• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.263-264
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• 2006

In this study, the threshold wind speed that causes physical damage on Kiwi fruit plant was investigated through wind tunnel experiments. Total 30 samples of Kiwi fruit branches were tested. On average, the wind speeds for tearing leaves and breaking side branch from the main branch were about 20m/s and 21.7m/s, respectively. For the cases of broken branches, the average length and diameter of the branches were 587.5mm and 7.2mm, respectively. The discoloration and dehydration of Kiwi plant were also observed by photographing leaves and branches after 24 hour later of the wind damage. In addition, the shelter effect of porous wind fences which have been used at agricultural districts was examined with varying several parameters.

• 한국군사과학기술학회지
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• 제18권4호
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• pp.469-477
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• 2015

In this study, the characteristics of main wind direction, vertical temperature and wind speed profile near the Moseulpo airfield for HALE UAV(High Altitude Long Endurance Unmaned Aerial Vehicle) is investigated. The results are summarized as follows, main wind direction is governed by air mass according to season and local wind such as land-sea breeze. The directions of landing and take-off of HALE UAV will be selected as the south-east direction in June ~ August, north-west direction in October ~ March, and south-east direction at daytime in April ~ May, September. Annual variation of temperature at 100 hPa showed that temperature in summer season is lower than winter season. On the other hands, wind speed at 250 hPa in winter season is higher than summer season. The threshold values of temperature and wind speed for HALE UAV flight are $-75^{\circ}C$ and $90ms^{-1}$, which were determined by 5 % frequency value($1.96{\sigma}$), respectively.

• Wind and Structures
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• 제35권4호
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• pp.255-268
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• 2022

Light-weight or low-damped structures may encounter the unsteady galloping instability that occurs at low reduced wind speeds, where the classical quasi-steady assumption is invalid. Although this unsteady phenomenon has been widely studied for rectangular cross sections with one side perpendicular to the incidence flow, the effect of the mean wind angle of attack has not been paid enough attention yet. With four sectional models of different side ratios and geometric shapes, the presented research focuses on the effect of the wind angle of attack on unsteady galloping instability. In static tests, comparatively strong vortex shedding force was noticed in the middle of the range of flow incidence where the lift coefficient shows a negative slope. In aeroelastic tests with a low Scruton number, the typical unsteady galloping, which is due to an interaction with vortex-induced vibration and results in unrestricted oscillation initiating at the Kármán vortex resonance wind speed, was observed for the wind angles of attack that characterize relatively strong vortex shedding force. In contrast, for the wind angles of attack with relatively weak shedding force, an "atypical" unsteady galloping was found to occur at a reduced wind speed clearly higher than the Kármán-vortex resonance one. These observations are valid for all four wind tunnel models. One of the wind tunnel models (with a bridge deck cross section) was also tested in a turbulent flow with an intensity about 9%, showing only the atypical unsteady galloping. However, the wind angle of attack with the comparatively strong vortex shedding force remains the most unfavorable one with respect to the instability threshold in low Scruton number conditions.

• 대한원격탐사학회지
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• 제24권1호
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• pp.1-16
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• 2008

Steam and advection fogs are frequently observed in the Yellow Sea from March to July except for May. This study uses remote sensing (RS) data for the monitoring of sea fog. Meteorological data obtained from the Ieodo Ocean Research Station provided a valuable information for the occurrence of steam and advection fogs as a ground truth. The RS data used in this study were GOES-9, MTSAT-1R images and QuikSCAT wind data. A dual channel difference (DCD) approach using IR and shortwave IR channel of GOES-9 and MTSAT-1R satellites was applied to detect sea fog. The results showed that DCD, texture-related measurement and the weak wind condition are required to separate the sea fog from the low cloud. The QuikSCAT wind data was used to provide the wind speed criteria for a fog event. The laplacian computation was designed for a measurement of the homogeneity. A new combined method, which includes DCD, QuikSCAT wind speed and laplacian computation, was applied to the twelve cases with GOES-9 and MTSAT-1R. The threshold values for DCD, QuikSCAT wind speed and laplacian are -2.0 K, $8m\;s^{-1}$ and 0.1, respectively. The validation results showed that the new combined method slightly improves the detection of sea fog compared to DCD method: improvements of the new combined method are $5{\sim}6%$ increases in the Heidke skill score, 10% decreases in the probability of false detection, and $30{\sim}40%$ increases in the odd ratio.

