共查询到20条相似文献，搜索用时 297 毫秒
1.
Dr. Adrian E. Scheidegger 《Pure and Applied Geophysics》1955,30(1):17-26
Summary The study of fluid flow in the ground is based upon the physics of flow through porous media. The author has recently proposed a theory (2) of such flow based upon the statistics of disordered phenomena which, however, was applicable to a special type of flow only. In the present paper, the earlier theory is developed into a general theory applicable to any type of microscopic flow equation. It is shown that the qualitative analogy which is observed between the equations of flow through porous media and the equations of flow through capillaries can be logically explained without the assumption of capillaric models. Thus, a theorem is proven stating that the flow through porous media is described by the superposition of two effects: firstly, one corresponding to the average flow through a set of small channels, and secondly, a dispersivity effect. Finally, the results are applied to a variety of flow equations such as laminar flow, turbulent flow, and molecular streaming, all of which may occur in groundwater flow.Published by permission of the Deputy Minister Department of Mines and Technical Surveys, Ottawa, Canada. 相似文献
2.
Peter F. Germann 《水文研究》2018,32(9):1166-1172
Preferential flow, a term that includes macropore flow, non‐equilibrium flow, and finger flow, stands in well known conflict with Richards' ( 1931 ) capillary flow. Acoustic velocity experiments demonstrate that preferential flow moves independently from, faster than, and before capillary flow during gravity‐driven infiltration. Viscous flow in permeable media is briefly introduced to the point where Richards' ( 1931 ) particular treatment of viscosity turns out as the hydro‐mechanical bifurcation from general laminar flow. Preferential flow is expected during significant infiltration, however, spatio‐temporarily limited according to the viscous‐flow regime. Two ways of delineating capillary flow from viscous flow reveal minimum path widths of preferential flow in the range of about 20 μm. 相似文献
3.
We introduce a 3D model for near-vent channelized lava flows. We assume the lava to be an isothermal Newtonian liquid flowing
in a rectangular channel down a constant slope. The flow velocity is calculated with an analytical steady-state solution of
the Navier-Stokes equation. The surface velocity and the flow rate are calculated as functions of the flow thickness for different
flow widths, and the results are compared with those of a 2D model. For typical Etna lava flow parameters, the influence of
levees on the flow dynamics is significant when the flow width is less than 25 m. The model predicts the volume flow rate
corresponding to the surface velocity, taking into account that both depend on flow thickness. The effusion rate is a critical
parameter to evaluate lava flow hazard. We propose a model to calculate the effusion rate given the lava flow width, the topograhic
slope, the lava density, the surface flow velocity, and either the lava viscosity or the flow thickness.
Received: 20 January 1998 / Accepted: 8 January 1999 相似文献
4.
Jianzhi NIU Xinxiao YU Zhiqiang ZHANG Yutao ZHAO 《国际泥沙研究》2007,22(4):292-303
Preferential flow is the ordinary phenomenon of rapid and non-equilibrium transport of water and solutes occurring in most soil. It causes latent pollution of ground and surface waters and affects runoff yield and flow concentration. This paper studies preferential flow for a dark coniferous ecosystem in the upper reach area of the Yangtze River, establishes a classification for the preferential flow and discusses types of preferential flow with a soil column experiment using a homemade apparatus and dye-tracer analysis. The preferential flow is mainly unsaturated gravitational flow in the upper layer of the slope deposit for mature forest soil, which is dominated by a wetness front, and the flow gradually transforms to macroporous flow as the soil layer deepens. The observed preferential flow in the young, middle-aged and over-mature forests that have grown on glacial lateral moraines is macroporous flow. The purpose of this research is to analyze systemically the behavior of soil water movement for a dark coniferous forest ecosystem in the upper reach area of the Yangtze River and to provide a theoretical basis for effective watershed management. 相似文献
5.
