• 생태와환경
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• 제43권4호
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• pp.492-502
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• 2010

The study objects were to analyze long-term and seasonal variations of nutrients (N, P), suspended solids, N:P ratios, algal chlorophyll, and trophic state along with general water quality parameters in four sampling sites including two intake tower sites supplying drinking water in Daechung Reservoir. For the analysis, we used water quality long-term data sampled during 1998~2007 by the Ministry of Environment, Korea. Interannual and seasonal trends in inflow and discharge near the intake tower facilities over the ten years were directly influenced by rainfall pattern. The distinct difference between wet year (2003) and dry year (2001) produced marked differences in water temperature, pH, dissolved oxygen, organic matter contents, nutrients, and these variables influenced algal biomass and trophic state. Values of TP varied depending on the year and locations sampled, but monthly mean TP always peaked during July~August when river inflow and precipitation were maxima. In contrast, TN varied little compared to TP, indicating lower influence by seasonal flow compared to phosphorus. The number of E. coli were highest in Site 2 (Chudong intake tower) and varied largely, whereas at other sites, the numbers were low and low variations. Contents of chlorophyll-${\alpha}$ (CHL), as an estimation of primary productivity, varied largely depending on the year and season. The maximum of CHL occurred at Muneu intake tower (S4) during 2006 when the precipitation and inflow were lowest. In contrast, another CHL peak was observed in Site 2 (Chudong intake tower) in 2006 when one of the largest typoons (Ewinia) occurred and river runoff were maximum. So the CHL maxima were associated with both wet year (high flow, high nutrient supply) and dry year (low flow, nutrient supply by littoral zone). Such conditions influenced trophic states, based on Trophic State Index of nutrients and CHL. Based on all analyses, we can provide some clues for management and protection strategies of two intake tower sites.

• 지질공학
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• 제24권1호
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• pp.91-98
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• 2014

본 연구는 지하댐 건설에 의한 지하수 증가량을 계산하고 지표수에 미치는 영향을 검토하는 것이 목적이다. 이를 위해 연구지역 면적과 지하수위, 유효공극률을 이용해 지하수량을 계산하였으며 영덕 오십천의 유황분석을 실시하여 지하수량 증가에 따른 지표수 변화를 검토하였다. 분석 결과 지하수 증가량은 지하댐 유역 기준으로 최대 $91,746m^3$이며 지하댐 하류의 지하수 감소량은 최대 $11,259m^3$인 것으로 계산되었다. 따라서 연구지역의 지하수 확보량은 총 $80,487m^3$이며 지하수 감소량은 지하수 증가량에 비해 12.27%에 불과한 것으로 나타났다. 댐 건설 후 하류지역의 유황곡선을 분석한 결과 댐건설로 인해 유출량의 변화가 최대 $3.00{\times}10^{-2}m^3/s$ 발생하였으나 댐 건설 전과 비교해 전반적인 차이는 거의 없는 것으로 나타났다. 이 연구 결과는 지하댐이 지표수 환경에 영향을 주지 않으며 충분한 대체 수자원이 될 수 있다는 것을 의미한다.

• Korean Chemical Engineering Research
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• 제44권5호
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• pp.505-512
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• 2006

직경이 0.102 m이고 높이가 2.5 m인 액체-입자 swirling(나선)흐름 유동층에서 유동 입자의 흐름 및 열전달 특성을 고찰하였다. 액체유속($U_L$), 유동 입자의 크기($d_p$) 그리고 연속상인 액체의 나선 유도흐름 액체량의 비($R_s$)가 유동층 내 유동입자의 체류량 유동층 내부 열원과 유동층간의 총괄 열전달 계수에 미치는 영향을 검토하였다. 액체-입자 나선흐름 유동층에서 입자 체류량은 입자의 크기와 나선유도흐름 액체량의 비가 증가함에 따라서 증가하였으나, 액체유속의 증가에 따라서는 감소하였다. 유동층 내부에서 나선 유도 흐름 액체량의 비가 0.1~0.3인 경우에 유동 입자의 국부체류량은 유동층 중심부에서 큰 값을 나타내었으나, $R_s$의 값이 0.5일 때는 반경 방향 입자 체류량은 거의 균일한 분포를 보이며, $R_s$의 값이 0.7일 때는 유동층 중심부의 입자 체류량이 상대적으로 감소하는 경향을 나타내었다. 유동층 내부열원과 유동층간의 열전달 특성은 열원 표면과 유동층간의 온도차 요동 자료의 위상공간 투영과 kolmogorov 엔트로피 해석으로 고찰할 수 있었으며, 나선 유도 흐름 액체량의 비($R_s$)가 0.1에서 0.5까지 증가할수록 온도차 요동 자료의 위상공간 투영은 점점 안정되고 규칙성이 증대되는 상태를 나타내고, kolmogorov 엔트로피 값은 감소하는 경향을 나타내었다. 열원 표면과 유동층간의 온도차 요동 자료의 kolmogorov 엔트로피 값은 액체의 유속이 증가함에 따라 최대값을 나타내었다. 열원과 유동층간의 총괄 열전달 계수는 액체유속, 층공극률, 나선 유도 흐름 액체량의 비가 증가함에 따라서 최대값을 나타내었으며, 유동 입자의 크기가 증가함에 따라 증가하였다. 내부 열원과 유동층간의 총괄 열전달 계수가 최대값을 나타낼 때의 액체의 유속 조건에서 온도차 요동자료의 kolmogorov 엔트로피의 값도 최대값을 나타내었다. 액체-입자 나선흐름 유동층에서 입자 체류량과 열전달 계수를 무차원군의 상관식으로 나타낼 수 있었다.

