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41.
Filip Nilenius Fredrik Larsson Karin Lundgren Kenneth Runesson 《国际地质力学数值与分析法杂志》2013,37(11):1535-1551
Effective moisture and chloride ion diffusivity coefficients for concrete are determined by computational homogenization, where concrete is modeled on the mesoscale as a heterogenous three‐phase composite material. By imposing moisture and chloride ion gradients on a representative volume element, effective macroscale properties are obtained through finite element analysis. A parametric study of the effects of the ballast content was carried out. The numerical results correspond well with an estimate of the Hashin–Shtrikman type available in the literature. The computational homogenization strategy proposed here also includes the interfacial transition zone, and its influence on the effective diffusivity coefficients is assessed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
42.
Kaj E. Williams Christopher P. McKay Fredrik Persson 《Planetary and Space Science》2012,60(1):376-385
The Huygens Probe provided a wealth of data concerning the atmosphere of Titan. It also provided tantalizing evidence of a small amount of surface liquid. We have developed a detailed surface energy balance for the Probe landing site. We find that the daily averaged non-radiative fluxes at the surface are 0.7 W m?2, much larger than the global average value predicted by McKay et al. (1991) of 0.037 W m?2. Considering the moist surface, the methane and ethane detected by the Probe from the surface is consistent with a ternary liquid of ethane, methane, and nitrogen present on the surface with mole fractions of methane, ethane, and nitrogen of 0.44, 0.34, and 0.22, respectively, and a total mass load of ~0.05 kg m?2. If this liquid is included in the surface energy balance, only a small fraction of the non-radiative energy is due to latent heat release (~10?3 W m?2). If the amount of atmospheric ethane is less than 0.6×10?5, the surface liquid is most likely evaporating over timescales of 5 Titan days, and the moist surface is probably a remnant of a recent precipitation event. If the surface liquid mass loading is increased to 0.5 kg m?2, then the liquid lifetime increases to ~56 Titan days. Our modeling results indicate a dew cycle is unlikely, given that even when the diurnal variation of liquid is in equilibrium, the diurnal mass variation is only 3% of the total liquid. If we assume a high atmospheric mixing ratio of ethane (>0.6×10?5), the precipitation of liquid is large (38 cm/Titan year for an ethane mixing ratio of 2×10?5). Such a flux is many orders of magnitude in excess of the photochemical production rate of ethane. 相似文献
43.
In this paper, Shell’s in-house reservoir simulator MoReS is applied to a recently introduced CO2 sequestration benchmark problem entitled “Estimation of the CO2 Storage Capacity of a Geological Formation” (Class et al. 2008). The principal objective of this benchmark is the simulation of CO2 distribution within a modeling region, and leakage of CO2 outside of it, for a period of 50 years. This study goes beyond the benchmarking exercise to investigate additional factors
with direct relevance to CO2 storage capacity estimations: water and gas relative permeabilities, permeability anisotropy, presence of sub-seismic features
(conductive fractures, thin shale layers), regional hydrodynamic gradient, CO2-enriched brine convection (due to brine density differences), and injection rates. The effects of hydrodynamic gradients
and gravitationally induced convection only become significant over 100 s of years. This study has thus extended simulation
time to 1,000 years. It is shown that grid resolution significantly impacts results. Vertical-grid refinement results in larger
and thinner CO2 plumes. Lateral-grid refinement delays leakage out of the model domain and reduces injection pressure for a given injection
rate. Sub-seismic geological features such as fractures/faults and shale layers are demonstrated to have impact on CO2 sequestration. Fractures located up-dip from the injector may lead to more leakage while the opposite may happen in the presence
of fractures perpendicular to the dip. Thin shale layers produce stacked CO2 blankets. They should be explicitly represented instead of being upscaled using a reduced vertical to horizontal permeability
ratio. Results are seen to be far more sensitive to gas relative permeability and hysteresis than to variations in the water
relative permeability models used. For a multi-injectors project, there is scope to optimize the phasing of injections to
avoid potential fracturing near injectors. 相似文献
44.
Improved confidence in climate change projections of precipitation further evaluated using daily statistics from ENSEMBLES models 总被引:4,自引:3,他引:1
Fredrik Boberg Peter Berg Peter Thejll William J. Gutowski Jens H. Christensen 《Climate Dynamics》2010,35(7-8):1509-1520
Probability density functions for daily precipitation data are used as a validation tool comparing station measurements to seven transient regional climate model runs, with a horizontal resolution of 25 km and driven by the SRES A1B scenario forcing, within the ENSEMBLES project. The validation is performed for the control period 1961–1990 for eight predefined European subregions, and a ninth region enclosing all eight subregions, with different climate characteristics. Models that best match the observations are then used for making climate change projections of precipitation distributions during the twenty-first century for each subregion separately. We find, compared to the control period, a distinct decrease in the contribution to the total precipitation for days with moderate precipitation and a distinct increase for days with more intense precipitation. This change in contribution to the total precipitation is found to amplify with time during all of the twenty-first century with an average rate of 1.1% K?1. Furthermore, the crossover point separating the decreasing from the increasing contributions does not show any significant change with time for any specific subregion. These results are a confirmation and a specification of the results from a previous study using the same station measurements but with a regional climate model ensemble within the PRUDENCE project. 相似文献
45.
