The Research On Roll Control Strategy With Dynamic Stall Constraint

In moderate to high sea, the effectiveness of hydrofoil can severely deteriorate due to unsteady hydrodynamic characteristics of fin stabilizer. Even make the ship not work well.Dynamic stall is the basic reason for this situation. When the ship sailing in high sea conditions, large disturbance torque of the waves will influence the stability of the ship, roll angle will increase quickly. Feedback signals of roll angle act on the fins electro-hydraulic servo controllers, the rotation angle of attack will increase in order to generate greater control torque to prevent rolling motion at the same. For an additional control system, Anti-rolling fin rotation angle of attack is a conservative constant value, no matter how fin angle variations are within the scope of control, there will be no dynamic stall phenomenon. But under the rough seas,the stability of a ship is vulnerable to serious damage. In this paper,under the high speed and different rotation periods of fin, the fin dynamic stall is studied. And the dynamic constraints angles are the maximum dynamic stall angles under the different rotation period of anti-rolling fin, Larger and more suitable for rotary Angle of fin to produce greater control moment to reinforce the stability of the ship.First of all, for a given NACA0015 fin type, GAMBIT software is used for graphical modeling and meshing. Computational fluid dynamics and turbulence models, discrete equations, algorithms models, UDF and so on is to understand and master. Numerical modeling and simulation of three-dimensional fin is done by FLUENT software. Static lift coefficient and drag coefficient characteristics of the fin are simulated at different speed, the static stall angles at different speeds are got and the analysis of the influence on the static lift coefficient and drag coefficient is also done. Under dynamic conditions,simulation of dynamic stall on the fin is done at different speeds, and analyzed the influence on the dynamic stall. Because the speed is relatively small impact on the static and dynamic stall, research methods of dynamic stall of fin at different rotation periods are proposed, simulations and researches on the dynamic stall angles at different rotation periods are also done, and the data are analyzed and summarized. The situations of the dynamic stall of the fin are obtained under different rotation periods in high speed, through the method of curve fitting, the maximum dynamic stall angles as a function of the different rotation periods of fin have been received,as well as the function relation between lift coefficients of the maximum dynamic stall angles and the periods is studied.Then, the ship roll motion is studied. the dynamic lift characteristics and the control torque of the fin are analyzed and modeled respectively; Nonlinear coupling of ship rolling motion mathematical model is established and and linearization for it; The ship rolling disturbance torque is also modeled and it is caused by the waves.Finally, the LQR controller is used to control the ship rolling motion, Constraints of the maximum dynamic stall angles act on the fin at different rotational periods. And the constraints of the dynamic lift coefficients under the different maximum dynamic stall angles are also done. The changes of the encounter angles can lead to the change of the ship rolling periods, and then the rolling period of the fin also change with the ship rolling periods. So the constraints of the maximum dynaimic stalls at different periods are applied to the fin, in the same condition, constraint of the static stall angle is also applied to the fin. The whole ship motion modeling and simulation is done by using the MATLAB software, the rolling simulation curves of the ship rolling motion are obtained under the static and dynamic stall constraints, and they are also carried on analyzed and compared. Compared to the constraint of static angle, the constraints of dynamic stall angles can control the roll motion of ship well,get a good anti-rolling effect, and strengthen the stability of the ship so well.