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1.
ABSTRACT The study presented herein forms part of a wider research project on dispersion prediction in open channel flows which include laboratory, field and numerical investigations. In this paper, a numerical model which uses finite elements in space and finite differences in time for the solution of the convective-dispersion equation is developed and verified. In the model, the dispersion coefficient is considered as a function of time (or distance) during the initial period. It is represented by a modified Fickian type model which has been calibrated by the authors using laboratory data. The numerical model has been used to predict concentration profiles of tracer studies carried out in the laboratory as well as in the field. 相似文献
2.
AbstractThe impact of pollution incidents on rivers and streams may be predicted using mathematical models of solute transport. Practical applications require an analytical or numerical solution to a governing solute mass balance equation together with appropriate values of relevant transport coefficients under the flow conditions of interest. This paper considers two such models, namely those proposed by Fischer and by Singh and Beck, and compares their performances using tracer data from a small stream in Edinburgh, UK. In calibrating the models, information on the magnitudes and the flow rate dependencies of the velocity and the dispersion coefficients was generated. The dispersion coefficient in the stream ranged between 0.1 and 0.9 m2/s for a flow rate range of 13–437 L/s. During calibration it was found that the Singh and Beck model fitted the tracer data a little better than the Fischer model in the majority of cases. In a validation exercise, however, both models gave similarly good predictions of solute transport at three different flow rates. 相似文献
3.
The assumptions and analysis of Part 1 are extended to the three model soil-water profiles having different immobile-water contents up to 0.08 m3 m?3. Concentration profiles in the mobile zone obtained with a constant dispersion coefficient are compared with those calculated with the same dispersion coefficient and no immobile water. The average concentration profiles were calculated from the concentration of the solution in both the mobile and immobile phases. Increasing the immobile-water content decreased and shifted the average concentration profiles further into the soil. The values of the dispersion coefficient calculated with the immobile-water fraction ignored, were found to be water content dependent and many times greater than that of the input dispersion coefficient. 相似文献
4.
Abstract A two-dimensional, nonlinear, time-dependent, non-hydrostatic, anelastic, numerical model is used to assess the effect of condensation on the evolution and structure of gravity waves generated by the passage of a stable, moist stream over topography. Precipation is ignored but water phase changes are taken into account explicitly. The main effect of condensation is to damp the wave intensity and to reduce the wave drag, which can be diminished by as much as 50% compared to its value in dry simulations. This result agrees with some earlier analytical models and some more recent fully compressible numerical models. This model also confirms that the presence of condensation delays the overturning of isentropes, and the formation of the critical layer that accompanies wave-breaking. 相似文献
5.
M. Ioualalen H. Perfettini S. Yauri Condo C. Jimenez H. Tavera 《Pure and Applied Geophysics》2013,170(3):433-451
Following the 2007, August 15th, M w 8.0, Pisco earthquake in central Peru, Sladen et al. (J Geophys Res 115: B02405, 2010) have derived several slip models of this event. They inverted teleseismic data together with geodetic (InSAR) measurements to look for the co-seismic slip distribution on the fault plane, considering those data sets separately or jointly. But how close to the real slip distribution are those inverted slip models? To answer this crucial question, the authors generated some tsunami records based on their slip models and compared them to DART buoys, tsunami records, and available runup data. Such an approach requires a robust and accurate tsunami model (non-linear, dispersive, accurate bathymetry and topography, etc.) otherwise the differences between the data and the model may be attributed to the slip models themselves, though they arise from an incomplete tsunami simulation. The accuracy of a numerical tsunami simulation strongly depends, among others, on two important constraints: (i) A fine computational grid (and thus the bathymetry and topography data sets used) which is not always available, unfortunately, and (ii) a realistic tsunami propagation model including dispersion. Here, we extend Sladen’s work using newly available data, namely a tide gauge record at Callao (Lima harbor) and the Chilean DART buoy record, while considering a complete set of runup data along with a more realistic tsunami numerical that accounts for dispersion, and also considering a fine-resolution computational grid, which is essential. Through these accurate numerical simulations we infer that the InSAR-based model is in better agreement with the tsunami data, studying the case of the Pisco earthquake indicating that geodetic data seems essential to recover the final co-seismic slip distribution on the rupture plane. Slip models based on teleseismic data are unable to describe the observed tsunami, suggesting that a significant amount of co-seismic slip may have been aseismic. Finally, we compute the runup distribution along the central part of the Peruvian coast to better understand the wave amplification/attenuation processes of the tsunami generated by the Pisco earthquake. 相似文献
6.
