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1.
A single fracture is usually idealized theoretically as smooth parallel plates, but the real fractures are rough-walled with points of contact. Though relative roughness is considered in quantifying the flow through a single rough fracture (SRF) previously, additional factors such as the distribution of rough elements and bending degree of streamlines should be considered in order to obtain more accurate results. Semiempirical friction factor (f) and discharge per unit width (q) equations are first deduced taking relative roughness, roughness elements distribution and streamline reattachment length into consideration. A horizontal SRF model was then set up and a series of experiments and simulations were performed. Main conclusions are drawn: Recirculation of streamlines arises in the rough element and the intensity of the recirculation increases with the angle from which the streamlines enter into the rough elements and Reynolds number (Re); streamlines are discontinuously distributed when asperity height is large and nonlinear flow occurs; the nonlinearity of the flow increases with the increasing the asperity height and Re; the critical value of related roughness used to judge whether the influence of roughness on water flow through a SRF can be ignored or not should be much lower than 0.033; the revised f and q equations under laminar flow through a SRF are proved to be better when calculating the f and q values.  相似文献   

2.
Multistage fracturing of the horizontal well is recognized as the main stimulation technology for shale gas development. The hydraulic fracture geometry and stimulated reservoir volume (SRV) is interpreted by using the microseismic mapping technology. In this paper, we used a computerized tomography (CT) scanning technique to reveal the fracture geometry created in natural bedding-developed shale (cubic block of 30 cm × 30 cm × 30 cm) by laboratory fracturing. Experimental results show that partially opened bedding planes are helpful in increasing fracture complexity in shale. However, they tend to dominate fracture patterns for vertical stress difference Δσ v  ≤ 6 MPa, which decreases the vertical fracture number, resulting in the minimum SRV. A uniformly distributed complex fracture network requires the induced hydraulic fractures that can connect the pre-existing fractures as well as pulverize the continuum rock mass. In typical shale with a narrow (<0.05 mm) and closed natural fracture system, it is likely to create complex fracture for horizontal stress difference Δσ h  ≤ 6 MPa and simple transverse fracture for Δσ h  ≥ 9 MPa. However, high naturally fractured shale with a wide open natural fracture system (>0.1 mm) does not agree with the rule that low Δσ h is favorable for uniformly creating a complex fracture network in zone. In such case, a moderate Δσ h from 3 to 6 MPa is favorable for both the growth of new hydraulic fractures and the activation of a natural fracture system. Shale bedding, natural fracture, and geostress are objective formation conditions that we cannot change; we can only maximize the fracture complexity by controlling the engineering design for fluid viscosity, flow rate, and well completion type. Variable flow rate fracturing with low-viscosity slickwater fluid of 2.5 mPa s was proved to be an effective treatment to improve the connectivity of induced hydraulic fracture with pre-existing fractures. Moreover, the simultaneous fracturing can effectively reduce the stress difference and increase the fracture number, making it possible to generate a large-scale complex fracture network, even for high Δσ h from 6 MPa to 12 MPa.  相似文献   

3.
As part of our study of the components of the hierarchic quadruple system ADS 11061, we acquired spectroscopic observations of the binary 40 Dra. Echelle spectra showing the separation of the components’ lines were obtained in the spectral range 3700–9200 Å. Effective temperatures and surface gravities were derived for the components from BV photometry and the hydrogen-line profiles. The components of the 40 Dra system have parameters close to T eff a = 6420 K, log g a = 4.17, T eff b = 6300 K, and log g b = 4.20. We find the microturbulence velocity in the component atmospheres to be V t = 2.6 km/s. The abundances of iron, carbon, nitrogen, and oxygen in the atmospheres of both components are estimated to be log N(Fe)a = 7.50, log N(Fe)b = 7.46, log N(C)a = 8.39, log N(C)b = 8.45, log N(N)a = 8.12, log(N)b = 8.15, log N(O)a = 8.77, log N(O)b = 8.74.  相似文献   

4.
We obtained speckle interferometric and spectroscopic observations of the system 41 Dra during its periastron passage in 2001. The components’ lines are resolved in the spectral interval 3700–9200 Å. The observed wavelength dependence of the brightness difference between the components is used to estimate the B-V indices separately for each of the components: B-V = 0.511 for component a and B-V = 0.502 for component b. We derived improved effective temperatures of the components from their B-V values and hydrogen-line profiles. The observations can be described with the parameters for the components T eff a = 6370 K, log ga = 4.05 and T eff b = 6410 K, log gb = 4.20. The iron, carbon, nitrogen, and oxygen abundances in the atmospheres of the components are log N(Fe)a = 7.55, log N(Fe)b = 7.60, log N(C)a = 8.52, log N(C)b = 8.58, log N(N)a = 8.05, log N(N)b = 7.99, log N(O)a = 8.73, log N(O)b = 8.76.  相似文献   

