• The Korean Journal of Applied Statistics
• /
• v.35 no.4
• /
• pp.543-552
• /
• 2022

When frost occurs, crops are directly damaged. When crops come into contact with low temperatures, tissues freeze, which hardens and destroys the cell membranes or chloroplasts, or dry cells to death. In July 2020, a sudden sub-zero weather and frost hit the Minas Gerais state of Brazil, the world's largest coffee producer, damaging about 30% of local coffee trees. As a result, coffee prices have risen significantly due to the damage, and farmers with severe damage can produce coffee only after three years for crops to recover, which is expected to cause long-term damage. In this paper, we tried to predict frost using frost generation data and weather observation data provided by the Korea Meteorological Administration to prevent severe frost. A model was constructed by reflecting weather factors such as wind speed, temperature, humidity, precipitation, and cloudiness. Using XGB(eXtreme Gradient Boosting), SVM(Support Vector Machine), Random Forest, and MLP(Multi Layer perceptron) models, various hyper parameters were applied as training data to select the best model for each model. Finally, the results were evaluated as accuracy(acc) and CSI(Critical Success Index) in test data. XGB was the best model compared to other models with 90.4% ac and 64.4% CSI, followed by SVM with 89.7% ac and 61.2% CSI. Random Forest and MLP showed similar performance with about 89% ac and about 60% CSI.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.11 no.2
• /
• pp.45-52
• /
• 2011

To improve fire-resistance of a high strength concrete against spalling under elevated temperature, fibers can be mixed to provide flow paths of evaporated water to the surface of concrete when heated. In this study, the experiment of a column under fire and mechanical loads is conducted and the material model for predicting temperature of reinforcement steel bar and mechanical behavior of fiber-mixed high strength concrete is suggested. The material model in previous studies is modified by incorporating physical behavior of internal concrete and thermal characteristics of concrete at the elevated temperature. Thermo-mechanical analysis of the fiber-mixed high strength concrete column is conducted using the calibrated material model. The performance of the proposed material model is confirmed by comparing thermo-mechanical analysis results with the experiment of a column under fire and mechanical loads.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.37 no.2
• /
• pp.95-101
• /
• 2024

This paper introduces an optimized design for a sensor bracket used to measure the wear amount of an automobile brake pad, based on a dynamic kriging surrogate model. During testing, the temperature of the brake pad can increase beyond 600℃, which often causes sensor malfunction. Therefore, it is essential to optimize the shape of the sensor bracket to minimize heat transfer. To reduce the computational cost of the optimization, the heat-transfer simulation is replaced by a dynamic kriging surrogate model. Dynamic kriging utilizes the best combination of correlation and basis functions and constructs an accurate surrogate model. Following optimization, the temperature of the sensor position decreases by 7.57%. The results from the surrogate model under optimum conditions are verified by a heat-transfer simulation, and the design optimization using a surrogate model is found to be effective.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.3 no.1
• /
• pp.65-71
• /
• 1999

An experimental study was carried out in order to investigate the effect of shock waves on the supersonic hydrogen-air jet flames stabilized in the Mach 2.5 model scramjet combustor. This experiment was the first reacting flow experiment interacting with shock waves. Two identical $10^{\cire}$ wedges were mounted on the diverging sidewalls of the combustor in order to produce oblique shock waves that interacted with the flame. Schlieren visualization pictures, wall static pressures, and combustion efficiency at two different air stagnation temperatures were measured and compared to corresponding flames without shock wave-flame interaction. It was observed that shock waves significantly altered the shape of supersonic jet flames, but had different effects on combustion efficiency depending on air temperatures. At the higher air stagnation temperature and higher fuel flow rates, combustion of efficiency showed a better result.

• Korean Journal of Environmental Agriculture
• /
• v.23 no.4
• /
• pp.264-271
• /
• 2004

A three-dimensional numerical mesoscale model by Pielke's estimation (University of Virginia Mesoscale Model, UVMM) was applied to investigate the effects of land characteristics including land-humidity, land-roughness and land-albedo on some micro-climatic coefficients and the air cooling capacity. The results indicated that land-characteristics exposed a significant effect on air cooling. Air cooling effects between in urban and agricultural areas were compared and the effects were much higher in agricultural area. Air cooling effects of weed species were different and when converted into economic values by diesel oil price the effects were ranged from 411 to 816 Won/plant.