A macroscopic transport model is developed, following the Taylor shear dispersion analysis procedure, for a 2D laminar shear flow between parallel plates possessing a constant specified concentration. This idealized geometry models flow with contaminant dissolution at pore-scale in a contaminant source zone and flow in a rock fracture with dissolving walls. We upscale a macroscopic transient transport model with effective transport coefficients of mean velocity, macroscopic dispersion, and first-order mass transfer rate. To validate the macroscopic model the mean concentration, covariance, and wall concentration gradient are compared to the results of numerical simulations of the advection–diffusion equation and the Graetz solution. Results indicate that in the presence of local-scale variations and constant concentration boundaries, the upscaled mean velocity and macrodispersion coefficient differ from those of the Taylor–Aris dispersion, and the mass transfer flux described by the first-order mass transfer model is larger than the diffusive mass flux from the constant wall. In addition, the upscaled first-order mass transfer coefficient in the macroscopic model depends only on the plate gap and diffusion coefficient. Therefore, the upscaled first-order mass transfer coefficient is independent of the mean velocity and travel distance, leading to a constant pore-scale Sherwood number of 12. By contrast, the effective Sherwood number determined by the diffusive mass flux is a function of the Peclet number for small Peclet number, and approaches a constant of 10.3 for large Peclet number. 相似文献
7.
Surface-wave tests are based on the solution of an inverse problem for shear-wave velocity profile identification from the experimentally measured dispersion curve. The main criticisms for these testing methodologies are related to the inverse problem solution and arise from the possible equivalence of different shear-wave velocity profiles. In this paper, some implications of solution non-uniqueness for seismic response studies are investigated using both numerical simulations and experimental data. A Monte Carlo approach for the inversion problem has been used to obtain a set of equivalent shear-wave velocity models. This selection is based on a statistical test which takes into account both data uncertainty and model parameterization. This set of solutions (i.e., soil profiles) is then used to evaluate the seismic response with a conventional one-dimensional analysis. It is shown that equivalent profiles with respect to surface-wave testing are equivalent also with respect to site amplification, thus countering the criticism related to inversion uncertainty for the engineering use of surface-wave tests. 相似文献
8.
It has been known for many years that dispersivities increase with solute displacement distance in a subsurface. The increase of dispersivities with solute travel distance results from significant variation in hydraulic properties of porous media and was identified in the literature as scale‐dependent dispersion. In this study, Laplace‐transformed analytical solutions to advection‐dispersion equations in cylindrical coordinates are derived for interpreting a divergent flow tracer test with a constant dispersivity and with a linear scale‐dependent dispersivity. Breakthrough curves obtained using the scale‐dependent dispersivity model are compared to breakthrough curves obtained from the constant dispersivity model to illustrate the salient features of scale‐dependent dispersion in a divergent flow tracer test. The analytical results reveal that the breakthrough curves at the specific location for the constant dispersivity model can produce the same shape as those from the scale‐dependent dispersivity model. This correspondence in curve shape between these two models occurs when the local dispersivity at an observation well in the scale‐dependent dispersivity model is 1·3 times greater than the constant dispersivity in the constant dispersivity model. To confirm this finding, a set of previously reported data is interpreted using both the scale‐dependent dispersivity model and the constant dispersivity model to distinguish the differences in scale dependence of estimated dispersivity from these two models. The analytical result reveals that previously reported dispersivity/distance ratios from the constant dispersivity model should be revised by multiplying these values by a factor of 1·3 for the scale‐dependent dispersion model if the dispersion process is more accurately characterized by scale‐dependent dispersion. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
9.
