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31.
Comparison of an algebraic multigrid algorithm to two iterative solvers used for modeling ground water flow and transport 总被引：1，自引：0，他引：1
Numerical solution of large-scale ground water flow and transport problems is often constrained by the convergence behavior of the iterative solvers used to solve the resulting systems of equations. We demonstrate the ability of an algebraic multigrid algorithm (AMG) to efficiently solve the large, sparse systems of equations that result from computational models of ground water flow and transport in large and complex domains. Unlike geometric multigrid methods, this algorithm is applicable to problems in complex flow geometries, such as those encountered in pore-scale modeling of two-phase flow and transport. We integrated AMG into MODFLOW 2000 to compare two- and three-dimensional flow simulations using AMG to simulations using PCG2, a preconditioned conjugate gradient solver that uses the modified incomplete Cholesky preconditioner and is included with MODFLOW 2000. CPU times required for convergence with AMG were up to 140 times faster than those for PCG2. The cost of this increased speed was up to a nine-fold increase in required random access memory (RAM) for the three-dimensional problems and up to a four-fold increase in required RAM for the two-dimensional problems. We also compared two-dimensional numerical simulations of steady-state transport using AMG and the generalized minimum residual method with an incomplete LU-decomposition preconditioner. For these transport simulations, AMG yielded increased speeds of up to 17 times with only a 20% increase in required RAM. The ability of AMG to solve flow and transport problems in large, complex flow systems and its ready availability make it an ideal solver for use in both field-scale and pore-scale modeling. 相似文献
32.
In the present paper storm time variations and 27-day geomagnetic periodicity have been analysed to estimate the depth of the substitute conductor, assuming an infinitely (super) conducting core model of the earth. The advantage of using data from a restricted longitude range is that the uncertainties arising from lateral contrasts in the upper mantle and contributions from Sq current systems are considerably reduced. The result of the present analysis, which has been done in the time domain, gives a value of 522 km for the depth of the substitute conductor in case of storm time variations which rises to 870 km for 27-day recurrent storms. A higher value of the depth for 27-day variations indicate that the rise in conductivity inside the earth is not like a step function rather is a gradual one. The value of 522 km for storm time variations for the Indian region is smaller than the global average. This is natural to expect because the Indian sub-continent is known to be a tectonically active region. 相似文献
33.
D. Majumdar B. Rajaram S. Meshram P. Suryawanshi C. V. Chalapati Rao 《International Journal of Environmental Science and Technology》2017,14(2):397-420
Polycyclic aromatic hydrocarbons (PAHs) are considered as one of the most important groups of organic environmental contaminants due to their toxicity, persistence and ubiquity. PAHs have been monitored in urban road dust at various locations worldwide in about last three decades. Resuspension of road dust containing PAHs is an important route of human exposure to PAHs. This paper collates the available information on reported concentrations of PAHs in urban road dust at various worldwide locations classified as industrial, residential, traffic, city and commercial and other areas, reported sources of PAHs and related interpretations. The available information has been reviewed and documented country-wise. Variation in PAHs concentrations over various worldwide locations have been scrutinized, and interestingly, most of the reported average PAHs concentrations were found to be distributed within a very narrow range of values, implying only little variation in average PAH concentrations in spite of great distances between locations, climatic variation and differences in anthropogenic activities. 相似文献
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Accurate representation of groundwater-surface water interactions is critical to modeling low river flows in the semi-arid southwestern United States. Although a number of groundwater-surface water models exist, they are seldom integrated with river operation/management models. A link between the object-oriented river and reservoir operations model, RiverWare, and the groundwater model, MODFLOW, was developed to incorporate groundwater-surface water interaction processes, such as river seepage/gains, riparian evapotranspiration, and irrigation return flows, into a rule-based water allocations model. An explicit approach is used in which the two models run in tandem, exchanging data once in each computational time step. Because the MODFLOW grid is typically at a finer resolution than RiverWare objects, the linked model employs spatial interpolation and summation for compatible communication of exchanged variables. The performance of the linked model is illustrated through two applications in the Middle Rio Grande Basin in New Mexico where overappropriation impacts endangered species habitats. In one application, the linked model results are compared with historical data; the other illustrates use of the linked model for determining management strategies needed to attain an in-stream flow target. The flows predicted by the linked model at gauge locations are reasonably accurate except during a few very low flow periods when discrepancies may be attributable to stream gaging uncertainties or inaccurate documentation of diversions. The linked model accounted for complex diversions, releases, groundwater pumpage, irrigation return flows, and seepage between the groundwater system and canals/drains to achieve a schedule of releases that satisfied the in-stream target flow. 相似文献
36.
