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Concrete sleepers in operation are commonly damaged by various internal and external factors, such as poor materials, manufacturing defects, poor construction, environmental factors, and repeated loads and driving characteristics of trains; these factors affect the vibration response, mode shape, and natural frequency of damaged concrete sleepers. However, current standards in South Korea require only a subjective visual inspection of concrete sleepers to determine the damage degree and necessity of repair or replacement. In this study, an impact hammer test was performed on concrete sleepers installed on the operating lines of urban railroads to assess the field applicability of the modal test method, with the results indicating that the natural frequency due to concrete sleeper damage was lower than that of the undamaged state. Furthermore, the discrepancy between the simulated and measured natural frequencies of the undamaged concrete sleeper was approximately 1.87%, validating the numerical analysis result. The natural frequency of the damaged concrete sleepers was lower than that of the undamaged concrete sleeper, and cracks in both the concrete sleeper core and the rail seat had the lowest natural frequency among all the damage categories. Therefore, the damage degrees of concrete sleepers can be quantitatively estimated using measured natural-frequency values. [ABSTRACT FROM AUTHOR]

In this study, dynamic numerical analysis was conducted on the existing sound barrier wall structure and the recently developed double-sided solar-module-integrated sound barrier wall structure using the finite-difference method for numerical modeling. A seismic safety evaluation was performed based on a series of numerical analysis results. Both structures were modeled using a 3D modeling technique with FLAC 3D to account for differences in lateral stiffness. For seismic considerations, the Pohang seismic wave was selected to represent short-period earthquakes in line with Korea's seismic characteristics. Additionally, the Hachinohe seismic wave was chosen to simulate long-period earthquakes and consider the effects of the seismic period. To calculate the input seismic waves based on the ground response, a site response analysis was conducted for a site designated for demonstrating a double-sided solar module-integrated sound barrier wall structure in Korea. The analysis reveals that the existing structure maintains overall structural integrity and ensures the safety of solar modules even in an earthquake with a return period of 2400 years. However, for a solar module-integrated sound barrier wall structure, stresses exceeding the compressive strength of the solar module occur in earthquakes with a return period exceeding 1000 years, necessitating additional design and reinforcement for preparation. [ABSTRACT FROM AUTHOR]

To model the COVID-19 infection and develop effective control measures, this paper proposes an SEIR-type epidemic model considering the impact of face-mask wearing and vaccination. Firstly, the effective reproduction number and the threshold conditions are obtained. Secondly, based on the data of South Korea from January 20, 2022 to March 21, 2022, the model parameters are estimated. Finally, a sensitivity analysis and the numerical study are conducted. The results show that the face-mask wearing is associated with 83 % and 90 % reductions in the numbers of cumulative cases and newly confirmed cases, respectively, after a period of 60 days, when the face mask wearing rate increases by 15 % . Furthermore, the vaccination rate is associated with 75 % and 80 % reductions in the numbers of cumulative cases and the newly confirmed cases, respectively, after the same period of 60 days when the vaccination rate is increased by 15 % . A combined measure involving face-mask wearing and vaccination may be more effective and reasonable in preventing and controlling this infection. It is also suggested that disease control departments should strongly recommended the wearing of face masks s as well as vaccination to prevent the unvaccinated people from becoming infected. [ABSTRACT FROM AUTHOR]

Floating ring seals are widely used as a leakage control solution for turbomachines because they effectively operate with small clearances between the shaft and seal. The oxidizer pump of the 7 tonf liquid engine in the Korea Space Launch Vehicle II (KSLV-II) operates at high rotational speeds and under cryogenic conditions and has floating ring seals in the bearing cooling path to reduce leakages. In this study, we evaluated the frictional force acting on the nose of the floating ring in the oxidizer pump of the 7 tonf turbopump using numerical analysis, and we investigated the radial force on the floating ring induced by the vibration of the rotor and the flow characteristics around the floating ring seal. Through a comparison of the frictional and floating forces according to the change in the diameter of the floating ring noses, we also estimated the dynamic positioning of the floating ring. In addition, we examined the leakage of the floating ring seals with the rotational speed and gap size of the floating ring, and we used the results as data for designing a floating ring seal. Finally, we performed turbopump real-propellant tests with the floating ring seal of the high and the middle noses, finding that the test result was in good agreement with the results of numerical analysis. [ABSTRACT FROM AUTHOR]

