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## Journal of Ocean Science and Technology

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자료건수 (37건)
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37

A Study of the HNS Gel Pack Absorbent

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.59-63

협약을 통해 무료로 제공되는 자료로, 원문이용 방식은 연계기관의 정책을 따르고 있습니다.

The volume of hazardous and noxious substance via ocean transportations has been increased continuously and the number of chemical complexes, whose size each is getting large, have been increased as well by geometrical progression. Internationally, the agreement (protocol) of OPRC HNS was adopted by IMO (International Marine Organization) in London, U. K in May 2000 and since then Korean government (MOMAF and KCG) has prepared for its execution in terms of practical affairs in line with the agreement of OPRC HNS. The numerous accidents and risks due to oil and HNS have occurred continuously at vessels and offshore facilities and they are expected to create tremendous amount of damage of human lives, assets and marine environment. In this study, we would like to preserve our marine environment when any pollution (HNS) accident happens by inventing HNS gel pack absorbent which can be used as a pollution prevention substance and by evaluating the capacity and efficiency for the HNS gel pack absorbent.

36

Applied Technologies and 'Cheong-Hae 30' for Short Sea Shipping Systems in North-East Asian Region

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.53-58

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Efficient, reliable, and yet environmentally sound, Short Sea Shipping systems in the north-east Asia region, especially in the Yellow Sea region, are urgently needed. Considering the 700 million inhabitants and 5 trillion USD of Gross Regional Products and the ever-expanding economy in the Yellow Sea rim area, the present marine transportation system needs to be modernized to keep up with the world-class standards. The Short Sea Shipping (SSS) concept, actively exploited and adopted, firstly in Europe and then in the U.S., is well suited to be applied to a Yellow Sea marine transportation system. The efficient SSS system should be flexible, fast in loading/unloading of cargos, and well connected with the inter-modal transportation means such as trucks, rails, airs and other waterways. Many technologies to realize the concept have been developed, and some new technologies are now under developing stage. In this paper technologies for efficient SSS systems are surveyed and some key technologies are proposed for more exploitation. Conceptual design of a new high speed container ship, namely "Cheong-Hae 30", which can be adopted as a fast container feeder in north-east Asian sea routes is introduced. Comparison of the calculated Required Freight Rates with "Cheong-Hae 30" and a conventional ship is given on the sea route between Incheon and Qingdao.

35

Non-Hydrostatic Model of Near Shore Flow Calculation

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.44-52

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In this paper, the fractional step approach is applied to calculation of flow in near shore area with complicated boundary shape in order to consider non-hydrostatic pressure induced by geometrical irregularities at the boundaries. At a time instant, intermediate solutions for flow velocities and free surface are obtained through the hydrostatic multi-layer calculation in the first step, and non-hydrostatic pressure field is predicted using the intermediate solutions in the second step. In the third step, final solutions are calculated considering not only hydrostatic pressure but also non-hydrostatic pressure. Present calculation algorithm with fully explicit finite difference scheme in ${\sigma}$a-coordinate is successfully applied to the near shore flow calculation. Hydrostatic model is thought practically good tool enough to predict general ocean circulation problems. However, effects of non-hydrostatic pressure on flow field and free surface movements are to be emphasized, not negligible, in the vicinity of irregularities both of continental and bottom boundaries. Present method can be applied to the mesoscale free surface flows with complex bottom topography where MAC-like 3-d hydrodynamic calculations are quite ineffective and uneconomic.

34

Modelling Transport of Suspended Sediment caused from Dredging Operation

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.38-43

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A three-dimensional particle-tracking model has been developed to predict far-field transport of suspended sediment loads resulting from dredging operation. The model was applied to the case study of waterway dredging operation in Asan Bay, Korea in which tidal currents are dominant. Numerical simulations for the transport of suspended sediments with multi-component mixtures of 5 different particle sizes were conducted under the spring and the neap tidal current conditions. The particle streaklines show that fine-grained sediments were transported up to ${\sim}20\;km$ downstream distance along the bay channel while coarse sediments were deposited immediately in the dredging area. The higher concentration of suspended sediments was found in the main channel of waterways where tidal currents were much stronger in the bay.

