• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.4
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• pp.37-44
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• 2009

The characteristics of strong wind occurring over the southwestern part of the Korean peninsula are analyzed by using hourly mean wind data observed in Gusan, Mokpo, Yeosu and Wando from 1970 to 2008. The strong wind here is defined as wind speed of more than 13.9 m/s according to Korea Meteorological Administration (KMA)'s strong wind advisory. The causes of strong wind are classified into typhoon, monsoonal (wintertime continent polar air mass) and frontal (cyclone) winds. Typhoon wind is characterized by abrupt change of its speed and direction after and before landfall of typhoon and monsoonal wind by periodicity of wind speed. And frontal wind tend to be changed from southwesterly to northwesterly at observation site with location of frontal surface. Strong winds are mainly occurred in Yeosu by typhoon, Gusan and Mokpo by monsoonal wind, and Mokpo and Yeosu by frontal wind. In particular, in case of frontal wind, the frequency of strong wind in Mokpo decreases while in Yeosu it increases. Monthly frequency of strong wind is high in August in Mokpo and September in Yeosu by typhoon, January in Gusan and December in Mokpo by monsoonal wind, and in April in Mokpo and Yeosu by frontal wind. The duration less than 1 hour of strong wind is prominent in all stations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.9
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• pp.796-803
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• 2004

The stack effect of a new type condenser installed in a high-rise apartment building was studied numerically A sirocco fan is introduced to the new type condenser instead of an axial flow In. The new type condenser intakes the cold air through the lower inlet and exhausts the hot air through the upper outlet. The effects of the building height and frontal wind on the performance of an air-conditioner were analyzed. The performance of an air-conditioner was evaluated by using COP (coefficient of performance) and CGPI (condenser group performance indicator). the hot air was exhausted by the new type condenser at an angle of 50$^{\circ}$ from the outer wall of the building. If there was no draft, the new type condenser installed in the high-rise apartment building had a good performance and its performance on each floor is not influenced by the stack effect. It is shown that the efficiency of the air-conditioner installed in several floors below the top floor decreased when the frontal wind velocity was greater than 8 m/s.

• Wind and Structures
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• v.19 no.3
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• pp.339-352
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• 2014

This paper discusses the appropriate duration for basic gust wind speeds in wind loading codes and standards, and in wind engineering generally. Although various proposed definitions are discussed, the 'moving average' gust duration has been widely accepted internationally. The commonly-specified gust duration of 3-seconds, however, is shown to have a significant effect on the high-frequency end of the spectrum of turbulence, and may not be ideally suited for wind engineering purposes. The effective gust durations measured by commonly-used anemometer types are discussed; these are typically considerably shorter than the 'standard' duration of 3 seconds. Using stationary random process theory, the paper gives expected peak factors, $g_u$, as a function of the non-dimensional parameter ($T/{\tau}$), where T is the sample, or reference, time, and ${\tau}$ is the gust duration, and a non-dimensional mean wind speed, $\bar{U}.T/L_u$, where $\bar{U}$ is a mean wind speed, and $L_u$ is the integral length scale of turbulence. The commonly-used Durst relationship, relating gusts of various durations, is shown to correspond to a particular value of turbulence intensity $I_u$, of 16.5%, and is therefore applicable to particular terrain and height situations, and hence should not be applied universally. The effective frontal areas associated with peak gusts of various durations are discussed; this indicates that a gust of 3 seconds has an equivalent frontal area equal to that of a tall building. Finally a generalized gust response factor format, accounting for fluctuating and resonant along-wind loading of structures, applicable to any code is presented.

• 한국해양학회지
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• v.19 no.2
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• pp.210-216
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• 1984

Diurnal variations of coastal surface wind speed are analyzed with five years of hourly wind from Port Aransas, Texas. These data reveal the highest frequency of occurrence of the nighttime wind maximum near midnight, especially during those seasons when onshore flow prevails. Nighttime wind maxima with a southerly component occurred approximately three times more frequently than with a northerly component on the annual average. The neutral atmospheric stability prevails near the coast. Thus it allows downward transfer of momentum from the nocturnal low level jet under the onshore wind situation and strong wind shear between an elevated frontal and ground-based inversion for offshore wind, resulting in the nocturnal coastal surface wind maximum.

• Wind and Structures
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• v.9 no.6
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• pp.419-440
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• 2006

This article synthesizes the literature on the meteorology, experimental simulation, and wind engineering ramifications of intense downburst outflows. A novel design of a large-scale test facility and experimental evidence of its validity are presented. A two-dimensional slot jet is used to simulate only the outflow region of a downburst. Profiles of mean velocity and turbulence quantities are acquired using hot-wire anemometry. Comparison with the literature provides empirical evidence that supports the current approach. A geometric analysis considers the validity of applying a two-dimensional approximation for downburst wind loading of structures. This analysis is applicable to power transmission lines in particular. The slot jet concept can be implemented in a large boundary layer wind tunnel to enable large-scale laboratory experiments of thunderstorm wind loads on structures.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.3
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• pp.223-233
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• 1999

The wind-flow characteristics over a two-dimensional triangular prism with a porous windbreak are numerically investigated. The geometry is a simplified model of large outdoor stack with a frontal wall-type windbreak which is used to prevent particle dispersion by reducing wind speed over stak surface. In the present numerical model, the RNG k-$\varepsilon$ model, the orthogonal grid system and the QUICK scheme are employed for the successful simulation of separated flow. The predicted results are compared and validated with the associated wind-tunnel experiments. In addition, the trajectories of dispersed particles and their sedimentation characteristics are quantitatively investingated using a Lagrangian turbulent-dispersion model.

