A high‐resolution local RBF collocation method for steady‐state poroelasticity and hydromechanical damage analysis          下载免费PDF全文

D. Stevens  H. Power  J. Polanco  A. Cliffe 《国际地质力学数值与分析法杂志》2015,39(4):436-456

In this work, we describe a meshless numerical method based on local collocation with RBFs for the solution of the poroelasticity equation. The RBF finite collocation approach forms a series of overlapping nodal stencils, over which an RBF collocation is performed. These local collocation systems enforce the governing PDE operator throughout their interior, with the intersystem communication occurring via the collocation of field variables at the stencil periphery. The method does not rely on a generalised finite differencing approach, whereby the governing partial differential operator is reconstructed at the global level to drive the solution of the PDE. Instead, the PDE governing and boundary operators are enforced directly within the local RBF collocation systems, and the sparse global assembly is formed by reconstructing the value of the field variables at the centrepoint of the local stencils. In this way, the solution of the PDE is driven entirely by the local RBF collocation, and the method more closely resembles the approach of the full‐domain RBF collocation method. By formulating the problem in this fashion, high rates of convergence may be attained without the computational cost and numerical ill‐conditioning issues that are associated with the full‐domain RBF collocation approach. An analytical solution is formulated for a 2D poroelastic fluid injection scenario and is used to verify the proposed implementation of the method. Highly accurate solutions are produced, and convergence rates in excess of sixth order are observed for each field variable (i.e. pressure and displacement) and field‐variable derivative (i.e. pressure gradients and stresses). The stress and displacement fields resulting from the solution of the poroelasticity equation are then used to describe the formation and propagation of microfractures and microfissures, which may form in the presence of large shear strain, in terms of a continuous damage variable which modifies the mechanical and hydraulic properties of the porous medium. The formation of such hydromechanical damage, and the resulting increase in hydraulic conductivity, is investigated for a pressurised injection into sandstone. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Continuous field estimation of dissolved organic carbon concentration and biochemical oxygen demand using dual‐wavelength fluorescence,turbidity and temperature          下载免费PDF全文

Kieran Khamis  Chris Bradley  Rob Stevens  David M. Hannah 《水文研究》2017,31(3):540-555

Dissolved organic matter (DOM) quality and quantity is not measured routinely in‐situ limiting our ability to quantify DOM process dynamics. This is problematic given legislative obligations to determine event based variability; however, recent advances in field deployable optical sensing technology provide the opportunity to address this problem. In this paper, we outline a new approach for in‐situ quantification of DOM quantity (Dissolved Organic Carbon: DOC) and a component of quality (Biochemical Oxygen Demand: BOD) using a multi‐wavelength, through‐flow fluorescence sensor. The sensor measured tryptophan‐like (Peak T) and humic‐like (Peak C) fluorescence, alongside water temperature and turbidity. Laboratory derived coefficients were developed to compensate for thermal quenching and turbidity interference (i.e., light attenuation and scattering). Field tests were undertaken on an urban river with ageing wastewater and stormwater infrastructure (Bourn Brook; Birmingham, UK). Sensor output was validated against laboratory determinations of DOC and BOD collected by discrete grab sampling during baseflow and stormflow conditions. Data driven regression models were then compared to laboratory correction methods. A combination of temperature and turbidity compensated Peak T and Peak C was found to be a good predictor of DOC concentration (R² = 0.92). Conversely, using temperature and turbidity correction coefficients provided low predictive power for BOD (R² = 0.46 and R² = 0.51, for Peak C and T, respectively). For this study system, turbidity appeared to be a reasonable proxy for BOD, R² = 0.86. However, a linear mixed effect model with temperature compensated Peak T and turbidity provided a robust BOD prediction (R² = 0.95). These findings indicate that with careful initial calibration, multi‐wavelength fluorescence, coupled with turbidity, and temperature provides a feasible proxy for continuous, in‐situ measurement of DOC concentration and BOD. This approach represents a cost effective monitoring solution, particularly when compared to UV – absorbance sensors and DOC analysers, and could be readily adopted for research and industrial applications.  相似文献   

Source controlled 87Sr/86Sr isotope variability in granitic magmas: The inevitable consequence of mineral-scale isotopic disequilibrium in the protolith     

Federico Farina  Gary Stevens 《Lithos》2011,122(3-4):189-200

The broad Sr isotopic variability exhibited by granitoid rocks is commonly interpreted to reflect the mixing of magmas from different sources. However, evidence from granites and migmatites indicates that melting and magma extraction from crustal sources can occur sufficiently rapidly that trace-element and isotopic equilibration between liquid and residual phases is commonly not achieved. Additionally, evidence from unmelted high-grade metamorphic rocks indicates that major reactant minerals in the fluid-absent melting process, principally biotite and plagioclase, do not always attain equilibrium during regional metamorphism. When these two circumstances occur in combination, the melt does not inherit its radiogenic isotopic signature from the bulk source in a simple way. In such situations, the isotopic composition of the melt will be dependent on the isotopic compositions of the reactant phases and the stoichiometry of the melting reaction. This study has used information from experimental studies of fluid absent partial melting in metapelites and metagreywackes to investigate the consequences of Sr isotopic disequilibrium between the reactant minerals for magma composition. The study demonstrates that a range of isotopically distinct magmas can arise from progressive melting of a single source that is able to undergo melting through different reactions as temperature increases. When translated to the typically layered sources constituted by sedimentary and volcano-sedimentary rocks, this process will produce magmas characterized by Sr isotope variability that reflects the differences in melting reaction stoichiometry within the different layers, even with no bulk-rock isotopic variability between layers. This study demonstrates that the Sr isotope variability commonly observed within granitic suites, as well as at the grain and sub-grain scale within individual magmatic bodies, can be primary, reflecting differences in composition between magma batches produced from the progressive melting of a single source.  相似文献   