Benoit Cushman-Roisin 《地球物理与天体物理流体动力学》2013,107(1-2):61-91
Abstract A new non-linear model of mixing and convection based on a modelling of two buoyant interacting fluids is applied to penetrative convection in the upper ocean due to surface cooling. In view of simple algebra, the model is one-dimensional. Dissipation is included, but no mean shear is present. A non-similar analytical solution is found in the case of a well-mixed layer bounded below by a sharp thermocline treated as a boundary layer. This solution is valid if the Richardson number, R i , defined as the ratio of the total mixed-layer buoyancy to a characteristic rms vertical velocity, is much greater than unity. The model predicts a deepening rate proportional to R i ?3/4. The thermocline remains of constant thickness, and the ratio thermocline thickness to mixed-layer depth decreases as R i ?3/4 as the mixed layer deepens. If the surface flux is constant, the mixed-layer depth increases with time as t ½. The vertical structure throughout the mixed layer and thermocline is given by the analytical solution, and vertical profiles of mean temperature and vertical fluxes are plotted. Computed profiles and available laboratory data agree remarkably well. Moreover, the accuracy of the simple analytical results presented here is comparable to that of sophisticated turbulence numerical models. 相似文献
10.
Abstract The study of sediment load is important for its implications to the environment and water resources engineering. Four models were considered in the study of suspended sediment concentration prediction: artificial neural networks (ANNs), neuro-fuzzy model (NF), conjunction of wavelet analysis and neuro-fuzzy (WNF) model, and the conventional sediment rating curve (SRC) method. Using data from a US Geological Survey gauging station, the suspended sediment concentration predicted by the WNF model was in satisfactory agreement with the measured data. Also the proposed WNF model generated reasonable predictions for the extreme values. The cumulative suspended sediment load estimated by this model was much higher than that predicted by the other models, and is close to the observed data. However, in the current modelling, the ANN, NF and SRC models underestimated sediment load. The WNF model was successful in reproducing the hysteresis phenomenon, but the SRC method was not able to model this behaviour. In general, the results showed that the NF model performed better than the ANN and SRC models. Citation Mirbagheri, S. A., Nourani, V., Rajaee, T. & Alikhani, A. (2010) Neuro-fuzzy models employing wavelet analysis for suspended sediment concentration prediction in rivers. Hydrol. Sci. J. 55(7), 1175–1189. 相似文献
11.
《水文科学杂志》2013,58(1):183-197
Abstract Abstract Correct estimation of the sediment volume carried by a river is important with respect to pollution, channel navigability, reservoir filling, hydroelectric equipment longevity, fish habitat, river aesthetics and scientific interests. However, conventional sediment rating curves are not able to provide sufficiently accurate results. In this study, models incorporating fuzzy logic are developed as a superior alternative to the sediment rating curve technique for determining the daily suspended sediment concentration for a given river cross-section. This study provides forecasting benchmarks for sediment concentration prediction in the form of a numerical and graphical comparison between fuzzy and rating curve models. Benchmarking was based on a five-year period of continuous streamflow and sediment concentration data from the Quebrada Blanca Station operated by the United States Geological Survey (USGS). Nine different fuzzy models were developed to estimate sediment concentration from streamflow. Each fuzzy model has a different number of membership functions. The parameters of the membership functions were found using a differential evolution algorithm. The benchmark results showed that the fuzzy models were able to produce much better results than rating curve models for the same data inputs. 相似文献
12.
The air pollution induced by urban traffic has addressed much attention in recent years as the rapid urbanization and the fast increase of vehicle number in urban area. In this study, we attempted to investigate the dispersion behavior of exhaust gas from exhaust pipe using computational fluid dynamics approach. The time-averaged CO2 concentration, velocity and temperature profiles along the centerline of the vehicular exhaust plume were simulated in varied situations. The computational results showed good agreement with the experimental data and the numerical model was validated to be an effective method to investigate the pollutant dispersion in the near-wake region of a vehicle. Based on it, the numerical simulations were extended to explore the impacts of the emit concentration, the emit direction and the incoming velocity on the flow dynamics and CO2 dispersion. The outputs indicated that the emit concentration could change the pollution level in the near-wake region of a vehicle and the emit direction may alter the spreading direction of the vehicular exhaust plume. The incoming velocity was found to have dominant influence on the dispersion of pollutant due to induced vortices and turbulence behind the vehicle. These findings are expected to provide important insight into evaluating the design and control strategies for alleviating mobile source emissions. 相似文献
13.
