• 한국수자원학회논문집
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• 제48권8호
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• pp.635-645
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• 2015

본 연구에서는 하도 내 수제 형 수리구조물을 설치하였을 때, 만곡수로와 수충부에서의 흐름 양상 변화를 3차원 유속 측정을 통해 확인하였다. 연구를 위해 길이 24.4m, 폭 1.5m, 하상경사 2%의 만곡수로에서 실험을 수행하였다. 실험은 단일 수제의 설치 여부에 따라 크게 두 가지 경우로 나누어 수행하였다. 유속의 측정에는 3차원 초음파 유속계(Acoustic Doppler velocimeter, ADV)를 사용하였으며 각 단면 당 약60개의 측점을 선정하여 일정한 시간 동안 측정하였다. 측정된 유속들은 시간 평균하였으며, 각 단면에서의 측정결과를 연결하여 만곡수로의 수면유속을 파악하였다. 그 결과, 수제설치로 인해 구조물 하류에 위치한 만곡부 외측에서의 유속이 현저하게 감소하였고 제방을 향했던 흐름의 방향이 내측으로 변화하였음을 확인할 수 있었다.

• 한국환경과학회지
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• 제17권7호
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• pp.783-793
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• 2008

The purpose of this study is to analyze the sensitivity of the RMA2 model parameters reflecting the flow characteristics of stream junction and thus understand the hydraulic characteristics of the channel confluence flow. This study dealt with the input parameters of the RMA-2 model, a two-dimensional numerical analysis model widely used for researches both at home and abroad. The parameters of the RMA-2 model are roughness coefficient, turbulent diffusion coefficient, Coriolis forces latitude, Density, and mesh size. This study those parameters estimated from actual heavy rainfall, and varied the parameter size by (-)30%${\sim}$+30% to review the characteristics of the flow characteristics of the channel section. Weobserved that when the ratio of the channel width was relatively small, the smaller the approaching angle was, the farther from the junctions became the generating place of the maximum flow velocity, however, when the ratio of the channel width was relatively large, the larger the approaching angle was, the farther the generating place of the maximum flow velocity from the junctions became. In particular, the distance between junctions and the place where the maximum flow velocity generated showed an absolute correlationover 90% of the relative channel width, but an inverse relationwas found when the distance to the place where the flow velocity generated was shortened as relative the channel width between the main channel and tributary increased.

• Design & Manufacturing
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• 제16권3호
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• pp.58-65
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• 2022

Micro-fluidic chip has been fabricated by lithography process on silicon or glass wafer, casting using PDMS, injection molding of thermoplastics or 3D printing, etc. Among these processes, 3D printing can fabricate micro-fluidic chip directly from the design without master or template for fluidic channel fabricated previously. Due to this direct printing, 3D printing provides very fast and economical method for prototyping micro-fluidic chip comparing to conventional fabrication process such as lithography, PDMS casting or injection molding. Although 3D printing is now used more extensively due to this fast and cheap process done automatically by single printing machine, there are some issues on accuracy or surface characteristics, etc. The accuracy of the shape and size of the micro-channel is limited by the resolution of the printing and printing direction or layering direction in case of SLM type of 3D printing using UV curable resin. In this study, the printing direction and thickness of each printing layer are investigated to see the effect on the size, shape and surface of the micro-channel. A set of micro-channels with different size was designed and arrayed orthogonal. Micro-fluidic chips are 3D printed in different directions to the micro-channel, orthogonal, parallel, or skewed. The shape of the cross-section of the micro-channel and the surface of the micro-channel are photographed using optical microscopy. From a series of experiments, an optimal printing direction and process conditions are investigated for 3D printing of micro-fluidic chip.

