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Diabetologia Notes de lecture     Hybrid Journal  
Diabetology Intl.     Hybrid Journal   (Followers: 1, SJR: 0.273, h-index: 5)
Dialectical Anthropology     Hybrid Journal   (Followers: 8, SJR: 0.314, h-index: 9)
Die Weltwirtschaft     Hybrid Journal   (Followers: 2)
Differential Equations     Hybrid Journal   (Followers: 2, SJR: 0.364, h-index: 15)
Differential Equations and Dynamical Systems     Hybrid Journal   (Followers: 1, SJR: 0.63, h-index: 7)
Digestive Diseases and Sciences     Hybrid Journal   (Followers: 5, SJR: 1.19, h-index: 89)
Directieve therapie     Hybrid Journal  
Discrete & Computational Geometry     Hybrid Journal   (Followers: 2, SJR: 1.269, h-index: 40)
Discrete Event Dynamic Systems     Hybrid Journal   (Followers: 2, SJR: 0.42, h-index: 32)
Distributed and Parallel Databases     Hybrid Journal   (Followers: 4, SJR: 0.766, h-index: 30)
Distributed Computing     Hybrid Journal   (Followers: 2, SJR: 1.41, h-index: 31)
DNP - Der Neurologe und Psychiater     Full-text available via subscription  
Documenta Ophthalmologica     Hybrid Journal   (Followers: 2, SJR: 0.946, h-index: 40)
Doklady Biochemistry and Biophysics     Hybrid Journal   (Followers: 2, SJR: 0.2, h-index: 10)
Doklady Biological Sciences     Hybrid Journal   (SJR: 0.248, h-index: 10)
Doklady Botanical Sciences     Hybrid Journal  
Doklady Chemistry     Hybrid Journal   (SJR: 0.272, h-index: 12)
Doklady Earth Sciences     Hybrid Journal   (SJR: 0.48, h-index: 17)
Doklady Mathematics     Hybrid Journal   (SJR: 0.345, h-index: 13)
Doklady Physical Chemistry     Hybrid Journal   (SJR: 0.299, h-index: 12)
Doklady Physics     Hybrid Journal   (Followers: 1, SJR: 0.293, h-index: 17)
Douleur et Analg├ęsie     Hybrid Journal   (SJR: 0.113, h-index: 6)
Drug Delivery and Translational Research     Hybrid Journal   (Followers: 2, SJR: 0.607, h-index: 8)
Drug Safety - Case Reports     Open Access  
Drugs : Real World Outcomes     Hybrid Journal   (Followers: 1)
Dynamic Games and Applications     Hybrid Journal   (Followers: 2, SJR: 0.481, h-index: 5)
Dysphagia     Hybrid Journal   (Followers: 91, SJR: 0.822, h-index: 52)
e & i Elektrotechnik und Informationstechnik     Hybrid Journal   (Followers: 9, SJR: 0.279, h-index: 9)
e-Neuroforum     Hybrid Journal  
Early Childhood Education J.     Hybrid Journal   (Followers: 14, SJR: 0.466, h-index: 16)
Earth Science Informatics     Hybrid Journal   (Followers: 3, SJR: 0.282, h-index: 7)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 7, SJR: 0.303, h-index: 29)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 7, SJR: 0.482, h-index: 21)
Earthquake Science     Hybrid Journal   (Followers: 8, SJR: 0.418, h-index: 9)
East Asia     Hybrid Journal   (Followers: 7, SJR: 0.18, h-index: 9)
Eating and Weight Disorders - Studies on Anorexia, Bulimia and Obesity     Hybrid Journal   (Followers: 9, SJR: 0.362, h-index: 27)
EcoHealth     Hybrid Journal   (Followers: 2, SJR: 0.88, h-index: 26)
Ecological Research     Hybrid Journal   (Followers: 8, SJR: 0.847, h-index: 43)
Economia e Politica Industriale     Hybrid Journal  
Economia Politica     Hybrid Journal   (SJR: 0.375, h-index: 6)
Economic Botany     Hybrid Journal   (Followers: 8, SJR: 0.527, h-index: 44)
Economic Bulletin     Hybrid Journal   (Followers: 4)
Economic Change and Restructuring     Hybrid Journal   (Followers: 1, SJR: 0.264, h-index: 9)
Economic Theory     Hybrid Journal   (Followers: 9, SJR: 2.557, h-index: 34)
Economic Theory Bulletin     Hybrid Journal   (Followers: 2)
Economics of Governance     Hybrid Journal   (Followers: 2, SJR: 0.408, h-index: 14)
Ecosystems     Hybrid Journal   (Followers: 19, SJR: 1.909, h-index: 93)
Ecotoxicology     Hybrid Journal   (Followers: 9, SJR: 1.333, h-index: 56)
Education and Information Technologies     Hybrid Journal   (Followers: 84, SJR: 0.366, h-index: 16)
Educational Assessment, Evaluation and Accountability     Hybrid Journal   (Followers: 19, SJR: 0.374, h-index: 15)
