The availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods. This study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials. A number of empirical, semi-empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content. One such relationship, named complex refractive index model or Lichteneker-Rother model has been extensively applied in recent years. Here we first analyse the characteristics of this Lichteneker-Rother model by means of theoretical considerations. This theoretical analysis indicates that the Lichteneker-Rother exponent is dependent upon the geometrical properties of the porous structure, as well as the permittivity contrast between the different phases. Pore-scale modelling and experimental data further support this result. The parameter estimation robustness in presence of synthetic data error is also assessed. This demonstrates that Lichteneker-Rother parameters cannot, in general, be independently identified on the basis of bulk dielectric constant versus moisture content data. 相似文献
Large-eddy simulation has become an important tool for the study of the atmospheric boundary layer. However, since large-eddy
simulation does not simulate small scales, which do interact to some degree with large scales, and does not explicitly resolve
the viscous sublayer, it is reasonable to ask if these limitations affect significantly the ability of large-eddy simulation
to simulate large-scale coherent structures. This issue is investigated here through the analysis of simulated coherent structures
with the proper orthogonal decomposition technique. We compare large-eddy simulation of the atmospheric boundary layer with
direct numerical simulation of channel flow. Despite the differences of the two flow types it is expected that the atmospheric
boundary layer should exhibit similar structures as those in the channel flow, since these large-scale coherent structures
arise from the same primary instability generated by the interaction of the mean flow with the wall surface in both flows.
It is shown here that several important similarities are present in the two simulations: (i) coherent structures in the spanwise-vertical
plane consist of a strong ejection between a pair of counter-rotating vortices; (ii) each vortex in the pair is inclined from
the wall in the spanwise direction with a tilt angle of approximately 45°; (iii) the vortex pair curves up in the streamwise
direction. Overall, this comparison adds further confidence in the ability of large-eddy simulation to produce large-scale
structures even when wall models are used. Truncated reconstruction of instantaneous turbulent fields is carried out, testing
the ability of the proper orthogonal decomposition technique to approximate the original turbulent field with only a few of
the most important eigenmodes. It is observed that the proper orthogonal decomposition reconstructs the turbulent kinetic
energy more efficiently than the vorticity. 相似文献
Twenty-eight samples of peat, peaty lignites and lignites (of both matrix and xylite-rich lithotypes) and subbituminous coals have been physically activated by pyrolysis. The results show that the surface area of the activated coal samples increases substantially and the higher the carbon content of the samples the higher the surface area.The adsorption capacity of the activated coals for NO, SO2, C3H6 and a mixture of light hydrocarbons (CH4, C2H6, C3H8 and C4H10) at various temperatures was measured on selected samples. The result shows a positive correlation between the surface area and the gas adsorption. In contrast, the gas adsorption is inversely correlated with the temperature. The maximum recorded adsorption values are: NO = 8.22 × 10− 5 mol/g at 35 °C; SO2 = 38.65 × 10− 5 mol/g at 60 °C; C3H6 = 38.9 × 10− 5 mol/g at 35 °C; and light hydrocarbons = 19.24 × 10− 5 mol/g at 35 °C. Adsorption of C3H6 cannot be correlated with either NO or SO2. However, there is a significant positive correlation between NO and SO2 adsorptions. The long chain hydrocarbons are preferentially adsorbed on activated lignites as compared to the short chain hydrocarbons.The results also suggest a positive correlation between surface area and the content of telohuminite maceral sub-group above the level of 45%. 相似文献
This review paper presents the results of an extensive study investigating whether addition of 3% w/w Greek lignite to 6.42% w/w water–bentonite suspensions, after being exposed to high temperatures, can prevent gelation and control filtration characteristics. Two different bentonites and eight lignites from different Greek basins have been used while a commercial lignite product has been used as standard. The lignite-free bentonite suspensions heated to 177 °C for 16 h (thermal aging) thicken considerably, increasing the yield stress and the yield point. Fluid consistency and flow behavior indices also change while no significant change is observed for plastic viscosity. Thermal aging of the suspensions results in unacceptably high fluid loss values.Addition of Greek lignite to water–bentonite suspensions, followed by thermal aging, provided the rheological stability of the suspensions by maintaining the low yield stress/point regardless of the type of bentonite. Some of the lignites