Vibration Analysis Of Shaft-hull Coupled System And Its Structure Optimizing

Underwater Vehicle is playing a more and more vital role in national defense in recentdecades. Vibration and noise level of the underwater vehicle is of the utmost importance asfar as concerning its survivability and undiscovered attacks. The machine is consisted oftwo basic system, shaft system and hull system. The sources of the vehicle noise andvibration generally involve three aspects: mechanical noise and vibration, flow noise andvibration, noise and vibration due to the movement of propeller. Among these, noise frompropeller movement is the main source during most of the time. So, precisely estimate andefficient control of the noise and vibration from this part become indispensable fordesigning and improving the machine. Vibration of the system owning to the movement ofpropeller can be divided into direct noise and vibration of propeller and indirect noise andvibration of propeller, the indirect noise and vibration can be further sourced from the timedependent propeller-excited vibration transferring to the whole system and the rotationbecause of the propeller running generating frictional vibration between the shaft and sternbearing.Regarding to the unsteady propeller-excited vibration and noise radiation of the system,in the thesis, the supporting surface property and simplified model between the shaft andthe hull are analized. Shaft subsystem model, shaft-hull coupled system model withoutwater as well as shaft-hull coupled system model with water are created separately based onthe spring-dashpot model of bearings. Modal analysis, forced vibration characters underlongitudinal and transverse swept excitations and the relation among these three models arealso involved in the paper. In addition, noise radiation property is discussed from theanalysis of surface sound pressure level and noise radiation level while the conclusion thatthrust bearing base is the most important part of longitudinal vibration transferring.For the frictional vibration between shaft and stern bearing generated by the rotation ofthe propeller, frictional characters of water lubricated stern bearing is researched,self-excited oscillation vibration and stick-slip phenomenon resulted from the frictionalexcitation using modal coordinate system transformation method are illustrated. The resultshows that the reason for the generated friction oscillation is the combined effect ofnegative slope friction coefficient and unsteady support force, and frictional self-oscillationvibration factors, including modal damping, shaft speed and support stiffness, are discussed.Characteristics of frictional vibration under aligned shaft as well as unaligned shaft andcomparing of respective effect of frictional vibration and unsteady propeller-excitedvibration under these two conditions are studied. Results show that frictional vibrationshould not be ignored if the shaft is not aligned. Vibration control measures and their effectiveness and feasibility such as changing thebearing stiffness and damping parameters, adding one or more longitudinal ribs, improvingthe base structure of thrust bearing and adding longitudinal isolator are based on theanalysis of noise and vibration characteristics. The paper argues that the most effectivemeasure is to change the structure of thrust bearing base into a symmetrical style, by doingthis, not only the vibration response of the whole system under both longitudinal andtransverse forces, but also the longitudinal and transversal coupling degree can be reduced.The studies have a certain significance for the engineering design.