• 한국대기환경학회지
• /
• 제14권5호
• /
• pp.397-410
• /
• 1998

Tracer experiments were performed 4 times in December 1992 on the relatively flat terrain and nearby building area adjacent to the Taedok Science Town in Korea. Each experiment was continued for relatively short period of 1 or 2 hours with intermittent release of SF6 up to 2.07g/s at 10m height. Movement of tracer plume was tracked by a continuous tracer analyzer installed on an air monitoring van. Simulation with INPUFF was carried out to analyze and predict experiments. Measured profiles of tracer plume were narrow and sharp while predicted profiles by INPUFF were broad and slowly varied. Tracer plumes were detected at a short distance of 0.5 to 2.2 km mainly due to intermittent release and high value of lower detectable limit. Various experimental conditions were tested by INPUFF simulation in order to find desirable conditions. Higher wind speed and less variable wind direction could yield longer distance of plume tracking only when the lower detectable limit was sufficiently low. Distance of plume tracking was long and did not much depend on the lower detectable limit in stable atmospheric conditions.

• 수산해양기술연구
• /
• 제33권4호
• /
• pp.360-369
• /
• 1997

We calculated the residual current forced by buoyancy, wind stress, and tidal stress in the Chinhae Bay using a three-dimensional diagnostic model. The calculated current was also compared with the observation. The flow directs outward from the central area of the Bay in the upper layer, and also forms eddy-shape stucture in the upper and middle layers. The flow of bottom layer shows an opposite pattern compared to those of top and middle layers. The maximum speed was 6.05 em/see (September) and 3.49 cm/sec (November) in the upper layer, and 4.39 cm/sec on both month in the middle layer. The Kinetic energy of November (8.39xlO' W) was larger than that of September (1.24xlO 'W), mainly resulting from larger buoyancy effect in September. In spite of the roughness of the grid size(1 km) and wind date, the calculated flow shows eorrelation(r=0.71) with the observation. We expect that the correlation be increased by increased by adopting the fine grid and the variable coefficients of diffusion and viscosity.

• Journal of Power Electronics
• /
• 제9권4호
• /
• pp.612-622
• /
• 2009

The short circuit ratio (SCR) of a given grid is able to show the stability of the system in the case of unwanted elements, such as wind turbulence. This paper presents the simulation of a model of the doubly fed induction generator in the simulation software PSCAD/EMTDC. This model has been used to study flicker during continuous operation and the effect of SCR and grid impedance angle on flicker emission. Simulation results show that compensation of the stator reactive power is an effective method to considerably reduce the flicker levels, irrespective of the grid conditions.

• 한국농림기상학회지
• /
• 제21권4호
• /
• pp.221-228
• /
• 2019

일출 이후부터 일몰 전까지 매시 간격으로 태양 일사로 인한 지표부근 기온상승 효과와 풍속이 미치는 영향을 추정하고자, 동향사면과 서향사면 간 대표 기상관측지점에 대하여 매시 일사량 편차에 따른 관측기온의 편차(기온변화량)을 풍속별로 구분하여 도출하였다. 일사편차 1 MJ/㎡ 당 기온변화량으로 일사효과를 표현하여 풍속과의 경험식을 구하고, 이것을 토대로 2018년 1월부터 2018년 12월까지 농산촌의 복잡지형에 위치한 기상관측지점 25곳에 대해 주간(06:00~19:00) 매시 기온을 추정한 후 검증하였다. 그 결과 추정값과 관측값의 평균 ME는 -0.98~0.67℃, 평균 RMSE는 0.95~2.04℃ 나타났다. 오후 3시 기준의 한낮기온은 선행연구에서 제시한 기존 모형과 추정신뢰도를 대조하였는데, 기존 모형의 추정오차(ME -0.91℃, RMSE 1.47℃)를 ME -0.45℃, RMSE 1.22℃까지 개선시킬 수 있었다.

• Journal of Power Electronics
• /
• 제14권2호
• /
• pp.271-281
• /
• 2014

Fluctuating wind conditions necessitate the use of a variable speed wind turbine (VSWT) with a AC/DC/AC converter scheme in order to harvest the maximum power from the wind and to decouple the synchronous generator voltage and frequency from the grid voltage and frequency. In this paper, a combination of a three phase diode bridge rectifier (DBR) and a modified topology of the diode clamped multilevel inverter (DCMLI) has been considered as an AC/DC/AC converter. A control strategy has been proposed for the DCMLI to achieve the objective of grid interface of a wind power system together with local load compensation. A novel fixed frequency current control method is proposed for the DCMLI based on the level shifted multi carrier PWM for achieving the required control objectives with equal and uniform switching frequency operation for better control and thermal management with the modified DCMLI. The condition of the controller gain is derived to ensure the operation of the DCMLI at the fixed frequency of the carrier. The converter current injected into the distribution grid is controlled in accordance with the wind power availability. In addition, load compensation is performed as an added facility in order to free the source currents being fed from the grid of harmonic distortion, unbalance and a low power factor even though the load may be unbalanced, non-linear and of a poor power factor. The results are validated using PSCAD/EMTDC simulation studies.

