• Journal of the Korean Geotechnical Society
• /
• v.37 no.3
• /
• pp.19-30
• /
• 2021

The presence of the hydrate-bearing sediments in Ulleung Basin of South Korea has been confirmed from previous studies. Researches on gas production methods from the hydrate-bearing sediments have been conducted worldwide. As production mechanism is a complex phenomenon in which thermal, hydraulic, and mechanical phenomena occur simultaneously, it is difficult to accurately conduct the productivity and stability analysis of hydrate bearing sediments through lab-scale experiments. Thus, the importance of numerical analysis in evaluating gas productivity and stability of hydrate-bearing sediments has been emphasized. In this study, the numerical parametric analysis was conducted to investigate the effects of the bottom hole pressure and the depressurization rate on the gas productivity and stability of hydrate-bearing sediments during the depressurization method. The numerical analysis results confirmed that as the bottom hole pressure decreases, the productivity increases and the stability of sediments deteriorates. Meanwhile, it was shown that the depressurization rate did not largely affect the productivity and stability of the hydrate-bearing sediments. In addition, sensitivity analysis for gas productivity and stability of the sediments were conducted according to the depressurization rate in order to establish a production strategy that prevents sand production during gas production. As a result of the analysis, it was confirmed that controlling the depressurization rate from a low value to a high value is effective in securing the stability. Moreover, during gas production, the subsidence of sediments occurred near the production well, and ground heave occurred at the bottom of the production well due to the pressure gradient. From these results, it was concluded that both the productivity and stability analyses should be conducted in order to determine the bottom hole pressure when producing gas using the depressurization method. Additionally, the stress analysis of the production well, which is induced by the vertical displacements of sediments, should be evaluated.

• Journal of Korean Society of Transportation
• /
• v.25 no.4
• /
• pp.123-133
• /
• 2007

This study analyzed whether a transit network with hierarchy is efficient or not, and if transit network hierarchy has cost efficiency, then which condition guarantees the efficiency of the transit network hierarchy. The authors modeled the total cost of the transit network and suggested the conditions in which the transit network hierarchy has cost efficiency through comparing the cost of the transit network with and without hierarchy. The efficiency of transit network hierarchy is guaranteed when the travel cost savings induced by using a higher hierarchy transit network is larger than the increasing non-travel cost, which is the sum of access cost, waiting cost, and operating cost, induced by the introduction of a higher hierarchy transit network. This result is consistent with common sense and with the concept of cost and benefit analysis. If a passenger traveling within the area divided by a higher hierarchy transit network uses only a lower hierarchy transit network and the passenger traveling out of the area divided by the higher hierarchy transit network uses both lower and higher hierarchy transit networks, the travel demand using the higher hierarchy transit network is inversely proportional to the square of the line spacing. This means that the transit network becomes more efficient and small increases of travel demand guarantee the efficiency of the transit network hierarchy as the connectivity of the network becomes higher. This result shows that transit networks have economies of aggregation. This study is the first analytical research on transit network hierarchy and is expected to be a basis for numerical research. However, numerical research should complement this study, since analytical research has some limitations for considering a real network.

• The Korean Journal of Archival Studies
• /
• no.19
• /
• pp.3-55
• /
• 2009

Records of architectural cultural properties, in case of accidents, show who are to blame, present what evidences are to establish the cause, and also are used for checking if there were any problem in policies and regulations in preserving and caring architectural cultural properties. These records are of great importance in their roles and are of essential use regardless of time and space. Considering its significance, In that architectural cultural properties requires setting clear goals and directions and as well, criteria, for management, we need methods of systematical control and consideration for its characteristics. This research started with the sense of purpose that managing architectural cultural properties are in need of systematic and concrete control, based on the perception that they need protecting and transmitting. The goal of this thesis is to work on the current archiving status of architectural cultural properties by monitoring patterns and processes in archival administration, to diagnose problems by looking into the records creation and management, and to present the improvement plan which would lead to the architectural cultural properties' more efficient management and better use in the future. The management of architectural cultural properties begins with registering and assigning. Cultural Heritage Administration is in charge of control, supervision, and budget and local governments deal with direct management. Accordingly, records are by the hands of each local governmental body. Currently, each cultural property has its management depending on every different working environment in each governmental body. Architectural cultural properties needs managing in one body through the synthetic and unified, concrete and systematic manual and guide for management. Archiving architectural cultural properties have need of unitive management through a professional system, considering the physical characteristics and history of archiving. Unified management system will enhance efficiency and actual use of architectural cultural property records if one governmental body undertakes uniting records through standardization and professional supervision, and data-based unified search engine would enhance efficiency and actual use. Therefore, I suggest that Archives for Architectural Cultural Properties should be established as a professional Archives and wholly responsible body for the purpose of systematically and unifiedly managing architectural cultural property records with professional personnel and facility and transmitting their historical, cultural, and academic value. In Korea, studies up to the present have mainly focused on managing architectural records and records of drawing while few efforts were made to directly deal with managing architectural cultural properties themselves. The focus of this thesis is to study the current status and establish problems of the management of architectural cultural properties in administrative process, and as a result, to propose to establish Archives for Architectural Cultural Properties as a professional archives.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.51 no.2
• /
• pp.94-102
• /
• 2023

