• Wind and Structures
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• 제20권2호
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• pp.213-236
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• 2015

For high-speed railways (HSR) in wind prone regions, wind barriers are often installed on bridges to ensure the running safety of trains. This paper analyzes the effect of wind barriers on the running safety of a high-speed train to cross winds when it passes on a bridge. Two simply-supported (S-S) PC bridges in China, one with 32 m box beams and the other with 16 m trough beams, are selected to perform the dynamic analyses. The bridges are modeled by 3-D finite elements and each vehicle in a train by a multi-rigid-body system connected with suspension springs and dashpots. The wind excitations on the train vehicles and the bridges are numerically simulated, using the static tri-component coefficients obtained from a wind tunnel test, taking into account the effects of wind barriers, train speed and the spatial correlation with wind forces on the deck. The whole histories of a train passing over the two bridges under strong cross winds are simulated and compared, considering variations of wind velocities, train speeds and without or with wind barriers. The threshold curves of wind velocity for train running safety on the two bridges are compared, from which the windbreak effect of the wind barrier are evaluated, based on which a beam structure with better performance is recommended.

• 한국농공학회논문집
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• 제63권5호
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• pp.63-71
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• 2021

Windbreak forests, which have a windproof effect against strong winds, are known to be effective in reducing the spread of odors and dust emitted from livestock farms. The effect of reducing the spread of odors and dust can be estimated through numerical models such as computational fluid dynamics, which require aerodynamic coefficients of the windbreaks for accurate prediction of their performance. In this study, we aimed to evaluate the aerodynamic coefficients, Co, C₁, C₂, and α, of two windbreaks, Thuja occidentalis and a mesh net, through wind tunnel experiments. The aerodynamic coefficients were derived by the relation between the incoming wind speed and the pressure loss due to the windbreaks which was measured by differential pressure sensors. In order to estimate the change in the aerodynamic coefficient concerning various leaf density, the experiments were conducted repeatedly by removing the leaves gradually in various stages. The results showed that the power law regression model more suitable for coefficient evaluation compared to the Darcy-Forchheimer model.

• 한국환경과학회지
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• 제7권1호
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• pp.20-26
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• 1998

In establishing artificial fences in a certain locality, type of its area or wind blown against them from the front side is primarily considered. Researchers on fences also concentrate on upstream, wand blown against them from the front side In 90$^{\circ}$ angle. In this research, simulations were carried out on the direction of wind changed by each season, and regardless of seasonal wind, on the fences effect of wind direction on fences, throu호 an atmospheric boondary layer wind tunnel. When I compared the velocity distribution of upstream against the fences in 90$^{\circ}$ angle with that of 75$^{\circ}$, 60$^{\circ}$, and 45$^{\circ}$ respectively, the velocity distribution at downstream of the latter cases generally surpassed that of the former one.

• 한국환경과학회지
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• 제4권1호
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• pp.29-40
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• 1995

Transport rate of windblown dusts such as soil, sand, snow is proportionate to $U*_^3 and U_*$, friction velocity, approximately to flow velocity of ink Therefore, through measurement and the flow velocity of wind, it turned out that, considering different velocity distributions caused by downstream distance and porosity percent, windbreaks with appropriate porosity rate to the Protection area should be chosen for the optimal fence effect. In the economic respects better are fences with gap of 20%~30%. Among the windbreaks to have the optimal fence effect.

• Wind and Structures
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• 제18권1호
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• pp.69-82
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• 2014

Flow around a small white fir tree was investigated with varying the length of the bottom trunk (hereafter referred to as bottom gap). The velocity fields around the tree, which was placed in a closed-type wind tunnel test section, were quantitatively measured using particle image velocimetry (PIV) technique. Three different flow regions are observed behind the tree due to the bottom gap effect. Each flow region exhibits a different flow structure as a function of the bottom gap ratio. Depending on the gap ratio, the aerodynamic porosity of the tree changes and the different turbulence structure is induced. As the gap ratio increases, the maximum turbulence intensity is increased as well. However, the location of the local maximum turbulence intensity is nearly invariant. These changes in the flow and turbulence structures around a tree due to the bottom gap variation significantly affect the shelter effect of the tree. The wind-speed reduction is increased and the height of the maximum wind-speed reduction is decreased, as the gap ratio decreases.

