• Wind and Structures
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• v.31 no.4
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• pp.351-362
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• 2020

In this study, the impact of roof slope on the flow characteristics over low-sloped gable roofs was investigated using steady computational fluid dynamics (CFD) simulations based on a k-ω SST turbulence model. A measurement database of the flow field over a scaled model of 15° was created using particle image velocimetry (PIV). Sensitivity analyses for the grid resolutions and turbulence models were performed. Among the three common Reynolds-averaged Navier-Stokes equations (RANS) models, the k-ω SST model exhibited a better performance, followed by the RNG model and then the realizable k-ε model. Next, the flow properties over the differently sloped (0° to 25°) building models were determined. It was found that the effect of roof slope on the flow characteristics was identified by changing the position and size of the separation bubbles, 15° was found to be approximately the sensitive slope at which the distribution of the separation bubbles changed significantly. Additionally, it is suggested additional attention focused on the distributions of the negative pressure on the windward surfaces (especially 5° and 10° roofs) and the possible snow redistribution on the leeward surfaces.

• Wind and Structures
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• v.26 no.1
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• pp.35-43
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• 2018

This paper describes the effect of different testing parameters (configuration of infrastructure and truck position on road) on truck aerodynamic coefficients under cross wind conditions, by means of a numerical approach known as Large Eddy Simulation (LES). In order to estimate the air flow behaviour around both the infrastructure and the truck, the filtered continuity and momentum equations along with the Smagorinsky-Lilly model were solved. A solution for these non-linear equations was approached through the finite volume method (FVM) and using temporal and spatial discretization schemes. As for the results, the aerodynamic coefficients acting on the truck model exhibited nearly constant values regardless of the Reynolds number. The flat ground is the infrastructure where the rollover coefficient acting on the truck model showed lowest values under cross wind conditions (yaw angle of $90^{\circ}$), while the worst infrastructure studied for vehicle stability was an embankment with downward-slope on the leeward side. The position of the truck on the road and the value of embankment slope angle that minimizes the rollover coefficient were determined by successfully applying the Response Surface Methodology.

• New & Renewable Energy
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• v.4 no.2
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• pp.87-93
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• 2008

Wind tunnel test for the 12% scaled model of NREL Phase VI wind turbine was conducted in KARI low speed wind tunnel for $2006{\sim}2007$. The 1st and 2nd test was designed to find out the wind tunnel test method for the blade manufacturing accuracy and surface treatment method by using the composite and aluminum blades. And the 3rd test was designed to study the scale effect. The chord extension method which was used for Bo-105 40% scaled model was adapted for scale effect correction. Test results shows that the chord extension method works well for the torque slope but the maximum torque for scaled model is about 8% below than the real scale model. New correction method to correct this offset was proposed.

• Journal of the Korean Solar Energy Society
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• v.28 no.6
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• pp.1-7
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• 2008

The wind resource potentials of South Korea are estimated as preliminary stage using the national wind map which has been being established by numerical wind simulation and GIS (Geographical Information System) exclusion analysis. The wind resource potentials are classifying into theoretical, geographical, technical and implementation potentials and the calculation results are verified by comparing to other countries' potentials. In GIS exclusion, urban, road, water body, national parks and steep slope area are excluded from onshore geographical potential while water depth and offshore distance from the shoreline are applied as offshore exclusion conditions. To estimate implementation potential, dissemination records of European countries are adopted which is about 1/8 of geographical potential. The implementation potential of South Korea would correspond 12.5GW which is 1.7 times of the national wind energy dissemination target until 2030.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.245-255
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• 2009

The low-rise buildings with gable roofs are commonly used in a number of industries. In order to study the characteristics of peak external pressure coefficient on low-rise buildings with gable roofs, wind-tunnel test have been carried out. Wind-induced pressures were measured simultaneously at many points on wind-pressure models, typical of simple low-rise buildings with gable roofs, which have seven different roof slope with constant width(D), height(H), and length(D). The pressure measurements were made in one kind of turbulent boundary layer, which simulated the natural winds over typical suburban terrains at a geometric scale of 1/150. The results indicate that peak external pressure coefficient on the roof and wall edges were increased. The results compared with wind standard of KBC-2005 and standards of various nations. The comparative resultant, experimental result appeared very similar at AIJ-2004. But the results were somewhat larger then wind standard of KBC-2005.

