• Atmosphere
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• v.25 no.4
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• pp.591-600
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• 2015

We have analyzed wind and eddy covariance data collected within roughness sublayer over sloping terrain. The study site is located on non-flat terrain with slopes in both south-north and east-west directions. The surface elevation change is smaller than the height of roughness element such as building and tree. This study examines the directional wind shear for data collected at three levels in the lowest 10 m in the roughness sublayer. The wind direction shear is caused by drag of roughness element and terrain-induced motions at this site. Small directional shear occurs when wind speed at 10 m is strong and wind direction at 10 m is southerly which is the same direction as upslope flow near surface at this site during daytime. Correlation between vertical shear of lateral momentum and lateral momentum flux is smaller over steeply sloped surface compared to mildly sloped surface and lateral momentum flux is not down-gradient over steeply sloped surface. Quadrant analysis shows that the relative contribution of four quadrants to momentum flux depends on both surface slope and wind direction shear.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.17-20
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• 2005

This paper presents an overview analysis on the observed wind shear at Pohang Steel Works, focusing on diurnal patterns and the frequency of high nighttime shear at the site in case of land breeze. In addition, this paper discusses the importance of accurate shear estimates for reliable evaluation of wind energy density. In order for a long-term correlation of the site, three Measure-Correlate-Predict methods were tested with Pohang wind data and it was shown that the linear MCP gives poor estimation due to the geographic characteristics of complex terrain where the severe transformation of wind direction was accompanied.

• New & Renewable Energy
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• v.1 no.2 s.2
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• pp.26-33
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• 2005

This paper presents and overview analysis on the observed wind shear at Pohang Steel Works. focusing on diurnal patterns and the frequency of high nighttime shear at the site in case of land breeze. In addition, this paper discusses the importance of accurate shear estimation for reliable evaluation of wind energy density. In order for long-term correlation of the site, three Measure-Correlate-Predict methods were tested with Pohang wind data and it was shown that the linear MCP gives poor estimation due to the topological characteristics of complex terrain where the severe transformation of wind direction was accompanied.

• Wind and Structures
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• v.36 no.3
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• pp.201-213
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• 2023

In this study, the effect of sea surface temperature (SST) on the distribution of vertical wind speed in the atmospheric boundary layer of coastal areas was analyzed. In general, coastal areas are known to be more susceptible to various meteorological factors than inland areas due to interannual changes in sea surface temperature. Therefore, the purpose of this study is to analyze the relationship between sea surface temperature (ERA5) and wind resource data based on the meteorological mast of Høvsøre, the test bed area of the onshore wind farm in the coastal area of Denmark. In addition, the possibility of coastal disasters caused by abnormal vertical wind shear due to changes in sea surface temperature was also analyzed. According to the analysis of the correlation between the wind resource data at met mast and the sea surface temperature by ERA5, the wind speed from the sea and the vertical wind shear are stronger than from the inland, and are vulnerable to seasonal sea surface temperature fluctuations. In particular, the abnormal vertical wind shear, in which only the lower wind speed was strengthened and appeared in the form of a nose, mainly appeared in winter when the atmosphere was near-neutral or stable, and all occurred when the wind blows from the sea. This phenomenon usually occurred when there was a sudden change in sea surface temperature within a short period of time.

• Computers and Concrete
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• v.29 no.2
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• pp.81-92
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• 2022

The influence of normal stress perpendicular to the potential shear plane was always neglected in existing researches, which may lead to a serious deviation of the shear strength of concrete members in practice designs and numerical analyses. In this study, a series of experimental studies are carried out in this paper, which serves to investigate the shear behavior of concrete under compression shear loading. Based on the test results, a three-phase shear failure model for cohesive elements are developed, which is able to take into consideration the influence of normal stress on the shear strength of concrete. To identify the accuracy and applicability of the proposed model, numerical models of a double-noted concrete plate are developed and compared with experimental results. Results show that the proposed constitutive model is able to take into consideration the influence of normal stress on the shear strength of concrete materials, and is effective and accurate for describing the complex fracture of concrete, especially the failure modes under compression shear loadings.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.399-406
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• 2016

