Authors:S. Trini Castelli; G. Tinarelli; T. G. Reisin Pages: 879 - 901 Abstract: Abstract Three different modelling techniques to simulate the pollutant dispersion in the atmosphere at the microscale and in presence of obstacles are evaluated and compared. The Eulerian and Lagrangian approaches are discussed, using RAMS6.0 and MicroSpray models respectively. Both prognostic and diagnostic modelling systems are considered for the meteorology as input to the Lagrangian model, their differences and performances are investigated. An experiment from the Mock Urban Setting Test field campaign observed dataset, measured within an idealized urban roughness, is used as reference for the comparison. A case in neutral conditions was chosen among the available ones. The predicted mean flow, turbulence and concentration fields are analysed on the basis of the observed data. The performances of the different modelling approaches are compared and their specific characteristics are addressed. Given the same flow and turbulence input fields, the quality of the Lagrangian particle model is found to be overall comparable to the full-Eulerian approach. The diagnostic approach for the meteorology shows a worse agreement with observations than the prognostic approach but still providing, in a much shorter simulation time, fields that are suitable and reliable for driving the dispersion model. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9520-5 Issue No:Vol. 17, No. 5 (2017)
Authors:Victor Dupuis; Sébastien Proust; Céline Berni; André Paquier Pages: 903 - 928 Abstract: Abstract Flows in a compound open-channel (two-stage geometry with a main channel and adjacent floodplains) with a longitudinal transition in roughness over the floodplains are experimentally investigated in an 18 m long and 3 m wide flume. Transitions from submerged dense vegetation (meadow) to emergent rigid vegetation (wood) and vice versa are modelled using plastic grass and vertical wooden cylinders. For a given roughness transition, the upstream discharge distribution between main channel and floodplain (called subsections) is also varied, keeping the total flow rate constant. The flows with a roughness transition are compared to flows with a uniformly distributed roughness over the whole length of the flume. Besides the influence of the downstream boundary condition, the longitudinal profiles of water depth are controlled by the upstream discharge distribution. The latter also strongly influences the magnitude of the lateral net mass exchanges between subsections, especially upstream from the roughness transition. Irrespective of flow conditions, the inflection point in the mean velocity profile across the mixing layer is always observed at the interface between subsections. The longitudinal velocity at the main channel/floodplain interface, denoted \(U_{int}\) , appeared to be a key parameter for characterising the flows. First, the mean velocity profiles across the mixing layer, normalised using \(U_{int}\) , are superimposed irrespective of downstream position, flow depth, floodplain roughness type and lateral mass transfers. However, the profiles of turbulence quantities do not coincide, indicating that the flows are not fully self-similar and that the eddy viscosity assumption is not valid in this case. Second, the depth-averaged turbulent intensities and Reynolds stresses, when scaled by the depth-averaged velocity \(U_{d,int}\) exhibit two plateau values, each related to a roughness type, meadow or wood. Lastly, the same results hold when scaling by \(U_{d,int}\) the depth-averaged lateral flux of momentum due to secondary currents. Turbulence production and magnitude of secondary currents are increased by the presence of emergent rigid elements over the floodplains. The autocorrelation functions show that the length of the coherent structures scales with the mixing layer width for all flow cases. It is suggested that coherent structures tend to a state where the magnitude of velocity fluctuations (of both horizontal vortices and secondary currents) and the spatial extension of the structures are in equilibrium. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9525-0 Issue No:Vol. 17, No. 5 (2017)
Authors:C. N. Whittaker; R. I. Nokes; H.-Y. Lo; P. L.-F. Liu; M. J. Davidson Pages: 929 - 958 Abstract: Abstract This paper presents a study of the waves generated by a solid block landslide moving along a horizontal boundary. The landslide was controlled using a mechanical system in a series of physical experiments, and laser-induced fluorescence measurements resolved both spatial and temporal variations in the free surface elevation. During its constant-velocity motion, the landslide transferred energy into ‘trapped’ offshore-propagating waves within a narrow frequency band. The wave trapping is demonstrated by investigating the wave dispersion characteristics using a two-dimensional Fourier Transform. The first of the trailing waves broke at Froude numbers greater than or equal to 0.625. The parametric dependence of the largest-amplitude waves and the potential energy within the wave field are discussed. The experimental results were compared to the predictions of an incompressible Navier–Stokes solver with and without turbulence models. The numerical model under-predicted the measured wave amplitudes, although it accurately predicted the measured wave phasing. The turbulent model more accurately predicted the shapes of the trailing waves. Both experimental and numerical results confirmed that investigations into wave generation by submerged objects moving at constant velocity should also consider the initial acceleration of the object, as this affects the overall evolution of the wave field. The applicability of the horizontal-boundary results to more realistic field scenarios is discussed. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9526-z Issue No:Vol. 17, No. 5 (2017)
