• Advances in nano research
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• v.15 no.1
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• pp.59-65
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• 2023

In this present article, the mechanical behavior of single-walled black phosphorene nanotubes (SW-αPNTs) is simulated using molecular dynamics (MD). The proposed model is subjected to the axial loading and the effects of morphological parameters, such as the mono-vacancy defect and strain rate on the tensile behavior of the zigzag and armchair SW-αPNTs are studied as a pioneering work. In order to assess the accuracy of the MD simulations, the stress-strain response of the current MD model is successfully verified with the efficient quantum mechanical approach of the density functional theory (DFT). Along with reproducing the DFT results, the accurate MD simulations successfully anticipate a significant variation in the stress-strain curve of the zigzag SW-αPNTs, namely the knick point. Predicting such mechanical behavior of SW-αPNTs may be an important design factor for lithium-ion batteries, supercapacitors, and energy storage devices. The simulations show that the ultimate stress is increased by increasing the diameter of the pristine SW-αPNTs. The trend is identical for the ultimate strain and stress-strain slope as the diameter of the pristine zigzag SW-αPNTs enlarges. The obtained results denote that by increasing the strain rate, the ultimate stress/ultimate strain are respectively increased/declined. The stress-strain slope keeps increasing as the strain rate grows. It is worth noting that the existence of mono-atomic vacancy defects in the (12,0) zigzag and (0,10) armchair SW-αPNT structures leads to a drop in the tensile strength by amounts of 11.1% and 12.5%, respectively. Also, the ultimate strain is considerably altered by mono-atomic vacancy defects.

• Asia-Pacific Journal of Business
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• v.14 no.4
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• pp.305-318
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• 2023

Purpose - This study analyzed the decoupling phenomenon between energy consumption and economic growth in Korea from 1990 to 2021. The main purpose of this study is to suggest policy implications for achieving a low-carbon society and decoupling that Korea must move forward in the face of the climate change crisis. Design/methodology/approach - This study investigated the relationship between energy consumption and economic growth by energy source and sector using the energy-EKC (EEKC) hypothesis which included the energy consumption on the traditional Environmental Kuznets Curve (EKC), and the impulse response function (IRF) model based on Bayesian vector auto-regression (BVAR). Findings - During the analysis period, the trend of decoupling of energy consumption and economic growth in Korea is confirmed starting from 1996. However, the decoupling tendency appeared differently depending on the differences in energy consumption by sources and fields. The results of the IRF model using data on energy consumption by source showed that the impact of GDP and renewable energy consumption resulted in an increase in energy consumption of bio and waste, but a decrease in energy consumption by sources, and the impact of trade dependence was found to increase the consumption of petroleum products. Research implications or Originality - According to the main results, efficient distribution by existing energy source is required through expansion of development of not only renewable energy but also alternative energy. Additionally, in order to increase the effectiveness of existing energy policies to achieve carbon neutrality, more detailed strategies by source and sector of energy consumption are needed.

• Steel and Composite Structures
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• v.50 no.3
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• pp.281-298
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• 2024

Stainless steel bolts (SSB) are increasingly utilized in bolted steel connections due to their good mechanical performance and excellent corrosion resistance. Fire accidents, which commonly occur in engineering scenarios, pose a significant threat to the safety of steel frames. The post-fire behavior of SSB has a significant influence on the structural integrity of steel frames, and neglecting the effect of temperature can lead to serious accidents in engineering. Therefore, it is important to evaluate the performance of SSB at elevated temperatures and their residual strength after a fire incident. To investigate the mechanical behavior of SSB after fire, 114 bolts with grades A4-70 and A4-80, manufactured from 316L austenitic stainless steel, were subjected to elevated temperatures ranging from 20℃ to 1200℃. Two different cooling methods commonly employed in engineering, namely cooling at ambient temperatures (air cooling) and cooling in water (water cooling), were used to cool the bolts. Tensile tests were performed to examine the influence of elevated temperatures and cooling methods on the mechanical behavior of SSB. The results indicate that the temperature does not significantly affect the Young's modulus and the ultimate strength of SSB. Up to 500℃, the yield strength increases with temperature, but this trend reverses when the temperature exceeds 500℃. In contrast, the ultimate strain shows the opposite trend. The strain hardening exponent is not significantly influenced by the temperature until it reaches 500℃. The cooling methods employed have an insignificant impact on the performance of SSB. When compared to high-strength bolts, 316L austenitic SSB demonstrate superior fire resistance. Design models for the post-fire mechanical behavior of 316L austenitic SSB, encompassing parameters such as the elasticity modulus, yield strength, ultimate strength, ultimate strain, and strain hardening exponent, are proposed, and a more precise stress-strain model is recommended to predict the mechanical behavior of 316L austenitic SSB after a fire incident.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.261-273
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• 2011