Educational Psychology Review     Hybrid Journal   (Followers: 17, SJR: 2.776, h-index: 61)
Educational Research for Policy and Practice     Hybrid Journal   (Followers: 8, SJR: 0.273, h-index: 9)
Educational Studies in Mathematics     Hybrid Journal   (Followers: 11, SJR: 0.825, h-index: 32)
Educational Technology Research and Development     Partially Free   (Followers: 74, SJR: 1.785, h-index: 52)
Electrical Engineering     Hybrid Journal   (Followers: 15, SJR: 0.336, h-index: 18)
Electrocatalysis     Hybrid Journal   (SJR: 0.883, h-index: 10)
Electronic Commerce Research     Hybrid Journal   (Followers: 3, SJR: 0.582, h-index: 16)
Electronic Markets     Hybrid Journal   (Followers: 5, SJR: 0.411, h-index: 8)
Electronic Materials Letters     Hybrid Journal   (Followers: 3, SJR: 1.407, h-index: 15)
Elemente der Mathematik     Hybrid Journal   (Followers: 1)
Emergency Radiology     Hybrid Journal   (Followers: 4, SJR: 0.678, h-index: 25)
Emission Control Science and Technology     Hybrid Journal   (Followers: 1)
Empirica     Hybrid Journal   (Followers: 3, SJR: 0.319, h-index: 16)
Empirical Economics     Hybrid Journal   (Followers: 8, SJR: 0.489, h-index: 31)
Empirical Software Engineering     Hybrid Journal   (Followers: 7, SJR: 1.285, h-index: 39)
Employee Responsibilities and Rights J.     Hybrid Journal   (Followers: 3, SJR: 0.361, h-index: 15)
Endocrine     Hybrid Journal   (Followers: 6, SJR: 0.878, h-index: 57)
Endocrine Pathology     Hybrid Journal   (Followers: 2, SJR: 0.638, h-index: 31)
Energy Efficiency     Hybrid Journal   (Followers: 12, SJR: 0.732, h-index: 14)
Energy Systems     Hybrid Journal   (Followers: 11, SJR: 1.176, h-index: 7)
Engineering With Computers     Hybrid Journal   (Followers: 5, SJR: 0.433, h-index: 30)
Entomological Review     Hybrid Journal   (Followers: 3, SJR: 0.144, h-index: 5)
Environment Systems & Decisions     Hybrid Journal   (Followers: 2)
Environment, Development and Sustainability     Hybrid Journal   (Followers: 29, SJR: 0.419, h-index: 29)
Environmental and Ecological Statistics     Hybrid Journal   (Followers: 5, SJR: 0.458, h-index: 32)
Environmental and Resource Economics     Hybrid Journal   (Followers: 18, SJR: 1.632, h-index: 54)
Environmental Biology of Fishes     Hybrid Journal   (Followers: 4, SJR: 0.725, h-index: 58)
Environmental Chemistry Letters     Hybrid Journal   (Followers: 2, SJR: 0.741, h-index: 28)
Environmental Earth Sciences     Hybrid Journal   (Followers: 12, SJR: 0.724, h-index: 63)
Environmental Economics and Policy Studies     Hybrid Journal   (Followers: 6, SJR: 0.524, h-index: 4)
Environmental Evidence     Open Access   (Followers: 1)
Environmental Fluid Mechanics     Hybrid Journal   (Followers: 2, SJR: 0.437, h-index: 24)
Environmental Geochemistry and Health     Hybrid Journal   (Followers: 2, SJR: 1.013, h-index: 36)
Environmental Geology     Hybrid Journal   (Followers: 11)
Environmental Health and Preventive Medicine     Hybrid Journal   (Followers: 3, SJR: 0.522, h-index: 19)
Environmental Management     Hybrid Journal   (Followers: 32, SJR: 0.942, h-index: 66)
Environmental Modeling & Assessment     Hybrid Journal   (Followers: 10, SJR: 0.533, h-index: 31)
Environmental Monitoring and Assessment     Hybrid Journal   (Followers: 9, SJR: 0.685, h-index: 52)
Environmental Science and Pollution Research     Hybrid Journal   (Followers: 14, SJR: 0.885, h-index: 46)
Epidemiologic Perspectives & Innovations     Open Access   (Followers: 4, SJR: 1.4, h-index: 17)
Epileptic Disorders     Hybrid Journal   (SJR: 0.608, h-index: 38)
EPJ A - Hadrons and Nuclei     Hybrid Journal   (Followers: 1, SJR: 1.287, h-index: 63)
EPJ B - Condensed Matter and Complex Systems     Hybrid Journal   (Followers: 3, SJR: 0.731, h-index: 89)
EPJ direct     Hybrid Journal  
EPJ E - Soft Matter and Biological Physics     Hybrid Journal   (Followers: 1, SJR: 0.641, h-index: 62)
EPMA J.     Open Access   (SJR: 0.284, h-index: 6)
ERA-Forum     Hybrid Journal   (Followers: 2, SJR: 0.128, h-index: 3)
