• Journal of Ecology and Environment
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• 제43권1호
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• pp.73-83
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• 2019

Background: Habitat selectivity and ecology of freshwater fishes were studied in two selected streams and their junction point which consist a total of 39 microhabitats. The aims of this study were to describe the habitat preference and its availability to fish assemblage, as well as ecology, habitat use, and habitat characteristics. Methods: We collected fish with backpack electrofishing three times during August 2013, December 2013, and March 2014. Using a variation partitioning approach of R software, we studied the relationship of fish abundances with stream type, habitat type, and abundance of key macroinvertebrate taxa. Results: A total of 6554 fishes representing four species belonging to the family Cyprinidae were caught. A higher total fish abundance was recorded from Gereb Tsedo (4870; 74.3%) than from Elala stream (1684; 25.7%). Taking both streams together, the overall total relative fish abundance was significantly higher in pools (53%) than in runs (35%) and in riffles (12%) at P < 0.05. Species-wise comparisons showed that 71%, 15%, 13%, and 1% of the pool fish community were occupied by Garra blanfordii, Garra ignestii, Garra dembecha, and Garra aethiopica, respectively. Stream type, habitat type, and key macroinvertebrate taxa each explained a significant proportion of the variation in fish abundance. Based on the variation partitioning approach, fish abundance was higher in Gereb Tsedo stream (P < 0.01). Moreover, fish abundance increased with pool habitat type (P < 0.01) and with availability of key macroinvertebrate taxa (P < 0.01). Conclusion: Fish abundance differed between stream types, among habitats and among key macroinvertebrate taxa availability. Among the factors, habitat type was the most important driving factor behind variation among fish abundances, and pool supports the highest fish abundance.

• 한국방재학회 논문집
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• 제6권4호통권23호
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• pp.49-56
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• 2006

도시지역의 우수를 배제하기 위한 방법으로 토구를 이용하여 하천으로 방류하고 있다. 그러나 이러한 토구를 설치 할 때 국내설계기준에는 어떠한 기준이나 제안이 없이 설계자나 시공자의 임의로 만들어 지고 있는 실정이다. 본 연구에서는 토구를 설치하는 방법에 대한 기초적인 자료를 제공하기 위하여 토구 방류 유량에 따른 흐름 변화 및 설치 각도, 돌출정도, 그리고 설치 위치에 따른 흐름변화를 실험을 통하여 분석함으로써 흐름에 보다 영향을 적게 미치는 토구설치 방법을 제안하였다. 총 10가지 경우에 대한 실험을 통하여, 같은 유량을 방류함에 있어서 한 곳으로의 방류보다는 상.하류 등으로 분리하여 방류하는 것이 흐름에 영향을 적게 미치는 것으로 나타났으며, 설치 각도 및 돌출에 따라 상류지역의 수위 상승 및 유속 감소 등의 현상이 나타나 토구 설치 시 보다 신중하고 흐름에 방해가 되지 않는 방향으로 설치할 수 있는 방안을 강구해야 한다.

• Journal of Preventive Medicine and Public Health
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• 제21권2호
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• pp.307-319
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• 1988

낙동강 중류의 수질과 그 수계에 서식하는 어류와 납, 카드뮴 및 아연과의 관계를 붕어를 대상으로 관찰하였다. 본 실험을 위한 표본은 비교적 갈수기라고 인정되는 3월 초순에 안동댐, 낙동교, 왜관, 강정, 개포 인근 그리고 낙동강의 주 오염원이 되는 금호강에서는 팔달교 부근에서 채취하였으며 수중 중금속 및 조직 중 납, 카드뮴과 아연은 원자흡광분광광도계(IL-551)로 분석하였다. 낙동강의 상류에서 하류로 내려올수록 납, 카드뮴, 아연 함량은 증가하였고, 팔달교 부근은 강정 상류보다 $3{\sim}5$배 더 높았으며 이는 낙동강과의 하류지점에서 약 40km 하류에 위치한 개포의 수질보다 약 1.5배 정도 높게 나타났다. 붕어의 뼈, 근육, 지느러미 중의 납, 카드뮴 함량도 상류에서 포획한 것보다 하류에서 포획한 것이 많았다. 강정을 포함한 상류보다 오염수역이라고 할 수 있는 개포 및 팔달교 근처의 붕어에서 유의성 있게 높았다. 붕어의 뼈조직 중 납, 카드뮴, 아연의 함량은 조사 전역에 걸친 그들 수환경보다 각각 $771{\sim}2,856$배, $188{\sim}564$배, $663{\sim}1,327$배이었으며 근육에서는 각각 $170{\sim}516$배, $62{\sim}169$배, $247{\sim}389$배이고 지느러미에서는 각각 $484{\sim}1,770$배, $122{\sim}360$배, $509{\sim}983$배 이었다. 이들 붕어의 성장 햇수별 납, 카드뮴 및 아연 함량은 연령이 증가할수록 증가했으며 각 수역에서의 동일 연령군까지 비교했을때는 상류에서 하류로 내려갈수록 그 함량이 많았다. 팔달교에서의 $0{\sim}1$세군에서의 뼈 중 납의 함량은 개포의 $4{\sim}5$세군과 근사하며 강정 상류의 $3{\sim}4$세군보다 높은 경향을 보였다. 이상과 같은 결과를 요약하면 낙동강은 금호강의 탁류의 영향을 크게 받아 오염 수역에서 포획한 어군은 비오염수역의 어군보다 중금속 함량이 유의하게 높으며 성장 햇수가 많아짐에 따라 중금속 함량은 높다는 것을 알 수있다.

