• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.657-673
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• 2019

A monitoring method based on acoustic emission (AE) sensor has been widely used to evaluate the damage of structures in underground rock. The acoustic emission signal generated from cracking in material is analyzed as various acoustic emission parameters in time and frequency domain. To investigate from initial crack generation to final failure of rock material, it is important to understand the characteristics of acoustic emission parameters according to the stress ratio and rock strength. In this study, uniaxial compression tests were performed using very strong and weak rock specimen in order to investigate the acoustic emission parameters when the failure of specimen occurred. In the results of experimental tests, the event, root-mean-square (RMS) voltage, amplitude, and absolute energy of very strong rock specimen were larger than those of the weak rock specimen with an increase of stress ratio. In addition, the acoustic emission parameters related in frequency were more affected by specification (e.g., operation and resonant frequency) of sensors than the stress ratio or rock strength. It is expected that this study may be meaningful for evaluating the damage of underground rock when the health monitoring based on the acoustic emission technique will be performed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.350-361
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• 2019

The fourth industrial revolution based on the intelligent revolution has revolutionized the society as a whole, and it has also affected the defense sector. Various aspects of the war have been changing with the development of technology. In particular, various strategies such as research and development of core technology related to defense unmanned system field and infrastructure are being established based on the fourth industrial revolution technology. In this paper, we have conducted a study to select the technology required for maritime unmanned systems, which can be considered as a priority consideration for the future development of the core technology to be secured prior to the development of the weapon system. First, the core technology prioritization model for the marine unmanned system was established, and the technology fields of the unmanned robot were reclassified and integrated in the related literature such as the classification of the defense technology standard. For the empirical analysis, a questionnaire survey was conducted for 12 specialists who are engaged in the planning of weapons systems, and the importance of technical fields that require development in the development of marine unmanned systems was analyzed. As a result, it was possible to identify the key technology areas that should be considered in selecting the key technologies proposed by the military groups, research institutes, and companies. This could contribute to the establishment of the technology roadmap to develop the marine unmanned system from the future point of view.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.3
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• pp.110-121
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• 2021

The importance of tidal flats lost due to industrialization has recently received attention, and attention is being paid to the creation of artificial tidal flats and maintenance of natural tidal flats. However, there is still a lack of understanding about the behavioral characteristics of mud, mud, and sand that form tidal flats. Although research on the movement characteristics of mixed soils such as tidal flats has been conducted through field investigations and hydraulic experiments, interest in developing a numerical model based on these results has not yet reached. In this paper, the purpose of this paper is to establish a mixed soil model that can efficiently manage the low quality of the tidal flats. In constructing a model for reproducing the surface movement of mixed soil, the numerical stability of the reproduction and movement of sand and mud constituting the mixed soil in the numerical model should be considered first, so first, the volume of sand and mud constituting the mixed soil A mixed soil model representing the relationship was proposed based on a topographical diagram representing the geometric structure of the mixed soil. In order to consider the dry bulk density of the mixed soil, it was possible to consider the dry bulk density of the mud by introducing the water content of the mud containing water. In addition, it was confirmed that the mud and sand movement calculation according to the slope collapse of the mixed soil was stably performed through the calculation of the slope collapse of the mixed soil through the numerical analysis model to which the proposed mixed soil model was applied.

• Journal of the Korean Geotechnical Society
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• v.37 no.6
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• pp.29-37
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• 2021

Since many geotechnical structures are constructed on a weathered granite layer, it is important to evaluate their characteristics. As a seismic design is the more important nowadays, the demands to estimate a shear wave velocity (V_S) based on acceptable methods are increasing. In this study, an empirical equation predicting V_S of the weathered granite layer is suggested based on the nonlinear multiple variable regression analysis whose independent variables are both SPT (Standard penetration test)-N₆₀ and chemical weathering index. It is concluded that the accuracy of the empirical equation estimating V_S of the weathered granite layer increases when it considers the chemical weathering index as an additional independent variable compared to the result of simple regression analysis using only N₆₀.

• The Journal of the Korea Contents Association
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• v.21 no.8
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• pp.337-355
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• 2021

Demographic changes such as an aging and low fertility, as well as changes in industrial structure and residential environment, revealed the limitations of urban development policies. Accordingly, the government is making efforts to ensure a prosperous life for the people by including the plan to expand the living SOC in the national urban regeneration policy. The main priority tasks of the Living SOC include the establishment of welfare infrastructure for children and the vulnerable. This means that interest in welfare is increasing recently. In this study, we analyzed the supply status of welfare facilities for the senior, child and the disabled in 17 cities and provinces nationwide using LQ (Location Quotient). After analyzing the causes of the imbalance in the supply of welfare facilities by region, the improvement plan was suggested. Each welfare facility was highly localized by region, especially the accessibility gap between cities and provinces is very large. Welfare finances were similar in most cities and provinces, with the exception of some cities and provinces. In the case of cities with very high living standards, sufficient facilities were not provided. Improvement methods are as follows; Combination of welfare facilities that can maximize space efficiency, Securing appropriate welfare finance in consideration of living standards by city and province, Differentiation of supply method considering demand and user types for welfare facilities.