• Korean journal of applied entomology
• /
• v.55 no.4
• /
• pp.445-452
• /
• 2016

Exorista japonica is one of the major natural enemies of noctuid larvae, Mythimna separata and Spodoptera litura. The examined parasitoid was obtained from host species M. separata, collected at Gimje city and identified by DNA sequences (partial cytochrome oxidase I, 16S, 18S, and 28S). For purposed of this study, laboratory reared S. litura served as the host species for the development of the E. japonica. The developmental period of E. japonica immature stages were investigated at seven constant temperatures (16, 19, 22, 25, 28, 31, $34{\pm}1^{\circ}C$, RH 20~30%). Temperature-dependent developmental rates and development completion models were developed. E. japonica was successfully developed from egg to adult in $16{\sim}31^{\circ}C$ temperature regimes. Developmental duration was the shortest at $34^{\circ}C$ (8.3 days) and the longest at $16^{\circ}C$ (23.4 days) from egg to pupa development. Pupal development duration was the shortest at $28^{\circ}C$ (7.3 days). Total immature-stage development duration decreased with increasing temperature, and was the shortest at $31^{\circ}C$ (16.3 days) and the longest at $16^{\circ}C$ (45.4 days). The lower developmental threshold was $7.8^{\circ}C$ and thermal constant required to complete total immature-stage development was 370.4 degree days. Among four non-linear temperature-dependent developmental rate models, Briere 1 model had the highest adjusted R-squared (0.96). The distribution model of development completion for total immature stage development of E. japonica was well described by all model ($r^2_{adj}=0.90$) based on the standardized development duration. These results of study would be necessary not only to develop population dynamics model but also to understand fundamental biology of E. japonica.

• Journal of Bio-Environment Control
• /
• v.26 no.1
• /
• pp.13-18
• /
• 2017

This study was conducted to investigate optimal temperature of garlic and develop bulb weight model in harvest time. Day and night temperature in chambers was set to $11/7^{\circ}C$, $14/10^{\circ}C$, $17/12^{\circ}C$, $20/15^{\circ}C$, $23/18^{\circ}C$, $28/23^{\circ}C$(16/8h). Bulb fresh and dry weight was heaviest on $20/15^{\circ}C$. In $11/7^{\circ}C$ and $14/10^{\circ}C$, leaf number and total leaf area increased slowly. But in the harvest, leaf number and total leaf area were not significant, except $28/23^{\circ}C$. Models were developed with fresh bulb weight. As a result of analyzing the model, $18{\sim}20^{\circ}C$ certified optimal mean temperature. And the growing degree day base temperature estimated $7.1^{\circ}C$, upper temperature threshold estimated $31.7^{\circ}C$. To verify the model, mean temperature on temperature gradient tunnel applied to the growth rate model. Lineal function model, quadric model, and logistic distribution model showed 79.0~95.0%, 77.2~92.3% and 85.0~95.8% accuracy, respectively. Logistic distribution model has the highest accuracy and good for explaining moderate temperature, growing degree day base temperature and upper temperature threshold.