• 한국가시화정보학회지
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• 제3권1호
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• pp.58-62
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• 2005

Flow characteristics at secondary recirculation zone in a liquid fuel ramjet combustor were investigated using CFD and Stereoscopic PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vanes were installed in each rectangular inlet to improve the flow stability. The tested angle of the air intakes was 60 degree. The experiments were performed in the water tunnel test with the same Reynolds number in the case of Mach 0.3 at inlet. The computational and experimental results showed that the secondary recirculation flow occurred at the front junction of inlet main stream and combustor chamber. The size of secondary recirculation regions are increased with approaching closer to the center of the combustor. Since the performance of combustor is closely dependent not only on the main recirculation in the dome region but also on the secondary recirculation flow in a junction region, the optimal angle of the air intakes should be considered the recirculation size as frame holder.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2003년도 추계학술대회 논문집
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• pp.115-120
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• 2003

Flow characteristics at secondary recirculation zone in a liquid fuel ramjet combustor are investigated using CFD and 3-D Stereoscopic PIV method. The combustors have two rectangular inlets that form 90 degree each other. Three guide vanes were installed in each rectangular inlet to improve the flow stability. The tested angle of the air intakes was 60 degree. The experiments were performed in the water tunnel test with the same Reynolds number in the case of Mach0.3 at inlet. Both computational and experimental results showed the secondary recirculation flow occurred at the front junction of inlet main stream and combustor chamber. The size of secondary recirculation region increased with upon closer center of axial combustor. Since the performance of combustor depends on not only the main recirculation in the dome region but also the secondary recirculation flow in a junction region, the optimal angle of the air intakes should consider the recirculation size as frame holder.

• 대한기계학회논문집
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• 제19권10호
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• pp.2595-2606
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• 1995

Buoyancy-assisted melting of an unconstrained ice in an isothermally heated horizontal enclosure was numerically analyzed in a range of wall temperatures encompassing the density inversion point. The problem as posed here involves two physically distinct domains each of which has its own scales and respective heat transfer mode. These two domains join at the junction where the liquid squeezed out of the film region flushes into the lower melt pool. Both of these domains have been treated separately in the literature by a patching technique which invokes several, otherwise unnecessary, assumptions. The present study eliminates successfully such a superfluous procedure by treating the film and lower melt pool regions as a single domain. As a result of this efficient solution procedure, the interaction of the water stream ejected at the junction and the natural convection in the melt pool could be clarified for different wall temperatures. Though limited by two-dimensionality, the present results conformed indirectly the earlier reported transition of the flow pattern, as the wall temperature was increased over the density inversion point. The transient evolution of the melting surface, the time rate of change in melt volume fraction, the local and temporal variation of the heat transfer coefficients are analyzed and presented.

