Numerical simulation of internal solitary wave—induced reverse flow and associated vortices in a shallow,two-layer fluid benthic boundary layer     

Øyvind Thiem  Magda Carr  Jarle Berntsen  Peter A. Davies 《Ocean Dynamics》2011,61(6):857-872

The wave-induced velocity and pressure fields beneath a large amplitude internal solitary wave of depression propagating over a smooth, flat, horizontal, and rigid boundary in a shallow two-layer fluid are computed numerically. A numerical ocean model is utilised, the set-up of which is designed and tuned to replicate the previously published experimental results of Carr and Davies (Phys Fluids 18(1):016,601–1–016,601–10, 2006). Excellent agreement is found between the two data sets and, in particular, the numerical simulation replicates the finding of a reverse flow along the bed aft of the wave. The numerically computed velocity and pressure gradients confirm that the occurrence of the reverse flow is a consequence of boundary layer separation in the adverse pressure gradient region. In addition, vortices associated with the reverse flow are seen to form near the bed.  相似文献   

Book reviews     

James R. Carr 《Mathematical Geology》1995,27(5):703-707

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Las campanas observatory seeing measurements     

S. E. Persson  D. M. Carr  J. H. Jacobs 《Experimental Astronomy》1990,1(3):195-212

Instrumentation built to record seeing data automatically via image motion measurements of bright stars in small telescopes is described. The centroid of the star image is found 256 times s^-1 in one dimension and is analyzed on-line. The device works over a range of FWHM values as would be seen through a large telescope between <0.1 and 3.0 arcsec. The first results for two identical instruments set up at two locations near the duPont Telescope at Las Campanas Observatory are reported. For a total of 61 nights of data (450 h at each site), the median seeing is 0.6 arcsec, with quartiles at 0.4 and 0.8 arcsec. These are FWHM values referred to 5000 Å at the zenith. So far, the two sites are indistinguishable on average.  相似文献   

High resolution spectroscopy with CSHELL     

T. P. Greene  A. T. Tokunaga  J. S. Carr 《Experimental Astronomy》1994,3(1-4):309-312

CSHELL, the NASA Infrared Telescope Facility Cryogenic Echelle Spectrograph was designed to fill a need for high sensitivity, high resolution, long slit near-infrared spectroscopy. Scientific programs in the areas of comets, planetary atmospheres, young stellar objects, the interstellar medium, and galactic dynamics have been pursued with CSHELL and are described herein. The future of the instrument is also discussed.  相似文献   

Classical novae from the POINT–AGAPE microlensing survey of M31 – I. The nova catalogue     

M. J. Darnley  M. F. Bode  E. Kerins  A. M. Newsam  J. An  P. Baillon  S. Calchi Novati  B. J. Carr  M. Crézé  N. W. Evans  Y. Giraud-Héraud  A. Gould  P. Hewett  Ph. Jetzer  J. Kaplan  S. Paulin-Henriksson  S. J. Smartt  C. S. Stalin  Y. Tsapras 《Monthly notices of the Royal Astronomical Society》2004,353(2):571-588

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Reply to “letter to the editor” by Hans Wackernagel     

James R. Carr 《Mathematical Geology》1991,23(7):985-986

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Book Review Volcanoes of the Solar System: By Charles Frankel, Cambridge University Press, 1996, 232 p., hardcover, $70.00 (U.S.), ISBN 0-521-47201-6; paperback, $70.00 (U.S.), ISBN 0-521-47201-6; paperback, 24.95 (U.S.), ISBN 0-521-47770-0     

James R. Carr 《Mathematical Geology》1997,29(8):1025-1026

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The effect of an offshore bank in attenuating waves     

M.J. Tucker  A.P. Carr  E.G. Pitt 《Coastal Engineering》1983,7(2):133-144

Waverider buoys were installed in approximately 16 m of water offshore of the Size-well-Dunwich Bank off the East Coast of England and in approximately 11 m of water inshore of it. Minimum water depth over the bank was approximately 4.5 m at mid-tide level. Simultaneous records were obtained for substantial periods between November 1978 and May 1979. These show negligible attenuation for small waves, but as the offshore waveheight increased, the inshore waveheight tended to saturate at an H_s of about 3 m. The form of the relationship between inshore and offshore waveheight is predicted theoretically assuming that high individual waves which cross the bank are limited by breaking. The theoretical curve agrees well with the measured data. The measured saturation level corresponds to a wave breaking when its height is approximately 0.5 the water depth, which is considerably lower than the usual engineering criterion. However, some published tank results also appear to show the same low value.  相似文献   