• 대한토목학회논문집
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• 제30권3B호
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• pp.305-313
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• 2010

하천 복원 설계는 하천 수리 및 유사 수리학적, 하천 지형 및 형태학적, 그리고 생태환경적인 측면까지 모두 고려하여 인위적이지 않고 자연 상태에 가까운 평형하천의 형태를 갖도록 안정성을 최대화하면서 유지 관리 작업은 최소화하는 방향으로 수행해야 한다. 이를 위해서는 우선 평형하상 이론을 고려한 복원 하천 및 하도의 안정성에 대한 평가가 선행되어야 한다. 이러한 평형하상 이론 방법은 일반적으로 크게 해석적 방법 또는 경험적 방법의 형태로 발전되어 왔다. 본 논문에서는 청미천 구하도 복원이 실시되는 구간에 대해서 해석적 방법의 대표적인 Copeland 방법을 기본 모듈로 채택하고 있는 SAM 프로그램을 이용하여 안정하도를 설계하였으며 경험적 방법의 평형공식(하류하천 수리기하 공식)들을 이용하여 현재하도의 안정성을 평가하고 분석하였다. 해석적, 경험적 방법들로 분석된 결과들은 구하도 구간의 하도 형태 설계를 위한 자료로 활용하기 위한 것이다. Copeland 방법을 이용한 분석 결과, 청미천 대상구간의 안정하도는 현재하도보다 폭이 좁고 수심이 큰 그리고 경사가 완만한 하도인 것으로 나타났다. 또한 수리기하공식을 이용하여 복원 하천의 하폭 및 경사를 예측한 결과, 예측된 평형하도의 하폭은 현재 하도의 하폭보다 폭이 좁은 것으로 예측되었으며, 특히 Julien and Wargadalam 방법으로 예측한 결과 현재하도가 평형상태에 도달하기 위해서는 경사가 현재상태보다 더 완만해져야 되는 것으로 나타났다.

• 한국농공학회지
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• 제18권2호
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• pp.4116-4120
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• 1976

With the use of many rivers increased nearly to the capacity, the need for information concerning daily quantities of water and the total annual or seasonal runoff has became increased. A systematic record of the flow of a river is commonly made in terms of the mean daily discharge Since. a single observation of stage is converted into discharge by means of rating curve, it is essential that the stage discharge relations shall be accurately established. All rating curves have the looping effect due chiefly to channel storage and variation in surface slope. Loop rating curves are most characteristic on streams with somewhat flatter gradients and more constricted channels. The great majority of gauge readings are taken by unskilled observers once a day without any indication of whether the stage is rising or falling. Therefore, normal rating curves shall show one discharge for one gauge height, regardless of falling or rising stage. The above reasons call for the correction of the discharge measurements taken on either side of flood waves to the theoretical steady-state condition. The correction of the discharge measurement is to consider channel storage and variation in surface slope. (1) Channel storage As the surface elevation of a river rises, water is temporarily stored in the river channel. There fore, the actual discharge at the control section can be attained by substracting the rate of change of storage from the measured discharge. (2) Variation in surface slope From the Manning equation, the steady state discharge Q in a channel of given roughness and cross-section, is given as {{{{Q PROPTO SQRT { 1} }}}} When the slope is not equal, the actual discharge will be {{{{ { Q}_{r CDOT f } PROPTO SQRT { 1 +- TRIANGLE I} CDOT TRIANGLE I }}}} may be expressed in the form of {{{{ TRIANGLE I= { dh/dt} over {c } }}}} and the celerity is approximately equal to 1.3 times the mean watrr velocity. Therefore, The steady-state discharge can be estimated from the following equation. {{{{Q= { { Q}_{r CDOT f } } over { SQRT { (1 +- { A CDOT dh/dt} over {1.3 { Q}_{r CDOT f }I } )} } }}}} If a sufficient number of observations are available, an alternative procedure can be applied. A rating curve may be drawn as a median line through the uncorrected values. The values of {{{{ { 1} over {cI } }}}} can be yielded from the measured quantities of Qr$.$f and dh/dt by use of Eq. (7) and (8). From the 1/cI v. stage relationship, new vlues of 1/cI are obtained and inserted in Eq. (7) and (8) to yield the steady-state discharge Q. The new values of Q are then plotted against stage as the corrected steadystate curve.

