• Journal of computational fluids engineering
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• v.13 no.2
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• pp.55-61
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• 2008

The Reynolds-Averaged Navier-Stokes(RANS) analysis of the 3-D steady flow around the NREL Phase VI horizontal axis wind turbine(HAWT) rotor was performed. The CFD analysis results were compared with experimental data at several different wind speeds. The present CFD model shows good agreements with the experiments both at low wind speed which formed well-attache flow mostly on the upper surface of the blade, and at high wind speed which blade surface flow completely separated. However, some discrepancy occurs at the relatively high wind speeds where mixed attached and separated flow formed on the suction surface of the blade. It seems that the discrepancy is related to the onset of stall phenomena and consequently separation prediction capability of the current turbulence model. It is also found that strong span-wise flow occurs in stalled area due to the centrifugal force generated by rotation of the turbine rotor and it prevents abrupt reduction of normal force for higher wind speed than the designed value.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.1
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• pp.20-27
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• 2017

This study investigated the problems in current practice of drive-train resonance analysis procedure and suggested solutions. The first problem is the resonance occurrence at the un-identified resonance point by the current practice, as for a solution the force spectrum analysis for each critical force transmitting component was suggested. The second one is the inaccurate estimation of potential resonance point in eigenfrequency analysis because of the non-consideration about the eigenfrequency dependency on rotor-speed, the fine linearization at each rotor speed point all over operational range was proposed to account for the affection. Lastly the insufficient time for resonance activation under run-up simulation condition was recognized as a problem in resonance load increasing analysis, as an alternative, steady state condition was suggested to estimate the maximum load increasing level.

• 한국태양에너지학회:학술대회논문집
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• 2008.11a
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• pp.96-102
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• 2008

For centuries now, wind tunnels have been a key element in scientific research in a number of fields. Experimenting with racecars, airplanes, weather patterns, birds, and various other areas has been made much easier because of its development. In the racing field, for example, the information gathered from this testing can mean the difference between winning and losing a race. Weather simulations can also provide valuable information regarding building stability and safety. This has become very important when designing buildings today. Valuable information concerning bird flight has also been collected based on wind tunnel testing. Wind tunnels have a variety of important uses in the world today. Wind tunnel that used here is an open loop low speed wind tunnel. The fundamental principles of this tunnel is moving the air using exhaust fan In the rear side, and placing the cube in the external balance system which used to measure the working force. This experiment is using 50mm cube of finished wood. From this experiment we can get Drag Force (FD), The Reynolds Number (Re) and The Coefficient of Brae (CD).

• Computational Structural Engineering : An International Journal
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• v.3 no.1
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• pp.61-68
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• 2003

A recently developed semi-active control system employing magneto-rheological (MR) fluid dampers is applied to vibration control of a wind excited tall building. The semi-active control system with MR fluid dampers appears to have the reliability of passive control devices and the adaptability of fully active control systems. The system requires only small power source, which is critical during severe events, when the main power source may fail. Numerical simulation studies are performed to demonstrate the efficiency of the MR dampers on the third ASCE benchmark problem. Multiple MR dampers are assumed to be installed in the 76-story building. Genetic algorithm is applied to determine the optimal locations and capacities of the MR dampers. Clipped optimal controller is designed to control the MR dampers based on the acceleration feedback. To verify the robustness with respect to the variation of the external wind force, several cases with different wind forces are considered in the numerical simulation. Simulation results show that the semi-actively controlled MR dampers can effectively reduce both the peak and RMS responses the tall building under various wind force conditions. The control performance of the MR dampers for wind is found to be fairly similar to the performance of an active tuned mass damper.

