• International Journal of Naval Architecture and Ocean Engineering
• /
• v.7 no.1
• /
• pp.212-225
• /
• 2015

In order to preserve the quality of fresh water in the artificial lake after the reclamation of an intertidal flat at the mouth of a river, we suggest two novel methods of water purification by using tidal potential energy and an enclosed permeable embankment called an utsuro (Akai et al., 1990) in the reclaimed region. One method uses an inflatable bag on the seabed within an utsuro, while the other uses a moored floating barge out of a dyke. Each case employs a subsea pipe to allow flow between the inside and outside of the utsuro. The change in water level in the utsuro, which is pushed through the pipe by the potential energy outside, caused circulation in the artificial lake. In this paper, we analyzed the inflatable bag and floating barge motion as well as the pipe flow characteristics and drafts as given by a harmonic sea level, and compared the theoretical value with an experimental value with a simple small model basin. The numerical calculation based on theory showed good agreement with experimental values.

• Ocean and Polar Research
• /
• v.29 no.1
• /
• pp.55-67
• /
• 2007

A reference to natural prolongation appeared for the first time in the North Sea Judgement. Although it was not suggested that the concept of natural prolongation would automatically allow for the fixing of a continental shelf boundary, that concept encouraged States to request international tribunals to determine continental shelf boundaries on the basis of the geological and geomorphological features of the seabed. In the Libya v. Malta Case, however, the rejection of geological and geomorphological factors was total. Especially, Natural prolongation was the then checkmated as a relevant fact in delimitation between coasts situated less than 400 nm. apart. There can be no doubt that, in several disputed cases, prominent geomorphological variations are simply ignored ; nevertheless, there are also a few agreements where geological and geomorphological characteristics come into play and, to a certain extent, affect maritime boundaries. Physical characteristics of sea-bed are generally given serious consideration in the boundary delimitation such as the final negotiated boundary of the Australia-Indonesia Continental Shelf boundary Agreement(Timor and Arafura seas) which follows the continental slope bordering the Timor Trench.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
• /
• 2004.03a
• /
• pp.429-434
• /
• 2004

현재 우리나라는 육역에 대한 조사와 영해관리를 위한 조사는 이루어져 있으나 연안해역에 대한 해저정보조사는 부족한 실정이다. 비록 국토지리정보원은 1976년부터 연안 해역기본도를 제작 및 배포하고 있으나 갱신주기가 매우 길며, 소축척으로 제작하여 정확도가 낮다. 따라서 해양수산행정 서비스를 위한 기초 자료가 매우 부족한 실정이다. 그리고 NGIS와 MGIS(해양수산부에서 추진하고 있는 해양 GIS사업)와의 연계를 위해 해양 분야에 대한 국가기본지리정보 D/B를 구축하여 디지털 국토 완성할 필요성이 있다. 관련법규를 조사하여 연안해역 해저정보의 조사 필요성과 타당성에 대해 법적인 근거를 마련하였고, 과거 진행되어왔던 연안관련 사업에 대한 조사를 현재 제작되거나 제작중에 있는 자료의 종류와 정확도에 대해 조사하고, 이미 제작된 자료의 문제점에 대해분석 하였다. 효과적인 연안해역 해저정보조사를 위해 우리나라 연안을 아래 그림과 같이 10개 권역으로 구분하고, 이를 다시 7.5'x 7.5'의 소구역으로 구분한 후 각 소구역의 중요도에 따라서 등급을 부여하고, 각 등급별로 IHO S-44 기준의 관측정확도를 따르도록 하였다. 또한 자료조사항목을 선정하여 중요도가 높은 조사항목에 대해 우선적으로 조사할 수 있도록 하였다. 연안해역 해저정보에 대한 조사가 이루어지면 연안 행정 업무 효율성 증대되고 긴급상황에 대처한 신속한 의사결정 가능하며, 다양한 자료의 복합적인 분석 가능할 것이다. 또한 NGIS와 MGIS를 연계하여 많은 부가가치를 창출할 수 있을 것이라 예상된다.

• Journal of Ocean Engineering and Technology
• /
• v.20 no.4 s.71
• /
• pp.58-63
• /
• 2006

When the costal zone surrounded by a breakwater has a narrow vertical opening, currents in the vicinity of a narrow entrance can result in a jet flow, coinciding with the tide. Such a Tidal-Jet Generator(TJG) can change the water mass distribution and transport processes in the domain of influence of the jet. Also, it can decrease the residual time of them. In the present study, the water purification utilizing tidal jets in the coastal zone over constant bathymetry are estimated numerically, using a finite-difference numerical scheme, named the NS-MAC-TIDE method, which isbased on the fully 3D Navier-stokes(NS) equations. The shear velocity near the inlet of the TJG are predicted from the flow field simulation, and are assessed qualitatively with the development of scouring or sediment that is caused by the change of diffusion or sweeping flowup from the seabed of sediment particles. Finally, through solving a transport equation of concentration, the residual time related on mass transport processes and the flushing mechanism for water purification are investigated.