Erkenntnis     Hybrid Journal   (Followers: 13, SJR: 0.621, h-index: 16)
Erwerbs-Obstbau     Hybrid Journal   (SJR: 0.206, h-index: 9)

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Journal Cover   Environmental Fluid Mechanics
  [SJR: 0.437]   [H-I: 24]   [2 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1573-1510 - ISSN (Online) 1567-7419
   Published by Springer-Verlag Homepage  [2292 journals]
  • Modeling investigation of asymmetric tidal mixing and residual circulation
           in a partially stratified estuary
    • Abstract: Abstract A three-dimensional hydrodynamic model was applied to the Danshuei River estuarine system in northern Taiwan to investigate the influence of flood-ebb, spring-neap tidal cycles, and salinity distribution on tidal mixing, residual circulation, stratification, and tidal asymmetry. The model was validated using observational data collected in 2008. The results from the model agreed well with observations of water surface elevation, tidal currents, and salinity. It was found that the depth-averaged tidal current during flood tide is weaker with a shorter duration than that during ebb tide in the estuary, which was attributed to tidal asymmetry. Vertical profiles of salinity, flow, eddy diffusivity, and Richardson number also showed a marked asymmetry between flood and ebb tides. Bottom boundary stresses were higher during flood tides than during ebb tides, resulting in more mixing occurrence and consequently decreasing the Richardson numbers. The tidally averaged salinity was more stratified during neap tides than during spring tides because the presence of the stronger vertical diffusivity and turbulent kinetic energy during spring tides. The modeling results also confirmed that the residual circulation was stronger during neap tides than during spring tides.
      PubDate: 2015-06-26
  • Dressler’s theory for curved topography flows: iterative derivation,
           transcritical flow solutions and higher-order wave-type equations
    • Abstract: Abstract The Dressler equations are a system of two non-linear partial differential equations for shallow fluid flows over curved topography. The theory originated from an asymptotic stretching method formulating the equations of motion in terrain-fitted curvilinear coordinates. Apparently, these equations failed to produce a transcritical flow profile changing from sub- to supercritical flow conditions. Further, wave-like motions over a flat bottom are excluded because the bed-normal velocity component is not accounted for. However, the theory was found relevant for several environmental flow problems including density currents over mountains and valleys, seepage flow in hillslope hydrology, the development of antidunes, the formation of geological deposits from hyper-concentrated flows, and shallow-water flow modeling in hydraulics. In this work, Dressler’s theory is developed in an alternative way by a systematic iteration of the stream and potential functions in terrain-fitted coordinates. The first iteration was found to be the former Dressler’s theory, whereas a second iteration of the governing equations results in velocity components generalizing Dressler’s theory to wave-like motion. Dressler’s first-order theory produces a transcritical flow solution over topography only if the total head is fixed by a minimum value of the specific energy at the transition point. However, the theory deviates from measurements under subcritical flow conditions, given that the bed-normal velocity component is significant. A second iteration to the velocity field was used to produce a second-order differential equation that resembles the cnoidal-wave theory. It accurately produces flow over an obstacle including the critical point and the minimum specific energy as part of the numerical solution. The new cnoidal-wave model compares well with the theory of a Cosserat surface for directed fluid sheets, whereas the Saint-Venant theory appears to be poor.
