The Application Of Roll And Pitch Motion Control Of Ships By Fin Stabilizer

Stabilizing fin is the most common device to stabilize roll, but movement controlling,more attentions are paid on lengthwise movement for the increasing requirements of ship navigation. As the latest report of ship pitching stabilization, most methods to stabilize pitch are elongating streamlined body on the bottom of the bow to increase the moment of inertia and the additional mass, which increase the costs. So researches on pitch stabilization are beginning to study stabilizing fins. In order to calculate heave force and pitching moment conveniently, it is assumed to have the same direction of left-and-right fins and the contrast direction of front-and-back fins, to increase the distance of the two fins, which has the limits in engineering practice for the ignorance of rolling stabilization of the fins itself.In the first part of the paper, it establishes the heave-pitch-roll three freedom model of ship, and gives the analysis of ship motion. To simplify the calculation of control algorithm of fins, with the condition of neglecting the coupling between heave and pitch movement, the theory is used to get the hydrodynamic force coefficient, analysis on the ship movements with different speeds and encounter angles is also given. On the base of the correct and steady ship motion model, the control force and moment of fins on ships are required to calculation under the consideration of the distribution of fins and current water speed.In the second part of the paper, LQG method is used to estimate the ship attitudes. Under the consideration of the varied direction of current water speed caused by ship sway and the influence of attacking-angle on ship control force, simulation experiments are designed to prove the practicability of LQG method with roll index and pitch-roll index. This method can greatly improve the effects of pitch stabilization on the basis of sacrifice roll stabilization. In this LQG method, fins limits of itself are ignored, such as the maximum fin angle, maximum rotate speed, maximum output force and power dissipation of fins. To solve these problems,the paper designed the section of control force allocation after the LQG, by which to allocate roll and pitch moment of ships and to ensure the minimum power dissipation of fins.In the third part of the paper, the reverse process is designed to ensure ship stability. It is a inertial object consisted of electric hydraulic drive system when stabilizing fin is used as actuating mechanism. Based on this feature and controller of reverse process, a algorithm of stability control on roll and pitch is proposed to solve the nonlinear problem.