• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.188-193
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• 2012

Recently, the nanofluid which is stably dispersing or suspending of nanoparticles in the conventional heat transfer fluids (HTF) such as water and ethylene glycol has attracted significant interests as a solar thermal energy absorbing medium because they have excellent absorption and thermophysical properties compared to the typical HTF. In the present study, the efficiency of nanofluid-based flat-plate solar collector is analytically evaluated using the theoretical model of energy balance equation. The theoretical model considers the incoming solar radiation as a volumetric heat generation and the water-based single wall carbon nanohorn(SWCNH) nanofluid is used as a solar energy absorbing medium. Finally, the efficiency of nanofluid-based collector is calculated according to the volume fraction of SWCNH using the analytical solution.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.688-691
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• 2004

We have studied the possibility of global noise reduction by the sound power control through selection of distribution and impedance of absorptive materials. It is necessary to investigate the relation between the global sound energy in the field and the total sound power radiated by sources. In the previous work (1,2), the authors presented a useful design method to change boundary condition that can be useful to reduce noise in acoustically small enclosures. The possibility of total acoustic potential energy reduction by acoustic source power control is examined in an acoustically small cavity. Using acoustic energy balance equation, the relation between global noise control performance and absorptive material's arrangement/impedance is deduced. Numerical simulation is performed to interpret its physical meaning in terms of absorbent's distribution and impedance.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2001년도 추계학술대회 논문집
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• pp.47-48
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• 2001

It is well known that atmospheric aerosols play an important role in the radiation balance of the earth and meteorological processes as well as in atmospheric chemistry. Aerosols may origin from both natural and/or anthropogenic sources. Thus, the chemical composition of aerosols can vary considerably. For example, the chemical composition of marine aerosol has been the subject of a considerable number of investigations, including the evaluation of long-range transport of anthropogenic constituents on the chemistry of the remote marine boundary layer. (omitted)

• 대한기계학회논문집
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• 제11권3호
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• pp.409-424
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• 1987

본 연구에서는 유한차분법보다는 정확도가 약간 떨어지지만 공기조화 분야의 계산에 적합하고 계산시간이 적게 소요되는 응답계수법을 사용하여 온수온돌방계의 비 정상 열전달을 해석하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2017년도 학술발표회
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• pp.183-183
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• 2017

Pan evaporation (Epan) is an important indicator of water and energy balance. Despite global warming, decreasing annual Epan has been reported across different continents over last decades, which is claimed as pan evaporation paradox. However, such trend is not necessarily found in seasonal data because the level of contributions on Epan vary among meteorological components. This study investigates long-term trend in seasonal pan evaporation from 1908 to 2016 across South Korea. Meteorological variables including air temperature (Tair), wind speed (U), vapor pressure deficit (VPD), and solar radiation (Rs) are selected to quantify the effects of individual contributing factor to Epan. We found overall decreasing trend in Epan, which agrees with earlier studies. However, mixed tendencies between seasons due to variation of dominant factor contributing Epan were found. We also evaluated the reference evapotranspiration based on Penman-Monteith method and compared this with Epan to better understand the physics behind the evaporation paradox.

• 한국초전도ㆍ저온공학회논문지
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• 제10권2호
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• pp.38-41
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• 2008

The relation between surface emissivity and temperature distribution is experimentally and analytically investigated for a conduction-cooled metal plate in vacuum. Experimental set-up consists of a rectangular metal plate placed vertically in a cryostat and thermally anchored to the coldhead of a GM cryocooler at the top. Temperature is measured at a number of locations over the plate with platinum resistors mounted on the plate. A parallel analysis on the balance of heat conduction through the plate and thermal radiation on its surface is performed to numerically calculate the temperature distribution having the same boundary conditions as experiment. By comparing the two results, an average emissivity of the plate is roughly estimated for different metal plates and different surface conditions. The estimated emissivity in present study is less than the listed values for highly polished stainless steel, and meets a fairly good agreement for oxidized copper surface.

• 한국농림기상학회지
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• 제21권2호
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• pp.85-96
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• 2019

일사량은 자연 생태계와 농업 생태계에서 에너지 수지와 물 순환을 추정하는데 중요한 변수이다. 일별 일사량을 추정하기 위해 심층 신경망(DNN) 모델이 개발되었다. 일조시간 등의 변수보다 기상 관측소에서의 가용성이 더 높은 온도와 강수량이 심층 신경망 모델의 입력 자료로 사용되었다. five-fold crossvalidation 을 사용하여 심층 신경망을 훈련시키고 검증하였다. 국내 15 개의 기상 관측소에서 30 년 이상 장기간의 기상 자료가 수집되었다. Cross-validation을 통해 얻어진 심층 신경망 모델은 수원 지역 기상 관측소의 일별 일사량 추정치에 대해 비교적 작은 RMSE($3.75MJ\;m^{-2}\;d^{-1}$) 값을 가졌다. 심층 신경망 모델은 수원 지역 기상 관측소의 일사량의 변위의 약 68%를 설명했다. 1985 년과 1998 년의 일사량 관측값은 일조시간에 비해 상당히 낮은 값이 관측되었다. 이는 후속 연구에서 일사량 관측 데이터의 품질 평가가 필요할 것임을 시사했다. 해당 연도의 데이터를 분석에서 제외했을 때, 심층 신경망 모델의 추정값은 통계적 수치가 약간 높게 나타났다. 예를 들어, $R^2$ 와 RMSE 의 값은 각각 0.72 와 $3.55MJ\;m^{-2}\;d^{-1}$ 이었다. 심층 신경망 모델은 기온과 강수량을 통해 일사량을 추정하는데 유용하며, 이는 미래 기후 시나리오 자료에 대해서 활용할 수 있을 것이다. 따라서, 공간에 대한 제약이 완화된 심층 신경망 모델은 작물 모델의 입력 자료로 일사량이 필요한 작물 생산성에 대한 기후 변화 영향 평가에 유용하게 활용될 수 있을 것이다.

