• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.10
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• pp.813-820
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• 2003

Conventional modal analysis techniques are known to be inappropriate for asymmetrical rotor systems, when the equations of motion are written in the stationary coordinates, due to the presence of time varying parameters. This paper presents a generalized modal analysis method for asymmetrical rotor systems in the stationary coordinates, employing the modulated coordinates and the lambda matrix formulation. A numerical example with a flexible asymmetric rotor model is provided to demonstrate the effectiveness of the proposed modal analysis method. As an application of the proposed method, modal analysis is also performed with an open cracked rotor system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.526-531
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• 2003

Conventional modal analysis techniques are known to be inappropriate for asymmetrical rotor systems. when the equations of motion are written in the stationary coordinates, due to the presence of time varying parameters. This paper presents a generalized modal analysis method for asymmetrical rotor systems in the stationary coordinates, employing the modulated coordinates and the lambda matrix formulation. A numerical example with a flexible asymmetric rotor model is provided to demonstrate the effectiveness of the proposed modal analysis method. As an application of the proposed method, modal analysis is also performed with an open cracked rotor system.

• Tribology and Lubricants
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• v.39 no.6
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• pp.221-227
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• 2023

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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.797-803
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• 2009

The accurate prediction of dynamic characteristics of high speed rotors, such as gas turbines, is important to avoid the possibility of operating the machinery near the critical speeds or unstable speed regions. However, the dynamic analysis methods and softwares for gas turbines have been developed in the process of producing many gas turbines by manufacturers and most of them have seldom been disclosed to the public. Recently, commercial FEM softwares, such as SAMCEF, ANSYS and NASTRAN, started supporting some rotordynamics analysis modules based on 3-D finite elements. In this paper, the dynamic analysis method using commercial S/W, especially ANSYS, is attempted for the small-size gas turbine engine rotor, and the analysis capability and limitations of its rotordyamics module are evaluated for further improvement of the module. As the preliminary procedure, the rotordyamic analysis capability of ANSYS was tested and evaluated with the reference models of the well-known dynamics. The limitations in application of the rotordynamics module were then identified. Under the current capability and limitations of ANSYS, it is shown that Lee diagram, a new frequency-speed diagram enhanced with the concept of $H{\infty}$ in rotating machinery, can be indirectly obtained from FRFs computed from harmonic response analysis of ANSYS. Finally, it is demonstrated based on the modeling and analysis method developed in the process of the S/W verification that the conventional Campbell diagram, Lee diagram, mode shapes and critical speeds of the small-size gas turbine engine rotor can be computed using the ANSYS rotordynamics module.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.36-44
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• 2010

The accurate prediction of dynamic characteristics of high speed rotors, such as gas turbines, is important to avoid the possibility of operating the machinery near the critical speeds or unstable speed regions. However, the dynamic analysis methods and softwares for gas turbines have been developed in the process of producing many gas turbines by manufacturers and most of them have seldom been disclosed to the public. Recently, commercial FEM softwares, such as SAMCEF, ANSYS and NASTRAN, started supporting some rotordynamics analysis modules based on 3-D finite elements. In this paper, the dynamic analysis method using commercial S/W, especially ANSYS, is attempted for the small-size gas turbine engine rotor, and the analysis capability and limitations of its rotordyamics module are evaluated for further improvement of the module. As the preliminary procedure, the rotordyamic analysis capability of ANSYS was tested and evaluated with the reference models of the well-known dynamics. The limitations in application of the rotordynamics module were then identified. Under the current capability and limitations of ANSYS, it is shown that Lee diagram, a new frequency-speed diagram enhanced with the concept of $H{\infty}$ in rotating machinery, can be indirectly obtained from FRFs computed from harmonic response analysis of ANSYS. Finally, it is demonstrated based on the modeling and analysis method developed in the process of the S/W verification that the conventional Campbell diagram, Lee diagram, mode shapes and critical speeds of the small-size gas turbine engine rotor can be computed using the ANSYS rotordynamics module.

• Journal of Domestic Journal Test
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• v.11 no.2
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• pp.221-227
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• 2023

− 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 equa- tion of motion for the rotordynamic system can be represented using complex coordinates. The directional fre- quency 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 pre- vious 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 pos- itive 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 uniso- tropic rotor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.619-628
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• 2010

Shape Memory Alloy (SMA) has recently received attention in developing implantable surgical equipments and it is expected to lead the future medical device market by adequately imitating surgeons' flexible and delicate hand movement. However, SMA actuators have not been used widely because of their nonlinear behavior called hysteresis, which makes their control difficult. Hence, we propose a parameter, $t_1$, which is necessary for temperature control, by analyzing the open-loop step response between current and temperature and by comparing it with the values of linear differential equations. $t_1$ is a pole of the transfer function in the invariant linear model in which the input and output are current and temperature, respectively; hence, $t_1$ is found to be related to the state variable used for temperature control. When considering the parameter under heat treatment conditions, $T_{max}$ was found to assume the lowest value, and $t_1$ was irrelevant to the heat treatment.