• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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• pp.95-101
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• 2004

Dynamic behavior of diffusive-thermal instability in diluted $CH_4/O_2$ diffusion flames is numerically investigated by adopting detailed chemistry and transport. Counterflow diffusion flame is adopted as a model flamelet. Particular attention is focused on the pulsating-instability regime, which arises for Lewis numbers greater than unity, and the instability occurs at high strain rate near extinction condition in this flame configuration. Once a steady flame structure is obtained for a prescribed value of initial strain rate. transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed Oil the steady flame. Transient evolution of the flame depends on the initial strain rate and the amount of perturbed strain rate. Basically, the dynamic behaviors can be classified into two types, namely non-oscillatory decaying solution and diverging solution leading to extinction. The peculiar oscillatory solution. which has been found in the previous study adopting one-step chemistry and constant Lewis numbers, is not observed in this study, which is attributed to both convective flow and preferential diffusion effects.

• 한국화재소방학회논문지
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• 제11권4호
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• pp.15-23
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• 1997

A series of measurements and visualization to investigate the extingushiment of water sprays with pool fires is presented. Fire source is a small-scale pool burner with methanol, ethanol and gasoline. Measurements of temperature, O2, CO2, and CO concentrations along the plume centerline are carried out to observe pool structures without water sprays. Visualization by the Ar-ion laser sheet flow pattern of droplets of the sprays above the pool fires. It is observed than in the case of methanol and ethanol, water sprays continuously penetrate into the center of fuel surfaces. The gasoline pool fire allows intermittent penetration of water sprays because of pulsating characteristics of the gasoline flame. To evaluate the cooling effect of the fuel surface by the sprays, the temperature was measured at the fuel surface. As soon as the mists reach the fuel surface of methanol and ethanol, the temperatures of the fuel surface decrease rapidly below the boiling point, and then the fires are extinguished. Due to the application of mist upon the gasoline fire, though the fuel temperature decrease abruptly at the time of the injection, such a repid decrease do not continue till the extinction point.

• 한국초전도ㆍ저온공학회논문지
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• 제14권3호
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• pp.43-47
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• 2012

A linear compressor generates pulsating pressure and oscillating flow in a cryocooler such as Stirling cryocooler and pulse tube refrigerator. It is driven by AC power source and designed to operate at resonance of piston motion. The driving voltage level is determined by electric parameters of resistance, inductance and thrust constant of linear motor. From voltage equation on linear motor, the power factor of driving power is inherently less than 1. The phase difference between voltage and current of supplied power can be zero using capacitor and this can minimize a supply voltage level. Especially, the linear compressor of kW class requires high voltage and thus can cause a difficulty in selecting power supply unit due to limitation of voltage level. The capacitor in driving electric circuit is useful to settle this problem. In this study, the electric circuit of linear compressor is analytically investigated with assumption of mechanical resonance. The electric parameters of commercial linear motor are used in the analysis. The effects of capacitor on driving voltage level and power factor are investigated. From analytic results, it is shown that the voltage level can be mimized with using capacitor in driving electric circuit.

• 한국화재소방학회:학술대회논문집
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• 한국화재소방학회 1997년도 International Symposium on Fire Science and Technology
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• pp.518-525
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• 1997

A series of measurements and visualization to investigate the interaction of water sprays with pool fires is presented. Fire source is a small-scale pool burner with methanol, ethanol and gasoline. Measurements of temperatures, $O_2$, $CO_2$, and CO concentrations along the plume centerline are carried out to observe pool fire structures without water sprays. Visualization by the Ar-ion laser sheet shows flow pattern of droplets of the sprays above the pool fires. It is observed that in the case of methanol and ethanol, water sprays continuously penetrate into the center of fuel surfaces. The gasoline pool fire allows intermittent penetration of water sprays because of pulsating characteristics of the gasoline flame. To evaluate the cooling effect of the fuel surface by the sprays, the temperature was measured at the fuel surface. As soon as the mists reach the fuel surface of methanol and ethanol, the temperatures of the fuel surface decrease rapidly below the boiling point, and then the fires are extinguished. Due to the application of mist upon the gasoline fire, though the fuel temperature decrease abruptly at the time of the injection, such a rapid decrease do not continue till the extinction point.

• Journal of Korean Neurosurgical Society
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• 제29권8호
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• pp.1019-1023
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• 2000

Objective : Endoscopic third ventriculostomy is gaining popularity as a minimally invasive surgical option for certain types of hydrocephalus as an alternative to shunting. The authors have tried to fenestrate down to the subdural space passing through the prepontine cistern to lessen or avoid the chance of redoing due to healing. Materials and Method : A 48-year-old male patient with several years of intractable headache was presented. Magnetic Resonance Image(MRI) of the brain revealed marked ventricular dilatation with stenotic cerebral aqueduct. A 2.3mm flexible steerable endoscope($Neuroview^{(R)}$) was introduced via precoronal route and accessed to the third ventricular floor. Using 3-French Fogarty balloon catheter, thin third ventricular floor and the arachnoid membrane of the prepontine cistern were fenestrated, so called "double fenestration". To confirm the fenestration, subdural compa-rtment of the left abducens nerve was identified during the procedure. Forceful pulsating flow through the orifice convinced the patency of the opening. Results : The patient was discharged on the third postoperative day without any postoperative complications. The postoperative follow-up MRI of the brain, at second and sixth months, clearly demonstrated the flow void through the third ventricular floor. Conclusions : Endoscopic third ventriculostomy was successfully performed on an adult hydrocephalus patient with aqueduct stenosis. The third ventricular floor and arachnoid membrane of the prepontine cistern were fenestrated to achieve double fenestration to minimize the chance for failure. The details of this procedure and results are described.

