• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.12
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• pp.2256-2261
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• 2010

A corona discharge system with needle point or wire type corona electrode has been well used as an ionic wind blower. The corona discharge system with a needle point electrode produces ions at lower applied voltage effectively. However, the corona discharge on the needle point electrode transits to the arc discharge at lower voltage, and it is hard to obtain the elevated electric field in the discharge airgap for enhancing the ion migration velocity due to the weak Coulomb force. A cylindrical corona electrode with sharp round tip is reported as one of effective corona electrode, because of its higher breakdown voltage than that of the needle electrode. A basic study, for the effectiveness of cylindrical electrode shape on the ionic wind generation, has been investigated to obtain an maximum wind velocity, which however is the final goal for the real field application of this kind ionic wind blower. In this paper, a parametric study for maximizing the ionic wind velocity utilizing the cylindrical corona electrode and a maximum ion wind velocity of 4.1 m/s were obtained, which is about 1.8 times higher than that of 2.3m/s obtained with the needle corona electrode from the velocity profile.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.4
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• pp.206-216
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• 2013

The present study considers the prediction of wind-induced heel of cruise ship and its stabilization. Wind load in ocean exerts on the surface of superstructure of cruise ship, which causes the heel moment on the ship. The calculation of wind load starts from choosing wind speed profile, so that the logarithmic wind profile model is applied in this study. Heel moment by wind load is calculated by adopting approximate formulation and applied to the ship motion analysis in time domain. Motion stabilizers, such as stabilizing fin and U-tube tank, are considered to reduce the heel effect as well as excessive roll motion. From this study, it is expected that the present method can be applied to the prediction and stabilization of the heel motion of cruise ships.

• Journal of Korean Society for Geospatial Information Science
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• v.20 no.2
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• pp.15-22
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• 2012

The variation in the wind speed with height above ground is called the wind shear profile. In the field of wind resource assessment, analysts typically use one of two mathematical relations to characterize the measured wind shear profile: the logarithmic profile (log law) and the power law profile (power law). The logarithmic law uses the surface roughness as a parameter, and the power law uses the power law exponent as a parameter. The shape of the wind shear profile typically depends on several factors, most notably the roughness of the surrounding terrain and the stability of the atmosphere. Since the atmospheric stability changes with season, time of day, and meteorological conditions, the surface roughness and the power law exponent also tends to change in time. For this study, Using the observed data from Met-mast, located in Pyeongdae, Handong in Jeju. we used the matlab and windograper to calculate roughness length and the law exponents. These calculations are similar to reference the data, but they have different ranges. In the ocean case, each reference data and calculated data was the same, but the crop area is higher than the earlier studies. In addition, the agricultural village is lower than the earlier studies.

• Journal of Biosystems Engineering
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• v.26 no.3
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• pp.221-228
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• 2001

Chemical application, one of the most important crop management processes happened to cause spray drift, that would threaten farmers in field as well as dwellers in rural region. Spray drift was affected by micro-meteorological parameters. A study to evaluate short distance drift characteristics of a boom sprayer in paddy fields has been undergoing. This study is the first step of the research. Main purpose of the was conducted to develop a mean wind profile and to get information on turbulence intensities above and within rice canopy. Wind in rice paddy field were measured at every 10cm from 10 to 180cm above the ground using a 2-dimensional probe and a hot wire anemometer system. Main results were summarized as follows. 1. Mean wind profile was modeled as; Equations. see full-text 2. Roughness length and zero-displacement in rice canopy were analyzed to be respectively 0.04 and 0.7∼0.72 times of the canopy height. The values are smaller comparing to those of other crops because rice canopy is flexible and uniform comparing to other crops. 3. Turbulence intensities (Tl) was greater as close to the ground and became constant at heights greater than 1.5Hc. where Tl’s were 0.4 and 0.15 in horizontal and vertical direction respectively.

