• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.4
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• pp.341-353
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• 2022

Pipelines are buried in urban area, and the position (depth and orientation) of buried pipeline should be clearly identified before ground excavation. Although various geophysical methods can be used to detect the buried pipeline, it is not easy to identify the exact information of pipeline due to heterogeneous ground condition. Among various non-destructive geo-exploration methods, ground penetration radar (GPR) can explore the ground subsurface rapidly with relatively low cost compared to other exploration methods. However, the exploration data obtained from GPR requires considerable experiences because interpretation is not intuitive. Recently, researches on automated detection technology for GPR data using deep learning have been conducted. However, the lack of GPR data which is essential for training makes it difficult to build up the reliable detection model. To overcome this problem, we conducted a preliminary study to improve the performance of the detection model using finite difference time domain (FDTD)-based numerical analysis. Firstly, numerical analysis was performed with homogeneous soil media having single permittivity. In case of heterogeneous ground, numerical analysis was performed considering the ground heterogeneity using fractal technique. Secondly, deep learning was carried out using convolutional neural network. Detection Model-A is trained with data set obtained from homogeneous ground. And, detection Model-B is trained with data set obtained from homogeneous ground and heterogeneous ground. As a result, it is found that the detection Model-B which is trained including heterogeneous ground shows better performance than detection Model-A. It indicates the ground heterogeneity should be considered to increase the performance of automated detection model for GPR exploration.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.527-532
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• 2009

In this paper simulations for the impact into ceramics and/or metal materials have been discussed. To model discrete nature for fracture and damage of brittle materials, we implemented cohesive-law fracture model with a node separation algorithm for the tensile failure and Mohr-Coulomb model for the compressive loading. The drawback of this scheme is that it requires a heavy computational time. This is because new nodes are generated continuously whenever a new crack surface is created. In order to reduce the amount of calculation, parallelization with MPI library has been implemented. For the high-speed impact problems, the mesh configuration and contact calculation changes continuously as time step advances and it causes unbalance of computational load of each processor. Dynamic load balancing technique which re-allocates the loading dynamically is used to achieve good parallel performance. Some impact problems have been simulated and the parallel performance and accuracy of the solutions are discussed.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.11-21
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• 2017

Ground subsidence mainly occurs due to the soil wash-away caused by cracked sewer pipes. It is necessary to understand the behavior surrounding soils with the formation of cavity and relaxation zone to set up counterplan. In this paper, a series of laboratory model tests and numerical analyses (Discrete Element Method) were performed to investigate the ground subsidence mechanism due to sewer pipe damage. For model tests, aluminum rod and trap door were used to simulate the behavior of model ground. Test results were compared with the numerical analyses conducted under the same boundary conditions with model tests. From this study, it was investigated the shape and size of cavity and relaxation zone due to the soil wash-away and a void ratio distribution of surrounding soils with relaxation properties.

• Geophysics and Geophysical Exploration
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• v.22 no.3
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• pp.132-148
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• 2019

Recently, safety and environmental concerns have become major social issues. Especially, a special underground-safety law has been made and enacted to prevent ground subsidence around construction sites. For environmental problems, several researches have started or will start on characterization of contaminated sites, in-situ environmental remediation in subsurface, and monitoring of remediation results. As a part of the researches, geophysical surveys, which have been mainly applied to explore mineral resources, geological features or ground, are used to characterize not only contaminated areas but also fluid flow paths in subsurface environments. As a basic study for the application of geophysical surveys to detect contamination in subsurface, this paper analyzes previous researches to understand changes in geophysical properties of contaminated zones by various contaminants such as leachate, heavy metals, and non-adequate phase liquid (NAPL). Furthermore, this paper briefly introduces how geophysical surveys like direct-current electrical resistivity, induced polarization and ground penetration radar surveys can be applied to detect each contamination, before analyzing case studies of the applications in contaminated areas by NAPL, leachate, heavy metal or nitrogen oxides.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.75-91
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• 2023

In this study, we explore the use of ground penetrating radar (GPR) for the nondestructive survey of subsurface conduits, focusing on the challenges posed by multichannel environments. A key concern is the shadow regions created by conduits, which significantly impact survey results. The shadow regions, which are influenced by conduit position and diameter, hinder signal propagation, thereby making detection within these regions challenging. Using finite-difference time-domain numerical analysis, we examined the characteristics of conduit signals, which typically manifest in hyperbolic patterns. Particularly, we investigated three conduit arrangements: horizontal, vertical, and diagonal. Automatic gain control was applied to amplify the signals, enabling the analysis of variations in shadow regions and signal characteristics for each arrangement. In the horizontal arrangement, the proximity of the two conduits resulted in the emergence of a new hyperbolic pattern between the existing conduits. In the vertical arrangement, the lower conduit could be detected using hyperbolic signals on either side, but the detection was challenging when the upper conduit diameter exceeded that of the lower conduit. In the diagonal arrangement, signal characteristics varied based on the position of shadow regions relative to the detection range of the equipment. Asymmetrical signal patterns were observed when the shadow regions fell within the detection range, whereas the signals of the two conduits were minimally impacted when the shadow regions were outside the detection range. This study provides vital insights into accurately detecting and characterizing subsurface multichannel conduits using GPR-a significant contribution to the field of subsurface exploration and management.

