Showing papers by "Korean Ocean Research and Development Institute published in 2002"

Low-Frequency Current Observations in the Korea/Tsushima Strait

Abstract: High resolution, continuous current measurements made in the Korea/Tsushima Strait between May 1999 and March 2000 are used to examine current variations having time periods longer than 2 days. Twelve bottom-mounted acoustic Doppler current profilers provide velocity profiles along two sections: one section at the strait entrance southwest of Tsushima Island and the second section at the strait exit northeast of Tsushima Island. Additional measurements are provided by single moorings located between Korea and Tsushima Island and just north of Cheju Island in Cheju Strait. The two sections contain markedly different mean flow regimes. A high velocity current core exists at the southwestern section along the western slope of the strait for the entire recording period. The flow directly downstream of Tsushima Island contains large variability, and the flow is disrupted to such an extent by the island that a countercurrent commonly exists in the lee of the island. The northeastern section is marked b...

Two‐layer tidal modeling of the Yellow and East China Seas with application to seasonal variability of the M2 tide

Abstract: [1] The baroclinic response of tide and tidal currents in the Yellow and East China Seas is investigated using a two-layer numerical model. Seasonal variability in the M2 tide, especially the smaller summer amplitudes prevailing along the Korea/Tsushima Strait [Kang et al., 1995], is investigated by a series of numerical experiments with varying degrees of stratification specific to winter and summer. Model results show that the summer amplitudes of the M2 tide around the southwestern tip of the Korean peninsula and Korea/Tsusima Strait decrease, with a peak decrease of about 14 cm off the southwestern tip of the Korean peninsula, while the summer amplitudes in other coastal regions tend to increase. This seasonal variability generally coincides with the observations. These models results indicate that seasonal stratification has several noticeable effects on the tides, including varying degrees of current shear, varying frictional dissipation, and varying barotropic energy flux. In particular, it drives complicated seasonal variability in the M2 tide, with a peak amplitude modulation of nearly 5% off the southwestern tip of the Korean peninsula. The seasonal variation of barotropic M2 energy flux through the eastern entrance of the Yellow Sea is thought to induce the corresponding variability in the M2 amplitude in the Korea/Tsusima Strait, with smaller amplitudes found in the summer.

Applying digital manufacturing technology to ship production and the maritime environment

Abstract: This paper is mainly concerned with the digital manufacturing technologies in the context of the shipbuilding industry. New concepts such as digital shipbuilding, virtual shipyard, and simulation‐based design (SBD) will be explored. After reviewing the digital shipbuilding, a case study will be presented using the virtual assembly simulation system for shipbuilding (VASSS), a simulation based tool, to evaluate block erection sequence taking account of shipyard facilities, operational efficiency and equipment replacement time.

A three-dimensional mixed finite-difference Galerkin function model for the oceanic circulation in the Yellow Sea and the East China Sea in the presence of M2 tide

Abstract: This paper, as a sequel to Lee et al. (Continental Shelf Research 20 (2000) 863) describes the simulation of the oceanic current in the Yellow Sea (YS) and the East China Sea (ECS) with forcings of M 2 tide as well as oceanic flows prescribed at the open boundary. The model is three dimensional and barotropic, and uses a finite-difference approximation in the horizontal plane and function expansions in the vertical direction. The bottom stress is represented by the conventional quadratic friction law and the vertical eddy viscosity takes a flow-related form. A radiation condition is employed along the open boundaries to handle the M 2 tide and oceanic flows simultaneously. From a series of numerical calculations with M 2 tide forcing only, the bottom friction coefficient, 0.0035, has been found as an optimum value with which RMS errors (amplitude, phase lag) are calculated as 16.4 cm, 19.5°. Calculations have also been carried out to investigate the effects of using an empirical function expansion for the current profiles below the main stream of Kuroshio. Despite the bias of the tidal propagation and the associated flux, the tidal chart has been calculated with tolerable accuracy. The model calculation confirms the results of Exp. 4 of Lee et al. (Continental Shelf Research 20 (2000) 863), in that the tide-enhanced bottom friction effectively blocks the penetration of northwestward flow into the YS known as the Yellow Sea Warm Current (YSWC). The presence of small gyres, however, complicates the circulation near the southern YS and west of Cheju Island and tidal residual currents omnipresent at the shallow sea region off the Chinese coast between 32°N and 34.5°N also contribute to the suppression of the formation of the YSWC. The distribution of the sea surface elevation averaged over the M 2 tidal period is qualitatively in good agreement with that of Yanagi et al. (Continental Shelf Research 17 (1997) 655), calculated from the TOPEX altimetric data. Calculation with an inflow of 25.1 Sv through open boundaries on both sides of Taiwan shows that 1.15 Sv goes through Korea/Tsushima Strait, 0.36 Sv through the north of Tokara Strait (between Kyushu and Yakushima Island), 20.95 Sv through Tokara Strait and 2.77 Sv through open boundaries along the Ryukyu Islands. Calculations with fortnightly variation in M 2 open boundary forcings show that the oceanic circulation as well as tidal residuals vary significantly in the southern Yellow Sea; penetration of oceanic flows into the Yellow Sea occurs deeper at the neap tide than at the spring tide. The seasonal variation in the volume transport of the oceanic inflows/outflows without baroclinic effects has little effect on the exchange between the YS and the ECS.