5.
Theoretical analysis, calculations, and comparison with the results of observations in Lake Baikal, Lake Tanganyika, and the World Ocean are performed for the vertical stability E and the Brunt-Väisäla frequency N in the form of N 2 with regard to all components (at the constant temperature T and the salinity S, the common adiabatic form at T, S Const). The adiabatic stability E ad and the Väisäla frequency N in the form of N ad 2 are always positive; at a change from the inverse to the direct temperature stratification, they have deep minimums reaching 10?16 m?1 and 10?15 s?2 and less; the minimums have the form of a special point, a reversal point of the first kind called a “cusp.” The reality of these reversal points is confirmed by the analysis of the investigation procedure, comparison with the results of previous theoretical (Sherstyankin, et al., 2007), and experimental (observations in Baikal, Shimaraev et al., 1994) works. The features of vertical profiles of E ad , E andN ad 2 , N 2, as well as the layers where the Brunt-Väisäla frequency is less than the inertial frequency, are studied. The analysis with regard to all components of the stability E ad and the Brunt-Väisäla frequency N makes a great contribution to understanding of mixing processes in theoretical and experimental investigations; it is valid in all reservoirs of the Earth with inverse and direct temperature stratification, including Lake Baikal, Lake Tanganyika, and the World Ocean.  相似文献   

6.
Transmissivity (T) is one of the most important parameters in groundwater studies, and is generally estimated from pumping tests. T can also be deduced from abundantly available specific-capacity (Q/s) data by using analytical and/or empirical approaches, further upscaled by geostatistical methods. A different, remote sensing based, hydrogeomorphological approach is proposed, to upscale T from point- or well-scale to aquifer-scale, and it is applied to the piedmont alluvial aquifer system of Doon Valley in India. In the first step, Q/s and T data-pairs available from aquifer tests were used to establish an empirical, logarithmic relation. Subsequently, satellite imagery along with available data from published and unpublished maps, literature sources and ground surveys were used to divide the aquifer system into major hydrogeomorphological domains that control the groundwater occurrence and flow. Then, the T data derived from Q/s (using the empirical relation) and that available from pumping tests at well-scale were upscaled to aquifer-scale by averaging the T values within each hydrogeomorphological domain. Such a stratification approach is especially useful in areas where availability of only a few data-pairs of known Q/s and T limit the use of geostatistical techniques. A comparative study of the published empirical relations between Q/s and T in various hydrogeologic settings revealed that the relation obtained for Doon Valley aquifer system is close to that found for a similar alluvial aquifer system in Morocco.  相似文献   

7.
A technique for IR spectroscopic determination of the total nitrogen content N S in the form of A-and B 1-defects is suggested. It provides for the computer processing and decomposition of IR spectra into constituent bands, calculation of the total absorption band area S N and individual areas S A and S B1 and their normalization with respect to the total area of the diamond intrinsic absorption S 0, with the normalization coefficients K S , K A , and K B1 being calculated. Based on the analysis of the IR spectra of 60 octahedral diamond crystals from the Mir and Yubileinaya pipes (Sakha-Yakutiya), the empirical functions N S = 911.85 K S 0.9919 ppm (R 2 = 0.9859), N A = 1185.6 K A 1.1511 ppm (R 2 = 0.8703), and N B1 = 911.85 K S 0.9919 ? 1185.6 K A 1.1511 ppm have been defined.  相似文献   

8.
We analyze the distribution of close binary stars in the orbital semimajor axis—primary mass plane. The reduced spatial density of stars with semimajor axes below 10R⊙ is confirmed. We identify the area in this plane occupied by precursors of W UMa stars, assuming that the driving force causing the components to approach each other is their magnetic stellar wind. This scenario enables us to estimate the rate of formation (0.02/year) and lifetime (108 yr) of W UMa stars. We derive a theoretical estimate of the ratio of the number of blue stragglers, N BS , and of horizontal-branch stars, N HB , in globular clusters based on the hypothesis that all blue stragglers are the result of component mergers in W UMa contact binaries. This ratio is N BS /N HB =0.4, close to the observed value for 62 Galactic globular clusters. We discuss possible reasons for the considerable dispersion of the observed estimates of this ratio for different clusters in our Galaxy.  相似文献   

