• 대한기계학회논문집
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• 제19권9호
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• pp.2328-2341
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• 1995

An experimental study on the flow over the axisymmetric backward-facing step was carried out. The purposes of the present study are to investigate the effect of the free stream turbulence intensity on the reattachment length and to understand the turbulence structure of the recirculating flows. Local mean and fluctuating velocity components were measured in the separated and reattaching axisymmetric turbulent boundary layer over the wall of convex cylinder placed in a water tunnel by using 2-color 4-beam fiber optics laser Doppler velocimetry. As the free stream turbulence intensity increased, the reattachment length became shorter due to the enhanced mixing in the separated shear layer. It was also observed that the reverse flow velocity and turbulent kinetic energy increase with increasing free stream turbulence intensity. Spectral data and flow visualization showed that low-frequency motions occur in the separated flow behind a backward-facing step. These motions have a significant effect on the time-averaged turbulence data.

• Journal of Astronomy and Space Sciences
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• 제17권1호
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• pp.107-116
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• 2000

본 연구는 지구 공전 궤도 근처의 Leonid의 출현 빈도와 속도 등을 예측하기 위한 연구의 초기 단계로서 meteoroid에 대한 기초 자료 조사와 더붙어 기존에 알려져 있는 meteoroid 입자의 분출 속도 모텔과 섭동 모델로부터 meteoroid의 운동 방향과 속도를 컴퓨터로 계산하기 위한 프로그램을 개발하고 이것을Leonid stream에 적용해 보았다. 입자의 초기 속도 모델로는Jones의 분출속도 분포모델을 사용하였으며, meteoroid의 궤도 운동 모델에는 태양과 달, 지구를 비롯한 각 행성들의 섭동 모델이 포함되었다. 태양계 천체들의 Ephemeris를 구하기 위해 JPL (Jet Propulsion L Laboratory)의 SSD (Solar System Dynamics) Laboratory에서 개발된 DE405 Solar System E Ephemeris 데이터 파일을 사용하였다. 이외에 중요한 섭동 요소로써 태양 복사압을 고려하였으며, 적분 알고리즘으로는 8차 Runge-Kutta 방법을 사용하였다.

• 한국농공학회지
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• 제32권3호
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• pp.87-101
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• 1990

The purpose of this study is to estimate the flood discharge and runoff volume at a stream by using geomorphologic parameters obtained from the topographic maps following the law of stream classification and ordering by Horton and Strahier. The present model is modified from Cheng' s model which derives the geomorphologic instantaneous unit hydrograph. The present model uses the results of Laplace transformation and convolution intergral of probability density function of the travel time at each state. The stream flow velocity parameters are determined as a function of the rainfall intensity, and the effective rainfall is calculated by the SCS method. The total direct runoff volume until the time to peak is estimated by assuming a triangular hydrograph. The model is used to estimate the time to peak, the flood discharge, and the direct runoff at Andong, Imha. Geomchon, and Sunsan basin in the Nakdong River system. The results of the model application are as follows : 1.For each basin, as the rainfall intensity doubles form 1 mm/h to 2 mm/h with the same rainfall duration of 1 hour, the hydrographs show that the runoff volume doubles while the duration of the base flow and the time to peak are the same. This aggrees with the theory of the unit hydrograph. 2.Comparisions of the model predicted and observed values show that small relative errors of 0.44-7.4% of the flood discharge, and 1 hour difference in time to peak except the Geomchon basin which shows 10.32% and 2 hours respectively. 3.When the rainfall intensity is small, the error of flood discharge estimated by using this model is relatively large. The reason of this might be because of introducing the flood velocity concept in the stream flow velocity. 4.Total direct runoff volume until the time to peak estimated by using this model has small relative error comparing with the observed data. 5.The sensitivity analysis of velocity parameters to flood discharge shows that the flood discharge is sensitive to the velocity coefficient while it is insensitive to the ratio of arrival time of moving portion to that of storage portion of a stream and to the ratio of arrival time of stream to that of overland flow.