Authors:Ting Zhang; Fangxin Fang; Ping Feng Pages: 959 - 979 Abstract: Abstract Dam failures usually cause huge economic and life losses , especially in urban areas where there is a high concentration of inhabitants and economic actors. In order to understand the physical mechanisms of the formation and development of dam-break flooding, lots of efforts have been put into different types of modelling techniques. However, most of existing models are 1D (one-dimensional) or 2D models based on the shallow water equations. In this paper, we present a 3D numerical modelling investigation of dam-break flow hydrodynamics in an open L-shape channel. A newly developed 3D unstructured mesh finite element model is used here. An absorption-like term is introduced to the Navier–Stokes equations in order to control the conditioning of the matrix equation in the numerical solution process and thus improve the stability. A wetting and drying algorithm is used here to allow the free surface height to be treated with a high level of implicitness and stability. The 3D model has been validated by comparing the results with the published experimental data. Good agreement has been achieved at six selected locations. This study shows that the 3D unstructured mesh model is capable of capturing the 3D hydraulic aspects and complicated local flows around structures in simulation of dam-break flows. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9530-3 Issue No:Vol. 17, No. 5 (2017)
Authors:Manish Pandey; P. K. Sharma; Z. Ahmad; Umesh Kumar Singh Pages: 981 - 995 Abstract: Abstract Scour is defined as the processes of removal of sediment particles from water stream bed by the erosive action of activated water, and also carries sediment away from the hydraulic structures. Scour is the main cause of pier failure. Numerous equations are available for estimating temporal and equilibrium scour depth. The present study describes the phenomenon of temporal scour depth variation at bridge piers and deals with the methods for its estimation. The accuracy of six temporal scour depth equations are also checked in this study. After graphical and statistical analysis, it was found that the relationship proposed by Oliveto and Hager (J Hydraul Eng (ASCE) 128(9):811–520, 2002) predicts temporal scour depth better than other equations. Three equations of equilibrium time of scour are also used for computing equilibrium time. Equilibrium time equation proposed by Choi and Choi (Water Environ J 30(1–2):14–21, 2016) gives better agreements with observed values. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9529-9 Issue No:Vol. 17, No. 5 (2017)
Authors:Olivier Oldrini; Patrick Armand; Christophe Duchenne; Christophe Olry; Jacques Moussafir; Gianni Tinarelli Pages: 997 - 1014 Abstract: Abstract Noxious atmospheric releases may originate from both accidents and malicious activities. They are a major concern for public authorities or first responders who may wish to have the most accurate situational awareness. Nonetheless, it is difficult to reliably and accurately model the flow, transport, and dispersion processes in large complex built-up environments in a limited amount of time and resources compatible with operational needs. The parallel version of Micro-SWIFT-SPRAY (PMSS) is an attempt to propose a physically sound and fast response modelling system applicable to complicated industrial or urban sites in case of a hazardous release. This paper presents and justifies the choice of the diagnostic flow and Lagrangian dispersion models in PMSS. Then, it documents in detail the development of the parallel algorithms used to reduce the computational time of the models. Finally, the paper emphasizes the preliminary model validation and parallel performances of PMSS based on data from both wind tunnel (Evaluation of Model Uncertainty) and in-field reduced-scale (Mock Urban Setting Test) and real-scale (Oklahoma City) experimental campaigns. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9532-1 Issue No:Vol. 17, No. 5 (2017)
