• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.238-248
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• 2019

In the high-temperature and high-pressure irradiation environments, the multi-field coupling processes of hydrogen diffusion, hydride precipitation and mechanical deformation in Zircaloy cladding tubes occur. To simulate this hydrogen-induced complex behavior, a multi-field coupling method is developed, with the irradiation hardening effects and hydride-precipitation-induced expansion and hardening effects involved in the mechanical constitutive relation. The out-pile tests for a cracked cladding tube after irradiation are simulated, and the numerical results of the multi-fields at different temperatures are obtained and analyzed. The results indicate that: (1) the hydrostatic stress gradient is the fundamental factor to activate the hydrogen-induced multi-field coupling behavior excluding the temperature gradient; (2) in the local crack-tip region, hydrides will precipitate faster at the considered higher temperatures, which can be fundamentally attributed to the sensitivity of TSSP and hydrogen diffusion coefficient to temperature. The mechanism is partly explained for the enlarged velocity values of delayed hydride cracking (DHC) at high temperatures before crack arrest. This work lays a foundation for the future research on DHC.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.3
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• pp.42-55
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• 2021

In this study, the effect of nozzle performance according to the selection of the center line equation. Three of S-type nozzles and three of double S-type nozzles were designed using the curve equation and design parameters, and the nozzle shielding performance was evaluated using the shielding ratio definition. In order to analyze the internal flow of the nozzle, the characteristics of the velocity distribution and pressure distribution were studied, and the nozzle performance was evaluated through the total thrust ratio(f) and the nozzle insulation efficiency coefficient(η). On the other hand, the centerline with a sharply change in curvature at the entrance has a low nozzle performance and a high shielding rate. The double S-type nozzle is excellent nozzle performance and shielding rate by using a smooth centerline at the first curvature.

• Journal of Korean Society on Water Environment
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• v.35 no.5
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• pp.409-417
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• 2019

In this study, a $480m^3/day$ pilot device was constructed through laboratory experiments based on the Ministry of Environment manual. The purpose of this study was to analyze the characteristics of CSO treatment and backwashing characteristics by applying the pilot device to the field. The purpose of this study was to acquire the basic data necessary for the design and operation management of the real scale filtration type non-point pollution control system. The filtration was conducted while maintaining the linear velocity of 20m/hour. The CSO treatment efficiencies of the pilot devices were 0.4-76.1%(mean 49.0 %), SS 51.4-91.6%(mean 77.8%), COD 22.2-59.4% (mean 38.3%) and TP 14.5-52.6%(mean 38.1%),respectively. The correlation coefficient between SS and the turbidity of influent water was 0.90, higher than that of CSO. To operate the treatment system effectively, the turbidity can be easily measured in real time as the monitoring item is the most appropriate because SS is the main target substance of the non-point source. As a result of analyzing the adsorbent treatment characteristics of PP filter material applied to this pilot device, the average particle diameter range of influent was $4.6-40.1{\mu}m$(mean $21.2{\mu}m$) and the treated water was $0.9-24.5{\mu}m$(mean $6.4{\mu}m$), respectively. Particles of approximately 10m or less are leached out, and so it is necessary to compensate for the raw water containing micro particulate matter.

• Atmosphere
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• v.32 no.2
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• pp.163-178
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• 2022

This study aims to evaluate the accuracy of retrieved horizontal winds with different quality control methods from three Doppler lidars deployed over the complex terrain during the PyeongChang 2018 Olympic and Paralympic games. To retrieve the accurate wind profile, this study also proposes two quality control methods to distinguish between meteorological signals and noises in the Doppler velocity field, which can be broadly applied to different Doppler lidars. We evaluated the accuracy of retrieved winds with the wind measurements from the nearby or collocated rawinsondes. The retrieved wind speed and direction show a good agreement with rawinsonde with a correlation coefficient larger than 0.9. This study minimized the sampling error in the wind evaluation and estimation, and found that the accuracy of retrieved winds can reach ~0.6 m s^-1 and 3° in the quasi-homogeneous wind condition. We expect that the retrieved horizontal winds can be used in the high-resolution analysis of the horizontal winds and provide an accurate wind profile for model evaluation or data assimilation purposes.

• Advances in concrete construction
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• v.14 no.2
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• pp.103-113
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• 2022

On the basis of fabrication, the utilization of nano material in numerous industrial and technological system, obtained the utmost significance in current decade. Therefore, the current investigation presents a theoretical disposition regarding the flow of electric conducting Williamson nanoliquid over a stretchable surface in the presence of the motile microorganism. The impact of thermal radiation and magnetic parameter are incorporated in the energy equation. The concentration field is modified by adding the influence of chemical reaction. Moreover, the splendid features of nanofluid are displayed by utilizing the thermophoresis and Brownian motion aspects. Compatible similarity transformation is imposed on the equations governing the problem to derive the dimensionless ordinary differential equations. The Homotopy analysis method has been implemented to find the analytic solution of the obtained differential equations. The implications of specific parameters on profiles of velocity, temperature, concentration and motile microorganism density are investigated graphically. Moreover, coefficient of skin friction, Nusselt number, Sherwood number and density of motile number are clarified in tabular forms. It is revealed that thermal radiation, thermophoresis and Brownian motion parameters are very effective for improvement of heat transfer. The reported investigation can be used in improving the heat transfer appliances and systems of solar energy.

