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The local surface deformation resulting from the oblique impact of a columnar water jet has been computed, using a three-dimensional large eddy simulation, as a model of the overturning jet of a breaking wave. The emergence of the secondary jet from the front face of the initial jet has been examined and the organisation of the vortices within the jet characterised. As the secondary jet emerges, the vorticity field becomes unstable under the action of the strong shear beneath the jet surface and pairs of longitudinal counter-rotating vortices stretched along the direction of the jet projection are formed. The presence of these longitudinal vortex pairs creates convergent surface flows, resulting in the formation of longitudinal scars on the rear face of the projecting jet. Following significant growth of the scars on both its upper and lower surfaces, the jet decouples into fingers. The lateral widths of the longitudinal vortices provide a minimum measure of the finger size. A horizontal Froude number Frh, representing a measure of strength of horizontal shear in a gravity-dominated impacting flow is defined, which characterises the organisation of the longitudinal vortices occurring in the shear flow, and the resultant formation of scars and fingers. For higher Frh, stronger longitudinal vortices and deeper scars are formed at longer lateral intervals, enhancing the fingering process during the splashing event. Fundamental features of material transport in the vicinity of the surface of jets (e.g. gas transfer across a sea surface) are related to the entrainment of surface fluid by the longitudinal vortices, and is thus also characterised by Frh. 相似文献
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Shaocheng Ji Kazuko Saruwatari David Mainprice Richard Wirth Zhiqin Xu Bin Xia 《Tectonophysics》2003,370(1-4):49-76
Ultra high-pressure (UHP) eclogites from Sulu region (China) represent mafic components of the continental crust, which were first subducted to mantle depths greater than 100 km and then exhumed to the earth's surface. Detailed investigation of microstructures, chemical compositions, petrofabrics and seismic properties of the UHP eclogites can provide important information on the operating deformation mechanisms and rheology of subducted continental crust and on the origin of seismic reflections within the upper mantle. We present here results from field, optical and TEM observations, electron back-scattered diffraction (EBSD) measurements and numerical computations of the seismic properties of UHP eclogites collected from fresh surface outcrops at the drill site (Maobei, Donghai County, Jiangsu Province) of the Chinese Continental Scientific Drilling Program (CCSD). Two types of eclogites have been distinguished: Type-1 (coarse-grained) eclogites deformed by recovery-accommodated dislocation creep at the peak metamorphic conditions, and Type-2 (fine-grained) eclogites which are composed of reworked Type-1 materials during recrystallization-accommodated dislocation creep in shear zones which were active during the exhumation of the UHP metamorphic rocks. Both garnet and omphacite in these eclogites deformed plastically and the flow strength contrast between these two constituent minerals is apparently much less than an order of magnitude under the UHP metamorphic conditions. Plasticity of eclogites under UHP conditions can effectively facilitate channeled flow along the interplate shear zone. The preservation of the relict crustal materials within the continental lithosphere may produce regionally extensive, strong, seismic reflections in the upper mantle. This may explain the origin of mantle reflections observed in many areas of the world. 相似文献
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J.R. Dungca J. Kuwano A. Takahashi T. Saruwatari J. Izawa H. Suzuki K. Tokimatsu 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):287-295
This paper presents an experimental study on the lateral resistance of a pile subjected to liquefaction-induced lateral flow. To observe the soil surrounding the pile during liquefaction, it was modeled as a buried cylinder that corresponded to a sectional model of the prototype pile at a certain depth in the subsoil. In order to create a realistic stress condition in the model ground, the model was prepared in a sealed container and the overburden pressure was applied to the ground surface by a rubber pressure bag. The model pile was actuated back and forth through rods attached on each side by an electro-hydraulic actuator.This paper focuses on observing the deformation of the liquefied soil surrounding the pile when a large relative displacement between the pile and the soil is induced. The loading rate effect on the lateral resistance of the pile in the liquefied sand and the influence of the relative density are also investigated.Test results show that a larger resistance is mobilized as the loading rate becomes higher. When the loading rate is higher, the cylinder displacement required for the lateral resistance becomes smaller. It has been also observed that as the relative density of the soil increases, dilatancy of the soil in front of the pile also increases. 相似文献
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Regional differences in climatic change are of importance in order to establish the counter-measures for the damage by anomalous climate to agricultural production. It is not unusual for some regions to suffer floods while droughts occur in nearby regions at the same time. This paper deals mainly with the regionality of climatic change in E Asia during recent years, using the year-climate method expressed by the Köppen's system of climatic classification. Occurrence frequencies of BW, BS, Cf, Cw, Dwa, Dwb, and Dwc-type showed striking regionalities, which were obtained from the data at the 134 observatories over E Asia during the period from 1951 to 1970. The distribution of climatic types in each year shows various tendencies: Wet and cold as in 1954 and 1957 shows a pattern in which the boundary between C-type and D-type runs south and the Cfa-zone is broad, extending from middle E China to SW Japan. In contrast, in dry and warm years like 1965, the Dwa regions disappear in the N of E China and the BS region is located just north of the Cwa region, which is distributed broadly from China to Japan. Occurrence frequencies of year climate during the last 100 years were calculated for the 4 stations: Hong Kong, Manila, Shanghai and Tokyo. The results were compared with the distribution types of winter temperature and summer precipitation in China. It seems that the precipitation conditions in summer were reversed between the Philippines and China. Summarizing the results obtained, a schema of the regionality of climatic fluctuation in E and SE Asia was given in relation to the upper air streams. The position of the subtropical jet stream in winter shows a close relationship to the N limit of the Aw and Am year climate regions and in summer with the S limit of Dw region in NE China and North Korea. The Cw and Cf year climate regions in E Asia are located roughly in the regions bounded by the axes of subtropical jet streams in winter and in summer. The Dw year climate region in the E of the Tibetan Plateau reflects the altitudinal effect of the Cw climate of SE China. The N of E China has the variable BS year climate, which may related to the summer and winter jet stream conditions. Finally, the interannual change of the agricultural production index was dealt with in relation to the occurrence frequency of year climate types over E Asia during the years 1967–1970. As far as this period is concerned, the drier conditions are more effective than the wetter conditions in reducing agricultural production. 相似文献
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