A Venlo-type greenhouse with a continuous roof vent (CR-Venlo greenhouse) was proposed by the Ministry of Agriculture, Food and Rural Affairs, South Korea (2019) for natural ventilation even during summers. It is ventilated through the buoyancy effect of the heated air using the high eave elevation. However, the CR-Venlo greenhouse was not distributed domestically, and its ventilation efficiency was not quantitatively evaluated. We aimed to analyze the natural ventilation efficiency of the greenhouse according to the eave height, using computational-fluid-dynamics. The simulation model was analyzed for hot summer conditions. The target greenhouse is ventilated only through the roof vent with all roof windows open; therefore, the air introduced through the roof window is easily exhausted. To evaluate the efficiency of ventilation, the external air entering through the roof window was calculated and evaluated. The amount of incoming air varied greatly with the location of the span and average temperature of the greenhouse; The temperature of the crop zone decreased lognormally with increasing height of the eave. Moreover, the ventilation efficiency of CR-Venlo greenhouse could be increased by improving the ventilation structure such as a shape, position or combination of roof window. [ABSTRACT FROM AUTHOR]

[Display omitted] • We have developed a Computational Fluid Dynamics model to calculate the release rate of the contents of a spent nuclear fuel transport cask lost in the deep sea. • To handle the scale difference between the flow path generated in the containment boundary of cask and the deep-sea environment, a sub-modeling technique was utilized. • Through comparisons with other models, we have concluded that considering the deep-sea environment is crucial for an accurate assessment of release rates. Given that all nuclear power plants in the Republic of Korea are located on the coast, their interim storage facilities are also likely to be located on the coast, making maritime transportation of spent nuclear fuel (SNF) inevitable. Developing a technology to assess the impact of immersion accidents is crucial to prevent severe radiological consequences. The accurate release rate of radionuclides should be calculated by determining the flow rate through a flow path in the breached containment boundary. The fluid flow through the micro-scale flow path can be evaluated by integrating the flow inside and outside the transport cask. In this study, we used a sub-modeling technique to evaluate the micro-scale flow. Its results are compared with the barrier effect model developed by CRIEPI. The model of this study will be used in the development of a maritime transportation risk assessment code suitable for the situation and environment in Korea. [ABSTRACT FROM AUTHOR]

A field scale productivity analysis is required for the development of gas hydrate in marine sedimentary layers to verify the field applicability of production techniques and to improve productivity. In this study, the productivity resulting from the application of depressurization using multi-wells for the development of gas hydrate in the Ulleung Basin, East Sea of Korea, was determined. A numerical analysis model reflecting the conditions of candidate sites for the Ulleung Basin was constructed, and the productivity and dissociation behavior were comparatively analyzed. The pressure propagation and gas hydrate dissociation region by the multi-wells were wider and the productivity was higher than that of a single well. Different depressurization effects according to the spacing of multi-wells affected productivity. The results provide basic data for productivity analysis when establishing a field test production plan for the Ulleung Basin. [ABSTRACT FROM AUTHOR]

Owing to the importance of land-surface temperature (LST) and its variability in ecosystems, long-term LST monitoring is necessary. Because direct field measurements and satellite images have drawbacks, an appropriate LST simulation model is required. Therefore, in this study, we developed an hourly land-surface temperature model for Jeju Island and evaluated the variability in the predicted LST. The LST model was developed based on numerical analysis using the finite element method and calibrated and validated by comparing the simulated and measured temperature data obtained from four weather stations on Jeju Island. The simulated and measured LST have coefficients of determination of 0.96 and root mean square errors of 2.29 °C in validation. The model was used to predict LST data for a representative day of every month in 2018 using the mean monthly air temperature, and the variability of the data was calculated using the information entropy-based disorder index (DI). Linear relationships among the geographic coordinates, terrain attributes, mean LST, and DI were analyzed. Latitude and shaded relief were significantly linearly related with the overall mean LST and mean DI of the entire period, whereas longitude, elevation, and slope were not. The overall mean LST and mean DI for the entire period were negatively linearly related, but significant linear relationship did not appear in the case of individual months. [ABSTRACT FROM AUTHOR]

• Invasive species management is necessary to minimize their detrimental effects. • Effective control of invasive species spread requires a spatial perspective. • Species distribution models can assist in prioritizing areas for management. Owing to their potentially wide-ranging adverse effects, invasive species are a growing global problem. The common ragweed (Ambrosia artemisiifolia var. elatior (L.) Desc) is one of the most important invasive plants, necessitating management because of its tendency to "spread." Various studies and management strategies are being conducted based on the concept of "density" because of the increasing importance of the spatial perspective in this application. Although eradicating from the outliers (low-density regions) has a high efficiency, there is a lack of validation methodology for deriving both spatial and statistical results. We formed a general validation methodology by assessing various removal scenarios based on two removal strategies, namely Outside-in and Inside-out. These approaches exhibited several removal rates, and take into account the spatial perspective by considering species density. The Outside-in strategy entails the removal of species, which commences from the low-density regions, whereas the Inside-out removal initiates from the high-density regions. To classify the spatial regions for priority removal using each strategy, we defined the density level and then processed the removal of the occurrence points for each strategy to derive generalized results. We used the species distribution model MaxEnt to determine the predicted distribution of the target species for each removal strategy applied; subsequently, the final randomly generalized occurrence point results were used as model input data. Assessment analyses were conducted based on the final probability distribution and appearance level for each scenario, which included a newly proposed index was termed the "removal effect index." Results indicated that the efficacy of the Outside-in removal strategy exceeded that of the Inside-out strategy for all assessment analyses, with the removal effect index showing a difference of about 2–5 times between strategies in each removal rate. In addition, through numerical analysis of the changed area of each scenario, the Outside-in strategy showed a successful removal effect in the "removal management priority spatial range," whereas the Inside-out strategy showed limitations. We confirmed the efficacy of the Outside-in strategy as an optimal removal approach that takes into account spatial information of the priority spatial range for eradication in terms of the removal effect. [ABSTRACT FROM AUTHOR]