• 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 Korean Society of Agricultural Engineers
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• v.61 no.1
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• pp.75-83
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• 2019

Fruit bagging is a traditional way to produce high-quality fruit and to prevent damage from insects and diseases. Growing pears by non-bagging is concerned about the damage from insect, it can be controlled by installing a insect net facility. Wind load should be considered to design the insect net facility because it has the risk of collapse due to the strong wind. So we carried out wind tunnel test for measurement of drag force, where the insect net with porosity about 65% is selected as an experimental subject. As a result of the test, drag force was measured to be 244.14 N when insect net area and wind speed are $1m^2$ and 22.7 m/s respectively. And, drag coefficients for the insect net were found to be about 0.55~0.57, which may be used as the preliminary data to design the insect net facilities at the orchard.

• Wind and Structures
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• v.34 no.5
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• pp.407-419
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• 2022

Many factors should be considered by architects and designers for designing a tall building. Wind load is one of these important factors that govern the design of tall building structures and can become a serious challenge when buildings tend to be built very tall and slender. On the other hand, through the initial stages of a design process, choosing the design geometry greatly affects the wind-induced forces on a tall building. With this respect, geometric shapes with 3-fold rotational symmetry are one of the applied plan shapes in tall buildings. This study, therefore, aims to investigate the aerodynamic characteristics of 8 different geometrical shapes using Computational Fluid Dynamics (CFD) by measuring the drag and lift forces. A case study approach was conducted in which different building shape models have the same total gross area and the same height of 300 meters. The simulation was an incompressible transient flow that ran 1700 timesteps (85 seconds on the real-time scale). The results show a great difference between wind-induced force performance of buildings with different plan shapes. Generally, it is stated that the shapes with the same area, but with smaller perimeters, are better choices for reducing the drag force on buildings. Applying the lift force, the results show that the buildings with plan shapes that have rounded corners act better in crosswind flow while, those with sharp corners induce larger forces in the same direction. This study delivers more analytical understanding of building shapes and their behavior against the wind force through the parametric modelling.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.4
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• pp.59-66
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• 1984

The dynamic behavior of a cable-stayed bridge due to random wind forces is investigated. The effects of the steady wind, the self-excited and the buffeting forces are studied. The dynamic analysis of the structure is carried out by the frequency domain method utilizing the mode superposition. Example analysis are performed for Dolsan Bridge, which is under construction at Yeosu, Jeonnam. Aerodynamic stability of the bridge is investigated and the vertical motion of the girder as well as the tension variations of the cables is obtained.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.62.1-62.1
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• 2011

The wind can be stronger and steadier further from shore, but water depth is also deeper. Then bottom-mounted towers are not feasible, and floating turbines are more competitive. There are additional motions in an offshore floating wind turbine, which results in a more complex aerodynamics operating environment for the turbine rotor. Many aerodynamic analysis methods rely on blade element momentum theory to investigate aerodynamic load, which are not valid in vortex ring state that occurs in floating wind turbine operations. So, vortex lattice method, which is more physical, was used in this analysis. Floating platform's prescribed positions were calculated in the time domain by using floating system RAO and waves that are simulated using JONSWAP spectrum. The average value of in-plane aerodynamic force increase, but the value of out-of-plane force decrease. The maximum variation aerodynamic force abruptly increases in severe sea state. Especially, as the pitch motion of the barge platform is large, this motion should be avoided to decrease the aerodynamic load variation.

• Ocean Systems Engineering
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• v.4 no.3
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• pp.169-183
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• 2014

For the reliable design of substructure supporting offshore wind turbines it is very important to reduce the effects of wave forces. Since the substructure is strongly influenced by the effects of wave forces as the size of substructure increases. In the present study, the hybrid substructure with multi-cylinder is newly suggested to reduce the effects of wave forces. Using diffraction theory the scattering waves in a fluid region are expressed by an Eigenfunction expansion method with three dimensional potential theory to calculate the wave force acting on the hybrid substructure. The wave force and wave run-up acting on the hybrid substructure is presented to examine the water wave interaction according to the variation of cylindrical size and the distance among cylinders. It is found that the suggested hybrid substructure with multi-cylinder is very useful to reduce the effects of wave forces acting on the substructure for offshore wind turbines.