• Journal of Welding and Joining
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• v.7 no.1
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• pp.42-50
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• 1989

The application of fracture mechanics is being increased gradually to assess the safety of welded structures containing crack. Fatigue crack propagation behavior and elastic-plastic fracture toughness J$_{IC}$ of home made flux cored wire(1.22mm) CO$_{2}$ weldments was discussed. Especially fatigue crack propagation test was carried out by .DELTA.K control instead of load control and elastic-plastic fracture toughness J$_{IC}$ was obtained by ASTM-R curve method on C.T.specimen in transverse direction of weldments. The results obtained are as follows; (1) Weld metal presented an almost complete similarity to base metal on fatigue crack propagation rate in transverse direction. (2) Weld metal was more than base metal on J$_{IC}$ value in transverse direction. (3) F.C.W. CO$_{2}$ weldments had an excellent characteristic of fatigue crack propagation rate and J$_{IC}$ in less than 50kg/mm$^{2}$ steel grade, this would result from that weld metal had good static strength.trength.

• Journal of Korean Society on Water Environment
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• v.36 no.6
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• pp.508-520
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• 2020

Dam reservoirs have been reported to contribute significantly to global carbon emissions, but unlike natural lakes, there is considerable uncertainty in calculating carbon emissions due to the complex of emission pathways. In particular, the method of calculating carbon dioxide (CO2) net atmospheric flux (NAF) based on a simple gas exchange theory from sporadic data has limitations in explaining the spatiotemporal variations in the CO2 flux in stratified reservoirs. This study was aimed to analyze the spatial and temporal CO2 distribution and mass balance in Daecheong Reservoir, located in the mid-latitude monsoon climate zone, by applying a two-dimensional hydrodynamic and water quality model (CE-QUAL-W2). Simulation results showed that the Daecheong Reservoir is a heterotrophic system in which CO2 is supersaturated as a whole and releases CO2 to the atmosphere. Spatially, CO2 emissions were greater in the lacustrine zone than in the riverine and transition zones. In terms of time, CO2 emissions changed dynamically according to the temporal stratification structure of the reservoir and temporal variations of algae biomass. CO2 emissions were greater at night than during the day and were seasonally greatest in winter. The CO2 NAF calculated by the CE-QUAL-W2 model and the gas exchange theory showed a similar range, but there was a difference in the point of occurrence of the peak value. The findings provide useful information to improve the quantification of CO2 emissions from reservoirs. In order to reduce the uncertainty in the estimation of reservoir carbon emissions, more precise monitoring in time and space is required.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
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• 2003.09a
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• pp.115-128
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• 2003

o What is the flux \ulcorner Flux is the transfer of a quantity per unit area per unit time. The quantities are mass, heat, moisture, momentum and pollutant in micrometeorology. Kinematic flux (Fluid). The reduction in wind speed due to frictional drag transfers momentum from the atmosphere to the surface, creating turbulence that mixes the air and transports heat and water from the surface into the lower atmosphere. (omitted)

• Korean Journal of Agricultural and Forest Meteorology
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• v.16 no.3
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• pp.233-245
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• 2014

Nighttime correction of $CO_2$ flux is one of the most important and challenging tasks in eddy covariance measurements over a complex mountainous terrain. In this study, we have scrutinized the quality and the credibility of the $CO_2$ flux datasets which were produced by employing three different methods of nighttime correction, i.e., (1) friction velocity ($u^*$) correction, (2) light response curve (LRC) correction, and (3) advection-based van Gorsel (VG) correction. The whole year datasets used in our analysis were collected at the two KoFlux tower sites (i.e., GDK deciduous forest site at the upper hill and GCK coniferous forest site at the lower hill) located in the valley of Gwangneung National Arboretum in central Korea. The resultant magnitudes and patterns of ecosystem respiration ($R_E$), gross primary productivity (GPP), and net ecosystem exchange (NEE) of $CO_2$ showed marked differences among the datasets produced with three different correction methods, which were also site-specific. The examination from micrometeorological and ecological perspectives suggests that the major cause of some inconsistency seems to be associated with the advection of $CO_2$ along the sloping terrain and the inappropriate selection of the correction data that might have been already affected by advective flows. The comparison with the results from other studies indicated that the overall characteristics of the corrected $CO_2$ fluxes at GDK and GCK (except those with LRC correction) were well within the ranges reported in the literature for various ecosystems in East Asia in similar latitudes. However, our study also implies that there will be always a room for further improvement in the present datasets. Therefore, caution must be exercised for the data users in order to properly use the updated version of datasets through transparent, open and participatory communication with data producers.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.6
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• pp.618-623
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• 2014

This study, analyzed the waveform and mechanical properties of flux cored arc Welding on SM45C. $CO_2$ 10% + Ar 90% shows the lowest standard deviation and shunt ratio at which the arc was most stable. $CO_2$ 10% + Ar 90% is equal to $CO_2$ 20% + Ar 80%. therefore, $CO_2$ 20% + Ar 80% is the best of mixture gases. The hardness test result for the gas mixture ratio of $CO_2$ 10% + Ar 90% was HV 249.7 which is the highest measured value. According to tensile test results, the tensile strength increased with increasing Ar in the mixture gas. This was because of the inertness of the argon, which does not combine with other elements, causing $CO_2$ to combine with pearlite and ferrite and decreasing the maximum tensile strength. Microstructural examination results show that with increasing Ar, ferrite generation decreases while the mild microstructure increases which influences the hardness.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.121-126
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• 2008