9.
The strong adaptability of Broussonetia papyrifera (L.) Vent. to low phosphorus (P) conditions can be attributed to the large amount of root-exuded organic acids and the high efficiency of P extraction. However, microelement contents are influenced by low-P stress, and their effects on the photosynthetic capability of B. papyrifera remain unknown. In this study, we investigated the effects of low-P treatment on net photosynthetic rate (P N); chlorophyll a fluorescence (ChlF) characteristics; and Fe, Mn, Cu, and Zn contents of B. papyrifera and Morus alba L. seedlings. Results show that B. papyrifera exhibited better photosynthetic capability under moderate P deficiency (0.125, 0.063, and 0.031 mmol/L P treatments), whereas the photosynthetic capability of M. alba decreased under moderate and severe P deficiency (0.016 and 0 mmol/L P treatments). Under moderate P deficiency, the decrease in Cu and Zn contents in B. papyrifera was lower than that in M. alba. Under severe P deficiency, a considerable decrease of photosynthetic capability in B. papyrifera and M. alba was associated with low Cu and Zn contents. The P N of the two Moraceae species exhibited a better correlation with Cu and Zn contents than with Fe or Mn content. P deficiency could not only decrease cyclic photophorylation and photosynthetic efficiency, but could also affect the stability of thylakoid membrane structure and electron transport efficiency by influencing the contents of Cu or Zn, thereby affecting photosynthesis.  相似文献   

10.
For many years, information on the solar mean magnetic field (SMMF) of the Sun—an important heliophysical and astrophysical parameter—was restricted to magnetographic measurements in only one spectral line, FeI λ525.02 nm. More informative observations of the Stokes-meter parameters of the SMMF were first initiated on a regular basis at the Sayan Solar Observatory. The availability of I and V data obtained simultaneously in several spectral lines has made it possible to study fundamentally new physical problems. In this paper, based on a comparison of SMMF observations in several spectral lines, we find high correlations in the data and important systematic differences in the magnetic-field strength B, which we interpret as a manifestation of kilogauss magnetic fields in fine-structure magnetic elements. Results of theoretical modeling of the SMMF strength ratios for the FeI λ525.02 nm-FeI λ524.70 nm and FeI λ630.15 nm-FeI λ630.25 nm lines are presented. The asymmetries of the V profiles of four lines near the FeI λ525.02 nm line are examined; these lines are important diagnostics for studies of small-scale dynamical processes. The Sayan Solar Observatory SMMF measurements are in good consistency with the Wilcox Solar Observatory data for 2003: for a comparison of N = 137 pairs of points in the two data sets, the correlation coefficient ρ is 0.92 for the linear regression between the datasets BWSO = 0.03(±0.05) + 0.93(±0.03)BSSO.  相似文献   

11.
This paper presents a new analytical criterion for brittle failure of rocks and heavily over-consolidated soils. Griffith’s model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith’s criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as half of the critical distance. This fracture criterion is known as the point method, and is part of the theory of critical distances, which is utilised in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, σ 0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, σ c and σ t. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils (σ c/σ t = 3–50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low-confining stresses.  相似文献   

12.
This paper presents side-by-side comparisons of blowcount values for the Texas cone penetration (TCP) test and the standard penetration test (SPT). The comparisons yielded statistically-significant regression models for both coarse-grained soils and fine-grained soils. Consistent with expected trends and published data, the TCP–SPT relationship is nonlinear, with weak to fair correlation strength (R2 = 23–44%). For TCP blowcounts (N60, TCP) varying from 25 to 200 blows/30 cm (1 ft), corresponding SPT blowcounts (N60, SPT) are typically 30–60% lower than N60, TCP in fine-grained soils. Likewise, corresponding N60, SPT blowcounts are 10–70% lower than N60, TCP in coarse-grained soils, all other things being equal. Comparative data were obtained from published sources and from project-specific field research sites used for full-scale deep foundation load tests. The final dataset consisted of 225 test pairs obtained in similar soils and geomaterials, at equivalent depths, with all blowcounts normalized to 30 cm (12 in.) penetration (i.e., blows/30 cm or blows/ft) within the bounds of typical test precision, and corrected to 60% hammer efficiency. The generally weak correlations do not support conversion of N60, TCP to N60, SPT (or vice versa) to compute foundation capacity for final design. But, engineers can certainly get an intuitive feel about site conditions and preliminary foundation capacity by using the correlation equations to translate their knowledge of one test to the other. This study extends previous work by formally comparing and contrasting the similar yet different SPT and TCP test methods in such a way as to make the results useful to users of both tests and to the broader geotechnical engineering community.  相似文献   

