Research On Active Control To Longitudinal Vibration Of Marine Propulsion Shafting

Because of the asymmetric circumference of hull, the uneven flow field of stern isunavoidably existent, which results in the propeller to generate unsteady exciting force.When the propulsion shafting is excited by the unsteady exciting force, it will oscillateperiodically along the axial direction. It is the common phenomenon of longitudinalvibration of propulsion shafting. The longitudinal vibration not only damages propulsionshafting itself, but also transforms the second exciting force to hull, which excites thehull’s vibration. The research shows the longitudinal vibration of propulsion shafting isone important sources of hull’s low frequency acoustic radiation. So it is necessary to doresearch of longitudinal vibration of propulsion shafting to improve its acoustic stealth.In this paper, one propulsion shafting model is studied by combining the vibrationtheory and numerical simulation methods. The content covers the properties oflongitudinal vibration, the acoustic radiation of hull induced by longitudinal vibration ofpropulsion shafting, theory of active vibration control and theoretic analysis of activecontrol of longitudinal vibration.Firstly, the relevant achievements and latest advances on the research of longitudinalvibration of propulsion shafting, acoustic radiation of hull, control technologies oflongitudinal vibration are summarized and discussed in detail, in order to comprehend thestudy profoundly.Secondly, the properties of longitudinal vibration of propulsion shafting are studied.Three computational models of propulsion shafting are presented and compared, includingcontinuous parameter model, lumped parameter model and finite element model. Theresponses of propulsion vibration by usual axial exciting force are also calculated. Takingthe importance of thrust bearing into account, the effects of longitudinal stiffness of thrustbearing to properties of longitudinal vibration are discussed.Then, based on the mode superposition method of FEM/BEM, the acoustic radiationof hull induced by longitudinal vibration of propulsion shafting is forecasted. Bycomparing the participation coefficient of each mode of hull, the largest participationcoefficient of mode can be detected. In order to analyze the control effect of dynamic vibration absorber (DVA) to acoustic radiation of hull, a DVA is installed between thrustbearing and its foundation. The simulation results show that the DVA has limited controleffect to acoustic radiation of hull.Next, the theory of active vibration control is expounded. The focuses are optimalvibration theory and modal control theory, including the LQR, LQG, IMC and CMC. Thedetailed theoretic derivations and differences of these control algorithms are presented andanalyzed. Then, the control simulation analysis of longitudinal vibration of propulsionshafting is carried out by applying above control algorithms from physical space andmodal space. What is more, the effects of control parameters are discussed. Some valuableconclusions are obtained to direct the design of control system.Finally, the whole research work and shortages of the paper are summed up. Thefuture studies are also briefly presented.