• The Korean Journal of Ecology
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• v.17 no.4
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• pp.533-545
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• 1994

The bleeding of 39 Acer mono trunks by wounding was investigated at the altitudes of 400m, 500m, 800m, and 1100m on Wangsirobong (1,214m), Mt. Chiri area (127°34'E., 35°14'N.) from February 4 to March 21, 1993 and from February 23 to March 23, 1994. The amount of sap in a day was clodely related to the change of air temperature and wind speed. Especially, the abundant sap was exudated at the ranges of -4~13℃ in the daily range of temperature and it was below 0.14m/s in wind speed. The most abundant bleeding was exudated from Acer mono trunk located south facing slope in 800m altitude. Also the amount of sap increased with incereasing suface area of crown. The maximum bleeding of sap was collected from the hole punctured at 80cm height from the ground surface at southern part of the trunks. And the number of exudation holes had an important effect on bleeding of sap but the number of holes should be controlled by DBH of trunks. These results suggested that the exudation was influenced by the daily range of temperature and wind speed. And the altitude, direction of sloped where the trees occurred, surface area of crown, the number of exudation holes, height form the ground surface and the direction of the hole was 91.6% when germicide (Dimethyl-4,4' -ophenylene bis 3-thio alonate) was treated from April to October after bleeding of sap in the year.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.27-33
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• 2012

This paper describes a new design of small-scale horizontal wind blade, called spiral wind turbine blade. Theoretical and numerical approaches on the prediction of aerodynamic performance of the blade have been conducted. A theoretical equation is successfully derived using the angular momentum equation to predict aerodynamic characteristics according to the design shape parameters of spiral blade. To be compared with the theoretical value, a numerical simulation using ANSYS CFX v12.1 is performed on the same design with the theoretical one. Large scale tip vortex is captured and graphically presented in this paper. The TSR-$C_p$ diagram shows a typical parabolic relation in which the maximum efficiency of the blade approximately 25% exists at TSR=2.5. The numerical simulation agrees well with that of the theoretical result except at the low rotational speed region of 0~20 rad/s.

• Journal of the Korean Solar Energy Society
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• v.33 no.1
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• pp.40-47
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• 2013

An aerodynamic design tool was developed for small wind turbine blades based on the blade element momentum theory. The lift and drag coefficients of blades that are needed for aerodynamic blade design were obtained in real time from the Xfoil program developed at University of Illinois. While running, the developed tool automatically accesses the Xfoil program, runs it with proper aerodynamic and airfoil properties, and finally obtains lift and drag coefficients. The obtained aerodynamic coefficients are then used to find out optimal twist angles and chord lengths of the airfoils. The developed tool was used to design a wind turbine blade using low Reynolds number airfoils, SG6040 and SG6043 to have its maximum power coefficient at a specified tip speed ratio. The performance of the blade was verified by a commercial code well known for its prediction accuracies.

• Journal of the Korean Solar Energy Society
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• v.38 no.2
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• pp.1-13
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• 2018

This paper deals with the NREL (National Renewable Energy Laboratory) 5-MW reference wind turbine. The controller which include MPPT (Maximum power point tracking) control algorithm and tower load reduction control algorithm was designed by MATLAB Simulink. This paper propose a tower damper algorithm to improve the existing tower damper algorithm. To improve the existing tower damper algorithm, proposed tower damper algorithm were applied the thrust sensitivity scheduling and PI control method. The thrust sensitivity scheduling was calculated by thrust force formula which include thrust coefficient table. Power and Tower root moment DEL (Damage Equivalent Load) was set as a performance index to verify the load reduction algorithm. The simulation were performed 600 seconds under the wind conditions of the NTM (Normal Turbulence Model), TI (Turbulence Intensity)16% and 12~25m/s average wind speed. The effect of the proposed tower damper algorithm is confirmed through PSD (Power Spectral Density). The proposed tower damper algorithm reduces the fore-aft moment DEL of the tower up to 6% than the existing tower damper algorithm.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.749-751
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• 1998

In this study, the wind-mill type ultrasonic motor was fabricated, and then revolution and temperature characteristics of the ultrasonic motor were measured. Brass metal was pressed with umbrella-type using metal mold, then slot of 4 kind was processed in each of thickness. Among sixteen's ultrasonic motors, heat loss on applied voltage was much at stator of the highest resonant point, but heat loss on applied voltage was almost neglected at the lowest resonant point of stator. The thickener thickness of elastic body, revolution speed was decreased. The more slot of elastic body, revolution speed was increased. Applied voltage was changed from $10V_{max}$ to $100V_{max}$. When applied voltage was under $20V_{max}$, ultrasonic motor was not rotated. When applied voltage was over $90V_{max}$, revolution of ultrasonic motor was saturated. Maximum revolution speed was 510[rpm].