• 한국태양에너지학회:학술대회논문집
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• 2008.11a
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• pp.310-313
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• 2008

The wind resource potentials of South Korea are estimated as preliminary stage using the national wind map which has been being established by numerical wind simulation and GIS (Geographical Information System) exclusion analysis. The wind resource potentials are classifying into theoretical, geographical, technical and implementation potentials and the calculation results are verified by comparing to other countries' potentials. In GIS exclusion, urban, road, water body, national parks and steep slope area are excluded from onshore geographical potential while water depth and offshore distance from the shoreline are applied s offshore exclusion conditions. To estimate implementation potential, dissemination records of European countries are adopted which is about 1/8 of geographical potential.

• New & Renewable Energy
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• v.3 no.3
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• pp.54-62
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• 2007

The present paper describes the scale effect correction methods for scaled NREL Phase VI wind turbines by using CFD[computational fluid dynamics). For the corrections of wind turbine scale effect, various researches on the helicopter rotor scale effect were investigated and the feasibility study of the methods was performed to correct wind turbine scale effect. The present paper also introduces scale effect correction methods based on two dimensional lift slope. In order to test the present method, performance analyses of NREL Phase VI wind turbines under various scale conditions were carried out and new correction method was applied. Granting that the new correction method is valid only above Reynolds No. 100,000, it showed reasonable agreement between model and full scale wind turbines in the linear torque region.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.5
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• pp.57-62
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• 2009

Flame spread velocity to virgin surface fuel bed on a ground slope increases as the flame gets closer to the slope according to the change of a ground slope angle. The existing studies have generally adopted the theory that flame gets closer to the slope as the slope angle increases, without considering the change of flame tilt against the slope. In this study, experiments were made on the actual characteristics of the flame on slopes of various angles, and as a result, this study offers the flame tilt equation according to the slope angle, and derive correlation between flame tilt and flame spread velocity on slope conditions.

• Wind and Structures
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• v.32 no.4
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• pp.293-308
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• 2021

For the past three decades a significant amount of research has been conducted on bridge flutter. Wind tunnel tests for a 2000 m class twin-box suspension bridge have revealed that a twin-box deck carrying 4 m tall 50% open area ratio wind screens at the deck edges achieved higher critical wind speeds for onset of flutter than a similar deck without wind screens. A result at odds with the well-known behavior for the mono-box deck. The wind tunnel tests also revealed that the critical flutter wind speed increased if the bridge deck assumed a nose-up twist relative to horizontal when exposed to high wind speeds - a phenomenon termed the "nose-up" effect. Static wind tunnel tests of this twin-box cross section revealed a positive moment coefficient at 0° angle of attack as well as a positive moment slope, ensuring that the elastically supported deck would always meet the mean wind flow at ever increasing mean angles of attack for increasing wind speeds. The aerodynamic action of the wind screens on the twin-box bridge girder is believed to create the observed nose-up aerodynamic moment at 0° angle of attack. The present paper reviews the findings of the wind tunnel tests with a view to gain physical insight into the "nose-up" effect and to establish a theoretical model based on numerical simulations allowing flutter predictions for the twin-box bridge girder.

• Journal of Wind Energy
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• v.9 no.4
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• pp.24-31
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• 2018

Wind lidar application is increasing and its calibration method is required to use wind lidar as an alternative to the meteorological mast. A nacelle lidar calibration method is now being discussed in IEC 61400-50-3 (Wind energy generation systems - Part 50-3: Use of nacelle-mounted lidars for wind measurements), and the method is mainly based on the wind lidar beam line of sight (LOS) wind speed calibration suggested by DTU as DTU E-0020 (Calibrating Nacelle Lidars). In this paper, a LOS wind speed calibration method is introduced and a calibration example performed on Jeju island is presented. The results showed a slope of 1.011 and R2 of 0.997, which means that the LOS wind speed is highly correlated with the reference wind speed and is comparable. But LOS wind speed calibration requires a very long time due to its principle and environmental conditions, and a calibration method that can overcome this problem of uncontrollable environments needs to be developed.