방향성 주파수 응답 함수를 이용한 회전체 동역학 해석
Rotordynamic Analysis Using a Direction Frequency Response Function
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초록
A rotordynamic system consists of components that undergo rotational motion. These components include shafts, impellers, thrust collars, and components that support rotation, such as bearings and seals. The motion of this type of rotating system can be modeled as two-dimensional motion and, accordingly, the equation of motion for the rotordynamic system can be represented using complex coordinates. The directional frequency response function (dFRF) can be derived from this complex coordinate system and used as an effective analytical tool for rotating machinery. However, the dFRF is not widely used in the field because most previous studies and commercial software are based on real coordinate systems. The objective of the current study is to introduce the dFRF and show that it can be an effective tool in rotordynamic analysis. In this study, the normal frequency response function (nFRF) and dFRF are compared under rotordynamic analysis for isotropic and unisotropic rotors. Results show that in the nFRF, the magnitude of the response is the same for both positive and negative frequencies, and the response is similar under all modes. Consequently, the severity of the mode cannot be identified. However, in the dFRF, the forward and backward modes are clearly distinguishable in the frequency domain of the isotropic rotor, and the severity of the mode can be identified for the unisotropic rotor.
Abstract
A rotordynamic system consists of components that undergo rotational motion. These components include shafts, impellers, thrust collars, and components that support rotation, such as bearings and seals. The motion of this type of rotating system can be modeled as two-dimensional motion and, accordingly, the equation of motion for the rotordynamic system can be represented using complex coordinates. The directional frequency response function (dFRF) can be derived from this complex coordinate system and used as an effective analytical tool for rotating machinery. However, the dFRF is not widely used in the field because most previous studies and commercial software are based on real coordinate systems. The objective of the current study is to introduce the dFRF and show that it can be an effective tool in rotordynamic analysis. In this study, the normal frequency response function (nFRF) and dFRF are compared under rotordynamic analysis for isotropic and unisotropic rotors. Results show that in the nFRF, the magnitude of the response is the same for both positive and negative frequencies, and the response is similar under all modes. Consequently, the severity of the mode cannot be identified. However, in the dFRF, the forward and backward modes are clearly distinguishable in the frequency domain of the isotropic rotor, and the severity of the mode can be identified for the unisotropic rotor.
참고문헌 (7)
- Rao, J. S., "Rotor Dynamics" (1996), New Age International Publishers
- Lee, C. W., "Vibration Analysis of Rotors" (1993), Kluwer Publishers
- Lee, C. W., "A New Test Theory in Rotating Machinery", Proceedings of the 8th IMAC, pp.148~154 (1990)
- Lee, C. W., "Complex Modal Testing Theory for Rotating Machinery", Mechanical System and Signal Processing, 5(2), pp.119~137 (1991)
- Mesquita, A. A., "A Comparison Between the Traditional Frequency Response Function and the Directional Frequency Response Function in Rotordynamic Analysis", First South American Congress on Computational Mechanics (2002)
- Kessler, C. L., "Complex Modal Analysis of Rotating Machinery", Doctor, pp.1999
- 이동현, "Rotordynamic analysis and operation test of the power turbine with the concept of the Lee diagram", Journal of Mechanical Science and Technology, 33(9), pp.4183~4190 (2019), 대한기계학회