• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.04a
• /
• pp.260-265
• /
• 1997

Large dynamic loads act on the rotor in rotary compressors. There are unbalance forces due to eccentric rotation parts and gas forces induced by the difference in pressure between compression and suction gases6 Rotor-journal bearing system is nonlinear since the stiffness and damping coefficients of the lubricating oil film are not constant in the bearings. In this paper, the program for predicting the behaviors of rotor-journal bearing system of rotary compressor is developed. Finite element modeling is used to analyze the flexible rotor. The numerical results are compared with experimental results. The location of balancer weight are suggested for reducing rotor whiring displacement.

• International Journal of Fluid Machinery and Systems
• /
• v.3 no.1
• /
• pp.67-79
• /
• 2010

Severe flexural vibration of the rotor shaft of a Francis turbine runner was experienced in the past. It was shown that the vibration was caused by the fluid forces and moments on the backshroud of the runner associated with the leakage flow through the back chamber. The aim of the present paper is to study the self-excited rotor vibration caused by the fluid force moments on the backshroud of a Francis turbine runner. The rotor vibration includes two fundamental motions, one is a whirling motion which only has a linear displacement and the other is a precession motion which only has an angular displacement. Accordingly, two types of fluid force moment are exerted on the rotor, the moment due to whirl and the moment due to precession. The main focus of the present paper is to clarify the contribution of each moment to the self-excited vibration of an overhung rotor. The runner was modeled by a disk and the whirl and the precession moments on the backshroud of the runner caused by the leakage flow were evaluated from the results of model tests conducted before. A lumped parameter model of a cantilevered rotor was used for the vibration analysis. By examining the frequency, the damping rate, the amplitude ratio of lateral and angular displacements for the cases with longer and shorter overhung rotor, it was found that the precession moment is more important for smaller overhung rotors and the whirl moment is more important for larger overhung rotors, although both types of moment due to the leakage flow can cause self-excited vibration of an overhung rotor.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.4 no.3
• /
• pp.193-198
• /
• 2003

A rotor dynamic analysis is implemented to confirm the vibration stability of the high speed centrifugal chiller coupled with gear system. As the rotating speed of the centrifugal chiller under investigated is increased up to 17,605 rpm at the pinion rotating part, the bearing instability is getting higher and, furthermore, the rotor-bearing system might experience a few critical speed which lead to system failure due to the excessive vibration. In this study, considering the loading capacity and stability conditions, offset journal bearings are adopted for the pinion rotating system and general cylindrical bearing are used for motor part. From the modal analysis, the system is found to be stable as the synchronous rotating frequency does not come across with any whirl natural frequency and, in addition, the critical damping ratio which shows the damping characteristics of the system are positive over the all operating ranges. From these results the authors confirm the vibration stability of the rotor-bearing system suggested in this study.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.14 no.10
• /
• pp.1035-1040
• /
• 2004

The vibration of an electric hand grinder originates from the motor, gear, bearing, and fan. Its excessive vibration can be harmful to workers. To reduce the vibration of an electric hand grinder. frequency analysis for the vibration signals of a running electric hand grinder and modal test for the each part were done. The results show that the vibration is due to the resonance of the case. To remove the resonance, the case structure was modified and the bearing cap was replaced on a basis of the results of the rotor dynamic analysis using SAMCEF. As a result, the vibration of the electric hand grinder was reduced greatly.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2011.10a
• /
• pp.236-241
• /
• 2011

An active trailing-edge flap blade named as Seoul National University Flap (SNUF) blade is designed for reducing helicopter vibratory loads and the relevant aeroacoustic noise. Unlike the conventional rotor control, which is restricted to 1/rev frequency, an active control device like the present trailing-edge flap is capable of actuating each individual blade at higher harmonic frequencies i.e., higher harmonic control (HHC) of rotor. The proposed blade is a small scale blade and rotates at higher RPM. The flap actuation components are located inside the blade and additional structures are included for reinforcement. Initially, the blade cross-section design is determined. The aerodynamic loads are predicted using a comprehensive rotorcraft analysis code. The structural integrity of the active blade is verified using a stress-strain recovery analysis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.838-843
• /
• 2001