33

Regional Co-Operation on Marine Pollution Preparedness and Response in the Northwest Pacific-with a Special Reference to NOWPAP Regional Oil Spill Contingency Plan

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.30-37

협약을 통해 무료로 제공되는 자료로, 원문이용 방식은 연계기관의 정책을 따르고 있습니다.

In today's world, oil spills are a major environmental problem. In total, millions of tones of oil have been spilled into the world's ocean, resulting in enormous impacts on fisheries, wildlife and their habitats, coastal industries and tourism, and even on political and social aspects, etc. The sea area of the far-eastern Asian countries-that is, Northwest Pacific region, was regarded as the area facing the highest risk of oil spill in the world. In fact, 19 major oil spills (greater than 1,000 tons), 124 intermediate spills ($50{\sim}1,000$ tons), and innumerable small spills (less than 50 tons) have been occurred in the area from 1990-2004. Based upon the perception of high risk of oil spill, the four countries bordering the Northwest Pacific (China, Japan, R. Korea and Russia) have developed effective measures for regional cooperation in marine pollution preparedness and response within the framework of the Northwest Pacific Action Plan (NOWPAP), agreed in 1994 by the governments. They have especially developed the NOWPAP Regional Oil Spill Contingency Plan and its Memorandum of Understanding, which will be a firm foundation in our strong partnership among NOWPAP Members in the relevant field. The present paper introduces current activities of MERRAC as a new regional initiative on marine pollution preparedness and response in the NOWPAP region, together with analysis of oil spill risk in the region and regional preparedness and response system to oil spill, with a special reference to NOWPAP Regional Oil Spill Contingency Plan.

32

The Oceanic Circulation of the Japan/East Sea -Its Present and Future-

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.23-29

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The end of "the Cold War" in 1991 activated the studies of the oceanic circulation of the Japan/East Sea (hereafter, JES) through international cooperative studies between countries surrounding the JES, clarifying many interesting aspects of the northern part of the JES, which have been masked by "the iron curtain" during the war. The existence of a large cyclonic circulation in upper 1000 m was confirmed north of $40^{\circ}N$ and east of $132^{\circ}E$ in the Japan Basin by hydrographic surveys and PALACE float experiments. The low salinity water along the Russian coast originating from the Amur River feeds the subsurface low salinity core along the Subpolar Front corresponding to the southern boundary of the circulation as well as the subsurface salinity minimum (JES intermediate water) in the Tsushima Warm Water region. ARGOS buoys tracks suggest additional wind driven gyres such as a cyclonic gyre northwest of Hokkaido and an anticyclonic gyre in winter west of the large cyclonic gyre mentioned above. These gyres are generated by the wind stress curl in winter influenced greatly by geographical features of the northern coast of the JES. Numerical model studies reproduced successfully these aspects in the upper layer of the JES as well as many other interesting phenomena such as the branching of the Tsushima Current, the formation of intermediate waters, Karman vortex in the lee of the Tsushima Islands. Long-term deep current measurements suggest that strong cyclonic circulations (about 5 cm/s) follow the slope region of the deep three basins, whereas strong variability exceeding 30 cm/s episodically are dominant in the central flat area of the deep basins except several exceptions. This episodic strong variability is closely related with meso scale eddies found frequently in the sea surface temperature field by satellite. The JES has experienced a monotonic warming and structural changes as dramatically revealed in deepening of dissolved oxygen minimum by more than 1000 meters for the last several decades. An analysis of dissolved oxygen profiles shows that these changes resulted from a shift in its ventilation system: a slow down of a bottom water formation and an enhancement of intermediate water formation instead in recent years. It is remarkable to note that this shift is similar to a possible change in the global conveyor-belt system in the future associated with recent global warming (Manabe and Stouffer, 1998), thus strongly implying that the JES may serve as "a litmus paper" for the global warming.