Distribution and origin of shallow gas in deep-sea sediments of the Ulleung Basin, East Sea (Sea of Japan)

Abstract: A synthesis of high-resolution (Chirp, 2–7 kHz) subbottom profiles in the Ulleung Basin reveals patchy distribution of shallow (<90 m subbottom depth) gassy sediments in the eastern basin plain below 1,800-m water depth. The shallow gases in the sediments are associated with acoustic turbidities, columnar acoustic blankings, enhanced reflectors, dome structures, and pockmarks. Analyses of gas samples collected from a piston core in an earlier study suggest that the shallow gases are thermogenic in origin. Also, published data showing high amounts of organic matter in thick sections of marine shale (middle Miocene to lower Pliocene sequence) and high heat flow in the basin plain sediments are consistent with the formation of deep, thermogenic gas. In multi-channel deep seismic profiles, numerous acoustic chimneys and faults reflect that the deep, thermogenic gas would have migrated upwards from the deeper subsurface to the near-seafloor. The upward-migrating gases may have accumulated in porous debrites and turbidites (upper Pliocene sequence) overlain by impermeable hemipelagites (Quaternary sequence), resulting in the patchy distribution of shallow gases on the eastern basin plain.

Trimaran type wing effect ship with small waterplane area

Abstract: A trimaran type WIG (Wing-In-Ground) effect ship with a minimum waterplane area is disclosed. This WIG ship comprises a main hull and two half-submerged sub-hulls each having a minimum waterplane area capable of minimizing the wave resistance and appendage resistance of the ship, thus reducing speed loss on rough water. The WIG ship also has main and sub-wings and an effective propelling mechanism, designed such that they produce a strong lift force allowing a take-off of the ship sailing on water even at a low speed. The WIG ship is thus excellent in its seakeeping and maneuverability on the rough water. In the WIG ship, the main hull is intermediately positioned between the main wings and comprises a slender and half-submerged body, and bears 60% of the total displacement of the ship. The sub-hulls are respectively provided under the outer ends of the main wings, and each bear 20% of the total displacement, and act as an end plate. This WIG ship also has two sailing propellers each supplying 25% of maximum required power of the ship, and a flight propeller supplying 50% of the maximum required power.

Bioactive Metabolites from Sponges -New Triterpenoid Saponins from the Sponge Erylus nobilis

Abstract: Erylosides G--J (1--4), four new triterpenoid saponins, were isolated from the sponge Erylus nobilis collected from Jaeju Island, Korea. On the basis of the results of combined chemical and spectral analyses, the structures of the aglycones were determined to be lanostane-based, modified penasterols. The oligosaccharide portions were composed of one unit each of L-arabinose, D-galactose, and 2-N-acetyl-D-glucosamine (1 and 3) or two units of L-arabinose and one unit of 2-N-acetyl-D-glucosamine (2 and 4). These compounds exhibited moderate cytotoxicty against a human leukemia cell line.