• Journal of Ocean Engineering and Technology
• /
• v.20 no.4 s.71
• /
• pp.37-42
• /
• 2006

This paper is concerned with experimental investigation of steering performance of a tracked vehicle on extremely soft soil. A tracked vehicle model with principal dimensions of 0.9 m(L)x0.75 m(B)x0.4 m(H) and weight of 167 kg was constructed with a pair of driving chain links, driven by two AC-servo motors. The tracks were configured with detachable grousers with variable span. A deep seabed was simulated by means of a bentonite-water mixture in a soil bin of 6.0 m(L)x3.7 m(B)x0.7 m(H). The turning radii of vehicle and driving torques of motors were measured with respect to experiment variables: steering ratio, driving speed, grouser chevron angle, grouser span, and grouser height. L8 orthogonal table is adopted for DOE (Design of experiment). The effects of experiment variables on steering performance are evaluated.

• Journal of Ocean Engineering and Technology
• /
• v.26 no.6
• /
• pp.39-45
• /
• 2012

Underwater robots are generally used for the construction of seabed structures, deep-sea ecosystem research, ocean energy development, etc. A ducted marine propulsor is widely used for the thruster of an underwater robot because of its collision protection, efficiency increase, cavitation reduction, etc. However, the flow of a ducted propeller is very complex because it involves strong flow interactions between the blade impeller and duct. The present work aimed to design a ducted propeller using 2-D strip theory and CFD analysis. The hydrodynamic forces (i.e. and ) were computed to set the local angle of attack in a spanwise direction of the propeller blade. After the propeller design, performance coefficients such as the thrust, torque, and efficiency were computed to check whether the designed performance was achieved. To validate the present analysis, the thrust was compared with experimental data and good agreement was obtained.

• Journal of Ocean Engineering and Technology
• /
• v.29 no.2
• /
• pp.128-134
• /
• 2015

Axial vibration analysis is very important for a deep-seabed mining system. In this study, an axial vibration analysis was carried out to estimate the natural frequencies and tensions of the umbilical cable using experimental data obtained from the first pre-pilot mining test. The axial vibrations of the umbilical cable with a pilot mining robot at the bottom end were analytically determined. The range of the added mass coefficients of the pilot mining robot is estimated by comparing the experimental and analytical data. The natural frequencies and maximum tensions are calculated using four estimated added mass coefficients.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2014.10a
• /
• pp.5-6
• /
• 2014

Pohang port have specified 19 anchorage and 3 quarantine anchorage, but this anchorage is insufficient required anchorage because the average daily use of more than 40 vessels, also Pohang anchorage have geographical characteristics that are open to offshore northeast direction. Recently, sinking ship accident was caused at Pohang port anchorage by dredging anchor due to strong wind from north or north-east. ${\cdots}$ (중략) ${\cdots}$.

• Ocean Systems Engineering
• /
• v.5 no.2
• /
• pp.109-123
• /
• 2015

In the present study, the coupled dynamic response of a Submerged Floating Tunnel (SFT) and mooring lines under regular waves is solved by using two independent numerical simulation methods, OrcaFlex and CHARM3D, in time domain. Variations of Buoyancy to Weight Ratio (BWR), wave steepness/period, and water/submergence depth are considered as design and environmental parameters in the study. Two different mooring-line configurations, vertical and inclined, are studied to find an optimum design in terms of limiting tunnel motions and minimizing mooring-line tension. The numerical results are successfully validated by direct comparison against published experimental data. The results show that tunnel motions and tether tensions grow with wave height and period and decrease with submergence depth. The inclined mooring system is more effective in restricting tunnel motions compared to the vertical mooring system. Overall, the present study demonstrates the feasibility of this type of structure as an alternative to traditional bridges or under-seabed tunnels.

• Structural Engineering and Mechanics
• /
• v.40 no.1
• /
• pp.29-48
• /
• 2011

Under large storm loads sections of a long pipeline on the seabed can be uplifted. Numerically this loss of contact is extremely difficult to simulate, but accounting for uplift and any subsequent recontact behaviour is a critical component in pipeline on-bottom stability analysis. A simple method numerically accounting for this uplift and reattachment, while utilising efficient force-resultant models, is provided in this paper. While force-resultant models use a plasticity framework to directly relate the resultant forces on a segment of pipe to the corresponding displacement, their historical development has concentrated on precisely modelling increasing capacity with penetration. In this paper, the emphasis is placed on the description of loss of penetration during uplifting, modelled by 'strain-softening' of the force-resultant yield surface. The proposed method employs uplift and reattachment criteria to determine the pipe uplift and recontact. The pipe node is allowed to become free, and therefore, the resistance to the applied hydrodynamic loads to be redistributed along the pipeline. Without these criteria, a localised failure will be produced and the numerical program will terminate due to singular stiffness matrix. The proposed approach is verified with geotechnical centrifuge results. To further demonstrate the practicability of the proposed method, a computational example of a 1245 m long pipeline subjected to a large storm in conditions typical of offshore North-West Australia is discussed.