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Publisher: Springer-Verlag   (Total: 2335 journals)

 Showing 1201 - 1400 of 2335 Journals sorted alphabetically J. of Communications Technology and Electronics       (Followers: 1, SJR: 0.267, h-index: 14) J. of Community Genetics       (Followers: 1, SJR: 0.699, h-index: 8) J. of Community Health       (Followers: 8, SJR: 0.676, h-index: 39) J. of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology       (Followers: 7, SJR: 0.98, h-index: 63) J. of Comparative Physiology B : Biochemical, Systemic, and Environmental Physiology       (Followers: 3, SJR: 0.981, h-index: 50) J. of Compassionate Health Care       (Followers: 1) J. of Computational Analysis and Applications       (SJR: 0.284, h-index: 16) J. of Computational Electronics       (Followers: 3, SJR: 0.457, h-index: 17) J. of Computational Neuroscience       (Followers: 19, SJR: 1.419, h-index: 54) J. of Computer and Systems Sciences Intl.       (SJR: 0.252, h-index: 11) J. of Computer Science and Technology       (Followers: 4, SJR: 0.342, h-index: 26) J. of Computer Virology and Hacking Techniques       (Followers: 5) J. of Computer-Aided Molecular Design       (Followers: 4, SJR: 0.951, h-index: 70) J. of Computers in Education       (Followers: 5) J. of Computing in Higher Education       (Followers: 12, SJR: 0.725, h-index: 16) J. of Consumer Policy       (Followers: 3, SJR: 0.44, h-index: 23) J. of Contemporary Mathematical Analysis       (SJR: 0.115, h-index: 4) J. of Contemporary Physics (Armenian Academy of Sciences)       (Followers: 1, SJR: 0.174, h-index: 4) J. of Contemporary Psychotherapy       (Followers: 3, SJR: 0.441, h-index: 16) J. of Control Theory and Applications       (Followers: 2, SJR: 0.406, h-index: 13) J. of Control, Automation and Electrical Systems       (Followers: 6, SJR: 0.168, h-index: 8) J. of Crop Science and Biotechnology       (Followers: 7) J. of Cross-Cultural Gerontology       (Followers: 3, SJR: 0.412, h-index: 23) J. of Cryptographic Engineering       (Followers: 5, SJR: 0.757, h-index: 6) J. of Cryptology       (Followers: 2, SJR: 1.598, h-index: 49) J. of Cultural Economics       (Followers: 2, SJR: 0.445, h-index: 24) J. of Database Marketing & Customer Strategy Management       (Followers: 8, SJR: 0.183, h-index: 5) J. of Derivatives & Hedge Funds       (Followers: 8, SJR: 0.207, h-index: 3) J. of Developmental and Physical Disabilities       (Followers: 8, SJR: 0.615, h-index: 23) J. of Digital Imaging       (Followers: 8, SJR: 0.535, h-index: 29) J. of Direct Data and Digital Marketing Practice       (Followers: 6, SJR: 0.296, h-index: 3) J. of Dynamical and Control Systems       (Followers: 2, SJR: 0.556, h-index: 22) J. of Dynamics and Differential Equations       (SJR: 1.33, h-index: 29) J. of Earth Science       (Followers: 6, SJR: 0.299, h-index: 11) J. of Earth System Science       (Followers: 27, SJR: 0.466, h-index: 27) J. of East Asian Linguistics       (Followers: 5, SJR: 0.669, h-index: 15) J. of Echocardiography       (Followers: 3, SJR: 0.136, h-index: 3) J. of Economic Growth       (Followers: 25, SJR: 5.251, h-index: 54) J. of Economic Interaction and Coordination       (SJR: 0.231, h-index: 11) J. of Economics       (Followers: 9, SJR: 0.463, h-index: 20) J. of Economics and Finance       (Followers: 7, SJR: 0.238, h-index: 15) J. of Educational Change       (Followers: 7, SJR: 0.694, h-index: 14) J. of Elasticity       (Followers: 4, SJR: 0.821, h-index: 38) J. of Electroceramics       (SJR: 0.566, h-index: 49) J. of Electronic Materials       (Followers: 2, SJR: 0.752, h-index: 