13.
The problem of estimating the bearing capacity of massive caisson foundations in frictional soil under combined vertical (N), horizontal (Q) and moment (M) loading is examined numerically by means of three-dimensional finite element analyses. The analysis is performed with due consideration to the foundation’s depth-to-width ratio (D/B), the magnitude of the vertical load and the caisson-soil contact interface conditions. The constitutive law for soil behavior is appropriately validated against experimental results from 1-g small-scale tests, available in the literature. The ultimate limit states are presented in the form of a bearing strength surface in dimensionless and normalized form, while detailed discussion is provided on the physical and geometrical interpretation of the kinematic mechanisms that accompany failure. A generalized closed-form expression for the failure envelope in M–Q–N space is then fitted to the numerical results with use of an appropriately trained artificial neural network. An upper-bound limit equilibrium solution for a certain failure mechanism (designated as the “sliding” mechanism) associated with maximum horizontal bearing capacity is also developed for verification purposes. One of the originalities of the paper lies with respect to the post-failure response of the caissons, where it is shown that the incremental displacement vector is accurately reproduced by assuming normality on the bearing strength surface irrespective of the considered plastic flow rule (associative or non-associative) at the microscale (soil element).  相似文献   

14.
The data on the distribution of elements in the Pb–Zn cross-section of the Gatsirovskaya vein (the Upper Zgid deposit, North Ossetia, Russia) have shown that the spectra of rare-earth elements (REEs) changed significantly in the ore samples during the vein formation. The sharp growth of the LaN/YbN, LaN/NdN, GdN/HoN, and GdN/YbN ratios is confined to the vein intervals, where the maximum amount of ore components is deposited. The comparison of the REE spectra of ores to the characteristics of the spectra of the rocks surrounding the vein and the host rocks suggests that the vein material deposited from the solutions in which the REE ratio changed with time. REE fractionation occurred due to the mobilization of components by hydrothermal solutions during their interaction with the Paleozoic host granites.  相似文献   

15.
Comparisons of the brightness distributions of the white corona observed at distances of several solar radii with solar wind velocities derived from interplanetary-scintillation observations, as well as analyses of solar wind data obtained on spacecraft from December 1994 to June 1995, indicate that the fast solar wind can contain plasma with velocities V ≈ 300–450 km/s, approaching those typical for the slow solar wind that flows in the streamer belt and chains of streamers. At the same time, certain other parameters, first and foremost the plasma density N and ratio T/N 0.5 (where T is the temperature), indicate that these two flows differ considerably. The slow solar wind flowing in the streamer belt and chains displays high densities N > 10 ± 2 cm?3 and low T/N 0.5 < 1.7 × 104 K cm3/2 at the Earth’s orbit. The number of slow solar-wind sources observed in chains can be comparable with the number observed in the belt. The fast solar wind flowing from coronal holes always displays low densities N≤ 8 cm?3 and high T/N 0.5 > 1.7 × 104 K cm3/2. These properties probably indicate different origins of the fast and slow solar winds.  相似文献   

16.
There is a need for research that advances understanding of flow alterations in contemporary watersheds where natural and anthropogenic interactions can confound mitigation efforts. Event-based flow frequency, timing, magnitude, and rate of change were quantified at five-site nested gauging sites in a representative mixed-land-use watershed of the central USA. Statistically independent storms were paired by site (n = 111 × 5 sites) to test for significant differences in event-based rainfall and flow response variables (n = 17) between gauging sites. Increased frequency of small peak flow events (i.e., 64 more events less than 4.0 m3 s?1) was observed at the rural–urban interface of the watershed. Differences in flow response were apparent during drier periods when small rainfall events resulted in increased flow response at urban sites in the lower reaches. Relationships between rainfall and peak flow were stronger with decreased pasture/crop land use and increased urban land use by approximately 20%. Event-based total rainfall explained 40–68% of the variance in peak flow (p < 0.001). Coefficients of determination (r2) were negatively correlated with pasture/crop land use (r2 = 0.92; p = 0.007; n = 5) and positively correlated with urban land use (r2 = 0.90; p = 0.008; n = 5). Significant differences in flow metrics were observed between rural and urban sites (p < 0.05; n = 111) that were not explained by differences in rainfall variables and drainage area. An urban influence on flow timing was observed using median time lag to peak centroid and time of maximum precipitation to peak flow. Results highlight the need to establish manageable flow targets in rapidly urbanizing mixed-land-use watersheds.  相似文献   

