• 대한기계학회논문집B
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• 제29권6호
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• pp.711-721
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• 2005

In order to design of emergency ventilation systems, the smoke movements in tunnel fire with natural and forced ventilation were investigated. Reduced-scale experiments were carried out under the Froude scaling with novel fire source consisting many wicks. Temperature profiles were measured under the ceiling and vertical direction along the center of the tunnel and poisonous gases were measured at emergency exit point in the natural ventilation case. In forced ventilation, temperature profiles were measured with various flow rate to obtain critical velocity. The results showed that the interval of emergency exit having 225m was estimated reasonably through the measurements of temperature variation and poisonous gas in the natural ventilation. In the case of forced ventilation, the temperature distribution near fire source is remarkably different from that of natural ventilation. Also, the critical velocity to prevent upstream smoke flow has the range of 0.57m/s between 0.64m/s. Finally, it was also identified that although the increase of flow rate can suppress the backward flow of smoke to upstream direction, brings about the increase of flame intensity near stoichiometric fuel/air ratio.

• 환경정책연구
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• 제7권3호
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• pp.1-40
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• 2008

본 논문에서는 산업구조상 수직적으로 연결된 과점산업들을 상정한 뒤, 상류 및 하류 산업의 과점으로 인해 발생하는 최적에 미달하는 산출수준, 하류부문의 투입물 사용에서 발생하는 비효율성, 그리고 상류부문 과점산업의 환경오염으로 인해 발생하는 네 가지 비효율성을 모두 고려할 수 있는 이론 모형으로 정식화하고, 정책당국이 세수중립적인 세제개혁을 통해서 어떻게 후생증진을 도모할 수 있는지 논증한다. 이를 위해서 상류부문이 생산하는 중간재과 하류부문이 생산하는 최종재에 각각 산출세를 부과하는 경우와 환경오염 자체에 피구세(稅)를 부과하는 경우를 분리 상정하고, 각각의 후생변화를 수식으로 도출한다. 그 결과, 오염에 부과되는 생산요소간 대체를 가능하게하는 피구세(稅)가 생산감축을 통한 환경오염감소를 허용하는 산출세에 비해서 더 효과적으로 후생을 증진시킬 수 있는 논거가 경쟁적 단일산업에서뿐만 아니라 수직적으로 연결된 과점산업구조하에서도 여전히 타당함을 증명하고, 세수중립적인 조세-보조금 정책조합을 이용한 조세개혁을 통해 정책당국이 후생증진을 도모할 수 있는 조건을 명시적으로 도출한다. 또한 상하류 과점산업들의 한계적 이윤비용구조 및 한계적 환경오염의 상대적 크기가 각 산업에 대한 조세-보조금 정책조합의 방향을 결정하는데 매우 중요한 역할을 한다는 점을 밝힌다.

• Wind and Structures
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• 제29권6호
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• pp.417-430
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• 2019

To study the wake influence of an upstream bridge on the wind-resistance performance of a downstream bridge, two adjacent long-span cable-stayed bridges are taken as examples. Based on wind tunnel tests, the static aerodynamic coefficients and the dynamic response of the downstream bridge are measured in the wake of the upstream one. Considering different horizontal and vertical distances, the flutter derivatives of the downstream bridge at different angles of attack are extracted by Computational Fluid Dynamics (CFD) simulations and discussed, and the change in critical flutter state is further studied. The results show that a train passing through the downstream bridge could significantly increase the lift coefficient of the bridge which has the same direction with the gravity of the train, leading to possible vertical deformation and vibration. In the wake of the upstream bridge, the change in lift coefficient of the downstream bridge is reduced, but the dynamic response seems to be strong. The effect of aerodynamic interference on flutter stability is related to the horizontal and vertical distances between the two adjacent bridges as well as the attack angle of incoming flow. At large angles of attack, the aerodynamic condition around the downstream girder which may drive the bridge to torsional flutter instability is weakened by the wake of the upstream bridge, and the critical flutter wind speed increases at this situation.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• 제2권4호
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• pp.259-273
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• 2021

We conducted a study to investigate the characteristics of the carbon cycle of two streams (located in Shig a Prefecture, Japan), having similar size, namely, the Adokawa stream (length: 52 km, area: 305 km², watershed population: 8,000) and the Yasukawa stream (length: 62 km, area: 380 km², watershed population: 120,000), but with different degree of human activity. Samples were collected from these two streams at 14 (Adokawa stream) and 23 (Yasukawa stream) stations in the flowing direction. The dissolved inorganic carbon (DIC) concentration and the stable carbon isotope ratio of DIC (δ¹³C-DIC) were measured in addition to the watershed features and the chemical variables of the stream water. The δ¹³C-DIC (-9.50 ± 2.54‰), DIC concentration (249 ± 76 µM), and electric conductivity (52 ± 13 µS/cm) in Adokawa stream showed small variations from upstream to downstream. However, the δ¹³C-DIC (-8.68 ± 2.3‰) upstream of Yasukawa stream was similar to that of Adokawa stream and decreased downstream (-12.13 ± 0.43‰). DIC concentration (upstream: 272 ± 89 µM, downstream: 690 ± 37 µM) and electric conductivity (upstream: 69 ± 17 µS/cm, downstream: 193 ± 37 µS/cm) were higher downstream than upstream of Yasukawa stream. The DIC concentration of Yasukawa stream was significantly correlated with watershed environmental variables, such as, watershed population density (r = 0.8581, p<0.0001, n = 23), and forest area percentage of the watershed (r = -0.9188, p<0.0001, n = 23). δ¹³C-DIC showed significant negative correlation with the DIC concentration (r = -0.7734, p<0.0001, n = 23), electric conductivity (r = -0.5396, p = 0.0079, n = 23), and watershed population density (r = -0.6836, p = 0.0003, n = 23). Our approach using a stable carbon isotope ratio suggests that DIC concentration and δ¹³C-DIC could be used as indicators for monitoring the health of stream ecosystems with different watershed characteristics.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1148-1156
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• 2000

