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991.
Seok Lee Heung-Jae Lie Kyu-Min Song Cheol-Ho Cho Eun-Pyo Lim 《Journal of Oceanography》2008,64(5):763-776
This study examined tidal modification and change in tidal currents caused by the construction of the Saemangeum dike, based
on field observations and a numerical model. The Saemangeum dike was completed in April 2006, enclosing an estuarine area
along the mid-western coast of South Korea. After closure of the dike, the tidal range outside the dike decreased slightly
but significantly, while the inside tidal range decreased drastically. The numerical model results show that the dike construction
has influenced tidal energy propagation and the tidal system in the Yellow Sea. The tidal current speed near the dike decreased
abruptly following closure of the dike, except in front of the sluice gates. Since completion of the dike, outflow water discharged
from the sluice gates has longer residence times due to the weakened tidal current; the change in the tidal current field
has also caused greater northward expansion of outflow water. The sluice gates release fresher water, which spreads over the
sea surface mainly by inertial momentum near the gate; this water is then gradually mixed with sea water farther from the
gate. The less saline, possibly more contaminated outflow impacts the marine environment near the Saemangeum dike. Controlling
the discharge and gate-opening timing can partially mitigate these impacts on the marine environment. 相似文献
992.
Abstract This paper describes the results of laboratory tests carried out on model pile shafts in a variety of reconstituted calcareous sands and on silica sand. The factors influencing both the skin friction under static loading and the degradation of skin friction under cyclic loading have been investigated. The grading and crushability of the particles appears to have a significant influence on both, with less favourable performance being found for uniformly graded crushable particles. Relative density and overconsolidation ratio also have some influence. Under cyclic loading, the amplitude of cyclic displacement and, more specifically, the cyclic slip displacement, influence the extent of cyclic degradation of skin friction. 相似文献
993.
Dongseop Lee Sangwoo Park Timothy D. Stark Younguk Kim 《Marine Georesources & Geotechnology》2013,31(4):348-359
Use of Terzaghi's one-dimensional consolidation theory is not suitable for consolidation of highly deformable soft clays such as dredged soils. To model this condition, it is necessary to consider non-linear finite strain consolidation behavior, i.e., changes in compressibility and permeability with increasing stress. A one-dimensional non-linear finite strain numerical model, Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF), has been used to predict the stress-dependent settlement of fine-grained dredged materials. In this paper, two case studies of using PSDDF are discussed to illustrate the applicability and accuracy of PSDDF. The first case study involves PSDDF simulations of laboratory-phased placement of a marine clay dredged from Busan, Korea. PSDDF results are in good agreement with the corresponding results of the laboratory large strain consolidation tests. The other involves estimating the service life of the Craney Island Dredged Material Management Area near Norfolk, Virginia, in the United States. The excellent agreement between measured and calculated values shows that PSDDF is a reliable tool for predicting settlement of dredged material. 相似文献
994.
Floating platform system has been extensively used in ocean exploitation, particularly for a tension-leg platform (TLP) system in deep water. Most of the TLPs are multi-mooring systems, where multi-joints are connected to the tension-legs so that the platform is not allowed to twist freely and may subject to enormous force induced by large incident waves in the weak-direction of the structure. This study aims to exploit a single moored offshore platform system that may attract less force and can be operated with less effort. In our analysis, in addition to mechanical properties of the tether, two important properties are also taken into consideration for the single mooring tether with expanded cross sectional dimension and utilization of stronger material, namely, the sag-extensibility and the flexural rigidity. Finally, the dynamic structural behavior produced by the mechanical effects on the new system is investigated and compared with that of traditional design while the wave-structure interactions of large body are also accounted for. Our study finds that the neglect of sag-extensibility or the flexural rigidity of large, strong mooring cable may result in a conservative but not necessarily safe design. 相似文献
995.
