• Wind and Structures
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• v.17 no.3
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• pp.275-298
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• 2013

This paper presents a number of approximated analytical formulations for the flutter analysis of long-span bridges using the so-called uncoupled flutter derivatives. The formulae have been developed from the simplified framework of a bimodal coupled flutter problem. As a result, the proposed method represents an extension of Selberg's empirical formula to generic bridge sections, which may be prone to one of the aeroelastic instability such as coupled-mode or single-mode (either dominated by torsion or heaving mode) flutter. Two approximated expressions for the flutter derivatives are required so that only the experimental flutter derivatives of ($H_1^*$, $A_2^*$) are measured to calculate the onset flutter. Based on asymptotic expansions of the flutter derivatives, a further simplified formula was derived to predict the critical wind speed of the cross section, which is prone to the coupled-mode flutter at large reduced wind speeds. The numerical results produced by the proposed formulas have been compared with results obtained by complex eigenvalue analysis and available approximated methods show that they seem to give satisfactory results for a wide range of study cases. Thus, these formulas can be used in the assessment of bridge flutter performance at the preliminary design stage.

• International conference on construction engineering and project management
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• 2005.10a
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• pp.814-819
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• 2005

There is growing consciousness of the environmental performance of buildings in Hong Kong. The Buildings Department, the Lands Department and the Planning Department of the Hong Kong Government issued the first of a series of joint practice notes [1] to promote the construction of green and innovative buildings. Green features are architectural features used to mitigate migration of noise and various air-borne pollutants and to moderate the transport of heat, air and transmission of daylight from outside to indoor environment in an advantageous way. This joint practice note sets out the incentives to encourage the industry in Hong Kong to incorporate the use of green features in building development. The use of green features in building design not only improves the environmental quality, but also reduces the consumption of non-renewable energy used in active control of indoor environment. Larger window openings in the walls of a building may provide better natural ventilation. However, it also increases the penetration of direct solar radiation into indoor environment. The use of wing wall, one of the green features, is an alternative to create effective natural ventilation. This paper therefore presents a preliminary numerical study of its ventilation performance using Computational Fluid Dynamics (CFD). The numerical results will be compared with the results of the wind tunnel experiments of Givoni.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.5
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• pp.15-20
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• 2014

The wind industry grew in the first decade of the 21st century at rates consistently above 20% a year. For wind turbine, gearbox failure can be extremely costly in terms of repair costs, replacement parts, and in lost power production due to downtime. In this paper, gear tooth micro-modification for the high speed stage was used to compensate for the deformation of the teeth due to load and to ensure a proper meshing to achieve an optimized tooth contact pattern. The gearbox was firstly modeled in a software, and then the various combined tooth modification were presented, and the prediction of transmission under the loaded torque for the helical gear pair was investigated, the normal load distribution and root stress were also obtained and compared before and after tooth modification under one torque. The simulation results showed that the transmission error and normal load distribution under the load can be minimized by the appropriate tooth modification. It is a good approach where the simulated result is used to improve the design before the prototype is available for the test.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.201-212
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• 2016

A Wind resource assessment and optimal micrositing of wind turbines were implemented for the development of an onshore wind farm of 30 MW capacity on Gadeok Island in Busan, Republic of Korea. The wind data measured by the automatic weather system (AWS) that was installed and operated in the candidate area were used, and a reliability investigation was conducted through a data quality check. The AWS data were measured for one year, and were corrected for the long term of 30 years by using the modern era retrospective analysis for research and application (MERRA) reanalysis data and a measure- correlate-predict (MCP) technique; the corrected data were used for the optimal micrositing of the wind turbines. The micrositing of the 3 MW wind turbines was conducted under 25 conditions, then the best-optimized layout was analyzed with a various wake model. When the optimization was complete, the estimated park efficiency and capacity factor were from 97.6 to 98.7 and from 37.9 to 38.3, respectively. Furthermore, the annual energy production (AEP), including wake losses, was estimated to be from 99,598.4 MWh to 100,732.9 MWh, and the area was confirmed as a highly economical location for development of a wind farm.

• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.97-101
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• 2011

Interplanetary space between Sun and Earth is area of flowing very fast solar wind which is contained X ray, flare, corona mass, etc. occurred Sun surface to Earth. This solar wind is affected directly to Earth magnetosphere and ionosphere so that this bring out broadcasting and communication interruptions, satellite operation obstacles and power gird defects and etc..Solar wind flow in interplanetary space is measured as solar wind speed, density and direction by measuring scintillation value to be produced during radio source is passed through solar wind. The wider effective collective areas and the more radio sources, accuracy of solar wind measuring is got higher. Function test was performed using 3 tiles which was manufactured as prototype. Restriction of quantity of tiles, test was performed to confirm whether measured beam pattern is complied with requirement or not. In this paper, it is shown design and their specification of ground interplanetary radio measurement system as well as technical issues and resolutions which were raised during design phase. Also result of function verification test using prototype is suggested. It is confirmed that measured beam pattern was met with requirement.