• 대한토목학회논문집
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• 제30권5B호
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• pp.479-486
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• 2010

신뢰성 있는 수문자료의 획득은 효율적인 물 관리를 위한 가장 기본적인 조건인 동시에 가장 필수적인 조건이다. 특히 최근 이상기후의 영향으로 빈번하게 발생하고 있는 도시홍수에 대응하기 위한 경보체계 등을 구축하는데 있어 사용자가 관측하고자 하는 임의 지점에서 유황자료의 획득은 매우 중요하다. 지속적인 하천정비 사업을 통해 외수범람에 의한 홍수 발생빈도는 점차 낮아지고 있지만, 하수관거의 노후화, 관리 소홀 등의 원인으로 내수배제가 원활하지 못해서 발생하는 내수침수로 인한 도시홍수는 지속적으로 발생하고 있다. 이러한 도시홍수 저감을 위해서는 도시배수시스템에 대한 지속적인 관리와 현황파악이 필수적이다. 본 연구에서는 CDMA(Code Division Multiple Access) 무선통신기술과 Bluetooth 근거리 무선통신기술을 사용하여 전문적인 지식이 없는 사용자라도 누구나 언제, 어디서든 도시배수시스템의 임의의 지점에서 유황을 파악하고, 배수관망에서는 유황 관측과 동시에 유출 경로 추적이 가능한 도시배수관망 유속측정 시스템의 개발을 목표로 하였다. 도시배수관망 유속측정 시스템은 세 단계로 구성되어 운영된다. 첫 번째 단계에서 ubiquitous floater를 사용하여 획득한 유황 정보를 서버로 전송하면, 두 번째 단계에서 서버 컴퓨터를 통해 도시 배수시스템의 현황을 판단하고, 마지막 단계에서 정보를 GUI(Graphic User Interface)를 통해 사용자에게 제공하게 된다. 개발된 도시배수관망 유속측정 시스템을 경기도 수원의 원천천에 위치한 배수관망에 적용하여 현장 실험한 결과, 도시 배수관리를 위해 필요한 정보들을 실시간으로 획득하고 관리할 수 있었다.

• Ecology and Resilient Infrastructure
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• 제4권4호
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• pp.216-225
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• 2017

We assessed the microhabitat conditions of three fish species (black shinner Pseudopungtungia nigra, striped shinner Pungtungia herzi, Korean shinner Coreoleuciscus splendidus) considering various stream order in the Geumgang River Basin. A total of 1,275 individuals were collected from 19 sites. And the microhabitat condition was assessed measuring flow velocity, water depth and substrate size at each site. The highest relative frequencies for P. herzi, C. splendidus and P. nigra were calculated 100% (n = 310), 78.9% (n = 784) and 47.3% (n = 181) respectively. P. herzi appeared in all streams, irrespective of their stream order; however, appearance in streams with the $2^{nd}$ order or lower was found to be scarcer than in the ones with the $3^{rd}$ order or higher. On the other hand, P. nigra and C. splendidus didn't appear in streams with the $2^{nd}$ order or lower. When it comes to P. nigra, the ones with 7 to 8 cm in length most frequently appeared. They inhabited streams, mainly, with 0.2 to $0.4m\;s^{-1}$ and 0.5 m in velocity and water depth, respectively. The three species all preferred runs as types of habitats with lots of coarse gravels-cobbles. P. herzi, the ones with 5 cm or shorter in length most frequently appeared. They inhabited streams, mainly, with 0 to $0.3m\;s^{-1}$ and 0.4 m in velocity and water depth, respectively. C. splendidus with 7 to 8 cm in length occupied the majority of them. They appeared in streams, mainly, with $0.9m\;s^{-1}$or higher and 0.3 m in velocity and water depth.

• 대한기계학회논문집
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• 제12권4호
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• pp.847-864
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• 1988

본 연구에서는 연료분출에 박리가 있는 경우와 없는 경우 각각에 대하여 화염 대 근처의 국부가속 현상이 박리에 의하여 어떻게 영향을 받는가를 실험적으로 규명하 고, 나아가서 종래에 행해져 왔던 관련 연구 결과를 재검토할려고 한다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.49-55
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• 2009

This paper evaluates performances of a recently developed divergence-free finite element method based on Hermite interpolated stream functions. Velocity bases are derived from Hermite interpolated stream functions to form divergence-free basis functions. These velocity basis functions constitute a solenoidal function space, and the simple gradient of the Hermite functions constitute an irrotational function space. The incompressible Navier-Stokes equation is orthogonally decomposed into a solenoidal and an irrotational parts, and the decoupled Navier-Stokes equations are projected onto their corresponding spaces to form proper variational formulations. To access accuracy and convergence of the present algorithm, three test problems are selected. They are lid-driven cavity flow, flow over a backward-facing step and buoyancy-driven flow within a square enclosure. Hermite interpolation functions from cubic to quintic are chosen to run the test problems. Numerical results are shown. In all cases it has shown that the present method has performed well in accuracies and convergences. Moreover, the present method does not require an upwinding or a stabilized term.