• Wind and Structures
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• v.36 no.2
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• pp.121-131
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• 2023

Aiming at the problem that fatigue characteristics of metal roof rely on local physical tests and lacks the cyclic load sequence matching with regional climate, this paper proposed a method of constructing the fatigue load spectrum based on integration of wind load model, measured data of long-span metal roof and climate statistical data. According to the turbulence characteristics of wind, the wind load model is established from the aspects of turbulence intensity, power spectral density and wind pressure coefficient. Considering the influence of roof configuration on wind pressure distribution, the parameters are modified through fusing the measured data with least squares method to approximate the actual wind pressure load of the roof system. Furthermore, with regards to the wind climate characteristics of building location, Weibull model is adopted to analyze the regional meteorological data to obtain the probability density distribution of wind velocity used for calculating wind load, so as to establish the cyclic wind load sequence with the attributes of regional climate and building configuration. Finally, taking a workshop's metal roof as an example, the wind load spectrum is constructed according to this method, and the fatigue simulation and residual life prediction are implemented based on the experimental data. The forecasting result is lightly higher than the design standards, consistent with general principles of its conservative safety design scale, which shows that the presented method is validated for the fatigue characteristics study and health assessment of metal roof.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2997-3009
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• 2023

The Passive containment Air-cooling System (PAS) can effectively remove the decay heat of the modular small nuclear reactor after an accident. The details of natural convection around the dome, which is a key part of PAS, were investigated numerically in the present study. The thermal dynamics around the dome were studied through the temperature, pressure and velocity contours and the streamlines. Additionally, the formation of the buoyant plume at the top of the dome was investigated. The results show that with the increase of Ra, the lift-off point moves toward the bottom of the dome, and the eddy under the buoyant plume grows larger gradually, which enhances the heat transfer. And the heat transfer along the dome surface with different truncation angles was investigated. As the angle increases, the heat transfer coefficient becomes stronger as well. Consequently, a newly developed heat transfer correlation considering the influence of truncation angle for the dome is proposed based on the simulated results. This study could provide a better understanding of natural convection around the dome of PAS and the proposed correlation could also offer more predictive value in the improvement of nuclear safety.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.154-165
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• 1993

A stochastic method using continuous time Markov process is presented to model the one-dimensional convective nuclide transport in geologic media, which have usually heterogeneous feature in physical/geochemical parameters such as velocity, dispersion coefficient, and retardation factor resulting poor description by conventional deterministic advection-dispersion model. The primary desired quantities from a stochastic model are the mean values and variance of the state variables as a function of time. The time-dependent probability distributions of nuclides are presented for each discretized compartment given the volumetric groundwater flux and the intensity of transition. Since this model is discrete in medium space, physical/geochemical parameters which affect nuclide transport can be easily incorporated for the heterogeneous media as well as remarkably layered media having spatially varied parameters. Even though the Markov process model developed in this study was shown to be sensitive to the number of discretized compartments showing numerical dispersion as the number of compartments are increased, this could be easily calibrated by comparing with the analytical deterministic model.

• Journal of the Korea Institute of Building Construction
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• v.23 no.3
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• pp.285-293
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• 2023

In this research, we embarked on a meticulous analysis of the challenges inherent in real-world scenarios relating to the durability design standards of engineered concrete structures and the assessment of carbonation durability in concrete guidelines. Our investigation brought to light substantial issues concerning constructability and quality assurance. The genesis of these problems is the exclusive application of prescribed strength to exterior walls, neglecting other elements to facilitate smoother licensing procedures. While this methodology aims to mitigate financial constraints in alignment with enhanced standards, it invariably invites complications. Furthermore, it is imperative to resolve the uncertainty surrounding durability evaluations by establishing a clear and definitive objective. Alongside this, actionable steps must be formulated to forestall the emergence of fissures between the floors of residential buildings, particularly apartment complexes. It is equally essential to tackle issues connected to application by devising a comprehensive management strategy for potential cracking during the phase of maintenance.

• Physical Therapy Rehabilitation Science
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• v.11 no.4
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• pp.488-492
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• 2022

Objective: The purpose of this study is to find out the reliability and validity of the newly updated Balancia 2.5 program using Wii balance board through equipment that can measure center of pressure data with the precision. Design: Cross-sectional study Methods: Twenty-seven healthy adults participated in the study. The subjects were assessed for static balance ability by Accusway, and were assessed for static balance ability on Wii balance board connected to theBalancia 2.5 program.To limit postural fluctuations due to stare, the subjects were asked to look at a 15 cm dot drawn 3 m in front of them for 30 seconds with their eyes open. Static balance ability data such as path length and sway velocity were extracted from all measurement tools.Intra-rater and inter-rater reliability and validity were extracted through intraclass correlation coefficient (ICC) and 95% confidence interval (CI). Results: The intra-rater reliability that the same rater shows consistent results through test-retest was a high level at ICC=0.968 (0.926~0.986), and inter-rater reliability that the requires consistent results even when measured by different raters was a high level at ICC=0.943 (0.870~0.975). The validity was a high level at ICC=0.948 (0.881~0.977), which shows whether the measurement tool is properly measuring what it is intended to measure. Conclusions: The Balancia 2.5 program, newly updated through this study, proved to be a program with high reliability and validity in evaluating static balance ability like the existingBalancia 2.0 program.