• 한국환경과학회지
• /
• 제24권1호
• /
• pp.81-96
• /
• 2015

The characteristics of atmospheric dispersion of radioactive material (i.e. $^{137}Cs$) related to local wind patterns around the Kori nuclear power plant (KNPP) were studied using WRF/HYSPLIT model. The cluster analysis using observed winds from 28 weather stations during a year (2012) was performed in order to obtain representative local wind patterns. The cluster analysis identified eight local wind patterns (P1, P2, P3, P4-1, P4-2, P4-3, P4-4, P4-5) over the KNPP region. P1, P2 and P3 accounted for 14.5%, 27.0% and 14.5%, respectively. Both P1 and P2 are related to westerly/northwesterly synoptic flows in winter and P3 includes the Changma or typhoons days. The simulations of P1, P2 and P3 with high wind velocities and constant wind directions show that $^{137}Cs$ emitted from the KNPP during 0900~1400 LST (Local Standard Time) are dispersed to the east sea, southeast sea and southwestern inland, respectively. On the other hands, 5 sub-category of P4 have various local wind distributions under weak synoptic forcing and accounted for less than 10% of all. While the simulated $^{137}Cs$ for P4-2 is dispersed to southwest inland due to northeasterly flows, $^{137}Cs$ dispersed northward for the other patterns. The simulated average 137Cs concentrations of each local wind pattern are $564.1{\sim}1076.3Bqm^{-3}$. The highest average concentration appeared P4-4 due to dispersion in a narrow zone and weak wind environment. On the other hands, the lowest average concentration appeared P1 and P2 due to rapid dispersion to the sea. The simulated $^{137}Cs$ concentrations and dispersion locations of each local wind pattern are different according to the local wind conditions.

• Wind and Structures
• /
• 제32권3호
• /
• pp.227-238
• /
• 2021

This study analyzed the pressure patterns and local pressure of tall buildings with corner modifications (recessed and chamfered corner) using wind tunnel tests and proper orthogonal decomposition (POD). POD can distinguish pressure patterns by POD mode and more dominant pressure patterns can be found according to the order of POD modes. Results show that both recessed and chamfered corners effectively reduced wind-induced responses. Additionally, unique effects were observed depending on the ratio of corner modification. Tall building models with recessed corners showed fluctuations in the approaching wind flow in the first POD mode and vortex shedding effects in the second POD mode. With large corner modification, energy distribution became small in the first POD mode, which shows that the effect of the first POD mode reduced. Among building models with chamfered corners, vortex shedding effects appeared in the first POD mode, except for the model with the highest ratio of corner modifications. The POD confirmed that both recessed and chamfered corners play a role in reducing vortex shedding effects, and the normalized power spectral density peak value of modes showing vortex shedding was smaller than that of the building model with a square section. Vortex shedding effects were observed on the front corner surfaces resulting from corner modification, as with the side surface. For buildings with recessed corners, the local pressure on corner surfaces was larger than that of side surfaces. Moreover, the average wind pressure was effectively reduced to 88.42% and 92.40% in RE1 on the windward surface and CH1 on the side surface, respectively.

• 한국대기환경학회지
• /
• 제14권5호
• /
• pp.479-490
• /
• 1998

The concentrations of ten inorganic (sodium, chloride, sulfate, ammonia, etc.) and three organic (acetate, formate, and MSA) ions associated with airborne particulate matter were measured from Cheju Island, Korea during the three field intensive campaigns conducted in (1) Sept./oct. 1997 (fall), (2) Dec. 1997 (winter), and (3) April 1998 (spring). The results of our measurements indicated that the concentration levels of most ionic species were decreasing significantly across the three experimental periods. The patterns of concentration reduction were clear as the sum of all cation and anion species changed dramatically across those periods such as 294> 144 > 65 and 193 >96>74 nequiv/m3, respectively. The changes were best explained in terms of the wind rose patterns of the study site. Since our sampling spot is located on the western-end point of Cheju Island, it is likely to reflect the effects of diverse sources such as natural, marine processes during NW and local non-maritime ones during SE winds. .Hence, the periodical changes in ionic concentrations may be accounted for by the comparable changes in wind direction. To further investigate environmental characteristics of these ionic components, correlation analysis was conducted not only between meteorological and ion data but between different ion-pairs. The results of these analyses confirm that the concentration levels of ionic species are strongly affected by wind speed and temperature and that there are certain patterns between ion species to which such effects apply. In light of the significance of the wind rose patterns in the area, we further extended these analyses into four data groups that were divided on the basis of wind direction. The results of these analyses showed that the strength of correlations between important pairs (e.g.:. between windspeed and most of major inorganic species including sodium and chloride) can be ranked on the distribution of major ions are very diverse, depending on data grouping scheme for such analysis. The results of this study thus suggest that environmental behavior of chemical components be analyzed in various respects, rather than simple standard, especially if measurements are made in complex environmental condition under which both natural and anthropogenic effects are competing each other.