Featured Application: Authors are encouraged to provide a concise description of the specific application or a potential application of the work. This section is not mandatory. A concrete track, such as Rheda 2000 is commonly used in high-speed railways in Korea, Germany, China, etc., to enhance the operational safety of trains and to reduce the maintenance costs. However, when settlement of embankment or a crack in the concrete slab track occurs, the durability of the concrete track deteriorates significantly. Transition zones are considered to be vulnerable and are often deformed in railway embankments. The characteristics of track support stiffness and stresses on the rail in a deformed section are different from those in an undeformed section. In this study, a field measurement and numerical analysis were carried out to identify the dynamic response on transition zones where the track is deformed. A numerical analysis model was built to simulate the deformed concrete slab track, and it was compared with measured data from field tests for verification. The field tests to measure the stresses on the rail were performed in a train speed range from 280 to 300 km/h. According to the numerical analysis, the dynamic characteristics of the track varied with train speeds, which were then compared with the allowable stresses of the concrete slab track. [ABSTRACT FROM AUTHOR]

In this study, risk analysis was conducted to evaluate the vulnerability of bridge columns to vehicle impact. A three-step risk analysis procedure was used. The first step involved a Preliminary Risk Analysis (PRA), which was an initial screening step to determine whether a bridge column requires second-step analysis or not. The second step was a Simplified Risk Analysis (SRA), which involved determining the level of risk (low, moderate, or high) for a bridge column. The third step comprised a Detailed Risk Analysis (DRA). Computer simulation was based on the results of SRA. In this study, the risk level of 8,267 bridges in South Korea was evaluated, and a resulting total of 58 bridge columns in the Risk Level High (RLH) category were selected as a result of SRA. These bridge columns were classified into five types based on their slenderness ratio. Using these five types of bridge column, DRA was conducted. As expected, larger deformations of the bridge column were observed if the vehicle velocity and slenderness ratio were both increased. Using the bridge columns in the categories of response high and response moderate under vehicle impact, fragility curves were proposed using statistical data of material strength and the few results of the numerical analysis. [ABSTRACT FROM AUTHOR]

In this study, we predicted the structural behavior of a track-bridge and a bridge based on the expected increases in future train speeds by modeling the Yeongjong Bridge (a part of the Incheon International Airport Expressway in Korea). To verify the train's safe operation, we performed a three-dimensional (3D) numerical analysis using full-scale bridge modeling. The rail-girder interaction force generated at one end of the direct fixation track of Yeongjong Bridge during train operations was evaluated by taking field measurements of the vertical displacements of the rail and girder at the center and end of a track girder. We further compared our predictions with various field measurements to evaluate the dynamic behavior of the entire Yeongjong Bridge. [ABSTRACT FROM AUTHOR]

In South Korea, the construction of new multi-unit residential structures has been continuously increasing in order to accommodate multiple households in single structures. However, the presence of walls and floors shared with neighbors makes these structures exceptionally vulnerable to floor noise transmission when the noise of everyday life occurs. In particular, South Korea has many social problems associated with such floor noise, which require the utmost attention and immediate resolution. In this study, a 17-story structure was selected as a test structure. Field measurements were carried out. A numerical model for the 17-story structure was developed in order to perform a vibro-acoustic analysis. The validation of the numerical model comparing with the field measurement data results shows a good agreement. Finally, it is concluded that numerical analysis can be applied to resolve floor noise problems arising in multi-unit residential structures. [ABSTRACT FROM AUTHOR]

Vehicle speeds have increased due to improved road condition. However, this increased speed can result in high energy collisions. Recently, a vehicle occupant in South Korea was killed by a fragment ejected from a concrete median barrier that was struck by a vehicle. The current design impact level of a concrete median barrier (CMB) is SB5-B (270 kJ). However, the impact level of the mentioned accident was estimated as over SB7 (2300 kJ). In the present work, a series of numerical analyses was conducted to reduce the fragmentations of CMB due to impact. Field test were utilized to verify the newly developed model of CMB in impact events. The wire-mesh reinforcements and increment of the cross section were considered as design modifications. In particular, a special device to absorb a significant collision energy has been developed without a dramatic increase in construction cost. This device consists of an empty space around the dowel bars which fix the barrier to the foundation. The empty space allows the dowel bars to deform to absorb collision energy. The performance of the new concrete median barrier equipped with the shock absorbing devices was verified by using carefully designed field test data. [ABSTRACT FROM AUTHOR]