      PubDate: 2015-06-06
  • Hydrodynamics of suspended canopies with limited length and width
    • Abstract: Abstract Experimental measurements and numerical simulations are carried out to determine the hydrodynamics induced by suspended canopies of limited width and height for canopies with six different densities and canopy element arrangements and two different upstream velocities. Measurements of velocity are obtained using acoustic Doppler velocimetry and the drag force via a load cell. Numerical simulation results using OpenFOAM agree very well with the experimental data and are used to investigate the generated flow fields in detail. The bulk features of the flow are similar to those of other canopies, including emergent and submerged canopies, but the finite dimensions of the canopy results in flow patterns that differ from suspended canopies of essentially infinite width. The detailed hydrodynamics of the flow are controlled by the blockage of the suspended canopy which depends both on the canopy density and the lateral spacing between consecutive longitudinal rows of canopy elements. Increased flow blockage results in increases in the drag coefficient from 0.72 to 1.4, reduction in the flow rate inside the canopy from 58 to 98 % (of the diverted flow, 20–43 % is diverted below the canopy) and increases in the steady wake zone length from 0.6 to 4 times the canopy length. Flow blockage has relatively little effect on the length of the upstream adjustment and total wake zones at 1.09 and 7 times the canopy length respectively. The flow also depends only weakly on the upstream velocity.
      PubDate: 2015-06-02
  • Diffusion of bedload particles in open-channel flows: distribution of
           travel times and second-order statistics of particle trajectories
    • Abstract: Abstract The motion of bedload particles is diffusive and occurs within at least three scale ranges: local, intermediate and global, each of which with a distinctly different diffusion regime. However, these regimes, extensions of the scale ranges and boundaries between them remain to be better defined and quantified. These issues are explored using a Lagrangian model of saltating grains over the uniform fixed bed. The model combines deterministic particle motion dynamics with stochastic characteristics such as probability distributions of step lengths and resting times. Specifically, it is proposed that a memoryless exponential distribution is an appropriate model for the distribution of rest periods while the probability that a particle stops after a current jump follows a binomial distribution, which is a distribution with lack of memory as well. These distributions are incorporated in the deterministic Lagrangian model of saltating grains and extensive numerical simulations are conducted for the identification of the diffusive behavior of particles at different time scales. Based on the simulations and physical considerations, the local, intermediate, and global scale ranges are quantified and the transitions from one range to another are studied for a spectrum of motion parameters. The obtained results demonstrate that two different time scales should be considered for parameterization of diffusive behavior within intermediate and global scale ranges and for defining the local–intermediate and intermediate–global boundaries. The simulations highlight the importance of the distributions of the step lengths and resting times for the identification of the boundaries (or transition intervals) between the scale ranges.
      PubDate: 2015-06-02
  • Numerical modeling of $$30^{\circ }$$ 30 ∘ and $$45{^\circ }$$ 45
           ∘ inclined dense turbulent jets in stationary ambient
    • Abstract: Abstract Dispersion of turbulent jets in shallow coastal waters has numerous engineering applications. The accurate forecasting of the complex interaction of these jets with the ambient fluid presents significant challenge and has yet to be fully elucidated. In this paper, numerical simulation of \(30{^\circ }\) and \(45{^\circ }\) inclined dense turbulent jets in stationary water have been conducted. These two angles are examined in this study due to lower terminal rise heights for \(30{^\circ }\) and \(45{^\circ }\) , this is critically important for discharges of effluent in shallow waters compared to higher angles. Mixing behavior of dense jets is studied using a finite volume model (OpenFOAM). Five Reynolds-Averaged Navier–Stokes turbulence models are applied to evaluate the accuracy of CFD predictions. These models include two Linear Eddy Viscosity Models: RNG \( k-\varepsilon \) , and realizable \(k-\varepsilon \) ; one Nonlinear Eddy Viscosity Model: nonlinear \(k-\varepsilon \) ; and two Reynolds Stress Models: LRR and Launder–Gibson. Based on the numerical results, the geometrical characteristics of the dense jets, such as the terminal rise height, the location of centerline peak, and the return point are investigated. The mixing and dilution characteristics have also been studied through the analysis of cross-sectional concentration and velocity profiles. The results of this study are compared to various advanced experimental and analytical investigations, and comparative figures and tables are discussed. It has been observed that the LRR turbulence model as well as the realizable \(k-\varepsilon \) model predicts the flow more accurately among the various turbulence models studied herein.