• Journal of Advanced Marine Engineering and Technology
• /
• 제37권7호
• /
• pp.799-806
• /
• 2013

As a first step to develop the hybrid power generation system, on this study, the time-variable resources of wind and solar radiation of Yeongdo, Busan, Korea had been measured during June and July 2013. And the quantity of generated wind power and solar photovoltaic had also been measured during the same period. It is found out that the wind mainly flew from southwest at the average speed of 2 m/s during 2 months. And it is clear that, because of the low wind velocity, the wind quality to generate the power seems not enough at this area. Meanwhile solar radiation was measured every daytime (6:00~19:00) and the peak solar radiation occurred around 12:00~14:00. And it is clear that the time-based variations of quantity of generated power were proportional to the variations of these resources, respectively. As a proposal, these 2 natural energies can be combined as resources of a hybrid system, because these 2 patterns are not overlapped so much on time base.

• 한국해안해양공학회지
• /
• 제4권4호
• /
• pp.231-242
• /
• 1992

분 연구에서는 수치모형을 이용하여 조류 및 취송류의 순환형태를 고찰하였다. 사용된 모형은 유체의 운동 및 연속방정식에 기초한 연직평균 2차편 모형으로서 양해법을 사용하며, 개방경계에서의 해수면 변화와 바람의 전단력에 의한 forcing을 포함한다. 모형의 영역은 북위 35$^{\circ}$~36$^{\circ}$40', 동경 125$^{\circ}$~126$^{\circ}$40'이며 경사간격은 x, y 방향 공히 5km이다. 피해측에서 22일간 관측된 조석(2개 지점) 및 조류(1개 지점) 자료와 비교한 결과 본 모형은 4개 주요 분조에 의한 조석 및 조류를 정확도 90% 이내로 재현하였다. 여섯 가지 경우의 가상적인 바람에 대한 해석을 통하여 흐름의 분포양상과 지역적인 특성을 고찰하였다. 그 결과, 풍향에 관계 없이 강한 연안류가 발생하며, 또한 해저지형의 영향으로 부안 외해측에 주반경 40km의 지역적인 과류가 발생함을 확인하였다.

• Wind and Structures
• /
• 제25권2호
• /
• pp.101-129
• /
• 2017

Local transient extreme wind loads caused by group tower-related interference are among the major reasons that lead to wind-induced damage of super-large cooling towers. Four-tower arrangements are the most commonly seen patterns for super-large cooling towers. We considered five typical four-tower arrangements in engineering practice, namely, single row, rectangular, rhombic, L-shaped, and oblique L-shaped. Wind tunnel tests for rigid body were performed to determine the influence of different arrangements on static and dynamic wind loads and extreme interference effect. The most unfavorable working conditions (i.e., the largest overall wind loads) were determined based on the overall aerodynamic coefficient under different four-tower arrangements. Then we calculated the one-, two- and three-dimensional aerodynamic loads under different four-tower arrangements. Statistical analyses were performed on the wind pressure signals in the amplitude and time domains under the most unfavorable working conditions. On this basis, the non-Gaussian distribution characteristics of aerodynamic loads on the surface of the cooling towers under different four-tower arrangements were analyzed. We applied the Sadek-Simiu procedure to the calculation of two- and three-dimensional aerodynamic loads in the cooling towers under the four-tower arrangements, and the extreme wind load distribution patterns under the most unfavorable working conditions in each arrangement were compared. Finally, we proposed a uniform equation for fitting the extreme wind loads under the four-tower arrangements; the accuracy and reliability of the equation were verified. Our research findings will contribute to the optimization of the four-tower arrangements and the determination of extreme wind loads of super-large cooling towers.