Geochemical-mineralogical-characteristics of the pre-Holocene sediments in Haenam Bay, west coast of Korea

Abstract: The geochemical and mineralogical characteristics of pre-Holocene core sediments from Haenam Bay, southwest coast of Korea, were examined for post-depositional diagenetic changes and used to assess the provenance of fine-grained sediments in the region. The geochemical and mineralogical compositions of the sediments vary very little with core depth (Holocene to pre-Holocene age), except for the upper part of the pre-Holocene sedimentary layer. In this case, smectite and chlorite are depleted, presumably due to intensive subaerial weathering and low pH conditions. Highly mobile elements (Ca, Mg, Na and K) were likely removed with the breakdown of labile minerals, such as carbonate minerals, feldspar, and clay minerals, during subaerial exposure of this layer, resulting in low weathering indices. In particular, the low smectite content (<5%) and low V/Al ratio (<13) suggest that the Holocene and pre-Holocene sediments along the southwestern coast of Korea did not originate from mainland China but rather mostly from the Korean Peninsula. This aspect has been a subject of debate since the mid-1970s.

Device for simultaneously collecting filtered water and filter paper

Abstract: The present invention relates to a filter paper (4) filtering a collected sample for water analysis, and a device wherein the filtered water filtered through the filter paper is also collected so that filtered water can be contained in a sample container (15) itself and wherein the collecting rate of the sample can be controlled The collecting device of the present invention comprises more than one filter funnel part (1), an upper plate (30) on which said funnel part placed, a mounting means (20) comprising a supporting rod (40) wherein one side of the supporting rod is combined with the edge of the said upper plate (30) and a waste box (50) fixing said supporting rod (40), several base container parts (60) wherein the said sample container is inserted and a outlet port is formed, and a vacuum pump connected to the said vacuum connecting port (56) by a pump tube (89) Therefore, in accordance with the collecting device of the present invention, the step transferring filtered water into the sample container (15) can be omitted, and the collecting time can be reduced by controlling the collecting rate of the sample

Pressure-balanced underwater acoustic transducer

Abstract: Provided is a pressure-balanced underwater acoustic transducer. The transducer includes an oscillator unit having an oscillator oscillating by an electrical signal supplied to electrodes, provided on its surface, a sound transmission material for transmitting sound from the oscillator, provided at its periphery, and a transducer housing provided at the exterior of the sound transmission material, a sound reflector positioned over the oscillator unit, for reflecting sound propagated from the oscillator, a water entry layer formed at a space between the oscillator unit and the sound reflector to allow water to enter and exit to the rear window of the oscillator, thereby leading to a balanced state of pressures applied to the front and rear windows of the oscillator, and a phase combiner for combining sound reflected from the sound reflector and straight traveling sound generated from the front window of the oscillator into one single phase. Therefore, the effect of underwater pressure on an oscillator is minimized, thereby manufacturing a highly reliable, cost-effective underwater acoustic transducer for deep sea. Also, even when the transducer is used for shallow sea, little deformation occurs over usage time.

Seasonal Variation of Global Volume Transport Calculated from an Ocean General Circulation Model

Abstract: Seasonal variation in global transport calculated from an ocean general circulation model (OGCM) has been assessed through the comparison with observational estimates. The OGCM based on the GFDL MOM1.1 has honzontal grid interval of 10 and 21 verticle levels, and was integrated for 31 years forced by climatological wind stress, freshwater flux, and heat flux with restoring. General features of the world ocean circulation are well reproduced, which include the western boundary currents such as the Kuroshio and the Agulhas Current, the Equatorial Current system, the Antarctic Circumpolar Current, and the Weddell Sea gyres. Also well resolved is the remarkable seasonal variation in the depth-integrated flows in the northern Indian Ocean due to the monsoonal wind. Monthly variation is found to be dominant in the transport of the Antarctic Circumpolar Current through the Drake Passage in accordance with observational estimates. It has been shown that the mid-latitude depth-integrated flows obey the Sverdrup relation, except for some regions such as continental shelf regions where the interaction between stratification and bottom topography is critical.

Simulation of the Mixed Layer in the Western Equatorial Pacific Warm Pool

Abstract: The upper ocean in the western equatorial Pacific warm pool during TOGA-COARE IMET IOP was simulated using a one-dimensional turbulence closure ocean mixed-layer model, which considered recent observations, such as the remarkable enhancement of turbulent kinetic energy near the ocean surface. The shoaling/deepening of the mixed layer and warming/cooling subsurface water in the model were in reasonable agreement with the observations. There was a significant improvement in simulating the cooling trend of the sea surface temperature under a westerly wind burst with heavy rainfall over previous simulations using bulk mixed-layer models. By contrast the simulated sea surface salinity (SSS) departed significantly from the observed SSS, especially during a westerly burst and the subsequent restratification period, which might be due to 3-D control processes, such as downwelling/upwelling or advection.