• Wind and Structures
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• v.28 no.4
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• pp.203-213
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• 2019

The topography and geomorphology are complex and changeable in western China, so the railway transition section is common. To investigate the aerodynamic effect of the subgrade-tunnel transition section, including a cutting-tunnel transition section, an embankment-tunnel transition section and two typical scenarios for rail infrastructures, is selected as research objects. In this paper, models of standard cutting, embankment and CRH2 high-speed train with the scale of 1:20 were established in wind tunnel tests. The wind speed profiles above the railway and the aerodynamic forces of the vehicles at different positions along the railway were measured by using Cobra probe and dynamometric balance respectively. The test results show: The influence range of cutting-tunnel transition section is larger than that of the embankment-tunnel transition section, and the maximum impact height exceeds 320mm (corresponding to 6.4m in full scale). The wind speed profile at the railway junction is greatly affected by the tunnel. Under the condition of the double track, the side force coefficient on the leeward side is negative. For embankment-tunnel transition section, the lift force coefficient of the vehicle is positive which is unsafe for operation when the vehicle is at the railway line junction.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.1
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• pp.9-17
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• 2022

In this paper, wind load on a semi-submersible rig was investigated using Computational Fluid Dynamics (CFD). A maritime atmospheric boundary layer model for wind profile was implemented such that the wind profile shapes were retained throughout the computational domain. Wind load on the semi-submersible rig was calculated under the maritime atmospheric boundary layer and matched well with the results from wind tunnel test within a ±20% error. Overturning moments with variation of draft were investigated by decomposing into drag and lift components. It was observed that the contribution from lift to the overturning moments increased as the draft got higher. The majority of the lift components originated from deckbox which served as a lifting body due to the accelerated streamlines between waterline and the bottom of the deckbox.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.2
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• pp.109-117
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• 2014

This paper reports a method to modify the gear tooth profile of a wind turbine gearbox to reduce the noise caused by the impact of the gear teeth. The major causes of tooth impact are the elastic deformation of the gear teeth, shafts, and case of the gearbox under loading, and the fabrication tolerances in gear manufacturing. In this study, the tooth profile was modified considering the elastic deformation of the gear tooth and the tooth lead modification to compensate for tooth interference in the lead direction as a result of shaft deformations. The method was applied to the gearbox of a 2.5MW wind turbine, and the transmission error was characterized before and after modifying the gear teeth. For the modified gear teeth, the transmission error (67.6%) was lower by 17.8%. Additionally, the gear contact stress was reduced by 6.3%, to 22.3%.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.118-124
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• 2012

The simulation of the air flow over models in atmospheric boundary layer wind tunnel is a research region based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid dynamics in the proximity of the Earth's surface. In this study, the atmospheric boundary layer wind tunnel of UCD is used, the mean velocities are measured by augmentation devices such as roughness blocks and spires. The experimental results of mean velocity profile are well fitted with the value of power law.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.5
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• pp.965-970
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• 2023

Wind profiler and wind lidar produce a vertical profile of winds in high spatiotemporal resolution in the atmospheric boundary layer. The wind lidar makes the wind vector using DBS (Doppler Beam Swinging) and VAD (Velocity Azimuth Display) methods. The DBS method has the advantage of obtaining a wind profile with a fast scan time. On the other hand, there is a restriction that requires at least two beams including vertical beam, which causes a decrease in the data acquisition rate. The VAD method was improved to produce more wind vector of the wind profiler as well as the wind lidar, which generally uses 5 beams. Fourier series was estimated with the radial velocity by the DBS method and wind vector was determined by setting the azimuth interval and applying the radial velocity by the Fourier series to the VAD method. The wind vectors were retrieved at the altitude where the wind was not calculated by the DBS method, and the results of the two methods were consistent.

• Wind and Structures
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• v.38 no.2
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• pp.129-146
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• 2024

Aiming at the problem of non-stationary wind field simulation of downbursts, a non-stationary down-burst generation system was designed by adding a nozzle and program control valve to the inlet of the original wall jet model. The computational fluid dynamics (CFD) method was used to simulate the downburst. Firstly, the two-dimensional (2D) model was used to study the outflow situation, and the database of working conditions was formed. Then the combined superposition of working conditions was carried out to simulate the full-scale measured downburst. The three-dimensional (3D) large eddy simulation (LES) was used for further verification based on this superposition condition. Finally, the wind tunnel test is used to further verify. The results show that after the valve is opened, the wind ve-locity at low altitude increases rapidly, then stays stable, and the wind velocity at each point fluctuates. The velocity of the 2D model matches the wind velocity trend of the measured downburst well. The 3D model matches the measured downburst flow in terms of wind velocity and pulsation characteris-tics. The time-varying mean wind velocity of the wind tunnel test is in better agreement with the meas-ured time-varying mean wind velocity of the downburst. The power spectrum of fluctuating wind ve-locity at different vertical heights for the test condition also agrees well with the von Karman spectrum, and conforms to the "-5/3" law. The vertical profile of the maximum time-varying average wind veloci-ty obtained from the test shows the basic characteristics of the typical wind profile of the downburst. The effectiveness of the downburst generation system is verified.