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11.
12.
13.
Upscaling is a major issue regarding mechanical and transport properties of rocks. This paper examines three issues relative
to upscaling. The first one is a brief overview of Effective Medium Theory (EMT), which is a key tool to predict average rock
properties at a macroscopic scale in the case of a statistically homogeneous medium. EMT is of particular interest in the
calculation of elastic properties. As discussed in this paper, EMT can thus provide a possible way to perform upscaling, although
it is by no means the only one, and in particular it is irrelevant if the medium does not adhere to statistical homogeneity.
This last circumstance is examined in part two of the paper. We focus on the example of constructing a hydrocarbon reservoir
model. Such a construction is a required step in the process of making reasonable predictions for oil production. Taking into
account rock permeability, lithological units and various structural discontinuities at different scales is part of this construction.
The result is that stochastic reservoir models are built that rely on various numerical upscaling methods. These methods are
reviewed. They provide techniques which make it possible to deal with upscaling on a general basis. Finally, a last case in
which upscaling is trivial is considered in the third part of the paper. This is the fractal case. Fractal models have become
popular precisely because they are free of the assumption of statistical homogeneity and yet do not involve numerical methods.
It is suggested that using a physical criterion as a means to discriminate whether fractality is a dream or reality would
be more satisfactory than relying on a limited data set alone. 相似文献
14.
Comparison of 15 evaporation methods applied to a small mountain lake in the northeastern USA 总被引:7,自引:0,他引:7
Donald O. Rosenberry Thomas C. Winter Donald C. Buso Gene E. Likens 《Journal of Hydrology》2007,340(3-4):149-166
Few detailed evaporation studies exist for small lakes or reservoirs in mountainous settings. A detailed evaporation study was conducted at Mirror Lake, a 0.15 km2 lake in New Hampshire, northeastern USA, as part of a long-term investigation of lake hydrology. Evaporation was determined using 14 alternate evaporation methods during six open-water seasons and compared with values from the Bowen-ratio energy-budget (BREB) method, considered the standard. Values from the Priestley–Taylor, deBruin–Keijman, and Penman methods compared most favorably with BREB-determined values. Differences from BREB values averaged 0.19, 0.27, and 0.20 mm d−1, respectively, and results were within 20% of BREB values during more than 90% of the 37 monthly comparison periods. All three methods require measurement of net radiation, air temperature, change in heat stored in the lake, and vapor pressure, making them relatively data intensive. Several of the methods had substantial bias when compared with BREB values and were subsequently modified to eliminate bias. Methods that rely only on measurement of air temperature, or air temperature and solar radiation, were relatively cost-effective options for measuring evaporation at this small New England lake, outperforming some methods that require measurement of a greater number of variables. It is likely that the atmosphere above Mirror Lake was affected by occasional formation of separation eddies on the lee side of nearby high terrain, although those influences do not appear to be significant to measured evaporation from the lake when averaged over monthly periods. 相似文献
15.
David J. Ampleford Andrea Ciardi Sergey V. Lebedev Simon N. Bland Simon C. Bott Jeremy P. Chittenden Gareth N. Hall Adam Frank Eric Blackman 《Astrophysics and Space Science》2007,307(1-3):29-34
We present experimental data on the steady state deflection of a highly supersonic jet by a side-wind in the laboratory. The
use of a long interaction region enables internal shocks to fully cross the jet, leading to the development of significantly
more structure in the jet than in previous work with a similar setup (Lebedev et al., 2004). The ability to control the length
of the interaction region in the laboratory allows the switch between a regime representing a clumpy jet or wind and a regime
similar to a slowly varying mass loss rate. The results indicate that multiple internal oblique shocks develop in the jet
and the possible formation of a second working surface as the jet attempts to tunnel through the ambient medium. 相似文献
16.
Solar p modes are one of the dominant types of coherent signals in Doppler velocity in the solar photosphere, with periods showing
a power peak at five minutes. The propagation (or leakage) of these p-mode signals into the higher solar atmosphere is one of the key drivers of oscillatory motions in the higher solar chromosphere
and corona. This paper examines numerically the direct propagation of acoustic waves driven harmonically at the photosphere,
into the nonmagnetic solar atmosphere. Erdélyi et al. (Astron. Astrophys.