• 생물환경조절학회지
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• 제29권4호
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• pp.448-455
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• 2020

본 연구에서는 서리의 피해 저감을 위하여 과수 무봉지 재배를 목적으로 사용하고 있는 그물망을 이용하고자, 서리의 양을 관측하는 장치를 대조구와 시험구에 설치하여 그 비교를 통해 서리 저감 효과를 구명하였다. 시험 결과 실제 서리가 관측된 날을 기준으로 시험구에서 37%에서 59%까지 저감 효과를 확인할 수 있었다. 또한 서리의 양을 자동으로 관측하는 장치를 개발하고 풍동실험을 통해 서리 측정 장치의 방풍함 높이를 30 cm로 결정하였다. 이러한 연구 결과는 그물망 설치함으로써 과수 개화기에 서리 피해를 저감할 수 있을 것으로 판단되며, 그물망의 농업적 이용에 대한 기초자료로 활용될 수 있을 것으로 기대된다.

• The Plant Pathology Journal
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• 제33권5호
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• pp.441-449
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• 2017

Citrus canker is an important bacterial disease of citrus in several regions of the world. Strains of Xanthomonas citri type-A (Xc-A) group are the primary pathogen where citrus canker occurs. After Xc-A entered the Northeast of Argentina in 1974, the disease spread rapidly from 1977 to 1980 and then slowed down and remained moving at slow pace until 1990 when it became endemic. Citrus canker was detected in Northwest Argentina in 2002. This paper presents the main steps in the fight of the disease and the management strategies that have been used to control citrus canker at this time. We think the process might be usefull to other countries with the same situation. Results from more than 40 years of research in Northeast (NE) Argentina indicate that we are at the limit of favorable environment for the disease. The severity of citrus canker is greatly affected by the environment and El $Ni{\tilde{n}}o$ Southern Oscillation (ENSO) phenomenon which causes cyclic fluctuations on the disease intensity in the NE region. Weather-based logistic regression models adjusted to quantify disease levels in field conditions showed that the environmental effect was strongly modulated by the distance from a windbreak. Production of healthy fruits in citrus canker endemic areas is possible knowing the dynamics of the disease. A voluntary Integrated Plan to Reduce the Risk of Canker has been in place since 1994 and it allows growers to export unsymptomatic, uninfested fresh fruit to countries which are free of the disease and require healthy, pathogen free fruits. The experience from Argentina can be replicated in other countries after appropriate trials.

• 대기
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• 제17권4호
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• pp.315-326
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• 2007

The effects of windbreaks on the reduction of suspended particles are investigated using a computational fluid dynamics (CFD) model with the ${\kappa}-{\varepsilon}$ turbulence closure scheme based on the renormalization group (RNG) theory. In the control experiment, the recirculation zones behind the storage piles are generated and, as a whole, relatively monotonous flow patterns appear. When the windbreaks with the 0% porosity are constructed, the recirculation zones are generated by the windbreaks and very complicated flow patterns appear due to the interference between the windbreaks and storage piles. The porosity of the windbreaks suppresses the generation of the recirculation zone and decreases the wind velocity in the windbreaks as well as that outside the windbreaks. As the emission of suspended particles from the storage piles are closely related with the friction velocity at the surfaces of the storage piles, variation of the friction velocity and total amount of the emission of the suspended particles with the height and porosity of the windbreaks are investigated. The results show that higher and more porous windbreaks emit less suspended particles and that the reduction effect of the porosity is still more effective than that of the height. In the case of the windbreak with 30 m height and 50% porosity, friction velocities above the storage piles are smaller than the critical friction velocity above which particles would be suspended. As a result, total amount of suspended particles are much fewer than those in other cases.

