• The Korean Journal of Petroleum Geology
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• v.7 no.1_2 s.8
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• pp.1-6
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• 1999

Natural gas hydrate, a solid compound of natural gas (mainly methane) and water in the low temperature and high pressure, is widely distributed in permafrost region and deep sea sediments. Gas hydrate stability field (GHSF), which corresponds to the conditions of a stable existence of solid gas hydrate without dissociation, depends on temperature, pressure, and composition of gas and interstitial water. Gas hydrate-saturated sediment are easily recognized by the bottom simulating reflector (BSR), a strong-amplitude sea bottom-mimic reflector in seismic profiles. It is known that BSR is associated with the basal boundary of the GHSF, The purpose of this study is to define the GHSF and its occurrence in the southwestern part of Ulleung Basin, East Sea. The hydrothermal gradient is measured using the expandable bathythermograph (XBT) and the geothermal gradient data are utilized from previous drilling results for the adjacent area. By the laboratory work using methane and NaCl $3.0 wt{\%}$ solution, it is shown that the equilibrium pressures of the gas hydrate reach to 2,920.2 kPa at 274.15 K and to 18,090 kPa at 289.95 K for the study area. Consequently, it is interpreted that the lower boundary of the GHSF is about 210 m beneath 400-m-deep sea bottom and about 480 m beneath 1,100-m-deep sea bottom. The resultant boundary is well matched with the depth of the BSR obtained from the seismic data analysis for the study area.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.3
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• pp.186-194
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• 2000

bottom as a reference basis, some theoretical elements which form bottom echoes during acoustic survey of demersal fish were considered. A stable bottom detection method based on maximum voltage difference, which was not influenced by variable levels and waveform transformation. The method has been shown to be effective using in-situ bottom echo waveforms and computer simulation data. A comparison between near-bottom SV profiles acquired in Funka Bay, Hokkaido, of Japan, the East China Sea and the Yellow Sea, of Korea, with the threshold method and maximum differential voltage method, shows that the SV obtained with the maximum differential voltage method is 4-6 dB higher than those with threshold method within 2m from the bottom.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.3
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• pp.195-201
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• 2000

This paper discusses methods for the stable bottom detection and the optimum bottom offset which enable to separate the fish echoes from the bottom echoes with echo integration of demersal fish. In preprocessing of the echo signal, the bottom detection has to be done stably against the fluctuation of echo level and the bottom offset has to be set to a minimum height such that near bottom fish echoes are included Two methods of bottom detection, namely echo level threshold method and maximum echo slope method were compared and analyzed. The echo level method works well if the ideal threshold level was given but it sometimes misses the bottom because of the fluctuation of the echo. Another method to detect the bottom which uses maximum echo slope indicates the simple and stable bottom detection. In addition, the bottom offset has to be set near to the bottom but not to include the bottom echo. Optimum bottom offset should be set a few samples before the detected bottom echo which relates the beginning of pulse shape and acoustic beam pattern to the bottom feature.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.4
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• pp.355-363
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• 2006

In this study, it was analyzed how the pore pressure behind a subsea tunnel influences on the stability of the tunnel. The tunnel is located in the soft rock layer, and a soft sandy layer and weathered soil layer are located on the top of it. Coupled numerical analyses are performed for both drained and undrained condition with varying coefficients of lateral earth pressure. In the case of undrained conditions, the stability of the tunnel was analyzed with different thicknesses of shotcrete. On the other hand, a sensitivity analysis was performed with different hydraulic conductivities and porosities of the shotcrete for the drained conditions. The stability of a subsea tunnel was evaluated in terms of safety factor suggested by You et al.(2000, 2001, 2005) based on the shear strength reduction technique. In this paper, the safety factor of a tunnel was calculated under steady state flow condition during hydro-mechanical coupled analysis. As a result, it was found that the stability of a subsea tunnel could be rather increased by allowing a proper amount of groundwater inflow into a subsea tunnel.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.138-140
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• 2006

한국전력공사(이하 한전)에서는 제주지역 전력공급의 안정을 위해 '98년부터 국내 최초로 육지전력 계통과 연계하여 장거리 해저케이블 송전선로를 건설하여 운영하고 있다. 해저케이블은 해저에 포설되고 외부적 환경에 견디기 위해 육상케이블과 다른 많은 보호층을 포함하고 있어 설비의 유지보수에 많은 제약사항을 안고 있다. 특히 해남${\sim}$제주 연계선로는 기술적 장점 때문에 AC송전 대신 HVDC 송전을 하고 있어 한단계 Upgrade된 설비운영 기술이 필요하다. 본 고에서는 HVDC 해저 케이블의 설비운영에 있어 선로의 고장시 케이블의 고장점 위치를 탐지하는데 중점을 두어 실제 고장점 탐지 사례를 중심으로 HVDC 해저 케이블 고장점 탐지 방법 및 시험 결과를 검토하고 향후 유사 고장 발생에 효과적으로 대응하기 위한 절차를 제시하였다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2013.06a
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• pp.548-550
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• 2013