• 대기
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• 제24권3호
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• pp.445-456
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• 2014

A real-time quality control system for meteorological data (air temperature, air pressure, relative humidity, wind speed, wind direction, and precipitation) measured by an integrated meteorological sensor has been developed based on comparison of quality control procedures for meteorological data that were developed by the World Meteorological Organization and the Korea Meteorological Administration (KMA), using time series and statistical analysis of a 12-year meteorological data set observed from 2000 to 2011 at the Incheon site in Korea. The quality control system includes missing value, physical limit, step, internal consistency, persistence, and climate range tests. Flags indicating good, doubtful, erroneous, not checked, or missing values were added to the raw data after the quality control procedure. The climate range test was applied to the monthly data for air temperature and pressure, and its threshold values were modified from ${\pm}2{\sigma}$ and ${\pm}3{\sigma}$ to ${\pm}3{\sigma}$ and ${\pm}6{\sigma}$, respectively, in order to consider extreme phenomena such as heat waves and typhoons. In addition, the threshold values of the step test for air temperature, air pressure, relative humidity, and wind speed were modified to $0.7^{\circ}C$, 0.4 hPa, 5.9%, and $4.6m\;s^{-1}$, respectively, through standard deviation analysis of step difference according to their averaging period. The modified quality control system was applied to the meteorological data observed by the Weather Information Service Engine in March 2014 and exhibited improved performance compared to the KMA procedures.

• 대한원격탐사학회지
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• 제29권6호
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• pp.645-655
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• 2013

As one of segmentation techniques for Synthetic Aperture Radar (SAR) image with oil spill, we applied a bimodal histogram method to discriminate oil pixels from non-oil pixels. The threshold of each moving window was objectively determined using the two peaks in the histogram distribution of backscattering coefficients from ENVISAT ASAR image. To reduce the effect of wind speed on oil spill detection, we selected ASAR image which satisfied a limit of wind speeds for successful detection. Overall, a commonly used adaptive threshold method has been applied with a subjectively-determined single threshold. In contrast, the bimodal histogram method utilized herein produces a variety of thresholds objectively for each moving window by considering the characteristics of statistical distribution of backscattering coefficients. Comparison between the two methods revealed that the bimodal histogram method exhibited no significant difference in terms of performance when compared to the adaptive threshold method, except for around the edges of dark oil spots. Thus, we anticipate that the objective method based on the bimodality of oil slicks may also be applicable to the detection of oil spills from other SAR imagery.

• Wind and Structures
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• 제16권4호
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• pp.355-372
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• 2013

The Gringorten estimator has been extensively used in extreme value analysis of wind speed records to obtain unbiased estimates of design wind speeds. This paper reviews the derivation of the Gringorten estimator for the mean plotting position of extremes drawn from parents of the exponential type and demonstrates how it eliminates most of the bias caused by the classical Weibull estimator. It is shown that the coefficients in the Gringorten estimator are the asymptotic values for infinite sample sizes, whereas the estimator is most often used for small sample sizes. The principles used by Gringorten are used to derive a new Consistent Linear Unbiased Estimator (CLUE) for the mean plotting positions for the Fisher Tippett Type 1, Exponential and Weibull distributions and for the associated standard deviations. Analytical and Bootstrap methods are used to calibrate the bias error in each of the estimators and to show that the CLUE are accurate to better than 1%.