• 한국수자원학회논문집
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• 제42권5호
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• pp.397-406
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• 2009

하천은 다양한 환경조건에 따라 변화될 수 있는 공간으로 구하도를 복원 설계하기 위해서는 현재 하도의 안정성 여부를 파악할 수 있는 하도평가가 필요하다. 하도평가는 대상하천의 지형 및 수리 수문 등 다양한 정보가 요구되지만 국내여건상 과거자료 미비로 인해 시 공간적으로 변화된 하천의 지형학적 정보를 파악하기에는 많은 어려움이 있다. 본 연구는 청미천의 과거 지형도 및 항공사진을 이용한 영상분석을 통해 과거와 현재 하천의 하도변화를 분석하고, 하도평가를 위한 영상분석기법에 대한 적용성을 검토하는데 목적이 있다. 영상분석을 통해 얻은 결과는 구하도 형태 규모, 하도 종 횡단 변화, 미지형 변화 등으로 정량적 분석이 가능하였다. 특히 모래사주의 형상변화는 현재하도의 상태를 파악하는 중요자료로 복원하도 설계 시 하도의 규모, 평수유입유량 등을 선정하기 위한 기초자료가 될 것이다. 이와 같은 결과에서 영상분석기법은 평면적인 정보의 한계는 있으나 복원하도 설계 시 국내 여건을 고려할수 있는 기법으로 활용될 수 있을 것이다.

• 동력기계공학회지
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• 제21권5호
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• pp.35-40
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• 2017

The effects of the different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on the heat transfer and pressure drops in a divergent channel with $45^{\circ}$ inclined ribs on one wall or two walls are checked out. The top and bottom walls are adiabatic; two side walls are uniformly heated in the divergent rectangular channel. The tested Reynolds numbers are ranged from 22,000 to 75,000. The channel with two opposite walls inclined only has the length of test section of 1 m and the channel divergence ratio of $D_{ho}/D_{hi}=1.49$, corresponding to $1.43^{\circ}$ inclined walls. The results show in the identical pumping power that the V-shaped continuous rib (case A) with two ribbed walls is the greatest, but the parallel broken rib (case B) with one ribbed wall is the worst in the thermal performance.

• Structural Engineering and Mechanics
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• 제70권4호
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• pp.499-511
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• 2019

In this study, the axial compressive behavior of novel quadruple C-channel built-up cold-formed steel columns with different slenderness ratio was investigated, using the experimental and numerical analysis. The axial compressive capacity and failure modes of the columns were obtained and analyzed. The finite element models considering the geometry, material and contact nonlinearity were developed to simulate and analyze the structural behavior of the columns further. There was a great correlation between the numerical analyses and test results, which indicated that the finite element model was reasonable and accurate. Then influence of, slenderness ratio, flange width-to-thickness ratio and screw spacing on the mechanical behavior of the columns were studied, respectively. The tests and numerical results show that due to small slenderness ratio, the failure modes of the specimens are generally local buckling and distortional buckling. The axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns decrease with the increase of maximum slenderness ratio. When the screw spacing is ranging from 150mm to 450mm, the axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns change little. The axial compressive capacity of quadruple C-channel built-up cold-formed steel columns increases with the decrease of flange width-thickness ratio. A modified effective length factor is proposed to quantify the axial compressive capacity of the quadruple C-channel built-up cold-formed steel columns with U-shaped track in the ends.

• 한국항행학회논문지
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• 제26권5호
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• pp.261-271
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• 2022

본 논문은 지상파 DTV (Digital TV) 방송 대역을 대상으로 서해상에서 활용 가능한 새로운 주파수 자원에 대한 연구이다. 우리나라 서해의 인천-제주도 해상 구간을 중심으로 DTV 방송 신호 (채널 14 51번, 470 698 MHz)의 TVWS (TV White Space) 주파수 이용 가능성을 연구하였다. 분석 결과 채널 19번(503 MHz), 채널 37번(611 MHz), 채널 39번(623 MHz) 3개 채널은 인천항-제주항 구간 및 인근 모든 바다에서 DTV와 혼신 없이 TVWS 가용 채널로 활용 할 수 있는 것으로 파악 되었다. 반면 채널 23번(527 MHz), 채널 33번(587 MHz) 2개 채널은 인천항-제주항 구간 전체에서 DTV 신호가 강한 것으로 분석되어 서해안에서 TVWS 가용 주파수로 활용이 어려운 것으로 분석되었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.297-300
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• 2009

The roll forming process is often used to manufacture long, thin-walled products such as a pipe. The final cross-section is a comparatively simple open-channel, a closed tube section or a complex profile with several bends. In recent years, that process is often applied to the bumper beam in the automotive industries. In this study, a optimal Center Floor Cross Member manufacturing technology, model deign and proper roll-pass sequences can be suggested by forming number of roll-pass and bending angle, and also effects of the process parameters on the final shape formed by roll forming defects were evaluated.