• 한국작물학회지
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• 제27권4호
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• pp.296-313
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• 1982

At a time when world population and food supply are in a delicate balance, it is essential that we look at factors to improve this balance. We can alter the environment to better fit the plant's needs, or we can alter the plant to better fit the environment. Improved technology has allowed us to increase the yield level. For moderately detrimental weather events technology has generally decreased the yield variation, yet for major weather disasters the variation has increased. We have raised the upper level, but zero is still the bottom level. As we concentrate the production of particular crops into limited areas where the environment is closest to optimum, we may be increasing the risk of a major weather related disaster. We need to evaluate the degree of variability of different crops, and how weather and technology can interact to affect it. The natural limits of crop production are imposed by important ecological factors. Production is a function of the climate, the soil, and the crop and all activities related to them. In looking at the environment of a crop we must recognize these are individuals, populations and ecosystems. Under intensive agriculture we try to limit the competition to one desired species. The environment is made up of a complex of factors; radiation, moisture, temperature and wind, among others. Plant response to the environment is due to the interaction of all of these factors, yet in attempting to understand them we often examine each factor individually. Variation in crop yields is primarily a function of limiting environmental parameters. Various weather parameters will be discussed, with emphasis placed on how they impact on crop production. Although solar radiation is a driving force in crop production, it often shows little relationship to yield variation. Water may enter into crop production as both a limiting and excessive factor. The effects of moisture deficiency have received much more attention than moisture excess. In many areas of the world, a very significant portion of yield variation is due to variation in the moisture factor. Temperature imposes limits on where crops can be grown, and the type of crop that can be grown in an area. High temperature effects are often combined with deficient moisture effects. Cool temperatures determine the limits in which crops can be grown. Growing degree units, or heat accumulations, have often been used as a means of explaining many temperature effects. Methods for explaining chilling effects are more limited.

• 한국산림과학회지
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• 제88권1호
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• pp.38-46
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• 1999

독일 중부(Solling Hills)의 가문비림 임관의 구조적인 수분증산 통도특성은 LE와 H의 유동량으로 측정되고, 1996년 6월중 재배열된 Penman-Monteith 식을 이용하여 SVAT 모형을 설계하여 도출하였다. 또한 SLODSVAT 모형을 통한 전체 임관 내 각 침엽의 연속적인 수분통도성을 평가하여 임관기공의 통도성을 비교하였다. 이와 같은 결과에서 나온 임관 표면 통도성과 유동량을 설계하고, SLODSVAT 모형에 의해 설계된 기공 통도성 사이에서 중요한 차이점을 알 수 있었다. 이 차이점은 산림 임관의 범위내에 빗물리적인 요소에 의해 영향을 받았음을 알 수 있으며, 일반적으로 임관 표변의 통도성은 전체 측정 기간 동안 임관 기공 전도력보다 크게 나타났다. 또한 산림의 전체 증발산량에 대한 하층부의 공헌도는 작았고, 임관의 복사에너지 균형에 의존하지는 않는 것으로 나타났다. 하층부 증발산량의 기각은 독일 가문비림에 대한 임관 표면 전도력의 과대 평가로서 나타난 결과이다.

• 한국항공우주학회지
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• 제40권2호
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• pp.129-138
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• 2012

에너지 균형조건을 고려하여 중형 태양광 추진 고고도 장기체공 무인기의 다분야 통합 최적설계를 수행하였다. 무인기의 공력 모델로 Vortex Lattice Method (VLM)를 사용하였으며 Cruz가 제안한 중량분석 모델로서 비행체 중량을 추정하였다. 비행체의 세로 정안정성 확보를 위하여 꼬리날개의 부피비를 고정하고 정안정성을 확보할 수 있도록 꼬리날개의 위치를 결정하였다. 태양전지, 축전지, 비행 고도 등 사용가능한 에너지와, 비행체의 필요에너지를 비교하여 24시간 지속비행 가능성을 결정하였다. 태양 입사 에너지는 북위 $36^{\circ}$의 여름을 기준으로 하였으며, 주간비행 중 태양에너지를 이용한 상승비행으로 확보한 위치에너지를 이용하여 야간 비행에 필요한 에너지를 보충하였다. 이를 바탕으로, 무인기의 주요 치수, 중량 분포 최적 설계와 장기체공을 실현할 수 있는 비행전략을 제시하였다.