Analysis And Evaluation Of Vibration Fatigue Life Of A Ship's Shock Absorption Support

The ship will be subjected to various forms of vibration loads,prone to fatigue fracture and lead to unexpected accidents during navigation.Shock absorption support is a kind of vibration-isolated device with excellent vibration-reduced performance.It can effectively prevent damage to the hull caused by vibration during the operation of diesel engine and gearbox on the upper part of the support.Therefore,it is particularly important to analyze vibration fatigue and evaluate the performance of the ship's shock absorption support in order to ensure its service life,safety and reliability.The results of this paper have a certain engineering practical value for prolonging the fatigue life of the support.In this paper,the ship's shock absorption support is chosen as the research object.Based on the power spectrum density method and the basic theory of fatigue life analysis,this paper analyzes the vibration fatigue life of the support by using finite element method.The effects of geometric parameters,material parameters and welding residual stresses on the vibration fatigue life of the support are also discussed.And,the key part of the ship's shock absorption support is improved.Furthermore,vibration fatigue life equation by considering welding residual stresses effect is proposed.The main work and conclusions of this paper are as follows:(1)Aim to gain high stress position and fatigue-vulnerable position of the ship's shock absorption support,the vibration response analysis is carried out to the overall structure under the excitation of simulated experimental loads.The results show that it is feasible to use the simulated loads to conduct the finite element analysis of the support.And the natural frequencies of the support is avoided by frequencies of the excited loads,which prevents the support from resonance under the action of the loads.The high stress area of the support are located at the local opening on the surface of the support and the stress-concentration position of the bracket.The maximum stress position of the support is located near the connection between the longitudinal plate,horizontal plate and a reinforcing plate.(2)Based on the power spectrum density method and the basic theory of fatigue life analysis,the vibration fatigue life of the ship's shock absorption support was analyzed.The influence of different factors on the life of the support is also studied.The results show that the lowest-life position of the support is in the area of the maximum stress position,that is,near the connection between the longitudinal plate,horizontal plate and a reinforcing plate.The material properties,welding residual stress and the stiffness of the shock absorber connecting the gearbox and the support have a greater impact on the fatigue life of the support.However,the stiffness of the coupling connecting the gear box and the diesel engine has a little influence on the vibration fatigue life of the structure.Furthermore,equation of vibration fatigue life of the ship's shock absorption support considering welding residual stresses is preliminarily proposed.(3)The improved schemes are designed partially in key part of the ship's shock absorption support.The vibration response analysis and vibration fatigue analysis of each scheme are carried out.The results show that the improved scheme of changing the key position to circular arc surface and the upper of the support not perforated reduces the stress response amplitude of the key parts to a certain extent,which helps to improve the vibration fatigue life of the support.