Dynamic Characteristics Of Marine Airbag-rotating Mechanical System Under Shock Excitation

Ships are often subjected to various shock excitation during work,therefore,it is great significance to ensure that the marine rotating machinery have a good capabi,lity of impact resistance and vibration absorption.In this thesis,marine airbag-rotating machinery system is studied,and the dynamic characteristics of the system under shock excitation are discussed.In addition,the displacement restrictor is installed in the airbag to limit the shock response of the marine rotating mechanical system.Finally,the influence of parameter changes on dynamic characteristics of the system is analyzed.The main contents and conclusions as follows:(1)The differential equation of motion of airbag floating-rotating mechanical system under shock excit.ation is established based on the short bearing theory.The dynamic characteristics of the simple mechanical vibration system under shock excitation are solved by theoretical and numerical methods.Finally,the influence of damping on the shock response of mechanical vibration system is discussed.The results show that the vibration isolation coefficient of the mechanical vibration system decreases first and then increases as the damping increases.(2)Nonlinear dynamic characteristics of the airbag-rotating mechanical system under shock excitation are solved by time domain dynamic analysis method,such as displacement response,acceleration response,and rotor orbit.The shock response characteristics under different shock amplitudes and frequencies are studied,also the influence of different parameters on dynamic characteristics of the system is analyzed such as rotational speed,stiffness,damping etc..The results show that shock excitation will cause large change in the state of the system,but will eventually return to stability.The shock response amplitude is smaller at high speed,and the displacement response of the system is more easily attenuated at low speed.The stiffness and damping of the airbag are beneficial to reduce displacement response of the system,and the airbag stiffness increases the acceleration while reducing the displacement response.(3)The dynamics characteristics of the piecewise linear vibration isolation system are studyed.The dynamic model of the airbag-rotary mechanical system with displacement restrictor under shock excitation is derived and the influence of parameter changes on the dynamic characteristics of the rotating mechanical system is analyzed.The results show that the displacement restrictor has a great obvious effect on reducing vibration and shock response.When the stiffness and damping of displacement restrictor are determined,the smaller the installation clearance,the better the vibration isolation effect of the displacement restrictor.The damping has a small influence on the system when the limiter stiffness is larger However,when the stiffness of displacement restrictor is smaller,there is an suitable damping which make the displacement restrictor have the best vibration isolation capability,and to some extent,the smaller the installation clearance,the greater the optimum damping.(4)The dynamic model of the airbag-rotary mechanical system under the combined action of shock excitation and base excitation is established and the dynamic characteristics of the airbag-rotating mechanical system under different parameters of base excitation are analyzed.The results show that the base excitation has little effect on the displacement amplitude and acceleration amplitude of the rotating mechanical system compared with the shock excitation.However,the base excitation will cause significant fluctuations in the displacement of the steady-state response of the system.When the amplitude is too large,the rotor will be in chaotic state.