      PubDate: 2015-06-01
  • Two dimensional river flow and sediment transport model
    • Abstract: Abstract This work presents the development and calibration of a two dimensional river flow, sediment transport and bed evolution model that couples the active-layer and multiple size-class approach for sediment transport modeling with an enhanced advection algorithm. The governing equations are solved using the fractional step method. This resulted in three successive steps (advection, diffusion and continuity) for the flow equations, and two steps (advection and diffusion) for the sediment transport and bed evolution equations. The focus of the research is the improvement of the advection computation (both in water and sediment computation) by reducing the limitation it imposes on the time step. Overcoming this restriction is enabled by introducing modifications to the characteristic method. Implementing these adjustments allows the characteristic curve to extend throughout multiple computational cells. After evaluating the advection computation for both flow and sediment transport by comparison of the proposed algorithm with various classical methods, the developed model is assessed using field measurements conducted on the Danube River. Analysis of the measured and computed values confirmed the developed model’s reliability.
      PubDate: 2015-06-01
  • Longitudinal dispersion of turbulent oscillatory pipe flows
    • Abstract: Abstract In the present study, we examine the longitudinal dispersion of oscillatory pipe flows in the turbulent range which is not well covered before. An analytical analysis was first performed using the homogenization approach (i.e. multiple scale perturbation analysis) to predict the magnitude of the longitudinal dispersion induced by a turbulent oscillatory flow forced by a sinusoidal pressure gradient inside a circular pipe. An axisymmetric co-axial eddy viscosity model was adopted to resolve the radial distribution of velocities and turbulent shear stresses. Based on the derived kinematic characteristics, the longitudinal dispersion coefficient for the turbulent oscillatory pipe flow was then quantified. The results demonstrated that a dimensionless parameter \(\alpha \) , which is the ratio of the oscillatory velocity amplitude divided by the frequency and pipe radius, determines the flow structure as well as the magnitude of the induced longitudinal dispersion coefficient. Experiments were also conducted to quantify the longitudinal dispersion coefficient under different frequencies and oscillatory velocity magnitudes. The measurement approaches were based on the non-invasive laser imaging techniques of particle image velocimetry and planar laser induced fluorescence. The experimental conditions covered a relatively wide range of boundary Reynolds number \((\hbox {Re}_\delta )\) from 100 to 1,000, and included both laminar and turbulent flow regimes. The results showed that when the flow enters the conditional turbulence regime, i.e. \(\hbox {Re}_\delta \ge 500\) , the longitudinal dispersion coefficient increases drastically. The analytical predictions based on the homogenization approach in the present study agree well with the measured longitudinal dispersion coefficients.
      PubDate: 2015-06-01
  • Modeling assessment of a saltwater intrusion and a transport time scale
           response to sea-level rise in a tidal estuary
    • Abstract: Abstract This paper documents a modeling investigation to comprehend the effect of future sea-level rise (SLR) on estuarine salinity and transport time scales, including the residence time and the water age of dissolved substances in a partially mixed estuary. A three-dimensional semi-implicit Eulerian–Lagrangian finite-element model was established and applied to the Tamsui River estuarine system and the adjacent coastal sea in northern Taiwan. The modeling results indicated reasonable agreement with the observed water levels, tidal currents, and salinity. The model was then applied to calculate the salt intrusion, residence time, and water age between the baseline (without SLR) and different scenarios, including SLRs of 0.34, 1.05, and 1.40 m for the year 2100. The numerical model results reveal that the average salt content and salt intrusion length will increase as the sea level rises. The 1 psu isohaline moves toward upstream reaches with an increase in SLR. The results reveal that the maximum increment of tidal-averaged and depth-averaged salinity would be 1.1, 2.4, and 3.0 psu, respectively, for the SLRs of 0.34, 1.05 and 1.40 m at the middle estuary under mean flow conditions. The regression between salt intrusion length and freshwater discharge are established corresponding to different SLR scenarios. The residence time of the entire Tamsui River system would increase from 6.3 to 23 % compared to the baseline under low flow conditions. The concentration of dissolved substances would have a longer transport time from upstream to downstream because water volume increases with SLR. This indicates that the water age will increase in the main Tamsui River estuary as the sea level rises.