《水文科学杂志》2013,58(3)
Abstract Two multi-tracer tests were performed in fissured rocks accessible in underground laboratories to examine a new fluorescent dye: pyrene-1,3,6,8-tetra sulphonic acid (PTS). The first test was carried out at the Lindau Rock Laboratory (LRL), Germany, in a highly permeable ore dike, and the second, at the Grimsel Test Site (GTS), Switzerland, in a heterogeneous granite fault zone (AU 126). At the LRL new tracer was injected together with uranine in a convergent flow field (monopole test), and slightly different tracer breakthrough curves were observed according to different diffusion coefficients of both tracers. The matrix porosity calculated with the aid of the one-dimensional (1-D) single-fissure dispersion model (SFDM) agrees well with that found in earlier tracer tests and with measurements performed on core samples. At the GTS, the PTS tracer was applied together with pyranine in two-well injection–withdrawal (dipole) tests. Both tracers yielded identical tracer concentration curves, which confirm their conservative behaviour. Mathematical simulations performed with the aid of a 3-D numerical model (FRAC3DVS) yielded equally good fits for different sets of parameters, independent of whether matrix porosity was included or neglected. That lack of unique solution and the difficulty in observing the influence of matrix diffusion result from a wide distribution of the transit times of particular streamlines, which is characteristic for injection–withdrawal tests. However, both tracer tests clearly indicated that the new tracer (PTS) behaves conservatively at high pH values and can be successfully used for groundwater labelling. 相似文献
14.
ABSTRACTHydrological modelling has undergone constant growth with the increase in information processing capabilities. Hydrological models have traditionally been used to study the effects of climate change on management and land-use changes and for water resources planning, among other purposes. The aim of this study was to determine and analyse the advantages of the HBV and HYMOD models, which are commonly used in hydrology on daily and monthly time scales. A regional sensitivity analysis was used to compare the processes that take on greater importance at different time scales in the two models. As a result, it was found that quick precipitation–runoff processes prove to be better represented in the HBV model, while slow, time-aggregated processes are better represented by the HYMOD model. This study confirms that both models are adequate for rain-dominated basins, such as those of the study area. Additionally, the HBV model proved to be more robust in comparison to HYMOD. 相似文献
15.
ABSTRACT Forward–backward solute dispersion with an intermediate point source in one-dimensional semi-infinite homogeneous porous media is studied in this paper. Solute transport under sorption conditions, first-order decay and zero-order production terms are included. The first type of boundary condition is taken as a constant point source at an intermediate point from where forward and backward solute dispersion is examined. The Laplace transform method is adopted to solve the governing equation analytically. All the analytical results are obtained in graphical form to investigate the forward–backward solute transport in porous media for various hydrological input data. The graphical nature of the analytical solution is compared with numerical data taken from existing literature and similar results are obtained. Also, numerical solution of the governing equation is obtained by the Crank-Nicolson finite difference scheme and validated with the analytical solution, which demonstrates good agreement between them. Accuracy of the solution is also observed by using RMSE. 相似文献
16.
《Advances in water resources》1996,19(3):163-180
A novel, non-intrusive fluorescence imaging technique has been used to quantitatively measure the pore geometry, fluid velocity, and solute concentration within a saturated, three-dimensional porous medium. Discrete numerical averages of these quantities have been made over a representative volume of the medium and used to estimate macroscopic quantities that appear in conventional continuum models of flow and transport. The approach is meant to illustrate how microscopic information can be measured, averaged, and used to characterize medium-scale processes that are typically approximated constitutively. The experimental system consisted of a clear, cylindrical column packed with clear spherical beads and a refractive index-matched fluid seeded with fluorescent tracer particles and solute dye. By illuminating the fluid within the column with a scanning planar laser beam, details of flow and concentration within the pore spaces can be quantitatively observed, allowing for three-dimensional, dimensional, time dependent information to be obtained at good resolution. In time dependent information to be obtained at good resolution. In the current experiment, volumetrically averaged velocities and void-to-volume ratios are first compared with bulk measurements of fluid flux and medium porosity. Microscopic measurements of concentration are then used to construct cross-sectionally averaged profiles, mean breakthrough curves, and direct measurements of the dispersive flux, velocity variance, and concentration variance. In turn, the dispersive flux measurements are compared with mean concentration gradients to provide a basis for confirming the Fickian dispersion model and estimating dispersion coefficients for the medium. Coefficients determined in this manner are compared with others based upon traditional length-scale arguments, mean breakthrough analyses, and curve fits with numerical simulations. 相似文献
17.
