• Wind and Structures
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• v.30 no.1
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• pp.15-27
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• 2020

This paper reports the study on development and verification of numerical models and analyzes of flow at high speed around structural elements in the shape of a curved pipe (e.g., a fragment of a water slide). Possibility of engineering estimation of wind forces acting on an object in the shape of a helix is presented, using relationships concerning toroidal and cylindrical elements. Determination of useful engineering parameters (such as aerodynamic forces, pressure distribution, and air velocity field) is presented, impossible to obtain from the existing standard EN 1991-1-4 (the so-called wind standard). For this purpose, flow at high speed around a torus and helix, arranged both near planar surface and high above it, was analyzed. Analyzes begin with the flow around a cylinder. This is the simplest object with a circular cross-section and at the same time the most studied in the literature. Based on this model, more complex models are analyzed: first in the shape of half of a torus, next in the shape of a helix.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.11
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• pp.76-81
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• 2013

In this paper, a corona motor with blade type electrodes has been employed as a wind blower. The rotation speed was influenced significantly by the polarity of applied voltage and the number of blades. Therefore the effect of polarity of applied voltage and the number of blades on the electrical and mechanical fundamental properties of corona motor were investigated experimentally. The rotation speed decreased for increasing of number of blades, because the mass of blades increased. But the amount of air blow increased despite decreasing of the rotation speed, because air volume is not only influenced by rotation speed but also the number of blades and ionic wind which generated between blade tips and a induction electrode. Although space occupied by blades of the corona motor is smaller than the whole area of the blast pipe, wind rises a whole range of a wind blower for such reasons.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.219-226
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• 2014

A bus duct system for wind tower is introduced. A marine cable has been widely used in wind tower or various offshore structures. However, as the electric load capacity is increases, large number of cable lines must be used to cover the huge amount of electric capacities. Therefore, the installation of the cable lines becomes very difficult due to the heavy weight and volume of the cables. On the other hand, by using a single bus duct system line, the power capacity amount of 16 cables can be delivered with significantly compacted form. However, unlike flexible cables, the bus duct is relatively stiff which could generate the resonance phenomenon in the operating condition of the wind tower. In this study, the vibration characteristics of the bus duct are investigated and its long-term reliability during the life time of the wind tower is verified.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.574-578
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• 2014

본 연구에서는 인접 구조물의 상호 간섭에 의한 풍압 변화에 대한 분석을 수행하였다. 두 개의 구조물 사이의 거리 및 위치를 변경하여 비교 해석하는 것으로써 사각형 구조물 구현을 위해 EDISON_CFD를 이용하여 수치해석을 하였고, 유한 체적 법(Finite Volume Method, FVM) 기반의 범용 비압축성 유동 해석을 위해 2D_Incomp-P_2.1 해석자를 사용하였다. 이 연구를 통하여 인접한 구조물의 영향을 분석하여 상호 간 거리와 위치를 결정할 수 있는 근거자료를 확보하였다.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Journal of the Korean earth science society
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• v.35 no.2
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• pp.104-114
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• 2014

The variation of acidity, conductivity, and ion components in precipitation depending on the dominant wind direction was investigated from January, 2009 to December 2009 in Busan, Korea. Both southwesterly and northeasterly winds were dominant in Busan area. The volume-weighted mean acidity showed pH 7, and the high conductivity indicated 200 ${\mu}scm^{-1}$ in westerly wind. The volume-weighted mean equivalent concentration showed higher value of $K^+$ and $Cl^-$ in all wind directions. The composition ratio of $NO{_3}^-/SO{_4}^{2-}$ showed over 3 in northerly wind. The neutralization factors have been found to have higher value for potassium ion in northeasterly, easterly, southwesterly, and westerly winds compared with different wind directions, which indicated significant neutralization of acidic components over the region by potassium. Also, the concentration of sea salt has been found over 800 ${\mu}sm^{-3}$ in northeasterly and southwesterly winds. Air masses passing through Manchuria, Inner Mongolia plateau, China, and Russia in spring, autumn, and winter covered Busan, Korea in northerly, westerly, and northwesterly winds. However, air masses passing through the ocean in summer covered Busan, Korea in easterly, northeasterly, and southwesterly winds. Therefore, the variation of acidity, conductivity, and ionic components contained in precipitation shows each seasonal characteristics with prevailing wind systems between the continental and coastal area in Busan, Korea.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.6
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• pp.635-641
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• 2019