performed as well as their commercial counterpart. No specific trends for rheological improvement have been identified with respect to various characteristics of lignites such as contents of humic, fulvic acids, humins and other parameters such as specific surface area and cation exchange capacity.Furthermore, addition of lignite in most cases provided very good filtration control of the water–bentonite suspensions after exposure to 177 °C, with some Greek lignites being superior to the commercial product. The same lignite parameters examined for rheological control, were also examined to determine their effect on fluid loss of these suspensions for both bentonites. The content of humic and fulvic acids of two groups of lignites showed weak inverse correlations with the fluid loss volumes for both bentonites, while all other parameters did not seem to directly correlate with the effectiveness of the lignites. 相似文献
We calculate explicitly some expectations (integrals over Hilbert spaces) of functionals of Gaussian random fields. Our work
is inspired by the formulas for the harmonic oscillator. We also show how to do similar calculations by considering continuum
limits of sequences of coupled harmonic oscillators. The results obtained in this work have applications in the study of random
media, renormalization and scaling, and in engineering perturbation analysis. 相似文献
We analyze the reliability of the Lagrangian stochastic micromixing method in predicting higher-order statistics of the passive scalar concentration induced by an elevated source (of varying diameter) placed in a turbulent boundary layer. To that purpose we analyze two different modelling approaches by testing their results against the wind-tunnel measurements discussed in Part I (Nironi et al., Boundary-Layer Meteorology, 2015, Vol. 156, 415–446). The first is a probability density function (PDF) micromixing model that simulates the effects of the molecular diffusivity on the concentration fluctuations by taking into account the background particles. The second is a new model, named VP\(\varGamma \), conceived in order to minimize the computational costs. This is based on the volumetric particle approach providing estimates of the first two concentration moments with no need for the simulation of the background particles. In this second approach, higher-order moments are computed based on the estimates of these two moments and under the assumption that the concentration PDF is a Gamma distribution. The comparisons concern the spatial distribution of the first four moments of the concentration and the evolution of the PDF along the plume centreline. The novelty of this work is twofold: (i) we perform a systematic comparison of the results of micro-mixing Lagrangian models against experiments providing profiles of the first four moments of the concentration within an inhomogeneous and anisotropic turbulent flow, and (ii) we show the reliability of the VP\(\varGamma \) model as an operational tool for the prediction of the PDF of the concentration. 相似文献
Shells of the mollusks Cerastoderma (Cerastoderma) edule (Linnaeus 1758) and Monodonta (Osilinus) articulata Lamark 1822 from salt evaporate basins in western Sicily are studied and the effect of environmental conditions (particularly salinity and water chemistry) on mineralogy and chemical composition is investigated and discussed.
The elements determined both in seawater and shell carbonate are: Ca, Mg, Mn, Fe, Ni, Co, Cu, Zn, Sr and Pb.
Both species studied discriminate against all the minor and trace elements determined; the degree of such discrimination, for some elements, is inversely related to salinity.
The mineralogical composition of the shells (Monodonta has a mixed mineralogy while Cerastoderma is entirely aragonitic) appears to be controlled neither by temperature nor by salinity.
In Monodonta shells direct correlations have been found between the following parameters: calcite-Sr (in younger shells only), calcite-Fe, calcite-Pb (in older shells only), calcite-Zn, salinity-Mg and salinity-Pb, whereas inverse correlations were observed between calcite and Sr (in older shells only) and calcite and Pb (in younger shells only). In Cerastoderma shells a direct correlation was found between salinity and Fe and Mg.
The thickness of the shells appears, in both species, to be an inverse linear function of salinity. 相似文献
Using monitored natural attenuation is an increasingly popular strategy for dealing with contaminated aquifers. This paper provides a statistical methodology for the estimation of the relative efficiency of natural attenuation mechanisms. The methodology provides estimates, with associated measures of uncertainty, of the relative efficiency of four types of bio-degradation (oxidation using oxygen as the electron-acceptor, denitrification, iron reduction and sulfate reduction). A data set from Trecate, Italy, is analysed using the methodology. The analysis shows that sulfate is the main cause of hydrocarbon removal on this site. It is also seen that oxidation using oxygen seems to be more preferential than the other reactions, in the sense that this reaction is relatively more efficient than other reactions at locations where the hydrocarbon concentration is low. 相似文献