31

Investigation on Wave Reduction Performances of Floating Hinge-Linked Breakwater

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.13-22

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This paper investigates the wave reduction performances of floating hinge-linked breakwater which are attached to very large floating structures (VLFS). The performance of breakwater is evaluated by analyzing the responses of VLFS under sea wave. Direct method is employed as a numerical tool to calculate responses of VLFS. Higher order boundary element method (HOBEM) is employed for the analysis of fluid flow. Structural stiffness and mass matrices and force vector are obtained by finite element method (FEM). One km-long VLFS is considered in numerical example. VLFS with flexible, stiff, two-hinged and rounded breakwater are analyzed to investigate the effect of stiffness and shape of breakwater.

30

Numerical Prediction of Effect of Seawater-Quality Enhancer Installed in Isahaya Bay

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.6-12

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Since the construction of Isahaya Dyke, it is said that the tidal current in Ariake Bay has changed. The change may bring on the environmental deterioration in Ariake Bay. Especially in Isahaya Bay and the offshore of Oura, the emergence of oxygen-deficient water has been prominent. In this study, firstly, we simulated the emergence of oxygen-deficient water by incorporating an ecosystem model into an ocean current model to elucidate the mechanism of the oxygen-deficient water both from physical and biological viewpoints. Next, we proposed a local engineering solution, a seawater-quality enhancer, and simulated numerically the diffusion of nutrient-rich water emitted by the apparatus and its effects on the ecosystems, particularly, on the oxygen-deficient water. The apparatus spreads horizontally the intermediate-density mixture of surface and deep waters. The numerical model considered 8 principal rivers because the nutrient-rich density currents of fresh water largely affect the currents and the ecosystems in Ariake Bay. It was shown that 16 % of the oxygen-deficient water in Isahaya Inlet was reduced by the apparatus, which emits 100-million-ton water per day, at 8 weeks after the start of operation. This may imply the possibility of improvement of water quality by this engineering countermeasure.

29

A Numerical Study on the Gravity Outflow of Oil from a Non-Pressurized Underwater Pipe

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.3 No.1 2006 pp.1-5

협약을 통해 무료로 제공되는 자료로, 원문이용 방식은 연계기관의 정책을 따르고 있습니다.

A two-dimensional numerical method for inviscid two-fluid flows having a significant entrainment into both directions is established, and the oil leakage from a non-pressurized underwater pipe is studied in the Boussinesq limit. The interface between two fluids is modeled as a vortex sheet, and the flow field with the subsequent interface evolution is solved by using the vortex-in-cell/front-tracking method, For a longer flow simulation with a realistic two fluids interaction, an efficient merging scheme is introduced. The flow in the pipe during the leak is basically lock-exchange and the speed of the external fluid's intrusion into the pipe is very close to the existing mathematical models even with a significant interfacial roll-up and entrainments.

28

On the Reverse of Streamwise Velocity Deficit in Formation of Boundary-layer Streaks

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.59-65

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The phenomenon of transformation of streamwise velocity deficit to excess in a near-wall wake behind a flat-plate roughness observed previously in numerous experiments is analyzed qualitatively by means of theories of optimal disturbances based on linearized Navier-Stokes and linearized boundary layer equations. It is shown that the reverse of the velocity deficit can accompany the excitation of a streak and that the formation of two maxima in the disturbance stream wise velocity profiles also observed in the experiments can be a side effect of the streak nonoptimality. An experimental approach aimed to provide quantitative data for comparison with a numerical solution of corresponding initial value problem is suggested.

27

The Response of Three-dimensional Boundary Layer over a Swept-wing to a Free Stream Axial Vortex

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.50-58

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A response of a swept wing boundary layer to a single free-stream stationary axial vortex of a limited spanwise extent is investigated. The response is dominated by streamwise velocity perturbations that grew quasi-exponentially downstream. It is shown that the formation of the boundary layer disturbance occurs for the most part close to the leading edge. The disturbance represents itself a wave packet consisted of the waves with characteristics specific for cross-flow instability. However, an admixture of growing disturbances which origin can be attributed to transient effects and distributed receptivity mechanism is also identified.