• Wind and Structures
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• 제13권1호
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• pp.57-82
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• 2010

The 486m-long roof of Shenzhen Citizens Centre is one of the world's longest spatial lattice roof structures. A comprehensive numerical study of wind effects on the long-span structure is presented in this paper. The discretizing and synthesizing of random flow generation technique (DSRFG) recently proposed by two of the authors (Huang and Li 2008) was adopted to produce a spatially correlated turbulent inflow field for the simulation study. The distributions and characteristics of wind loads on the roof were numerically evaluated by Computational Fluid Dynamics (CFD) methods, in which Large Eddy Simulation (LES) and Reynolds Averaged Navier-Stokes Equations (RANS) Model were employed. The main objective of this study is to explore a useful approach for estimations of wind effects on complex curved roof by CFD techniques. In parallel with the numerical investigation, simultaneous pressure measurements on the entire roof were made in a boundary layer wind tunnel to determine mean, fluctuating and peak pressure coefficient distributions, and spectra, spatial correlation coefficients and probability characteristics of pressure fluctuations. Numerical results were then compared with these experimentally determined data for validating the numerical methods. The comparative study demonstrated that the LES integrated with the DSRFG technique could provide satisfactory prediction of wind effects on the long-span roof with complex shape, especially on separation zones along leading eaves where the worst negative wind-induced pressures commonly occur. The recommended LES and inflow turbulence generation technique as well as associated numerical treatments are useful for structural engineers to assess wind effects on a long-span roof at its design stage.

• 한국산업융합학회 논문집
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• 제23권5호
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• pp.773-787
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• 2020

In the injection molding process, the controlling stability of products quality is a very important factor in terms of productivity. Even when the optimum process conditions for the desired product quality are applied, uncontrollable external factors such as ambient temperature and humidity cause inevitable changes in the state of the melt resin, mold temperature. etc. Therefore, it is very difficult to maintain prodcut quality. In this study, a system that learns the correlation between process variables and product weight through artificial neural networks and predicts process conditions for the target weight was established. Then, when a disturbance occurs in the injection molding process and fluctuations in the weight of the product occur, the stability control of the product quality was performed by ANN predicting a new process condition for the change of weight. In order to artificially generate disturbance in the injection molding process, controllable factors were selected and changed among factors not learned in the ANN model. Initially, injection molding was performed with a polypropylene having a melt flow index of 10 g/10min, and then the resin was replaced with a polypropylene having a melt floiw index of 33 g/10min to apply disturbance. As a result, when the disturbance occurred, the deviation of the weight was -0.57 g, resulting in an error of -1.37%. Using the control method proposed in the study, through a total of 11 control processes, 41.57 g with an error of 0.00% in the range of 0.5% deviation of the target weight was measured, and the weight was stably maintained with 0.15±0.07% error afterwards.

• ALGAE
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• 제22권4호
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• pp.297-304
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• 2007

This study is intended to clarify the effects of heated effluents on intertidal benthic marine algal community in Korea. The species composition and biomass of marine algae at the discharge canal of Gori nuclear power plant on the southeastern coast of Korea were investigated seasonally from February 2001 to October 2006. As a result, 54 species (7 blue-green, 12 green, 9 brown and 26 red algae) of marine algae were found at the discharge canal during the past six years. In general, the number of species observed was abundant during winter to spring and less in autumn. Enteromorpha compressa, E. intestinalis, E. prolifera and Caulacanthus ustulatus were common species found more than 80% frequency during the study period. Seasonal fluctuations of mean biomass were 1-440 g dry wt m–2 and dominant species in biomass were Enteromorpha spp. (contribution to a total biomass proportion 28%), Sargassum horneri (14%) and Amphiroa beauvoisii (14%). It is evident from the floristic composition and biomass data that unique micro-environment of the discharge canal support different communities from those on the intake or control area. Results from the large numbers of surveys before and during plant operation showed that, in the regions influenced by thermal effluents such as the discharge canal of power plants, the process of ecological succession has been proceeded. It is assumed that the uni-directional water flow and the time of overhaul largely affect the development and succession of benthic marine algal communities of the discharge canal.

