• Wind and Structures
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• v.20 no.4
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• pp.509-525
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• 2015

A three-dimensional aerodynamic model and a vehicle dynamics model are established to investigate the effect of noise barrier on the dynamic performance of a high-speed train running on an embankment in crosswind in this paper. Based on the developed model, flow structures around the train with and without noise barrier are compared. Effect of the noise barrier height on the train dynamic performance is studied. Then, comparisons between the dynamic performance indexes of the train running on the windward track and on the leeward track are made. The calculated results show that the noise barrier has significant effects on the structure of the flow field around the train in crosswind and thus on the dynamic performance of the high-speed train. The dynamic performance of the train on the windward track is better than that on the leeward track. In addition, various heights of the noise barrier will have different effects on the train dynamic performance. The dynamic performance indexes keep decreasing with the increase of the noise barrier height before the height reaches a certain value, while these indexes have an inverse trend when the height is above this value. These results suggest that optimization on the noise barrier height is possible and demonstrate that the designed noise barrier height of the existing China Railway High-speed line analysed in this article is reasonable from the view point of the flow field structure and train dynamic performance although the noise barrier is always designed based on the noise-related standard.

• Proceeding of KASS Symposium
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• 2006.05a
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• pp.91-101
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• 2006

We have conducted the study about the shelter effect against the wind by using the wind fence with various porosities and the measured distance from the wind fence, in three different types of it ; (Circle wind fence, Vertical wind fence, Horizontal wind fence) The shelter effect and turbulence characteristics of the selected wind barrier is throughly investigated by wind tunnel test. flow characteristics of velocities and turbulences behind wind fence were measured using hot-wire anemometer. we characterize the turbulence behind the wind fence by varying the porosity of 0 %, 20 %, 40%, and 60%, and the distances from the wind fence from 1 H to 9 H with maintaining the uniform flow velocity of 6 m/s. In addition, we investigated the overall characterization of the wind fence by measuring total of twenty eight points on the wind fence, which forms the lattice structure on it with seven points in lateral direction and four points in vertical direction. The results of analysis from the circle wind fence indicate that the degree of the turbulence is lowered and the velocity of the wind is decreased when the porosity of 40 % are used at the distance from 3 H to 9 H. On the other hand, the vertical, horizontal wind fence with the porosity of 20% is more advantageous at the distance of 2 H to 9 H. For the effectiveness of the wind fence depending on the position, the center part is the greatest and it decreases at the edges with 10 % to 30 % less than that of at the center.

• Wind and Structures
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• v.11 no.5
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• pp.413-426
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• 2008

A wind tunnel study has been carried out to determine the influence of spacing between buildings on wind characteristics above rural and suburban type of terrain. Experiments were performed for two types of buildings, three-floor family houses and five-floor apartment buildings. The atmospheric boundary layer (ABL) models were generated by means of the Counihan method using a castellated barrier wall, vortex generators and a fetch of roughness elements. A hot wire anemometry system was applied for measurement of mean velocity and velocity fluctuations. The mean velocity profiles are in good agreement with the power law for exponent values from ${\alpha}=0.15$ to ${\alpha}=0.24$, which is acceptable for the representation of the rural and suburban ABL, respectively. Effects of the spacing density among buildings on wind characteristics range from the ground up to $0.6{\delta}$. As the spacing becomes smaller, the mean flow is slowed down, whilst, simultaneously, the turbulence intensity and absolute values of the Reynolds stress increase due to the increased friction between the surface and the air flow. This results in a higher ventilation efficiency as the increased retardation of horizontal flow simultaneously accompanies an intensified vertical transfer of momentum.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.755-761
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• 2009

The major advantage of transparent materials over traditional materials in noise barriers is aesthetics. The transparent panel materials such as clear plastic or glass are an ideal way of reducing or virtually eliminating the visual impact of a noise barrier. With the use of transparent materials, the drivers' view of the roadside and the sunlight penetration to the highway would not be blocked. With the use of transparent materials, the highway and barrier appear less imposing. Korean Industrial Standards for soundproof panels have been established. But, transparent soundproof panels are not included in this standards. And, some specifications provide only a few basic characteristics for transparent soundproof panels. To develop guidelines on quality criteria for transparent soundproof panel, their mechanical properties such as wind load resistance, safety under impact, and abrasion resistance were experimentally investigated.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.27-32
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• 2003

The effect of non-thermal plasma on diffusion flames in co-flow jets has been studied experimentally by adopting a dielectric barrier discharge technique. The generation of streamers was enhanced with a flame due to increased reduced electric fields by high temperature burnt gas and the abundance of ions in the flame region. The effect of streamers on flame behavior reveals that the flame length was significantly decreased as the applied voltage increased and the yellow luminosity by the radiation of soot particles was also significantly reduced. The formation of PAH and soot was influenced appreciably by the non-thermal plasma, while the flame temperature and the concentration of major species were not influence much with the plasma generation. The results demonstrated that the application of non-thermal plasma can be a viable technique in controlling soot generation in flames with low power consumption in the order of 1 W.