17.
Debris flow density determined by grain composition   总被引：1，自引：1，他引：0  
Density is one of the most important parameters of debris flows. Because observing an active debris flow is very difficult, finding a method to estimate debris flow density is urgently needed for disaster mitigation engineering. This paper proposes an effective empirical equation in terms of grain size distribution (GSD) parameters based on observations in Jiangjia Gully, Yunnan Province, China. We found that the GSD follows P(D) = KD -μ exp(? D/Dc), with μ and Dc representing the fine and coarse grains, respectively. In particular, μ is associated with some characteristic porosity of soil in the natural state and increases with increased porosity. Dc characterizes the grain size range of the flow and increases with the grain concentration. Studies show that flow density is related to both parameters in power law. Here, we propose an empirical equation for estimating flow density: ρ = 1.26μ -0.132 + 0.049Dc0.443, which provides not only an estimation of the density for a flow, but also describes the variation in density with the GSD of material composition; this provides important information related to the design of debris flow engineering structures.  相似文献   

18.
A criterion for the choice of optimal softening length ε for the potential and the choice of time step dt for N-body simulations of a collisionless stellar system is analyzed. Plummer and Hernquist spheres are used as models to analyze how changes in various parameters of an initially equilibrium stable model depend on ε and dt. These dependences are used to derive a criterion for choosing ε and dt. The resulting criterion is compared to Merritt’s criterion for choosing the softening length, which is based on minimizing the mean irregular force acting on a particle with unit mass. Our criterion for choosing ε and dt indicate that ε must be a factor of 1.5–2 smaller than the mean distance between particles in the densest regions to be resolved. The time step must always be adjusted to the chosen ε (the particle must, on average, travel a distance smaller than 0.5 ε during one time step). An algorithm for solving N-body problems with adaptive variations of the softening length is discussed in connection with the task of choosing ε, but is found not to be promising.  相似文献   

19.
For feasibility studies and preliminary design estimates, field measurements of shear wave velocity, V s, may not be economically adequate and empirical correlations between V s and more available penetration measurements such as cone penetration test, CPT, data turn out to be potentially valuable at least for initial evaluation of the small-strain stiffness of soils. These types of correlations between geophysical (Vs) and geotechnical (N-SPT, q c-CPT) measurements are also of utmost importance where a great precision in the calculation of the deposit response is required such as in liquefaction evaluation or earthquake ground response analyses. In this study, the stress-normalized shear wave velocity V s1 (in m/s) is defined as statistical functions of the normalized dimensionless resistance, Q tn-CPT, and the mean effective diameter, D 50 (in mm), using a data set of different uncemented soils of Holocene age accumulated at various sites in North America, Europe, and Asia. The V s1–Q tn data exhibit different trends with respect to grain sizes. For soils with mean grain size (D 50) < 0.2 mm, the V s1/Q tn 0.25 ratio undergoes a significant reduction with the increase in D 50 of the soil. This trend is completely reversed with further increase in D 50 (D 50 > 0.2 mm). These results corroborate earlier results that stressed the use of different CPT-based correlations with different soil types, and those emphasized the need to impose particle-size limits on the validity of the majority of available correlations.  相似文献   

20.
Excellently preserved organic-walled and silicified microfossils are first found in the Lower Riphean Ust-Il’ya and Kotuikan formations of the Billyakh Group in the northern slope of the Anabar Uplift (the Fomich River basin). Similar assemblages were previously known only from sections located southward in the Kotuikan River basin, and taxonomic composition of organic-walled microbiotas from the Ust-Il’ya and Kotuikan formations became a corner stone in competitive microphytological models that are based on different approaches. In their composition and general appearance, microbiotas from the Kotuikan and Ust-Il’ya formations in the Fomich River basin are similar to microbiotas reported from the Kotuikan River basin, although northern sections of the above formations characterize deeper sedimentation settings than in localities known before. The Ust-Il’ya and Kotuikan assemblages of organic-walled microfossils include sphaeromorphic Chuaria circularis and Leiosphaeridia, two-layer vesicles the genus Simia, filamentous Plicatidium and Taenitrichoides, and some others. The silicified microbiota from the lower Kotuikan Subformation is largely composed of akinetes of Anabaena-like cyanobacteria Archaeoellipsoides, spherical Myxococcoides grandis, and short trichomes Filiconstrictosus and Orculiphycus representing initial germination stages of Anabaena-like cyanobacterial spores. Acanthomorphic acritarchs known from lithology-similar Lower and Middle Riphean (Mesoproterozoic) formations of Australia and China have not been observed in the Ust-Il’ya and Kotuikan microbiotas, which are probably of older age. The found microbiotas outline substantially wider distribution area of organic-walled and silicified microfossils, supplement microphytological characteristics of Riphean sediments in the Anabar Uplift, provide information on taxonomic composition of microbiotas from a wider spectrum of facies, and specify relationships between Early and Middle Riphean assemblages of microorganisms from different continents.  相似文献   

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