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131.
Multi-phase simulations of turbulent driven flow in a dense medium cyclone with magnetite medium have been conducted in Fluent, using the Algebraic Slip Mixture model to model the dispersed phases and the air-core, and both the Large Eddy Simulation turbulence model (LES) and Reynolds Stress Models (RSM) for turbulence closure. The predicted air-core shape and diameter were found to be close to the experimental results measured by gamma ray tomography. It is possible to use the LES turbulence model with ASM multi-phase model to predict the air/slurry interface accurately. Multi-phase simulations (air/water/medium) show appropriate medium segregation effects but over-predict the level of segregation compared to that measured by gamma ray tomography near the wall. This is believed to be because of unaccounted back-mixing of the dispersed phase due to turbulence in the basic Algebraic Slip Mixture model. The predictions of accurate axial segregation of magnetite medium are investigated using the LES turbulence model in conjunction with the multi-phase mixture model and viscosity corrections according to the feed particle loading factor. At higher feed densities the agreement between the Dunglison [Dunglison, M.E., 1999, A general model of the dense medium cylone, PhD thesis, JKMRC, University of Queensland] correlations and experimental measurements and the CFD is reasonably good, but the overflow density is lower than the model predictions. It is believed that the excessive underflow volumetric flow rates are responsible for under prediction of the overflow density. The effect of size distribution of the magnetite has been fully studied. As expected, the ultra-fine magnetite sizes (i.e. 2 and 7 microns) are distributed uniformly throughout the cyclone. As the size of magnetite increases, more segregation of magnetite occurs close to the wall. 相似文献
132.
Identification of homogeneous rainfall regimes in parts of Western Ghats region of Karnataka 总被引:1,自引:0,他引:1
In view of the ongoing environmental and ecological changes in the Western Ghats, it is important to understand the environmental
parameters pertaining to the sustenance of the region. Rainfall is one such parameter governing the hydrological processes
crucial to agriculture planning, afforestation and eco-system management. Therefore, it is essential to understand rainfall
distribution and its variation in relevance to such activities. The present study is an attempt to gain in-depth understanding
in this direction. The study area comprises of one coastal district and its adjoining areas in Karnataka State. Mean annual
rainfall data of 93 rain gauge stations distributed over the study area for a period of 10–50 years are used for the study.
In order to assess the variation of rainfall across the ghats, several bands were constructed parallel to the latitudes to
facilitate the analysis. The statistical analyses conducted included cluster analysis and analysis of variance. The study
revealed that there exist three distinct zones of rainfall regimes in the study area, namely, Coastal zone, Transition zone
and Malanad zone. It is observed that, the maximum rainfall occurs on the windward side ahead of the geographical peak. Further,
mean monthly rainfall distribution over the zones has been depicted to enable agricultural planning in the study area. 相似文献
133.
Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution 总被引:4,自引:6,他引:4
Barnier Bernard Gurvan Madec Thierry Penduff Jean-Marc Molines Anne-Marie Treguier Julien Le Sommer Aike Beckmann Arne Biastoch Claus Böning Joachim Dengg Corine Derval Edmée Durand Sergei Gulev Elizabeth Remy Claude Talandier Sébastien Theetten Mathew Maltrud Julie McClean Beverly De Cuevas 《Ocean Dynamics》2006,56(5-6):543-567
Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4°) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy–enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10° resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current–topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution. 相似文献
134.
Hetu C. Sheth George Mathew Kanchan Pande Soumen Mallick Balaram Jena 《Journal of Earth System Science》2004,113(4):831-838
Rootless cones, also (erroneously) called pseudocraters, form due to explosions that ensue when a lava flow enters a surface
water body, ice, or wet ground. They do not represent primary vents connected by vertical conduits to a subsurface magma source.
Rootless cones in Iceland are well studied. Cones on Mars, morphologically very similar to Icelandic rootless cones, have
also been suggested to be rootless cones formed by explosive interaction between surface lava flows and ground ice. We report
here a group of gentle cones containing nearly circular craters from Mount Pavagadh, Deccan volcanic province, and suggest
that they are rootless cones. They are very similar morphologically to the rootless cones of the type locality of Myvatn in
northeastern Iceland. A group of three phreatomagmatic craters was reported in 1998 from near Jabalpur in the northeastern
Deccan, and these were suggested to be eroded cinder cones. A recent geophysical study of the Jabalpur craters does not support
the possibility that they are located over volcanic vents. They could also be rootless cones. Many more probably exist in
the Deccan, and volcanological studies of the Deccan are clearly of value in understanding planetary basaltic volcanism. 相似文献
135.