• 한국신재생에너지학회:학술대회논문집
• /
• 2011.11a
• /
• pp.73.1-73.1
• /
• 2011

분류층 석탄가스화기에서 슬래그의 원활한 배출은 가스화 플랜트 운전 및 성능에 중대한 영향을 미치는 것으로 알려져 있다. 가스화기의 운전 온도에서 슬래그 점도가 일정수준 이상인 경우에는 가스화기 하부 슬래그 배출구 막힘 현상을, 일정 수준 이하일 경우에는 Membrane wall의 slag 두께가 얇아져 가스화기 수냉벽에 열적 악영향을 미친다. 가스화기의 안정적인 운전을 위한 석탄 선정 시, 석탄 슬래그의 용융온도 및 점도의 파악이 중요하다. 일반적으로 석탄슬래그의 용융온도는 ASTM D-1857 절차에 따른 환원분위기에서의 회융유온도(FT)측정을 통해, 점도는 고온점도측정 실험을 통해 분석하고 있다. 이런 실험적인 분석방법은 다양한 슬래그조성 및 온도 변화에 따른 영향을 살펴보기에는 많은 시간과 비용이 발생하므로 슬래그조성 및 온도 변화에 따른 용융온도 및 점도 예측이 필요하다. 본 연구에서는 200여 탄종의 회용유점 측정 결과와 FactSage에서 예측되는 슬래그 결정상 생성 및 회용유점(FT)에서의 고체분율과의 상관관계를 분석하였다. 이를 바탕으로 다양한 Ash 조성(SiO2, Al2O3, Fe2O3, CaO)에 대한 회용유점(FT)을 예측할 수 있는 프로그램을 개발하였다. 또한 50여 탄종의 슬래그 점도 측정 결과를 Facsage에서 예측되는 결정상 종류 및 Ash 조성을 기준으로 분류하였다. 결정상 종류 및 Ash 조성을 기준으로 기존 슬래그점도예측모델를 활용하여 보다 정확한 슬래그 점도 예측 프로세스를 개발하였다. 본 연구 결과는 플랜트 운전 결과 검증을 통하여 석탄 가스화 플랜트에 적합한 석탄의 선정, 혼탄 비율 및 첨가제 투입량 결정을 위해 활용될 것으로 기대된다.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05b
• /
• pp.707-712
• /
• 1996

중대사고시 원자로 압력용기내 또는 원자로 공동(cavity) 내에서의 노심용융물은 주입되는 물로 인하여 물과 접촉하는 표면이 냉각되면서 피막층(crust)이 형성된다. 이러한 피막층의 형성은 노심용융물과 냉각수 사이의 열전달 현상에 영향을 미치며 중대사고 발생시 사고 진행에 중요한 역할을 한다. 본 연구에서는 이러한 용융물의 피막층 형성의 해석모델을 수립하기 위해 전이현상과 전도와 대류를 포함하는 2차원 열전달과 상변화를 수반하는 문제를 포함하는 운동량방정식과 에너지방정식을 2차원으로 구성하였으며 에너지방정식은 엔탈피의 함수로 나타내었다. 그리고 이러한 2차원 지배방정식을 해석하기 위해 유한차분법 및 SIMPIER 알고리즘을 이용하였다. 비교대상으로는 한국원자력연구소에서 수행한 냉각수의 비등과 기체주입 효과가 고려되지 않은 실험을 대상으로 하였다. 계산결과 용융물의 피막층은 파동(wave) 형태로 형성되었으며 일정시간이 경과하면 변화가 없는 안정한 상태가 되었다. 용융물 내에서의 온도분포는 액체상태일 경우에는 하부가열면과 상변화가 일어나는 경계면부근을 제외하고는 거의 일정한 온도분포를 나타내고 있으며 용융물이 고화된 피막층에서는 급격한 온도변화를 보여주고 있다.

• Journal of Bio-Environment Control
• /
• v.7 no.4
• /
• pp.311-323
• /
• 1998

This study was conducted to analyze the temperature characteristics under tunnel type greenhouse to cultivate watermelon in Sungju region. Air temperature of tunnel type greenhouse was descending rapidly after sunset, and the time required the air temperature inside greenhouse nearly reached the outside air temperature was about 2.5 hours. The maximum air temperature in tunnel type greenhouse, in case of high air temperature day, was exceeding 4$0^{\circ}C$ during day time. Air temperature inside greenhouse during night time could sustain about 2~3$^{\circ}C$ higher than the outside air temperature. But it was necessary to supply supplemental heat when the air temperature was below optimum growth temperature. Soil temperature in the depth of 20cm under soil surface could maintain higher than 2$0^{\circ}C$ and the variation range in a day was 3~5$^{\circ}C$, and the soil temperature descending due to irrigation was about 5~6$^{\circ}C$.