• Tunnel and Underground Space
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• v.31 no.4
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• pp.270-288
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• 2021

We proposed a numerical method to simulate the hydro-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) in the paper. As a part of DECOVALEX-2023 Task G, we verified the method via benchmarks with analytical solutions. DECOVALEX-2023 Task G aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as a group of tetrahedral grains and calculated the interaction of the grains and their interfaces using 3DEC. The micro-parameters of the grains and interfaces were determined by a new methodology based on an equivalent continuum approach. In benchmark modeling, a single fracture embedded in the rock was examined for the effects of fracture inclination and roughness, the boundary stress condition and the applied pressure. The simulation results showed that the developed numerical model reasonably reproduced the fracture slip induced by boundary stress condition, the fracture opening induced by fluid injection, the stress distribution variation with fracture inclination, and the fracture roughness effect. In addition, the fracture displacements associated with the opening and slip showed good agreement with the analytical solutions. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Maritime Security
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• v.2 no.1
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• pp.151-184
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• 2021

Global warming due to climate change is one of the biggest challenges in the 21st century. Global warming is not only a disaster that threatens the global ecosystem but also an opportunity to reduce logistics costs and develop mineral resources by commercializing Arctic routes. The Arctic paradox, in which ecological and environmental threats and new economic opportunities coexist, is expected to have a profound impact on the global environment. As the glaciers disappear, routes through the Arctic Ocean without passing through the Suez and Panama Canals emerged as the 'third route.' This can reduce the distance of existing routes by 30%. Global warming has also brought about changes in the geopolitical paradigm. As Arctic ice begins to melt, the Arctic is no longer a 'constant' but is emerging as the largest geopolitical 'variable' in the 21st century. Accordingly, the Arctic, which was recognized as a 'space of peace and cooperation' in the post-Cold War era, is now facing a new strategic environment in which military and security aspects are emphasized. After the Cold War, the Arctic used to be a place for cooperation centered on environmental protection, but it is once again changing into a stage of competition and confrontation between superpowers, heralding 'Cold War 2.0.' The purpose of this study is to evaluate the strategic value of the Arctic Ocean from geopolitical and geoeconomic perspectives and derive strategic implications by analyzing the dynamics of the New Cold War taking place in the Arctic region.

• The Journal of the Convergence on Culture Technology
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• v.8 no.1
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• pp.483-497
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• 2022

Recently, due to COVID-19, non-face-to-face online lectures are being held all over the world. In higher education in the post-corona era, distance learning has become the main teaching and learning method. At this time, Metaverse is being proposed as a new alternative. Metaverse has basic elements such as avatars, 3D space, and activities accompanied by interaction, which can be seen as a difference compared to existing VR (Virtual Reality) contents. This study designed and built an educational metaverse platform that can be applied to actual lectures by reflecting the three elements of the metaverse.In addition, we implemented a cross-device-platform that supports various devices such as HMDs, smartphones, tablets, and PCs by reflecting user requirements through usability tests such as middle school, high school, college students, and parents, so that anyone can easily participate in Metaverse lectures. Currently, the metaverse platform is being developed and serviced in various ways, but there are hardly any services designed for education. Just as services such as Zoom, the existing video conferencing solution, were used for non-face-to-face education, some functions of the currently serviced metaverse are utilized for education and used in the form of a one-time event. The educational metaverse platform developed through this study is expected to be a reference in constructing the metaverse for education in the future.

• Journal of the Korean GEO-environmental Society
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• v.23 no.1
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• pp.39-49
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• 2022

Expandable steel pipe piles are installed by inserting expansion equipment to increase the cross-sectional area of steel pipes, which can improve the pile performance compared to micro-piles. In this paper, a hydraulic expansion device was developed to expand steel pipe piles in practice. A series of laboratory and field tests were conducted to verify the performance of the developed expansion device to expand steel pipes. The expansion capability and expandable range was evaluated by measuring the strain and expansion time at the maximum pressure of the hydraulic expansion device. The thinner steel pipe, the larger strain but longer expansion time required in the test. For example, the 4.0-mm-thick steel pipe showed strain reduction by 30% and a decrease in the required expansion time by 40% compared to the 2.9-mm-thick steel pipe. In addition, in-situ expansion tests were performed to verify the expandability of steel pipes under the ground, and the exhumed specimen showed clear expanded sections. The structural integrity was determined by comparing the material performance the original and expanded specimens.

• Journal of Space Technology and Applications
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• v.2 no.2
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• pp.146-168
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• 2022

Witnessing current military conflicts in South China Sea and Eastern Europe, most defense analysts evaluate one of the most serious security threat toward the US is coming from the superpower competitions with Russia and China. The main means for such super power hegemonic competitions is military power and space power is a key enabler to maximize the efficiency and effectiveness of military employment. Reflecting above circumstances, the space hegemonic competition between the Unites States and China is spreading into all aspects of national powers. Under such an environment, R.O.K needs to significantly develop national space power to preserve life and assets of people in space. On the other hand, the R.O.K has a lot of limitations in launching space assets into orbits by land-based space rockets due to its geographic locations. The limitation of rocket launching direction, the failure to secure a significant area enough to secure safety and the limitation to secure open area enough to build associated facilities are among them. On this paper, I will suggest the need to build the 2nd space rocket launching site after analyzing a lot of short-falls the current 'Naro' space center face, compared to those of advanced space powers around the world.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.593-609
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• 2021

