatus, gets the transverse information through the sensors, converts it into fin-angle information, then drives the fins by hydraulic system. With the control system, it produces the counteracting torque to stabilize the ship.Fin stabilizers system in engineering usually uses the PID controller. Recently Intelligent control technology has been applied in fin stabilizers system, which promotes the anti-roll effects in simulation. Both the PID control method and Intelligent Control technology compute the lift through constant lift coefficient of the fins, and adjust the control parameters according to it. But the lift coefficient of the fins when the angle increased is not the same as that when the angle decreased, and the experimentation has shown that it is a close curve when the angle changes in sine. The fins move in the water constantly, so error occurs when computing the lift through constant lift coefficient of the fins. Just for such reasons the anti-roll effect to use in the ship is not as well as the simulation effect. And it also limits the application of the Intelligent Control technology in the fin stabilizers system.Later a new type of fin stabilizers system, which added a lift feedback component to the original system, was advanced. We call it lift-feedback fin stabilizers system (or lift fin stabilizers) . It gets the lift not by computing but the lift-detecting devices which have been affixed to the fins, and advances the precision. But it also has many shortages. The first one is that it is inconvenient to install them because the lift-detecting devices should be affixed to the surface of the fins and need professional techniques to install them. The second is that it takes more money and time to mend it. The third is that there are noreferences to estimate the validity of the information transmitted by the lift-detect device. To deal with them, the thesis emphasis on modeling and simulating the dynamic hydrodynamic character of the fins when they roll in sine.The thesis models the dynamic hydrodynamic coefficient when fins rolling around the axis at the sine speed on the base of the Theodorsen theory, which based on the superposed theory. It means that the oscillation hydrodynamic coefficient of the zero thickness and surround hydrofoil rolling in the zero angle cun-ent. which is superposed the constant hydrodynamic coefficient of the small tliickness and surround hydrofoil in the given angle current, is the dynamic hydrodynamic coefficient of the fins rolling around the axis. So the dynamic hydrodynamic coefficient can be divided into two parts: the constant hydrodynamic coefficient and the oscillation hydrodynamic coefficient.The thesis computes the constant part by experience formulas and models the oscillation part according to plane potential flow theory. With the software of MATLAB6.5/Simulink5.0, the dynamic hydrodynamic coefficient of the fins is simulated, and the result is similar to the experimentation result, so the method to compute the dynamic hydrodynamic coefficient can be applied to the real system to enhance the precision. The torque-feedback fin stabilizers system, which bases on the original fin stabilizers system and the dynamic hydrodynamic coefficient of the fins, has been modeled. Heights (2.68m, 3.75m, 4.26m) and angles (45°, 90", 135") of ocean wave are simulated, and the results are given. And the result shows that the fin stabilizers system can stabilizer the ship better under every state of the sea.