• Ocean Systems Engineering
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• 제13권3호
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• pp.247-268
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• 2023

Tidal stream energy extraction remains a site-specific resource due to the "first generation" criteria requiring high-velocity tidal streams. Most studies on tidal energy and turbine blade design heavily focus on installation sites with higher velocity conditions that are non-existent in tropical countries such as the Philippines. To shorten this gap, this review paper tackles tidal turbine design considerations for low-energetic regions such as the tropics. In-depth discussions of operating principles, methods of analysis, and designs of tidal turbine blades are presented. Notable tidal stream projects around the world are also mentioned in the paper. Also, it provides a perspective on the potential of this renewable energy to produce electricity for various sites in the Philippines. Finally, the paper emphasizes the need for new tidal turbine blade designs to be viable in tropical regions, such as the Philippines.

• 한국환경과학회지
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• 제24권4호
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• pp.371-381
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• 2015

In the mountain streams in Jeju Island, strong turbulence and roughness usually made it nearly impossible to utilize most of intrusive instrumentation for streamflow discharge measurements. Instead, a non-intrusive fixed electro-magnetic wave surface velocimetry (fixed EWSV: Kalesto) became alternatively popular in many representative streams to measure stream discharge seamlessly. Currently, Kalesto has shown noteworthy performance with little loss in flood discharge measurements and also has successfully provided discharge for every minute. However, Kalesto has been operated to regard its measured one-point velocity as the representative mean velocity for the given cross-section. Therefore, it could be highly possible to potentially encompass discharge measurements errors. In this study, we analyzed the difference between such Kalesto discharge measurements and other alternative concurrent discharge measurements such as Acoustic Doppler Current Profiler (ADCP) and mobile EWSV which were able to measure velocity in multi-points in the cross-section. Consequently, Kalesto discharge deviated from ADCP discharge in amount of 48% for relatively low flow, and more than 20% difference for high flow compared with mobile EWSV discharge measurements. These results indicated that the one-point velocity measured by Kalesto should be used as a cross-sectional mean velocity, rather it should be accounted for as an index-velocity in conjunction with directly measured cross-sectional mean velocity by using more reliable instrumentations. After inducing Kalesto Discharge Correction Coefficient (KDCC) that actually means relationship between index velocity and cross-sectional mean velocity, the corrected discharge from Kalesto was significantly improved. Therefore, we found that index velocity method should be applied to obtain better accuracy of discharge measurement in case of Kalesto operation.

• 한국방재학회 논문집
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• 제9권3호
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• pp.101-106
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• 2009

우리나라의 경우 1990년대 후반부터 ADCP(Acoustic Doppler Current Profiler)가 도입되기 시작하였으나 아직까지는 ADCP를 이용한 유량측정 기법과 현장 적용성 문제가 충분히 검토되지 못하고 있는 실정이다. 따라서, 본 연구의 목적은 회전식 유속계와 ADCP를 이용한 유속측정의 검증 및 적용에 관한 것이다. 검증방법은 실험실에서 측정된 유속 값을 이용하였다. ADCP와 회전식 유속계를 이용한 유속측정의 차이는 2.1% 이내로 이는 ADCP을 현장에 적용해도 무방한 것으로 나타났다. 검증을 실시 후 ADCP를 실제 하천에 적용하였다. 현장적용 대상하천으로는 매곡천을 선정하여 ADCP의 유속 및 회전식 유속계의 유속을 비교하였다. 결과에서 ADCP에 의한 유속측정 값은 기존에 전통적으로 사용되는 회전식 유속계의 측정과 비교해서 평균 10.5% 이내의 오차로 잘 일치하는 것으로 나타났다.