• Journal of Korea Water Resources Association
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• v.55 no.1
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• pp.43-57
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• 2022

Advances in measurement techniques have reduced measurement costs and enhanced safety resulting in less uncertainty. For example, an acoustic doppler current profiler (ADCP) based suspended sediment concentration (SSC) measurement technique is being accepted as an alternative to the conventional data collection method. In Korean rivers, horizontal ADCPs (H-ADCPs) are mounted on the automatic discharge monitoring stations, where SSC can be measured using the backscatter of ADCPs. However, automatic discharge monitoring stations and sediment monitoring stations do not always coincide which hinders the application of the new techniques that are not feasible to some stations. This work presents and analyzes H-ADCP-SSC models for 9 discharge monitoring stations in Korean rivers. In application of the Gaussian mixture model (GMM) to sediment-related variables (catchment area, particle size distributions of suspended sediment and bed material, water discharge-sediment discharge curves) from 44 sediment monitoring stations, it is revealed that those characteristics can distinguish sediment monitoring stations regionally. Linking the two results, we propose a protocol determining the H-ADCP-SSC model where no H-ADCP-SSC model is available.

• Korean Journal of Construction Engineering and Management
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• v.23 no.2
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• pp.16-23
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• 2022

This study examined the trend of international competitiveness over the past 10 years (2011-2020), focusing on comparative analysis with China and the United States, targeting seven major export items of Korean construction machinery based on 6 units of HS code. To this end, the export similarity index and trade competitiveness index were calculated and analyzed using UN Comtrade and Korea International Trade Association trade statistics. As a result of the analysis, competition between Korea and China has intensified over the past decade, and competition with the United States has remained at a certain level. Korean forklifts (8427.20) are exporting to the world with strong competitiveness in the global market. Excavators (8429.52) and loaders (8429.51), which have the largest export share of Korean construction machinery, have a weight advantage, but they are exporting due to price inferiority. The rest of the items were found to be inferior in price and weight, and were not competitive in the global market. These analysis results suggest the following implications. First, it is necessary to strengthen efforts to expand exports of universal construction machinery items, which are expected to increase in demand in the future, by boosting the economy and expanding infrastructure investment in accordance with eco-friendly policies. Second, excavators, which have been shown to have a quality advantage and a price competitive advantage, need to further strengthen export marketing activities not only in China and the United States but also in emerging developing countries.

• 한국노년학
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• v.41 no.3
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• pp.373-396
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• 2021

This study aims to examine the effect of housing characteristics of older adults on the willingness to continue living in local communities in order to realize the Aging in place of the elderly in Korea. Considering that the health status of the elderly is important for aging in place, both healthy and unhealthy cases were analyzed in the analyses. Housing characteristics include home ownership, housing cost burden, housing convenience, housing satisfaction, and residential environment satisfaction. The study sample is 9,798 elderly people from the 2017 survey on the elderly. Key findings are as follows: First, while 6,704 older adults (68.4%) chose to continue living in the community, 3,094 (31.6%) of the elderly did not choose to live in the local community. Second, the elderly who chose to stay in the local community are likely to have more real estate assets and less burden of housing expenses than the elderly group who did not. Third, the results report that older adults with more real estate assets and lower the housing cost burden are likely to choose sustainable living in the local community. The findings suggest that the majority of the elderly actually preferred Aging in place. This study concludes with practice and policy implications for realizing aging in place considering the elderly's needs.

• Journal of Korea Port Economic Association
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• v.38 no.3
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• pp.69-86
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• 2022

This study analyses the necessity of the large-size shipyard and explores competitiveness factors of it. Furthermore, the competitiveness is evaluated and the economic feasibility of building and operation of shipyard is examined. As a result of AHP analysis of the determining factors of the competitiveness of the repairing shipyard, the importance of the factors was found in the order of arrival and departure safety, repair technology, dock and wharf facilities, repair cost, repair period (on time delivery), and repair parts supply. Moving distance, repair service quality, repair parts supply, arrival and departure safety, repair technology, dock and quay wall facilities, and repair period (on time delivery) were identified as key factors in the AHP analysis for competitiveness of the Busan Port repair shipyard to be built in the future. As a result of the analysing economic feasibility, the net present value of the Busan Port repair shipyard construction and operation investment project was KRW 435.6 billion, and the internal rate of return was 9.8%, higher than the social discount rate (4.5%), and the cost-benefit ratio (B/C) was high at 1.167. As a result of the study, the necessity and economic feasibility of the Busan Port repair shipyard are sufficiently ensured, and the competitiveness assessment was highly positive.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.30-42
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• 2022

Due to the increase in construction of tunnels, the burdens of maintenance works for tunnel structures have been increasing in Korea. In addition, the increase of traffic volume and aging of materials also threatens the safety of tunnel facilities, therefore, maintenance costs are expected to increase significantly in the future. Accordingly, automated condition assessment technologies like image-based tunnel scanning system for inspection and diagnosis of tunnel facilities have been proposed. For image-based tunnel scanning system, it is key to create a planar image through stitching of multiple images captured by tunnel scanning system. In this study, performance of feature-based stitching algorithms suitable for stitching tunnel scanning images was evaluated. In order to find a suitable algorithm SIFT, ORB, and BRISK are compared. The performance of the proposed algorithm was determined by the number of feature extraction, calculation speed, accuracy of feature matching, and image stitching result. As for stitching performance, SIFT algorithm was the best in all parts of tunnel image. ORB and BRISK also showed satisfactory performance and short calculation time. SIFT can be used to generate precise planar images. ORB and BRISK also showed satisfactory stitching results, confirming the possibility of being used when real-time stitching is required.