• 대한기계학회논문집
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• 제17권6호
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• pp.1547-1555
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• 1993

본 연구에서는 원관외벽에 일정 열유속이 가해지는 스터링 사이클용 가열기 튜브내부로 열전달이 일어나는 경우 원관내부의 유체온도의 시간적 변화를 측정하여 왕복유동에서의 열전달 특성을 규명하고자 하였다. 본 실험에서 사용한 물리적 모델 을 Fig.1에 나타내었으며, 스터링기기에서와 같이 원관의 양끝에서 2개의 피스톤이 90˚의 위상차를 가지면서 왕복운동하도록 설정하였다. 이와같은 왕복유동에서 일정 열유속이 주어진 경우 진동수, 체적 치환비, 원관내부의 평균압력이 온도 및 열전달 특성에 미치는 영향을 실험적으로 규명하였다. 그리고 원관내부 작동 유체의 영향을 규명하기 위해 스터링기기에서 작동유체로 많이 사용되는 헬륨 뿐아니라 공기도 사용 하여 그 결과를 비교하였다.

• Journal of Trauma and Injury
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• 제18권2호
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• pp.172-174
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• 2005

Trauma of the vascular structure is not poplular event. In obstructive atherosclerotic vascular disease, we sometimes have needed bypass surgery. The long length subcutaneous prosthetic vascular graft are vulnerable to injury. But prosthetic vessel rupture after trauma has been rare report. A 68-year-old man was referred to Department of Emergency of the Gyeongsang National University Hospital. After he had had a blunt trauma, he found a newly appearing pulsating mass of 10 cm diameter on his right chest wall. The lesion had a turbulent blood flow in the cavity of the mass by ultrasonographic finding. The lesion was a rupture of superficial prosthetic vascular graft under the skin.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.606-611
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• 2007

Pulsation is an inherent phenomenon in reciprocating compressors. It interacts with piping to cause vibrations and performance problems. Indiscriminately connecting to a compressor can be dangerous and cost money in the form of broken equipment and piping, poor performance, inaccurate metering, unwanted vibration, and sometimes noise. Piping connected to a compressor can materially affect the performance and response. To minimize these detrimental effects, reciprocating compressor system should be equipped by pulsation suppression system. This study discusses pressure pulsation phenomena occurred in a reciprocating compressor system. An experiment applied air compressor unit, as pulsating pressure generator, has been done. The compressor was connected sequentially to a snubber model and pressure tank. Sensor probes were placed on the inlet and outlet pipes of snubber. Compressor was driven by a motor controlled by a frequency regulator. The experiment was conducted by adjusting the regulator at 40Hz. General information about an internal gas flow can be achieved by numerical analysis approach. Information of the velocity, pressure and turbulence kinetic energy distribution are presented in this paper. Based on this result, the design improvement might be done.

• Journal of Chest Surgery
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• 제18권4호
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• pp.537-541
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• 1985

Recently, we met a 12 year old female patient who suffered from bacterial endocarditis and pericarditis which were complicated by patent ductus arteriosus. She was admitted to our hospital because of dyspnea, fever, headache, and generalized ache for 10 days. The initial diagnosis was bacterial endocarditis and pericarditis complicated by patent ductus arteriosus and congestive heart failure. At first, we tried to treat the patient medically with digitalis, diuretics, and massive antibiotics. On echocardiography large amount of pericardial fluid was accumulated mainly right anterior aspect and also noted a large vegetation at pulmonary valve area. With vigorous medical treatment including repeated pericardiocentesis, the patient showed no improvement. So we decided to perform pericardiectomy for elimination of the most probable septic focus. On operation, we encountered an unpredicted event, the pericardium was thickened, distended, and its surface showed pulsating which meant connecting to systemic circulation. We decided to close the operative wound and reoperate her under cardiopulmonary bypass later. On the next day, we operated her under cardiopulmonary bypass later. On the next day we operated her under cardiopulmonary bypass. The operative findings were ruptured main pulmonary artery about 1.5cm in diameter on its ventral portion, the blood from the ruptured main pulmonary artery was filled up the localized pericardial sac due to previous pericarditis. Through the ruptured main pulmonary artery, we also found 0.5cm diametered patent ductus arteriosus. With the aid of partial cardiopulmonary bypass and inserting 24F ballooned Foley catheter at aorta, pericardiectomy was performed first. After completion of the pericardiectomy, total cardiopulmonary bypass was established. With minimum pump flow [0.3L/min/m2] the PDA was closed with two Teflon-felted 4-0 Prolene interrupted sutures. The ruptured main pulmonary artery was also closed using thickened pericardium with three Teflon-felted 4-0 Prolene interrupted sutures. The operation was successful and postoperative course was uneventful. She was discharged on the 16th POD. We report this case as a very rare secondary complication of bacterial endocarditis complicated by patent ductus arteriosus.

• Structural Engineering and Mechanics
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• 제70권4호
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.