• New & Renewable Energy
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• v.4 no.4
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• pp.30-36
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• 2008

The possibility of whether the induced wind from a vehicle traveling on highway can be used in wind power generation has been verified through computational flow analysis. The bus which is presumed to accompany relatively strong and wide range of induced wind compared to passenger vehicles because of its wide frontal area has been set as the subject of research. In order to ensure the reliability of research, the flow analysis surrounding the bus on a flat road where median strip is not installed has been compared with a preceding research while the validity of grid system and interpretation method used in this research have been assured by a qualitative method. In case of the median strip type wind power generator system, because it has been verified that a strong streamwise wind speed (5 m/s) is derived from the contraction effect of flow passage between the bus and the median strip while maintaining a relatively consistent upwind wind speed (1.4 m/s) in vertical direction in the wake area after the bus passes by although the change of wind speed is intense, it was decided as having some possibility of wind power generation. In case of the traffic sign panel type wind power generator system installed at the upper top of highway, because the wind speed of 2 m/s level has been derived for a limited time only at a section equal to the length of the bus and a faint induced wind speed less than 0.5 m/s was shown at other regions, it was decided as having almost no possibility of wind power generation.

• Wind and Structures
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• v.12 no.1
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• pp.77-88
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• 2009

A pulsed impinging jet is used to simulate the gust front of a thunderstorm downburst. This work concentrates on investigating the peak transient loading conditions on a 30 mm cubic model submerged in the simulated downburst flow. The outflow induced pressures are recorded and compared to those from boundary layer and steady wall jet flow. Given that peak winds associated with downburst events are often located in the transient frontal region, the importance of using a non-stationary modelling technique for assessing peak downburst wind loads is highlighted with comparisons.

• Wind and Structures
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• v.7 no.3
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• pp.159-172
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• 2004

The study of how buildings affect wind flow is an important part of the research being conducted on urban climate and urban air quality. NJU-UCFM, a standard $k-{\varepsilon}$ turbulence closure model, is presented and is used to simulate how the following affect wind flow characteristics: (1) an isolated building, (2) urban canyons, (3) an irregular shaped building cluster, and (4) a real urban neighborhood. The numerical results are compared with previous researchers' results and with wind tunnel experiment results. It is demonstrated that the geometries and the distribution of urban buildings affect airflow greatly, and some examples of this include a changing of the vortices behind buildings and a "channeling effect". Although the mean air flows are well simulated by the standard $k-{\varepsilon}$ models, it is important to pay attention to certain discrepancies when results from the standard $k-{\varepsilon}$ models are used in design or policy decisions: The standard $k-{\varepsilon}$ model may overestimate the turbulence energy near the frontal side of buildings, may underestimate the range of high turbulence energy in urban areas, and may omit some important information (such as the reverse air flows above the building roofs). In ideal inflow conditions, the effects of the heights of buildings may be underestimated, when compared with field observations.

• Atmosphere
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• v.17 no.4
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• pp.381-391
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• 2007

The characteristics of flow around a single obstacle with fixed height and varied length and width are numerically investigated using a computational fluid dynamics (CFD) model. As the obstacle length increases, flow distortion near the upwind side of the obstacle increases and the size of the recirculation zone behind the obstacle also increases. As the obstacle width increases, the size of the recirculation zone decreases, despite almost invariable flow distortion near the upwind side of the obstacle. Flow passing through an obstacle is separated, one part going around the obstacle and the other crossing over the obstacle. The size of the recirculation zone is determined by the distance between the obstacle and the point (reattachment point) at which both the flows converge. When the obstacle width is relatively large, flows are reattached at the obstacle surface and their recoveries occur. Resultant shortening of the paths of flows crossing over and going around decreases the size of the recirculation zone. To support this, the extent of flow distortion defined based on the change in wind direction is analyzed. The result shows that flow distortion is largest near the ground surface and decreases with height. An increase in obstacle length increases the frontal area fraction of flow distortion around the obstacle. In the cases of increasing the width, the frontal area fraction near the upwind side of the obstacle does not change much, but near the downwind side, it becomes larger as the width increases. The frontal area fraction is in a better correlation with the size of the recirculation zone than the building aspect ratios, suggesting that the frontal area fraction is a good indicator for explaining the variation in the size of the recirculation zone with the building aspect ratios.