• 상하수도학회지
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• 제19권5호
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• pp.557-564
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• 2005

The objective of this study is to evaluate a criteria of intercepting capacity and a reduction goal of overflow pollution load in combined sewer system. In the current criteria of intercepting capacity in the domestic sewage facility standard, it is known that three times of peak sewage (Q) in dry period or runoff flow by 2mm/hr is not appropriate since the intercepted flow is estimated by runoff and show different result even in the same watershed. Though a reduction goal of overflow pollution load can be determined from 1) same level of storm-water runoff pollution load in separated storm sewer, 2) less than 5% sewage load in dry weather period, by the domestic sewage facility standard, the simulated results from storm-water model show large differences between two criteria. While it is predicted that sewage pollution load standard three time larger than separated storm sewer standard in high population density and urbanized area, it is shown that separate storm sewer standard larger than sewage pollution load standard in middle population density and developing area. Accordingly, it is proposed that more reasonable intercepting flow and reduction goal of overflows pollution load should be established to minimize discharging pollution load in combined sewer systems. For the purpose, a resonable standard has to be amended by pollution load balance considering the characteristics of a watershed for generation, collection, treatment, and discharging flow.

• 드라이브 ㆍ 컨트롤
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• 제16권4호
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• pp.1-8
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• 2019

The HPM (High-speed Power Matching) system is an electro-hydraulic control system. It directly controls the swash plate of the pump by selecting four-loop logic based on joystick signals, pump flow, and pressure signal to improve the efficiency and controllability of construction machines. In the NFC (Negative Flow Control) system, a typical pump control system using conventional open center type MCV, the loss is continuously generated by flow through the center bypass line even when the excavator is not in operation. Also, due to the slow response of the pump that indirectly controls the flow rate using the pressure regulator, peak pressure occurs at the start or stop of the operation. Conversely, the HPM system uses an MCV without center-by-pass flow path and the swash plate of a pump for the HPM is controlled by a high-speed proportional flow control valve. As a result, the HPM system minimizes energy loss in standby state of the excavator and enables peak pressure control through rapid electro-hydraulic control of a pump. In this paper, the concept of the HPM system algorithm is introduced and the hydraulic system efficiency is compared with the NFC system using the excavator SAT (System Analysis Tool).

• Wind and Structures
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• 제27권4호
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• pp.213-221
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• 2018

In the desert and Gobi regions with strong wind and large sediment discharge, sand transporting engineering is more effective than sand blocking and sand fixing measures in sand prevention. This study uses the discrete phase model of 3D numerical simulation to study the motion trail, motion state and distribution rule of sand particles with different grain diameters when the included angle between the main shaft of the feather-row lateral transportation sand barrier and the wind direction changes, and conducts a comparison in combination with the wind tunnel test and the flow field rule of common sand barrier. According to the comparison, when wind-sand incoming flow passes through a feather-row sand barrier, sand particles slow down and deposit within the deceleration area under the resistance of the feather-row sand barrier, move along the transportation area formed by the transportation force, and accumulate as a ridge at the tail of the engineering. With increasing wind speed, the eolian erosion of the sand particles to the ground and the feather-row sand barrier is enhanced, and the sand transporting quantity and throw-over quantity of the feather-row sand barrier are both increased. When sand particles with different grain diameters bypass the feather-row sand barrier, the particle size of the infiltrating sands will increase with the included angle between the main shaft of the feather-row sand barrier and the wind direction. The obtained result demonstrates that, at a constant wind speed, the flow field formed is most suitable for the lateral transportation of the wind-drift flow when the included angle between the main shaft of the feather-row sand barrier lateral transportation engineering and the wind speed is less than or equal to $30^{\circ}$.

• Journal of Chest Surgery
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• 제13권2호
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• pp.85-91
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• 1980