      PubDate: 2015-06-01
  • Coherent structures and their interactions in smooth open channel flows
    • Abstract: Abstract The study presents experimental results of coherent structures and their interactions in a smooth open channel flow based on measurement of instantaneous two-dimensional velocity vectors with particle image velocimetry. The sampled data were analyzed through techniques of ensemble average, vortex extraction, and proper orthogonal decomposition (POD). Redistribution of turbulent kinetic energy is observed in the near-surface region. The spanwise vortices, which are closely related to hairpin vortices, exhibit a clear dependence on Reynolds number of the flow. Hairpin vortex packets and long streamwise vortices are identified as typical large-scale and super-scale coherent structures, respectively, and their interaction is revealed by examining the relationship between the population density of spanwise vortices and the coefficient functions of the first POD mode. Interactions between large-scale and super-scale structures have been recognized to support the hypothesis of closed-loop feedback cycle.
      PubDate: 2015-06-01
  • Erratum to: Turbulent velocity, sediment motion and particle trajectories
           under breaking tidal bores: simultaneous physical measurements
    • PubDate: 2015-06-01
  • Environmental hydraulic engineering: a perspective
    • PubDate: 2015-06-01
  • Influence of jet aeration on pressures around a block embedded in a plunge
           pool bottom
    • Abstract: Abstract The influence of the air entrained by water jets on the dynamic pressures applied on the bottom of a plunge pool and inside underlying fissures was analyzed with systematic experiments. The large experimental facility reproduced aerated high-velocity jets up to 22.1 m/s impinging on a pool and impacting on an instrumented cubic block embedded on the bottom. Plunging and submerged jets are compared, as well as jet impingement on the center or on the side of the block. A relationship is proposed to describe the time-averaged pressures at stagnation as a function of the relative pool depth, considering pressure measurements in this position as well as recent experimental evidence on the jet centerline velocity decay. Air bubbles influence the dynamic pressures on the rock bottom by reducing jet momentum, but also by reducing the jet dissipation rates in the water pool. These two processes are opposed. The reduction of momentum, consequence of a jet with a lower apparent density, results in lower pressures, while lower jet dissipation in the pool results in higher kinetic energy of the jet impacting the bottom and higher pressures. Finally, the spectral contents show that the resonance frequencies of aerated jets are shifted as a consequence of wave celerity reduction caused by lower mean densities inside the fissures, which is an evidence of the presence of air bubbles.
      PubDate: 2015-06-01
  • Turbulent velocity, sediment motion and particle trajectories under
           breaking tidal bores: simultaneous physical measurements
    • Abstract: Abstract A tidal bore is a hydrodynamic discontinuity propagating upstream in an estuarine zone with a funnel shape as the tide starts rising under spring tidal conditions. The transient sediment motion beneath tidal bores was investigated in laboratory under controlled flow conditions by measuring simultaneously the fluid and sediment particle velocities. Although no sediment transport was observed in the initially steady flow and in undular bores, a transient sheet flow motion was observed beneath the breaking bores. The sediment transport was initiated during the passage of the bore roller toe by the large longitudinal pressure gradient force, and the sediment particles were subjected to large horizontal accelerations. About 5 % of all particles were accelerated in excess of 1 g. The sediments were advected upstream with an average velocity close to the instantaneous fluid velocity. The time evolution of instantaneous particle velocity for each trajectory was analysed, using the starting point of particle trajectory corresponding to the entrainment point, and the end point to the particle stoppage point. The present data provided some quantitative data in terms of force terms acting on sediment particles beneath a tidal bore and their trajectory characteristics.
