Nonlinear Dynamics Characteristics Of Marine Rotor-Bearing System Under Heaving And Rolling

The large-amplitude,low-frequency transport motions produced by the ship when sailing,including swaying,heaving,surging,rolling,pitching,and yawing are typical transport motions for rotor-bearing system,which can have a severe impact on marine rotor-bearing system.Therefore,it is of theoretical significance and engineering application value to study the dynamic characteristics of the rotor system under the transport motion.In the thesis,considering two important forms of transport motion of the ship:heaving and rolling and based on the theory of short bearing,we have established the dynamic model of the marine rotor-bearing system under the heaving and rolling respectively,as well,the nonlinear dynamics of rotor system have been studied with various nonlinear dynamics theories.The main contents and results are as follows:(1)Considering the heaving motion,the dynamic model of the rotor-bearing system under heaving is established based on the short bearing theory in the non-inertial reference system,which shows that the marine rotor-bearing system has the evident geometric nonlinear characteristics under the action of heaving.Afterwards,the dynamics of the system are analyzed by numerical methods combined with nonlinear dynamics analysis methods.The results suggest that the heaving motion significantly affects the dynamic behavior of the rotor.At low speeds,the system exhibits period 1 motion;as the speed increases,the dynamic characteristics of system exhibits some dynamic features,such as quasi-period,period 2,chaos,and double Hopf bifurcation and so on.(2)The dynamics of the system of the rotor-bearing system under heaving motion caused by the changes of parameters are analyzed.Specifically,the effects of the amplitude of the heaving,the frequency ratio and the eccentricity of the rotor on the nonlinear dynamic characteristics of the rotor system are studied.The results show that both the increase of the amplitude of the heaving and the the eccentricity of the rotor will make the inertial force of the system go up,as a consequence,the displacement of the rotor will raise constantly and the dynamic characteristics will become more and more complex.With the increase of the frequency ratio,the motion state of the system gradually remains steady after a complex chaotic state.As a result,parameter analysis shows that the effect of the heave motion on the vertical motion of the rotor system is greater than the effect on the lateral motion.(3)In view of the rolling motion,the dynamic model of the marine rotor-bearing system under rolling motion is established based on the kinematics theory and the short bearing theory,which makes it clear that the rolling motion will cause obvious Coriolis inertial force in the rotor system.Accordingly speaking,through the calculation and analysis of the nonlinear dynamic response of the system,it is found that the rolling action will make the displacement of the rotor system increase more obviously than without rolling.Besides,the rotation speed of the rotor entering the unsynchronized quasi-periodic motion is greatly advanced,and at the same time,the system will no longer exhibit simple synchronous periodic motions such as period 1,period 2,etc.when without rolling.(4)The dynamics of the system of the rotor-bearing system under heaving motion caused by the changes of parameters are analyzed.The results reveal that when the amplitude of the roll increases,the steady-state displacement of the system will gradually increase,what's more,the motion state of the rotor will change from the quasi-period to the chaotic motion.When the frequency is small,the rotor motion state is complicated and variable,and its displacement amplitude is large.As the frequency ratio increases,the displacement of the rotor system gradually decreases,and the motion state presents a quasi-periodic motion.Meanwhile,when the rotor eccentricity increases,the system motion state will change evidently at a certain critical value.The parameter analysis shows that the effect of the rolling motion on the motion of the rotor system is greater in the lateral direction.