The time evolution of a two-dimensional line thermal-a turbulent flow produced by an initial element with signifi-cant buoyancy released in a large water body, is numerically studied with the two-equation k - e model for turbulence closure. The numerical results show that the thermal is characterized by a vortex pair flow and a kidney shaped concentra-tion structure with double peak maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless time around 10. There are two regions in the flow field of a line thermal: a mixing region where the concentration of tracer fluid is high and the flow is turbulent and rotational with a pair of vortex eyes, and an ambient region where the concentration is zero and the flow is potential and well-described by a model of doublet with strength very close to those given by early experimental and analytical studies. The added virtual mass coeffi-cient of the thermal motion is found to be approximat 相似文献
Mud volcanoes, mud cones, and mud ridges have been identified on the inner portion of the crestal area, and possibly on the inner escarpment, of the Mediterranean Ridge accretionary complex. Four areas containing one or more mud diapirs have been investigated through bathymetric profiling, single channel seismic reflection profiling, heat flow measurements, and coring. A sequence of events is identified in the evolution of the mud diapirs: initially the expulsion on the seafloor of gasrich mud produces a seafloor depression outlined in the seismic record by downward dip of the host sediment reflectors towards the mud conduit; subsequent eruptions of fluid mud may create a flat topped mud volcano with step-like profile; finally, the intrusion of viscous mud produces a mud cone.The origin of the diapirs is deep within the Mediterranean Ridge. Although a minimum depth of about 400 m below the seafloor has been computed from the hydrostatic balance between the diapiric sediments and the host sediments, a maximum depth, suggested by geometric considerations, ranges between 5.3 and 7 km. The presence of thermogenic gas in the diapiric sediments suggests a better constrained origin depth of at least 2.2 km.The heat flow measured within the Olimpi mud diapir field and along a transect orthogonal to the diapiric field is low, ranging between 16 ± 5 and 41 ± 6 mW m–2. Due to the presence of gas, the thermal conductivity of the diapiric sediments is lower than that of the host hemipelagic oozes (0.6–0.9 and 1.0–1.15 W m–1 K–1 respectively).We consider the distribution of mud diapirs to be controlled by the presence of tectonic features such as reverse faults or thrusts (inner escarpment) that develop where the thickness of the Late Miocene evaporites appears to be minimum. An upward migration through time of the position of the décollement within the stratigraphic column from the Upper Oligocene (diapiric sediments) to the Upper Miocene (present position) is identified. 相似文献
The Karman Vortex Street generated by a circular cylinder is investigated by the numerical solution of the compressible Navier–Stokes equations in the incompressible Mach number range (Mach<0.3) using the Beam and Warming implicit scheme. The agreement with the fully incompressible projection method (Chorin, 1968) is fairly good while convergence time is very much better. The investigation suggests that the compressible Navier–Stokes equations may be used as an efficient alternative to study incompressible flows as well. Mach numbers just below 0.3 are enough to simulate incompressible flow behavior and at the same time do not cause numerical ill-conditioning in the solution. In addition, some relevant features of the vortices generated and carried by the wake of the cylinder could be fairly well captured. 相似文献
Rock-magnetic measurements along with grain size, acid-insoluble residue (AIR), organic carbon (OC), CaCO3 and δ18O of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of India. Magnetic susceptibility (MS) values in the surficial sediments reflect the land-derived input and, in general, are the highest in terrigenous sediment-dominated sections of the cores off Saurashtra–Ratnagiri, followed by the sediments off Indus–Gulf of Kachchh and then Mangalore–Cape Comorin.
The down-core variations in mineral magnetic parameters reveal that the glacial sediments off the Indus are characterized by low MS values/S-ratios associated with high AIR-content, low OC/CaCO3 contents and relatively high δ18O values, while those off SW India are characterized by low MS values/high S-ratio% associated with low AIR content, and relatively high OC, CaCO3 and δ18O values. Conversely, the Early Holocene sediments of all cores are characterized by high MS values/S-ratio% associated with high AIR content, low OC, CaCO3 contents and gradually decreased δ18O values. These results imply that during the Last Glacial Maximum (LGM), the cores off northwestern India received abundant continental supply leading to the predominance of eolian/fluvial sedimentation. In the SW region the influence of hinterland flux is less evident during this period, but convective mixing associated with the NE monsoon resulted in increased productivity. During the early Holocene intense SW monsoon conditions resulted in high precipitation on land, which in turn contributed increased AIR content/MS values in the continental margin sediments. A shallow water core off Kochi further suggests that the intense SW monsoon conditions prevailed until about 5 ka. The late Holocene organic-rich sediments of the SW margin of India were, however, subjected to early diagenesis at different intervals in the cores. Therefore, caution is needed when interpreting regional climatic change from down-core changes in sediment magnetic properties. 相似文献
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