We proposed a numerical method for the thermo-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) and simulated thermally induced fracture slip. The present study is the benchmark simulation performed as part of DECOVALEX-2023 Task G, which aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as an assembly of Voronoi grains and calculated the interaction of the grains (blocks) and their interfaces (contacts) using a distinct element code, 3DEC. Based on an equivalent continuum approach, the micro-parameters of grains and contacts were determined to reproduce rock as an elastic material. Then, the behavior of the fracture embedded in the rock was characterized by the contacts with Coulomb shear strength and tensile strength. In the benchmark simulation, we quantitatively examined the effects of the boundary stress and thermal stress due to heat conduction on fracture behavior, focusing on the mechanism of thermally induced fracture slip. The simulation results showed that the developed numerical model reasonably reproduced the thermal expansion and thermal stress increment, the fracture stress and displacement and the effect of boundary condition. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Land and Housing Review
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• v.13 no.1
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• pp.23-38
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• 2022

As city tourism has recently been evaluated as a major indicator of urban competitiveness, strengthening the role of cities as tourist destinations has received more attention. However, industrialization and urbanization of many cities lead to population decline, extinction of traditional industries, and deterioration of living environments, weakening urban functions and competitiveness. Thus, it is essential for declining cities to build a measure to restore urban competitiveness by enhancing urban functions. Accordingly, this study focused on socio-cultural urban regeneration by exploring physical spaces for tourism destinations in declining cities. Different from general tourist destinations, tourism destinations of urban regeneration have a temporal perspective covering the past, present, and future. How does the temporal perspective of urban regeneration tourist destinations affect tourists' satisfaction and behavioral intention? In order to address these questions, this study conducts an empirical analysis based on structural equation modeling (SEM) using the sample of tourists who have visited urban regeneration tourism destinations. With SEM, this paper investigates structural relationships across variables by testing the hypothesis established in the proposed research model. The results show that precious memories of the past are the most important factor for tourists to visit urban regeneration tourist destinations. The empirical findings of this study will contribute to the research areas of urban tourism, urban regeneration tourism, and urban regeneration tourism destinations. In addition, this study can provide practical implications to develop socio-cultural contents of urban regeneration areas as tourism resources to establish plans for urban regeneration projects and achieve sustainable development strategies.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.469-479
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• 2021

As a material for preventing spalling of concrete, the effectiveness of PP fiber has already been confirmed. However, it is necessary to consider the maximum temperature that occurs during a fire, and to solve the mixing problem and the strength reduction problem that occur depending on the mixing amount. In this study, the fire resistance performance of tunnel segment linings according to the PP fiber content and air volume under the RABT fire scenario was investigated. As a result, no spalling or cross-sectional loss occurred in all test specimens, and when the PP fiber content was small, the maximum temperature was relatively high and the maximum temperature arrival time was also fast. On the other hand, no trend was found for the maximum temperature and arrival time according to the difference in air volume. In the internal temperature distribution results for the PP fiber mixing amount of 0.75, 1.0, 1.5, and 2.0 kg/m³, the results of 0.75 and 1.0 kg/m³ showed similar temperature distribution, and the results of 1.5 and 2.0 kg/m³ were similar. It was confirmed that the internal temperature distribution tends to decrease at the same depth when the amount of PP fiber mixed is large, and it was confirmed that a remarkable difference occurred from the results of 1.0 kg/m³ and 1.5 kg/m³ of PP fiber mixed amounts.

• Journal of The Korean Association of Information Education
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• v.26 no.2
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• pp.105-120
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• 2022

In addition to the rapid changes in the times caused by the pandemic, the revision of the new curriculum coincides with the change in the proportion of the three elements of learners, society, and subjects that make up the curriculum. In particular, along with the proportion of 'social' in the curriculum, the scope of the word 'educational community' has increased, and the allowable range of curriculum restructuring centered on it has expanded. In order for the intended direction of education to be properly established in the new curriculum, various educational method studies are needed to cultivate newly emerged competencies and literacy. In this study, after selecting the contents and goals of the convergence curriculum based on various criteria for subject selection, the data science program was designed by reconstructing Living Lab's PDIE methodology. As an evaluation factor for this, we tried to analyze the effectiveness of 'creativity', 'problem-solving ability', 'communication ability', 'collaboration ability' among future competencies emphasized in the curriculum. As a result of the study, it was effective in improving creative and communication skills, and this study focuses on verifying the effectiveness of School Living Lab, suggesting the necessity of post-research that expands the application space of research and diversifies the role of educational community subjects.

• Journal of Korea Foundry Society
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• v.41 no.6
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• pp.535-542
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• 2021

In this study, to improve the interfacial bond strength of cast iron-aluminum dissimilar materials, graphite was removed to a certain depth from the cast iron surface through de-graphitization heat treatment. As the heat treatment time increased, the depth at which graphite was removed increased, showing a linear relationship between the heat treatment time and depth. Aluminum was filled to a certain depth on the de-graphitized cast iron surface through die-casting method, and no intermetallic compounds were formed on the cast iron-aluminum interface. The interfacial bonding strength showed a value of 90 MPa regardless of the heat treatment time, which is very high compared to the 12MPa bonding strength of the material without de-graphitization heat treatment. This result is thought to be due to the mechanical bonding of the undercut structure as the liquid aluminum, penetrated by the high pressure die-casting process, solidified in the de-graphitized region of the cast iron.