26

Risk-Based Approaches to the Safety in New Ship Design

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.43-49

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With the increase of the importance of the safety and environmental protection at sea, safety is a core design factor of maritime systems. Safety is defined as a perceived quality that determines to what extent the management, engineering and operation of a system is free of danger to life, property and the environment (Kuo 1998). There are many possible ways of dealing with the safety of ships. The rule-based approach is most commonly used in ship design. However there are many drawbacks to assure the safety objectives for a new ship and marine systems. This paper aims to investigate a systematic and rational approach to achieve the safety objectives of new ship in design process. Risk-based methodologies including the FSA (Formal Safety Assessment) and their applications to maritime systems are reviewed. Based on the principles of systems engineering and risk assessment, a process of safety assessment in ship design is established and proposed.

25

Propulsive Efficiency and Cavitation Behavior Affected by Propeller Rotational Direction for a Twin Skeg Tanker

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.37-42

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Twin skeg types for merchant ships are now under construction as they have dimensional limitation due to cruising route, the lack of required power with a single engine, station keeping ability, and so on. The ships of wide-beam and shallow-draught are investigated in recent days. It has been well known that the effect of propeller rotational direction on propulsive efficiency and cavitation behavior is significant in such ships, which is somewhat depending on the skeg hull form design. However, it is not easy to find the relevant papers related to the subject. In this research, using a wide beam tanker and her propellers, we performed calm water tests including wake survey, and analysis of propeller rotational direction effects. Through numerical cavity simulation, cavitation behavior was predicted and cavitation tests were also performed. We compared the cavitation test results with those of simulation and also surveyed the difference of the cavitation behavior between inward and outward propeller rotational direction. Propulsive efficiency and cavitation behavior showed much difference according to the rotational direction of the propeller. The research results will provide valuable information for the design of propeller and the choice of rotational direction.

24

Four Cranes Lifting Analysis with Application to Shipyard Practice

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.28-36

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This study focuses on an analytical approach to calculate four crane lifting forces for heavy ship hull blocks considering elongations of lifting slings. Four-crane-lifting is a redundant problem. For lifting analysis, the Euler angles are defined to represent the inclination of a hull block. In addition to the force and moment equilibrium equations, a compatibility condition is introduced to determine four unknown lifting forces. For verification of the method, ship hull blocks with field measurements data are analyzed and the results show that the information obtained by the current method could be useful for engineers to conduct similar lifting work at shipyards.

23

Numerical and Experimental Simulation on Bubble Plume Behaviour in Stratified Flow

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.21-27

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We developed a 3D Eulerian-Lagrangian two-phase CFD code, which can cope with distributions of bubble radius. The simulation results were compared moderately well with those of bubbling experiments conducted in a channel for circulating stratified water. It was elucidated how the difference of the simulation conditions effects the behaviour of bubbles, dye distribution, and the intrusion of dissolved $CO_2$ into the stratification. From the results, suggested is the possibility of the code to apply to the behaviour of $CO_2$ droplets released in the deep ocean for sequestering the greenhouse gas.

22

Caissons with Drains for Accelerating Consolidation of Marine Clay under Reclamation

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.16-20

협약을 통해 무료로 제공되는 자료로, 원문이용 방식은 연계기관의 정책을 따르고 있습니다.

Caissons tend to be used increasingly as the foundations of quay walls for retaining the reclaimed materials on soft clay layers because they can transfer vertical loads from the walls to the bearing strata and resist effectively the lateral plastic flow of soft clay as well as the lateral loads due to surcharge. This paper examines the feasibility of improving the conventional caisson design by including drains at the back face. Theoretical solutions for two-dimensional consolidation with a lateral drainage boundary are presented. A simple numerical example involving isotropic clay shows that the lateral influence distance of the caisson drains is roughly equal to the height of the caissons. This procedure should allow the marine clay in close proximity to the caissons to gain strength at a faster rate, hence reducing earth pressures acting on the caisson foundations. In addition, it may not be necessary to install vertical drains close to the quay wall and caissons.

21

Outline of the Ocean Nutrient Enhancer 'TAKUMI'

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.9-15

협약을 통해 무료로 제공되는 자료로, 원문이용 방식은 연계기관의 정책을 따르고 있습니다.

