• International Journal of Fluid Machinery and Systems
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• 제3권3호
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• pp.211-220
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• 2010

The objective of this study is to clarify the occurrence of the high-speed mode of unsteady swirling flows in straight tubes. The unsteady flows generated in the tube were measured by means of a semiconductor-type pressure transducer and an FFT analyzer. The high-speed mode measured has rotational speed which is approximately equal to or higher than the peripheral velocity of the swirling flow. The unsteady flow is due to cell rotation in the circumferential direction of the tube. The occurrence of the high-speed mode was confirmed, and the characteristics (rotational speed, pressure amplitude, and phase) of this mode were clarified. In order to understand the measured unsteady flows, the three dimensional vortex core profiles were discussed based on the distributions of the pressure amplitude and phase.

• Journal of Mechanical Science and Technology
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• 제18권11호
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• pp.1969-1977
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• 2004

To model and understand the physics of partial rub, a nonlinear rotor model is sought by applying a nonlinear parameter identification technique to the experimental data. The results show that the nonlinear terms of damping and stiffness should be included to model partial rotor rub. Especially, the impact and friction during the contact between rotor and stator are tried to explain with a nonlinear model on the basis of experimental data. The estimated nonlinear model shows good agreements between the numerical and the experimental results in its orbit. Also, the estimated nonlinear model could explain the backward whirling orbit and jump phenomenon, which are the typical phenomena of partial rub.

• Journal of Chest Surgery
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• 제33권1호
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• pp.112-115
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• 2000

A-13-urar-old with a history of Alport syndrome had been suffering from progressive dysphagia and postprandial vomiting for over 7 years. Exophagogram and manoemtric studies were consistent with achalasia. Barum study demonstrated marked esophageal dilatation and smooth tapered narrowing of the distal esophagus. However in spite of the medical treatment including the injection of the distal esophagus. However in spite of the medical treatment including the injection of botulinum toxin at the lesion site using an endoscope symptom did not improved and he suffered growth failure and malnutrition. Esophagectomy and esophagogastrostomy were performed to relieve the dysphagia. A firm circumferential intramural mass about 7$\times$5$\times$5 cm was found in the distal esophagus. The lumen of the esophagus was markedly dilated and esophageal wall was hypertrophied. Histologic examination of the neoplasm revealed a rather ill defined tumor tissue consisting of interlacing or whirling spindle cells without significant mitosis and esophageal leiomyo-matosis was confirmed. The patient was discharged uneventfully.

• Tribology and Lubricants
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• 제19권6호
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• pp.342-348
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• 2003

The purpose of the paper is to investigate the noise characteristics of cylindrical roller bearings. For the sake of simplicity, it is assumed that the cylindrical roller bearing is infinitely long, and there is no outside force acting on the bearing. The effects of radial clearance of the bearing, viscosity of the lubricant and number of the roller on the noise of the bearing are also examined. Results show that the fundamental frequency of the bearing noise corresponds to the multiplication of number of the roller and whirling frequency of the roller center or the retainer. The acoustical frequency spectra of the roller bearing are pure tone spectra, containing the fundamental frequency of the bearing and its super­harmonics. The low viscosity of the lubricant, high radial clearance of the bearing, and low number of the roller decrease the bearing noise. The results and discussions of the present paper could aid in the low­noise design of the cylindrical roller bearing.

• Journal of Advanced Marine Engineering and Technology
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• 제22권1호
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• pp.35-41
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• 1998

A Self-compensating liquid balancer is proposed, which consists of the vessel contains liquid available to compensate for rotor unbalance, and the vessel provides four sets of suction pipe and reservior. Under the centrifugal field the liquid moves through the pipe from the side of the unbalance mass to the reservior located on the symmetrically opposite side. The liquid balancer was confirmed experimentally to be useful for the balancing of rotor over the critical speed, and the whirling amplitude after balancing decreases to almost constant value in spite of the location and size of unbalance.

• 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.

• 대한기계학회논문집
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• 제9권1호
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• pp.24-30
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• 1985

본 연구에서는 풍동을 사용한 모델 실험을 통하여 어긋난 배열을 갖는 파이프 집합체 모델의 고유진동수와 감쇄비를 변화시키면서 3가지 P/D값에서의 불안정 임계속 도를 실험으로 구하였다. 이와 같은 실험은 Connors, Pettigrew Gorman, Weaver & Grover, Tanaka등 많은 사람에 의하여 산발적으로 발표되어 졌으나 본 연구에서는 파 이프 집합체의 P/D값을 바꾸어 가며 넓은 질량―감쇄비 영역에서 체계적으로 실험을 수행하고 그 결과를 비교 분석하였다.

• 소음진동
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• 제9권3호
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• pp.461-465
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• 1999

This paper presents theoretical analyses for unstable vibrations caused by the couple of bending and torsion in a rotating shaft driven through a universal joint. A driving shaft is assumed to be rigid and to rotate with a constant angular velocity. The driven shaft system consists of a flexible shaft with a circular section and a symmetrical rotor attached at a point between the shaft ends. Equations of motion derived hold with an accuracy of the second order of shaft deformations, and are analyzed by the asymptotic method. The vibrations become unstable when the driving shaft rotates with the angular velocity to be approximately equal to half of the sum of the natural frequencies for whirling and torsional vibrations.

• Tribology and Lubricants
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• 제18권1호
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• pp.9-15
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• 2002

The nonlinear vibration characteristics of hydrodynamic journal bearings with a circumferential groove we analyzed numerically when the external sinusoidal disturbances are given to the rotor-bearing system continuously. Furthermore, a cavitation algorithm, implementing the Jakobsson-Floberg-Olsson boundary condition, is adopted to predict cavitation regions in a fluid film more accurately than the conventional analysis. which uses the Reynolds boundary condition. It is found that the difference between linear and nonlinear analysis is much more remarkable as the amplitude of external disturbance increases, and it depends upon the excitation frequency of the external disturbance. It is also shown that the cavity region in the fluid film increases as the amplitude or excitation frequency of the external disturbance increases. The whirling center of the steady state orbit moves closer to the bearing center as the amplitude or excitation frequency of the external disturbance increases.