Analysis And Experiment On Vibration And Acoustic Radiation Of The Shafting-Hull Coupled System

Current investigation on submarine vibration and noise reduction is mainly focused on the isolation of machinery vibration. However, only the shafting or the hull system is considered in the analysis of hull's acoustic radiation induced by the propeller's oscillatory forces through the propulsion shafting. In order to control vibration and acoustic radiation of the hull structure, particularly vibration and acoustic radiation at low frequencies, analyzing only excitation forces and vibration characteristics of the hull structure cannot achieve this purpose. Fundamental theory can be established to control aouctic radiation of the hull structure provided the vibration transmission and coupling of the propeller-shaft-bearing- foundation-hull structure are taken into account. This thesis considers the propeller-shafting-hull structure synthetically to investigate vibration transmission from the propeller to the hull structure and analyzes thoroughly the influence of bearing dynamic characteristics on vibration transmission and acoustic radiation, which will provide a theoretical base to the control engineering of structural vibration and noise.In Chapter 1, the background and significance of the investigation in this thesis is introduced at first, and then detailed literature review is given about methods, results and shortcomings in three aspects: propulsion shafting, vibration and acoustic radiation of underwater structures, and especially vibration and acoustic radiation of the shafting- hull coupled system.In Chapter 2, an impedance model of the sliding thrust bearing's oil film is established on the basis of the hydrodynamic lubrication theory, and dynamic characteristics of the bearing are analyzed under two different working conditions of the propeller. These results are useful to the vibration experiment as well as the analysis of dynamic characteristics of the shafting system and the coupled system.In Chapter 3, the shafting system as well as the coupled system is modelled by using the finite element mothod, and in addition to the natural vibration modes, also analyzed is the influence of the thrust bearing's oil film stiffness on the longitudinal oscillatory force transmission characteristics and the influence of the characteristics of the three transmission paths on the transverse oscillatory force. Moreover, power flow based on the finite element mothod is calculated, energy transmission and all factors affecting energy transmission in the system under longitudinal or transverse oscillatory force are analyzed.In Chapter 4, an acoustics-vibration model is established with the FE/DBE method, and the surface and far-field pressure distribution as well as the primary influence factors to the pressure distribution are analyzed at first. Based on the analysis, some suggestions to reduce the pressure level are put forward. Then, from the pointview of energy, the spectrum characteristics of acoustic radiation and radiation efficiency are analyzed. Finally, acoutic radiation characteristics under longitudinal and transverse oscillatory forces are compared. Conclusions in this chapter are helpful to the optimal design of submarines'acoustic charateristics.In Chapter 5, experiments are completed on a test rig simulating the shafting-hull system. Modal testing and vibration transmission measurement under different conditions are carried out. Measured data have proved that the vibration model of the shafting-hull system is effective. Some conclusions are drawn from the experiment. These results are useful to the optimal design of low noise submarines.In Chapter 6, conclusions of this thesis are summarized. Contribution and further investigations are also presented.