Authors:Sayed Mahdi Zandi; Amin Rafizadeh; Ahamd Shanehsazzadeh Pages: 1015 - 1034 Abstract: Abstract A meshless method based on exponential basis functions (EBFs) is developed to simulate the propagation of solitary waves and run-up on the slope. The presented method is a boundary-type meshless method applying the exponential basis functions with complex exponents. The solution of governing equations is considered as a series of these basis functions. Boundary conditions are satisfied through a point-wise collocation approach. Based on the presented EBF meshless method, a new formula is introduced for the maximum run-up height on different slopes, valuable for engineering applications. The results obtained through the numerical method in the prediction of solitary wave propagation and estimation of run-up are verified through the comparison with experimental data. The comparison with 159 experimental data indicates that this new formula is more accurate than the preceding formulas in predicting the maximum run-up of non-breaking solitary waves. Minimum calculation time and convenient performances are the other advantages of this method. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9533-0 Issue No:Vol. 17, No. 5 (2017)
Authors:Xiaoguang Liu; Yuhong Zeng Pages: 1035 - 1050 Abstract: Abstract Drag coefficient has been commonly used as a quantifying parameter to represent the vegetative drag, i.e., resistance to the flow by vegetation. In this study, the measured data on the drag coefficient for rigid vegetation in subcritical open-channel flow reported in previous studies are collected and preprocessed for multi-parameter analysis. The effect of Froude number (Fr) on the drag coefficient for rigid vegetation in subcritical flow cannot be ignored, especially when \(Fr < 0.12\) . The drag coefficient is observed to exponentially decrease with the stem Reynolds number (R d ) and logarithmically decreased with the vegetation density (λ) when \(0.012 < \lambda < 0.12\) . The relative submergence (h * ) has a significant effect on the drag coefficient, and a positive logarithmic relationship is summarized. A simplified three-stage empirical formula is obtained based on the divisions of Fr. Laboratory tests (with \(Fr < 0.02\) ) prove that the present empirical model has higher precision compared with existing models. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9534-z Issue No:Vol. 17, No. 5 (2017)
Authors:Quentin Rendu; Emmanuel Mignot; Nicolas Riviere; Barbara Lamberti-Raverot; Sara Puijalon; Florence Piola Pages: 1051 - 1065 Abstract: Abstract Seed and fruit dispersal along watercourses favours the long-distance migration of invasive species, not only for aquatic or wetland species, but also for terrestrial wind-dispersed plants, like the Japanese knotweed. The present paper aims at investigating the role of watercourses in the dispersal of the knotweed due to its frequent occurrence on riverbanks and production of fertile achenes (type of fruit of the Japanese knotweed). This dispersal occurs along two steps after the fruits deposit on the water surface: floatation first and then sinking towards the bottom of the watercourse. Regarding the first step, the effects of agitation of the water, temperature, surface tension and luminosity on the achenes floatability are experimentally studied. While no influence of luminosity is observed, an increase of temperature greatly decreases the floating time. Floating time also decreases as the contact between water and the fruit is enhanced (through submersion of achenes, agitation of the water or lower surface tension). Regarding the second step, the fall velocity of the fruits in water at rest is measured and appears to be independent of the seed history (floating time). 3D helical motions are systematically observed with constant tangential velocity with respect to the falling velocity. The trajectory of the fruits in a shear flow is then measured and the evolution of their velocity components along the sinking process is discussed. Finally, the contribution of both steps to the long-distance migration of the seeds is estimated. PubDate: 2017-10-01 DOI: 10.1007/s10652-017-9537-9 Issue No:Vol. 17, No. 5 (2017)
Authors:Thomas Ducrocq; Ludovic Cassan; Jacques Chorda; Hélène Roux Pages: 629 - 645 Abstract: Abstract This paper investigates flows around a free surface piercing cylinder with Froude number F > 0.5 and Reynolds number around Re = 50,000. The aim of this work is to gain a better understanding of the flow behaviour in environmental systems such as fishways. The advances are based upon experimental and numerical results. Several flow discharges and slopes are tested to obtain both subcritical and supercritical flows. The drag force exerted on the cylinder is measured with the help of a torque gauge while the velocity field is obtained using particle velocimetry. For the numerical part, two URANS turbulence models are tested, the k- \(\omega\) SST and the RNG k- \(\varepsilon\) models using the OpenFOAM software suite for subcritical cases, and then compared with the corresponding experimental results. With fishways applications in mind, the changes in drag coefficient \(C_d\) versus Froude number and water depth are studied and experimental correlations proposed. We conclude that the most suitable URANS turbulence model for reproducing this kind of flow is the k- \(\omega\) SST model. PubDate: 2017-08-01 DOI: 10.1007/s10652-016-9505-9 Issue No:Vol. 17, No. 4 (2017)