• Water Engineering Research
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• 제3권1호
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• pp.45-55
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• 2002

The Szentgotthard Flood Protection Project is located in the southeasters part of Austria, very close to the Hungarian border and to the Hungarian town of Szentgotthard situated near the Junction of the rivers Lafnitz and Raab. During heavy rainstorms, this area has always been liable to severe floodings, affecting the town itself and upstream reaches, where major industrial and commercial development is planned. In order to solve these problems, several solutions have been developed by means of a series of model tests performed at the hydraulic laboratory of the Technical University of Graz, Austria. The model was constructed to scales 1:75 (lengths) and 1:25 (heights). This trebled scale allowed greater accuracy in the measurement of discharge depths. The results from the model tests have led to the following proposals: - Construction of a flood relief trough with an inflow section 3.5 km upstream of the junction of the rivers Lafnitz and Raab. - Use of a former river bed for the flood relief trough. - Design of a lowered embankment crest section to pass one-third of the maximum flood flow of the river Lafnitz. - Connection of the flood relief trough to the Lahnbach stream, a tributary of the river Raab.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.137-140
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• 2003

The flow characteristics of secondary recirculation region in a liquid fuel ramjet combustor are measured using PIV method. The model combustor has two rectangular inlets that form 90 degree angle each other. The tested angles of the air intakes were 30, 45 and 60. Three guide vanes are installed in each rectangular inlet to improve the flow stability. The experiments are performed in the water tunnel test with the same Reynolds number as the case of Mach 0.3 at the inlet. PIV software is developed to measure the characteristics of the flow field in the combustor. The accuracy of the developed PIV program is verified with rotating disk experiment and standard data. The experimental results show that the secondary recirculation flow occurred at the front junction of inlet main stream and combustorchamber. The size of secondary recirculation regions are increased with increasing air inlet angles. Since the performanceof combustor is very dependant on not only the main recirculation in the dome region but also the secondary recirculation flow in a junction region, the optimal angle of the air intakes should consider the both recirculation size as a frame holder.

• 한국방재학회 논문집
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• 제11권1호
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• pp.85-91
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• 2011

RV-GIUH는 Horton의 차수법칙을 따르는 유역에 대하여 유도되었으며, 소유역의 출구부분, 또는 대상유역의 최고차 하천이 본류에 합류하는 지점에서 RV-GIUH를 적용하여 단위도를 산정하는 것이 바람직하다. 그러나 현실적으로는 유출량 산정지점이 다양한 지점에서 결정되며, 이런 지점들은 반드시 소유역의 출구부분과 일치하지는 않는다. 따라서 실무적인 필요에 의하여 결정된 유출량 산정지점에서 RV-GIUH를 적용하기 위한 최소한의 가이드라인이 필요하다. 본 연구에서는 미계측 유역에 RVGIUH를 적용하는데 있어 유역 출구를 적절하게 결정하기 위한 기준을 제시하고자 하였다. 평창강의 상안미 유역의 출구지점으로부터 상류로 이동하며 유출량 산정지점을 선정하였으며, 각 소유역에 대하여 RV-GIUH 유도식과 간략식을 사용하여 단위도를 산정하고 소유역의 출구에서 산정한 단위도와 비교하였다. 그 결과 상류로 이동할수록 단위도의 첨두가 증가하는 양상을 확인할 수 있었다. 이는 길이비의 왜곡에 의한 총 유하길이의 차이 때문에 발생하는 오차이다. 이러한 오차를 피하기 위해서는 최고차 하천의 시작지점에서 총 길이의 60% 지점보다 하류에서 단위도를 산정해야 할 것으로 분석되었다. RV-GIUH를 좀 더 다양한 지점에 적용할 수 있도록 하기 위하여 총 유하길이의 차이를 보정할 수 있는 보정식을 제안하였다. 제안된 보정식을 사용하면, 최고차 하천의 시작지점에서 총 길이의 20% 지점부터 RV-GIUH를 적용할 수 있는 것으로 판단된다. 본 연구를 통하여 RV-GIUH를 적용성 및 정확성을 향상시킬 수 있을 것으로 판단된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2059-2063
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• 2008

When a thermocouple is placed in a high temperature gas-flow stream, the measured temperature could be biased from the true gas temperature due to a large radiation heat loss from a thermocouple surface to its surroundings. In this study, two thermocouples of unequal diameters with 1/8 inch and 1/16 inch are used to correct the radiation effect. The method is called the reduced radiation error (RRE). The preliminary test results show that the radiation and the sheath conduction cannot be negligible for the gas temperature measurement. To minimize the sheath conduction effect, all the thermocouples will have a grounded junction and 1/8 inch thermocouple will be replaced with 1 mm thermocouples. In addition, the computational fluid dynamics code analysis shows that there is a negligible temperature difference between the positions where the thermocouples were installed.