Recently, the demands for steel frame are increasing because of the trend and due to the demand for bigger and higher buildings. In the analysis of typical steel frame, connections are based on the idealized fixed or pinned connection. A fixed connection assumes that the relative angle of each member before deformation is the same after the transformation. Therefore, the stiffener reinforces the connection to sufficient rigidity and stability of the panel zone. In the economical aspect, however, the necessity of connection that the stiffener reinforcement has omitted is increasing due to the excessive production as well as labor costs of connection. In contrast, pinned connection is assumed that bending moments between the beams and columns do not transfer to each member. This is easy to make in the plant and the construction is simple. However, the structural efficiency is reduced in pinned connection because connection cannot transfer moments. The introduction of this semirigid process can decide efficient cross-sectional dimensions that promote ease in the course of structural erection, as performed by members in the field-a call for safety in the entire frame. Therefore, foreign countries exert efforts to study the practical behavior and the results are applied to criterion. This paper analyzes the semirigid connection of domestic steel by design specifications of AISC/LRFD and make data bank that pertain to each steel. After wards, the results are compared to those of idealized connection; at the same time, this paper presents a design method that matches economic efficiency, end-fixity, and rotational stiffness.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.2
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• pp.91-99
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• 1985

The acceleration levels and durations of seismic inputs for nuclear power plant design are surveyed. Among those inputs, two artificial acceleration time histories with same acceleration level and duration are selected and their characteristics are studied by calculating response spectra and spectrum intensity. The selected time histories which have the duration of 24 sec. satisfy the design response spectra of US Nuclear Regulatory Commission Regulatory Guide 1. 60. One of the selected time histories is improved to have the duration of 15 sec. without significant changes in the other characteristics. A case study of a plane model with 3 lumped masses is done using three time histories, i.e, two selected and one improved time histories. It is found that the improved curve gives almost the same results as the original one and reduces the computer time by about half, whereas two selected time histories give the results with same trend but much different magnitudes each other. It is claimed, however, that the improved time history is not the optimal one, but very economical in practical applications.

• The Journal of Engineering Geology
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• v.20 no.1
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• pp.47-60
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• 2010

This study is focused on the analysis of tunnel behavior to estimate the stability on tunnel design. An estimation method was proposed as a hybrid consideration, which contains the displacement analysis by 3D numerical simulation, the maximum displacement obtained after field measurement, and an assessment of tunnel stability using a deformation analysis proposed by Sakurai(1988, 1997). The points of case study by Sakurai(1988, 1997) were replotted considering his analysis. From the new analysis of the tunnel case study, the trend line for analyzed points is analogized, which curve is divided into stable, unstable and failure zone. To evaluate the estimation method, a special shape of railway tunnel was selected, which are the Inchon international airport rail way connected to subway line 9 in Gimpo, Korea. The point s of upper and below track on the Inchon international airport rail way were satisfied to the stability of tunnel after reinforcing. Also the points shows the higher apparent Young's modulus, which resulted from improvement on shear strength by the micro silica grouting and the supporting of umbrella method. Therefore, if new analysis used, proper tunnel reinforcing method could be selected according to tunnel strain and geological property.

• Journal of Korea Water Resources Association
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• v.56 no.11
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• pp.775-784
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• 2023

