Upscaling of two-phase discrete fracture simulations using a convolutional neural network     

Andrianov  Nikolai 《Computational Geosciences》2022,26(5):1237-1259

Upscaling methods such as the dual porosity/dual permeability (DPDP) model provide a robust means for numerical simulation of fractured reservoirs. In order to close the DPDP model, one needs to provide the upscaled fracture permeabilities and the parameters of the matrix-fracture mass transfer for every fractured coarse block in the domain. Obtaining these model closures from fine-scale discrete fracture-matrix (DFM) simulations is a lengthy and computationally expensive process. We alleviate these difficulties by pixelating the fracture geometries and predicting the upscaled parameters using a convolutional neural network (CNN), trained on precomputed fine-scale results. We demonstrate that once a trained CNN is available, it can provide the DPDP model closures for a wide range of modeling parameters, not only those for which the training dataset has been obtained. The performance of the DPDP model with both reference and predicted closures is compared to the reference DFM simulations of two-phase flows using a synthetic and a realistic fracture geometries. While the both DPDP solutions underestimate the matrix-fracture transfer rate, they agree well with each other and demonstrate a significant speedup as compared to the reference fine-scale solution.

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Nouveaux développements de l’imagerie et du suivi temporel à partir du bruit sismique     

Michel Campillo  Haruo Sato  Nikolai M. Shapiro  Robert D. van der Hilst 《Comptes Rendus Geoscience》2011,343(8-9):487-495

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石榴辉石岩的电导率及对岩浆底侵的约束     

门清波  王勤  NikolaiBagdassarov  夏群科  樊祺诚 《岩石矿物学杂志》2013,32(5):652-662

河北汉诺坝新生代玄武岩携带的石榴辉石岩为岩浆底侵于上地幔顶部40～45 km形成的堆晶岩,是壳-幔过渡带的典型样品。本文使用Solartron 1260阻抗分析仪,测量1.2 GPa和380～900 ℃下石榴辉石岩WD958的电阻率。样品电导率(σ)与温度的关系遵守Arrhenius方程: σ=σ₀exp(-ΔH/kT),其中T是样品的绝对温度,k是Boltzmann常数,指前因子σ₀为97.5 S/m,活化焓ΔH为1.27 eV。使用傅立叶红外光谱仪测定样品中单斜辉石的平均含水量为117×10^-6 H₂O,橄榄石无水,石榴子石的含水量因蚀变无法测定。使用Hashin-Shtrikman平均方法计算样品WD958的电导率,发现样品可看作由含水单斜辉石、无水石榴子石和无水橄榄石组成的高阻集合体,电导率同时受小极化子导电和质子导电的影响。如果原位的石榴辉石岩的矿物含水量保持平衡,其电导率将提高1个数量级,质子导电成为主控导电机制。石榴辉石岩在高温的壳-幔过渡带(～1 000℃)表现为高导层,而在正常地温梯度下,与尖晶石二辉橄榄岩的电导率近似,为高阻层。因此,在岩浆底侵作用下,电性上的壳-幔边界将随着温度和含水量的变化而改变。  相似文献   

Circular polarization in comets: Observations of Comet C/1999 S4 (LINEAR) and tentative interpretation     

Vera Rosenbush  Ludmilla Kolokolova  Nikolai Shakhovskoy 《Icarus》2007,186(2):317-330

Comet C/1999 S4 (LINEAR) was exceptional in many respects. Its nucleus underwent multiple fragmentations culminating in the complete disruption around July 20, 2000. We present circular polarization measurements along the cuts through the coma and nucleus of the comet during three separate observing runs, in June 28-July 2, July 8-9, and July 21-22, 2000. The circular polarization was detected at a rather high level, up to 0.8%. The left-handed as well as right-handed polarization was observed over the coma with the left circularly polarized light systematically observed in the sunward part of the coma. During our observations the phase angle of the comet varied from 61 up to 122°, which allowed us to reveal variations of circular polarization with the phase angle. Correlation between the degree of circular polarization, visual magnitude, water production rate, and linear polarization of Comet C/1999 S4 (LINEAR) during its final fragmentation in July 2000 was found. The mechanisms that may produce circular polarization in comets and specifically in Comet C/1999 S4 (LINEAR) are discussed and some tentative interpretation is presented.  相似文献   

Using SNAP for Galactic &; extragalactic astronomy     

Olga K. Sil’chenko  Alexei S. Rastorguev  Nikolai G. Bochkarev 《Astrophysics and Space Science》2007,307(4):385-393

