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排序方式: 共有881条查询结果,搜索用时 15 毫秒
1.
A 4.96-m-long sediment core from the Hanon paleo-maar in Jeju Island, Korea was studied to investigate the paleoclimatic change and East Asian monsoon variations during the latest Pleistocene to early Holocene (23,000-9000 cal yr BP). High-resolution TOC content, magnetic susceptibility, and major element composition data indicate that Jeju Island experienced the coldest climate around 18,000 cal yr BP, which corresponds to the last glacial maximum (LGM). Further, these multi-proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14,000 cal yr BP, which represents the commencement of the last major deglaciation. After the last major deglaciation, the TOC content decreased from 13,300 to 12,000 cal yr BP and from 11,500 to 9800 cal yr BP, thereby reflecting the weakening of the summer monsoon. The LGM in Jeju Island occurred later in comparison with the Chinese Loess Plateau. Such a disparity in climatic change events between central China and Jeju Island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central China and by the buffering effect of the Pacific Ocean. 相似文献
2.
Numerical and experimental study on hydrodynamic interaction of side-by-side moored multiple vessels 总被引:2,自引:0,他引:2
This paper aims to investigate the basic interaction characteristics of side-by-side moored vessels both numerically and experimentally. A higher-order boundary element method (HOBEM) combined with generalized mode approach is applied to analysis of motion and drift force of side-by-side moored multiple vessels (LNG FPSO, LNGC and shuttle tankers). Model tests were carried out for the same floating bodies investigated in the numerical study in regular and irregular waves. Global and local motion responses and drift forces of three vessels are compared with those of calculations. Discussions is highlighted on applicability of numerical method to prediction of sophisticated multi-body interaction problem of which motion behavior is very important to analysis of mooring dynamics of deep sea floating bodies. 相似文献
3.
A coupled wave–tide–surge model has been developed in this study in order to investigate the effect of the interactions among tides, storm surges, and wind waves. The coupled model is based on the synchronous dynamic coupling of a third-generation wave model, WAM cycle 4, and the two-dimensional tide–surge model. The surface stress, which is generated by interactions between wind and wave, is calculated by using the WAM model directly based on an analytical approximation of the results using the quasi-linear theory of wave generation. The changes in bottom friction are created by the interactions between waves and currents and calculated by using simplified bottom boundary layer model. In consequence, the combined wave–current-induced bottom velocity and effective bottom drag coefficient were increased in the shallow waters during the strong storm conditions. 相似文献
4.
To use two small fish Rivulus marmoratus (Cyprinodontiformes, Rivulidae) and the Japanese medaka Oryzias latipes (Belloniformes) as testing models in molecular ecotoxicology, we have cloned the cytochrome P450 1A (CYP1A) gene after screening of both genomic DNA libraries, and sequenced 11,863 and 7,243 bp including all the exons and introns with promoter regions, respectively. The Rivulus and the medaka CYP1A gene consisted of seven exons (including non-coding exons) with high homology to mammals. In the promoter region, Rivulus CYP1A gene has seven xenobiotic response elements (XREs) and two metal response elements (MREs), while the Japanese medaka CYP1A gene has six XREs and four MREs. Interestingly, medaka CYP1A gene has a number of MREs at the promoter, which may affect its response on metal exposure. We describe here the gene structure of both fish CYP1A genes. 相似文献
5.
Ho Il Yoon Myung Woo Han Byong-Kwon Park Jae-Kyung Oh Soon-Keun Chang 《Marine Geology》1997,140(3-4):265-282
High-resolution (3.5 kHz and multi-channel) seismic profiles and piston cores were collected from Maxwell Bay and its tributary embayment, Marian Cove, in the South Shetland Islands, Antarctica, during the Korea Antarctic Research Program (1992/93 and 1995/96) to elucidate the glaciomarine sedimentation processes and recent glacial history of the area. Seismic data from Maxwell Bay reveal a rugged bay margin and flattened basin floor covered with well-stratified hemipelagic muds. On the base-of-slope, acoustically transparent debris flows occur, indicating downslope resedimentation of glaciomarine sediments. Despite the subpolar and ice-proximal settings of Marian Cove, the seafloor is highly rugged with a thin sediment drape, suggesting that much of the area has been recently eroded by glaciers. Sediment cores from the cove penetrated three distinct fining-upward lithofacies: (1) basal till in the lower part of the core, accumulated just seaward of the grounding line of the tidewater glacier; (2) interlaminated sand and mud in the middle part, deposited in ice-proximal zone by a combination of episodic subglacial meltwater inflow and iceberg dumping; and (3) pebbly mud in the upper part, deposited in ice-distal zone by both surface meltwater plume and ice-rafting from the glacier front. A reconstruction of the glacial history of these areas since the late glacial maximum shows an ice sheet filling Maxwell Bay in late Wisconsin time and grounding of the tidewater glacier in Marian Cove until about 1300 yr BP. 相似文献
6.