해양 석유 가스생산의 증가로 해저장비 시장이 급속하게 확대되고 있다. 해저 장비 중 Subsea Tree는 핵심적인 기자재이나 현재 기술의 안정성은 미흡한 상황이다. Subsea Tree는 기술개발 완료 시 독점적 이윤이 확보 가능하고 우리나라 해양플랜트 업체의 해상설비 설계기술과 결합하여 패키지 확보에 기여할 수 있다. 특히 국내업체가 확보한 광구에 설치 시 최소 5천억 원의 수입대체효과가 발생할 수 있다. 본 연구에서는 Subsea Tree의 국산화 기술개발 현황 및 성과와 더불어 이에 대한 사업화 전략의 수립에 대해 살펴보고자 한다.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06a
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• pp.403-406
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• 2011

한국해양연구원에서는 국토해양부의 지원을 받아 2010년 7월부터 새로운 개념의 해저로봇 개발에 착수하였다. 새로이 개발되는 해저로봇은 프로펠러 방식으로 추력을 얻는 기존의 해저로봇과는 달리 여러 개의 관절로 이루어진 6개의 다리를 이용하여 해저면에 근접해서 보행과 유영으로 이동하는 해저로봇으로 강조류와 악시계의 환경에서도 운용이 가능한 로봇이다. 이 해저보행로봇 시스템은 선상시스템과 완충기, 그리고 해저보행로봇으로 구성되며, 이들 사이는 광변환기를 통해서 광케이블로 연결된다. 선상시스템에는 해저로봇의 제어 및 모니터링을 위하여 10대의 컴퓨터가 설치되어 있고, 완충기와 해저로봇에 각각 1대의 입출력 컴퓨터가 내장되어 장착된 센서와 모터의 인터페이스를 담당한다. 본 논문에서는 해저보행로봇의 통신 시스템을 소개하고, 이 통신 시스템에서 사용되기 위하여 설계된 메시지의 통신 프로토콜을 설명한다. 해저보행로봇 시스템의 주 네트워크는 기가비트 이더넷이며, 안정된 통신 환경의 소규모 독립 네트워크이다. 완충기와 해저보행로봇에는 최대 100㎐로 동작하는 다양한 직렬 통신 방식을 갖는 다수의 센서와 모터가 장착되어 있는데, 입출력 컴퓨터가 이더넷 네트워크와의 인터페이스 역할을 수행하여 계층적 네트워크를 구성한다. 로봇 제어에서는 실시간성이 중요하기 때문에 이더넷에서 통신 메시지는 한 번의 전송으로 여러 컴퓨터에 전달할 수 있도록 멀티캐스팅을 사용하여 전송된다. 설계된 통신 프로토콜은 이러한 해저로봇 시스템의 특성에 적합한 간결한 구조로 설계되었으며, 최대 255개의 주소를 지정할 수 있고 255 종류의 메시지 형태를 설정할 수 있다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.829-843
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• 2017

Subsea tunnel needs to be built over 50 km long to connect between nations and continents. However there are only 19 tunnels longer than 5 km until recently. And there is no history of constructing and operating tunnel longer than 50 km. In Korea, subsea tunnels with a length of more than 50 km are being planned, such as Korea~Japan, Korea~China, Honam~Jeju subsea tunnels. Because of the geographical conditions of Korea, most of these tunnels are inter-contry tunnels. So technology preemption for the subsea tunnel construction is getting more and more important. Most of these subsea tunnels are ultra-long tunnels under high water pressure conditions. So new technologies are required such as ventilation and disaster prevention of high-speed tunnels, securing of structural stability under high pressure conditions, and pressure reduction in high-speed conditions. These technologies are different from those of ground tunnels. Therefore, this paper describes the ultra-long subsea tunnel design under high water pressure of maximum 16 bars through the Honam (land) - Jeju (island) virtual subsea project. We proposed a reasonable solution to various problems such as securing structural stability in high pressure condition and ventilation disaster prevention system of ultra long-tunnel.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.743-749
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• 2015

In this paper, we describe the dynamic tumble-stability analysis of a seabed-walking robot named Crabster (CR200) in forward-incident currents. CR200 is designed to be operated in tidal-current conditions, and its body shape is also designed to minimize hydrodynamic resistances considering hydrodynamics. To analyze its tumble stability, we adopt the dynamic stability margin of a ground-legged robot and modify the definition of the margin to consider tidal-current effects. To analyze its dynamic tumble stability, we use the estimated hydrodynamic forces that act on the robot in various tidal-current conditions, and analyze the dynamic tumble-stability margin of the robot using the estimated results obtained for the various tidal-current conditions. From the analyses, we confirm the improved tumble stability of the robot according to the movement of the tumble axis caused by the supporting points of the legs.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.2
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• pp.54-62
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• 2003

The free span of a subsea pipeline due to seabed scouring can result in structural failure by severe ocean environmental loads and vortex induced vibrations. This Paper examines the safety of subsea pipelines with free spans under axial compressive load. The variation of allowable lengths of static and dynamic free spans is examined for generalized boundary conditions. The free span is modelled as a beam with an elastic foundations and the boundary condition is replaced by linear and rotational springs at each end. The static and dynamic free span curves are obtained with a function of non-dimensional parameters. A case study is carried out to introduce the application method of the curve. The results of this study can be usefully applied for the design of subsea pipelines with a free span.