Impacts of the ‘<Emphasis Type="Italic">Pacific Adventurer</Emphasis>’ Oil Spill on the Macrobenthos of Subtropical Sandy Beaches     

Thomas Alfred Schlacher  Andrew Holzheimer  Tim Stevens  David Rissik 《Estuaries and Coasts》2011,34(5):937-949

Biological impacts of oil on sandy shore ecosystems remain incompletely understood, especially following smaller spills on subtropical beaches. Here we quantified changes to benthic assemblages on a sandy beach following the 270-t spill of heavy fuel oil from the Pacific Adventurer that occurred in March 2009 off Moreton Island in Eastern Australia. Assessments of ecological impacts are based on spatial contrasts between multiple reference and impact sites sampled 1 week and 3 months after the spill. Benthic invertebrate assemblages exposed to oil had significantly fewer individuals of fewer species 1 week after the spill, markedly changing their ecological structure. Biological differences consistent with oil-related mortality were significant on the lower shore and in the swash and remained so 3 months after the spill. This signals a lack of recovery of these communities in the short term, despite the fairly rapid removal of oil. Results show that, despite the relatively small size of the spill, heavy fuel oil contamination can cause substantial impacts on sandy beach ecosystems, and that recovery may be prolonged.  相似文献   

The SCUBA HAlf Degree Extragalactic Survey – III. Identification of radio and mid-infrared counterparts to submillimetre galaxies     

R. J. Ivison  T. R. Greve  J. S. Dunlop  J. A. Peacock  E. Egami  Ian Smail  E. Ibar  E. van Kampen  I. Aretxaga  T. Babbedge  A. D. Biggs  A. W. Blain  S. C. Chapman  D. L. Clements  K. Coppin  D. Farrah  M. Halpern  D. H. Hughes  M. J. Jarvis  T. Jenness  J. R. Jones  A. M. J. Mortier  S. Oliver  C. Papovich  P. G. Pérez-González  A. Pope  S. Rawlings  G. H. Rieke  M. Rowan-Robinson  R. S. Savage  D. Scott  M. Seigar  S. Serjeant  C. Simpson  J. A. Stevens  M. Vaccari  J. Wagg  C. J. Willott 《Monthly notices of the Royal Astronomical Society》2007,380(1):199-228

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Erratum: Observations of flat-spectrum radio sources at λ850 μm from the James Clerk Maxwell Telescope – I. 1997 April to 2000 April     

E. I. Robson  J. A. Stevens  T. Jenness 《Monthly notices of the Royal Astronomical Society》2003,343(4):1376-1376

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Multiwaveband studies of the hard ROSAT SMC transient 1WGA J0053.8−7226: a new X-ray pulsar     

D. A. H. Buckley  M. J. Coe  J. B. Stevens  K. van der Heyden  L. Angelini  N. White  P. Giommi 《Monthly notices of the Royal Astronomical Society》2001,320(2):281-288

We report on two optical candidates for the counterpart to an X-ray source in the Small Magellanic Cloud , 1WGA J0053.8−7226, identified as a serendipitous X-ray source from the ROSAT Position Sensitive Proportional Counter (PSPC) archive, and also observed by the Einstein Imaging Proportional Counter . Its X-ray properties, namely the hard X-ray spectrum, flux variability and column density, indicate a hard, transient source, with a luminosity of ∼     XTE and ASCA observations have confirmed the source to be an X-ray pulsar, with a 46-s spin period. Our optical observations reveal two possible candidates within the error circle. Both exhibit strong H α and weaker H β emission. The optical colours indicate that both objects are Be-type stars. The Be nature of the stars implies that the counterpart is most likely a Be/X-ray binary system. Subsequent infrared (IR) photometry ( JHK ) of one of the objects shows that the source varies by at least 0.5 mag, while the     measured nearly simultaneously with the UBVRI and spectroscopic observations indicate an IR excess of ∼0.3 mag.  相似文献   

Two-colour photometric selection of high-redshift galaxies     

Robin Stevens †  Mark Lacy 《Monthly notices of the Royal Astronomical Society》2001,325(3):897-906

In this paper we describe a set of models to predict the colours of galaxies over a wide range of redshifts. We present examples of output from the simulations, and discuss their application to the selection of galaxies at high redshifts, particularly through identification of the Lyman break. Additionally we consider the optimal choices of filters for selection at a range of redshifts.
An interface to a subset of the simulations has been made available on the World Wide Web for the benefit of the community at the location http://www-astro.physics.ox.ac.uk/~rejs/research/galcols.html/  相似文献   

On the atmospheric limitations of ground-based submillimetre astronomy using array receivers     

E. N. Archibald  T. Jenness  W. S. Holland  I. M. Coulson  N. E. Jessop  J. A. Stevens  E. I. Robson  R. P. J. Tilanus  W. D. Duncan  J. F. Lightfoot 《Monthly notices of the Royal Astronomical Society》2002,336(1):1-13

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Preface     

Bonnie A. Stevens  Andrzej J. Maciejewski 《Celestial Mechanics and Dynamical Astronomy》2004,90(1-2):1-2

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