Nalân Koç Dorthe Klitgaard-Kristensen Kristine Hasle Carl Fredrik Forsberg ers Solheim 《Polar research》2002,21(2):307-314
Timing and structure of the Late and post-glacial development of the northern Svalbard margin, together with the initial influx of Atlantic water into the Arctic Ocean are still very poorly constrained. We investigated a sediment core (NP94-51) from a high accumulation area on the continental shelf north of Hinlopen Strait with the purpose of resolving the timing and structure of the last deglaciation. Detailed analyses of ice-rafted detritus, benthic and planktonic foraminiferal fauna, diatom flora, grain size and radiocarbon dates are used to reconstruct the palaeoceanographic evolution of the area. Our results indicate that the disintegration of Hinlopen Strait ice and possibly the northern margin of the Svalbard Ice Sheet commenced between 13.7 and 13.9 14 C Ky BP. Influx of subsurface Atlantic waters into the area (12.6 14 C Ky BP) and the retreat of the sea ice cover, with the accompanying opening of the surface waters (10.8 14 C Ky BP), happened at different times and both much later than the disintegration of the ice sheets. The transition into the Holocene shows a two-step warming. 相似文献
46.
The rocks of western Ny-Friesland, northern Svalbard, are part of a tectonostratigraphy including four thrust sheets, each composed mainly of orthogneisses overlain by younger metasedimentary rocks. Previous geochronological studies have shown that the orthogneisses are dominated by ca. 1750 Mya granitoids. This study of a quartz-monzonite in one of the thrust sheets, the Nordbreen Nappe, yields a single-zircon U-Pb ion-microprobe age of 2709 Ø 28 My. This is the oldest rock unit so far reported in the Svalbard Caledonides. However, age-determinations on detrital zircons in the metasediments of western Ny-Friesland have shown that Late Archean rocks were prominent sources. The new ages presented here provide the first evidence of a local source for these sedimentary rocks. 相似文献
47.
48.
49.
Fredrik Høgaas Louise Hansen Ivar Berthling Martin Klug Oddvar Longva Helle Daling Nannestad Lars Olsen Anders Romundset 《Boreas: An International Journal of Quaternary Research》2023,52(3):295-313
This study discusses the timing and maximum flood level of the Nedre Glomsjø outburst flood, Norway, based on sediment records retrieved from 15 bog and lake basins located close to the purported maximum flooded level. The sediment records in 12 of the basins consist of a distinct light-coloured silty bed that is correlated to the outburst-flood-deposited ‘Romerike Silt Bed’ identified elsewhere in the region. The silt bed is recorded in basins up to a certain elevation and is absent above this level. The new maximum flood level inferred from the basin sediment records exceeds the established landform-induced palaeostage indicators by 5–10 m. The data indicate a higher maximum flood level and larger inundation area than previously suggested and highlight the importance of acquiring a wide range of geological data when reconstructing palaeofloods. Radiocarbon dates of terrestrial macrofossils found stratigraphically above and below the Romerike Silt Bed suggest that the glacial lake Nedre Glomsjø outburst flood occurred between 10.5 and 10.3 cal. ka BP. The new and well-constrained timing of the outburst flood is beneficial for reconstructing regional deglaciation and provides a precise age for the Romerike Silt Bed chronostratigraphical marker, which is of value for studies in SE Norway and adjacent regions. 相似文献
50.
The solar and longwave environmental irradiance geometry (SOLWEIG) model simulates spatial variations of 3-D radiation fluxes and mean radiant temperature (T mrt) as well as shadow patterns in complex urban settings. In this paper, a new vegetation scheme is included in SOLWEIG and evaluated. The new shadow casting algorithm for complex vegetation structures makes it possible to obtain continuous images of shadow patterns and sky view factors taking both buildings and vegetation into account. For the calculation of 3-D radiation fluxes and T mrt, SOLWEIG only requires a limited number of inputs, such as global shortwave radiation, air temperature, relative humidity, geographical information (latitude, longitude and elevation) and urban geometry represented by high-resolution ground and building digital elevation models (DEM). Trees and bushes are represented by separate DEMs. The model is evaluated using 5?days of integral radiation measurements at two sites within a square surrounded by low-rise buildings and vegetation in G?teborg, Sweden (57°N). There is good agreement between modelled and observed values of T mrt, with an overall correspondence of R 2?=?0.91 (p?<?0.01, RMSE?=?3.1?K). A small overestimation of T mrt is found at locations shadowed by vegetation. Given this good performance a number of suggestions for future development are identified for applications which include for human comfort, building design, planning and evaluation of instrument exposure. 相似文献