Three-dimensional discrete element method for granular materials     

Jamshid Ghaboussi  Ricardo Barbosa 《国际地质力学数值与分析法杂志》1990,14(7):451-472

This paper describes a three-dimensional discrete element method of analysis for granular materials. Individual particles are modelled as rigid, six-sided solids with six degrees of freedom. Various types of contacts are possible among the three-dimensional discrete elements. Models for these contact types are described. Computational aspects of the method, such as techniques for contact detection and data structure, are addressed. Selective results of three examples that demonstrate the application of the method to granular flow problems are presented and discussed.  相似文献   

Preface     

Ricardo A. Olea 《Mathematical Geosciences》1996,28(4):383-384

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Book review     

Ricardo A. Olea 《Mathematical Geosciences》1988,20(2):135-137

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Two-Way Regionalized Classification of Multivariate Datasets and its Application to the Assessment of Hydrodynamic Dispersion     

Fernando António Leal Pacheco  Paulo Milton Barbosa Landim 《Mathematical Geology》2005,37(4):393-417

Zones of mixing between shallow groundwaters of different composition were unravelled by “two-way regionalized classification,” a technique based on correspondence analysis (CA), cluster analysis (ClA) and discriminant analysis (DA), aided by gridding, map-overlay and contouring tools. The shallow groundwaters are from a granitoid plutonite in the Fundão region (central Portugal). Correspondence analysis detected three natural clusters in the working dataset: 1, weathering; 2, domestic effluents; 3, fertilizers. Cluster analysis set an alternative distribution of the samples by the three clusters. Group memberships obtained by correspondence analysis and by cluster analysis were optimized by discriminant analysis, gridded over the entire Fundão region, and converted into “two-way regionalized classification” memberships as follows: codes 1, 2 or 3 were used when classification by correspondence analysis and cluster analysis produced the same results; code 0 when the grid node was first assigned to cluster 1 and then to cluster 2 or vice versa (mixing between weathering and effluents); code 4 in the other cases (mixing between agriculture and the other influences). Code-3 areas were systematically surrounded by code-4 areas, an observation attributed to hydrodynamic dispersion. Accordingly, the extent of code-4 areas in two orthogonal directions was assumed proportional to the longitudinal and transverse dispersivities of local soils. The results (0.7–16.8 and 0.4–4.3 m, respectively) are acceptable at the macroscopic scale. The ratios between longitudinal and transverse dispersivities (1.2–11.1) are also in agreement with results obtained by other studies.  相似文献   

Time-lapse traveltime change of singly scattered acoustic waves     

C. Pacheco  R. Snieder 《Geophysical Journal International》2006,165(2):485-500

We present a technique based on the single-scattering approximation that relates time-lapse localized changes in the propagation velocity to changes in the traveltime of singly scattered waves. We describe wave propagation in a random medium with homogeneous statistical properties as a single-scattering process where the fluctuations of the velocity with respect to the background velocity are assumed to be weak. This corresponds to one of two end-member regimes of wave propagation in a random medium, the first being single scattering, and the second multiple scattering. We present a formulation that relates the change in the traveltime of the scattered waves to a localized change in the propagation velocity by means of the Born approximation for the scattered wavefield. We validate the methodology with synthetic seismograms calculated with finite differences for 2-D acoustic waves. Potential applications of this technique include non-destructive evaluation of heterogeneous materials and time-lapse monitoring of heterogeneous reservoirs.  相似文献   

The carbon dioxide system in the oceans     

Prof. Ricardo M. Pytkowicz 《Aquatic Sciences - Research Across Boundaries》1973,35(1):8-28

A model of the carbon dioxide system in nature is derived and is used to further our understanding of the factors which control this system in the oceans, the atmosphere, and the sediments.  相似文献   

Ground-Water Network Design for Northwest Kansas, Using the Theory of Regionalized Variables     

Marios Sophocleous  James E. Paschetto  Ricardo A. Olea 《Ground water》1982,20(1):48-58

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Turbulent Structure of a Simplified Urban Fluid Flow Studied Through Stereoscopic Particle Image Velocimetry     

Bruno Monnier  Sepehr A. Goudarzi  Ricardo Vinuesa  Candace Wark 《Boundary-Layer Meteorology》2018,166(2):239-268