Sok Kuh Kang Kyung Tae Jung Ki-Dai Yum Kwang-Soo Lee Jin-Soon Park Eun Jin Kim 《Ocean Science Journal》2012,47(4):453-463
Uldolmok waterway, located between an island off the southwestern tip of Korean peninsula and mainland, is famous for its strong tidal current that has a maximum current of about 6.0m/s. A series of field observations along with numerical modeling have been carried out in order to understand the tidal dynamics in terms of the force balance along the whole waterway and the energy balance in the narrowest part of the waterway. First, analysis of the ADCP current and the tide level variation data reveals that the tidal dynamics along the total waterway (channel) is balanced dominantly between the pressure gradient and linear bottom frictional forces, with the phase lag of sea level difference for the semi-diurnal constituents leading the current phase about by 10°. Secondly, the result of the numerical modeling reveals that the tidal energy flux vector flows toward the narrowest section, indicating that there should be related nonlinear processes. Through the numerical model experiment with multi-components, the convergence of (M2 + S2) tidal energy flux of 6.68 × 107 Joule/s in the narrow area of the Uldolmok waterway is explained mainly by the energy consumption of 73% through the nonlinear generation of shallow water components and by the bottom frictional energy dissipation of 27%. This reveals that the remarkably strong nonlinear process dominates in the narrowest section of the Uldolmok waterway, compared with other areas, such as Yellow and East China Seas where the total M2 energy flux through the open boundary is balanced in terms of the bottom dissipation (Kang et al. 2003; Choi 1980). 相似文献
996.
Natural marine gas hydrate was discovered in Korean territorial waters during a 2007 KIGAM cruise to the central/southwestern
Ulleung Basin, East Sea. The first data on the geochemical characterization of hydrate-bound water and gas are presented here
for cold seep site 07GHP-10 in the central basin sector, together with analogous data for four sites (07GHP-01, 07GHP-02,
07GHP-03, and 07GHP-14) where no hydrates were detected in other cores from the central/southwestern sectors. Hydrate-bound
water displayed very low concentrations of major ions (Cl−, SO42−, Na+, Mg2+, K+, and Ca2+), and more positive δD (15.5‰) and δ18O (2.3‰) signatures compared to seawater. Cl– freshening and more positive isotopic values were also observed in the pore water at gas hydrate site 07GHP-10. The inferred
sulfate–methane interface (SMI) was very shallow (<5 mbsf) at least at four sites, suggesting the widespread occurrence of
anaerobic oxidation of methane (AOM) at shallow sediment depths, and possibly high methane flux. Around the SMI, pore water
alkalinity was very high (>40 mM), but the carbon isotopic ratios of dissolved inorganic carbon (δ13CDIC) did not show minimum values typical of AOM. Moreover, macroscopic authigenic carbonates were not observed at any of the
core sites. This can plausibly be explained by carbon with high δ13C values diffusing upward from below the SMI, increasing alkalinity via deep methanogenesis and eventually escaping as alkalinity
into the water column, with minor precipitation as solid phase. This contrasts, but is not inconsistent with recent reports
of methane-fuelled carbonate formation at other sites in the southwestern basin sector. Methane was the main hydrocarbon component
(>99.85%) of headspace, void, and hydrate-bound gases, C1/C2+ ratios were at least 1,000, and δ13CCH4 and δDCH4 values were in the typical range of methane generated by microbial reduction of CO2. This is supported by the δ13CC2H6 signatures of void and hydrate-bound gases, and helps clarify some contradictory interpretations existing for the Ulleung
Basin as a whole. In combination, these findings suggest that deep biogenic gas and pore waters migrate upward through pathways
such as hydrofractures, and measurably influence the shallow carbon cycle. As a result, cation-adjusted alkalinity/removed
sulfate diagrams cannot always serve to estimate the degree of alkalinity produced by sulfate reduction and AOM in high methane
flux areas. 相似文献
997.
