• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.4
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• pp.11-17
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• 2010

본 논문의 주된 목적은 농업용 이동로 또는 농업용수의 공급을 위하여 사용되는 파형 강판 파이프아치 암거가 고속도로 및 지방국도를 통과할 때 설계 및 시공 시 요구되는 최소 토피 두께를 제안하는데 있다. 1998년 이후 농업용 목적으로 사용되는 파형 강판 암거는 서해안 고속도로의 건설과 더불어 그 수요량이 증가하였으며, 이에 따른 설계 및 시공의 빈도수 또한 지속적으로 증가하고 있는 추세이다. 그러나 이를 뒷받침 할 수 있는 국내 규정은 아직 미약한 실정이다. 따라서 본 연구에서는 파형 강판 암거의 설계 및 시공 시 고려해야 할 가장 중요한 인자 중 하나인 최소 토피에 대한 연구를 수행하고 그 두께를 제안하였다. 현재 국내 및 미국에서 사용되고 있는 최소 토피 두께는 암거의 스판 길이 또는 스판 길이와 암거의 높이 비율의 관계로부터 정해지는 것으로 구조적인 특성치를 포함하고 있지 않다. 제안된 최소 토피 두께는 암거의 형상적 특성, 설계 하중, 강판의 구조적특성과 손상 등을 반영하여 파형 강판 암거의 안전성을 극대화 하였다. 제안된 토피 두께는 미국과 국내 도로공사에서 규정하고 있는 토피 두께와 비교 분석하였으며, 그 결과 국내 규정이 더욱 안전성을 고려하고 있음을 알 수 있었다.

• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.88-90
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• 1998

In this paper, the indirect BIEM(boundary integral equation method) is adopted to analyze 3-D eddy currents in cover plate of power transformer. In indirect BIEM, the equivalent magnetic surface charge density and the eqivalent magnanetic surface current density are the unknowns. Using triangular constant elements, the integral equations are discretized into boundary element equations of minimum order. Eddy currents are obtained in terms of euqivalent magnetic surface sources. And the locad overheating can be predicted using the eddy currents distribution in cover plate of power transformer.

• Korean Journal of Remote Sensing
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• v.28 no.4
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• pp.409-420
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• 2012

Since the Industrial Revolution, CO2 levels have been increasing with climate change. In this study, Analyze time-series changes in snow cover quantitatively and predict the vanishing point of snow cover statistically using remote sensing. The study area is Mt. Kilimanjaro, Tanzania. 23 image data of Landsat-5 TM and Landsat-7 ETM+, spanning the 27 years from June 1984 to July 2011, were acquired. For this study, first, atmospheric correction was performed on each image using the COST atmospheric correction model. Second, the snow cover area was extracted using the NDSI (Normalized Difference Snow Index) algorithm. Third, the minimum height of snow cover was determined using SRTM DEM. Finally, the vanishing point of snow cover was predicted using the trend line of a linear function. Analysis was divided using a total of 23 images and 17 images during the dry season. Results show that snow cover area decreased by approximately $6.47km^2$ from $9.01km^2$ to $2.54km^2$, equivalent to a 73% reduction. The minimum height of snow cover increased by approximately 290 m, from 4,603 m to 4,893 m. Using the trend line result shows that the snow cover area decreased by approximately $0.342km^2$ in the dry season and $0.421km^2$ overall each year. In contrast, the annual increase in the minimum height of snow cover was approximately 9.848 m in the dry season and 11.251 m overall. Based on this analysis of vanishing point, there will be no snow cover 2020 at 95% confidence interval. This study can be used to monitor global climate change by providing the change in snow cover area and reference data when studying this area or similar areas in future research.

• Steel and Composite Structures
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• v.42 no.6
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• pp.747-764
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• 2022

The design codes and calculation methods related to soil-steel composite bridges and culverts only specify the minimum soil cover depth. This value is connected with the bridge span and shell height. In the case of static and dynamic loads (like passing vehicles), such approach seems to be quite reasonable. However, it is important to know how the soil cover depth affects the behaviour of soil-steel composite bridges under seismic excitation. This paper presents the results of a numerical study of soil-steel bridges with different soil cover depths (1.00, 2.00, 2.40, 3.00, 4.00, 5.00, 6.00 and 7.00 m) under seismic excitation. In addition, the same soil cover depths with different boundary conditions of the soil-steel bridge were analysed. The analysed bridge has two closed pipe-arches in its cross section. The load-carrying structure was constructed as two shells assembled from corrugated steel plate sheets, designed with a depth of 0.05 m, pitch of 0.15 m, and plate thickness of 0.003 m. The shell span is 4.40 m, and the shell height is 2.80 m. Numerical analysis was conducted using the DIANA programme based on the finite element method. A nonlinear model with El Centro records and the time history method was used to analyse the problem.

• Journal of the Korean Operations Research and Management Science Society
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• v.15 no.2
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• pp.97-104
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• 1990

The problem is a variation of the weighted set-covering problem (SCP) which requires the minimum-cost cover to be self-covering. It is shown that direct extension of the well-known greedy heuristic for SCP can have an arbitrarily large error in the worst case. It remains an open question whther these exists a greedy heuristic with a finite error bound.