The cooling heat transfer coefficient of $CO_2$ (R-744) in a horizontal and helically coiled tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, evaporator and gas cooler (test section). The test section consists of a horizontal stainless steel tube and hellically coiled copper tube of 4.57 and 7.75 mm. The experiments were conducted at saturation temperature of 100 to $20^{\circ}C$, and mass flux of 200 to $500kg/m^2s$. The test results showed the variation of the heat transfer coefficient tended to decrease as cooling pressure of $CO_2$ increased. The heat transfer coefficient with respect to mass flux increased as mass flux increased. The experimental results were also compared with the existing correlations for the supercritical heat transfer coefficient, which generally underpredicted the measured data. However, the experimental data showed a relatively good agreement with the correlations of Pitla et al. except for the pseudo critical temperature.

• Atmosphere
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• v.34 no.1
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• pp.69-81
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• 2024

In this paper, Annual flux variations in the Boseong Tall Tower (BTT) from 2016 to 2020 were analyzed using data from three levels (2.5 m, 60 m, and 300 m). BTT was installed in Boseong-gun, Jeollanam-do in February 2014 and continued to conduct energy exchange observations such as CO2, sensible heat, and latent heat using the eddy covariance method until March 2023. The BTT was located in a very flat and uniform paddy field, and flux observations were conducted at four levels: 2.5 m, 60 m, 140 m, and 300 m above ground. Surface energy balance was confirmed from observed data of net radiation flux, soil heat flux, sensible heat flux, and latent heat flux. Additionally, 2.5 m height surface fluxes, which are most influenced by agricultural land, were compared with data from Local Data Assimilation and Prediction System (LDAPS) of the Korea Meteorological Administration to evaluate the accuracy of LDAPS flux data. The correlation coefficient between LDAPS flux data and observed values was 0.95 or higher. Excluding summer latent heat flux data, there was a general tendency for LDAPS data to be higher than observed values. The footprint areas estimated below 60 m height mainly covered agricultural land, and flux observations at 2.5 m and 60 m heights showed typical agricultural characteristics. In contrast, the footprint estimated at 300 m height did not show agricultural characteristics, indicating that observations at this height encompassed a wide range, including mountains, sea, and roads. The analysis results of long-term flux observations can contribute to understanding the energy and carbon dioxide fluxes in agricultural fields. Furthermore, these results can be utilized as essential data for validating and improving numerical models related to such fluxes.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.2
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• pp.47-53
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• 2004

The salient pole rotor type single phase SRM (switched reluctance motor) uses radial and axial direction magnetic flux simultaneously. Therefore, the output power per unit volume is very high and the shaft length is shorter than other types of SRMs with the same output. Furthermore, it can be manufactured with low cost owing to its simple structure and driving circuit. The prototype was designed using the theory of the traditional rotating machine and 3D FEM analysis. On this paper, the experiment apparatus, which includes the fabricated prototype in previous researches, was fabricated to measure the current and voltage of the prototype. Then the flux linkage, inductance and magnetic co-energy were calculated using the experimental results. Finally, the measured magnetic co-energy was compared with the simulated magnetic co-energy.

• Journal of Applied Biological Chemistry
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• v.64 no.4
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• pp.351-356
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• 2021

Changing environmental conditions can affect plant growth by influencing water and nutrient transport and photosynthesis. Plant physiological responses under changing environmental conditions can be non-destructively monitored using electrodes as plant induced electrical signal (PIES). Objective of the study was to monitor PIES in response to increased CO₂ and decreased photosynthetic photon flux density (PPFD). The PIES increased during day time when transpiration and photosynthesis occurs and monitored CO₂ concentration was negatively correlated to the PIES. Enhanced CO₂ concentration slightly reduced PIES, but the effect of increased CO₂ was limited by light intensity. The effect of reduced PPFD was not appeared immediately because water and nutrient transport was not promptly affected by the light. The study was conducted to evaluate short-term effect of increasing CO₂ and decreasing PPFD, hence proline content and chlorophyll fluorescence was not significantly affected by the conditions.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.24 no.3
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• pp.375-388
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• 2019

Accurate evaluation of sea-to-air $CO_2$ flux and its variability is crucial information to the understanding of global carbon cycle and the prediction of atmospheric $CO_2$ concentration. $fCO_2$ observations are sparse in space and time in the East Sea. In this study, we derived high resolution time series of surface $fCO_2$ values in the southwest East Sea, by feeding sea surface temperature (SST), salinity (SSS), chlorophyll-a (CHL), and mixed layer depth (MLD) values, from either satellite-observations or numerical model outputs, to three machine learning models. The root mean square error of the best performing model, a Random Forest (RF) model, was $7.1{\mu}atm$. Important parameters in predicting $fCO_2$ in the RF model were SST and SSS along with time information; CHL and MLD were much less important than the other parameters. The net $CO_2$ flux in the southwest East Sea, calculated from the $fCO_2$ predicted by the RF model, was $-0.76{\pm}1.15mol\;m^{-2}yr^{-1}$, close to the lower bound of the previous estimates in the range of $-0.66{\sim}-2.47mol\;m^{-2}yr^{-1}$. The time series of $fCO_2$ predicted by the RF model showed a significant variation even in a short time interval of a week. For accurate evaluation of the $CO_2$ flux in the Ulleung Basin, it is necessary to conduct high resolution in situ observations in spring when $fCO_2$ changes rapidly.