• Journal of Ecology and Environment
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• v.45 no.2
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• pp.78-87
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• 2021

Background: To understand shade and wind effects on seedling traits of common reed (Phragmites australis), we conducted a mesocosm experiment manipulating day length (10 h daytime a day as open canopy conditions or 6 h daytime a day as partially closed canopy conditions) and wind speed (0 m/s as windless conditions or 4 m/s as windy conditions). Results: Most values of functional traits of leaf blades, culms, and biomass production of P. australis were higher under long day length. In particular, we found sole positive effects of long day length in several functional traits such as internode and leaf blade lengths and the values of above-ground dry weight (DW), rhizome DW, and total DW. Wind-induced effects on functional traits were different depending on functional traits. Wind contributed to relatively low values of chlorophyll contents, angles between leaf blades, mean culm height, and maximum culm height. In contrast, wind contributed to relatively high values of culm density and below-ground DW. Conclusions: Although wind appeared to inhibit the vertical growth of P. australis through physiological and morphological changes in leaf blades, it seemed that P. australis might compensate the inhibited vertical growth with increased horizontal growth such as more numerous culms, indicating a highly adaptive characteristic of P. australis in terms of phenotypic plasticity under windy environments.

• Smart Structures and Systems
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• v.19 no.6
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• pp.653-663
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• 2017

The modal parameters of the deck of Runyang Suspension Bridge (RSB) as well as their relationships with wind and temperature are studied based on the data recorded by its Structural Health Monitoring System (SHMS). Firstly, frequency analysis on the vertical responses at the two sides of the deck is carried out to distinguish the vertical and torsional vibration modes. Then, the vertical, torsional and lateral modal parameters of the deck of RSB are identified using Hilbert-Huang Transform (HHT) and validated by the identified results before RSB was opened to traffic. On the basis of this, the modal frequencies and damping ratios of RSB during the whole process of Typhoon Masta are obtained. And the correlation analysis on the modal parameters and wind environmental factors is then conducted. Results show that the HHT can achieve an accurate modal identification of RSB and the damping ratios show an obvious decay trend as the frequencies increase. Besides, compared to frequencies, the damping ratios are more sensitive to the environmental factors, in particular, the wind speed. Further study on configuring the variation law of modal parameters related with environmental factors should be continued.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.22 no.1
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• pp.24-32
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• 1994

A special upper-air observation including airsonde and pibal observations was performed to investigate the characteristics features of the vertical distribution of the meteorological elements over Taegu on a selected clear day of each season from October 1991 to August 1992. The diurnal and seasonal variations of the vertical profiles of air temperature and mixing ratio were obtained from airsonde observations and wind speed and direction from pibal observations. The results of these special upper-air observations are as follow : The diurnal variation of the vertical distribution of air temperature reveals the characteristic features associated with the atmospheric boundary layer. All case days, except for the summer season, show upper-level inversion layer which influenced by surface high, and surface inversion layer produced by radiative cooling. The diurnal variation of mixing ratio shows the maximum vale at 1500 LST in both the upper and low levels, and is larger on the lower level than the upper level. The mixing ratio of the lower level is larger than that of the upper level. On the average the mixing ratio decrease with the height, and is the wettest on the summer case day and the driest on the winter case day. The diurnal variation of the wind velocity and direction are variable in the lower level with time and height, while they are steady in the upper level. On the average, the wind direction is southerly or southeasterly for the summer case day, westerly or northwesterly for the spring and fall case days, and northerly or northwesterly for the winter case day.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.2
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• pp.94-100
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• 2013

A convergent-divergent nozzle or venturi nozzle has been used to accelerate the wind speed at its throat. The wind speed at the throat is inversely proportional to its area according to the continuity equation. In this numerical study, an airflow phenomena in the venturi system placed at a vertical structure was investigated to understand the vortex effect occurred at the rear-side of the vertical structure on the air speed increment at the throat of the venturi system. For this study, a venturi system sized by $20(m){\times}20(m){\times}6(m)$ was modelled and the area ratio(AR) of the model venturi was 2.86. To see the vortex effect on the air flow acceleration in the venturi throat, two different boundary conditions was defined From the study, it was found that the pressure coefficient(CP) of the venturi system with the vortex formed at the exit of the venturi was about 2.5times of the CP of the venturi system without the vortex effect. The velocity increment rate of the venturi system with the vortex was 61% but 9.5% only at the venturi system without the vortex. Conclusively, it can be said that the venturi system installed in a vertical structure has very positive effect on the flow acceleration at its throat due to the vortex formed at the rear-side of the vertical structure.

• Wind and Structures
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• v.17 no.6
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• pp.647-670
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• 2013

The paper presents a numerical approach to study of fluid flow characteristics and to predict performance of wind turbines. The numerical model is based on Finite-volume method (FVM) discretization of unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The movement of turbine blades is modeled using moving mesh technique. The turbulence is modeled using commonly used turbulence models: Renormalization Group (RNG) k-${\varepsilon}$ turbulence model and the standard k-${\varepsilon}$ and k-${\omega}$ turbulence models. The model is validated with the experimental data over a large range of tip-speed to wind ratio (TSR) and blade pitch angles. In order to demonstrate the use of numerical method as a tool for designing wind turbines, two dimensional (2-D) and three-dimensional (3-D) simulations are carried out to study the flow through a small scale Darrieus type H-rotor Vertical Axis Wind Turbine (VAWT). The flows predictions are used to determine the performance of the turbine. The turbine consists of 3-symmetrical NACA0022 blades. A number of simulations are performed for a range of approaching angles and wind speeds. This numerical study highlights the concerns with the self-starting capabilities of the present VAWT turbine. However results also indicate that self-starting capabilities of the turbine can be increased when the mounted angle of attack of the blades is increased. The 2-D simulations using the presented model can successfully be used at preliminary stage of turbine design to compare performance of the turbine for different design and operating parameters, whereas 3-D studies are preferred for the final design.