Effect of vegetation cover and sediment type on 3D subsurface structure and shear strength in saltmarshes     

Clementine Chirol  Kate L. Spencer  Simon J. Carr  Iris Möller  Ben Evans  Jason Lynch  Helen Brooks  Katherine R. Royse 《地球表面变化过程与地形》2021,46(11):2279-2297

The vulnerability of saltmarshes to lateral erosion at their margin depends on the local biogeomorphological properties of the substrate. In particular, the 3D architecture of pore and root systems is expected to influence shear strength, with repercussions for the wider-scale stability of saltmarshes. We apply X-ray computed microtomography (μCT) to visualize and quantify subsurface structures in two UK saltmarshes at Tillingham Farm, Essex (silt/clay rich substrate) and Warton Sands (sand-rich substrate), with four types of ground cover: bare ground, Spartina spp, Salicornia spp and Puccinellia spp. We extracted μCT structural parameters that characterize pore and root morphologies at each station, and compared them with field measurements of shear strength using a principal component analysis and correlation tests. The 3D volumes show that species-dependent variations in root structures, plant colonization events and bioturbation activity control the morphology of macropores, while sediment cohesivity determines the structural stability and persistence of these pore structures over time, even after the vegetation has died. Areas of high porosity and high mean pore thickness were correlated to lower values of shear strength, especially at Tillingham Farm, where well-connected vertical systems of macropores were associated with current or previous colonization by Spartina spp. However, while well-connected systems of macropores may lower the local deformation threshold of the sediment, they also encourage drainage, promote vegetation growth and reduce the marsh vulnerability to hydrodynamic forces. The highest values of shear strength at both sites were found under Puccinellia spp, and were associated with a high density of mesh-like root structures that bind the sediment and resist deformation. Future studies of marsh stability should ideally consider time series of vegetation cover, especially in silt/clay-dominated saltmarshes, in order to consider the potential effect of preserved buried networks of macropores on water circulation, marsh functioning and cliff-face erosion.  相似文献   

Marcellus Shale Lithofacies Prediction by Multiclass Neural Network Classification in the Appalachian Basin   总被引：4，自引：0，他引：4  

Guochang Wang  Timothy R. Carr 《Mathematical Geosciences》2012,44(8):975-1004

Marcellus Shale is a rapidly emerging shale-gas play in the Appalachian basin. An important component for successful shale-gas reservoir characterization is to determine lithofacies that are amenable to hydraulic fracture stimulation and contain significant organic-matter and gas concentration. Instead of using petrographic information and sedimentary structures, Marcellus Shale lithofacies are defined based on mineral composition and organic-matter richness using core and advanced pulsed neutron spectroscopy (PNS) logs, and developed artificial neural network (ANN) models to predict shale lithofacies with conventional logs across the Appalachian basin. As a multiclass classification problem, we employed decomposition technology of one-versus-the-rest in a single ANN and pairwise comparison method in a modular approach. The single ANN classifier is more suitable when the available sample number in the training dataset is small, while the modular ANN classifier performs better for larger datasets. The effectiveness of six widely used learning algorithms in training ANN (four gradient-based methods and two intelligent algorithms) is compared with results indicating that scaled conjugate gradient algorithms performs best for both single ANN and modular ANN classifiers. In place of using principal component analysis and stepwise discriminant analysis to determine inputs, eight variables based on typical approaches to petrophysical analysis of the conventional logs in unconventional reservoirs are derived. In order to reduce misclassification between widely different lithofacies (for example organic siliceous shale and gray mudstone), the error efficiency matrix (ERRE) is introduced to ANN during training and classification stage. The predicted shale lithofacies provides an opportunity to build a three-dimensional shale lithofacies model in sedimentary basins using an abundance of conventional wireline logs. Combined with reservoir pressure, maturity and natural fracture system, the three-dimensional shale lithofacies model is helpful for designing strategies for horizontal drilling and hydraulic fracture stimulation.  相似文献