Physics-based distributed models for simulating flow in karst systems are generally based on the discrete–continuum approach in which the flow in the three-dimensional fractured limestone matrix continuum is coupled with the flow in discrete one-dimensional conduits. In this study we present a newly designed discrete–continuum model for simulating flow in karst systems. We use a flexible spatial discretization such that complicated conduit networks can be incorporated. Turbulent conduit flow and turbulent surface flow are described by the diffusion wave equation whereas laminar variably saturated flow in the matrix is described by the Richards equation. Transients between free-surface and pressurized conduit flow are handled by changing the capacity term of the conduit flow equation. This new approach has the advantage that the transients in mixed conduit flow regimes can be handled without the Preissmann slot approach. Conduit–matrix coupling is based on the Peaceman’s well-index such that simulated exchange fluxes across the conduit–matrix interface are less sensitive to the spatial discretization. Coupling with the surface flow domain is based on numerical techniques commonly used in surface–subsurface models and storm water drainage models. Robust algorithms are used to simulate the non-linear flow processes in a coupled fashion. The model is verified and illustrated with simulation examples. 相似文献
6.
《国际泥沙研究》1999,(2)
IINTRODUCTIONWhileriverflowsareusuallydeepandturbulent,overlandflowisextremelyshallowandcanbelaminar,transitionalandturbulent.Becauseoftheshallownessoftheflolw,overlandflowhydraulicsisgreatlyaffectedbysurfaceroughness,raindropimpact,andinthecaseoflaminarflow,flui(Iviscosity.Theinitiationofsedimentmovementinoverlandflowisthereforeexpectedtodifferfromthatinriverflows.InriverstUdies,bedshearStressgbhastraditionallybeenusedtocharacterizethecriticalflowconditionatwhichsedimentbeginstomove.At… 相似文献
7.
Assessing the digital filter method for base flow estimation in glacier melt dominated basins 
下载免费PDF全文
下载免费PDF全文 Base flow is an important component of streamflow. Although the simple digital filter method is widely used for base flow separation, the applicability in alpine rivers mainly dominated by glacier melt has not been described in detail. To assess and improve the performance of base flow estimates using the filter method for catchments dominated by glacier melt, the enhanced Soil Water Assessment Tool (SWAT) is used to obtain the estimates of streamflow and base flow for three catchments with different glacier melt contribution in arid and cold Northwestern China. The digital filter is then applied to the simulated streamflow to separate base flow and assess how well the base flow by the filter method matches these obtained using the SWAT model. In order to obtain the best match between the base flow by the filter method and those using the SWAT model, the linear regression model is used to estimate the relation between the filtered base flow and the glacier melt. It was found that the filtered base flow was matched well with base flow using the SWAT model during the low‐flow period. However, the base flow based on the digital filter method was overestimated during the high‐flow period, especially for the Manas River and Kumarik River. The base flow indexes by the digital filter estimates were 2.9%, 33.3% and 100% larger than those of the model method for the Gongnaisi River, Manas River and Kumarik River, respectively. The differences are larger with bigger glacier melt contribution. The performance of the digital filter is affected by the glacier melt, and it can be improved significantly by the combination of filtered base flow and the glacier melt. The base flow indexes by the improved filter are 1.5%, 4.4% and 10.7% larger than those of the model method for the Gongnaisi River, Manas River and Kumarik River, respectively. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
8.
A miniaturized flume experiment was carried out to measure impact forces of viscous debris flow. The flow depth (7.2–11.2 cm), velocity (2.4–5.2 m/s) and impact force were recorded during the experiment. The impact process of debris flow can be divided into three phases by analyzing the variation of impact signals and flow regime. The three phases are the sudden strong impact of the debris flow head, continuous dynamic pressure of the body and slight static pressure of the tail. The variation of impact process is consistent with the change in the flow regime. The head has strong–rapid impact pressure, which is shown as a turbulent‐type flow; the body approximates to steady laminar flow. Accordingly, the process of debris flows hitting structures was simplified to a triangle shape, ignoring the pressure of the tail. In order to study the distribution of the debris flow impact force at different depths and variation of the impact process over time, the impact signals of slurry and coarse particles were separated from the original signals using wavelet analysis. The slurry's dynamic pressure signal appears to be a smooth curve, and the peak pressure is 12–34 kPa when the debris flow head hits the sensors, which is about 1.54 ± 0.36 times the continuous dynamic pressure of the debris flow body. The limit of application of the empirical parameter α in the hydraulic formula was also noted. We introduced the power function relationship of α and the Froude number of debris flows, and proposed a universal model for calculating dynamic pressure. The impact pressure of large particles has the characteristic of randomness. The mean frequency of large particles impacting the sensor is 210 ± 50–287 ± 29 times per second, and it is 336 ± 114–490 ± 69 times per second for the debris flow head, which is greater than that in the debris flow body. Peak impact pressure of particles at different flow depths is 40–160 kPa, which is 3.2 ± 1.5 times the impact pressure of the slurry at the bottom of the flow, 3.1 ± 0.9 times the flow in the middle, and 3.3 ± 0.9 times the flow at the surface. The differences in impact frequency indicate that most of the large particles concentrate in the debris flow head, and the number of particles in the debris flow head increases with height. This research supports the study of solid–liquid two phase flow mechanisms, and helps engineering design and risk assessment in debris flow prone areas. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
9.
