Investigation On Modeling And Experiment Of The Multidirectional Coupled Vibrations Of The Marine Propulsion Shaft For Large Vessels

The vessels are the main equipment for the development of water transport and the maintenance of the rights of the sea.Along with the enlargement of the tonnage and structural size of the vessels,the main engine which is a key component of the propulsion system and exports more power than before.Thus,the failure of the shaft suffered from complex operating loads is increased frequently.The marine propulsion shaft functions as the heart part of the power system and plays an important role on the reliability during the sailing.The hull deformation of vessels produced by the fluidstructure interaction affects the shaft rotation and puts forward higher requirements for the shaft's environmental adaptability.The hull deformation of the vessels with complex operating conditions and modes is therefore critical for the reliability research of the shaft.Thus,the main purpose of the research is to enhance the navigation performance of the vessel by improve the reliability of the marine propulsion shaft.This dissertation focus the research object on the marine propulsion shaft.The hull deformation caused by the waves is investigated with the dynamical theory of fluidstructrue interaction.On this based,the calculational methods of multiple coupled vibrations for the marine propulsion shaft with the effect of various hull deformation is established.The method solves significant problems for the safety performance of power system caused by the influence of complex vibrations.Hence,the proposed technologies provide theoretical support for the improvements of sailing reliability of vessels in complicated wave environment.The main research contents and results are as follows:(1)According to the characteristics of the research contents,the theoretical basis and calculational method of the coupled dynamics for the fluid-structure interaction is proposed at first.Various influence factor including initial conditions,boundary conditions,wave loads and vessel masses are included in the established dynamical theory.A calculation for the numerical model is conducted in the solution process.The dynamical response including hull deformation,pressure and strain of the vessel is obtained through numerical analysis.The influence of different material parameters on the motion regularities of hull deformation is thus investigated.Moreover,the experiment is conducted in the towing tank to validate the numerical model,and several general rules for the design and manufacture of structural curve and material strength are concluded.(2)The theoretical model with lumped-mass method of coupled torsionallongitudinal vibration for marine propulsion shaft is investigated.The rotational speed,coupled coefficient,external force and damping are consided in the model.And the torque and longitudinal force are the inputs as different kind of hull deformation.The torsional and longitudinal response of the shaft in frequency and time domain are solved with high-order Runge-Kutta method.Experimental tests are conducted to validate the applicability of the numerical model,over a range of rotational speeds and loading conditions.The range of coupling coefficient is proposed based on the discussion on numerical and experimental results.It provides theoretical guidance for the structural and dimensional design of the marine propulsion shaft.(3)Based on a detailed study of the structural and operational characteristic of the marine propulsion shaft,a new numerical model for shaft coupled longitudinaltransverse vibration is investigated with finite element method.The boundary condition,coupling constraints,rotational speed and sectional eccentricity are considered,the vertical force is added and acted as the input of hull deformation.Based on this model,the coupled natural frequencies and the maximum acceleration are determined in different case studies.The applicability of the numerical model is validated with experiments,over a series of rotational speeds.The influence of sectional eccentricity is discussed based on modeling and experimental results,a technological support for sectional design of the shaft is thus obtained.(4)The experimental tests for the coupled torsional,longitudinal and transverse vibration of the shaft are conducted.The principle of measurement for the equipment and sensors applied in the test are introduced.The coupled response with different loading position and forms are measured,the orbits of shaft center are analyzed during the experiments.The influence of the hull deformation on the multiple coupled vibrations is discussed based on the above measurement.Practical guarantee is provided for the efficient of the vessels.In conclusion,this dissertation analyzes the hull deformation of the vessels with waves.On this basis,the coupled torsional-longitudinal virabtion and coupled transverse-longitudinal vibration of the marine propulsion shaft are investigated with lumped-mass method and finite element method,respectively.Meanwhile,the experimental response of coupled virabtions for three directions are measured on the shaft platform.Thus,the calculational methods for natural frequencies and ultimate amplitudes of the coupled vibraitons are proposed.The research provides technical support for the optimization and design of the marine propulsion shaft.