The QUICK scheme for convection terms is modified for unstructured finite volume method by using linear reconstruction technique and validated through the computation of two well defined laminar flows. It uses two upstream grid points and one downstream grid point in approximating the convection terms. The most upstream grid point is generated by considering both the direction of flow and local grid line. Its value is calculated from surrounding grid points by using a linear construction method. Numerical error by the modified QUICK scheme is shown to decrease about 2.5 times faster than first order upwind scheme as grid size decreases. Computations are also carried out to see effects of the skewness and irregularity of grid on numerical solution. All numerical solutions show that the modified QUICK scheme is insensitive to both the skewness and irregularity of grid in terms of the accuracy of solution.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.278-281
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• 2008

This study demonstrates the advantages of a shear-free structure designed to modify vertical profiles of wind speed in the atmospheric surface layer. Computational fluid dynamics(CFD) software, FLUENT is used to interpret the velocity field modification around the structure and wind turbine. The shapes of shear-free structure, installed at upstream toward prevailing wind direction, would be fences, buildings and trees, etc. According to the simulation results, it is obvious that wind shear between heights of wind turbine's blades is decreased together with a speed-up advantage. This would lead decrease of periodic wind loading caused by wind shear and power-out increase by flow uniformity and wind speed-up.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1313-1318
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• 2000

Crack behaviors at the downstream face of the concrete gravity dam were studied considering influence of the wintertime air temperature. It is assumed that inside area of 15m away from the dam surface in which temperature is presumed to be $15^{\circ}C$ is not affected from the annual air temperature variation. Water temperature at the upstream face and air temperature at the other faces were considered as outer boundary conditions to get temperature distribution inside of the dam using ADINA-T. These temperature distributions were transferred to FRANC2D to obtain equivalent stress intensity factors and crack propagation paths. Results obtained from changing initial crack locations and direction, air temperatures, and water levels were discussed. And crack behaviors at the upstream face were studied partly.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2008년도 학술발표회 논문집
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• pp.1151-1154
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• 2008

The water level data sets among hydrologic observation data are correspond to the hydraulic head for each observation point and determine flow direction. The level difference among reservoir, river, and groundwater determines groundwater flow direction, just like water flows in the downstream direction because the water level of upstream point is higher than that of downstream point. We can analyze the relationship among the components in hydrologic cycle by comparing the water level differences. This research dealt with the data from Nakdong river watershed in Gyungsangnam-Do. Three data group are used for the analysis and onr group is composed of reservoir, river, and groundwater data sets. The data sets are closely(within 10 km) located in the interested area.

• 한국환경과학회지
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• 제12권6호
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• pp.615-626
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• 2003

The applied model for this study area is WINFLOW using mite element method, It is thought that the simulation result by WINFLOW model under the steady flow state reflects well the ground water distribution within the reliability level which shows the error range of 1.1% to 8.0% from the comparison between the computed values and the observed, and analyzed that the constant head distribution is shown along the east-west direction and gentle and stable head gradient along the north-south direction. Ground water of the study area shows stable movement from the south to the stream area, and the particle trace for each location shows relatively linear shape from the upstream to the pumping location while the radius of influence according to the pumping amount shows a significant difference at the down stream area from the pumping location. The simultaneous pumping from P and P1 shows more complicated appearance, not the increase of the radius of influence than pumping from a single well P or P1, and it is analyzed that the particle path takes nearly linear form. It is known that the flow direction of the ground water and the velocity of the flow affect on the magnitude of the radius of influence of the wells from the fact that the more decreasing pattern of the ground water head is observed at the side of the well and the down stream area than the upstream area when the ground water moves from south to north regarding the radius of influence according to the pumping amount. Satisfactory results in analyses of ground water movement are obtained through the significant reduction of the physical uncertainties in the flow system as well as the relatively convenient model application using WINFLOW model which is proposed in this study.

• 한국수자원학회논문집
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• 제37권10호
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• pp.823-836
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• 2004

두개의 지표면과 그 사이에 있는 하도로 이루어진 유역을 가정하여 이동강우에 대한 유출을 운동파 이론을 적용하므로서 해석하여 다양한 강우이동속도의 경우를 비교 분석하였다. 이동강우는 하천의 상류방향, 하류방향, 횡방향으로 0.25∼2.0m/s의 속도로 이동시켰으며, 이때 강우분포형은 균등분포형, 전진형, 지연형, 중앙집중형을 적용하였다. 횡방향 이동강우의 경우에 첨두유량이 가장 크게 나타났고, 상류방향의 이동강우에 대한 첨두유량이 가장 작게 나타났다. 강우분포형에 대한 유출의 민감도는 강우이동속도가 빠를수록 감소하였다. 강우이동속도가 빠를수록 첨두시간이 빨라지며, 수문곡선은 급격히 얇아짐을 알 수 있다.