• 한국유체기계학회 논문집
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• 제7권1호
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• pp.51-57
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• 2004

The waterhammer has recently become more important because the pumping stations were big and the systems conveying the fluid through the large and long transmission pipelines were complex. When the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity As the pressure waves are propagating between the pumping station and the distributing reservoir, the pressure inside the pipe drops to the liquid vapor pressure with the pipeline profile, at which time a vapor cavity forms, and finally the column separation occurs. If the pressure in the pipe is less than the atmospheric pressure, the pipe can be collapsed and destroyed after the water columns separated by the vapor cavity rejoin. During the reverse flow, the pressure is so abnormally increased at the pumping station that the accident of flooding may happen due to the failure of system. In this paper, the field tests on the waterhammer by the startup, stoppage, and power failure of a centrifugal pump were carried out for Yongma transmission pumping station in Seoul. The experimental results were compared with that of the numerical calculations, in which results the procedure of controlled pump normal shut-down and the two-step closing mode of controlling the ball valve for pump emergency stop are proposed to reduce the pressure surge.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.89-90
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• 2002

Ball reducer (HERB Drive: High Efficient Wave Rolling Ball Drive) with waved grooves has many advantages over other types of reducers for high-reduction ratio, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in contact behaviors. In this study, we have investigated the traces of contact between ball and outer ring, and the dynamic contact behaviors of elastohydodynamic lubrication(EHL) with a certain reduction ratio. In order to verify the contact behaviors between ball and outer ring for the critical endurance lift, the contact velocity and load are computed for a cycle. During some intervals of a cycle, the contact velocity reverses its direction very suddenly. It is expected that changing the contact direction causes undesirable endurance performance because EHL film frequently col lapse at the moment of velocity reversal. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very typical in many contact phenomena.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.143-149
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• 2002

Ball reducer with waved grooves has many advantages over other reducers for the high-reduction ratios, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in the contact geometry. In this study, we have investigated the traces of contact between ball and outer race and the working behaviors with a certain reduction ratio. In order to verify the contact behaviors between ball and outer race, which determines the critical endurance life the contact velocity and load are computed for a cycle. During some period of a cycle, the contact velocity reverses its direction very suddenly, which causes undesirable endurance performance of this machinery. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very common in many contact phenomena.

• Journal of Chest Surgery
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• 제10권2호
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• pp.315-326
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• 1977

From 1958 to October 1977, 294 cases of acquired heart disease were operated. There were 68 cases of pericardium, 3 trauma, 2 foreign body, one cardiac thrombus, 3 atrial myxoma, 2 left atrial and 1 right atrial, 2 Budd-Chiari syndrome, and 214 valvular heart disease. Out of 214 cases of valve operation 73 valves were replaced in 64 patients. Male to female ratio was 1.46: 1. The youngest age was 14 years in male and 18 in female. The oldest was 54 years in male and 52 in female. Fifty-five cases of single valve were replaced, consisting of 47 mitral and 8 aortic valves. There were 9 double valve replacement cases which consist of 7 mitral and aortic and 2 mitral .and tricuspid valves. Six varieties of prosthetic valves, 3 ball and 3 disc types and 3 kinds of xenograft tissue valves were utilized. Beall, BjSrk-Shiley and Starr-Edwards prosthetic valves and Hancock valves were used mainly. For single valve 34. 5% and for double valve replacement 44% mortality were noted. There were 23 operative deaths out of 64 patients, over all mortality rate of 36.9%. Mortality for mitral valve replacement was 29.5%. But in recent 12 consecutive cases one death occurred, showing 8.3% mortality. In earlier days thrombocyte anti-adhesive drug dipyramidole-persantin-aspirin and/or SP 54 were adminstered. But in recent cases after heparinization, coumadin and Persantin were prescribed routinely.

• 한국산학기술학회논문지
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• 제21권1호
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• pp.387-392
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• 2020

본 논문은 산업용 밸브의 유량제어시스템을 제안하였다. 산업용 밸브는 주로 배관시스템에 장착되어 유량 및 압력 제어에 사용된다. 제어밸브의 구조 및 작동 방식은 설치환경과 작업용도에 따라 상이하다. 밸브는 그 형태에 따라 그루브 밸브, 버터플라이 밸브 및 볼 밸브 등으로 분류되고, 구동방식은 모터를 이용하거나, 유압 및 공압을 이용하는 것이 일반적이다. 제어밸브를 이용한 유량제어시스템은 유량을 계측하여 피드백시스템을 구현하여야 하지만, 본 논문에서는 고가의 유량센서를 사용하지 않고 밸브의 개폐에 따른 유량변화를 실험하여 밸브 전후단의 압력차와 개폐정도를 이용하는 방법을 제안하였다. 밸브의 유량은 유량계수를 이용하여 밸브 전후단의 압력차와 밸브의 개폐정도로 표현할 수 있으므로 이를 이용하여 유량제어시스템을 설계하였다. 제어입력에 따른 밸브의 개폐를 나타내는 전달함수는 신호압축법을 이용하여 구하였으며, 이를 이용하여 밸브 스템의 명령추종성능을 향상시킬 수 있는 외란관측기를 설계하였다. 제안된 제어시스템의 성능을 검증하기 위해 제어밸브 전후단에 압력센서를 장착하여 제안된 제어방법의 성능이 유량센서를 이용한 경우에 준함을 확인하였다.