The Florence Charter, established in 1981 by the ICOMOS-IFLA International Commission on Historic Gardens, considered the historic garden as a plant-dominated architectural composition, a perpetual balance between the artist and the artisan's desire to remain unaltered in perpetuity. Trees, the main component of the garden, require continuous management as they repeat their creation and calling according to the cycle of the seasons and accordingly, it is suggested that management to maintain the appearance of trees in Korean palaces was an indispensable element. Although it is an important matter to historically verify the tree management techniques of the palaces of the past, research has been difficult due to the absence of historical records and the disconnection of life due to the Japanese colonial period. In addition, according to the view that trees were not generally managed in the palace, research on palace tree management techniques has not been conducted so far. Therefore, this study aimed to examine whether or not the tree management of the palaces was performed in the past through expert interviews based on photographs taken in modern times. With the identification of tree species and pruning through in-depth interviews with experts using photographs taken in the modern period, the results are as follows. First, it was found that the shapes of trees and leaves could be identified through photographs and by observing the phenomena caused by planting and pruning, it was possible to estimate whether or not the tree management was implemented in the modern palace. Second, as a result of in-depth interviews with 8 experts in 4 fields, it was possible to determine the tree species and pruning status, purpose, and method. There was no significant difference in opinions between groups, and the evidence was clearly presented. Third, the type of management of trees in the palace was mainly found to be determination of the types of tree, removal of hazardous factors of trees, and management of lower vegetation and through the photographs of Jondeokjeong and Gwanwanjeong, it was confirmed that the trees were managed even before the Japanese colonial era, considering the time of filming. Based on the photographs taken, it was possible to estimate whether the trees were managed before the Japanese colonial period through expert interviews. However, it could not be clarified due to lack of historical materials as to whether it was carried out on its own according to the circumstances of the times or by the Japanese Empire. Still, in this study, evidence was obtained to refute the view that trees of the palace were not managed in the past through the collected data. Expert opinions supporting this view were collected to make the conclusion. In addition, based on the general theory of pruning, an empirical review of expert opinions was conducted to secure the reliability of the research results.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.51 no.2
• /
• pp.1-11
• /
• 2023

This study intended to develop a technique for quantitatively and 3-dimensionally predicting the potential failure zone and impulse that may occur when trees are fall down. The main outcomes of this study are as follows. First, this study established the potential failure zone and impulse calculation formula in order to quantitatively calculate the risks generated when trees are fallen down. When estimating the potential failure zone, the calculation was performed by magnifying the height of trees by 1.5 times, reflecting the likelihood of trees falling down and slipping. With regard to the slope of a tree, the range of 360° centered on the root collar was set in the case of trees that grow upright and the range of 180° from the inclined direction was set in the case of trees that grow inclined. The angular momentum was calculated by reflecting the rotational motion from the root collar when the trees fell down, and the impulse was calculated by converting it into the linear momentum. Second, the program to calculate a potential failure zone and impulse was developed using Rhino3D and Grasshopper. This study created the 3-dimensional models of the shapes for topography, buildings, and trees using the Rhino3D, thereby connecting them to Grasshopper to construct the spatial information. The algorithm was programmed using the calculation formula in the stage of risk calculation. This calculation considered the information on the trees' growth such as the height, inclination, and weight of trees and the surrounding environment including adjacent trees, damage targets, and analysis ranges. In the stage of risk inquiry, the calculation results were visualized into a three-dimensional model by summarizing them. For instance, the risk degrees were classified into various colors to efficiently determine the dangerous trees and dangerous areas.

• Journal of Korean Society of Environmental Engineers
• /
• v.34 no.10
• /
• pp.684-693
• /
• 2012

The stormwater runoff from the increasing paved roads and vehicles resulted in the increase in the pollutants load to adjacent water bodies. The granular media filtration facilities are the most widely adopted to minimize the non-point source pollution from motorways. It is essential to consider the severe variation of hydraulic condition, suspended solid (SS) characteristics, and the medium characteristics for stormwater management filter. In this study, different types of media, including sand, were tested and the performance of downflow sand filters was investigated under various linear velocity and influent solid particle size. Results showed that the best medium is the coarse sand with large grain size, which showed the specific SS removal before clogging of more than $8.498kg/m^2$, the SS removal of higher than 95%, and minimum head loss. Linear velocity did not affect the total solid removal, while the performance was improved when fine solid was introduced. It is suggested that the life of a downflow sand filter bed can be extended by deep bed filtration when influent particles are fine. However, the captured particles can be washed out after a long period of operation.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.10
• /
• pp.69-80
• /
• 2011