• Journal of Bio-Environment Control
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• v.24 no.2
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• pp.100-105
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• 2015

The calculation method of infiltration loss in greenhouse has different ideas in each design standard, so there is a big difference in each method according to the size of greenhouses, it is necessary to establish a more accurate method that can be applied to the domestic. In order to provide basic data for the formulation of the calculation method of greenhouse heating load, we measured the infiltration rates using the tracer gas method in plastic greenhouses equipped with various thermal curtains. And then the calculation methods of infiltration loss in greenhouses were reviewed. Infiltration rates of the multi-span and single-span greenhouses were measured in the range of $0.042{\sim}0.245h^{-1}$ and $0.056{\sim}0.336h^{-1}$ respectively, single-span greenhouses appeared to be slightly larger. Infiltration rate of the greenhouse has been shown to significantly decrease depending on the number of thermal curtain layers without separation of single-span and multi-span. As the temperature differences between indoor and outdoor increase, the infiltration rates tended to increase. In the range of low wind speed during the experiments, changes of infiltration rate according to the outdoor wind speed could not find a consistent trend. Infiltration rates for the greenhouse heating design need to present the values at the appropriate temperature difference between indoor and outdoor. The change in the infiltration rate according to the wind speed does not need to be considered because the maximum heating load is calculated at a low wind speed range. However the correction factors to increase slightly the maximum heating load including the overall heat transfer coefficient should be applied at the strong wind regions. After reviewing the calculation method of infiltration loss, a method of using the infiltration heat transfer coefficient and the greenhouse covering area was found to have a problem, a method of using the infiltration rate and the greenhouse volume was determined to be reasonable.

• Journal of Bio-Environment Control
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• v.29 no.1
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• pp.73-79
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• 2020

The objective of this study is to analyze the heat transfer loss of covering materials in a single-span plastic greenhouse under the steady-state wind environment. To achieve this objective, the following were conducted: (1) design of a small-scaled wind tunnel (SCWT) to analyze heat losses of the greenhouse and its performance; (2) determination of the overall heat transfer coefficient (OHTC) for the covering materials using a small-scaled greenhouse model. The SCWT consists of the blowing, dispersion, steady flow, reduction and testing areas. Each part of the SCWT was customized and designed to maintain air flow at steady state and to minimize the variances in the SCWT test. In this study, the OHTCs of the covering materials were calculated by separating each with the roof, side wall, front and back of the small-scaled greenhouse model. The results of this study show that the OHTC of the roof increases as wind speed increases but the zones in which the increase rate of the OHTC decreased, were distinguished by wind tunnel wing speed of 2 ms^-1. For the side wall, the increase rate of the OHTC was particularly higher in the 0-1 ms^-1 zone.

• Journal of Bio-Environment Control
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• v.32 no.1
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• pp.57-63
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• 2023

The external weather conditions including temperature and wind speed in the Saemangeum reclaimed land is different from that of the inland, affecting the internal environment of the greenhouse. Therefore, it is important to select an appropriate covering material considering the insulation effect according to the type and characteristics of the covering material considering the weather condition in the Saemangeum reclaimed land. A hexahedral insulation chamber was designed to evaluate the insulation efficiency of each glass-clad material in the outside weather condition in reclaimed land. In order to evaluate the insulation effect of each covering material, a radiator was installed and real-time power consumption was monitored. 16-mm PC (polycarbonate), 16-mm PMMA (polymethyl methacrylate), 4-mm greenhouse glass, and 16-mm double-layered glass were used as the covering materials of the chamber. In order to understand the effect of the external wind directions, the windward and downwind insulation properties were evaluated. As a result of comparing the thermal insulation effect of each greenhouse cover material to single-layer glass, the thermal insulation effect of double-layer glass was 16.9% higher, while PMMA and PC were 62.5% and 131.2% higher respectively. On average the wind speed on the windward side was 53.1% higher than that on the lee-wind side, and the temperature difference between the inside and outside of the chamber at the wind ward side was found to be 52.0% larger than that on the lee ward side. During the experiment period, the overall heating operation time for PC was 39.2% lower compared to other insulation materials. Showing highest energy efficiency, and compared to PC, single-layer glass power consumption was 37.4% higher.

• Korean Journal of Computational Design and Engineering
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• v.18 no.3
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• pp.189-199
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• 2013

The need for reusing synthetic environment data that are employed in the field of modeling and simulation has recently been rising. SEDRIS (Synthetic Environment Data Representation & Interchange Specification) is a standard to exchange synthetic environment data, and is the specification utilized in various military simulations of the Pentagon for representing and exchanging 3D data. SEDRIS represents environmental areas based on a data model; it can represent wind speed, wind directions, weather changes, the information of buildings, as well as terrain data. In some situations, however, the synthetic environment data stored in SEDRIS format should be converted to various visualization formats. First, because SEDRIS is a form of a super-set, it is necessary to verify whether large scale SEDRIS files are stored successfully through visualization. Second, the synthetic environment data should be visualized in some visualization programs for the simulation results to provide an immersive and realistic sense. In this study, we have developed converters for converting SEDRIS data to various visualization formats and visualized the converted results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.3
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• pp.177-182
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• 2007

The effects of three fuselage head shapes and nonplanar ground surface on the aerodynamic characteristics of FAST fuselages are investigated using a boundary element method. Wind tunnel test is also performed to validate the present method and to identify the wall effect on the frictional drag which cannot be analyzed using the present method. It is found that the channel has an effect of increasing the lift of those investigated fuselages. The optimal head shape depends on the design conditions of the FAST and its guideway channel. Comparing the calculated induced drag with the measured total drag, it can be concluded that the profile drag is independent of the ground height. Thus, the present numerical method can be applied to the conceptual design of the high-speed ground transporters if only the profile drag of the vehicle in free flight is assumed to be known.