• Atmosphere
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• v.33 no.5
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• pp.441-456
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• 2023

The mobile observation method, in which a meteorological drone observes while ascending, can observe the vertical profile of wind at 1 m-interval. In addition, since continuous flights are possible at time intervals of less than 30 minutes, high-resolution observation data can be obtained both spatially and temporally. In this study, we verify the accuracy of mobile observation data from meteorological drone (drone) and fill the spatio-temporal observation gaps in the lower atmosphere. To verify the accuracy of mobile observation data observed by drone, it was compared with rawinsonde observation data. The correlation coefficients between two equipment for a wind speed and direction were 0.89 and 0.91, and the root mean square errors were 0.7 m s^-1 and 20.93°. Therefore, it was judged that the drone was suitable for observing vertical profile of the wind using mobile observation method. In addition, we attempted to resolve the observation gaps in the lower atmosphere. First, the vertical observation gaps of the wind profiler between the ground and the 150 m altitude could be resolved by wind observation data using the drone. Secondly, the temporal observation gaps between 3-hour interval in the rawinsonde was resolved through a drone observation case conducted in Taean-gun, Chungcheongnam-do on October 13, 2022. In this case, the drone mobile observation data every 30-minute intervals could observe the low-level jet more detail than the rawinsonde observation data. These results show that the mobile observation data of the drone can be used to fill the spatio-temporal observation gaps in the lower atmosphere.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.5
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• pp.1455-1461
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• 2014

In this study, using flux data measured in Deokgokje reservoir watershed near Deokyu mountain in May, June, and July 2011, statistical analysis was conducted for outlier detection and replacement for vertical wind speed in the measurement of evapotranspiration based on eddy covariance method. To statistically analyze the outliers of vertical wind speed, the outlier detection method based on interquartile range (IQR) in boxplot was employed and the detected outliers were deleted or replaced with mean. The comparison was conducted for the measured evapotranspiration before and after the outlier replacement. The study results showed that there is a difference between evapotranspiration before outlier replacement and evapotranspiration after outlier replacement, especially during the rainy day. Therefore, based on the study results, the outliers should be deleted or replaced in the measurement of evapotranspiration.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.498-500
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• 2009

When we urgently need to develop and supply an alternative energy, wind power is growing with much interest because it has relative low cost for generating power and small area for wind turbine. To estimate the wind power resource, it is necessary to make an observation first. Although the large wind farm and resources are near coast and mountain area, the wind energy in urban area has the strong thing of direct access to power generator. In this study, we estimate the probability of wind energy in urban mountain area using A2C (Atmospheric to CFD) model, which is used for horizontally urban scale phenomena. In the steady state results, the site C is most suitable for wind power in the point of the only wind speed. But, estimating the TKE and vertical wind shear, the site B is showing the better results than the site C.

• Journal of Environmental Science International
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• v.21 no.4
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• pp.517-533
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• 2012

This study calculated wind speed at the height of 10 m using a disaster prediction model(Florida Public Hurricane Loss Model, FPHLM) that was developed and used in the United States. Using its distributions, a usable information of surface wind was produced for the purpose of disaster prevention when the typhoon attack. The advanced research version of the WRF (Weather Research and Forecasting) was used in this study, and two domains focusing on South Korea were determined through two-way nesting. A horizontal time series and vertical profile analysis were carried out to examine whether the model provided a resonable simulation, and the meteorological factors, including potential temperature, generally showed the similar distribution with observational data. We determined through comparison of observations that data taken at 700 hPa and used as input data to calculate wind speed at the height of 10 m for the actual terrain was suitable for the simulation. Using these results, the wind speed at the height of 10 m for the actual terrain was calculated and its distributions were shown. Thus, a stronger wind occurred in coastal areas compared to inland areas showing that coastal areas are more vulnerable to strong winds.

• International Journal of Fluid Machinery and Systems
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• v.7 no.1
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• pp.16-27
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• 2014

Double-blade vertical axis wind turbines (DB-VAWTs) can improve the self-starting performance of lift-driven VAWTs. We here propose the quadruple-multiple streamtube model (QMS), based on the blade element momentum (BEM) theory, for simulating DB-VAWT performance. Model validity is investigated by comparison to computational fluid dynamics (CFD) prediction for two kinds of two-dimensional DB-VAWT rotors for two rotor scales with three inner-outer radius ratios: 0.25, 0.5, and 0.75. The BEM-QMS model does not consider the effects of an inner rotor on the flow speed in the upwind half of the rotor, so we introduce a correction factor for this flow speed. The maximum power coefficient predicted by the modified BEM-QMS model for a DB-VAWT is thus closer to the CFD prediction.