Coastal areas are being increasingly damaged by the expansion of seawater‐intrusion areas. This study suggested a three‐step method to prioritize the countermeasures adopted to reduce the areas affected by seawater intrusion. First, the most vulnerable area to damage from seawater intrusion was selected among 25 areas on the western coast of the Republic of Korea using three multicriteria decision‐making (MCDM) methods. As a result, Taean‐gun was selected as the most vulnerable area for seawater intrusion. Second, a numerical model called SEAWAT was configured to predict the areas where seawater intrusion could potentially occur. For future scenarios, Representative Concentration Pathways (RCPs) 4.5 and 8.5 were used as the sea‐level rise scenarios. To predict the future use of groundwater, the future groundwater extraction rate was predicted using a linear regression of the groundwater‐use data over the past 10 years. As a result, it was predicted that 68.5% of the total Taean‐gun area would be affected by seawater intrusion for RCP 8.5 and current trends in groundwater use. Third, the effectiveness of the measures adopted for the reduction of seawater‐intrusion areas were analysed by considering the projected future scenario and the local characteristics (including the total population, population density, groundwater‐level distribution, salinity distribution, groundwater‐use characteristics, and ground‐elevation distribution) of the Taean‐gun district. After considering the effects of the countermeasures adopted for the different locations in Taean‐gun and the data related to seawater intrusion, the priority areas for applying countermeasures against seawater intrusion were determined using three MCDM methods. It was concluded that the Taean‐myeon is a priority area for applying countermeasures. [ABSTRACT FROM AUTHOR]

Aims: We propose a novel nomogram, which graphically expresses the numerical relationship between type 2 diabetes (T2D) and disease-related risk factors.Methods: Data of 8999 patients from the 2013-2014 Korean National Health and Nutrition Examination Survey were analyzed. Multiple logistic regression analysis was performed to assess risk factors for T2D and a nomogram was constructed based on screened risk factors. A receiver operating curve (ROC) and calibration plot were created to evaluate the accuracy of the nomogram.Results: The risk factor with the greatest impact on the prevalence of T2D was age over 60 years (95% CI 5.97-15.00, OR = 9.46), followed by presence of dyslipidemia and cardiovascular disease (95% CI 5.90-13.68, OR = 8.98), family history of T2D (95% CI 2.33-3.64, OR = 2.92), abdominal obesity (OR = 1.76), hypertension (OR = 1.75), male gender (OR = 1.55), current-smoking status (OR = 1.52), lower education level (OR = 1.42), and lower income (OR = 1.30). The area under the ROC curve (AUC) showed statistically significant determination (AUC = 0.83). The equation of the calibration plot was drawn along the ideal line; coefficient of determination was 0.864.Conclusion: Our proposed nomogram could accurately predict the risk of T2D from nationwide data. The novel nomogram can be a useful tool for screening patients with T2D risk in a Korean population. [ABSTRACT FROM AUTHOR]

Kim, H.J.; Cho, S.M., and Cho, W.C., 2018. Numerical analysis of beach erosion at Jeongdongjin Beach in South Korea using field survey and measurement data. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 596–600. Coconut Creek (Florida), ISSN 0749-0208. Recently, Jeongdongjin Beach in Gangneung, Gangwon–do, in the eastern part of South Korea, has been seriously eroded, and several parts of the revetments along the coast were subsided due to frequent high wave attacks. Thus, several parts of the Jeongdongjin rail bike track and facility in the southern part of Jeongdongjin station were damaged and washed out. In this study, field surveys and measurements (including waves, current, water depth, seabed material, beach profile, and shoreline) at Jeongdongjin Beach 2014–2015 were conducted to analyze and determine the erosion process. From the surveys and measurements, it reveals that longshore currents moving to the south and north are generated in winter and summer season due to dominant NE and ENE wave directions, respectively. Rip currents are also generated in several points near the coast due to waves coming from various directions and morphological characteristics. Beach erosion at the front of Jeongdongjin station has repeatedly occurred due to high wave attacks. Numerical simulations on the generation of long-shore current, sediment transport, and shoreline change were conducted using field data, and the erosion process at Jeongdongjin Beach was analyzed to determine the characteristics of seasonal longshore sediment transport and the effect of the construction of revetments to beach erosion. From these monitoring data and numerical results, the process of Jeongdongjin Beach erosion was predicted and beach maintenance and protection plans at Jeongdongjin Beach are established. [ABSTRACT FROM AUTHOR]

