• 대한기계학회논문집A
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• 제25권9호
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• pp.1432-1437
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• 2001

In this paper, a control algorithm which is synchronously excitating the bearing with whirl speed of rotor is employed to suppress the whirl instability and unbalance response of the rotor-bearing system. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than a conventional analysis with the Reynolds condition. The stabilities and unbalance responses of the rotor-bearing system are investigated for various control gains and phase differences between the bearing and journal motion. It is shown that the unbalance response of the system can be greatly improved by synchronous control of the bearing, and there is an optimum phase difference, which gives the minimum unbalance response of the system, for given operating condition. It is also found that the onset speed of the instability can be greatly increased by synchronous control of the bearing.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1055-1056
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• 2007

Asymmetric electro-magnetic force caused by the frictional worn bearing, rotor misalignment and unbalanced rotor etc. generates an asymmetrical operation, vibration and electro-magnetic noise. The need for detection of these rotor eccentricities has pushed the development of monitoring methods with increasing sensitivity and noise immunity. This paper is proposed the analysis method of the squirrel-cage induction motor driven by IGBT inverter using finite element method (FEM) and subroutine. The effect of the unbalanced magnetic pull in the inverter-fed induction motor which is in asymmetrical whirling motion is presented. The analysis results of rotor eccentricity could compare with motors which have been made normal air-gap motor and irregular air-gap motor and verify reliability. The simulation and experiment results can be useful for on-line faults detection monitoring system of induction motors.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1630-1638
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• 2001

Partial rotor rub occurs when an obstacle on the stator of a rotating machinery disturbs the free whirling motion of the rotor, which is more common than full annular rub among the cases of rubbing in rotating machinery. The intermittent contacts and friction during partial rotor rub makes the phenomenon complex. The several nonlinear phenomena of superharmonics, subharmonics, and jump phenomenon are demonstrated for the partial rub using an experimental apparatus in this study. The orbit patterns are also measured experimentally. In order to explain the phenomena of partial rotor rub, the analytical model for the contact between the rotor and stator should be chosen carefully. In this respect, a piecewise-linear model and a rebound model using the coefficient of restitution are investigated on the basis of the experimental observations. Also, Numerical simulations for the two models of contact are done for the various system parameters of clearance, contact stiffness, and friction coefficient. The results show that the piecewise-linear model for partial rotor rub is more plausible to explain the experimental observgations.

• 대한기계학회논문집A
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• 제25권4호
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• pp.748-755
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• 2001

This paper concerns rotor vibration reduction using magnetic damper system. The fuzzy control logic is utilized to fulfill desired motion. The fuzzy system structure and membership function were first determined by simulation results. The researched control logic contains two fuzzy controller : reference position variation according to the rotor whirling status and error compensation algorithm to minimize the rotor vibration due to unbalance and unstable fluid film force. The Sugeno type output membership function was utilized by several trials and optimized membership function constants were selected from experiments. The experimental results show that the proposed method effectively control and reduce the rotor vibration with fluid film bearings.

• 한방안이비인후피부과학회지
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• 제17권2호
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• pp.106-111
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• 2004

Vertigo is a symptom, not a disease. The tenn vertigo refers to the sensation of spinning or whirling that occurs as a result of a disturbance in balance. It's sometimes referred to as a hallucination of motion. The cause of vertigo is very various and generally divided into peripheral and central. A patient presented with severe vertigo, nystagmus and heteophoria. She has taken the BanHaBaekChulChunMa-tang and treated by acupuncture. After 2 days, her symptoms become disappeared and about 1 week, all symptoms except heterophoria were disapperaed. And after 2 weeks, heterophoria was disappeared. In conclusion, we diagnosed her case as vestbular neuronitis by her clinical course, but we also considered her illness as vertebrobasilar insufficiency, TIA etc.

• 한방안이비인후피부과학회지
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• 제17권2호
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• pp.146-152
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• 2004

Introduction: Vertigo is one of the common symptoms that we can see often clinically. It is hallucination to motion of oneself or surroundings. Vertigo include not only simple whirling sensation but also leaning or falling down sensation. Particularly in vestibular neuritis, the principal symptoms is dizziness and accompanied by nystagmus, gait imbalance, nausea, vomiting. Cause of vestibular neuritis is inflammatory disease such as common cold. Objective: The aim of this study was to estimate the efficacy of oriental-treatment on vestibular neuritis patient Subjects: We diagnosed one patient who had severe vertigo and gait imbalance as "dizziness retention of phlegm"(담훈) and treat orientally. Conclusion: After oriental-treatment for 15 days, walk balance was improved and no more vertigo was appeared. We could assume that in the vertigo and gait inbalance due to vestibular neuritis, the acupuncture and herbal medicine can be used.

• 한방안이비인후피부과학회지
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• 제16권1호
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• pp.214-219
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• 2003

Vertigo is one of the common symptoms that we can see often clinically. It is hallucination to motion of oneself or surroundings. Vertigo include not only simple whirling sensation but also leaning or falling down sensation. Particularly in benign paroxysmal positional vertigo(BPPV), the principal symptom is dizziness and accompanied by nausea, lightheadness, vomiting. They are induced by positional change which like shake ones head or lay down or turn over in one' s sleep. Cause of BPPV is otoconium fragments which are released from inner ear and stimulate ampulla of semicircular canal. So in treatment BPPV, we often using the Dix-hallpike maneuver that realignment otoconium fragments. A case of vertigo patient suggested BPPV who is diagnosed oriental medically as weakly dizziness showed prominent improvement by medicate Bojungikgi-tang and operate otoconium-realignmentation (improved Dix-hallpike maneuver) maneuver so we reported.

• International Journal of Fluid Machinery and Systems
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• 제3권1호
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• pp.67-79
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• 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.