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.3
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• pp.274-284
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• 2003

The analysis of wave parametric characteristics in sea regions in the vicinity of Korean Peninsula have been carried out using the third generation wave model, WAVEWATCH-III (Tolman, 1999) and four observed buoy data of Korea Meteorological Administration (KMA). Significant wave height increases about 2-3 hours later after the increase of wind speed. Maximum correlation coefficient between two parameters appears in Donghae buoy data, which is at off-shore region. When land breeze occurs, it can be found that the correlation coefficient decreases. Time differences between wind speeds and wave heights correspond to significant tidal periods at all of the buoy locations except for Donghae buoy. After verifying the WAVEWATCH-III model results by the comparing with observed buoy data, we have carried out numerical experiments near the Kuroshio current and East Sea areas, and then reconfirmed that when there exist an opposite strong current in the propagation direction of the waves or wind direction, wave height and length get higher and shorter, respectively and vice versa. It has been shown that these modulations of wave parameters are considerable when wind speed is week or mean current is relatively strong, and corresponding values have been represented.

• Journal of The Korean Society of Grassland and Forage Science
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• v.36 no.1
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• pp.1-6
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• 2016

The growth of Italian ryegrass (IRG) after wintering was very low in 2015 when IRG was broadcasted under growing rice in fall of 2014. To determine growth inhibitory factors of IRG, we examined the growth conditions of IRG in Nonsan region and meteorological conditions in Daejeon nearby Nonsan. Minimum temperature and maximum instantaneous wind speed on Feb. $8^{th}$ and $9^{th}$ of 2015 after wintering of IRG were $8.8^{\circ}C$, 10.7 m/s and $12.4^{\circ}C$, 9.6m/s, respectively. Air temperature was suddenly dropped due to strong wind with snow showers, which had unfavorable effect on root growth of IRG exposed at the soil surface. The minimum temperature and maximum instantaneous wind speed on Feb. $12^{th}$, $13^{th}$, and $14^{th}$ of 2015 were $4.1^{\circ}C$, 11.6 m/s, $-5.6^{\circ}C$, 10.3 m/s, and $-4.7^{\circ}C$, 7.5 m/s, respectively. The growth circumstance of IRG was not good because soil was dried due to drought continued from January. The minimum temperature and maximum instantaneous wind speed on Feb. $26^{th}$, $27^{th}$, and $28^{th}$ of 2015 were $1.8^{\circ}C$, 13.7 m/s, $-3.5^{\circ}C$, 10.6 m/s, and $4.1^{\circ}C$, 6.8 m/s, respectively. The number of wilting of IRG was more than 59% until Mar. $3^{rd}$ of 2015. IRG faced irreparable environment (low minimum temperatures and extreme instantaneous wind speeds) for 9 days from Mar. $4^{th}$ to Mar. $12^{th}$ of 2015. The main reason for the decrease of IRG productivity was collection delay of rice straw after rice harvest because there was continuous rain between Oct. and Nov. of 2014. For this reason, weakly grown IRG under rice straw was withered after wintering. IRG was withered by frost heaving, drought, and instantaneous wind speed in the spring. Furthermore, the root of IRG was damaged while growing in excess moisture in the surface of paddy soil during the winter season due to rain.

• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.395-402
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• 2006

When an active SONAR works in the subsurface. its detection Performance is limited by the reverberation. The winds Play a primary role in the Production of bubbles in the ocean. And the bubbles as efficient scatters contribute to the reverberant field. In this Paper the effects of wind-generated bubbles on sound propagation in the subsurface are investigated as a mid-frequency Hull-mounted SONAR works. The active signal excess is calculated at source depths 3. 5. and 10m considering bubble layer for frequencies 5. 7.5, and 10kHz. The change of the near-surface sound speed tend to increase surface reverberation levels and change the active signal excess. In the 10m/s winds. the maximum detection range reduces over 3km through the near-surface . The reason is the upper refraction due to the wind-generated bubbles.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.1
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• pp.11-15
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• 2011

In this paper, a methodology for the power control of a wind turbine, which is the variable-speed and variable-pitch (VSVP) control system, is introduced. This control methodology maximizes the capability of the turbine to extract maximum power from the wind in the regions with low wind speeds. Further, it regulates the wind-turbine power as the rated power in the case of the regions with high wind speeds. A simple drive train model is used to design the VSVP control system. The methodology for VSVP control is mechanized by controlling the generator torque and blade pitch. Finally, some simulation results for the VSVP control to a MW wind turbine are discussed in this paper.

• Journal of Korean Society of Disaster and Security
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• v.6 no.2
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• pp.1-8
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• 2013

This study is concerned with the estimation of fluctuate wind velocity statistic properties in the major cities reflecting the recent meteorological with largest data samples (yearly 2003-2012). The basic wind speeds were standardized homogeneously to the surface roughness category C, and to 10m above the ground surface. The estimation of the extreme of non-Gaussian load effects for design applications has often been treated tacitly by invoking a conventional wind design (gust load peak factor) on the basis of Gaussian processes. This assumption breaks down when the loading processes exhibits non-Gaussianity, in which a conventional wind design yields relatively non conservative estimates because of failure to include long tail regions inherent to non-Gaussian processes. This study seeks to ascertain the probability distribution function from recently wind data with effected typhoon & maximum instantaneous wind speed.