Domestic southwest offshore wind farms have problems such as the reduction in fishing rights by prohibiting vessel traffic, which delays their development. As such, there is a need to develop offshore windfarms in Europe to permit the passage of vessels and fishing operations in specific offshore windfarm areas. In this study, we used the environmental stress (ES model) and the IALA Waterway Risk Assessment Program (IWRAP) to determine the ratio of risk to the route type (cross pattern, grid pattern) and traffic volume (present, 3 times, 5 times and 10 times) to derive the risk factors of specific vessels for offshore windfarms. As a result, ship operators' risk related to offshore windfarms did not rise in both route types and there was no significant difference in the annual probability of collision in the present traffic volume. In conditions that increased traffic volume by 3 times, 5 times and 10 times, the risk ratio increased as ship operator risk and collision probability increased at the crossing points. Furthermore, when the traffic volume of the ship increased, the risk could be more effectively distributed in the grid route compared to the cross route. The results of this study are expected to apply to the operation type, route operation method, safety measures, etc. in offshore wind farms.

• Wind and Structures
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• v.38 no.4
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• pp.261-275
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• 2024

Before performing an experimental study on the downburst-generated wave, it is necessary to examine the scale effects and corresponding corrections or compensations. Analysis of similarity is conducted to conclude the non-dimensional force ratios that account for the dynamic similarity in the interaction of downburst with wave between the prototype and the scale model, along with the corresponding scale factors. The fractional volume of fluid (VOF) method in association with the impinging jet model is employed to explore the characteristics of the downburst-generated wave numerically, and the validity of the proposed scaling method is verified. The study shows that the location of the maximum radial wind velocity in a downburst-wave field is a little higher than that identified in a downburst over the land, which might be attributed to the presence of the wave which changes the roughness of the underlying surface of the downburst. The impinging airflow would generate a concavity in the free surface of the water around the stagnation point of the downburst, with a diameter of about two times the jet diameter (D_jet). The maximum wave height appears at the location of 1.5D_jet from the stagnation point. Reynolds number has an insignificant influence on the scale effects, in accordance with the numerical investigation of the 30 scale models with the Reynolds number varying from 3.85 × 10⁴ to 7.30 × 10⁹. The ratio of the inertial force of air to the gravitational force of water, which is denoted by G, is found to be the most significant factor that would affect the interaction of downburst with wave. For the correction or compensation of the scale effects, fitting curves for the measures of the downburst-wave field (e.g., wind profile, significant wave height), along with the corresponding equations, are presented as a function of the parameter G.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1455-1468
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• 2016

This paper presents a grid-connected dual stator-winding induction generator (DWIG) wind power system suitable for wide wind speed ranges. The parallel connection via a unidirectional diode between dc buses of both stator-winding sides is employed in this DWIG system, which can output a high dc voltage over wide wind speed ranges. Grid-connected inverters (GCIs) do not require booster converters; hence, the efficiency of wind energy utilization increases, and the hardware topology and control strategy of GCIs are simplified. In view of the particularities of the parallel topology and the adopted generator control strategy, we propose a novel excitation-capacitor optimization solution to reduce the volume and weight of the static excitation controller. When this excitation-capacitor optimization is carried out, the maximum power tracking problem is also considered. All the problems are resolved with the combined control of the DWIG and GCI. Experimental results on the platform of a 37 kW/600 V prototype show that the proposed DWIG wind power system can output a constant dc voltage over wide rotor speed ranges for grid-connected operations and that the proposed excitation optimization scheme is effective.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.3
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• pp.211-223
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• 2000

The atmospheric dispersion of a pollutant emitted from a hypothetical source located in the middle of the Yochon Industrial Estate was simulated by using the Regional Atmospheric Modeling System (RAMS). Four horizontally nested grids were employed: the coarsest one covered the southern part of the Korean Peninsula including Mt. Chiri and the finest one covered the Yochon Industrial Estate and the surrounding area. Wind fields were initially assumed horizontally homogeneous with a wind speed of 4m/s, the average for the Yosu area, and were developed without both external forces and diurnal changes in order to investigate the terrain-induced phenomena. Wind directions that could emphasize the terrain effects on the pollutant transport and that could carry pollutants to a highly-popluated area were selected for the dispersion study. A pollutant was released for 24hours from a grid-base volume source after a 24-h blank run for developing the wind field. The dispersion study showed that the pollutant from the present source location did not directly affect the Yosu City, but showed high concentrations at locations behind the hills 5 to 6 km away from the source according to wind directions. When the wind speed was low, close to calm condition, the pollutant was detected at upstream locations 6 to 7 km from the source. In comparison with the results from the RAMS simulation, the Industrial Source Complex Short-Term Model(ISCST3) predicted a narrow dispersion that was sensitive to the wind direction. When the wind velocity was affected by the local environment, the ISCST3 calculation using that data also gave a lop-sided result, which was different from the distribution of the pollutant reproduced by RAMS.