Dynamic Characteristics of a Rotor-Journal Bearing System Driven by Gearboxes

기어박스로 구동되는 축-저널베어링계의 동적특성에 관한 연구

  • Published : 1995.12.01

Abstract

Gearboxes are often used in the petrochemical and electrical power plants to transmit mechanical power between two branches of a machinery train rotating at different speeds. When the gearboxes are connected with rotors supported by journal bearings, bearing loads vary in magnitude and direction with rotor speed and torque transmitted by the gearboxes. In this study, dynamic characteristics of the system which consists of gearboxes and a rotor supported by journal bearings are investigated analytically and experimentally by employing the polynomial transfer matrix method and modal analysis under different speeds and torque levels. Journal bearing loads due to the transmitted torque are claculated analytically and the stiffness and damping coefficient of the journal bearings are obtained using finite element method. Comparison of the analytical and experimental results shows that the cross coupled stiffness coefficients increase with increasing rotor speed, while the cross coupled damping coefficients decrease. This generates the oil whirl instability in the journal bearings. As the transmitted torque level goes up, the stiffness coefficients of the journal bearing and the first horizontal natural frequency increase. High levels of the transmitted torque produce high bearing stiffness since the contact loads of the mating gear teeth increase. The logarithmic decrement, which is a stability indicator, is shown to decrease with increasing speed and decreasing torque. Thus, at the low torque level, the system become unstable even at the low shaft speed.

Keywords

References

  1. Procs. of the Eighth International Pump Users Symposium Changes in Pump Vibration Levels Caused by the Misalignment of Different Style Couplings Lorenc,J.A.
  2. Technical Document No. TD-001300 High Ratio Gearing James,R.P.
  3. Pros. of IMechE Conf. on Vibrations in Rotating Machinery v.C432 Design of the Speed Changing Gearbox Fluid Film Support Bearings for Minimum Vibrations and Maximum Life Bielk,J.R.
  4. 대한기계학회논문집 v.18 no.3 동력전달용 베벨기어의 강도평가 및 설계시스템개발(1) 정태형;변준형
  5. 대한기계학회논문집 v.17 no.1 저소음 치형의 설계 및 실험에 관한 연구 김호룡;안승준
  6. ASLE Trans. v.25 no.3 Experiments on Stability and Response of a Flexible Rotor in Three Types of journal Bearings Lanes,R.F.;Flack,R.D.
  7. Ph.D. Dissertation Eigenvalues of Rotating Machinery Murphy,B.T.
  8. International Journal of Modal Analysis Modal Testion of Rotor Bearing Systems Muszynska,A.
  9. Mechanical Engineering Design Shigley,J.E.;Mitchell,L.D.
  10. ASLE Proprint No. 78-LC-6B-2 Analysis of Step Journal Bearings-Finite Length, Stability Nicholas,J.C.;Allaire,P.E.
  11. ASME Journal of Engineeing for Industry Stability and Damped Critical Speeds of a Flexible Rotor in Fluid-Film Bearings Lund,J.W.
  12. Star Modal Analysis User's Manual
  13. Journal of Sound and Vibration v.110 Whirl and Whip Rotor/Bearing stability Problems Muszynska,A.
  14. Rotordynamics of Turbomachinery Vance,J.M.
  15. ASLE Trans. v.30 no.2 Experiments on the Stability of an Overhung Rotor in Pressure Dam and Multilobe Bearings Zuck,C.J.;Flack,R.D.
  16. ASLE Trans. v.25 no.3 Experiments on the Stability and Response of a Flexible Rotor in Three Types of Journal Bearings Lanes,R.F.;Flank,R.D.;Lewis,D.W.