10.
Vittorio Di Federico Marco Pinelli Rita Ugarelli 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(7):1067-1076
An understanding of the interplay between non-Newtonian effects in porous media flow and field-scale domain heterogeneity
is of great importance in several engineering and geological applications. Here we present a simplified approach to the derivation
of an effective permeability for flow of a purely viscous power–law fluid with flow behavior index n in a randomly heterogeneous porous domain subject to a uniform pressure gradient. A standard form of the flow law generalizing
the Darcy’s law to non-Newtonian fluids is adopted, with the permeability coefficient being the only source of randomness.
The natural logarithm of the permeability is considered a spatially homogeneous and correlated Gaussian random field. Under
the ergodic hypothesis, an effective permeability is first derived for two limit 1-D flow geometries: flow parallel to permeability
variation (serial-type layers), and flow transverse to permeability variation (parallel-type layers). The effective permeability
of a 2-D or 3-D isotropic domain is conjectured to be a power average of 1-D results, generalizing results valid for Newtonian
fluids under the validity of Darcy’s law; the conjecture is validated comparing our results with previous literature findings.
The conjecture is then extended, allowing the exponents of the power averaging to be functions of the flow behavior index.
For Newtonian flow, novel expressions for the effective permeability reduce to those derived in the past. The effective permeability
is shown to be a function of flow dimensionality, domain heterogeneity, and flow behavior index. The impact of heterogeneity
is significant, especially for shear-thinning fluids with a low flow behavior index, which tend to exhibit channeling behavior. 相似文献
11.
首先以Lorenz混沌方程产生的非线性时间序列为例,讨论了在不同时间序列长度下各种延迟时间算法对噪声的适用性.研究发现,采用C_C算法计算延迟时间的鲁棒性强.在此基础上,给出了垂直上升管中气水两相流电导波动信号混沌表征结果,发现在较低水相表观速度时,随着气相表观速度增加,泡状流及混状流动力学特性变得愈加复杂,而段塞流动力学特性受液相表观速度影响较大;在较高水相表观速度时,随着气相表观速度增加,当流型从泡状流向段塞流转变时,气液两相流动力学特性变得相对简单.但是,由于受液相湍流作用影响,段塞流的动力学特性表现出了涨落现象,呈现不稳定性,当流型从段塞流向混状流转变时,气液两相流动力学特性则变得愈加复杂.研究结果表明：基于电导波动信号的混沌分析可以较好地表征气液两相流流型变化,是理解流型转变机理及其动力学演变特性的有用工具. 相似文献
12.
A generalized discrete-continuum model is developed to simulate ground water flow in the karst aquifers of North China. The model is a hybrid numerical flow model, which takes into account both quick conduit flow and diffusive fissure flow. The conduit flow is represented by a discrete network model, and the fissure flow is modeled by a continuum approach. The developed model strongly emphasizes the function of the conduits in the flow fields. They control the general drainage pattern, as demonstrated in the simulation of a complex karst aquifer in North China. The model reproduces reasonably well the flow field in response to an unanticipated discharge of ground water from the karst aquifer into an underground mine based on the aquifer parameters that are manually calibrated from a multiple-well pumping test. Sensitivity of the model to the aquifer parameters was evaluated in the context of the case study. 相似文献
13.