The five years project of increasing a primary production and making a new fishing ground by upwelling Deep Ocean Water (DOW) which is very rich in nutrient salt such as Nitrogen, Phosphorus, etc. was commenced in the year of 2000, sponsored by the Fisheries Agency of Japanese Government and Marino-Forum 21. In the open ocean, so far, there are no successful means to upwell DOW artificially and to make a fishing ground. Therefore, the focus of the project is a creation and proposition of the concept of Ocean Nutrient Enhancer (ONE) to contribute for increasing primary productions and fish productions, furthermore, conducting the experiment in actual sea to" confirm the effect of the ONE. The requisite technologies for the ONE such as making an artificial density current, a spar type floating structure, a hang off steel riser pipe, a set-up way of upending the riser pipe, etc. was discussed and integrated to create proto-type of ONE, whose main specifications are the DOW upwelling depth and capacity of 200 m and 100,000 $m^3/day$, the displacement of about 1,700tons, and Diesel engine of 100 KW. The ONE was set-up with the single point mooring system at the centre of rotational flow in Sagami Bay in the depth of about 1,000 m, and came into the operation in June 2003. In this paper, the outline of the prototype of ONE which was named "TAKUMI" is introduced.

20

Consideration on Scale Effect of Vortical Flow Induced by Artificial Upwelling Structure

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.2 No.1 2005 pp.1-8

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There are some sea areas where the upwelling current rises from sea bottom up to sea surface and brings the deep sea water including a plenty of nutritive salts accumulated on the sea bottom up to the sunny sea surface. Such sea areas are well known to be rich fishing grounds. Therefore, in order to make rich fishing ground artificially, various kinds of marine structures for generating the upwelling current are studied. At the same time, it is important to evaluate the influence on local ocean environment by such artificial ocean fertilization. The purpose of the present study is to investigate the scale effect on the vortical flow induced by artificial upwelling structure in order to evaluate an effectiveness of a full-scale upwelling generator from the model test results. The type of upwelling generator adopted in this study is basically a V-shaped structure placed against to the horizontal bottom flow. The V-shaped structure consists of two long flat plates which are connected with each other with a dihedral angle, and the top view is as a letter of V with its vertical angle directing downstream. By use of two geometrical similar models of V-shaped structure with different sizes, flow visualization tests and velocity measurements in their wake were carried out. The Reynolds number based on uniform flow velocity and model height is in range from 3900 to 67200. The vorticity distributions at two vertical planes in downstream of the models were obtained from the measured results. It is shown that non-dimensional vorticity of the center of vortices produced by V-shaped structure models increases slightly with model size. On the other hand, theoretical consideration was made on the scale effect of the above vortical flow. An approximate equation was introduced for estimation of Reynolds number effect on the vorticity. According to the equation, the non-dimensional vorticity of the vortices produced by the V-shaped structure is proportional to Reynolds number to the one tenth. It is found that this estimation agrees well with the results of measurements.

19

Parametric Study of Piled Raft Foundation on Soft Clay

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.1 No.2 2004 pp.147-152

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For the structure foundation, under the soft clay layer conditions, the design charts are first presented for the evaluation of both bearing capacity and total settlement in the basic raft foundation system. Load settlement relationship curves are used to evaluate the ultimate soil bearing capacity. The total settlement is evaluated by applying various traditional safety factors into the ultimate bearing capacity. Then, the parametric studies are carried out for the piled raft foundation system. In the numerical analyses, the elasto-plastic finite element model (Mohr-Coulomb model) is used to present the foundation response and the design charts, which enable the determination of the raft size and pile length and spacing.

18

A Slamming Experiment Using Air Pressure Cylinder

[Kisti 연계] The Korean Association of Ocean Science and Technology Societies Journal of Ocean Science and Technology Vol.1 No.2 2004 pp.140-146

협약을 통해 무료로 제공되는 자료로, 원문이용 방식은 연계기관의 정책을 따르고 있습니다.

This paper proposes an alternative experimental technique for slamming experiments. The main idea of the proposed experiment is to replace the free-fall of the specimen, by accelerating the specimen using an air pressure cylinder at a very short distance from the water surface. The travel distance of the specimen was less than 10cm. The experiments have high repeatability. The maximum pressure peak was almost the same when the results from the free-fall experiment were compared with those from the air pressure cylinder experiment. The proposed experimental technique on slamming, by using an air pressure cylinder, was shown to be quite promising.

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