• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.461-461
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• 2016

이상기후로 인하여 제방붕괴에 대한 위험성이 높아지고 있고, 이로 인해 발생하는 제내지 내 붕괴 홍수파에 대한 연구가 증가하고 있다. 특히 홍수파 선단의 이동 속도 추정은 제내지의 위험성을 예측하고, EAP 등을 수립하는데 매우 중요한 자료가 될 수 있다. 제내지에서의 선단 홍수파에 대한 예측을 하기 위해서는 해당 지역의 하천특성, 수리특성 및 제방 등 수공구조물 특성뿐만 아니라, 제내지의 지형 및 토지이용 현황 등을 조사하여 수리실험이나 수치모의를 수행해야 하는 것이 일반적이다. 수치해석의 경우 수리실험에 비하여 경제성 및 효율성 측면에서 뛰어날 수 있으나, 제방 붕괴과정 및 메커니즘을 반영하기가 불가능하다. 이에 반해 수리모형실험의 경우 제방붕괴 양상 및 그 과정의 재현이 가능하기 때문에, 제내지에서의 선단홍수파 전파에 관한 보다 정확한 양상을 파악할 수 있을 것이다. 그러나 이러한 실험은 실제 크기의 하천이 아닌 축소모형 또는 개수로에서 수행되었기 때문에, 초기 홍수파의 전파가 축척효과(Scale effect)의 영향을 받을 가능성이 매우 크다. 특히 선단 홍수파의 경우 파가 진행되면서 수심이 낮아지고, 유속이 느려지기 때문에 그 영향은 점차 증대된다고 할 수 있다. 이에 본 연구에서는 이러한 초기 선단 홍수파의 표면장력 영향을 고려한 보정 계수 산정에 대한 연구를 수리실험을 통해 수행하였다. 연구는 크게 4가지 과정으로 구성되었다. 첫째는 농도-표면장력의 관계 규명이며, 둘째는 표면장력-홍수파 전파 속도 관계 규명이다. 셋째는 표면장력과 Weber Number(We)의 관계를 도출하는 것이며, 마지막은 We를 이용하여 한계조건을 제시하는 것이다. 실험은 계면활성제의 농도를 변화시켜가며, 얇은 유리관(D=1.0 mm)에서 물의 상승 높이 및 접촉각을 측정하여 농도와 표면장력의 관계를 측정하였으며, 이러한 결과를 바탕으로 물의 표면장력을 변화시켜 가며 $0.5(B){\times}0.3(L){\times}0.2(H)m$의 Head-tank에 설치된 수문을 빠르게 개방하여, 홍수파가 퍼지는 양상을 관측하였다. 홍수파의 이동 속도는 진행시간에 따라서 퍼짐 넓이를 측정하여 제곱근을 취하는 방식으로 평균속도를 산정하였다. 이러한 관계를 이용하여 표면장력이 없을 경우의 이동속도 및 ??를 도출하였다. 본 연구를 통해 홍수파 전파 특성에 대한 수리실험 자료를 바탕으로 Weber 수를 도출하여 표면장력의 영향을 받는지 여부를 판단할 수 있으며, 표면장력의 영향을 받을 경우, 제시된 결과를 이용하여 홍수파 선단의 속도를 보정할 수 있다. 본 연구 결과는 토대로 축소모형으로 수행되는 홍수파 전파에 대한 수리실험결과의 보정 기초자료로 매우 유용할 것으로 판단된다.

• Tunnel and Underground Space
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• v.12 no.3
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• pp.142-151
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• 2002

Claesson(2001)'s analytical solution, and two numerical models with Dirichlet and Neuman interior boundary condition respectively were investigated to estimate the transient temperature distribution with distances from the Taejon underground food cold storage pilot cavern. Claesson's solution, which is based on constant temperature boundary condition at the rock wall during a temperature decline step, showed relatively good agreement with temperature measurements in the rock mass in order of average error difference, 0.89$\^{C}$ without any adjustments on laboratory thermal properties to represent the rock mass. For the numerical model with heat flux through the rock wall, a boundary condition setting technique was newly proposed to overcome the difficulty of prescribing variable convective heat tranfer coefficient and far-field air temperature inside the cavern as they may be certainly changed according to the cooling-down time. The results showed also good agreement with measurements in order of average error difference, 1.58$\^{C}$, and were compared to those of the numerical model with fixed temperature at the rock wall. Finally, the most proper procedure to precisely predict the temperature profile around a cavern was proposed as a series of analysis steps including an analytical exact solution and numerical models.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1656-1660
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• 2006