• 신재생에너지
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• 제16권1호
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• pp.1-14
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• 2020

Liquid air energy storage (LAES) using gas liquefaction has attracted considerable attention because of its mature technology, high energy density, few geographical constraints, and long life span. On the other hand, LAES has not yet been commercialized and is being developed recently. Therefore, few studies have performed an economic analysis of LAES. In this study, the levelized cost of electricity was calculated and compared with that of other energy storage systems. As a result, the levelized cost of electricity of LAES was $371/MWh. This is approximately $292/MWh, $159/MWh, $118/MWh, and $3/MWh less than that of the LiCd battery, VRFB battery, Lead-acid battery, and NaS battery. In addition, the cost was approximately $62/MWh and $195/MWh more than that of Fe-Cr flow battery and PHS. Sensitivity analysis of the levelized cost of electricity according to the main economic factors was performed, and economic uncertainty analysis was performed through a Monte-Carlo simulation. The cumulative probability curve showed the levelized cost of electricity of LAES, reflecting price fluctuations in the air compressor cost, electricity cost, and standing reserve hourly fee.

• 한국물환경학회지
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• 제25권1호
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• pp.102-111
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• 2009

Turbid storm runoff from intensive highland agriculture area has emerged as the major problem of water quality deterioration in the upstream region of the Han River. High slope of the upland combined with high rate of fertilization and intensive plowing causes high rate of soil erosion, and subsequently high suspended sediment and phosphorus content in the runoff water. The variations of water quality during rain spells were surveyed for two years (2005 and 2006) in the Jawoon Stream that is one of hot spots of intensive horticulture discharging turbid storm runoff. SS and TP showed large increase according to the increase of flow rate, whereas TN and BOD showed less fluctuations. Mean EMCs of SS and TP measured for nine rain events were as high as $207mgSS{\cdot}L^{-1}$ and $0.27mgP{\cdot}L^{-1}$, respectively. The export coefficient of SS and TP per area of cultivated field were calculated as $11,912kgSS{\cdot}yr^{-1}{\cdot}km^{-2}$ and $785kgP{\cdot}yr^{-1}{\cdot}km^{-2}$, repectively, which are significantly higher than reports of other area. It can be concluded that SS and TP in the runoffs were high enough to impose major threat to aquatic habitats, and the highland agriculture should be the main target of water quality management or habitat conservation in the study area.

• 대한기계학회논문집B
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• 제36권9호
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• pp.923-930
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• 2012

입구유동 가진이 있는 층류 후향계단 유동에서 Pr수의 변화에 따른 열전달 특성변화를 조사하기 위하여 비정상 수치해석을 수행하였다. 입구는 가진주파수와 가진진폭의 변화에 따른 교란이 주어졌고, 온도함수의 물성치가 적용되었다. 열전달 변화에 대한 다양한 특징들이 열경계층 변화에 의해서 설명되었다. 물성치가 일정한 경우와 비교하였을 때, 물성치가 온도의 함수성이 있는 경우 Pr < 1인 조건에서 열전달은 감소하였고, 반대로 Pr > 1인 조건에서 열전달은 증가하였다. 또한 가진진폭이 증가함에 따라 계단 후류 바닥면에서 열전달도 증가하였다. 그렇지만 가진주파수 변화의 경우 St < 0.2인 조건에서 열전달이 크게 증가하는 특정주파수 영역이 존재하였다. 특히, 열전달의 증가는 재부착 길이의 rms값의 변동정도와 밀접한 관련이 있음을 보여주었다.

• 한국해양학회지
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• 제21권1호
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• pp.56-71
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• 1986

京畿 植物플랑크톤의 群集生態에 영향을 미치는 環境特性을 알기 위하여 物理化學的 環境要因에 대한 분석이 1981년 5월부터 1982년 9월까지 20회에 걸쳐 채취된 시료를 토대로 행하여 졌다. 物理的 조건은 灣의 入口쪽이 河口쪽보다 안정 된 상태를 보인다. 灣안쪽은 江水의 유입으로 水溫과 鹽分의 계절변화가 크게 나타 난다. 염화수로에서 팔미도까지는 담수의 영향으로 상하로 약한 두층의 흐름이 형 성된다. 팔미도 부근과 灣바깥쪽은 하계에 수온의 층상분포가 나타나나 동계에는 수온의 수직경사가 안나타난다. 灣의 안쪽과 仁川港 부근 수역은 담수의 유입과 인 천공단에서 유입된 폐수의 영향으로 오염되고 富營養化된 상태를 보인다. 대체로 낮은 수소이온 농도, 높은 생화학적 산소요구량과 높은 영양염 분포를 보인다. 그러 나 灣의 바깥쪽낮은 BOD와 높은 산소 포화도로 外海의 영향을 많이 받는 것으로 사료된다.