Theoretical And Experimental Research On Nonlinear Virbartion Characteristic Of Gear-rotor-oil Journal Bearing System

Geared rotor system is the most primary origin of the vibration problem of power transmission system, the security and concealment of system are affected by the severe vibration significantly. At present, the vibration mechanism of geared rotor bearing system is still not clear. Aiming at this problem, on the basis of gear dynamic and rotor dynamic, the effect of clearance, time-varying mesh stiffness, static transmission error, flexible shaft, bearing, input and output torque excitation are considered, and the nonlinear dynamic model of geared rotor system is derived. Numerical integration method is used to study the dynamic model, the effects of speed on the dynamic mesh force and vibration characteristic of system are also studied. On the process of judge the vibration is chaos or not, the maximum Lyapunov exponent of high dimensional nonlinear equation is calculated by chaotic time series analysis theory. The results of numerical integration show that the dynamic model can reveal three kind of impact status of gear mesh in reason. The chaotic time series analysis theory can calculate the maximum Lyapunov exponent of high dimensional nonlinear equation effectively.The gear pair torsional vibration system is the most basical gear system, in order to study the effect of clearance's size on the gear pair torsional vibration system's amplitude-frequency response curve from approximate analytical solution method, the multi-term harmonic balance method is connected with the generalized inverse method which used to solve the minimum least-square solutions of nonlinear equation group. The results show that the effect of clearance on the amplitude-frequency response curve of gear pair torsional vibration system relates with the size of clearance, the damping, time-varying mesh stiffness and preload. When the damping is relatively small, the amplitude-frequency response curve of system affected by clearance obviously, the amplitude jump phenomena appear in primary resonance and super harmonic resonance under different clearance. When damping increases to certain value, with the increase of clearance, the amplitude jump phenomena always appear in primary resonance, but it is not obvious in the super harmonic resonance whose amplitude is relative small. When damping increases to large value, the amplitude-frequency response curves of system approach to the response curves of linear system under different clearance. Whit the increase of the first harmonic term of mesh stiffness's value, when the clearance is relatively small, the amplitude-frequency response curve of system will reflect the character of hardening type curve. When clearance increase to certain value, no matter the first harmonic term of mesh stiffness's value is small or large, the amplitude-frequency response curve of system just reflects the character of softening type curve. On the condition of preload is relatively small, when clearance is also relatively small, the amplitude-frequency response curve just reflect the character of hardening type curve in local speed range. When clearance is relatively large, the amplitude-frequency response curve reflects the character of softening type curve. On the condition of preload is relatively large, when the learance is small, with the preload becomes larger and larger, and then the character of hardening type curve also becomes more obvious, the clearance need to increase to larger value to make the amplitude-frequency response curve becomes softening type curve in the primary resonance.The model of gear pair torsional vibration system assumes rotor and bearing are rigid, it has certain difference comparing with practical geared rotor system, in order to study the effect of clearance on geared rotor system, numerical integration method is used to study the effect of clearance on the bifurcation and chaos of system, the results show that the first lateral critical speed of system is affected by clearance greatly, when the clearance is relatively small, the vibration state is relatively preferable. Bearing stiffness also has important effect on the bifurcation and chaos of system, except for clearance. The effect of bearing stiffness on the bifurcation and chaos of system is studied by numerical integration. The results show that the lateral-torsion critical speed will increase with the increase of bearing stiffness, and the region of bifurcation and chaos also change accordingly.On the basis of considering nonlinear dynamic force, the effect of nonlinear oil film force is considered further, dynamic model of geared rotor-oil journal bearing system is proposed. The nonlinear dynamic responses of system are investigated by numerical integration method. The results show that with the increase of rotational speed, the nonlinear vibration characteristic of system is affected by nonlinear mesh force and nonlinear oil film force respectively in different speed range. The vibration characteristic of system is mainly affected by nonlinear mesh force when speed is relatively low. With the increase of speed, the influence of nonlinear oil film force on the vibration also increases gradually, and the sub-synchronous forward precession phenomena appear when the speed approaches the twice of first order critical speed (it can be lateral-torsional critical speed caused by gear mesh, it is not need to be pure lateral critical speed of rotor). By comparing the effect of linear eight parameter oil film fore and nonlinear oil film fore on mesh force, the results show that when rotational speed increases to twice of the first order critical speed of system (it can be lateral-torsional critical speed), the nonlinear mesh force is affected by nonlinear oil film force gradually, the sub-synchronous forward precession frequency appears in spectrum plot of mesh force. With the increase of speed, the effect of nonlinear oil film fore on nonlinear mesh force also increase, it may exceed the effect of unbalance on mesh force. However, the conventional linear oil film force does not affect the mesh force.In order to validate the correctness of numerical integration's results, a geared rotor bearing system vibration test-bed is designed, and a kind of equipment which is used to adjust clearance is innovated independently, the effect of clearance on the vibration characteristic of geared rotor bearing system is studied on the test-bed by this new equipment. The experimental data show that when the speed is not resonance speed, there is the undesirable range of clearance which causes the vibration of system relatively large, there is also the preferable range of clearance which cause the vibration of system relatively small. When clearance increase to certain value, the meshing state of system commonly retains the single side impact, the vibration amplitude of system will retain in certain range, continue to increase clearance will not affect the vibration of system greatly. The rolling bearing of driving geared rotor system is transformed to oil journal bearing on the basis of geared rotor rolling bearing system test-bed, the vibration of system is measured under several speed, the experimental data show that when the rotational speed is low and far from the first order lateral critical speed, the vibration of system is affected by nonlinear mesh force mainly, the results of numerical integration are validated by the experimental results basically.