• Title/Summary/Keyword: Unbalance Response Analysis

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Vibration Analysis of Cracked Rotor (균열 회전체의 진동해석)

  • Jun, Oh-Sung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.05a
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    • pp.925-934
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    • 2005
  • The dynamic response due to the unbalance and crack and the quasi-static response due to gravity are analytically derived based on the complex transfer matrix. The additional slope is expressed as function of the bending moment at crack position based on the fracture mechanics concept, and inversely the bending moment is expressed as function of the additional slope at the crack position. At each angle step during the shaft revolution, the additional slope and bending moment are calculated by an iterative method. The transient behavior is considered by introducing Fourier series expansion concept for the additional slope. Simulation is carried out for a simple rotor similar to those available in the literature and comparison of the basic crack behavior is shown. Using the additional slope, the cracked rotor behavior is explained with the crack depth increased: the magnitude of the additional slope increases and the closed crack duration during a revolution decreases as the crack depth increases. The direction of unbalance is also shown as a factor to affect the crack breathing. Whirl orbits are shown near the sub-critical speed ranges of the rotor.

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Vibration Analysis of Flexible Rotor Having a Breathing Crack (개폐균열이 존재하는 유연 회전체의 진동해석)

  • Jun, Oh-Sung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.10 s.103
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    • pp.1137-1147
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    • 2005
  • The dynamic response due to the unbalance and crack and the quasi-static response due to gravity are analytically derived based on the complex transfer matrix. The additional slope is expressed as function of the bending moment at crack position based on the fracture mechanics concept, and inversely the bending moment is expressed as function of the additional slope at the crack Position. At each angle step during the shaft revolution, the additional slope and bending moment are calculated by an iterativemethod. The transient behavior is considered by introducing Fourier series expansion concept for the additional slope. Simulation is carried out for a simple rotor similar to those available in the literature and comparison of the basic crack behavior is shown. Using the additional slope, the cracked rotor behavior is explained with the crack depth increased: the magnitude of the additional slope increases and the closed crack duration during a revolution decreases as the crack depth increases. The direction of unbalance is also shown as a factor to affect the crack breathing. Whirl orbits are shown near the sub-critical speed ranges of the rotor.

Vibration Analysis of Rotor Systems Using Finite Dynamic Elements (동적 유한요소에 의한 회전축 계의 진동 해석)

  • 양보석;황형섭
    • Journal of KSNVE
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    • v.7 no.3
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    • pp.467-475
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    • 1997
  • A rotor-bearing system has been investigated, including internal damping and axial torque using finite dynamic elements. A procedure is presented for dynamic modeling of rotor-bearing system which consist of finite dynamic shaft elements, rigid disk, and bearing and seal. A finite dynamic element model including the effects of rotatory inertia, gyroscopic moments, axial force, and axial torque is developed using the frequency dependent shape function. The natural whirl speeds, stability, and unbalance response of rotor system are calculated on several cases and compared with the conventional finite elements.

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Journal Bearing Design Retrofit for Process Large Motor-Generator - Part II : Rotordynamics Analysis (프로세스 대형 모터-발전기의 저어널 베어링 설계 개선 - Part II : 로터다이나믹스 해석)

  • Lee, An Sung
    • Tribology and Lubricants
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    • v.28 no.6
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    • pp.265-271
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    • 2012
  • In the preceding Part I study, for improving the unbalance response vibration of a large PRT motor-generator rotor fundamentally by design, a series of design analyses were carried out for bearing improvement by retrofitting from original plain partial journal bearings, applied for operation at a rated speed of 1,800 rpm, to final tilting pad journal bearings. To satisfy evenly key basic lubrication performances such as the minimum lift-off speed and maximum oil-film temperature, a design solution of 5-pad tilting pad journal bearings and maximizing the direct stiffness by about two times has been achieved. In this Part II study, a detailed rotordynamic analysis of the large PRT motor-generator rotor-bearing system will be performed, applying both the original plain partial journal bearings and the retrofitted tilting pad journal bearings, to confirm the effect of rotordynamic vibration improvement after retrofitting. The results show that the rotor unbalance response vibrations with the tilting pad journal bearings are greatly reduced by as much as about one ninth of those with the plain partial journal bearings. In addition, for the tilting pad journal bearings there exist no critical speed up to the rated speed and just one instance of a concerned critical speed around the rated speed, whereas for the plain partial journal bearings there exist one instance of a critical speed up to the rated speed and two instances of concerned critical speeds around the rated speed.