      PubDate: 2015-06-01
  • Non-Newtonian power-law gravity currents propagating in confining
    • Abstract: Abstract The propagation of viscous, thin gravity currents of non-Newtonian liquids in horizontal and inclined channels with semicircular and triangular cross-sections is investigated theoretically and experimentally. The liquid rheology is described by a power-law model with flow behaviour index \(n\) , and the volume released in the channel is taken to be proportional to \(t^{\alpha }\) , where \(t\) is time and \(\alpha \) is a non-negative constant. Some results are generalised to power-law cross-sections. These conditions are representative of environmental flows, such as lava or mud discharges, in a variety of conditions. Theoretical solutions are obtained in self-similar form for horizontal channels, and with the method of characteristics for inclined channels. The position of the current front is found to be a function of the current volume, the liquid rheology, and the channel inclination and geometry. The triangular cross-section is associated with the fastest or slowest propagation rate depending on whether \(\alpha <\alpha _c\) or \(\alpha >\alpha _c\) . For horizontal channels, \(\alpha _c=n/(n+1)<1\) , whereas for inclined channels, \(\alpha _c=1\) , irrespective of the value of \(n\) . Experiments were conducted with Newtonian and power-law liquids by independently measuring the rheological parameters and releasing currents with constant volume ( \(\alpha =0\) ) or constant volume flux ( \(\alpha =1\) ) in right triangular and semicircular channels. The experimental results validate the model for horizontal channels and inclined channels with \(\alpha =0\) . For tests in inclined channels with \(\alpha =1\) , the propagation rate of the current front tended to lower values than predicted, and different flow regimes were observed, i.e., uniform flow with normal depth or instabilities resembling roll waves at an early stage of development. The theoretical solution accurately describes current propagation with time before the transition to longer roll waves. An uncertainty analysis reveals that the rheological parameters are the main source of uncertainty in the experiments and that the model is most sensitive to their variation. This behaviour supports the use of carefully designed laboratory experiments as rheometric tests.
      PubDate: 2015-06-01
  • Velocity profiles in a real vegetated channel
    • Abstract: Abstract Most of the studies regarding vegetation effects on velocity profiles are based on laboratory experiments. The main focus of this paper is to show how the laboratory knowledge established for submerged vegetation applies to real-scale systems affected by vegetation growth (mainly Ranunculus fluitans). To do so, experiments are conducted at two gage stations of an operational irrigation system. The analysis of first- and second-order fluctuations of velocities is based on field measurements performed by micro-acoustic doppler velocimeter during 8 months, completed with flow measurement campaigns in different seasons. The Reynolds stresses are used to determine shear velocities and deflected plant heights. Then, the modified log–wake law (MLWL), initially derived from laboratory flume experiments, is applied with a unique parametrisation for the whole set of velocity profiles. The MLWL, along with a lateral distribution function, is used to calculate the discharge and to show the influence of vegetation height on the stage–discharge relationships.
      PubDate: 2015-05-21
  • A recycling method for the large-eddy simulation of plumes in the
           atmospheric boundary layer
    • Abstract: Abstract A method for the large-eddy simulation (LES) of dispersion and mixing of passive scalars is developed and evaluated. The new method addresses the requirements of tracking the evolution of plumes for large distances from their sources while attaining a low computational cost. To reduce computational cost, the velocity and thermodynamic fields are solved on a doubly periodic domain in the horizontal directions. In contrast, when the plume reaches the downstream end of the computational domain, it is reintroduced at the upstream plane but as a different scalar field. The same procedure is repeated when the new scalar field reaches the downstream boundary. By using several scalar fields to describe the evolution of a single plume, the simulation is computationally cheaper since the same velocity and thermodynamic fields are reused, or recycled, when computing the plume evolution. The recycling method is verified by showing that low-order plume statistics are identical to a single-domain LES. Three cases of dispersion and mixing from a point ground source in diverse boundary layer conditions (stable, convectively unstable, and shallow cumulus convection) are considered. Moreover, the LES results are compared with the predictions a Gaussian plume model, which is found to perform satisfactorily in all cases when accurate information about the state of the boundary layer is provided.
      PubDate: 2015-05-17
  • Large eddy simulations of 45° inclined dense jets
    • Abstract: Abstract Submerged inclined dense jets (negatively buoyant jets) occur in many engineering applications such as brine discharges from seawater desalination plants and de-cooling water discharges from liquefied natural gas plants, and their mixing behavior needs to be examined in details for the environmental impact analysis. In the present study, a detailed numerical investigation was performed using the large eddy simulation (LES) approach with both the Smagorinsky and Dynamic Smagorinsky sub-grid scale (SGS) models to simulate the characteristics of the inclined dense jet with 45° inclination. The numerical predictions included the jet trajectory, geometrical characteristics, jet spread and eddy structures. Experimental measurements were also obtained for the validation of the LES predictions, and data from existing studies in the literature were included for comparison. Overall, the LES predictions were able to reproduce the geometric characteristics of the inclined dense jet in a satisfactory manner in most aspects. The dilution was however generally underestimated, which was attributed primarily to the inability of the SGS models to reproduce the convective mixing induced by the buoyancy-induced instability using the adopted grid spacing in the bottom half of the inclined dense jet.