Subways are used for public transportation as a commuting medium in Korea. Subway trains operate mainly through tunnels. Fine particles generated by friction between rails and train wheels affect the air quality inside a train because the particles enter the ventilation system of the train passing through a tunnel. The PM10 concentration has been mainly used to evaluate indoor air quality, and the PM2.5 concentration has measured recently. Therefore, in this study, the concentrations of the particles entering the air-inlet with respect to particle sizes including 0.1, 1, 2.5 and 10 µm were investigated by using numerical analysis with ANSYS FLUENT software. The particle analysis was performed corresponding to 10, 40 and 80 km/h. It is expected that the numerical results would be helpful in studying the effect of particles corresponding to PM2.5 on the ventilation system, to improve the air quality inside a train passing through a tunnel. [ABSTRACT FROM AUTHOR]

When a gas hydrate reservoir is depressurized for gas production, the production tendency and dissociation behavior may differ depending on conditions such as the bottom hole pressure and depressurization rate. Gas hydrate dissociation is a complex process that involves the transfer of materials and heat, and on-site analysis based on laboratory-scale results is critical. In the present study, a field-scale numerical analysis was performed to reflect the conditions of the Ulleung Basin in the East Sea of Korea. The dissociation behavior, which varies depending on the conditions in the gas hydrate-bearing sediment, was analyzed under various conditions of bottom hole pressure and depressurization rate. This study also identified the effects of depressurization conditions on gas hydrate saturation. As the bottom hole pressure decreased and the depressurization rate increased, the production rate and cumulative production of gas and water increased, and the radius of the pressure propagation effect at the beginning of production increased. In sediments with a gas hydrate saturation of ≥70%, the pressure propagation was unstable and the dissociation rate was low. These results can serve as preliminary data for the field production of gas hydrates in the Ulleung Basin. • Analysis of dissociation behavior at field-scale under depressurization conditions. • Confirmation of gas hydrate dissociation distribution in multilayered sediments. • Productivity and production efficiency change due to depressurization conditions. • Identification of changes in pressure and temperature with a specific saturation. [ABSTRACT FROM AUTHOR]

This study quantitatively analyzed the effect of fog cooling on temperature reduction and conducted an optimization study on the layout for planning a fog cooling system in the Daegu Metropolitan City. First, the design and verification of a single fog cooling unit was identified through an indoor experiment. Second, the temperature reduction effect of the installed fog cooling system was measured based on a sensor and verified through a finite volume method (FVM)-based computational fluid dynamics (CFD) analysis. Third, a numerical analysis of the optimal fog cooling arrangement was designed and performed in the Indongchon area. The temperature reduction design manual and model equations, which can be used by decision-makers, were analyzed through numerical analysis. The measured temperature reduction and simulation values had a high accuracy of R2 ≥ 0.8. Based on the verified model, scenarios A–D were designed and analyzed according to the fog cooling arrangement. Scenario B, in which the fog cooling was arranged vertically to the wind direction, appeared to be the most efficient. In this case, the volume average temperature where fog cooling was installed could be reduced by up to 3.02 °C. It was also found that efficiency is higher when the fog cooling system is positioned at narrow intervals of ≤5 m than at wide intervals of ≥10 m, considering the wind direction. The results of this study can aid decision makers—including urban policymakers and planners—for estimating the potential extent of temperature reduction and increase in humidity by adopting fog cooling. • The use of fog cooling under temperature near 40 °C in Korea can reduce the temperature by about 3 °C (7%.) • Cooling fog arrangement with an interval of 5 m installed perpendicular to wind direction is most effective. • The temperature reduction effect of fog cooling is greater at 1 m from the ground, the sensible height of the vulnerable groups, than 1.5 m. • A fog cooling system having an interval of 5 m is most effective to reduce heatwave. [ABSTRACT FROM AUTHOR]

• The optimal content of DG for the CRAM was determined by evaluating the tensile strength tests. • Dynamic modulus of CRAM w/DG were compared with HMA to evaluate the performance. • Finite element analysis was performed to assess the mechanical behavior of CRAM w/DG for the base course. • CRAM w/DG needs to increase the thickness to perform on equivalent with general asphalt base course. The purpose of this study is to find and evaluate the optimal mixing ratio of Cold Recycled Asphalt Mixtures (CRAM) with Desulfurized Gypsum (DG) mineral additives that satisfies the newly revised quality standard of the pavement in South Korea, and to evaluate their mechanical behavior. The optimal content of inorganic materials for CRAM is determined by the evaluation of the indirect tensile strength tests by DG contents. The performance evaluation of mixture for the common mixture type for the asphalt base course (Black Base course, hereafter BB course) and two types of developed CRAM with DG(w/DG) was conducted through Dynamic modulus. 3D FEA (Finite Element Analysis) of asphalt pavement applying the dynamic modulus through the experiments was performed in order to compare the behavior of the typical BB course and CRAM course for the alternative. When 7% of DG mineral additive is mixed into CRAM, it was found that the newly changed standard was satisfied. For CRAM 7%, since inorganic materials were mixed and the impact of temperature in the overall binder was relatively low, the stiffness change in the high-temperature region was less sensitive than in BB. As a result of the finite element analysis, the horizontal and vertical strain of the pavement using 0% CRAM and 7% CRAM as the substrate was 1.6 to 3.5 times greater than that of the pavement using BB. Based on the results of the experiment and 3D FE analysis, it is concluded that the thickness of the CRAM w/DG course should be designed and constructed to be thicker for the same performance as the BB course. [ABSTRACT FROM AUTHOR]

