• Journal of the Korean Institute of Gas
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• v.16 no.1
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• pp.33-38
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• 2012

Analysis on gas accidents by types occurred has been made to prevent the recurrence of accidents, through analysis of past history of gas accident occurring environment. The number of gas accidents has been decreasing, but still accidents are occurring steadily. Gas-using environment and gas accidents are estimated to be closely connected since gas-using types are changing by time period, weather, etc. in terms of accident contents. As a result of analysing gas accidents by 7 meteorological elements, such as the mean temperature, the highest temperature, the lowest temperature, relative humidity, the amount of clouds, precipitation and wind velocity, it has been found out that gas accidents are influenced by temperature or relative humidity, and accident occurs more frequently when the sky is clean and wind velocity is slow. Possibility of gas accidents can be provided in real time, using the proposed model made to predict gas accidents in connection with the weather forecast service. Possibility and number of gas accidents will be checked real time by connecting to the business system of Korea Gas Safety Corp., and it is considered that it would be positively used for preventing gas accidents.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.153-160
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• 2011

Recently there are many long span cable supported bridges like Cable Stayed Bridge and Suspension Bridge already constructed or planned. Reconsidering of proper design wind load of long span bridge is required since the meteorological value based on the data only from 1960s to 1995 has been used when we estimate the wind load for designing long span bridges. In this paper, the research area was confined to western and southern coasts where many long span bridges have constructed. The method of moment and the least-squares method were used to estimate the expected wind speeds of 100 year's return period for girder bridges and for 200 year's return period for long span bridges based on the Gumbel's distribution. As the return-period wind speed on the land face was revised because of recent high speed velocity, the revised return-period wind speed is increased by 17%. Compatibility of return-period wind speed was also evaluated using RMS (Root Mean Square) error method. Aa a result of this paper, the least-squares method is more compatible than the method of moment in the case of western and southern coasts in Korea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.3
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• pp.122-130
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• 2021

A wind-speed estimation at the arbitrary elevations is key component for the design of the offshore wind energy structures and the computation of the wind-wave generation. However, the wind-speed estimation of the target elevation has been carried out by using the typical functions and their typical parameters, e.g., power and logarithmic functions because the available wind speed data is limited to the specific elevation, such as 2~3m, 10 m, and so on. In this study, the parameters of the vertical profile functions are estimated with optimal and analyzed the parameter ranges using the HeMOSU-1 platform wind data monitored at the eight different locations. The results show that the mean value of the exponent of the power function is 0.1, which is significantly lower than the typically recommended value, 0.14. The values of the exponent, the friction velocity, and the roughness parameters are in the ranges 0.0~0.3, 0~10 (m/s), and 0.0~1.0 (m), respectively. The parameter ranges differ from the typical ranges because the atmospheric stability condition is assumed as the neutral condition. To improve the estimation accuracy, the atmospheric condition should be considered, and a more general (non-linear) vertical profile functions should be introduced to fit the diverse profile patterns and parameters.

• Food Science and Preservation
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• v.8 no.4
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• pp.356-361
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• 2001

This study was conducted to improve the storability of onion bulbs by assembly simple house storage and the reduce the rotteness caused by field open storage. Allium cepa cv. Changnyungdeago, late strain was used for the test at the storage condition of natural ventilation of levels 2, forced ventilation of levels 2, field open storage and 75mm, 100mm, and 125mm ventilating holes. Mean tamperature and relative humidity were not significantly different by ventilation conditions. Mean temperature was lower in forced ventilation than that of in natural ventilation and non-ventilation, and relative humidity was a little higher in ventilation treatment than those of the others. Weight loss of onion bulbs were 2.5%, 2.9%, 3%, 4.3% in field open storage, non ventilation, natural ventilation of levels 2 and forced ventilation of levels 2 respectively. Rotting rate in natural ventilation of levels 2 and farced ventilation of levels 2 were 27.7% and 25.4% respectively but 34.6% and 37.8% in non ventilation and field open storage. Therefore, the treatment of ventilation reduced the rotteness of storage onion bulbs. The smaller the size of a ventilating hole, the lower mean temperature was maintained. The relative humidity was some high in July, but didn’t showed significantly difference in August and September. With small size of a ventilating hole, the strong wind velocity was obtained, and wind velocity by position was weaker in the middle part than both ends. Rutting rates in 75㎜, 100㎜, and 125㎜ ventilating holes were 17.9%, 15.3% and 14.1% respectively.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.6
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• pp.61-71
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• 2017