SNAP, the SuperNova Acceleration Probe, is planned as a space-based telescope designed specifically to search for and monitor cosmological supernovae and weak lensing. In this paper we propose some other mission objectives which are of great importance in the fields of Galactic and extragalactic astronomy and which can be done as by-products with the same instrumentation and survey strategy as currently proposed for the main SNAP mission.  相似文献   

Variability of surface wind directions over Finnmark, Norway, and coupling to the larger-scale atmospheric circulation     

Nikolai Nawri  Knut Harstveit 《Theoretical and Applied Climatology》2012,107(1-2):15-33

This study documents the temporal and spatial variability of surface wind conditions over the Norwegian county of Finnmark and the coupling of local surface winds to the larger-scale atmospheric circulation, represented by the mean sea level pressure field. At locations along the northern coast, thermally driven offshore winds from the south dominate, especially during the cold season. During the warm season, downward mixing of westerly overlying winds becomes more important as the stability of the boundary layer stratification decreases. In the western part, locations are situated in valleys, resulting in two opposing along-channel dominant wind directions. Seasonal changes in atmospheric conditions are reflected in a reversal of the dominant wind direction, with a component towards the coast during the cold season. At all locations, a clear separation between different prevailing surface wind directions in each season can be achieved based exclusively on local mean sea level geostrophic wind direction. This allows statistical downscaling of the prevailing surface wind conditions from lower-resolution simulations of the surface pressure field and may improve local wind forecasts over complex terrain.  相似文献   

Learning about parameter and structural uncertainty in carbon cycle models     

Brian C. O’Neill  Nikolai B. Melnikov 《Climatic change》2008,89(1-2):23-44

Uncertainty in the response of the global carbon cycle to anthropogenic emissions plays a key role in assessments of potential future climate change and response strategies. We investigate how fast this uncertainty might change as additional data on the global carbon budget becomes available over the twenty-first century. Using a simple global carbon cycle model and focusing on both parameter and structural uncertainty in the terrestrial sink, we find that additional global data leads to substantial learning (i.e., changes in uncertainty) under some conditions but not others. If the model structure is assumed known and only parameter uncertainty is considered, learning is rather limited if observational errors in the data or the magnitude of unexplained natural variability are not reduced. Learning about parameter values can be substantial, however, when errors in data or unexplained variability are reduced. We also find that, on the one hand, uncertainty in the model structure has a much bigger impact on uncertainty in projections of future atmospheric composition than does parameter uncertainty. But on the other, it is also possible to learn more about the model structure than the parameter values, even from global budget data that does not improve over time in terms of its associated errors. As an example, we illustrate how one standard model structure, if incorrect, could become inconsistent with global budget data within 40 years. The rate of learning in this analysis is affected by the choice of a relatively simple carbon cycle model, the use of observations only of global emissions and atmospheric concentration, and the assumption of perfect autocorrelation in observational errors and variability. Future work could usefully improve the approach in each of these areas.  相似文献   

Phytoplankton in the south-western Kara Sea: composition and distribution   总被引：1，自引：0，他引：1  

Nikolai V. Druzhkov  Pavel R. Makarevich  Elena I. Druzhkova 《Polar research》2001,20(1):95-108

The taxonomic composition and spatial distribution of pelagic algae were studied in the south-western Kara Sea in August-September 1981. In the north-western and easternmost regions of the study area the phytoplankton community, dominated by neritic diatoms and autotrophic dinoflagellates, was at the late spring bloom stage of the seasonal succession. In the central deep-water zone of the sea, there was a predominance of heterotrophic dinoflagellates from the genera Protoperidinium and Dinophysis , and the autotrophic compartment of the algal community was clearly in a stage of decline. The distribution of the phytoplankton assemblages followed closely the major routes of receding marginal ice zones. Three stages of the seasonal succession were established for the area of interest: (1) early spring (ice edge) bloom of arcto-boreal neritic diatoms; (2) late spring bloom of neritic diatoms and autotrophic dinoflagellates, fuelled by continental run-off; and (3) summer minimum with a predominance of heterotrophic dinoflagellates, followed by autumnal decline of the phytoplankton community.  相似文献   

The Barents Sea capelin-a review of trophic interrelations and fisheries     

Ushakov  Nikolai G.; Prozorkevich  Dmitry V. 《ICES Journal of Marine Science》2002,59(5):1046-1052

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Ambient noise Rayleigh wave tomography across Europe   总被引：27，自引：0，他引：27  

Yingjie Yang  Michael H. Ritzwoller  Anatoli L. Levshin  Nikolai M. Shapiro 《Geophysical Journal International》2007,168(1):259-274

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