• Journal of Environmental Impact Assessment
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• v.20 no.4
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• pp.539-555
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• 2011

Newly constructed, high-rise dense building areas by urban development can cause changes in local wind fields. Wind fields were analyzed to assess the impact on the local meteorology due to the land use changes during the urban redevelopment called "Eunpyeong new town" in north-western Seoul using CFD_NIMR_SNU (Computational Fluid Dynamics, National Institute of Meteorological Research, Seoul National University) model. Initial value of wind speed and direction use analysis value of AWS (Automatic Weather Station) data during 5 years. In the case of the pre-construction with low rise built-up area, it was simulated that the spatial distribution of horizontal wind fields depends on the topography and wind direction of initial inflow. But, in the case of the post-construction with high rise built-up area, it was analyzed that the wind field was affected by high rise buildings as well as terrain. High-rise buildings can generate new circulations among buildings. In addition, small size vortexes were newly generated by terrain and high rise buildings after the construction. As high-rise buildings act as a barrier, we found that the horizontal wind flow was separated and wind speed was reduced behind the buildings. CFD_NIMR_SNU was able to analyze the impact of high-rise buildings during the urban development. With the support of high power computing, it will be more common to utilize sophisticated numerical analysis models such as CFD_NIMR_SNU in evaluating the impact of urban development on wind flow or channel.

• Journal of Wind Energy
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• v.14 no.1
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• pp.29-36
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• 2023

The analysis of the floating offshore wind turbine platform is based on the procedures provided by the IEC including the International Classification Society, which recommends the analysis in the time domain. But time-domain simulation requires a lot of time and resources to solve tens of thousands of DLCs. This acts as a barrier in terms of floating structure development. For final verification, it requires very precise analysis in the time domain, but from an initial design point of view, a simplified verification procedure to predict the quantity of materials quickly and achieve relatively accurate results is crucial. In this study, a structural design procedure using a design wave applied in the oil and gas industries is presented combined with a conservative turbine load. With this method, a quick design spiral can be rotated, and it is possible to review FOWTs of various shapes and sizes. Consequently, a KRISO Semi-Submersible FOWT platform was developed using a simplified design procedure in frequency-domain analysis.

• Journal of Astronomy and Space Sciences
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• v.28 no.1
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• pp.17-26
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• 2011

Bow shock, formed by the interaction between the solar wind and a planet, is generated in different patterns depending on the conditions of the planet. In the case of the earth, its own strong magnetic field plays a critical role in determining the position of the bow shock. However, in the case of Mars of which has very a small intrinsic magnetic field, the bow shock is formed by the direct interaction between the solar wind and the Martian ionosphere. It is known that the position of the Martian bow shock is affected by the mass loading-effect by which the supersonic solar wind velocity becomes subsonic as the heavy ions originating from the planet are loaded on the solar wind. We simulated the Martian magnetosphere depending on the changes of the density and velocity of the solar wind by using the three-dimensional magnetohydrodynamic model built by modifying the comet code that includes the mass loading effect. The Martian exosphere model of was employed as the Martian atmosphere model, and only the photoionization by the solar radiation was considered in the ionization process of the neutral atmosphere. In the simulation result under the normal solar wind conditions, the Martian bow shock position in the subsolar point direction was consistent with the result of the previous studies. The three-dimensional simulation results produced by varying the solar wind density and velocity were all included in the range of the Martian bow shock position observed by Mariner 4, Mars 2, 3, 5, and Phobos 2. Additionally, the simulation result also showed that the change of the solar wind density had a greater effect on the Martian bow shock position than the change of the solar wind velocity. Our result may be useful in analyzing the future observation data by Martian probes.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.25-32
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• 2015

Dielectric barrier discharge (DBD) plasma actuator was designed to reduce aerodynamic drag in a cylindrical model and wind tunnel test was performed at various wind velocities. In addition, computational fluid dynamics (CFD) analysis and flow visualization were used to investigate the effect of the plasma on the flow stream in the cylinderical model. At low wind velocity, the plasma actuator had no effects because flow separation did not appear. The aerodynamic drag was reduced by 14% at 14 m/s and by 27% at 17 m/s, respectively. It was confirmed by CFD analysis and flow visualization that the DBD plasma actuator decreased in pressure difference around the cylindrical model, thus decreasing the magnitude of wake vortex.

• Journal of Convergence for Information Technology
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• v.8 no.6
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• pp.187-192
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• 2018

This thesis is about the study of inverter terminal boxes in a explosion proof type exhaust fan that can control wind volume and operating time. In Korea, there is no ventilator to adjust the amount of wind and operating time when working in poor conditions. The purpose of the project is to create a explosion terminal box that can control the operating time and wind speed of a suitable explosion ventilator in hazardous environments. The two explosion-proof switches allow the operation time to be driven 1 hour, 3 hours and continuous time, and the speed of the induction motor rotation was set in 3 stages at 2000 rpm, 2600 rpm and 3000 rpm to control the volume. The tested motor used a half-horsepower barrier three-phase induction motor and a full-bridge inverter to set the desired flow rate and operating time.