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1.
Time–space fractional governing equations of transient groundwater flow in confined aquifers: Numerical investigation 下载免费PDF全文
In order to model non‐Fickian transport behaviour in groundwater aquifers, various forms of the time–space fractional advection–dispersion equation have been developed and used by several researchers in the last decade. The solute transport in groundwater aquifers in fractional time–space takes place by means of an underlying groundwater flow field. However, the governing equations for such groundwater flow in fractional time–space are yet to be developed in a comprehensive framework. In this study, a finite difference numerical scheme based on Caputo fractional derivative is proposed to investigate the properties of a newly developed time–space fractional governing equations of transient groundwater flow in confined aquifers in terms of the time–space fractional mass conservation equation and the time–space fractional water flux equation. Here, we apply these time–space fractional governing equations numerically to transient groundwater flow in a confined aquifer for different boundary conditions to explore their behaviour in modelling groundwater flow in fractional time–space. The numerical results demonstrate that the proposed time–space fractional governing equation for groundwater flow in confined aquifers may provide a new perspective on modelling groundwater flow and on interpreting the dynamics of groundwater level fluctuations. Additionally, the numerical results may imply that the newly derived fractional groundwater governing equation may help explain the observed heavy‐tailed solute transport behaviour in groundwater flow by incorporating nonlocal or long‐range dependence of the underlying groundwater flow field. 相似文献
2.
A constitutive model that captures the material behavior under a wide range of loading conditions is essential for simulating complex boundary value problems. In recent years, some attempts have been made to develop constitutive models for finite element analysis using self‐learning simulation (SelfSim). Self‐learning simulation is an inverse analysis technique that extracts material behavior from some boundary measurements (eg, load and displacement). In the heart of the self‐learning framework is a neural network which is used to train and develop a constitutive model that represents the material behavior. It is generally known that neural networks suffer from a number of drawbacks. This paper utilizes evolutionary polynomial regression (EPR) in the framework of SelfSim within an automation process which is coded in Matlab environment. EPR is a hybrid data mining technique that uses a combination of a genetic algorithm and the least square method to search for mathematical equations to represent the behavior of a system. Two strategies of material modeling have been considered in the SelfSim‐based finite element analysis. These include a total stress‐strain strategy applied to analysis of a truss structure using synthetic measurement data and an incremental stress‐strain strategy applied to simulation of triaxial tests using experimental data. The results show that effective and accurate constitutive models can be developed from the proposed EPR‐based self‐learning finite element method. The EPR‐based self‐learning FEM can provide accurate predictions to engineering problems. The main advantages of using EPR over neural network are highlighted. 相似文献
3.
The cosmological, astrophysical, and nucleocosmochronological methods for estimating the age of the universe and the corresponding uncertainties are comparatively studied in the present paper. We are led to the conclusion that the new measurements of cosmological parameters, and the recent estimates of the age of globular clusters have led to the gradual disappearance of the age problem from the arena of modern cosmology. 相似文献
4.
5.
SHRIMP zircon dating and Sm/Nd isotopic investigations of Neoproterozoic granitoids, Eastern Desert, Egypt 总被引:2,自引:0,他引:2
Ewais M.M. Moussa Robert J. Stern William I. Manton Kamal A. Ali 《Precambrian Research》2008,160(3-4):341-356
There is an increasing evidence for the involvement of pre-Neoproterozoic zircons in the Arabian–Nubian Shield, a Neoproterozoic crustal tract that is generally regarded to be juvenile. The source and significance of these xenocrystic zircons are not clear. In an effort to better understand this problem, older and younger granitoids from the Egyptian basement complex were analyzed for chemical composition, SHRIMP U–Pb zircon ages, and Sm–Nd isotopic compositions. Geochemically, the older granitoids are metaluminous and exhibit characteristics of I-type granites and most likely formed in a convergent margin (arc) tectonic environment. On the other hand, the younger granites are peraluminous and exhibit the characteristics of A-type granites; these are post-collisional granites. The U–Pb SHRIMP dating of zircons revealed the ages of magmatic crystallization as well as the presence of slightly older, presumably inherited zircon grains. The age determined for the older granodiorite is 652.5 ± 2.6 Ma, whereas the younger granitoids are 595–605 Ma. Xenocrystic zircons are found in most of the younger granitoid samples; the xenocrystic grains are all Neoproterozoic, but fall into three age ranges that correspond to the ages of other Eastern Desert igneous rocks, viz. 710–690, 675–650 and 635–610 Ma. The analyzed granitoids have (+3.8 to +6.5) and crystallization ages, which confirm previous indications that the Arabian–Nubian Shield is juvenile Neoproterozoic crust. These results nevertheless indicate that older Neoproterozoic crust contributed to the formation of especially the younger granite magmas. 相似文献
6.