467, 1299, 2007) investigated the acoustic response to a single point-source driver. In the follow-up work here we generalise this previous
study to more structured, coherent, photospheric drivers mimicking solar global oscillations. When our atmosphere is driven
with a pair of point drivers separated in space, reflection at the transition region causes cavity oscillations in the lower
chromosphere, and amplification and cavity resonance of waves at the transition region generate strong surface oscillations.
When driven with a widely horizontally coherent velocity signal, cavity modes are caused in the chromosphere, surface waves
occur at the transition region, and fine structures are generated extending from a dynamic transition region into the lower
corona, even in the absence of a magnetic field. 相似文献
17.
We present the results of gravitational direct N-body simulations using the commercial graphics processing units (GPU) NVIDIA Quadro FX1400 and GeForce 8800GTX, and compare the results with GRAPE-6Af special purpose hardware. The force evaluation of the N-body problem was implemented in Cg using the GPU directly to speed-up the calculations. The integration of the equations of motions were, running on the host computer, implemented in C using the 4th order predictor–corrector Hermite integrator with block time steps. We find that for a large number of particles (N 104) modern graphics processing units offer an attractive low cost alternative to GRAPE special purpose hardware. A modern GPU continues to give a relatively flat scaling with the number of particles, comparable to that of the GRAPE. The GRAPE is designed to reach double precision, whereas the GPU is intrinsically single-precision. For relatively large time steps, the total energy of the N-body system was conserved better than to one in 106 on the GPU, which is impressive given the single-precision nature of the GPU. For the same time steps, the GRAPE gave somewhat more accurate results, by about an order of magnitude. However, smaller time steps allowed more energy accuracy on the grape, around 10−11, whereas for the GPU machine precision saturates around 10−6 For N 106 the GeForce 8800GTX was about 20 times faster than the host computer. Though still about a factor of a few slower than GRAPE, modern GPUs outperform GRAPE in their low cost, long mean time between failure and the much larger onboard memory; the GRAPE-6Af holds at most 256k particles whereas the GeForce 8800GTX can hold 9 million particles in memory. 相似文献
18.
Richard L. Branham Jr. 《Planetary and Space Science》2010,58(10):1307-1313
Comet C/1845 D1 (de Vico) is one of a large number of comets with parabolic orbits. Given that there are sufficient observations of the comet, 291 in right ascension and 269 in declination, it proves possible to calculate a better orbit. The calculations are based on a 12th order predictor-corrector method. The comet's orbit is hyperbolic and, from calculated mean errors, statistically different from a parabola. Bulirsch-Stoer integration, although more flexible and of comparable precision, proves considerably more laborious. 相似文献
19.
The measurements of pulsar frequency second derivatives have shown that they are 102−106 times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain
these paradoxical results on the basis of the statistical analysis of the rotational parameters ν,
and
of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between
and
for both
and
, as well as between ν and
. We interpret these dependencies as evolutionary ones due to
being nearly proportional to the pulsars’ age. The derived statistical relations as well as “anomalous” values of
are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore,
consists of secular change of ν
ev(t),
and
according to the power law with n≈5, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that—several
decades.
This work has been supported by the Russian Foundation for Basic Research (grant No 04-02-17555), Russian Academy of Sciences
(program “Evolution of Stars and Galaxies”), and by the Russian Science Support Foundation. The authors would also like to
thank the anonymous referee for valuable comments. 相似文献
20.
以徐州市地质灾害详细调查资料为依据,总结了徐州市地质灾害的主要类型,归纳分析了徐州市地质灾害形成的地质环境条件、诱发因素、发育现状及造成的损失。根据近年来省内外尤其是徐州市地质灾害调查评价和邳州石膏矿区地面塌陷现状及预防措施的建议,结合徐州市地质灾害隐患的具体特点,提出了加强地质灾害防治的有关制度建设、宣传培训工作、科学部署地质灾害防治、监测工程、强化建设项目的地质灾害危险性评估等地质灾害防灾减灾措施。 相似文献