• 한국해양환경ㆍ에너지학회지
• /
• 제3권2호
• /
• pp.11-17
• /
• 2000

해양에서 해수보다 비중이 낮은 유류의 이동.확산은 해면 (0m) 유동에 따라 좌우된다. 해양에서의 유류확산에 대한 현실에 부합되는 모델 개발의 일환으로 한반도 연안역 4개 해역에서 해양 표면 취송류 (skin drift) 추정에 대한 연구를 수행하였다. 본 연구에서는 해면과 수면하 1.5m의 유동을 동시 관측하여 둘간의 차이로서 바람에 의한 해양표면 취송류를 추정하였다. 표면취송류 유속의 평균 크기는 바람의 2.9% 였으며, 풍향에 대한 표면취송류 편향의 평균치는 바람의 오른쪽 18.6° 였다. 관측 결과는 표면취송류의 모델링에 활용하였다. 모델링에서는 바람에 따른 표면 취송류의 공간적 변동을 재현하였으며, 관측된 결과와 비교하여 검증하였다.

• Journal of Electrical Engineering and Technology
• /
• 제12권1호
• /
• pp.145-150
• /
• 2017

This paper present a unified method of steady state performance analysis and limits characteristics of an autonomous three-phase self-excited induction generator (SEIG) driven by a wind turbine under different types of loads and speeds. The proposed method is based on a new mathematical function to solve for the real and imaginary components of the complex equation of the mathematical model. Performances limits, regulation and characteristics of different configurations will be thoroughly examined and compared. The proposed system will be modeled and simulated and the performance limits characteristics will be compared with variable speed and variable capacity.

• Journal of the Korean Data and Information Science Society
• /
• 제26권6호
• /
• pp.1409-1416
• /
• 2015

기온의 변화는 인간의 건강뿐 아니라 동식물의 성장, 경제, 사회, 산업, 문화 등의 전 분야에 영향을 준다. 본 연구에서는 수원시 2003년-2012년 기온을 기상자료, 온실가스자료, 대기자료를 이용하여 자기회귀오차 (autoregressive error)모형으로 월별로 분석하였다. 기온을 위한 기상자료로는, 풍속, 강수량, 일사량, 운량, 습도를 사용했고, 온실가스자료는 이산화탄소 ($CO_2$), 메탄 ($CH_4$), 아산화질소 ($N_2O$), 염화불화탄소 ($CFC_{11}$), 대기자료는 미세먼지 ($PM_{10}$), 이산화황 ($SO_2$), 이산화질 소 ($NO_2$), 오존 ($O_3$), 일산화탄소 (CO)을 사용하였다. 기온을 월별 분석한 결과 기상변수로는 일사량, 운량, 풍속이 영향을 많이 주는 것으로 분석되었다. 특히 일사량은 봄, 여름, 가을에 영향을 많이 주고 풍속은 겨울에 영향을 많이 주는 것으로 나타났다. 온실가스변수로는 염화불화탄소와 메탄이 기온에 영향을 많이 주고 대기변수로는 오존이 영향을 많이 주는 것으로 타났다. 자기회귀오차모형으로 월별 기온을 43%~69% 정도 설명할 수 있다.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
• /
• 제22권1호
• /
• pp.24-32
• /
• 1994

A special upper-air observation including airsonde and pibal observations was performed to investigate the characteristics features of the vertical distribution of the meteorological elements over Taegu on a selected clear day of each season from October 1991 to August 1992. The diurnal and seasonal variations of the vertical profiles of air temperature and mixing ratio were obtained from airsonde observations and wind speed and direction from pibal observations. The results of these special upper-air observations are as follow : The diurnal variation of the vertical distribution of air temperature reveals the characteristic features associated with the atmospheric boundary layer. All case days, except for the summer season, show upper-level inversion layer which influenced by surface high, and surface inversion layer produced by radiative cooling. The diurnal variation of mixing ratio shows the maximum vale at 1500 LST in both the upper and low levels, and is larger on the lower level than the upper level. The mixing ratio of the lower level is larger than that of the upper level. On the average the mixing ratio decrease with the height, and is the wettest on the summer case day and the driest on the winter case day. The diurnal variation of the wind velocity and direction are variable in the lower level with time and height, while they are steady in the upper level. On the average, the wind direction is southerly or southeasterly for the summer case day, westerly or northwesterly for the spring and fall case days, and northerly or northwesterly for the winter case day.

• Smart Structures and Systems
• /
• 제18권4호
• /
• pp.683-705
• /
• 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.