Research On Control Mechanism Of Bionic Ship Fin Stabilizers At Zero Speed

Ships that were tossed by stormy waves are inevitable, among which roll is marked and severest. The roll is increased and severer than shipping state when the frequency of wave is similar as the natural rolling frequency of ships. Nevertheless, the traditional fin stabilizers could only anti rolling ship at higher ship speed effectively and the fin stabilizers could barely anti rolling ship at lower navigating speed or at anchor. The lift of fin would vanish at anchor. Because the speed of water flow across the surface of fin stabilizers is zero on this condition. The traditional fin stabilizers would not be applicable for the ships which still need anti rolling at lower speed or at anchor. New expectation of capability of anti roll ship is put forward with the development of ship roll stabilization. Anti roll capacity of anti rolling tank is limited, furthermore, sometimes the phenomenon of increasing rolling occurred. In ship anti roll field, the technology of ship roll stabilization at zero forward speed that becomes a focus and so the concept of anti roll ship at anchor is proposed.The dissertation is based on the project supported by national science foundation of China: research on lift theory of ship bionic roll stabilization at zero speed (50575048). Main research area is that based on the bionic hydrodynamics, the mechanism of lift produced by swaying the fin actively in the zero speed flow field is researched and the lift model of bionic fin stabilizers is established at anchor.In the dissertation, on the basis of extensive investigation and study on the bionic hydrodynamics such as theory, experiment, numerical calculation and model developed of insect and bird flight, fish cruising mechanism, the lift produced pattern of zero speed fin stabilizer, insect hovering, birds flight, the boost pattern of fish sways the pectoral fin and tail are researched, the lift model of variable chord Weis-Fogh fin stabilizers and lift model of single-bionic zero speed fin stabilizers are built with the complex method of theoretical analysis, simulation and numerical calculation, the influence of lamina clearance on characteristics of lift is demonstrated, the sensitive factor of lift on the lamina clearance is defined. The conclusion that lift is not influenced by clearance when non-dimensional factor of clearance on fin chord is less than 10 is obtained, this conclusion could be referenced in practical design. The movement characteristics and mechanical mechanism of the proposed two kinds of zero speed fin stabilizers are thoroughly analyzed and the lift control is induced into fin stabilizers control system at zero speed combined the technology of anti rolling ship, and the control system of fin stabilizers with energy restricted at anchor is established.By the methods of simulation analysis and numerical experiment, the lift characteristics of variable chord Wes-Fogh lift model with different motion law is researched and the results indicate that the different lift characteristics could be provided for ship according to different wave periods by dynamical changing chord length at stated fling law, the lift model proposed could be able to reflect the lift characteristic in still flow field.According to Kutta-Jucowski and "slowly moving" hypothesis that is extensive applied in the research of ship maneuvering, lift model of single-bionic zero speed fin stabilizers is built on the basis of revision to classical blade-element theory in unsteady flow field. The simulation results show that the characteristics of lift is different with the different motion parameters such as pitching angle and heaving amplitude, frequency and phase angle between pitch and heave. The pitching played a major role to lift of fin stabilizers. The lift is larger at 45°phase angle between pitch and heave.In recent years, lift control is always the point of anti roll ship, it is undoubtedly another development to introduce lift control to ship roll stabilization at zero forward speed. According to lift feedback and lift limit, the original servo system of fin stabilizers is improved and lift control system of zero speed fin stabilizers is established. The simulation results of 90°wave direction and different sea conditions indicate that effectiveness of anti rolling ship at zero speed is over 60% and much greater than anti roll tank whose effectiveness is less than 50%. It shows that the lift model of bionic fin stabilizers and control system could be able to satisfied the need of ship roll stabilization at zero forward speed.