AbstractLittle is known about the salt intrusion behaviour in Malaysian estuaries. Study of salt intrusion generally requires large amounts of data, especially if 2-D or 3-D numerical models are used; thus, in data-poor environments, 1-D analytical models are more appropriate. A fully analytical 1-D salt intrusion model, which is simple to implement and requires minimal data, was tested in six previously unsurveyed Malaysian estuaries (Kurau, Perak, Bernam, Selangor, Muar and Endau). The required data can be collected during a single day of observations. Site measurements were conducted during the dry season (June–August 2012 and February–March 2013) near spring tide. Data on cross-sections (by echo-sounding), water levels (by pressure loggers) and salinity (by moving boat) were collected as model input. A good fit was demonstrated between the simulated and observed salinity distribution for all six estuaries. Additionally, the two calibration parameters (the Van der Burgh coefficient and the boundary condition for the dispersion) were compared with the existing predictive equations. Since gauging stations were only present in some nested catchments in the drainage basins, the river discharge had to be up-scaled to represent the total discharge contribution of the catchments. However, the correspondence between the calibration coefficients and the predictive equations was good, particularly in view of the uncertainty in the river discharge data used. This confirms that the predictive salt intrusion model is valid for the cases studied in Malaysia. The model provides a reliable, predictive tool, which the water authority of Malaysia can use for making decisions on water abstraction or dredging.
Editor D. Koutsoyiannis; Associate editor A. Fiori 相似文献
18.
Steven D. London 《地球物理与天体物理流体动力学》2013,107(3-4):205-222
Abstract The ray method is used to study slow hydromagnetic waves in an incompressible, inviscid, perfectly conducting fluid of constant density in the presence of a constant toroidal magnetic field. The fluid is bounded below by a rigid sphere and above by a rigid spheroidal surface, and the mean fluid layer thickness is assumed to be small. Both the general time-dependent and time-harmonic (free oscillation) problems are studied and dispersion relations and conservation laws are derived. These results are applied to free oscillations with constant azimuthal wave number in a spherical shell and then compared to those of previous authors. Such oscillations propagate to the east and are trapped between circles of constant latitude. Wave propagation in axisymmetric shells is then studied with emphasis on the relationship between shell shape and direction of propagation, and it is found that such shells can sustain westward propagating modes wherever the shell thickness decreases sufficiently rapidly from a maximum at the poles to zero at the equator; no shells exist which can sustain westward propagation at the equator. 相似文献
19.
NABIL ROFAIL 《水文科学杂志》2013,58(4):503-504
Abstract The problem of stratified groundwater flow (salt water intrusion) is considered in the general case where the hydrological boundaries can have any shape and the impervious bed can have any configuration. The recharge and discharge can also be considered according to any given function of time. The fluid density is assumed to be constant throughout each layer. The effect at the boundaries is considered, whether these are a river or a continuation of the aquifer with different parameters. The systems of equations are taken in alternative matrix forms. The three time level implicit scheme is used and the multi sweep method is applied for the computation. The numerical procedure of the mathematical model is linearly unconditionally stable. In this procedure, no iteration routines are introduced, therefore it is considered exceptionally economical in memory and in computing time. 相似文献
20.
Density-dependent dispersion in heterogeneous porous media Part II: Comparison with nonlinear models 总被引：1，自引：0，他引：1
Anke Jannie Landman Ruud Schotting Andrey Egorov Denis Demidov 《Advances in water resources》2007,30(12):2481-2498
The results of a series of high-resolution numerical experiments are used to test and compare three nonlinear models for high-concentration-gradient dispersion. Gravity stable miscible displacement is considered. The first model, introduced by Hassanizadeh, is a modification of Fick’s law which involves a second-order term in the dispersive flux equation and an additional dispersion parameter β. The numerical experiments confirm the dependency of β on the flow rate. In addition, a dependency on travelled distance is observed. The model can successfully be applied to nearly homogeneous media (σ2 = 0.1), but additional fitting is required for more heterogeneous media.The second and third models are based on homogenization of the local scale equations describing density-dependent transport. Egorov considers media that are heterogeneous on the Darcy scale, whereas Demidov starts at the pore-scale level. Both approaches result in a macroscopic balance equation in which the dispersion coefficient is a function of the dimensionless density gradient. In addition, an expression for the concentration variance is derived. For small σ2, Egorov’s model predictions are in satisfactory agreement with the numerical experiments without the introduction of any new parameters. Demidov’s model involves an additional fitting parameter, but can be applied to more heterogeneous media as well. 相似文献