In this study unsaturated seepage analysis of 8 large rockfill dam managed by Korea Water Resources Corporation, were carried out, and the seepage rate of rockfill dam was analyzed by changing reservoir water level, shape, saturated and unsaturated seepage properties of core zone to present an equation to estimate steady-state seepage rate of rockfill dam. This equation considers unsaturated seepage flow and is applicable to domestic large scale Rockfill dam with the height of more than 50m. Estimated values by the proposed equation are greater than those by the method of Sakamoto (1998), which does not consider unsaturated seepage flow. The difference of estimated values increases with the lower reservoir water level and decreases with the higher reservoir water level. We can be sure that the comparison between the measured seepage rate and the estimated seepage rate by the proposed equation for the existing rockill dam was well-matched. The proposed equation is close to the actual phenomenon compared with the existing equations (Sakamoto, 1998; Chapuis and Aubertin, 2001) because it is based on the results of unsaturated seepage analysis of dams, has upstream and downstream slopes in the range of 1Vertical: (0.2~0.3)Horizontal.

• Journal of the Korean earth science society
• /
• v.27 no.2
• /
• pp.221-235
• /
• 2006

In order to understand the transport mechanism of tidal beach sediments in Deukryang Bay, south coast of Korea, beach profiles, surface sediments, sedimentation rates and hydrodynamic conditions have been investigated. The beach is composed of a steep beach face and gentle low-tide terrace, showing general morphologic characteristics of tide dominated beach. Central beach face of an indented coast becomes flattened in summer, but ridge and runnel system developed in other seasons makes the beach profile rather irregular. These seasonal variations of beach profiles and sedimentation rate indicate that beach sedimentation is mainly controlled by both tide and wave processes. Erosion is prevalent in winter when strong wind wave is dominant, while deposition is dominant in other seasons. However, central beach showed an apparent erosional phase in summer. This is caused by strong waves induced by southerly strong winds occurring ephemerally during the summer. On the other hand, sedimentation rates are -89.2 mm/yr on the central beach and 60.5 mm/yr and 38.2 mm/yr on the sides. This result suggests that sediments are eroded on the central beach and subsequently transported to the both sides. Therefore, the central part of Sumun beach, used as a beach bathing site, will be continuously eroded, if nearby dyke continues to prevent the sediment supply from sources.

• The Journal of Engineering Geology
• /
• v.5 no.3
• /
• pp.289-300
• /
• 1995

At the initial stage of the underground reservoir design one should thoroughly consider surface and subsurface hydrology, hydrogeologic characteristics of aquifer system, and the function of cut - off wall because it is linked to the effective management. In this study, three dimensional finite difference model was applied to analyse the function of Ian underground reservoir at Kyungbuk Province. The steady and unsteady state conditions after construction of the underground dam were simulated through the model, and from these results the groundwater budget and the safe yield were determined. The model simulation indicates the infiltration of irrigation water to be one of the major factors of seasonal fluctuation of groundwater level. The recharge rates of irrigation water were estimated as 4.3mm/d during May and June, and 1.7mm/d during July and Agust. Groundwater recharge from the watershed area estimated to about $0.04m^3/s$, almost consistent through the year. In 1984, groundwater discharge through the transverse section of the dam was $0.002m^3/s$ and the optimum yield for two momths(July and Aguest)was $254000m^3$, however, the discharge became $0.013m^3/s$ in1993, implying the failure of cut -off function. without appropaiate of the cut - off wall, optiumum yield during the irrigaton period would be $93, 000m^3$.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.18 no.2
• /
• pp.1-15
• /
• 2015

Urban flooding threatens human beings and facilities with chemical and physical hazards since the beginning of human civilization. Recent studies have emphasized the integration of data and models for effective urban flood inundation modeling. However, the model set-up process is tend to be time consuming and to require a high level of data processing skill. Furthermore, in spite of the use of high resolution grid data, inundation depth and velocity are varied with building treatment methods in 2-D inundation model, because undesirable grids are generated and resulted in the reliability decline of the simulation results. Thus, it requires building generalization process or enhancing building orthogonality to minimize the distortion of building before converting building footprint into grid data. This study aims to develop building generalization method for 2-dimensional inundation analysis to enhance the model reliability, and to investigate the effect of building generalization method on urban inundation in terms of geographical engineering and hydraulic engineering. As a result to improve the reliability of 2-dimensional inundation analysis, the building generalization method developed in this study should be adapted using Digital Building Model(DBM) before model implementation in urban area. The proposed building generalization sequence was aggregation-simplification, and the threshold of the each method should be determined by considering spatial characteristics, which should not exceed the summation of building gap average and standard deviation.