Summary During the pre-onset regime of MONEX-79, the short period (1–2 weeks) time series measurements of surface meteorological elements, vertical profiles of temperature (BT) and salinity (Nansen casts) made from 5 former USSR and 2 Indian research vessels were utilised to investigate the observed near-surface heating rates at a few selected locations in the Arabian Sea. The influence of local surface heat fluxes on the upper ocean heat content variability is explored. The associated synoptic scale variability in the thermohaline structure of the upper layers is presented. The efficacy of a simple Kraus-Turner type one dimensional numerical model in simulating the observed variability of mixed layer heating rates is evaluated.With 7 Figures 相似文献
136.
Geostrophic velocities are computed across meridians 37 °E and 105 °E using hydrographic data. The estimated mass transport is represented on a temperature-salinity diagram. The characteristics of the water within the Antarctic circumpolar current at 37 °E and 105 °E are discussed. The computed transport agrees with the previous estimates. Transports due to the current between 45 °S and the Antarctic continent at these two meridians are comparable. The westerly flow south of 42 °S at 105 °E is associated with a cyclonic eddy which appears to be a permanent feature, whereas the one at 50 °S is related to the topography of the region. 相似文献
137.
M. Hourston R.M. Warwick F.J. Valesini I.C. Potter 《Estuarine, Coastal and Shelf Science》2005,64(4):601-612
This study has determined the ways in which the characteristics of the nematode assemblages in nearshore marine waters along the microtidal lower west coast of Australia are influenced by habitat type, time of year and shore-perpendicular zones. The habitat types (1, 2 and 6), which had previously been identified on the basis of a suite of enduring environmental characteristics, could be broadly described as highly sheltered from wave activity and containing dense seagrass (1), moderately sheltered from wave activity with sparse seagrass (2) and relatively exposed to wave activity with no seagrass (6). Sampling in five consecutive seasons yielded 15 751 nematodes representing 75 species, of which, at present, only three can be referred to described species. The number of species and densities in habitat type 1, and particularly those in its subtidal zone (C), were far greater than those in the other two habitat types. Both of these biotic variables underwent marked seasonal changes, declining to low levels during winter. The compositions of the assemblages differed significantly among the three habitat types, with the differences between habitat types 1 and 6 being particularly marked. Species of Paracomesoma, Dichromadora, Marylynnia, and Pomponema, which are assumed to feed primarily on benthic diatoms, were particularly abundant at the most sheltered habitat type, whereas those of Gonionchus, Theristus and Bathylaimus, which are assumed to be deposit feeders, were relatively abundant at the most highly exposed habitat type. The compositions of the assemblages differed among seasons and were most discrete in spring, due to marked increases in the densities of certain species. However, differences in the compositions in the different zones of each habitat type were relatively small, presumably reflecting the presence of only a small tide in the region. 相似文献
138.
Bernard Barnier Gurvan Madec Thierry Penduff Jean-Marc Molines Anne-Marie Treguier Julien Le Sommer Aike Beckmann Arne Biastoch Claus Böning Joachim Dengg Corine Derval Edmée Durand Sergei Gulev Elizabeth Remy Claude Talandier Sébastien Theetten Mathew Maltrud Julie McClean Beverly De Cuevas 《Ocean Dynamics》2009,59(3):537-537
139.
TRIASSIC OROGENESIS IN SOUTHWEST CHINA: THE STRUCTURAL ORIGINS OF THE NORTHEAST TIBETAN PLATEAU 相似文献
140.
Elizabeth M. Douglass Steven R. Jayne Frank O. Bryan Synte Peacock Mathew Maltrud 《Journal of Oceanography》2012,68(5):625-639
A high-resolution ocean model forced with an annually repeating atmosphere is used to examine variability of the Kuroshio, the western boundary current in the North Pacific Ocean. A large meander (LM) in the path of the Kuroshio south of Japan develops and disappears in a highly bimodal fashion on decadal timescales. The modeled meander is comparable in timing and spatial extent to an observed feature in the region. Various characteristics of the LM are examined, including relative vorticity, transport, and velocity shear. The many similarities between the model and observations indicate that the meander results from intrinsic oceanic variability, which is represented in this climatologically forced model. Each LM is preceded by a smaller “trigger” meander that originates at the south end of Kyushu, moves up the coast, and develops into the LM. However, there are also many meanders very similar in character to the trigger meander that do not develop into LMs. Formation of an LM only occurs when a deep anticyclone associated with the trigger meander forms near Koshu Seamount. Furthermore, the major axis of that deep anticyclone must be oriented away from the coast, rather than alongshore. In the specific case of interaction of a trigger meander with a deep anticyclone with major axis oriented away from the coastline, LM formation occurs. 相似文献