Study Of Dynamic Characteristics Of Rotor System With Metal Rubber Ring And Conical Bearing Combined Support

Conical hybrid (hydrodynamic-hydrostatic) bearing has the advantages ofdynamic pressure bearing and aero-static bearing, such as the capability of bearingthe axial and radial load, steady start, easy adjustment for axial clearance, lessfrictional power loss in high-speed rotation, etc. These advantages had widden itsapplication in high speed rotation machines. However, the rotor supported byjournal bearing may generate severe vibration when it runs across the critical speedcaused by the unbalanced mass or the external disturbance. The nonlinearity of oilfilm force may also generate the self-excited vibration which may lead to theinstability of the rotor system. In order to control the vibration of high-speedrotating machinery, the damping elements made of Metal Rubber (MR) materialhave been widely used in the field of vibration reduction because of its gooddamping performance, light weight, accessibility to produce elements with variousshapes, suitability of severe environment, adjustable stiffness, and so on.In the present study, a high speed rotor system with combined supportconsisted with conical hybrid sliding bearing and MR ring was designed. Thecalculation method for the dynamic characteristics of MR ring, the lubricationperformance of conical hybrid bearing, the systematic modeling and designingmethods of this system have been researched. The dynamic characteristics of thiscombined bearing high-speed system have been studied experimentally.Based on the experimental results of MR segment,model building was used tobuild a hysteretic restoring stress mathematical model of MR microelement innon-molding direction and shaping direction. The expression for the nonlinearhysteresis force versus relative density was derived, and a formula for thecalculation of dynamics parameters of MR damping ring was deduced. The dynamicparameters of MR ring were tested which shows the accordance with the theoreticalsimulation results. Theoretical and experiment results show that the frequency andamplitude of vibration are dependent on the stiffness and damping of MR ring. Thepreloaded deformation and relative density of the ring have great influence on itsradial dynamic stiffness and energy dissipation. The radial stiffness and energydissipation factor are greater numerically than those in axial direction.The oil film force of conical hybrid sliding bearing in the combined supportwas researched. With consideration of the effects of parameters of turbulence,thermal effect and axial velocity, the generalized Reynolds’ equation, energycontrol equation and the oil film lubrication related expressions in polar coordinatesystem were derived, and then discretized using finite difference method which coefficients and constants were treated using Patankar positive coefficientprincipals. The three dimensional pressure field and temperature distribution wereanalyzed numerically. The effects of bearing clearance on the performance ofjournal bearing, as well as the stiffness and damping coefficients of the bearing,were studied. The static pressure, hydrodynamic lubrication and flow characteristicswere tested experimentally. The theoretical results show good agreements with theexperimental results which prove the correctness of the theory.The differential equations of motion for the rotor system with rigid support andcombined support were set up separately. A systematic model based on H_∞theorywas presented. Based on this, a criterion for evaluating the effect of vibrationcontrol and dynamic stability considering the index γ for H_∞theory was proposed.The smaller the index γ for H_∞theory is, the stronger the capability of the system toprevent the disturbance of unbalanced forces is, and the smaller the amplitude of thesystem response is. Through a specific example, index γ for the description of H_∞performance and trail-and-error were used to optimize the parameters for thedynamic design, considering uncertainty of the MR damping ring. The accordanceof simulated and experimental results based on H_∞show the validity of themodeling method.The MR–conical hybrid sliding bearing-high-speed rotor test system was setup. The dynamic characteristics of the conical hybrid sliding bearing with a rigidsupport and a support with a MR ring were compared. Results show that for anoperational conical hybrid sliding bearing at operational stage, it may may generateself excitation and cause the systematic instability. The oil supply pressure to therotor system has a significant effect on the stability range of the system. Theimprovement of oil supply pressure is beneficial to expand this range, but it haslimit to make this range widened. When the MR damping ring is put into the elasticsupport, the primary frequency of the system caused by the unbalanced mass wasreduced, and the frequency for self excitation was increased obviously, whichindicates that the stability range became large. With the increase of oil supplypressure, the system of regional stability was improved significantly. When theparameters of conical hybrid sliding bearing and MR ring to dynamic parametersare matched reasonably, the vibration energy can be dissipated effectively, whichreduces the vibration of the system, improves the system stable speed essentially.The test results show good agreement with the theoretical analysis results.The experimental and theoretical results of this paper are beneficial to thefurther application of MR–conical hybrid sliding bearing joint support in highspeed rotating machinery.