Seok Lee Heung-Jae Lie Cheol-Ho Cho Sok Kuh Kang William J. Teague Kyung-Il Chang Kyu-Min Song Kyung-Hee Oh 《Ocean Science Journal》2011,46(2):73-84
The vertical structure of the M2 tidal current in the Yellow Sea is analyzed from data acquired using an acoustic Doppler current profiler. The observed vertical
profiles of the M2 tidal current are decomposed into two rotating components of counter-clockwise and clockwise, and restructured using a simple
one-point model with a constant vertical eddy viscosity. The analyzed results show that the internal fictional effect dominates
the vertical structure of the tidal current in the bottom boundary layer. In the Yellow Sea, the effect of the bottom friction
reduces the current speed by about 20–40% and induces the bottom phase advance by about 15–50 minutes. In the shallower coastal
regions, the effects of bottom topography are more prominent on the vertical structure of tidal currents. The vertical profile
of the tidal current in summer, when the water column is strongly stratified, is disturbed near the pycnocline layer. The
stratification significantly influences the vertical shear and distinct seasonal variation of the tidal current. 相似文献
998.
In experiments aimed at measuring the spectral volume scattering function of light, we obtain an additional confirmation of
the existence of two-dimensional inhomogeneities of water on scales of 10-7–10-3 m. In the case of mixing of pure water with small amounts of filtered water with different temperature or salinity, we observe
an 1.8–4.5-fold intensification of the scattering of light in the entire range of angles. It is shown that this effect can
be explained neither by turbulence nor by the formation of dissipative structures. We estimate the sizes of inhomogeneities
affecting the spectral volume scattering function of light. 相似文献
999.
Bo Y. Yi Gwang H. Lee Senay Horozal Dong G. Yoo Byong J. Ryu Nyeon K. Kang Sung R. Lee Han J. Kim 《Marine and Petroleum Geology》2011,28(10):1953-1966
The presence of gas hydrate in the Ulleung Basin, East Sea (Japan Sea), inferred by various seismic indicators, including the widespread bottom-simulating reflector (BSR), has been confirmed by coring and drilling. We applied the standard AVO technique to the BSRs in turbidite/hemipelagic sediments crosscutting the dipping beds and those in debris-flow deposits to qualitatively assess the gas hydrate and gas concentrations. These BSRs are not likely to be affected by thin-bed tuning which can significantly alter the AVO response of the BSR. The BSRs crosscutting the dipping beds in turbidite/hemipelagic sediments are of low-seismic amplitude and characterized by a small positive gradient, indicating a decrease in Poisson’s ratio in the gas-hydrate stability zone (GHSZ), which, in turn, suggests the presence of gas hydrate. The BSRs in debris-flow deposits are characterized by a negative gradient, indicating decreased Poisson’s ratio below the GHSZ, which is likely due to a few percent or greater gas saturations. The increase in the steepness of the AVO gradient and the magnitude of the intercept of the BSRs in debris-flow deposits with increasing seismic amplitude of the BSRs is probably due to an increase in gas saturations, as predicted by AVO model studies based on rock physics. The reflection strength of the BSRs in debris-flow deposits, therefore, can be a qualitative measure of gas saturations below the GHSZ. 相似文献
1000.
Patrick Martin Richard S. LampittMary Jane Perry Richard SandersCraig Lee Eric D'Asaro 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(4):338-349
Spring diatom blooms are important for sequestering atmospheric CO2 below the permanent thermocline in the form of particulate organic carbon (POC). We measured downward POC flux during a sub-polar North Atlantic spring bloom at 100 m using thorium-234 (234Th) disequilibria, and below 100 m using neutrally buoyant drifting sediment traps. The cruise followed a Lagrangian float, and a pronounced diatom bloom occurred in a 600 km2 area around the float. Particle flux was low during the first three weeks of the bloom, between 10 and 30 mg POC m−2 d−1. Then, nearly 20 days after the bloom had started, export as diagnosed from 234Th rose to 360-620 mg POC m−2 d−1, co-incident with silicate depletion in the surface mixed layer. Sediment traps at 600 and 750 m depth collected 160 and 150 mg POC m−2 d−1, with a settled volume of particles of 1000-1500 mL m−2 d−1. This implies that 25-43% of the 100 m POC export sank below 750 m. The sinking particles were ungrazed diatom aggregates that contained transparent exopolymer particles (TEP). We conclude that diatom blooms can lead to substantial particle export that is transferred efficiently through the mesopelagic. We also present an improved method of calibrating the Alcian Blue solution against Gum Xanthan for TEP measurements. 相似文献