• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.82-87
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• 1997

Large dynamic loads act on the rotor in rotary compressors. There are unbalance forces due to eccentric parts and gas forces induced by the pressure difference between compression and suction gases. Rotor-journal bearing system is nonlinear since the stiffness and damping coefficients of the lubricating oil film are not constant in the bearings. The system is considered as a coupled problem of flexible rotor and the journal bearings. Bearing reaction force is calculated from pressure of oil film using Reynolds equations in journal bearings. Pressure distribution in journal bearing is analyzed by finite difference method. The dynamic response of rotor and bearing characteristic are discussed when rotary compressor has a relative misalignment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.528-534
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• 2001

Basic equations and its solution procedure are derived for the analysis of an annular pump seal in which the rotor has a large static displacement from the centered position. The Bulk-flow is assumed for a control volume set in the seal clearance and the flow is assumed to be completely turbulent in axial and circumferential direction. Moody's wall-friction-factor formula is used for the calculation of wall shear stresses in the control volume. For the reaction force developed by the seal, linearized zeroth-order and first-order perturbation equations are developed for small motion about an eccentric position. Flow variables are expanded by using Fourier series for the solution procedure. Integration of the resultant first-order pressure distribution along and around the seal defines the 12 elements of rotordynamic coefficients of the eccentric annular pump seal. The results of leakage and rotordynamic coefficients are presented and compared with the Marquette's experimental results and the San Andres' theoretical analysis.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.201-209
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• 1999

This paper presents a general analytical method for analyzing mechanical unbalance response of unbalanced electromagnetic forces produced in induction motors with an eccentric rotor and a phase unbalance. The equations to be solved are a set of second order differential equations which give matrices with periodic coefficients that are a function of time due to the unbalanced electro-magnetic force. Unbalance response is processed by Newmark $\beta$ method. Two examples are given including an industrial application. The results show that the method proposed is satisfactory.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1201-1203
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• 2005

This paper presents results of the finite-element(FE) analysis and experiment of air-gap flux variation in induction motor when rotor eccentricity vibration conditions occur. An accurate modeling and analysis of rotor vibration in the machine are developed using commercial FE analysis tool and search coils are used for measuring the actual air-gap flux. In the FE analysis and experiment, the induction motor with 380[V], 5[HP], 4r, 1742[rpm] ratings is used. The simulation and experimental results can be useful for rotor vibration monitoring of the induction motor.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.9
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• pp.454-461
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• 2001

Acoustic noise and vibration of a BLDC motor is a coupled phenomenon between mechanical characteristics and electromagnetic origins through the motor air-gap. When a relative misalignment of rotor in the air-gap center exists on the assemblage, it is considered to influence the motor system characteristics. In this paper, the back electro motive force(BEMF) is analyzed by Finite Element Method(FEM) and verified by experiments for the SPM and IPM type motors. For magnetic field analysis, a FEM is used to account for the magnetic saturation. Using these results, the FEM is made to determine the appropriate electromagnetic field analysis in BLDC motors with rotor eccentricity ratio. A radial magnetic imbalance force of BLDC motor with rotor eccentricity is analyzed. Results demonstrate that the imbalance force is increased according to the degree of misalignment. An IPM motor, mostly chosen to realize high-speed operation, shows a worse effect on magnetic unbalanced forces and dynamic responses compared with SPM motor due to magnetic saturation when the rotor eccentricity exists.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.611-613
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• 2000

Rotor eccentricity exists extensively in BLDC motors because of manufacturing imprecision or bearing defects. In this paper, magnetic fields of a BLDC motor with static rotor eccentricity are analyzed by the time- stepping finite element method. Torque ripple, cogging torque, winding current, counter-em! and unbalanced magnetic force characteristics are obtained. These results are compared with those of a non-eccentric BLDC motor.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.545-548
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• 2002

Turbines have been known to be particularly susceptible to flow-induced self-excited vibration. In such vibrations, direct damping and cross stiffness effects of aerodynamic forces determine rotordynamic stability. In axial turbines with eccentric shrouded rotors, the non-uniform sealing gap causes azimuthal non-uniformities in the seal gland pressure and the turbine torque which destabilize the rotor system. Previously, research efforts focused solely on either the seal flow or the unshrouded turbine passge flow. Recently, a model for flow in a turbine with a statically offset shrouded rotor has been developed and some stiffness predictions have been obtained. The model couples the seal flow to the passage flow and uses a small perturbation approach to determine nonaxiymmetric flow conditions. The model uses basic conservation laws. Input parameters include aerodynamic parameters (e.g. flow coefficient, reaction, and work coefficient); geometric parameters (e.g. sealing gap, depth of seal gland, seal pitch, annulus height); and a prescribed rotor offset. Thus, aerodynamic stiffness predictions have been obtained. However, aerodynamic damping (i.e. unsteady aerodynamic) effects caused by a whirling turbine has not yet been examined. Therefore, this paper presents a new unsteady model to predict the unsteady flow field due to a whirling shrouded rotor in turbines. From unsteady perturbations in velocity and pressure at various whirling frequencies, not only stiffness but also damping effects of aerodynamic forces can be obtained. Furthermore, relative contributions of seal gland pressure asymmetry and turbine torque asymmetry are presented.

• Tribology and Lubricants
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• v.22 no.6
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• pp.342-349
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• 2006

In this study, a dynamic behavior of rotor-bearing system used in CNG compressor has been investigated using the combined methodologies of finite elements and transfer matrices. The finite element is formulated including the field element for a shaft section and the point element for roller bearings. The Houbolt method is used to consider the time march for the integration of the system equations. The transient whirl response of rotating shaft supported on roller bearings is obtained, considering compression forces and unbalance forces at eccentric crank-pin part. And, the steady state displacements of the rotor are compared with a variation in stiffness coefficient of roller bearings. Results show that the loci of crankshaft considering unbalance forces and external compression forces are more severe in whirl motion than with only unbalance forces.

• Journal of KSNVE
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• v.8 no.6
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• pp.1086-1092
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• 1998

This paper presents a general analytical method for analyzing the instability of unbalanced electromagnetic forces produced in induction motors with an eccentric rotor. The equations to be solved are a set of second order differential equations which give matrices with periodic coefficients that are a function of time due to the unbalanced electromagnetic force. The method is based on an extension of the Floquet theory. A transfer matrix over one period of the motion is obtained. and the stability of the system can be determined with the eigenvalues of the matrix. The analysis results of instability zone were coincided upon comparing that of transfer matrix method with that of rotating frame. Two examples are given. including an industrial application. The results show that the method proposed is satisfactory.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.3
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• pp.104-109
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• 1999

In order to design and predict the performance of the harmonic side drive motor, it is necessary to analyze the torque generated by the structure. In this paper, an analytical model is proposed for design. Conformal mapping is used to model the capacitance and torque of the motor as a function of the rotor angular position with two-dimensional approximation. Then the result of conformal mapping analysis is verified with F.E.M result.