• Journal of Korea Multimedia Society
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• v.24 no.6
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• pp.768-788
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• 2021

The reversible data hiding technique safely transmits secret data to the recipient from malicious attacks by third parties. In addition, this technique can completely restore the image used as a transmission medium for secret data. The reversible data hiding schemes have been proposed in various forms, and recently, the reversible data hiding schemes based on interpolation are actively researching. The reversible data hiding scheme based on the interpolation method expands the original image into the cover image and embed secret data. However, the existing interpolation-based reversible data hiding schemes did not embed secret data during the interpolation process. To improve this problem, this paper proposes embedding the first secret data during the image interpolation process and embedding the second secret data into the interpolated cover image. In the embedding process, the original image is divided into blocks without duplicates, and the maximum and minimum values are determined within each block. Three way searching based on the maximum value and two way searching based on the minimum value are performed. And, image interpolation is performed while embedding the first secret data using the PVD scheme. A stego image is created by embedding the second secret data using the maximum difference value and log function in the interpolated cover image. As a result, the proposed scheme embeds secret data twice. In particular, it is possible to embed secret data even during the interpolation process of an image that did not previously embed secret data. Experimental results show that the proposed scheme can transmit more secret data to the receiver while maintaining the image quality similar to other interpolation-based reversible data hiding schemes.

• Atmosphere
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• v.19 no.2
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• pp.169-182
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• 2009

To improve the performance of climate and numerical models, concerns on the land-atmosphere schemes are steadily increased in recent years. For the realistic calculation of land-atmosphere interaction, a land surface information of high quality is strongly required. In this study, a new land cover map over the Korean peninsula was developed using MODIS (MODerate resolution Imaging Spectroradiometer) data. The seven phenological data set (maximum, minimum, amplitude, average, growing period, growing and shedding rate) derived from 15-day normalized difference vegetation index (NDVI) were used as a basic input data. The ISOData (Iterative Self-Organizing Data Analysis), a kind of unsupervised non-hierarchical clustering method, was applied to the seven phenological data set. After the clustering, assignment of land cover type to the each cluster was performed according to the phenological characteristics of each land cover defined by USGS (US. Geological Survey). Most of the Korean peninsula are occupied by deciduous broadleaf forest (46.5%), mixed forest (15.6%), and dryland crop (13%). Whereas, the dominant land cover types are very diverse in South-Korea: evergreen needleleaf forest (29.9%), mixed forest (26.6%), deciduous broadleaf forest (16.2%), irrigated crop (12.6%), and dryland crop (10.7%). The 38 in-situ observation data-base over South-Korea, Environment Geographic Information System and Google-earth are used in the validation of the new land cover map. In general, the new land cover map over the Korean peninsula seems to be better classified compared to the USGS land cover map, especially for the Savanna in the USGS land cover map.

• Journal of the Korea Society for Simulation
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• v.18 no.4
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• pp.165-173
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• 2009

Recent portable devices are so versatile that they have multiple communication channels and play several multimedia formats. Especially, many services are under development for users who connect Internet or nearby devices via WWAN (Wireless Wide Area Network) and/or WLAN (Wireless LAN). In case of paying the telecommunication cost proportional to the amount of data downloaded, it is necessary to reduce the cost by constructing a special ad hoc network in which each participating peer downloads a specific portion of the want-to-be-shared content over the payable WWAN channel and exchanges the remaining portion with other peers using the cost-free WLAN channel. If all peers participate in forwarding packets, some transmissions are redundant which results in the unnecessary consumption of bandwidth as well as the delayed content distribution time. In order to reduce the redundant transmission, this paper proposes both the excluding method which discourages some peers not to forward redundant packets, and the minimum cover set method in which only the minimum number of peers are in charge of forwarding packets. These two methods obviate redundant packet forwarding, and result in reduction of content distribution time by up to around 29%.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.2
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• pp.55-62
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• 2005

There are many risk factors of electrical shock caused by a minimum of protective devices, loose working environments, deterioration of installations at temporary power installations of construction sites. An insulation cover for instrument transformer(MOF) used in 22.9[kV] class power receiving system hasn't shown good performance in terms of electrical safety because of short clearance between insulation cover and each input and output wire junction part. The insulation cover is easily moved by outside environment as wind or rain because of different size between insulation cover and busing, also can be leaded to breakdown by tracking. Therefore, we have proposed the insulation cover which effectively can prevent from electrical disaster in this paper, and a utility model patent had been registered already. To decrease the electric field concentrated on specific part, we had roundly designed the shape of insulation cover and the clearance between cover and live part was adjusted to be longer than the existing thing. The proposed insulation cover was evaluated by using the electric field solution program.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.4
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• pp.13-18
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• 2007

The research was performed to review the design factors which affect the durability of structures. For the study, domestic and foreign literature review were performed on various design criteria. Based on Korean standard specifications, the results showed that the durability of structure as the diameter of reinforcing steel bar becomes smaller and the distance between reinforcing bar is closer than the normal gap. The results were also presented that the minimum required bar cover is 6.6cm to obtain the durability index value. In addition, the maximum limited bar cover was 12cm considering the durability index and the change of increasing value of durability index. In case that there is no specified regulation for the bar cover thickness change, the durability life by neutralization is proportional to the thickness of bar cover.