Stereoscopic particle image velocimetry was used to provide a three-dimensional characterization of the flow around a simplified urban model defined by a 5 by 7 array of blocks, forming four parallel streets, perpendicular to the incoming wind direction corresponding to a zero angle of incidence. Channeling of the flow through the array under consideration was observed, and its effect increased as the incoming wind direction, or angle of incidence (AOI), was changed from \(0^{\circ }\) to \(15^{\circ }\), \(30^{\circ }\), and \(45^{\circ }\). The flow between blocks can be divided into two regions: a region of low turbulence kinetic energy (TKE) levels close to the leeward side of the upstream block, and a high TKE area close to the downstream block. The centre of the arch vortex is located in the low TKE area, and two regions of large streamwise velocity fluctuation bound the vortex in the spanwise direction. Moreover, a region of large spanwise velocity fluctuation on the downstream block is found between the vortex legs. Our results indicate that the reorientation of the arch vortex at increasing AOI is produced by the displacement of the different TKE regions and their interaction with the shear layers on the sides and top of the upstream and downstream blocks, respectively. There is also a close connection between the turbulent structure between the blocks and the wind gusts. The correlations among gust components were also studied, and it was found that in the near-wall region of the street the correlations between the streamwise and spanwise gusts \(R_{uv}\) were dominant for all four AOI cases. At higher wall-normal positions in the array, the \(R_{uw}\) correlation decreased with increasing AOI, whereas the \(R_{uv}\) coefficient increased as AOI increased, and at \({\textit{AOI}}=45^{\circ }\) all three correlations exhibited relatively high values of around 0.4.  相似文献   

Precipitation trends using in-situ and gridded datasets     

Sharlene Lata Beharry  Ricardo Marcus Clarke  Kishan Kurmarsingh 《Theoretical and Applied Climatology》2014,115(3-4):599-607

Six in situ precipitation time series of varying time periods in the northwestern region and the Global Precipitation Climatology Centre (GPCC) v6 0.5° monthly dataset (1901–2010) were statistically examined for monotonic trends in Trinidad. The Pettit test was used to investigate the abrupt changes in the mean while the Mann–Kendall test was employed to assess the monotonic trends. It was found that three in situ stations and the six grids experienced abrupt changes in the rainfall patterns and that there was an apparent shift in the seasons. In addition, for five out of the six in situ stations no monotonic change was detected in the monthly, seasonal, and annual rainfall patterns. Gradual decreases were detected in the calculated weighted area average for five stations, the GPCCv6 dataset and St. Ann’s time series. The GPCCv6 data indicated that the dry season in the southern Trinidad is becoming drier. Results also suggested that the range between the greatest and lowest recorded rainfall values for some months have increased while others decreased. The gridded dataset appears to give a good representation of the dry season (January to May) rainfall compared with the wet season (June to December) and was found to be negatively biased for the north-western region but may not necessarily be so for the entire island. The results suggested that in the north-western region mirco-climates may exist. It is recommended that further investigations are needed using in situ data.  相似文献   

Unexpected records of ‘deep‐sea’ carnivorous sponges Asbestopluma hypogea in the shallow NE Atlantic shed light on new conservation issues          下载免费PDF全文

Pierre Chevaldonné  Thierry Pérez  Jean‐Michel Crouzet  Wilfried Bay‐Nouailhat  Anne Bay‐Nouailhat  Maïa Fourt  Bruno Almón  Jacinto Pérez  Ricardo Aguilar  Jean Vacelet 《Marine Ecology》2015,36(3):475-484

Marine cave communities have been a continued source of ecological surprises, among other things because of their close ecological and evolutionary ties with the deep sea. The discovery of cladorhizid sponges, the deepest occurring poriferan family, in shallow Mediterranean caves in the 1990s was one such surprise, leading to the generally accepted hypothesis that the whole family was carnivorous, an unprecedented feeding mode for sponges. The recent observation of the cave species Asbestopluma hypogea in the Mediterranean bathyal, confirmed the view that some shallow caves can occasionally shelter otherwise deep‐dwelling species. Here we present new distribution data of A. hypogea, from deep Mediterranean locations, and for the first time from Atlantic locations. Among the new Atlantic records, the most surprising ones are located in three different geographic areas (Ria de Arousa, Groix Island and Cherbourg) of the NW European coasts, from the Iberian Peninsula to the English Channel, where A. hypogea reaches SCUBA depths (5–50 m), while not sheltered in marine caves. The carnivorous sponge however reaches its shallowest occurrence (5 m), in a small cave at Groix Island. The ecological significance of these discoveries, particularly the very patchy distribution and peculiar dynamics, are noteworthy, and the shallow occurrence of A. hypogea, together with other deep‐water or uncommon species, constitute unique assemblages that must be considered in conservation plans.  相似文献