The tracer gas method has an advantage that can estimate total and local ventilation rate by tracing air flow. However, the field measurement using tracer gas has disadvantages such as danger, inefficiency, and high cost. Therefore, the aim of this study was to evaluate ventilation rate in pig house by using the thermal distribution data rather than tracer gas. Especially, LMA (Local Mean Age), which is an index based on the age of air theory, was used to evaluate the ventilation rate in pig house. Firstly, the field experiment was conducted to measure micro-climate inside pig house, such as the air temperature, $CO_2$ concentration and wind velocity. And then, LMA was calculated based on the decay of $CO_2$ concentration and air temperature, respectively. This study compared between LMA determined by $CO_2$ concentration and air temperature; the average error and root mean square error were 3.76 s and 5.34 s. From these results, it was determined that thermal distribution data could be used for estimation of LMA. Finally, CFD (Computational fluid dynamic) model was validated using LMA and wind velocity. The mesh size was designed to be 0.1 m based on the grid independence test, and the Standard $k-{\omega}$ model was eventually chosen as the proper turbulence model. The developed CFD model was highly appropriate for evaluating the ventilation rate in pig house.

• Atmosphere
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• v.27 no.1
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• pp.41-54
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• 2017

Organic carbon (OC) and elemental carbon (EC) in $PM_{2.5}$ were measured using Sunset OC/EC Field Analyzer at Seoul Hwangsa Monitoring Center from March to April, 2016. The mean concentrations of OC and EC during the entire period were $4.4{\pm}2.0{\mu}gC\;m^{-3}$ and $1.4{\pm}0.6{\mu}gC\;m^{-3}$, respectively. OC/EC ratio was $3.4{\pm}1.0$. The average concentrations of $PM_{10}$ and $PM_{2.5}$ were $57.4{\pm}25.9$ and $39.7{\pm}19.8{\mu}g\;m^{-3}$, respectively, which were detected by an optical particle counter. The OC and EC peaks were observed in the morning, which were impacted by vehicle emission, however, their diurnal variations were not noticeable. This is determined to be contributed by the long-range transported OC or secondary formation via photochemical reaction by volatile organic compounds at afternoon. A conditional probability function (CPF) model was used to identify the local source of pollution. High concentrations of $PM_{10}$ and $PM_{2.5}$ were observed from the westerly wind, regardless of wind speed. When wind velocity was high, a mixing plume of dust and pollution during long-range transport from China in spring was observed. In contrast, pollution in low wind velocity was from local source, regardless of direction. To know the effect of long-range transport on pollution, a concentration weighted trajectory (CWT) model was analyzed based on a potential source contribution function (PSCF) model in which 75 percentiles high concentration was picked out for CWT analysis. $PM_{10}$, $PM_{2.5}$, OC, and EC were dominantly contributed from China in spring, and EC results were similar in both PSCF and CWT. In conclusion, Seoul air quality in spring was mainly affected by a mixture of local pollution and anthropogenic pollutants originated in China than the Asian dust.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2737-2742
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• 2007

Strong wind flow around a building complex was numerically studied by LES. The original motivation of this work stemmed from the efforts to develop a risk assessment technique for windstorm hazards. Lagrangian-averaged scale-invariant dynamic subgrid-scale model was used for turbulence modeling, and a log-law-based wall model was employed on all the solid surfaces including the ground and the surface of buildings to replace the no-slip condition. The shape of buildings was implemented on the Cartesian grid system by an immersed boundary method. Key flow quantities for the risk assessment such as mean and RMS values of pressure on the surface of the selected buildings are presented. In addition, characteristics of the velocity field at some selected locations vital to safety of human beings is also reported.

• Journal of Korean Society for Atmospheric Environment
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• v.9 no.4
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• pp.295-302
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• 1993

The nature of the cavity region and dispersion around trianglular ridge was investigated using model. The artifical neutral boundary layer was simulated in water channel. Two dimensional trianglar ridges, having height of 1.2 cm and various width were placed normal to the flow. Mean velocity with many dimensionless parameters were measured and compared with wind tunnel results by other studies. Using vorticity generator and roughness, the neutral boundary layer was well represented by the water channel. concentration patterns resulting from dye source placed 0.2 cm height above were examined. Narrower the trianglar ridge width resulted in increased amplification factor and the larges amplification factor was observed near downward top of the ridge.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.11
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• pp.78-83
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• 2010

Since a tower crane is too high for a worker to ascend and by the wind in the high altitude, the possibility of a safety accident is very high, a lift assist is used. In this study, the hydraulic fall prevention device using the pressure generation device by Seok, et al. was developed. For this, the effects on the fall prevention performances of factors such as gear clearance, oil viscosity, rotative velocity and so on were evaluated by the analysis of fluid flow using FEM and the prototype was producted and a function test was performed.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.401-402
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• 2006

The turbulent flow around a sphere was investigated using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5300, 11000 and PIV measurements in a circulating water channel. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. The mean velocity field measured using a PIV technique in x-y center plane demonstrates the detailed near-wake structure such as nearly symmetric recirculation region, two toroidal vortices, laminar separation, transition and turbulent eddies. The PIV measurements of turbulent wake in y-z planes show that a recirculating vortex pair dominates the near-wake region.