• Wind and Structures
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• 제37권1호
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• pp.57-78
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• 2023

In this study, a generalized three-degree-of-freedom (3-DoF) analytical model is formulated to predict linear aerodynamic instabilities of a prism under quasi-steady (QS) conditions. The prism is assumed to possess a generic cross-section exposed to turbulent wind flow. The 3-DoFs encompass two orthogonal horizontal directions and rotation about the prism body axis. Inertial coupling is considered to account for the non-coincidence of the mass center and the rotation center. The aerodynamic force coefficients-drag, lift, and moment-depend on the Reynolds number based on relative flow velocity, angle of attack, and the angle between the wind and the cable. Aerodynamic forces are linearized with respect to the static equilibrium configuration and mean wind velocity. Routh-Hurwitz and Liénard and Chipart criteria are used in the eigenvalue problem, yielding an analytical solution for instabilities in galloping and static divergence types. Additionally, the minimum structural damping and stiffness required to prevent these instabilities are numerically determined. The proposed 3-DoF instability model is subsequently applied to a conductor with ice accretion and a full-scale dry inclined cable. In comparison to existing models, the developed model demonstrates superior prediction accuracy for unstable regions compared with results in wind tunnel tests.

• 설비공학논문집
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• 제17권11호
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• pp.1060-1071
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• 2005

Passive gas dispersions over a 1/1000 scale terrain model at Eiffel type wind tunnel were reproduced by numerical simulation. Large eddy simulation was used to treat the sub-grid scale turbulences. The terrain features were represented by millions of point forces densely distributed over the solid surface using the virtual boundary method. The model simulations agreed very well with the experiments in a consistent fashion for all wind directions. The measured profiles of the wind speeds as well as the tracer gas concentrations were nicely simulated by the CFD model at most locations scattered over the model terrain. With scale factor adjusted and the thermal stratification effects incorporated, the CFD model was expected to provide reliable information on pollutant dispersions over the real complex terrains.

• 한국대기환경학회지
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• 제15권3호
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• pp.267-280
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• 1999

To investigate the characteristics of high-ozone occurrences in the Greater Seoul Area(GSA), three high-ozone episodes were selected, for which the ozone warning for concentration above 120 ppb might be issued. The selection was on the basis of morning wind directions and speeds, and daily maximum ozone concentrations measured between 1990 and 1997. The episodes chosen to meet selection criteria were seven days in July 1992, nine days in July 1994, and three days in August 1994, as respectively characterized by southwesterly, easterly, and calm winds in the morning. However, more than 80% of high-ozone days in the GSA were associated with calm winds and the concomitant accumulation of local emission in the morning, rather than being due to transport of ozone or its precursors. This is believed to be the primary reason why ozone concentrations in the GSA varied in a completely different manner even between adjacent monitoring stations. Several premises for initiating research studies for resolving these local variations of ozone concentrations in the GSA are also discussed.

• 한국환경과학회지
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• 제12권10호
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• pp.1101-1108
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• 2003

We studied the relationship between a civil affair occurrence of bad smell and meteorological conditions around Seongseo district for recent 2 years. The results were as follows; (1) The civil affair occurrence days of bad smell were concentrated from May to August. (2) Daily mean temperatures were mostly 20∼28$^{\circ}C$ and daily mean relative humidities were 60∼80%. (3) Wind speeds were mostly less than 2㎧(75%), and wind directions were southerly winds(50%). It was hardly occurred for relatively well-ventilated conditions in cases of wind speeds 2㎧ over. And the Lagrangian particle dispersion model were used to figure out the transport route in a civil affair occurrence days of bad smell. It was found that the south-western winds transported the bad smelling materials from Jungni-dong(the place of source) to the housing complex located along a piedmont district.

• Wind and Structures
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• 제34권3호
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• pp.259-274
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• 2022

The present paper is focused on analyzing a set of Computational Fluid Dynamics (CFD) simulation data on reducing orthogonal peak base moment coefficients on a high-rise rectangular building with wings. The study adopts an aerodynamic optimization procedure (AOP) composed of CFD, artificial neural network (ANN), and genetic algorithm (G.A.). A parametric study is primarily accomplished by altering the wing positions with 3D transient CFD analysis using k - ε turbulence models. The CFD technique is validated by taking up a wind tunnel test. The required design parameters are obtained at each design point and used for training ANN. The trained ANN models are used as surrogates to conduct optimization studies using G.A. Two single-objective optimizations are performed to minimize the peak base moment coefficients in the individual directions. An additional multiobjective optimization is implemented with the motivation of diminishing the two orthogonal peak base moments concurrently. Pareto-optimal solutions specifying the preferred building shapes are offered.

• Wind and Structures
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• 제6권2호
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• pp.107-126
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• 2003

This paper describes a simple and practical approach through the application of Linear Stochastic Estimation (LSE) to reconstruct wind-induced pressure time series from the covariance matrix for structural load analyses on a low building roof. The main application of this work would be the reduction of the data storage requirements for the NIST aerodynamic database. The approach is based on the assumption that a random pressure field can be estimated as a linear combination of some other known pressure time series by truncating nonlinear terms of a Taylor series expansion. Covariances between pressure time series to be simulated and reference time series are used to calculate the estimation coefficients. The performance using different LSE schemes with selected reference time series is demonstrated by the reconstruction of structural load time series in a corner bay for three typical wind directions. It is shown that LSE can simulate structural load time series accurately, given a handful of reference pressure taps (or even a single tap). The performance of LSE depends on the choice of the reference time series, which should be determined by considering the balance between the accuracy, data-storage requirements and the complexity of the approach. The approach should only be used for the determination of structural loads, since individual reconstructed pressure time series (for local load analyses) will have larger errors associated with them.