The movement of bedload in subcritical flow produces additional roughness as compared to flow in a rigid bed. The magnitude of this bed load roughness is proportional to the thickness of the sediment layer moving along the bed, the particle size and the sediment concentration. In a supercritical flow, however, further resistance is expected due to the momentum absorption by the high flow velocity. In this study the effect of sediment movement on the flow resistance in supercritical flow was experimentally investigated. The experiments included flows over smooth and rough beds carrying sediment of mean diameters D50=2.80, 5.42 and 7.06 mm in a rigid rectangular channel. The results show that the sediment transport may increase the friction factor by up to 90% and 60% in smooth and rough beds, respectively. Bedload extracts its momentum from the flow, which causes a reduction of near bed flow velocity and steeper velocity gradient near the bed resulting in an increase in shear velocity as well as in roughness height. The increase in friction factor is directly related to bedload concentration and particle size. 相似文献
14.
许多证据表明缓慢的水动力条件是水华暴发的重要诱因,尽管以临界流速和水体置换为基础的流量管理实践在水华控制中已见成效,但受限于水动力对藻类生长小生境的干扰机制尚不明晰,长期的流量管理实践效果并不理想.在长期野外观测、围隔实验和室内模拟等一系列研究的基础上,以现有水动力对藻类影响机制的讨论为依据,从细胞学角度提出了水动力对藻类生长影响的3种不同的概念机制,即低强度的水力扰动导致藻细胞外扩散层厚度变薄,有利于周边水体向藻细胞输送营养物质,促进藻类生长;中等强度的水力扰动导致藻类营养盐吸收及光合作用能力受损,抑制藻类生长;高强度的水流剪切导致藻细胞壁破损.基于该机制认为流量管理中临界流速应分别从水体置换和细胞学两方面考虑.研究结果可为流量管理中控制藻类水华暴发和维持水体水质的策略提供重要的理论支持. 相似文献
15.
Information flow and controlling in regularization inversion of quantitative remote sensing 总被引：1，自引：0，他引：1
YANG Hua XU Wangli ZHAO Hongrui CHEN Xue & WANG Jindi Research Center for Remote Sensing GIS School of Geography Beijing Normal University State Key Laboratory of Remote Sensing Science Beijing Key Laboratory for Remote Sensing of Environment Digital Cities Beijing China Department of Mathematics Beijing Normal University Beijing China 《中国科学D辑(英文版)》2005,48(1):74-83
In order to minimize uncertainty of the inversed parameters to the largest extent by making full use of the limited information in remote sensing data, it is necessary to understand what the information flow in quantitative remote sensing model inversion is, thus control the information flow. Aiming at this, the paper takes the linear kernel-driven model inversion as an example. At first, the information flow in different inversion methods is calculated and analyzed, then the effect of information flow controlled by multi-stage inversion strategy is studied, finally, an information matrix based on USM is defined to control information flow in inversion. It shows that using Shannon entropy decrease of the inversed parameters can express information flow more properly. Changing the weight of a priori knowledge in inversion or fixing parameters and partitioning datasets in multi-stage inversion strategy can control information flow. In regularization inversion of remote sensing, information matrix based on 相似文献
16.
IRINA KRASOVSKAIA 《水文科学杂志》2013,58(2):251-264
Abstract A river regime describes the average seasonal behaviour of flow. This seasonal pattern reflects climatic and physiographic conditions in the basin. An inherent characteristic of a flow regime is its stability, i.e. regularity or irregularity of the seasonal pattern. A temperature rise, as predicted by climatic models, might cause changes in the patterns and stability of river flow regimes. Sensitivity of the stability of flow regimes to small fluctuations in temperature (= ± 1°C) is investigated with the help of historical temperature and flow series for Scandinavia. The concept of entropy is utilized for quantification of the stability of the flow regimes conditioned on temperature which also allows forecasting of possible changes in this stability due to changes in temperature. The study shows that the stability of flow regime types with rain or mixed rain and snowmelt sources of flow formation is already sensitive to small changes in temperature, especially concerning flow minima. 相似文献
17.