Extracorporeal circulation by hemodilution technique has been currently used with its clinical safety and good peripheral tissue perfusion in open heart surgery. There is no doubt that $O_{2}$ carrying capacity of the blood is disturbed by decreased hemoglobin level resulting from hemodilution of the circulating blood. From the view point of the blood gas exchange, these experimental studies were undertaken to determined the sate limit of hemodilution in the condition of cardiopulmonary bypass with a constant perfusion flow rate. Twelve adult mongrel dogs weighing 10 to 13 Kg. were anesthetized with pentobarbital and then respiration was controlled with Harvard volume respirator using room air. The cardiopulmonary by pass was performed by use of Sarns heart lung machine (console 5000, 5 head and 2 roller pumps) and Travenol pediatric bubble oxygenator. The perfusion rate during bypass was maintained at a constant rate of 80 ml/min/Kg of body weight. The ratio of oxygen gas flow to blood flow was kept in 3 to 1 constantly. International hemodilution was attained by serial blood withdrawals and immediate infusion of equal volumes of diluants composed of Ringer's lactate, 5% dextrose in water and 25% mannitol solution, proportionally 60%, 30%, and 10%. Arterial and venous blood samples were obtained between 15 and 20 minutes following each hemodilution. Hematocrits and hemoglobin values, $PO_{2}$, $PCO_{2}$ and pH were measured. Oxygen and carbon dioxide contents oxygen consumption and carbon dioxide elimination were calculated groups according to different hematocrit values and the correlations were evaluated. Result were as follows. 1. the arterial $O_{2}$ tension and $O_{2}$ saturation were maintained at the physiological level irrespective of the hematocrit value. 2. The venous $O_{2}$ tension and $O_{2}$ saturation showed a tendency to decline with the decrease in hematocrit value and positive correlation between them (r = +0.49, r = +0.76), The mean values of venous $O_{2}$ tension and $O_{2}$ saturation, however, were not decreased when the hematocrit levels were lower than 20%. 3. The arterial $O_{2}$ content declined lineally in proportion to the fall of hematocrit level with a positive correlation between them (r = +0.95). 4. The venous $O_{2}$ contents were decreased gradually as the hematocrit value decreased with positive correlation between them ( r =+0.89). The trend of diminution of venous $O_{2}$ content, however, was became low according to progressive decrease of hematocrit level. 5. Systemic oxygen consumption was in higher range than $O_{2}$ requirement of basal metabolism when the hematocrit value was above 20%, but abruptly decreased when the hematocrit value became to below 20%. 6. The arterial $CO_{2}$ tension and $CO_{2}$ content showed trend of increasing with progressive decrease of hematocrit value but exhibited a rather broad range and there was no relationship between those value and the hematocrit value. 7. The venous $CO_{2}$ tension and $CO_{2}$ content have also no correlation with change of Ht. value but related directly to those value of arterial blood with positive correlation between them (r = +0.78, r = +0.95_. 8. A-V difference of $CO_{2}$ content and $CO_{2}$ elimination wasnot significantly influenced by Ht. value. From the results, we obtained that feasible limit in inteneional hemodilution is above the hematocrit value of 20% under the given experimental condition.

• Journal of Chest Surgery
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• 제39권7호
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• pp.505-510
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• 2006

배경: 쥐를 이용한 심폐바이패스 모델은 시간 및 비용의 절감, 관리의 용이, 큰 실험실의 불필요, 그리고 반복실험의 용이 등 많은 장점이 있으나 기술적인 어려움 또한 크다. 열교환기를 이용한 효율적인 중심체온 유지 및 조절 역시 이러한 문제점 중의 하나이다. 이에 본 연구에서는 쥐 심폐바이패스 모델을 위해 기존의 상용화된 산화기를 소동물용으로 개조한 뒤 심정지액 주입용 소형 열교환기를 이용하여 충전액을 최소화한 상태에서 인공심폐기에 의한 효율적인 체온 유지가 가능한지를 보고자 하였다. 대상 및 방법: 수컷 쥐(Sprague-Dawley,평균 530 g) 10마리를 각 5예씩 나누어 열교환기를 사용한 군과 사용하지 않은 군으로 구분하였다. 열교환기는 심정지액 주입용 열교환기를 개조하여 사용하였으며 산화기를 포함한 전체 정지 충전용량은 40 cc였다. 열교환기를 사용하지 않은 군에서는 저혈조 주위에 온수를 순환시켰다. 실험동물 마취 후 동맥 삽관은 대퇴동맥 및 내경동맥에 정맥 삽관은 외경정맥에 시행하고 부분 심폐바이패스(40 ml/kg/min)를 20분간 유지하였다. 두 군간의 비교 분석을 위해 직장 체온을 각각 마취 직후, 동정맥 삽관 후, 심폐바이패스 후 5, 10, 15, 20분에 측정하였다. 심폐바이패스 후 5, 15분에는 헤모글로빈 및 동맥혈 가스분석을 동시에 측정하였다. 결과: 쥐에서의 심폐바이패스 운용은 안정적으로 유지되었으며, 심폐바이패스 후 5분부터 두 군간의 체온 차이는 유의하였다(p<0.01). 20분 후 체온은 각각 $36.16{\pm}0.32^{\circ}C$ 및 $34.22{\pm}0.36^{\circ}C$였다. 결론: 본 연구는 소동물 심폐바이패스 모델에서 심정지액 주입용 열교환기를 이용하여 충전액에 대한 영향을 최소화하면서 효율적인 체온유지가 가능함을 증명하였다. 이러한 실험 결과는 향후 저체온 심폐바이패스 운용에 관한 실험 모델로 쥐를 폭넓게 이용할 수 있다는 가능성을 제시한다는 점에서 그 의의가 크다.