      PubDate: 2015-05-16
  • Measurements of sediment pickup rate over dune-covered bed
    • Abstract: Abstract Laboratory experiments were conducted to measure sediment pickup rate over two-dimensional fixed dunes. Measurements were performed over both stoss and lee sides of the dune with sediments of D 50 = 0.23, 0.44 and 0.86 mm. Flow velocity and turbulence were also measured by using an acoustic Doppler velocimeter. By analysing the experimental data, an empirical sediment pickup function based on depth-averaged flow parameters was proposed to estimate the pickup rate over the dune.
      PubDate: 2015-05-16
  • Tsunami forcing by a low Froude number landslide
    • Abstract: Abstract The waves generated by a submarine landslide, of great concern to coastal communities, exhibit strong dependence on the landslide motion along the sea floor. A series of two-dimensional physical experiments investigate the waves generated by a solid block landslide moving along a horizontal boundary, allowing measurement of both onshore- and offshore-propagating waves using the laser-induced fluorescence technique. This technique provides high-quality free surface measurements over the entire length of the experimental flume, and hence a data set that can be used to validate numerical models for this idealised scenario. The landslide motion is provided by a mechanical system, allowing testing of a range of landslide accelerations and terminal velocities. The landslide Froude number governs the overall behaviour of the wave field. At lower Froude numbers, the waves are almost entirely generated by the landslide acceleration and deceleration, and the offshore- and onshore-propagating wave groups contain approximately equal energy. Interactions between the landslide and the offshore-propagating waves become more important as the Froude number increases. Two inviscid-irrotational models demonstrate the importance of dispersive effects for tsunamis generated by a submarine landslide, and correctly predict the behaviour of the entire wave field at low Froude numbers. The predictions in the vicinity of the landslide worsen with increasing Froude number, due to the linear free surface conditions used by the models. Lower Froude numbers appear to be more representative of previous sloping-boundary experimental geometries, although rigid block landslides still represent an idealisation of a field scenario.
      PubDate: 2015-05-07
  • Experimental study on growth and spread of dispersed particle-laden plume
           in a linearly stratified environment
    • Abstract: Abstract We present results of laboratory experiments conducted to study the evolution, growth, and spreading rate of a dispersed particle-laden plume produced by a constant inflow into a density varying environment. Particles having mean size, \(d_p=100\ \upmu \) m, density \(\rho _p=2500 \ {\text{ kg/m}}^3\) , volume fraction, \(\phi _v =\) 0–0.7 % , were injected along with the lighter buoyant fluid into a linearly stratified medium. It was observed that a particle-laden plume intruding at the neutral density layer is characterized by four spreading regimes: (i) radial momentum flux balanced by the inertia force; (ii) inertia buoyancy regime; (iii) fluid-particle inertia regime, and (iv) viscous buoyancy regime. Regimes (i), (ii), and (iv) are similar to that of a single-phase plume, for which \(\phi _v = 0\,\%\) . The maximum height, \(Z_m\) , for \(\phi _v > 0\,\%\) was observed to be consistently lower than the single-phase case. An empirical parameterization was developed for the maximum height for particle-laden case, and was found to be in very good agreement with the experimental data. In the inertia buoyancy regime, the radial spread of the plume, \(R_f\) , for \(\phi _v > 0\,\%\) , advanced in time as \(R_f \propto t^{0.68 \pm 0.02}\) which is slower compared to the single-phase plume that propagates at \(R_f \propto t^{0.74 \pm 0.02}\) . Due to the presence of particles, ‘particle fall out’ effect occurs, which along with the formation of a secondary umbrella region inhibits the spreading rate and results in slower propagation of the particle-laden plume. The effect of particles on spreading height of plume, \(Z_s\) , and thickness of the plume, \(h_p\) , were also studied, and these results were compared with the single-phase case. Overall from these experiments, it was found that the evolution, growth, and spread of dispersed particle-laden plume is very different from that of the single-phase plume, and presence of low concentration of particles ( \( \phi _v < 1\,\%\) ) could have significant effects on the plume dynamics.
      PubDate: 2015-05-03
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