In order to clarify the formation and circulation of the Japan/East Sea Intermediate Water (JESIW) and the Upper portion of
the Japan Sea Proper Water (UJSPW), numerical experiments have been carried out using a 3-D ocean circulation model. The UJSPW
is formed in the region southeast off Vladivostok between 41°N and 42°N west of 136°E. Taking the coastal orography near Vladivostok
into account, the formation of the UJSPW results from the deep water convection in winter which is generated by the orchestration
of fresh water supplied from the Amur River and saline water from the Tsushima Warm Current under very cold conditions. The
UJSPW formed is advected by the current at depth near the bottom of the convection and penetrates into the layer below the
JESIW. The origin of the JESIW is the low salinity coastal water along the Russian coast originated by the fresh water from
the Amur River. The coastal low salinity water is advected by the current system in the northwestern Japan Sea and penetrates
into the subsurface below the Tsushima Warm Current region forming a subsurface salinity minimum layer.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
A new three-dimensional, non-hydrostatic free surface flow model is presented. For simulating water wave motions over uneven bottoms, the model employs an explicit project method on a Cartesian the staggered gird system to solve the complete three-dimensional Navier–Stokes equations. A bi-conjugated gradient method with a pre-conditioning procedure is used to solve the resulting matrix system. The model is capable of resolving non-hydrostatic pressure by incorporating the integral method of the top-layer pressure treatment, and predicting wave propagation and interaction over irregular bottom by including a partial bottom-cell treatment. Four examples of surface wave propagation are used to demonstrate the capability of the model. Using a small of vertical layers (e.g. 2–3 layers), it is shown that the model could effectively and accurately resolve wave shoaling, non-linearity, dispersion, fission, refraction, and diffraction phenomena. 相似文献
8.
Evaluation of bending moments and shear forces at unit connections of very large floating structures using hydroelastic and rigid body analyses 总被引:1,自引:0,他引:1
Byoung Wan Kim Sa Young Hong Jo Hyun Kyoung Seok Kyu Cho 《Ocean Engineering》2007,34(11-12):1668-1679
This paper investigates the characteristics of bending moments, shear forces and stresses at unit connections of very large floating structures (VLFS) under wave loads. The responses of VLFS are calculated by solving multi-body motion equation considering hydroelasticity and connection stiffness. Hydroelastic responses are calculated by the direct method. Higher-order boundary element method (HOBEM) is used for fluid analysis and finite element method (FEM) is introduced for structural analysis. The equation of motion is modified to describe the unit connections by employing spring elements. Bending moments and shear forces at the connections are obtained from the dynamic equilibrium condition for pressures and inertia forces. Two types of VLFS units such as tandem arranged units and side-by-side arranged units are considered in the numerical examples. The influences of connection stiffness, wave frequency and heading angle on responses of VLFS are investigated through the numerical examples. Rigid body analysis along with hydroelastic analysis is also carried out in the numerical analysis and comparison of those two approaches is discussed. 相似文献
9.
Free spanning analysis of offshore pipelines 总被引:1,自引:0,他引:1
H. S. Choi 《Ocean Engineering》2001,28(10)
A rigorous procedure was established on the free span analysis of offshore pipelines. The closed form solutions of the beam–column equation, considering tension and compressive force, were derived for the various possible boundary conditions. The solutions can be used to find the natural frequencies of the free spans using the energy balance concept. The results can be applied to improve the current design codes. The improved procedure will yield more realistic calculations of the allowable free span lengths of offshore pipelines. Some calculations are included to present the sensitivity of the axial forces on the allowable free spanning lengths. 相似文献
10.
Major variations in type and rate of tectonic movement in the southwestern margin of the Ulleung Basin coincide in time with
changes in stratal patterns at succession boundaries, suggesting that the effect of tectonism was dominant for the development
of sequence architecture. During the back-arc opening (16–12 Ma), the rise of relative sea level and the high rate of sediment
supply gave rise to sequences with sigmoid progradational patterns. During the back-arc closing (12–6.5 Ma), fall- and rise-dominated
relative sea-level fluctuations resulted in sequences with varying stratal patterns depending upon changes in deposition rate.
The rise-dominated relative sea level has been prevalent during the later stage (6.5 Ma–Present) with low sedimentation rate.
Received: 16 January 1996 / Revision received: 7 February 1997 相似文献