• 대한토목학회논문집
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• 제37권1호
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• pp.239-246
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• 2017

국내 중소하천의 횡단구조물인 보 또는 낙차공은 대부분 고정식 콘크리트 구조물이며, 저층수의 배제가 쉽지 않다. 횡단구조물로 인해 유사가 퇴적되며, 유사에 흡착한 오염물들이 그대로 하천의 바닥을 오염시키고 있다. 이에 저층수 및 퇴적유사에 대한 관심이 증가하고 있는 실정이며, 이러한 대안의 하나로 횡단구조물 상류와 하류를 하상 아래로 연결시키는 구조물로써, 보 상류 저층의 물 및 유사 배제를 목적으로 저층수배출관을 설치하는 방안이 있다. 그러나 사석이 유입되고, 배제 되지 않을 경우 효율성이 크게 저하될 가능성이 있다. 이에 본 연구에서는 저층수 배출관 내 사석을 배제할 수 있는 능력에 대한 연구를 수행하였다. 사석과 거동이 유사한 유사(sediment)의 한계조건(critical condition) 중 한계전단력(critical shear stress) 유도과정과 달랑베르의 원리(d'Alembert principle)를 응용하여 이동 중인 사석이 배제될 수 있는 조건(${\tau}_c{^*}$)을 유도하였다. 그러나 저층수 배출관 내 유입된 사석은 정지상태가 아닌 이동 중이므로, Lagrangian 기법을 활용하여 수리실험에서 도출된 유속으로 상대속도(relative velocity)를 제시하였다. 수리실험은 축척효과(scale effect)를 최소화하기 위해 폭이 5.0 m이고, 높이가 1.0 m인 광폭 개수로를 제작하였으며, 사용된 사석은 가공된 완전 구형을 사용하였다. 실험 결과 유속과 구형 입자 속도와의 비가 0.5~0.7 사이로 나타났으며, 이러한 결과를 유도된 식에 적용하여, 최종적으로 사석이 배제되는 조건을 도출하게 되었다. 구간은 입자레이놀즈수($Re_p$)와 무차원 한계 전단력(${\tau}_c{^*}$)에 따라 크게 3가지로 구분되었다. 배제 구간(exclusion section), 확률적 배제 구간(probabilistic exclusion section), 비배제 구간(no exclusion section)이다. 본 연구결과는 횡단구조물의 저층수 배출관 설계시 유용한 기초 정보를 제공할 수 있을 것이다.

• 항공우주기술
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• 제4권1호
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• pp.143-149
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• 2005

로켓엔진용 연료펌프의 수력 성능과 흡입 성능을 관찰하기 위해 연료펌프에 대한 성능시험을 실시하였다. 성능 시험은 수력 성능 시험과 흡입 성능으로 나뉘며 시험의 편의를 위해 상온의 물을 매질로 택하였다. 수력 성능 시험 결과 양정, 효율, 볼류트 압력 분포 등은 상사 법칙을 잘 만족하는 것으로 드러났으나, 이차 유로의 압력 분포는 상사 법칙과 약간의 차이를 보였다. 그리고 플로팅 링 간극을 줄였을 때 펌프의 양정과 효율 모두 좋아지는 것을 확인할 수 있었고, 바이패스 배관의 오리피스 변화는 연료펌프의 효율 변화와 특별한 경향성을 보이지 않았다. 마지막으로 흡입 성능 시험 결과 펌프의 시험 회전수를 높였을 때 펌프의 흡입 성능이 증가하는 것을 관찰할 수 있었다.

• 한국환경과학회지
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• 제18권7호
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• pp.755-765
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• 2009

Some sections of the exhaust system to determine the shape of the duct is to suffer the difficulties by space constraints to install new equipment of the environment post-treatment for existing operation of the power plants. In this paper the large duct in flue gas desulfurization equipments of the 500MW coal-fired power plant on the current operation is numerically analyzed from induced draft fan exit to booster up fan inlet section which is in the narrow space of the exhaust system with four times bending and is connected to emergency duct to bypass the exhaust gas on the emergency operation. The procedure and method using computational fluid dynamics are proposed to maintain the stability of the guide vane with the uniform flow and a minimum pressure loss of exhaust gas in the case of normal and emergency operation between the direction of the flow of exhaust gas duct at different.

• 대한기계학회논문집B
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• 제23권11호
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• pp.1410-1417
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• 1999

A thorough understanding of the transient behavior during start-up is essential in the design and operation of the heat recovery steam generator(HRSG). During this period of time, material that is exposed to high temperature and experiences a large temperature variation is subject to high thermal stress. In this work, a transient formulation of the HRSG is constructed including the estimation of the thermal stress and fatigue of the drum wall. Start-up behavior of a single-pressure HRSG is analyzed and the effect of bypassing part of the gas turbine exhaust flow on the thermal stress evolution is examined. It is found that the modulation of the gas flow rate using a bypass damper is very useful in view of reducing the thermal stress of the drum and ensuring the fatigue lifetime.

• 대한기계학회논문집
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• 제12권3호
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• pp.534-540
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• 1988

본 연구에서는 디이젤분무 주위기체의 유동특성중에서 유동속도에 관하여 보 고 하였다. 본모에서는 분무기간중 분사압력의 시간경과특성이 상이한 두 종류의 분 사계를 사용하여 생성된 분무와 주위 기체와의 유동방향의 시간경과 및 유입시기, 정 상유입속도 도달시간등을 분무의 축방향과 반경방향에 대하여 상세한 측정결과를 얻었 기에 보고한다.