• Journal of Radiation Protection and Research
• /
• 제41권4호
• /
• pp.315-327
• /
• 2016

Background: This study evaluated the atmospheric dispersion of radioactive material according to local weather conditions and emission conditions. Materials and Methods: Local weather conditions were defined as 8 patterns that frequently occur around the Kori Nuclear Power Plant and emission conditions were defined as 6 patterns from a combination of emission rates and the total number of particles of the $^{137}Cs$, using the WRF/HYSPLIT modeling system. Results and Discussion: The highest mean concentration of $^{137}Cs$ occurred at 0900 LST under the ME4_1 (main wind direction: SSW, daily average wind speed: $2.8ms^{-1}$), with a wide region of its high concentration due to the continuous wind changes between 0000 and 0900 LST; under the ME3 (NE, $4.1ms^{-1}$), the highest mean concentration of $^{137}Cs$ occurred at 1500 and 2100 LST with a narrow dispersion along a strong northeasterly wind. In the case of ME4_4 (S, $2.7ms^{-1}$), the highest mean concentration of $^{137}Cs$ occurred at 0300 LST because $^{137}Cs$ stayed around the KNPP under low wind speed and low boundary layer height. As for the emission conditions, EM1_3 and EM2_3 that had the maximum total number of particles showed the widest dispersion of $^{137}Cs$, while its highest mean concentration was estimated under the EM1_1 considering the relatively narrow dispersion and high emission rate. Conclusion: This study showed that even though an area may be located within the same radius around the Kori Nuclear Power Plant, the distribution and levels of $^{137}Cs$ concentration vary according to the change in time and space of weather conditions (the altitude of the atmospheric boundary layer, the horizontal and vertical distribution of the local winds, and the precipitation levels), the topography of the regions where $^{137}Cs$ is dispersed, the emission rate of $^{137}Cs$, and the number of emitted particles.

• Wind and Structures
• /
• 제8권6호
• /
• pp.427-442
• /
• 2005

Numerical and wind tunnel simulations of pollutant dispersion around rectangular obstacles with five aspect ratios have been conducted in order to identify the effects of flow patterns induced by buildings on plume dispersion in the near wake of buildings. An emission from a low source located upwind of obstacles was used in this simulation. The local flow patterns and concentrations around a cubical obstacle were initially investigated using three RANS turbulence models, (the standard $k-{\varepsilon}$, Shear Stress Transport (SST), Reynolds-Stress RSM turbulence model) and also using Large-eddy simulation (LES). The computed concentrations were compared with those measured in the wind tunnel. Among the three turbulence models, the SST model offered the best performance and thus was used in further investigations. The results show, for normal aspect ratios of width to height, that concentrations in the near wake are appreciably affected because of plume capture by the horseshoe vortex and convection by the vertical vortex pairs. These effects are less important for high aspect ratios. Vertical vortex pairs present a strong ability to exchange mass vertically and acts efficiently to reduce ground-level concentrations in the near wake.

• 한국환경과학회지
• /
• 제15권8호
• /
• pp.759-774
• /
• 2006

We employed two data assimilation techniques including MM5 Four Dimensional Data Asssimilation (FDDA) and Local Analysis and Prediction System (LAPS) to find out the effects of the changed inetial conditions on the wind fields simulation according to the objective analysis methods. We designed 5 different modeling cases. EXP B used no data assimilation system. Both EXP Fl using surface observations and EXP F2 with surface and upper-air observations employed MM5 FDDA. EXP Ll using surface observations and EXP L2 with surface and upper-air observations used LAPS. As results of, simulated wind fields using MM5 FDDA showed locally characterized wind features due to objective analysis techniques in FDDA which is forcefully interpolating simulated results into observations. EXP Fl represented a large difference in comparison of wind speed with EXP B. In case of LAPS, simulated horizontal distribution of wind fields showed a good agreement with the patterns of initial condition and EXP Ll showed comparably lesser effects of data assimilation of surface observations than EXP Fl. When upper-air observations are applied to the simulations, while MM5 FDDA could hardly have important effects on the wind fields simulation and showed little differences with simulations with merely surface observations (EXP Fl), LAPS played a key role in simulating wind fields accurately and it could contribute to alleviate the over-estimated winds in EXP Ll simulations.

• 대기
• /
• 제25권3호
• /
• pp.449-459
• /
• 2015

Effects of buildings and topography on observation environment of surface wind in central regions of urban areas are investigated using a computational fluid dynamics (CFD) model. In order to reflect the characteristics of buildings and topography in urban areas, geographic information system (GIS) data are used to construct surface boundary input data. For each observation station, 16 cases with different inflow directions are considered to evaluate effects of buildings and topography on wind speed and direction around the observation station. The results show that flow patterns are very complicated due to the buildings and topography. The simulated wind speed and direction at the location of each observation station are compared with those of inflow. As a whole, wind speed at observation stations decreases due to the drag effect of buildings. The decrease rate of wind speed is strongly related with total volume of buildings which are located in the upwind direction. It is concluded that the CFD model is a very useful tool to evaluate location of observation station suitability. And it is expected to help produce wind observation data that represent local scale excluding the effects of buildings and topography in urban areas.