A unified approach to modeling flows of slightly compressible fluids through naturally fractured media is presented. The unified fractional differential model is derived by combining the flow at micro scale for matrix blocks and macro scale for fractures, using the transient interporosity flow behavior at the interface between matrix blocks and fractures. The derived model is able to unify existing transient interporosity flow models formulated for different shapes of matrix blocks in any medium dimensions. The model is formulated in the form of a fractional order partial differential equation that involves Caputo derivative of order 1/2 with respect to time. Explicit solutions for the unified model are derived for different axisymmetrical spatial domains using Hankel or Hankel–Weber finite or infinite transforms. Comparisons between the predictions of the unified model and those obtained from existing transient interporosity flow models for matrix blocks in the form of slabs, spheres and cylinders are presented. It is shown that the unified fractional derivative model leads to solutions that are very close to those of transient interporosity flow models for fracture-dominant and transitional fracture-to-matrix dominant flow regimes. An analysis of the results of the unified model reveals that the pressure varies linearly with the logarithm of time for different flow regimes, with half slope for the transitional fracture-to-matrix dominant flow regime vs. the fracture and matrix dominant flow regimes. In addition, a new re-scaling that involves the characteristic length in the form of matrix block volume to surface area ratio is derived for the transient interporosity flow models for matrix blocks of different shapes. It is shown that the re-scaled transient interporosity flow models are governed by two dimensionless parameters Θ and Λ compared to only one dimensionless parameter Θ for the unified model. It is shown that the solutions of the transient interporosity flow models for different shapes of matrix blocks are almost identical for the re-scaled variables. Furthermore, the driving parameters for solution behavior are identified based on asymptotic approximations for different flow regimes. It is found that the matrix diffusion and the matrix area-to-volume ratio affect the solution behavior only for the transitional fracture-to-matrix dominant flow regime, that the capacitance ratio affects the solution behavior only for transitional and matrix dominant flow regimes and that the fracture diffusion is involved in all three flow regimes. Similar identification of the driving parameters is also presented in the re-scaled case. 相似文献
18.
不同容重的泥石流淤积厚度计算方法研究 总被引：3，自引：0，他引：3
泥石流的淤积厚度是泥石流灾害评估和防治的最重要的参数之一,但迄今还没有较好的方法计算不同容重的泥石流淤积厚度。本文通过研究泥石流屈服应力的特点,提出了用地区参数和泥石流体积浓度来计算泥石流屈服应力,进而计算泥石流淤积厚度的方法。采用本文方法计算已发生泥石流地区不同容重泥石流的淤积厚度,可以很好地应用于泥石流灾害评估和防治。 相似文献
19.
LinTRODUCTIONANDAIMSTheaimsofthisStUdyaretointroducenewtechniquesforanalysingfloodflowsfromsedimentarrangementmsapproachincorporatestheeffectsofflotvonthedevelopmentofrouglmessontheriverbed,andnot,asismostlythecase,theeffectsofbedroughnessonflow.Differentacsofflows,includingthemaalmumfloodflowarereconsmictedfromfloworientahonsofparticlesoveranentiregravCIbar.DuetOtheddricultiesinvolvedinobtaininglargeparticlesamples,studiesonpAncleOrientationsintheliteratUrearerare.WhilstmoStanalyse… 相似文献
20.
T.SONG Post-Doctoral Fellow School of Civil Structural Engineering Nanyang Technological University Nanyang Avenue Singapore . Presently Civil Engineer Engineering Depatment Technology Division Maritime Port Authority of Singapore. 《国际泥沙研究》1997,(3)
I.INTRODUCTIONBedloadtransportinsteadyuniformopenchannelflowhasbeenextensiVelystudied.Manyoftheformulasdevelopedforthepredictionofbedloadtransportinuniformopen-channelflowcanbebroughtinthefollowingform(ChienandWan,1983);ac=f(O)(l)xvhereacisthedimensionlessparameterofbedloadtranSPortandOisthedimensionlessparameterofflowintensity.TheseparametersaredefinedasfwheregsisthebedloadtranspoftratePerunitwidthindryweight;disthesedimentdiameter,Sisthebedslopeofthechannel;Rbisthehydraulicradiusdue… 相似文献