• 한국해안·해양공학회논문집
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• 제34권6호
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• pp.303-314
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• 2022

해양 물리 환경 인자의 지속시간 분석은 작업시간, 설계와 같은 해안공학적 관점에서 요구되는 분석으로 해역 이용에 필수로 선행되어야하는 기초 분석이다. 본 연구에서는 기상청 해양기상관측부이 중 우리나라 서남해안 4개 관측 지점(덕적도, 외연도, 거문도, 거제도)의 풍속 및 유의파고 자료의 지속시간 분석을 수행하였다. 기준풍속은 1~15 m/s, 기준유의파고는 0.25~3.0 m의 범위를 설정하고 관측자료가 이를 넘어서 지속되는 시간을 산정했다. 분석결과, 풍속과 유의파고의 지속시간은 기준값이 높아질수록 급격히 감소했으며, 최대 기준 조건에서 지속시간의 중간값은 풍속이 최대 5시간, 유의파고는 최대 8시간으로 계산되었다. 1% 미만의 확률로 발생하는 지속시간은 기준풍속이 15 m/s일 때 최대 52시간, 기준유의파고가 3m일 때 최대 56시간으로 나타났다. 향후 우리나라 전 해역을 대상으로 해양기상 자료의 지속시간 분석을 수행할 수 있으며, 다양한 공학적 활용이 기대된다.

• 한국농림기상학회지
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• 제14권4호
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• pp.277-282
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• 2012

냉기호 지대 안에서도 일정 수준의 바람이 부는 장소에서는 일 최저기온이 기존 공간기후모형에 의해 예측된 만큼 떨어지지 않음이 관찰되었다. 경남 하동군 악양 집수역 출구부근의 실측자료를 토대로 냉기호가 형성된 25일에 대하여 기존 방법에 의한 일 최저기온 예측 시 발생하는 추정오차를 그 때 관측된 풍속과 비교한 결과 바람이 강해질수록 추정오차가 커지는 경향이 뚜렷해서 풍속이 2m/s에 이르면 냉기호 효과가 완전히 소멸되는 것으로 나타났다. 풍속과 추정오차 간 관계는 Y=2X+0.4 ($R^2$=0.76)로 표현되며 이 식에서 Y는 추정오차($^{\circ}C$), X는 풍속(m/s)이다. 이 식을 기존 일 최저기온 추정모형의 냉기집적효과에 결합하여 악양 집수역 냉기호 수몰지역에 위치한 3곳의 일 최저기온 추정에 이용하였다. 이때 입력 풍속은 바람장 모형 구동에 의한 모의풍속이었다. 추정된 일 최저기온은 오차의 평균평방근(RMSE)이 기존 모형의 1.72에서 1.20으로 줄어들고, 평균오차(ME)로 표현한 편기성(bias)도 -1.33에서 -0.37로 개선되었다.

• 전기학회논문지
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• 제57권12호
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• pp.2173-2178
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• 2008

A doubly-fed induction generator(DFIG) system has been widely used in the modem wind turbines due to variable-speed operation, high efficiency and small converter size. It is well known that an inter-turn fault of a generator is very difficult to be detected. The DFIG system uses a wound rotor induction machine so that the magnetizing current of the generator can be fed from both the stator and the rotor. This paper proposes a protection algorithm for a DFIG using the d-q equivalent circuit in the time domain. In the case of a DFIG, the voltages and currents of the rotor side as well as the voltages and currents of the stator are available. The proposed algorithm estimates the instantaneous(i.e., converted into the stationary frame) induced voltages from the rotor and the stator sides. If the difference between the two estimated induced voltages exceeds the threshold, the proposed algorithm detects the inter-turn fault. The algorithm can detect a inter-turn fault of a winding. The performance of the proposed algorithm is validated using a PSCAD/EMTDC simulator under inter-turn fault conditions and normal operating conditions such as an external fault and the change of the wind speed.