도시 주변의 급격한 택지개발, 도시 인구의 집중, 대규모 계획단지의 개발은 유역의 유출특성에 큰 영향을 주게 되고, 도시화가 진행됨에 따라 불투수 표면이 증가되고 침투율이 감소됨으로써 유출계수의 증가요인이 되고 있다. 이에 따라 유역의 자연 저류지 기능이 저하되고, 우수가 하천으로 유입되는 시간이 단축됨으로써 첨두홍수량 뿐만 아니라 유출총량의 증대를 초래하여 도시 주변의 중소하천 유역에서는 막대한 재산 및 인명 피해가 발생하고 있다. 이러한 도시화로 인해 증가된 유출량을 저감시키는 구조적 방안으로 대부분 강우 유출수를 일시 저류하여 유출량을 조절하는 우수유출 억제시설이 권장되고 있으나, 이들 시설에 대한 수리학적 침수방어능력이 명확히 규명되지 못한 실정이다. 본 연구의 목적은 도시지역 침수방지 대책 수립에 필요한 On/Off-Line 저류지의 평가 및 설계에 기존 부정류 모형들의 모의가능성을 평가 비교하고, 가상하도와 실제하도에 적용하여 모형을 검보정 함으로서 저류지 해석의 실용화 모형을 확립함에 있다. 본 연구 결과는 도시지역에 적용할 수 있는 도시홍수방어시스템의 일환으로 구축함으로써, 도시지역에서 저류지 홍수저감효과를 평가하는 등 침수재해와 연계된 구조적 대책 수립에 필요한 기초자료로 활용하고자 한다. 본 연구에서 연구된 저류지 모형을 이용하여 On-Line 및 Off-Line 저류지에 적용한 결과 두 종류의 저류지 모두 홍수방어를 위해 이용될 수 있었다. On/Off-Line 저류지 모두 첨두유량이 발생할 경우 어느정도의 첨두값의 감쇠를 발생시킬 수 있는 것으로 판단된다. 그러나 저류지 상류단의 수위감소는 저류지로 유출로 인해 저류지 상류 하도부에서 유속의 증가를 발생시켰고 이로 인해 수위는 저류지가 존재하지 않는 경우보다 낮게 나타나고 있다. On-Line 저류지의 경우 Off-Line 의 경우에 비해 수위, 유량이 저류지의 상류단에서 크게 나타났다. On-Line 저류지의 경우 Off-Line 의 경우에 비해 같은 값의 첨두홍수량을 저류하기 위해서 상대적으로 넓은 저류면적이 필요한 것으로 나타난다. 대등한 수위감소값의 홍수저감효과를 발휘하기 위해서 본 연구에서는 On-Line 저류지 면적은 Off-Line 저류지에 비 두배 이상이 필요한 것으로 보여졌다.

• Membrane Journal
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• v.21 no.3
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• pp.236-246
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• 2011

In this study, we used prepared a cylindrical module consisting 100 hollow fibers of commercialized (hydrophobic) polyethylene membrane of $0.4{\mu}m$ pore size and systematically studied performance of direct contact membrane distillation (DCMD) and sweep gas membrane distillation (SGMD) in terms of variation of permeate flux and salt rejection with respect to temperature drop across the membrane, salt concentrations in feed, and flow rates of cooling water and sweep gas. SGMD was regarded as DCMD with a sweep gas layer between permeate-side membrane surface and cooling water. Sweep gas flow decreases the permeate flux from that of DCMD by providing an additional gas-layer resistance. We compared DCMD and SGMD performance by using mass balance with a fitting parameter (${\omega}$), indicating fraction of permeate flow rate.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.5
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• pp.534-543
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• 2008

The experimental study with the prototype provides more acceptable data than the others. But there are so many limited conditions to perform the experimental study with the prototype. So the theoretical similitude with the scaled model and the numerical study with the CFD method have been chosen alternatively to analysis the fume movement. In this study, the ventilation was estimated from the results of the numerical study based on the experimental results as the boundary conditions. The grid A and B were same size and shape with the models which was used in the experimental study and consisted with 163,839, 122,965 cells respectively. The height of the fume layer was estimated form the mole fraction of fume components and the ventilation was determined by the velocity and temperature of the fume. The results of this study showed that the fume movements estimated from the numerical study are enough to apply to the prototype if there are proper heat loss correction factors. The numerical study is easier to change study conditions and faster to get results from the study than the experimental study. So if we find some proper heat loss correction factors, it's possible to execute the various and advanced study with the numerical study.