• 한국가스학회지
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• 제23권4호
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• pp.28-39
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• 2019

OGI(Optical Gas Image) 기술에서 주요 가스의 이미지 특성연구는 누출가스의 종류 파악 및 배출량 추정의 기초자료가 될 수 있다. 본 연구의 목적은 산업에서 중요한 methane과 propane 두 탄화수소의 분출가스 이미지의 차이를 관찰하기 위함이다. 적외선을 투과하는 성질을 지닌 석영을 끼운 바람차단막을 제작하여 methane과 propane을 동시에 누출하게 하여 적외선 OGI 카메라로 촬영하고, 그 영상을 분석하였다. 석영차단막이를 활용하여 바람의 영향을 최소화하여 안정된 영상을 확보하였다. 누출 기준값을 1 L/min로 하여 두 탄화수소의 영상을 분석한 결과 OGI 카메라로 쉽게 식별 가능한 거리가 methane의 경우 6 m, propane의 경우 9 m로 나타났다. 적외선 카메라와 누출지점의 거리 1~10 m까지에서 propane의 경우가 methane의 경우 보다 gas plume의 크기가 컸으며 선명하였다. 영상 이미지의 점의 수로 비교하면 propane이 methane보다 평균 3.8배 많았다.

• 한국작물학회지
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• 제32권2호
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• pp.163-172
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• 1987

동해안 냉조풍지대의 풍해상습지에 대한 방풍망설치방법과 설치시기에 의한 풍해 경감 효과를 구명하고자 1983년부터 1985년까지 3개년간 경북영덕지방에서 실시한 결과를 요약하면 다음과 같다. 1. 동해안 냉조풍지대의 1954년부터 1985년까지 32년 동안 강풍 발생빈도는 8월 10일부터 9월 10일 사이에 높아 이 지역의 수도 안전출수한계기는 8월 10일 이전 안전하다고 생각된다. 2. 이 지대에 주로 풍해를 유발시키는 바람은 태백산맥을 넘어오면서 휀(Fohn) 현상에 의한 고온건조한 편서풍과 해양에서 내륙으로 부는 한냉과습한 냉조풍이었으며 도작기간중 발생빈도가 각각 25 %였다. 3. 방풍망 설치에 따른 1차 효과는 감풍효과였으며 방풍망이 설치된 지점으로부터 1m에서는 23.9%, 10m에서는 35.8%, 20m에서는 26.9% 감풍효과가 있었으며 그 효과는 설치된 방풍망 높이의 10배 거리까지 있었다. 4. 방풍망 설치에 따른 2차 효과는 기온, 지온, 수온의 상승효과였으며 무방풍구에 비해 기온은 최고 0.7$^{\circ}C$, 최저 0.4$^{\circ}C$, 평균 0.1$^{\circ}C$ 상승되었으며 수온은 최고 0.3$^{\circ}C$, 최저 0.3$^{\circ}C$ 상승되었고 지온도 0.3$^{\circ}C$ 상승효과가 있었다. 5. 방풍망 설치에 따른 3차 효과는 생육촉진 감수경감, 품질향상의 효과가 있었으며 무방풍구에 비해 출수기가 2~5일 단축되었고 간장, 주당수수, 수당영화수, 임실율의 증가로 20~28% 증수효과가 있었으며 완전중의 비율도 높았다. 6. 벼알의 변색정도가 심할수록 등숙율과 정조 1,000 입중이 현저하게 떨어졌으며 그 감소정도와 부의 상관관계가 있었다. 7. 방풍망 설치방법별로는 한냉과습한 냉조풍과 고온건조한 편서풍을 모두 방풍할 수 있는 종합방풍시설이 가장 효과가 컸으며 방풍망 설치시기별로는 수잉기에 설치하는 것이 가장 효과가 컸다.