Authors:Ignacio J. Moncho-Esteve; Frederik Folke; Manuel García-Villalba; Guillermo Palau-Salvador Pages: 695 - 714 Abstract: Abstract This paper presents large eddy simulation of turbulent flow in a meandering open channel with smooth wall and rectangular cross-section. The Reynolds number based on the channel height is 40,000 and the aspect ratio of the cross-section is 4.48. The depth-averaged mean stream-wise velocity agree well to experimental measurements. In this specific case, two interacting cells are formed that swap from one bend to the other. Transport and mixing of a pollutant is analysed using three different positions of release, e.g. on the inner bank, on the outer bank and on the centre of the cross section. The obtained depth-average mean concentration profiles are reasonably consistent with available experimental data. The role of the secondary motions in the mixing processes is the main focus of the discussion. It is found that the mixing when the scalar is released on the centre of the cross-section is stronger and faster than the mixing of the scalar released on the sides. When the position of release is close to a bank side, the mixing is weaker and a clear concentration of scalar close to the corresponding side-wall can be observed in both cases. PubDate: 2017-08-01 DOI: 10.1007/s10652-017-9513-4 Issue No:Vol. 17, No. 4 (2017)
Authors:G. C. Cuchiara; B. Rappenglück Pages: 777 - 798 Abstract: Abstract In the present study, the well-known case of day 33 of the Wangara experiment is resimulated using the Weather Research and Forecasting (WRF) model in an idealized single-column mode to assess the performance of a frequently used planetary boundary layer (PBL) scheme, the Yonsei University PBL scheme. These results are compared with two large eddy simulations for the same case study imposing different surface fluxes: one using previous surface fluxes calculated for the Wangara experiment and a second one using output from the WRF model. Finally, an alternative set of eddy diffusivity equations was tested to represent the transition characteristics of a sunset period, which led to a gradual decrease of the eddy diffusivity, and replaces the instantaneous collapse of traditional diagnostics for eddy diffusivities. More appreciable changes were observed in air temperature and wind speed (up to 0.5 K, and 0.6 m s−1, respectively), whereas the changes in specific humidity were modest (up to 0.003 g kg−1). Although the representation of the convective decay in the standard parameterization did not show noticeable improvements in the simulation of state variables for the selected Wangara case study day, small changes in the eddy diffusivity over consecutive hours throughout the night can impact the simulation of distribution of trace gases in air quality models. So, this work points out the relevance of simulating the turbulent decay during sunset, which could help air quality forecast models to better represent the distribution of pollutants storage in the residual layer during the entire night. PubDate: 2017-08-01 DOI: 10.1007/s10652-017-9518-z Issue No:Vol. 17, No. 4 (2017)
Authors:Suhas U. Pol; Harindra J. S. Fernando Pages: 799 - 814 Abstract: Abstract An experimental study was conducted to investigate the penetration of a convective mixed layer into an overlying stably (solutally) stratified layer contained in a narrow, tall vessel when the fluid is subjected to a destabilizing heat flux from below. The interest was the evolution of the bottom mixed-layer height ( \(h\) ) with time ( \(t\) ) in the presence of side-wall effects, but without the formation of conventional double-diffusive layers. The side-wall effects are expected at small mixed-layer aspect ratios, \(\varGamma_{h} = (W/h)\) , where \(W\) is the container width. This case has not been studied hitherto, although there are important environmental and industrial applications. The mixed-layer growth laws for low aspect ratio convection were formulated by assuming a balance between the vertical kinetic energy flux at the interface and the rate of change of potential energy of the fluid system due to turbulent entrainment. The effects of sidewalls were considered using similarity arguments, by taking characteristic rms velocities to be a function of \(\varGamma_{h}\) , in addition to buoyancy flux ( \(q_{0}\) ) and \(h\) . In all stages of evolution, the similarity variables \(\xi = h/W\) and \(t^{\prime } = Nt/A\) , where \(A = N^{3} W^{2} /4q_{0}\) and \(N\) is the buoyancy frequency, scaled the mixed-layer evolution data remarkably well. Significant wall effects were noted when \(\varGamma_{h} < 1\) , and for this case the interfacial vertical turbulent velocity and length scales were identified via scaling arguments and experimental data. PubDate: 2017-08-01 DOI: 10.1007/s10652-017-9522-3 Issue No:Vol. 17, No. 4 (2017)
Authors:M. X. Bao; C. W. Li Pages: 815 - 831 Abstract: Abstract In this work we investigate experimentally and numerically the flow structure around foliaged plants deployed in a channel with gravels on the bed under submerged and barely submerged conditions. Velocity and Reynolds stress were measured by using a NORTEK Vectrino profiler. Visual observation shows that the initial motion of gravels is easier to be triggered under the condition of flow with barely submerged vegetation. This is confirmed by the measured velocity, Reynolds stress and total kinetic energy (TKE) profiles. The velocity exhibits a speed up in the near-bed region, and the associated Reynolds stress and TKE increase there. A 3D numerical model is then verified against the experiments and used to investigate systematically the effect of degree of submergence of foliaged plants on the channel bed shear stress. The results show that the maximum bed shear stress occurs when the foliage is situated slightly below the water surface, which can enhance channel bed instability. PubDate: 2017-08-01 DOI: 10.1007/s10652-017-9524-1 Issue No:Vol. 17, No. 4 (2017)