Karst aquifers represent important water resources in many parts of the world. Unfortunately, karst aquifers are characterised
by high contamination risks. This paper presents a travel time based method for the estimation of karst groundwater vulnerability.
It considers (1) physics-based lateral flow within the uppermost weathered zone (epikarst) in a limestone-dominated region
and (2) high velocities of vertical infiltration at discrete infiltration points (e.g. sinkholes) or lines (e.g. dry valleys,
faults). Consequently, the Transit Time Method honours the actual flow path within the unsaturated zone of a karst aquifer
system. A test site in Northern Jordan was chosen for the demonstration of the assessment technique, i.e. the catchment area
of the Qunayyah Spring north of the capital Amman. The results demonstrate that zones of highest vulnerability lie within
valleys and nearby main fault zones. It also reveals that regions, categorised as protected areas by other methods due to
thick unsaturated zones, contribute to a major degree to the total risk. 相似文献
7.
The Upper Cretaceous and Paleocene Gottero Sandstone was deposited as a small deep-sea fan on ophiolitic crust in a trench-slope basin. It was thrust northeastward as an allochthonous sheet in Early and Middle Cenozoic time. The Gottero, as thick as 1500 m, was probably derived from erosion of Hercynian granites and associated metamorphic rocks in northern Corsica. Outcrops of inner-fan channel, middle-fan channel and interchannel, outer-fan lobe, fan-fringe, and basin-plain facies associations indicate that the depositional model of Mutti and Ricci Lucchi for mixed-sediment deep-sea fans can be used. The original fan had a radius of 30 to 50 km. 相似文献
8.
This paper presents the results of a numerical performance analysis to demonstrate the worthiness of a recently patented new concept propulsor, the so-called “thrust-balanced propeller (TBP)”. The main advantage of this unconventional propulsor is its inherent ability to reduce the unsteady effect of blade forces and moments when it is operating in a non-uniform wake flow. The propulsor comprises a pair of diametrically opposed blades that are connected to one another and mounted so as to be rotatable together through a limited angle about their spindle axis. A quasi-hydrodynamic approach is described and applied to perform the numerical analysis using a state-of-the-art lifting surface procedure for conventional propellers. Performance comparisons with a conventional fixed-pitch propeller are made for the blade forces and moments, efficiency, cavitation extents and fluctuating hull pressures. Bearing in mind the quasi-static nature of the analyses, the results present favourable performance characteristics for the thrust-balanced propeller and support the worthiness of the concept. However, the concept needs to be proved through physical model tests, which are planned to take in a cavitation tunnel. 相似文献
9.
A giant three-stage submarine slide off Norway 总被引:8,自引:0,他引:8
Tom Bugge Stein Befring Robert H. Belderson Tor Eidvin Eystein Jansen Neil H. Kenyon Hans Holtedahl Hans Petter Sejrup 《Geo-Marine Letters》1987,7(4):191-198
One of the largest submarine slides known, The Storegga Slide, is located on the Norwegian continental margin. The slide is up to 450 m thick and has a total volume of about 5,600 km3. The headwall of the slide scar is 290 km long and the total run-out distance is about 800 km. The slide involved sediments of Quaternary to Early Tertiary age and occurred in three stages. Earthquakes combined with decomposition of gas hydrates are believed to be the main triggering agents for the slides. The first slide event is tentatively dated to be about 30,000 to 50,000 years B.P. and the two last major events are dated to be at 6,000 to 8,000 years B.P. 相似文献
10.