Rotordynamic Analysis of a Dry Vacuum Pump Rotor-Bearing System for High-Speed Operation (고속 운전용 건식진공펌프 로터-베어링 시스템의 회전체동역학 해석)

  • Lee, An-Sung;Lee, Dong-Hwan;Kim, Byung-Ok
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.11a
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    • pp.523-530
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    • 2006
  • A rotordynamic analysis was performed with a dry vacuum pump, which is a major equipment in modern semiconductor and LCD manufacturing processes. The system is composed of screw rotors, lobes picking air, helical gears, driving motor, and support rolling element hearings of rotors and motor. The driving motor-screw rotor system has a rated speed of 6,300rpm, and was modeled utilizing a rotordynamic FE method for analysis, which was verified through the results of its 3-D finite element model. As loadings on the bearings due to the gear action were significant in the system considered, each resultant bearing load was calculated determinately and indeterminately by considering the generalized forces of the gear action as veil as the rotor itself. Each resultant hearing loading was used in calculating each stiffness of rolling element bearings. Design goals are to achieve wide separation margins of critical speeds and favorable unbalance responses of the rotor in the operating range. Then, a complex rotordynamic analysis of the system was carried out to evaluate its forward synchronous critical speeds, whirl natural frequencies and mode shapes, and unbalance responses under various unbalance locations. Results show that the entire system is well designed in the operating range. In addition, the procedure of rotordynamic analysis for dry vacuum pump rotor-bearing system was proposed and established.

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A Rotordynamic Analysis of Dry Vacuum Pump Rotor-Bearing System for High-Speed Operation (고속 운전용 건식진공펌프 로터-베어링 시스템의 전체동역학 해석)

  • Kim, Byung-Ok;Lee, An-Sung;Noh, Myung-Keun
    • The KSFM Journal of Fluid Machinery
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    • v.10 no.3 s.42
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    • pp.47-54
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    • 2007
  • A rotordynamic analysis was performed with a dry vacuum pump, which is a major equipment in modem semiconductor and LCD manufacturing processes. The system is composed of screw rotors, lobes picking air, helical gears, driving motor, and support rolling element bearings of rotors and motor. The driving motor-screw rotor system has a rated speed of 6,300rpm, and was modeled utilizing a rotordynamic FE method for analysis, which was verified through the results of its 3-D finite element model. As loadings on the bearings due to the gear action were significant in the system considered, each resultant bearing load was calculated determinately and indeterminately by considering the generalized forces of the gear action as well as the rotor itself. Each resultant bearing loading was used in calculating each stiffness of rolling element bearings. Design goals are to achieve wide separation margins of critical speeds and favorable unbalance responses of the rotor in the operating range. Then, a complex rotordynamic analysis of the system was carried out to evaluate its forward synchronous critical speeds, whirl natural frequencies and mode shapes, and unbalance responses under various unbalance locations. Results show that the entire system is well designed in the operating range. In addition, the procedure of rotordynamic analysis for dry vacuum pump rotor-bearing system was proposed and established.

Vibration Analysis of Pump/Turbine and Generator/Motor Rotor System for Pumped Storage Power Stations (양수발전소용 펌프수차${\cdot}$발전기 전동기 축계의 진동해석)

  • Yang, Bo-Suk;Choi, Byung-Gun;Kim, Young-Han;Ha, Hyun-Cheon
    • The KSFM Journal of Fluid Machinery
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    • v.2 no.2 s.3
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    • pp.39-45
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    • 1999
  • Pumped-storage power plants pumps the water from the lower reservoir to the upper reservoir using the extra electric power at night and generates electric power in the daytime. Currently it tends to be a high-head large-capacity machine. In this paper, we developed the computer programs for vibration analysis of the pump/turbine and generator/motor rotor system considering electromagnetic force, hydrodynamic unbalance force, dynamic characteristics of guide bearings and add mass of water. This program was verified by applying it to the real model and calculating the critical speed, natural mode and unbalance response.

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Analysis of Rotordynamic Design Characteristics and Vibration Reduction of an Air Turbo Compressor for Oxygen Plant (산소공장 공기터보압축기(ATC)의 회전체동역학 설계특성 분석 및 진동저감)

  • Kim, Byung-Ok;Lee, An-Sung
    • The KSFM Journal of Fluid Machinery
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    • v.13 no.3
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    • pp.43-48
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    • 2010
  • In this study rotordynamic characteristics of an air turbo-compressor (ATC) used in oxygen plant are analyzed and its operating-speed balancing is performed to solve the vibration trouble caused by rotor unbalance. Three dimensional model of the ATC rotor is completed and then analytical FE (finite element) model, which is verified by experimental modal testing, is developed. A rotordynamic analysis includes the critical map, Campbell diagram, and unbalance response, especially considering the pedestal housings supporting tilting pad bearings. A test run of operating-speed, using tilting-pad bearing of actual use, showed that the vibration level increased very sharply as approaching the rated speed. The operating-speed balancing specified by API 684 was carried out by using influence coefficient method. The results showed that the vibrations at the bearing pedestal housings represented good levels of 0.1 mm/s. From the test run and operating-speed balancing, the analytical results, that is, critical speeds are in good agreement with the test results and unbalance responses introducing the correction masses are similar to the as-is test responses in its aspect.