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151.
Pickering & Hiscott, (1985) have demonstrated amply the presence of reverse-flow units within the thick-bedded calcareous wacke (TCW) beds of the turbiditic Cloridorme Formation (Middle Ordovician, Gaspé Peninsula, Quebec, Canada). These reverse-flow units are underlain and overlain by units which reveal flow in the primary (obverse) direction. In this paper, a model is proposed for this reverse flow, based on the probable nature of the primary turbidity flow. It appears that the initial flow was highly elongated (thickness h? length L), with h~ 500 m, velocity U~ 2 m s-1 and sediment concentration C~ 1·25%o. The rate of momentum loss of the flow is estimated by means of a useful parameter which we call the ‘drag distance’, symbol dD, defined by where h and L are the thickness and length of the flow, respectively; cCd is a combined drag coefficient representing friction on the bottom and at the upper interface; and fCd is a form-drag coefficient related to the shape and size of the head. dD is the distance travelled by a current of constant h and L, flowing over a horizontal bottom and obeying a quadratic friction law, for an e-fold reduction in velocity. Simple considerations, confirmed by our own experiments (described in this paper), show that such an elongated turbidity current cannot be reflected as a whole from an adverse slope: when the nose of the current reaches the slope, it forms a hump, which surges backwards and sooner or later breaks up into a series of internal solitons. The latter, probably numbering 4–7, will cause reverse flow at a given point as they pass by, provided that the residual velocity in the tail is not too great. Flow in the original (obverse) direction will be re-established after the passage of the solitons. Quiescent periods in front of, between and behind the solitons, when soliton-associated currents cancelled out the residual obverse flow, would allow the deposition of thin mud-drapes. Additional flow reversals observed in a few of the TCW beds cannot be explained readily by the re-passage of solitons, since wave breaking at the ends of the basin would cause massive energy loss; internal seiches are the preferred explanation for these later reversals. 相似文献
152.
153.
154.
R. Touzani 《Boundary-Layer Meteorology》1987,41(1-4):279-285
A finite element model for the computation of thermally stratified flows is described. The model includes a special treatment of the pressure gradient term by splitting it into hydrostatic and hydrodynamic contributions. Four-node elements are used for space-discretization and a semi-implicit scheme for time integration. The computed flow is used to simulate pollutant transport by a finite element model. Numerical results from such simulations, in particular for urban heat islands are described and compared with experimental data. 相似文献
155.
156.
In this paper we report on the MEM power spectrum analysis of brightness temperature fluctuations observed at 2.8 GHz during the total solar eclipse of 16 February 1980. The observed periodicities range from 3.5 min to 64 min. These periodicities may arise due to spatial and/or temporal variations in the solar radio emission. The observed periodicities imply presence of scale sizes ranging from 70,000 to 600,000 km assuming that the brightness fluctuations arise because of spatial variation only. On the other hand, if these fluctuations are due to temporal variation, the observed periodicities correspond well to predicted modes of solar global oscillations. 相似文献
157.
158.
L. N. Germanovich R. L. Salganik A. V. Dyskin K. K. Lee 《Pure and Applied Geophysics》1994,143(1-3):117-149
159.
LI Yucheng
Professor the State Key Laboratory of Coastal Offshore Engineering Dalian University of Technology Dalian P. R. China. 《中国海洋工程》1999,(2)
-The hydrodynamic coefficients C_d and C_m are not only dependent on the size of slender cylin-der,its location in water,KC number and Re number,but also vary with environmental conditions,i.e.,in regular waves or in irregular waves,in pure waves or in wave-current coexisting field.In this paper,thenormalization of hydrodynamic coefficients for various environmental conditions is discussed.When aproper definition of KC number and proper characteristic values of irregular waves are used,a unified re-lationship between C_d,C_m and KC number for regular waves,irregular waves,pure waves and wave-cur-rent coexisting field can be obtained. 相似文献
160.
The distribution of diamonds within individual kimberlite pipes is poorly documented in the public domain due to the proprietary
nature of the data. The study of the diamond distribution within two pipes, Fox and Koala, from the EKATI Diamond Mine, NWT,
Canada, in conjunction with detailed facies models has shown several distinct relationships of deposit type and grade distribution.
In both pipes, the lithological facies represent grade units which can be distinguished from each other in terms of relative
size and abundance of diamonds. A positive relationship between olivine grain size and abundance with diamond size and abundance
is observed, indicating that sorting of fragmental kimberlites influences diamond distribution. Though surface geological
processes do not control the diamond potential of the erupting magma, they can be responsible for concentrating diamonds into
economically significant proportions. A good understanding of the eruption, transport and depositional processes responsible
for the individual lithological units and the diamond distribution within them is important for successful resource estimation.
This may lead to recognition of areas suitable for selective mining, making a marginal deposit economic. 相似文献