Observations of mesospheric winds over a period of four years with the partial reflection radar at Tirunelveli (8.7°N, 77.8°E), India, are presented in this study. The emphasis is on describing seasonal variabilities in mean zonal and meridional winds in the altitude region 70–98 km. The meridional winds exhibit overall transequatorial flow associated with differential heating in the Northern and Southern Hemispheres. At lower altitudes (70–80 km) the mean zonal winds reveal easterly flow during summer and westerly flow during winter, as expected from a circulation driven by solar forcing. In the higher altitude regime (80–98 km) and at all altitudes during equinox periods, the mean zonal flow is subjected to the semi-annual oscillation (SAO). The interannual variability detected in the occurrence of SAO over Tirunelveli has also been observed in the data sets obtained from the recent UARS satellite mission. Harmonic analysis results over a period of two years indicate the presence of long-period oscillations in the mean zonal wind at specific harmonic periods near 240, 150 and 120 days. Results presented in this study are discussed in the context of current understanding of equatorial wave propagation. 相似文献
37.
Girija Rajaram A. N. Hanchinal R. Kalra K. Unnikrishnan K. Jeeva M. Sridharan A. Dhar 《Journal of Earth System Science》2002,111(1):51-62
The Indian Antarctic station Maitri (geog. 70‡45’S, 11‡45’E, geom. 66‡.03S, 53‡.21E) occupies a sub-auroral location during
magnetically quiet conditions(Σκρ < 10), but attains an auroral position when the auroral oval shifts equatorwards with increasing strength of magnetic disturbance.
At the latter times, triangulation with 3 fluxgate magnetometers located at the vertices of a suitable triangle provides a
means of monitoring mobile auroral ionospheric current systems over Maitri. The spacing between the magnetometers is typically
kept at 75–200 km, keeping in mind the scale-sizes of ∼ 100 km for these mobile current systems. This work reports the results
of two triangulation experiments carried out around Maitri in January 1992 and January 1995, both during Antarctic summer.
The velocities estimated for pulsations of the Pc4 and Pc5 type were about 0.59 km/sec in the direction 102‡.7 east of due
north, in the first case, and about 1–3 km/sec in the second case in the east-west direction.
While several magnetometer arrays exist in the northern auroral regions (e.g., the Alberta array in Canada, the Alaskan array
in the U.S. and the IMS Scandinavian array), there is no report in literature of triangulation through arrays in Antarctica,
except for a one-day study by Neudegget al 1995 for ULF pulsations of the Pc1 and Pc2 type. The velocities obtained for the Pi3 type of irregular pulsations over Antarctica
in the present study tally well with those obtained for northern auroral locations. 相似文献
38.
The composite stereographic projection of orientations of the compression and tension axes using thirty-nine fault-plane solutions
of earthquakes from two active seismogenic sources of Nepal and adjoining areas were examined and the nature of stress pattern
and their influence on tectonics in the region have been studied. The seismogenic source located in Eastern Nepal region,
which has been the site of 1934 Bihar-Nepal great earthquake of M 8.4, is presently experiencing N-S to NE-SW directed compressive stresses. The inferred pattern of compression axes in Western
Nepal region suggests a shallow compressive stress, dipping N-S to NE-SW. Approximately similar nature of the stress regime
is observed in Western and Eastern regions of Nepal, separated by nearly 700 km; it shows N-S to NNE-SSW direction of compression
and underthrusting of the Indian Plate beneath the Himalaya at a shallow angle.
Present study indicates that the stress is being released along the strikes of some of the transverse faults present in the
region since the compressive stress exerted by the northward movement of the Indian Plate is approximately perpendicular to
the Himalayan collision belt. Unilateral stress pattern generated by the northward movement of the Indian Plate in the central
part of the Himalaya reveals that the present day collision occurs roughly perpendicular to the local strike of the Himalaya. 相似文献
39.
Ajay Kumar Sreerama Rajaram Chenna Mishra Shashank Pradeep Kumar Ramancharla Karnath Anoop 《Natural Hazards》2017,85(3):1851-1875
Natural Hazards - Methods capable of assessing the vulnerability of houses for future earthquakes are of fundamental importance for the safety and development of an area. As the detailed assessment... 相似文献