Internal damping plays an important role in some rotor dynamic systems with the use of various materials for shafts, for example, composite material. However, although the effects of internal damping have been investigated for a couple of decades, there are several different internal damping models in use, none of which are accepted as the most reliable model. The purpose of this paper is to compare the results of dynamic analysis of rotor systems with several different internal damping models. The exact dynamic element method is used to formulate and analyze the problem. The simulation results provided in this paper may be useful for the dynamic analysis of high rotor systems subject to significant internal damping.

• Proceedings of the KIPE Conference
• /
• 2008.10a
• /
• pp.85-87
• /
• 2008

This paper presents dynamic characteristics in Switched Reluctance Motor (SRM) with rotor eccentricity and proposes the reduction method of rotor eccentricity effects by the different winding connections. These characteristics investigations are computed by 2D transient magnetic FEM analysis coupled with external circuits. The radial and unbalance magnetic force in the stator, which is the main exciting force of the vibration, is calculated using Maxwell stress method and compared with the performance characteristics according to the serial and parallel connections of windings. The influence of winding method counteracting unbalance forces on the rotor vibration behavior is estimated by the current waveforms of the paralleled paths under rotor eccentricity.

• Journal of Electrical Engineering and Technology
• /
• v.5 no.3
• /
• pp.462-467
• /
• 2010

This paper presents the rotor shape optimization of an interior type permanent magnet (IPM) motor for a reduction of vibration and Electromagnetic Interference (EMI). The vibration and EMI in permanent magnet motors is generated by cogging torque ripple, radial force and commutation torque ripple. Consequently, in order to improve vibration and EMI, the optimal notches are put on the rotor pole with an arc shape proposed. The variation of vibration frequency due to the cogging torque and radial force of each model is computed by the finite element method (FEM). From the analysis result and experiment, we confirmed the proposed model has remarkably improved the vibration and EMI.

• Journal of Mechanical Science and Technology
• /
• v.15 no.2
• /
• pp.152-159
• /
• 2001

In this paper it is intended to set-up a sound model of the 60,000rpm 100kW prototype APU gas turbine rotor-bearing system, and particularly to investigate the influences of the tie shaft on the rotordynamic characteristics of the entire APU gas turbine rotor-bearing system, employing the dual shaft model. Firstly, a mock-up APU rotor has been constructed to test and verify the model. Analytical natural frequency results have agreed with the corresponding modal test ones to within 5% difference. Then, the rotordynamic characteristics of the prototype APU rotorbearing system have been investigated. Natural vibration and unbalance response analyses results have shown that the inner tie shaft resonance can cause high enough vibration of the outer main rotor shaft. This could be a concern as the rotor journals operate on very thin air film at high speed. It is concluded as a conservative design practice that the inner tie shaft should be explicitly modeled in the rotordynamic analysis of the APU rotor-bearing system.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.55 no.7
• /
• pp.346-352
• /
• 2006

In Brushless DC Motor, there are Permanent Magnets (PMs) with driving circuit and sensor for detecting to rotor position and rotation speed. In the case of using hall IC sensor which response to magnetic flux, that is required to additional sensor magnet for rotor position detecting. Most of BLDC motor, However, take asymmetrical overhang of PM in rotor instead of additional sensor magnet for operating of hall IC sensor. The asymmetrical overhang of PM occur rotor thrust to z-axis direction that is lead to not only damage of bearing but also intensive noise and vibration. Therefore, the analysis of magnet overhang effect in the side of vibration and drive to hall If sensor is required to precise. In this paper, 2-D Finite Element Method is used to solve precise field computation and thrust of z-axis direction considering asymmetrical magnet overhang. And also the z-axis thrust from the analysis result is compared to experimental result. In conclusion, the purpose of this paper minimize to noise and vibration of BLDC Motor as analyzes to asymmetrical magnet overhang effect.