• Journal of the Korean GEO-environmental Society
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• v.12 no.4
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• pp.43-51
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• 2011

Many electric poles in the softground have been collapsed due to external load. In this study, 10 types of tests were performed with variation of location, numbers and depths of anchor blocks as well as depth of poles to find horizontal earth pressure through full scale pull-out tests. The horizontal earth pressure increased with embedded depth of electric pole, and earth pressure of lower passive zone decreased. The deeper of anchor block, earth pressure of passive zone becomes less. lateral displacements showed differences depending on location, numbers and depth of poles. The bending is generated in the upper part at the initial load, but it moved to central part as load increased. The maximum horizontal displacement decreased to 1/1.6 at -0.5m depth of anchor block and 1.3m additional laying depth of poles into ground.

• International Journal of Highway Engineering
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• v.7 no.4 s.26
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• pp.31-39
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• 2005

Tests are conducted to analyze the compaction characteristics of domestic river sand used frequently for backfill in construction of electrical pipeline. As a result of test, the range of specific gravity of sand is found to be in between 2.63 and 2.67, and of maximum dry weight of sand is in between $1.70g/cm^3\;and\;1.86g/cm^3$. Also, the optimum moisture content is found to be in between 11.3% and 13.8%. The variability of compaction degree with respect to compaction energy is well captured by hyperbolic function.

• Proceedings of the KOR-BRONCHOESO Conference
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• 1978.06a
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• pp.3.3-3
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• 1978

Foreign bodies in the esophagus are common in the field of otolaryngology. They are usually due to ingestion of a coin or two, especially in the cases of children. Almost always, a coin in the esophagus can be easily removed under esophagoscope. However, untoward complications have not infrequently ensued. The authors have recently experienced an interesting case of foreign body in the mediastinum. It was found to be a 50-Hwan coin that had remained between the tracheal bifurcation and the esophagus for 13 years without causing any serious complication. At age of 17 years, he visited ENT department of our hospital, where the coin was removed safely by trans- thoracic approach under general anesthesia. So we report this case along with literature review.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.2
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• pp.239-245
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• 2013

In this paper, we propose a time-frequency domain reflectometry (TFDR) based measurement method for localizing concentric neutrals corrosion on live underground power cable. It consists of two inductive couplers which can transmit the reference signal into live underground power cable and measure the reflected signals from the impedance discontinuities of concentric neutrals corrosion. In order to compensate the dispersion of the measured reflected signal via inductive coupler, an equalizer based on Wiener filtering is designed. To improve the localizing performance of concentric neutrals corrosion in the vicinity of the measurement point, the reference signal is removed from the measured reflected signals. The localization performance of the proposed method is verified by the concentric neutrals corrosion localization experiment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.503-503
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• 2007

본 논문에서는 지중배전(22.9kV) 선로에 사용되는 지상변압기를 대상으로 수행한 방열해석 및 개선과 변압기수명연장에 관한 검토 결과를 수록하였다. 변압기의 열화메커니즘에 대한 문헌 조사를 통해 변압기 온도와 수명간의 관계를 작도하였는바, 수명 평가를 위한 핵심 인자로 열에 의한 절연지의 열화에 초점을 맞추었다. 기존 외함에 설치된 방열구중 상부 위치를 상부판에도 변경하는 경우 약25%의 통풍량 증가 효과를 기대할 수 있을 것으로 평가 되었으며 상부판과 내함 사이에 형성되던 고온 영역에서의 온도를 약$15^{\circ}C$정도 낮출 수 있는 것으로 나타났다. 절연지의 인장강도 변화로 평가한 수명예측 곡선에 따르면 약$10^{\circ}C$의 은도 저감은 약10배의 수명 연장 효과를 가져오는 것으로 나타난바, 본 연구에서 확인한 방열구의 위치 변경에 따른 지상기기 내부의 온도 저하는 변압기 수명을 연장하는데 일조할 것으로 기대된다. 기존 지상변압기에서의 방열구조를 통해 변압기 온도와 수명간의 관계를 작도하였는바, 수명 평가를 위한 핵심인자로 효과적으로 방열할 수 있는 새로운 외함의 구조 및 디자인을 제시하고 시뮬레이션을 통해 개선효과를 예측하였다. 또한, 개선된 모델을 가지고 실제 변압기를 제작한 후 부하를 인가하여 개선전과 후에 대한 방열효과를 실증시험을 통해 확인하였다.