Bending And Torsional Vibration Of A Propulson Shafting System Excited By The Friction Force Of Stern Bearing

The submarine propulsion shafting system often produces abnormal vibrationand noise during operation, which not only affects the stability of its own operation,but also causes Hull structural vibration and radiates noise.Most of time, the sternsupporting of Propulsion shafting system iswater-lubricated rubber bearing.The stern bearingbecomes the biggest load ofsupporting because of its own weight, propeller and the shafting alignment. Due topropeller cantilever load, the pressure of bearing is very large and the load distributesvery unevenly. the good water film lubrication state between shafting and bearing isoften destroyed by excessive load, falling into the boundary lubrication or mixedlubrication state easily, the bearing and the shafting even contact directly and thefriction force increase between them.It is not easy to form continuous and stable fluidfilm lubrication between bearing and shafting because of longitudinal groove on therubber pad and enter the "stick-slip" state easily. Even no obvious external excitation,the shafting may still produce abnormal bending, torsional vibration and noise, evencause self-excited vibration and excite shell vibration, which impact sound recessiveand reduce operational stability and reliability. The alternating friction or frictiontorque between bearing and shafting may induced vibration modes of system,which ispotential reason of self-excited of shafting system.Currently, analyzing the overall dynamic behavior of system has becomemainstream method when it comes to self-excited vibration problems. In the past,most researchers analyzed self-excited vibration of propulsion shafting system intheory through simple lumped models, analyzing basicself-excited vibration law ofpropulsion shafting system in qualitative, which is limited to thestructure of the bearing and oversimplified structure makes it impossible to explain actual dynamicsbehavior of overallshafting system excited by friction force. In addition, those modelscan only be applied to simulate open, stop conditions. In fact, thenormaloperationpropulsion shafting system may still produce self-excited vibrationunder low speed and overloaded condition, even excite hull vibration. In this paper,establishing bending–torsional coupledself-excited vibration dynamics model ofsimplifiedpropulsion shafting system under low speed and overloaded condition,regarding of friction force between stern bearing and shafting, to reveal thecharacteristics of friction induced shaft vibration and noise and its’ main factors intheory, providing theoretical basis for the identification of abnormal vibration andnoise of propulsion shafting system, benefiting for Reasonable design and installation,benefiting for controlling the shafting system operation state and ensurethe stableoperation, especially benefiting for reducing hull vibration, reducing noise.In chapter1, the background and significance of this study is introduced at first,then detailed introduce in following aspects: torsional vibration, bending vibration,bending-torsional coupled vibration of the propulsion shafting system,frictioncharacteristics of water lubricated rubber bearing, mechanical characteristicsof water lubricated rubber bearing, rotor dynamics.In chapter2,analyze force and deformation of stern water lubricated rubberbearing of propulsion shafting system under working condition, thensimplifyMechanical model of its stiffness characteristics. Then, using the finiteelement analysis software ABAQUS as a tool to calculate the stiffness of thebearing,including the stiffness of vertical direction andhorizontal direction. To savestoragespace of computerand computing time, simplify three-dimensional finite elementmodel as two-dimensional finite element model. After analysis and comparison,simplify the two-dimensional finite element model further,reducing the computationtime greatly, without affecting the accuracy requirement.In chapter3, establishbending–torsional coupledself-excited vibration dynamicsmodel of simplifiedpropulsion shafting system under low speed and overloadedcondition, regarding of friction force between stern bearing and shafting, to reveal the characteristics of friction induced shaft vibration and noise and its’ main factors intheory. Getting bending-torsional vibration characteristic equations of shafting systemunder friction force in the view overall dynamics, which include the vertical andhorizontalbending vibration. Make clear of mechanism and main factors, causingabnormal vibration of the shafting system, through analyzing dynamic responsecharacteristics of it.In chapter4, Test Stationary and Dynamicmodal characteristics of model byhammering for modifying dynamic model. Test dynamic response characteristics of itunder low speed and overloaded condition.In chapter5, conclusions of this thesis are summarized. Contribution and furtherinvestigations are also presented.