• The Korean Journal of Ecology
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• v.22 no.3
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• pp.101-108
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• 1999

This survey was performed from March 1993 to March 1998, in order to clarify the relationships between water quality and topographical factor. The study sites were two reservoir basins; Kaesim and Jangchan in Iwon-myon, Okchon-gun, Chungcho'ngbukdo Province. Basin shape factors of Kaesim reservoir were at 0.030∼0.210 (mean value 0.090), those of Jangchan reservoir were at 0.217∼0.452 (mean value 0.325). The mean basin shape factor of Jangchan reservoir was 3.61 times larger than that of Kaesim reservoir because its stream width was narrower and mean stream length was shorter. In the correlation between distance from the source of stream (L) and basin area (A), Iwonchon basin was calculated as L=1.44A/sup 0.6/. Circularity ratio was 17.114 in Kaesim (22% of Kum River), and 7.444 in Jangchan. Elongation ratio was 0.357 in Kaesim, 0.636 in Jangchan and 0.282 in Kum River. Precipitation summation period of Jangchan was 1.54 times slower than that of Kaesim. Rainfall reaching time in each small basin was 337.53 min. in A'(Jangchan-ri) basin of Jangchan and 49.26 min in H (Iwon-ri) basin of Kaesim. In the relationship between watershed frequency (Df) and drainage density (Dd), the regression equation was Df=0.023Dd² in Kaesim and Df=0.189Dd² in Jangchan reservoir. As slope degree increased, DO became higher (Y/sub DO/=0.19X＋6.5927, r=0.8l), but COD(Y/sub COD/=-0.2092X＋9.7104, r=0.52) became lower. Total nitrogen was increased with the increase of basin shape factor and circularity ratio. Ratio of B/sub OD/ to COD was 1/1.2(Y/sub BOD/ = 1.2984 X/sub COD/-3.2004, r=0.9l).

• Journal of Korean Society of Environmental Engineers
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• v.32 no.8
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• pp.739-746
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• 2010

The purposes of this study are 1) to develop an advanced chamber system within ${\pm}10%$ of air velocity at the particulate matter (PM) collection area, 2) to research theoretical characteristics of PM10 and PM2.5 samplers, 3) to assess the performance characteristics of PM10 and PM2.5 samplers through chamber experiments. The total six one-hour experiments were conducted using the cornstarch with an mass median aerodynamic diameter (MMAD) of $20\;{\mu}m$ and an geometric standard deviation of 2.0 at the two different air velocity conditions of 0.67 m/s and 2.15 m/s in the chamber. The aerosol samplers used in the present study are one APM PM10 and one PM2.5 samplers accordance with the US federal reference methods and specially designed three mini-volume aerosol samplers (two for PM10 and one for PM2.5). The overall results indicate that PM10 and PM2.5 mini-volume samplers need correction factors of 0.25 and 0.39 respectively when APM PM samplers considered as reference samplers and there is significant difference between two mini-volume aerosol samplers when a two-way analysis of variance is tested using the measured PM10 mass concentrations. The PM10 and PM2.5 samplers with the cutpoints and slopes (PM10: $10{\pm}0.5\;{\mu}m$ and $1.5{\pm}0.1$, PM2.5: $2.5{\pm}0.2\;{\mu}m$ and $1.3{\pm}0.03$) theoretically collect the ranges of 86~114% and 64~152% considering the cornstarch characteristics used in this research. Furthermore, the calculated mass concentrations of PM samplers are higher than the ideal mass concentrations when the airborne MMADs for the cornstarch used are smaller than the cutpoints of PM samplers and the PM samplers collected less PM in another case. The chamber experiment also showed that PM10 and PM2.5 samplers had the bigger collection ranges of 37~158% and 55~149% than the theocratical calculated mass concentration ranges and the relatively similar mass concentration ranges were measured at the air velocity of 2.15 m/s comparing with the 0.67 m/s.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.531-541
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• 2020

In this study, a computed tide of a real tide was introduced to improve the numerical solutions for tides and tidal flow simulations. The real tide was defined considering the nodal modulation amplitude, phase correction factor, astronomical argument, and tidal harmonic constants of all the constituents. The numerical simulation was performed using the real tide parameters for the west-south coastal waters of Korea, where the observation data for tides, tidal currents, waves, and winds over two seasons exist. The tidal flow simulation of the real tide was simulated successfully. The correlation coefficient between the observed and calculated values was 1.0, which indicated both accurate amplitude and phase. The U- and V-components of the tidal current obtained for the real tide had average valid correlations of 0.83 and 0.936, respectively. The speed error for the residual current was 0.006 m/s on the average, which indicated an insignificant difference, and the directional behavior of the residual current was very similar. In addition, the velocity error was attributed to various weather effects, such as high waves and wind storms. Therefore, this model is expected to improve current solutions provided that weathering forces, such as waves and winds, are considered.