Authors:L. A. Morales-Marín; J. R. French; H. Burningham Abstract: Abstract A community numerical ocean model is used to extend the understanding of wind-driven circulation in small upland lakes. A 3D model of a case study lake (Llyn Conwy, Wales, UK) is calibrated against measured velocity profiles via adjustment of the bottom roughness coefficient. Validation against a separate set of measured velocity profiles confirms the ability of the model to resolve key features of the flow field. Sensitivity analysis shows that the velocity field responds rapidly to changes in the wind forcing. Analysis of the gross circulation using Empirical Orthogonal Functions reveals a persistent two-gyre circulation pattern in the upper half layer of the water column driven by the interaction of wind and bathymetry. At the bottom, the flow is characterised by locally strong currents and analysis of vertical circulation over short time scales shows strong currents in the deepest parts of the lake basin and the responsiveness of the water column to changes in wind speed and direction. Even in small lakes, the assumption of uniform wind stress across the water surface is not always justified and topographic sheltering or other catchment roughness effects give rise to heterogeneity in the wind field. An idealized experiment for the case study lake shows that differences in circulation emerge if the wind stress is allowed to vary across the lake. Energetic wind forcing in upland areas can drive an energetic lake circulation that has important implications for mixing and sediment dynamics. 3D numerical modelling of wind-driven circulation should be more widely used to provide insights into physical limnology to support a wide range of ecological, biogeochemical and palaeoenvironmental studies. PubDate: 2017-10-12 DOI: 10.1007/s10652-017-9548-6
Authors:Sho Harada; S. Samuel Li Abstract: Abstract Hydraulic jumps have complex flow structures, characterised by strong turbulence and large air contents. It is difficult to numerically predict the flows. It is necessary to bolster the existing computer models to emphasise the gas phase in hydraulic jumps, and avoid the pitfall of treating the phenomenon as a single-phase water flow. This paper aims to improve predictions of hydraulic jumps as bubbly two-phase flow. We allow for airflow above the free surface and air mass entrained across it. We use the Reynolds-averaged Navier–Stokes equations to describe fluid motion, the volume of fluid method to track the interface, and the k–ε model for turbulence closure. A shear layer is shown to form between the bottom jet flow and the upper recirculation flow. The key to success in predicting the jet flow lies in formulating appropriate bottom boundary conditions. The majority of entrained air bubbles are advected downstream through the shear layer. Predictions of the recirculation region’s length and air volume fraction within the layer are validated by available measurements. The predictions show a linear growth of the shear layer. There is strong turbulence at the impingement, and the bulk of the turbulence kinetic energy is advected to the recirculation region via the shear layer. The predicted bottom-shear-stress distribution, with a peak value upstream of the toe of the jump and a decaying trend downstream, is realistic. This paper reveals a significant transient bottom shear stress associated with temporal fluctuations of mainly flow velocity in the jump. The prediction method discussed is useful for modelling hydraulic jumps and advancing the understanding of the complex flow phenomenon. PubDate: 2017-10-11 DOI: 10.1007/s10652-017-9549-5
Authors:Gert-Jan Duine; Stephan F. J. De Wekker Abstract: Abstract The influence of grid spacing on daytime planetary boundary layer (PBL) depths is investigated using 2 years of hourly output from a weather forecast system run operationally for an area of complex terrain in Utah. The model domain includes Dugway Proving Ground, the target area for the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program. Differences in PBL depths between a coarse- (10 km horizontal grid spacing) and a fine-grid (3.3 km) domain are expressed as a function of several parameters that describe the terrain variability, including the standard deviation and the Laplacian of the terrain elevation. PBL depths on fair weather days are larger in the coarse domain than in the fine-grid domain by more than 200 m over areas with unresolved ridges in the coarse-grid domain. Absolute differences are an order of magnitude larger in summer than in winter while relative differences are similar and on the order of 10%. The PBL depth differences can only be partly removed after correcting for the fine-grid terrain elevation in the coarse domain, indicating that unresolved atmospheric processes in the coarse-grid domain also account for the PBL depth differences. The results also demonstrate the importance of distinguishing between PBL depths and PBL heights when evaluating the performance of coarse-grid numerical models. PubDate: 2017-09-14 DOI: 10.1007/s10652-017-9547-7