• 대한의용생체공학회:의공학회지
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• 제29권4호
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• pp.323-328
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• 2008

A patient with respiratory disorders such as a sleep apnea is increasing as the obese patient increase on the modern society. Positive Airway Pressure (PAP) devices are used in curing patient with respiratory disorders and turn out to be efficacious for patients of 75%. However, these devices are required for evaluating their performance to improve their performance by the mechanical breathing simulator. Recently, the mechanical breathing simulator was studied by the real time feedback control. However, the mechanical breathing simulator by an open loop control was specially required in order to analyze the effect of flow rate and pressure after operating the breathing auxiliary devices. Therefore the aims of this study were to make the mechanical breathing simulator by a piston motion and a valve function from the characteristic test of valve and motor, and to duplicate the flow rate and pressure profiles of some breathing patterns: normal and three disorder patterns. The mechanical simulator is composed cylinder, valve, ball screw and the motor. Also, the characteristic test of the motor and the valve were accomplished in order to define the relationship between the characteristics of simulator and the breathing profiles. Then, the flow rate and pressure profile of human breathing patterns were duplicated by the control of motor and valve. The result showed that the simulator reasonably duplicated the characteristics of human patterns: normal, obstructive sleep apnea (OSA), mild hypopnea with snore and mouth expiration patterns. However, we need to improve this simulator in detail and to validate this method for other patterns.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.291-296
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• 2004

Cast austenitic stainless steel piping pump, valve casings, and elbows are susceptible to reductions in toughness and ductility because of long term exposure at the operating temperatures in LWR(light water reactor). In this paper, we have measured the material properties of long term aged CF-8A cast stainless steel, accelerated aging at $400^{\circ}C$. These studies have been carried out using Indentation tests(automated ball indentation and nano-indentation) and EDS(energy dispersive spectroscopy). The fracture toughness of CF-8A cast stainless steel was also determined by using standard fracture toughness and Automated Ball Indentation.

• 한국자동차공학회논문집
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• 제10권6호
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• pp.202-208
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• 2002

Ball k nut type steering gear box has disadvantages on on-center range as compared with rack & pinion type because of many linkages. In this study, a technique which can improve the on-center loose feel is introduced. The improvement can be obtained by putting simple devices on steering gear box valve body which can change the stiffness of steering gear on on-center handling range. Analysis and test of the vehicle with improved steering system are performed.

• 한국가스학회지
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• 제14권1호
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• pp.47-54
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• 2010

가스 파이프의 배관 작업 중 작업 공정 수 및 단가를 낮추는 방법으로 PE관과 강관 일체형 볼 밸브를 개발하였다. 이를 위하여 먼저 유한요소해석을 근간으로 한 가상생산 지원 설계를 수행하여 누설에 대한 안전성을 갖는 프로토타입 제품 설계안을 제시하고, 이를 검증하기 위하여 누설 시험을 병행하는 통합적인 방법을 취하였다. 다양한 설계 모델을 대상으로 내압에 대한 접촉해석을 수행하여 제안된 최종설계안으로부터, 여름(${\Delta}T\;=\;60^{\circ}C$)과 겨울(${\Delta}T\;=\;-50^{\circ}C$)의 과장된 온도의 변화조건에도 비교적 광범위한 부분에서 최대 접촉압력이 각각 71 MPa, 및 8.1 MPa을 유지할 것을 예측하였다. 최종설계안을 바탕으로 시제품을 만들어, 열간 내압크리프 시험을 수행하였으며 사용압력(0.25 MPa)보다 훨씬 높은 가압조건(54 MPa)에서도 기밀을 유지하는 것을 확인하였다.

• 한국자동차공학회논문집
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• 제16권2호
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• pp.1-7
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• 2008

In order to enhance the performance of an automotive engine, many researchers have been carried out. An oil jet cooling a piston is one of important parts for engine performance. Therefore, the efficient cooling system of an oil jet is needed. In this paper, unsteady flow analysis of the oil jet which consists of a check valve and a nozzle has been accomplished. And the reaction between mass flow rate and ball movement was also investigated.