Research On Active Control Of The Longitudinal Vibration Of Propulsion Shafting Systems

The vibration and noise of ships can affect the comfort of ships, the reliability of marine electronic equipments and the ecological environment in the surrounding waters. For submarines, noise can still make their stealth performance and fighting capability degraded, and endanger their safety, especially the more and more advanced underwater detection technology has brought new challenges to the stealth performance of submarines. The shafting-hull coupled vibration due to the propeller fluctuating thrust forces is the main reason of the low frequency sound radiation of submarines, which is difficult to be controlled and has become a key factor of restricting stealth performance of submarines. Reducing the transmission of the fluctuating thrust forces to the hull is the basic measure to control the low frequency sound radiation, the study on which will help to control the underwater sound radiation of the shafting-hull coupled system at the source and is practically important.The paper is supported by a GF973 project and a project of National Natural Science Foundation of China ―Research on active control of the shafting-hull coupled vibration induced by the propeller fluctuating thrust forces‖. Aimed at the vibration induced by the fluctuating thrust forces, the active control methods of the longitudinal vibration of the shafting are presented to suppress the vibration of the hull induced by the thrust fluctuation. The researches including theoretical research and experimental verification are as follows:(1) In the view of control, the shafting-elastic foundation coupled system is simplified into a shaft-plate coupled system. The analytical model of the coupled vibration induced by a longitudinal excitation is established by the substructure method and verified with the finite element method. Based on this model and considering the characteristics of the bearings, the characteristics of the coupled vibration and the affect of the supporting stiffness on the longitudinal vibration of the coupled system are analyzed. The influence of the action point of the longitudinal control force on the longitudinal vibration of the coupled system is also analyzed. The principle study on control provides the theoretical basis for the active vibration isolation design。(2) A model-free adaptive harmonic narrow-band control method is proposed for the time-varying shafting based on the anti-saturation LMS algorithm. The control method incorporates an anti-saturation-LMS-based adaptive feedback controller and a logic-based instrumental mechanism named ―X-adjustment‖ to adjust the threshold and the weight stepping direction of the adaptive controller. The control method can adjust the gain of the adaptive controller only by the error and needn’t set up the dynamic model of the control channel. A adaptive tracking filter is adopted in the model-free adaptive control system to suppress tonal vibrations selectively and the control method is a kind of narrow-band adaptive control. Simulation results have demonstrated the control scheme is effective in attenuating tonal vibrations of the system.(3) Considering the sudden change of the stiffness of the water-lubricated rubber bearing between static and dynamic state, a simplified model of the shafting is introduced to explore the mechanism of the speed-dependent characteristics of the stiffness of the rubber bearing. Then an online model identification method and a periodic vibration suppression scenario are presented on the basis. The LMS-based adaptive identification algorithm and the subspace filtering algorithm are applied to get the impulse response of the control channel and filter out the speed-modulated periodical disturbances. The transmission suppression is realized via the Filtered-x LMS algorithm enforced with two additional units for disturbance reconstruction and saturation alleviation. This control method based on online identification of control channel model can realize a broadband control. The simulation results have demonstrated that the online model identification of the control channel is effective and the active control method is able to suppress the speed-modulated periodical vibration of the shafting bearing.(4) In the experimental research, the control results of the two control algorithms are verified by the establishment of a shafting-shell coupled vibration active control experiment system. The experimental results have demonstrated that two control algorithms can effectively suppress tonal vibrations of the shafting and shell. The Filtered-x LMS algorithm enforced with two additional units for disturbance reconstruction and saturation alleviation is also able to attenuate random vibrations of the shafting and shell. Moreover, the control results of the Filtered-x LMS algorithm enforced with two additional units for disturbance reconstruction and saturation alleviation are verified via a propeller-shafting vibration transmission active control experiment system. The experimental results have demonstrated that this control method is able to effectively suppress the speed-modulated periodical vibration.The research results in this paper will provide a solid theoretical basis for the active vibration control methods applied to suppress the low-frequency sound of propulsion systems.