With the increasing trend of extreme rainfall that exceeds the design frequency of man-made structures due to extreme weather, it is necessary to review the safety of agricultural reservoirs designed in the past. However, there are no local government-managed reservoirs (13,685) that can be discharged in an emergency, except for reservoirs over a certain size under the jurisdiction of the Korea Rural Affairs Corporation. In this case, it is important to quickly deploy a mobile siphon to the site for preliminary discharge, and this study evaluated the applicability of a mobile siphon with a diameter of 200 mm, a minimum water level difference of 6 m, 420 (m²/h), and 10,000 (m²/day), which can perform both preliminary and emergency discharge functions, to the Yugum Reservoir in Gyeongju City. The test bed, Yugum Reservoir, is a facility that was completed in 1945 and has been in use for about 78 years. According to the hydrological stability analysis, the lowest height of the current dam crest section is 27.15 (EL.m), which is 0.29m lower than the reviewed flood level of 27.44 (EL.m), indicating that there is a possibility of lunar flow through the embankment, and the headroom is insufficient by 1.72 m, so it was reviewed as not securing hydrological safety. The water level-volume curve was arbitrarily derived because it was difficult to clearly establish the water level-flow relationship curve of the reservoir since the water level-flow measurement was not carried out regularly, and based on the derived curve, the algorithm for operating small and medium-sized old reservoirs was developed to consider the pre-discharge time, the amount of spillway discharge, and to predict the reservoir lunar flow time according to the flood volume by frequency, thereby securing evacuation time in advance and reducing the risk of collapse. Based on one row of 200 mm diameter mobile siphons, the optimal pre-discharge time to secure evacuation time (about 1 hour) while maintaining 80% of the upper limit water level (about 30,000 m²) during a 30-year flood was analyzed to be 12 hours earlier. If the pre-discharge technology utilizing siphons for small and medium-sized old reservoirs and the algorithm for reservoir operation are implemented in advance in case of abnormal weather and the decision-making of managers is supported, it is possible to secure the safety of residents in the risk area of reservoir collapse, resolve the anxiety of residents through the establishment of a support system for evacuating residents, and reduce risk factors by providing risk avoidance measures in the event of a reservoir risk situation.

• Korean Chemical Engineering Research
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• v.52 no.6
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• pp.826-833
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• 2014

Driven by both environmental and economic reasons, the development of small to medium scale GTL(gas-to-liquid) process for offshore applications and for utilizing other stranded or associated gas has recently been studied increasingly. Microchannel GTL reactors have been prefrered over the conventional GTL reactors for such applications, due to its compactness, and additional advantages of small heat and mass transfer distance desired for high heat transfer performance and reactor conversion. In this work, multi-microchannel reactor was simulated by using commercial CFD code, ANSYS FLUENT, to study the geometric effect of the microchannels on the heat transfer phenomena. A heat generation curve was first calculated by modeling a Fischer-Tropsch reaction in a single-microchannel reactor model using Matlab-ASPEN integration platform. The calculated heat generation curve was implemented to the CFD model. Four design variables based on the microchannel geometry namely coolant channel width, coolant channel height, coolant channel to process channel distance, and coolant channel to coolant channel distance, were selected for calculating three dependent variables namely, heat flux, maximum temperature of coolant channel, and maximum temperature of process channel. The simulation results were visualized to understand the effects of the design variables on the dependent variables. Heat flux and maximum temperature of cooling channel and process channel were found to be increasing when coolant channel width and height were decreased. Coolant channel to process channel distance was found to have no effect on the heat transfer phenomena. Finally, total heat flux was found to be increasing and maximum coolant channel temperature to be decreasing when coolant channel to coolant channel distance was decreased. Using the qualitative trend revealed from the present study, an appropriate process channel and coolant channel geometry along with the distance between the adjacent channels can be recommended for a microchannel reactor that meet a desired reactor performance on heat transfer phenomena and hence reactor conversion of a Fischer-Tropsch microchannel reactor.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.3
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• pp.169-173
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• 2015

This study is to predict the life exponent by measuring, over 7 years, the insulation resistance of high-voltage cables in 22 kV operation for 13 years. We found out the lifetime index in order to determine the time-dependent trend of deteriorating performance of power cables. The insulation resistances decreased according to elapsed time. We found that: the initial measurements of the cable systems were in agreement with the deterioration properties of the Arrhenius Law. By analyzing the life curve of the cable system, we also verified that the value of the life exponent (n) in the v-t characteristics defined by Weibull distribution has values from 10 to 11. When designing the cable system, the initial value of life exponent was chosen as 9 without any grounding. We have verified that the theoretical grounding based on the design safety of n=9 was actually the best one available. In the short term, we apply our research result to the diagnosis and evaluation of the power cables. In the long run, however, we plan to reduce the cost of the installation and management of cable systems in operation at power stations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3006-3013
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• 2015

Flat tube heat exchangers can improve the thermal performance significantly compared with round tube heat exchangers. For proper design of flat tube heat exchangers, one should know the tubeside heat transfer coefficients. In this study, convective boiling heat transfer coefficients of R-410A were obtained in a flat extruded aluminum tube with $D_h=1.41mm$. The test range covered mass flux from 200 to $600kg/m^2s$, heat flux from 5 to $15kW/m^2$ and saturation temperature from $5^{\circ}C$ to $15^{\circ}C$. The heat transfer coefficient curve shows a decreasing trend after a certain quality(critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kaew-On et al. correlations reasonably predicted the present data.