The interest in the seismic performance of nuclear power plants has increased worldwide since the Fukushima Daiichi Nuclear Power Plant incident. In Korea, interest in the seismic safety of nuclear power plants has increased since the earthquake events in Gyeongju (2016) and Pohang (2017). In Korea, studies have been conducted to apply seismic isolation systems to ensure seismic safety while minimizing the design changes to nuclear power plants. Nuclear power plants with seismic isolation systems may have a higher seismic risk due to the failure of the piping system in the structure after a relatively large displacement. Therefore, it is essential to secure the seismic safety of pipes for the safe operation of nuclear power plants. The seismic safety of pipes is determined by seismic fragility analysis. Seismic fragility analysis requires many seismic response analyses because it is a statistical approach to various random variables. Typical numerical conditions affecting the seismic response analysis of pipes are the convergence conditions and mesh size in numerical analysis. This study examined the change in the seismic safety of piping according to the numerical conditions. The difference in the seismic response analysis results of the piping according to the mesh size was analyzed comparatively. In addition, the change in the seismic fragility curve of the piping according to the convergence conditions was investigated. [ABSTRACT FROM AUTHOR]

Airworthiness standards of Korea recommend verifying structural safety by experimental tests and analytical methods, owing to the development of analysis technology. In this study, we propose a methodology to verify the structural safety of aircraft components based on airworthiness requirements using an analytical method. The structural safety and fatigue integrity of a linear actuator for flap control of aircraft was evaluated through numerical analysis. The static and fatigue analyses for the given loads obtained from the multibody dynamics analysis were performed using the finite element method. Subsequently, the margin of safety and vulnerable area were acquired and the feasibility of the structural safety evaluation using the analytical method was confirmed. The proposed numerical analysis method in this study can be adopted as an analytical verification methodology for the airworthiness standards of civilian aircraft in Korea. [ABSTRACT FROM AUTHOR]

Methane hydrate has attracted attention as a next-generation resource, and many researchers have conducted various studies to estimate its productivity. Numerical simulation is the optimal method for estimating methane gas productivity. Meanwhile, using a reasonable input parameter is essential for obtaining accurate numerical modeling results. Permeability is a geotechnical property that exhibits the greatest impact on productivity. The permeability of hydrate-bearing sediment varies based on the sediment pore structure and hydrate saturation. In this study, an empirical permeability model was derived from experimental data using soil specimens from the Ulleung Basin, and the model was applied in numerical analysis to evaluate the sediment gas productivity and ground stability. The gas productivity and stability of hydrate-bearing sediments were compared by applying a widely used permeability model and the proposed model to a numerical model. Additionally, a parametric study was performed to examine the effects of initial hydrate saturation on the sediment gas productivity and stability. There were significant differences in the productivity and stability analysis results according to the proposed permeability model. Therefore, it was found that for accurate numerical analysis, a regional permeability model should be applied. [ABSTRACT FROM AUTHOR]

As buildings generally have become larger and more airtight, the ventilation rate has decreased further, causing insufficient ventilation which leads to moisture problems such as condensation, mold growth, reduction of thermal insulation performance and corrosion of building materials. In order to prevent moisture problems, it is essential to understand the thermal and hygric status of a climatic region. In this study, the hygrothermal environmental zone considering not only the thermal environment but also the hygric environment was derived by analyzing the climate environment in Korea. The hygrothermal environmental zone has the advantage of being able to take into account the hygrothermal environment of the unexplored regions and to cope with climate change by quantifying the thermal and hygric environmental indexes in each region. Finally, the long-term moisture risk of the building envelopes was evaluated. As the results, it is considered that the proposed hygrothermal environmental zone is appropriate and it is necessary to consider the hygric environment in order to secure the moisture stability of the building envelope. • Existing regional classification and insulation performance standards were reviewed. • Climate indexes considering thermal and hygric environmental impacts were presented. • Hygrothermal environmental zones were derived that quantified the climatic conditions. • Moisture problems were assessed according to wall assembly and region. [ABSTRACT FROM AUTHOR]

