Research On The Theory And Experiment Of Coupled Vibration For Marine Complex Propulsion Shafting

Serving as the heart of ship, marine propulsion system is one of the most important components of marine power plant. It plays a vital role on aspects of marine's economy, mobility, safety and reliability. Due to the higher requirements on the process and technology in shipbuilding industry and the put-forward of global low-carbon economy concept, marine propulsion system is required to meet higher requirements like more complex structure, function and performance. As a result, the former method for shaft vibration calculation, which sometimes leads to unacceptable error, is out of requirements. At the same time, due to the strengthening of international norms, there are many points which are unresolved or worthy to consider in-depth in the field of vibration calculation of ship shafting, more efforts need to be put in analysis of complex ship shafting vibration. This paper, based on the self-designed comprehensive experiment platform with multi-engine parallel operation power plant, focusing on the research hotspot in current marine propulsion system and in combination of mathematical derivation, numerical calculation, dynamics simulation, experimental testing, etc., performed the calculation of the coupling vibration of beam element and computational analysis of key parts and the whole system. The main research work is as follows:1) Analyzed the current shortcomings in the coupled vibration research; analyzed the causes of coupled vibration based on basic principles of mechanics of materials and elasticity; summarized the axial-transverse and torsional-lateral coupling vibration equation for beam with round section and performed derivation of torsion-axial coupling vibration equation, analyzed the rules of coupled natural frequency, derived-transverse-torsion coupling vibration equation for beam with round section axial from twin-coupled vibration equation.2) Since marine gearbox is the root course of the complex structure and function, the common methods of solving the gear mesh stiffness and mesh damping have been summarized, the torsional vibration equation taking gear meshing in marine gearbox into account has been established. The influence of system natural frequency and the gear meshing error on torsional vibration has been analyzed by means of theoretical calculation, modeling and simulation. Through the stress analysis of helical gear, a complete explanation of helical gear meshing coupled vibration is given and the gear pair coupling vibration model is derived. Comparing the results between the test data of measurement and calculation from various theories, it can be found that the torsional vibration equation considering gear meshing in marine gearbox is more accurate and consistent with the measurement.3) As the joints'application has made the shafting performance more complicated and the cross-joint-type universal coupling is wildly used in marine propulsion system, it is set as the research object in chapter4. The motion law between driving and driven shaft is derived and the equations of motion for cross joint shaft is given. The basic nonlinear equations of the torsional vibration for the universal coupling have been derived from the first class of the Lagrange equation. The simulation analysis of the impact of the angle on the natural frequency of the universal coupling system has been performed. From this, it can be found that the torque fluctuations coming from angle changing can be ignored when angle changing is within a small range. Based on the kinematics of universal coupling, the torsional vibration equation in consideration of the cross shaft universal coupling has been derived from the Lagrange equation. Analysis reveals that no matter how the angle changes within the driving shaft, intermediate shaft and the driven shaft the system is stable. Meanwhile, while gradually increasing the angle between the intermediate shaft and the driven shaft, the time that the system takes to reach a stable state extends accordingly, but the amplitude is lower and the frequencies corresponding to the maximum peak value decreases.4) Based on the experiment platform and developed software for calculation of complex shafting torsional vibration, the natural frequency of vibration of three-cylinder diesel engine with a dynamometer, four-cylinder diesel engine with a dynamometer and two-engine parallel operation with a dynamometer is calculated and analyzed. Meanwhile, with consideration of the influence of phase difference between the parallel engines, the three-dimensional model has been built. Assisted by the dynamic simulation software and considering the influent of the gear system and coupling vibration, the intermediate shaft angular velocity in different speed of revolution is given.5) Designed and built the multi-engine parallel operation power plant platform, a brief description of its hardware components and the monitoring system is given. An overview of three test program in different conditions is given and test data proved the correction and convenience of the theory above.