Authors:Yingying Yu; Hong Zhang; Charles Lemckert Abstract: Abstract Severe floods usually result in harmful sediment and pollutant dispersion in shallow coastal regions. This study therefore presents a three-dimensional hydrodynamic and transport model investigation into the sediment transport behaviour following severe flooding which occurred in the Brisbane River catchment. It was found that the flood-driven sediment plume formed in the adjacent Moreton Bay and then spread into the northern part of the bay. Based on analysis of the variations in horizontal sediment flux, four distinct characteristics of sediment transport were identified, corresponding to the combined effects of flooding runoff and tidal currents. Firstly, within the estuary, sediment was driven by the flood discharge and primarily transported in the seaward direction. Secondly, at the river mouth, the transport pattern of the sediment was similar that of the first region, however, the horizontal flux was significantly smaller by 50%. Thirdly, a short distance from the river mouth, variations occurred not only in magnitude but also in transport pattern. Lastly, within the coastal bay, the sediment transport was mainly driven by tides, resulting in the changing direction of sediment movement. It was estimated that approximately 1.01 × 106 tonnes was discharged from the Brisbane River estuary into the bay during the flood event in January 2011. This study exhibited the characteristics of sediment transport within a tidal dominant estuary following a severe flood event. The results would be used to assist the implementation of coastal management strategies. PubDate: 2017-08-21 DOI: 10.1007/s10652-017-9546-8
Authors:Vladimir Maderich; Kyung Tae Jung; Igor Brovchenko; Kyeong Ok Kim Abstract: Abstract A new 3D radioactivity transport model coupled with multiscale circulation and multi-fractional sediment transport modules is presented. The sediment transport module simulates the transport of a mixture of one cohesive sediment fraction and a number of fractions of non-cohesive sediments of different sizes and densities. The model of radionuclide transport describes the key transport and exchange processes in the system of water-suspended and bottom multi-fraction sediments. Two-step kinetics with two successive reversible fast and slow reactions is used in the model. A noticeable feature of the model is approximation of the sediment and contamination profiles in the bed by multiple well-mixed layers to describe the vertical migration of radioactivity within bottom sediments due to erosion/deposition, molecular diffusion and bioturbation. The model accurately reproduced a laboratory experiment on the uptake of radiocesium by lake sediments. An analytical solution describing mutual adjustment of the concentrations of radioactivity in the pore water and in the multi-fraction sediment showed that activity was redistributed between different fractions of sediments far slower than between water and the total concentration in the sediment. The extended one-layer model of bottom contamination of multi-fraction sediments was derived from a general model and compared with a multi-layer model. It was found, however, that the one-layer approximation was not capable of correctly predicting the inventory due to the fact that one-layer averaged concentration can essentially differ from the near-surface value in the multi-layer model. Radionuclide transport in channel with bottom depression was simulated to estimate the effects of erosion/deposition and the multi-fractionality of sediments on the transport process. It was shown that these factors affect the distribution of sediments by forming local maxima and minima of activity at the beginning and end of the depression, respectively, due to the redistribution of contaminated bottom sediments by flow. The developed model can also be used to simulate the transport of a wide class of toxic substances sorbed on sediments. PubDate: 2017-08-16 DOI: 10.1007/s10652-017-9545-9
Authors:Yuhang Guo; Baozhi Pan; Lihua Zhang; Chunhui Fang Abstract: Abstract As the existing model is not suitable for tight sandstone reservoirs, a new model has been derived theoretically to correlate the relative permeability of wetting phase, saturation and the tortuosity ratio based on revised Kozeny–Carman equation. According to the similarity between the flow of fluid and current, we found that the wetting phase relative permeability is a function of the tortuosity ratio, saturation and the saturation index. In order to verify the new model, 11 cores were taken from tight sandstone reservoirs in northwestern and northeastern China. By comparing with the existing models, the new model is more suitable for the core which has low permeability (<10 mD) and saturation index (<1.8). PubDate: 2017-07-20 DOI: 10.1007/s10652-017-9543-y
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