The large scale wind turbine blades usually experience periodic change of inflow speed due to blade rotation inside the ground shear flow region. Because of the vertical wind shear, the inflow velocity in the boundary layer region is maximum at uppermost position and minimum at lowermost position. These spatial distribution of wind speeds can lead to the periodic oscillation of the 6-component loads at hub and low speed shaft of the wind turbine rotor. In this study we compare the aerodynamic loads between two inflow conditions, i.e, uniform flow (no vertical wind shear effect) and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially bending moment and thrust at hub, and bending moments at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue analysis.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.387-390
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• 2007

Recently the diameter of the 5MW wind turbine reaches 126m, and the tower height is nearly the same with the wind turbine diameter. The blade will experience periodic inflow oscillation due to blade rotation inside the ground shear flow region, that is, the inflow velocity is maximum at uppermost position and minimum at lowermost position. In this study we compare the aerodynamic data between two inflow conditions, i.e, uniform flow and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially My at hub and $F_x$, $M_y$, $M_z$ at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue load analysis.

• Journal of Korean Association for Spatial Structures
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• v.11 no.1
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• pp.47-56
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• 2011

In general, shear walls are employed as lateral resistance system. Most of shear wall structures require openings in shear walls and thus shear walls are linked by floor slabs or coupling beams resulting in the coupled shear wall structures. In this study, an LRB (lead rubber bearing) was introduced in the middle of the coupling beam of the coupled shear wall structures and the wind-induced response reduction effect of this system was investigated. In order to evaluate the control performance of the proposed method, 20- and 30-story building structures were used as example structures and boundary nonlinear time history analyses have been performed using artificial wind excitation. Japanese vibration evaluation criteria was employed to evaluate whether the proposed system could improve the serviceability of the tall coupled shear wall structures under wind excitation. Based on analytical results, it has been shown that the proposed method that connects shear walls with LRBs can improve the wind-induced response control effect.

• Computers and Concrete
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• v.33 no.5
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• pp.509-518
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• 2024

In this study, we investigated the effect of shear-key placement on the performance of grouted connections in offshore wind-turbine structures. Considering the challenges of height control during installation, we designed and analyzed three grouted connection configurations. We compared the crack patterns and strain distribution in the shear keys under axial loading. The results indicate that the misalignment of shear keys significantly influences the ultimate load capacity of grouted connections. Notably, when the shear keys were positioned facing each other, the ultimate load decreased by approximately 15%, accompanied by the propagation of irregular cracks in the upper shear keys. Furthermore, the model with 50% misalignment in the shear-key placement exhibited the highest ultimate strength, indicating a more efficient load resistance than the reference model. This indicates that tensile-load-induced cracking and the formation of compressive struts in opposite directions significantly affect the structural integrity of grouted connections. These results demonstrate the importance of considering buckling effects in the design of grouted connections, particularly given the thin and slender nature of the inner sleeves. This study provides valuable insights into the design and analysis of offshore wind-turbine structures, highlighting the need for refined design formulas that account for shifts in shear-key placement and their structural implications.

• Atmosphere
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• v.33 no.4
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• pp.413-422
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• 2023

Urban Air Mobility (UAM) is promising, sustainable and efficient air transportation in a metropolitan area. Korean government has recently announced operation demonstration plans as a step toward commercialization of UAM. However, there is lack of understanding on the potential impact of weather on UAM operation. We collected weather observations from Gimpo International Airport and 5 automatic weather stations (AWS) along UAM corridor of the Han-River to assess weather barriers such as low visibility, wind gust and wind shear. The results show the frequency of low visibility near the corridor fluctuated significantly from year to year depending on the concentration of fine particulate matter (PM_2.5) in Seoul. The frequency of high wind speed-shift calculated using 1-minute wind observations was increased not only during the spring season (March, April, and May) but also the beginning of rainy season (Jun). In addition, a chance of high wind shear from 1-minute wind observations varied by the stations, suggesting that the condition is largely affected by topography including a river and high-rise buildings. These basic weather properties suggest that there are substantial weather barriers to UAM operations along the Han-River Corridor, while they cannot properly surveil micro-scale weather conditions in detail such as wind gust and wind shear over the corridor. Thus, this study suggests that potential barriers related to adverse weather need to be evaluated, building high-density weather observations infrastructure prior to UAM demonstration and commercialization.