• Weather, soil moisture, CO 2 concentration and fluxes were monitored for 965 days in South Korea. • Heterogeneities of soils have little effect on simulated CO 2 fluxes. • Increased soil moisture content results to high CO 2 concentration in soil profile. In Eumseong, Republic of Korea, a controlled CO 2 release site was designed by Korea CO 2 Storage Environmental Management (K-COSEM) Research Center to evaluate properly integrated CO 2 monitoring tools at the soil surface. CO 2 was released from the 55 m-length PVC-pipe buried at 2.5 m-depth, and then, CO 2 concentration and flux were monitored from August 1, 2015 to March 21, 2018 (965 days). Influencing environmental factors such as meteorological data, soil moisture and temperature at 5 different depths were monitored concurrently. The measured soil moisture content decreased rapidly when the soil temperature dropped below 0 °C. When CO 2 release began, both surface CO 2 flux and soil CO 2 concentration increased with a time lag. However, with occurrence of precipitation events, CO 2 flux decreased to almost 0 cm3 cm−2 day−1 but soil CO 2 concentration increased rapidly. The HYDRUS-SOILCO2 predicted soil moisture, temperature and natural background CO 2 flux compared to measured data (R2 = 0.74, 0.89, and 0.85). The 10 scenarios were constructed with different soil characteristic curves. Unlike soil moisture content, the simulated natural CO 2 flux did not depend heavily on soil characteristics. The mass of released CO 2 was estimated by the difference between the measured CO 2 flux data during the release test and natural CO 2 prediction model. At the 2nd CO 2 release test, there was 1.5 times difference between the actual released CO 2 mass and calculated CO 2 mass. [ABSTRACT FROM AUTHOR]

• Multi-layer repository design for high-level radioactive waste disposal is proposed. • Applicability of the multi-layer concept is analyzed by numerical simulations. • Multi-layer repositories meet the temperature criterion of 100 °C. • Stress evolutions in bentonite buffer materials are not significantly different from existing repository concept. • Rock mechanical behavior is different and potential for spalling failure exists. A multi-layer repository concept is proposed as an alternative to the single-layer repository concept to improve the disposal density of high-level radioactive waste (HLW) in Korea. Numerical simulations are performed to compare the coupled thermo-hydro-mechanical (THM) behavior in the existing Korean reference HLW disposal system (KRS) based on the single-layer repository concept to that in the new multi-layer repository concept. The applicability of the multi-layer repository concept, such as double- and triple-layer repositories, for the disposal of HLW is analyzed with respect to a maximum temperature criterion of 100 °C, evolution of saturation and pore pressure, and mechanical stability. Maximum temperatures are below 100 °C in the double- and triple-layer repository concepts, as in the single-layer reference, although two peaks in simulated temperatures are observed during the evolution of the thermal pulse, resulting from superposition of decay heat at different vertical levels in the multi-layer repository concept. There is no significant difference in the evolution of pore pressure and saturation among the three concepts. The evolutions of mean effective stress at the bentonite blocks and backfill materials are also not significantly different between the single-, double-, and triple-layer repository concepts, because the hydraulic behavior is quite similar, resulting in almost the same change in swelling pressure. Stress states in the rock mass near the tunnels and deposition holes remain below the Mohr-Coulomb failure envelopes at the repositories of 500 m depth in the single-, double-, and triple-layer repository concept simulations. However, the stress states exceed the Mohr-Coulomb failure envelopes at the repositories below 500 m depth (beneath the top layer) in the double- and triple-layer repository concepts. Also, mechanical analysis shows high potential for spalling failure around the deposition holes and tunnel roof in the double- and triple-layer repository concepts. Subsidence in the double- and triple-layer concepts due to the construction of repositories is much deeper than that in the single-layer concept, and uplift induced by heating the rock mass due to the decay heat in the double- and triple-layer concepts is much higher than in the single-layer concept. These results indicate that multi-layer repositories with larger depth intervals between layers are a feasible alternative to the KRS to safely achieve higher disposal density. [ABSTRACT FROM AUTHOR]

This study focused on finding the maximum productivity by optimizing vertical multi-effect diffusion solar distiller (VMED) and lowering the water cost of that. The numerical model of the VMED was experimentally validated, and then used to find the optimal conditions for the essential variables. The VMED consists of a glass cover, plates, wicks, and a seawater feeding unit. Each effect has a cotton-cloth wick attached to one side of the plate. This VMED repeatedly using condensation latent heat can get more production than that of conventional solar still. The numerical result showed that the optimum values of the gap distance of double glass cover and the number of effects were 25–30 mm and 10–15, and the feed flow rates of spring, summer, fall, and winter were optimal in 9, 16, 10, and 3 g/min, respectively in supplying same flow rate into all the effects. The maximum productions for all seasons (spring, summer, fall, and winter) were 16.6, 36.0, 19.0, 2.5 kg/(m2·d), respectively in South Korea. Economic analysis showed that the potential water price of the VMED was 6.1 $/m3, which was more competitive in the market than other solar desalination systems with a small capacity of <100 m3/d. • The maximum production is 36.0 kg/(m2·d) in summer. • This solar still is more competitive in small capacity <100 m3/d. • The best water cost is 6.1 $/m3. • Supplying the same flow rate to all effects is better. [ABSTRACT FROM AUTHOR]