• 응용통계연구
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• 제29권7호
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• pp.1373-1383
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• 2016

풍력에너지 산업이 발전하고 풍력발전에 대한 의존율이 높아짐에 따라 안정적인 공급이 중요해지고 있다. 원활한 전력수급계획을 세우기 위해서 풍력발전량을 정확히 예측하는 것이 중요하다. 본 논문에서는 강원도 평창 횡계리에 설치된 대관령 2풍력(2MW 1기)의 시간별 풍력발전 데이터와 강원도 대관령 기상대에서 관측되는 시간별 풍속과 풍향 데이터를 기상청 지상관측자료에서 수집하여 연구하였다. 풍력발전량 예측을 위하여 신경망 모형과 시계열 모형인 ARMA, ARMAX, ARMA-GARCH, Holt Winters 모형을 비교하였다. 모형 간 예측력을 비교하기 위해 mean absolute error(MAE)를 사용하였다. 모형의 예측 성능 비교 결과 1시간에서 3시간의 단기 예측에 있어서 ARMA-GARCH 모형이 우수한 예측력을 보였다. 6시간 이후 예측에서는 신경망 모형이 우수한 예측을 보였다.

• Ocean Science Journal
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• 제42권2호
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• pp.89-102
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• 2007

The surface circulation of northern South China Sea (hereafter SCS) for the period 1987-2005 was studied using the data of more than 500 satellite-tracked drifters and wind data from QuikSCAT. The mean flow directions in the northern SCS except the Luzon Strait (here after LS) during the periods October_March was southwestward, and $April{\sim}September$ northeastward. A strong northwestward intrusion of the Kuroshio through the LS appears during the $October{\sim}March$ period of northeasterly wind, but the intrusion became weak between April and September. When the strong intrusion occurred, the eddy kinetic energy (EKE) in the LS was $388cm^2/s^2$ which was almost 2 times higher than that during the weak-intrusion season. The volume transport of the Kuroshio in the east of the Philippines shows an inverse relationship to that of the LS. There is a six-month phase shift between the two seasonal phenomena. The volume transport in the east of the Philippines shows its peak sis-month earlier faster than that of the LS. The strong Kuroshio intrusion is found to be also related to the seasonal variation of the wind stress curl generated by the north easterly wind. The negative wind stress curl in the northern part of LS induces an anticyclonic flow, while the positive wind stress curl in the southern part of LS induces a cyclonic flow. The northwestward Kuroshio intrusion in the northern part of LS happened with larger negative wind stress curl, while the westward intrusion along $20.5^{\circ}N$ in the center of the LS occurred with weaker negative wind stress curl.

• Wind and Structures
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• 제20권1호
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• pp.37-58
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• 2015

As wind flows around a sharp-edged body, the resulting separated flow becomes complicated, with multiple separations and reattachments as well as vortex recirculation. This widespread and unpredictable phenomenon has long been studied academically as well as in engineering applications. In this study, the flow characteristics around rectangular prisms with five different aspect ratios were determined through wind tunnel experiments and a detached eddy simulation, that placed the objects in a simulated deep turbulent boundary layer at $Re=4.6{\times}10^4$. A series of rectangular prisms with the same height (h = 80 mm), different longitudinal lengths (l = 0.5h, h, and 2h), or different transverse widths (w = 0.5h, h, and 2h) were employed to observe the effects of the aspect ratio. Furthermore, five wind directions ($0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$, and $45^{\circ}$) were selected to observe the effects of the wind direction. The simulated results of the surface pressure were compared to the wind tunnel experiment results and the existing results of previous papers. The vortex and spectrum were also analyzed to determine the detailed flow structure around the body. The paper also highlights the pressure distribution around the rectangular prisms with respect to the different aspect ratios. With an increasing transverse width, the surface suction pressure on the top and side surfaces becomes stronger. In addition, depending on the wind direction, the pressure coefficient experiences a large variation and can even change from a negative to a positive value on the side surface of the cube model.

• 미술이론과 현장
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• 제3호
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• pp.155-172
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• 2005

Kim Whan-ki is an unusual instance in Korean modern artists, who payed attention to emotional and expressive effects of colors. The color of Whan-ki's paintings have been recognized as linked with 'blue' in spite that he used colors within the category of 'Colors of Five Directions(五方色)', which are traditional oriental colors composed of red, lue, yellow, white, green and black. Kim Whan-ki unearthed upon similarity of Five Directions Colors to the three(five) primary colors which modern abstract painter like Mondrian layed down. Whan-ki switched the five directions colors to modern ones. Kim Whan-ki's dot painting in which pure and watery color is sucked in ground is modernistic adaptation from ink painting. He packs a dot with sky and earth, moon and stars, forest and tree, birds and flowers, friends at his hometown, wind, sound and so on. Putting tens of thousands of these shapes and colors into a dot is modernistic version from ink painting. In that point there is a possibility to say that 'dark blue' of the dot painting is 'Hyun-saec(玄色)'. Eventually we can make sure that Kim Whan-ki's view of Art originated in oriental philosophy and beauty.