A simple yet accurate photovoltaic (PV) performance curve as a function of satellite-based solar irradiation is necessary to develop a PV power forecasting model that can cover all of South Korea, where more than 35,000 PV power plants are currently in operation. In order to express the nonlinear power output of the PV module with respect to the hourly global horizontal irradiance derived from satellite images, this study employed the Gompertz model, which is composed of three parameters and the sigmoid equation. The nonphysical behavior of the Gompertz model within the low solar irradiation range was corrected by combining a linear equation with the same gradient at the conjoint point. The overall fitness of Linear-Gompertz regression to the 242 PV power plants representing the country was R2 = 0.85 and nRMSE = 0.09. The Gompertz model coefficients showed normal distributions and equivariance of standard deviations of less than 15% by year and by season. Therefore, it can be conjectured that the Linear-Gompertz model represents the whole country's PV system performance curve. In addition, the Gompertz coefficient C, which controls the growth rate of the curve, showed a strong correlation with the capacity factor, such that the regression equation for the capacity factor could be derived as a function of the three Gompertz model coefficients with a fitness of R2 = 0.88. [ABSTRACT FROM AUTHOR]

The purpose of this study is to develop a "PCM cool roof system", and to evaluate its performance by applying the PCM cool roof system to the roof envelop. The study methods and procedures are as follows: First, the optimal PCM and finish materials were selected utilizing the indoor artificial climate chamber. Second, the PCM cool roof system was applied to the testbed, and the changes in surface temperatures were measured to determine the effect on the reduction of the heat island phenomenon. Third, the air currents in Gangdong-gu Seoul Korea were analyzed through a numerical analysis based on the data derived from the testbed to verify the reduction in the UHI. The experimental groups were set to A: WPC, B: WPC+PCM, and the control group to C: PCM cool roof system in the testbed experiment. The experimental environments were divided into winter, intermediate, and summer periods to increase the performance evaluation reliability in Seoul, where there are four distinct seasons. The study results showed that all seasons saw an effect of a reduction of roof surface temperatures when using the PCM cool roof system. The maximum temperature difference for each season was 2.5°C in winter, 4.7°C in intermediate season, and 5.7°C in summer. The a numerical analysis results showed that the reduction in roof surface temperature due to the "PCM cool roof system" was effective in the mitigation of the heat island phenomenon. [ABSTRACT FROM AUTHOR]

The dynamic impact force of debris flows on a check dam was investigated by using numerical analysis and an analytical investigation. The emphasis was on quantifying the magnitude and distributions of the dynamic impact force due to the moving debris flows and the static force due to the deposited material of debris flows. The behavior of debris flows on a check dam and the corresponding response of the significant factors influencing the dynamic impact force of debris flows, such as the entrainment of the soil layer, thickness of sedimentation, and flow velocity, were analyzed by using a three dimensional coupled Eulerian-Lagrangian (CEL) approach. The prediction method can adequately analyze the behavior of debris flows involving the entrainment of the soil layer. The obtained results indicate that the impact force of a debris flow with a high flow velocity cannot be predicted accurately by using the conventional static empirical model, especially when the dynamic empirical model is overestimated. The proposed method was verified by comparing the characteristics of the laboratory test results and the actual debris flows that occurred in Mt. Umyeon, South Korea in 2011. [ABSTRACT FROM AUTHOR]

In South Korea, the number of vehicles is gradually increasing. The number of heavy vehicles in 2010 increased up to 19% in less than five years. Therefore, the chances of heavy vehicle-concrete median barrier (CMB) collision also became higher than in the past; therefore, a need to study a stricter design level for improving the current CMB (CMB-15) under harsher environments arose. Accordingly, in the present study, a new concrete median barrier was designed under a stricter impact severity, SB6(420 kJ), compared to the current design impact severity, SB5-B (270 kJ). In particular, shock absorbing devices to absorb impact energy were applied to the CMB. An empty space allows the dowel bars to deform and absorb collision energy. Therefore, deformable CMB was designed and tested. The key parameters selected in our study were dowel bar and wire-mesh. A series of numerical analyses were conducted to evaluate the proposed new deformable CMB designs with shock absorbers. Finally, the optimal design, CMB-17S, was proposed after several evaluations of the proposed designs and a full-scale field test. It was found that, although the developed model did not accurately predict the impact sequence due to certain differences between the actual truck and the truck model, the permanent deformation after collision could be well predicted. Based on the observations from a full-scale impact test, it was recommended that the top part of the CMB should be strengthened since major volume loss occurred due to local impact, which appeared to be due to punching shear failure. [ABSTRACT FROM AUTHOR]