68) J. of Electronic Testing       (Followers: 2, SJR: 0.241, h-index: 24) J. of Electronics (China)       (Followers: 3, SJR: 0.127, h-index: 7) J. of Elementary Science Education       (Followers: 8) J. of Engineering Mathematics       (SJR: 0.707, h-index: 32) J. of Engineering Physics and Thermophysics       (Followers: 1, SJR: 0.132, h-index: 8) J. of Engineering Research J. of Engineering Thermophysics       (Followers: 1, SJR: 0.294, h-index: 7) J. of Environmental Studies and Sciences       (Followers: 2) J. of Ethology       (Followers: 2, SJR: 0.484, h-index: 21) J. of Evolution Equations       (SJR: 1.312, h-index: 22) J. of Evolutionary Biochemistry and Physiology       (SJR: 0.127, h-index: 9) J. of Evolutionary Economics       (Followers: 8, SJR: 0.878, h-index: 42) J. of Experimental and Theoretical Physics       (Followers: 2, SJR: 0.565, h-index: 34) J. of Experimental Criminology       (Followers: 26, SJR: 1.587, h-index: 22) J. of Failure Analysis and Prevention       (Followers: 5, SJR: 0.256, h-index: 12) J. of Family and Economic Issues       (Followers: 6, SJR: 0.532, h-index: 27) J. of Family Violence       (Followers: 15, SJR: 0.552, h-index: 45) J. of Financial Services Marketing       (Followers: 3, SJR: 0.241, h-index: 6) J. of Financial Services Research       (Followers: 16, SJR: 1.196, h-index: 29) J. of Fixed Point Theory and Applications       (SJR: 0.467, h-index: 10) J. of Fluorescence       (Followers: 4, SJR: 0.553, h-index: 47) J. of Food Measurement and Characterization       (SJR: 0.104, h-index: 1) J. of Food Science and Technology       (Followers: 5, SJR: 0.839, h-index: 21) J. of Forest Research       (Followers: 3, SJR: 0.578, h-index: 22) J. of Forestry Research       (Followers: 6, SJR: 0.271, h-index: 10) J. of Fourier Analysis and Applications       (Followers: 1, SJR: 1.248, h-index: 36) J. of Friction and Wear       (Followers: 6, SJR: 0.263, h-index: 6) J. of Fusion Energy       (Followers: 3, SJR: 0.389, h-index: 16) J. of Gambling Studies       (Followers: 3, SJR: 1.122, h-index: 50) J. of Gastroenterology       (Followers: 13, SJR: 1.724, h-index: 73) J. of Gastrointestinal Cancer       (Followers: 3, SJR: 0.371, h-index: 36) J. of Gastrointestinal Surgery       (Followers: 5, SJR: 1.632, h-index: 87) J. of General Internal Medicine       (Followers: 13, SJR: 2.379, h-index: 115) J. of General Plant Pathology       (SJR: 0.357, h-index: 17) J. of Genetic Counseling       (Followers: 4, SJR: 0.535, h-index: 32) J. of Genetics       (Followers: 4, SJR: 0.42, h-index: 24) J. of Geodesy       (Followers: 8, SJR: 4.049, h-index: 48) J. of Geographical Sciences       (Followers: 1, SJR: 0.58, h-index: 14) J. of Geographical Systems       (Followers: 2, SJR: 0.839, h-index: 32) J. of Geometric Analysis       (SJR: 1.496, h-index: 23) J. of Geometry       (Followers: 1, SJR: 0.349, h-index: 13) J. of Global Optimization       (Followers: 3, SJR: 0.919, h-index: 51) J. of Global Policy and Governance       (Followers: 8) J. of Grid Computing       (SJR: 0.727, h-index: 32) J. of Hand and Microsurgery       (Followers: 1) J. of Happiness Studies       (Followers: 14, SJR: 0.785, h-index: 30) J. of Hematopathology       (Followers: 3, SJR: 0.194, h-index: 11) J. of Heuristics       (Followers: 5, SJR: 1.718, h-index: 43) J. of High Energy Physics       (Followers: 4, SJR: 1.027, h-index: 139) J. of Homotopy and Related Structures       (SJR: 0.102, h-index: 1) J. of Housing and the Built Environment       (Followers: 6, SJR: 0.553, h-index: 21) J. of Huazhong University of Science and Technology [Medical Sciences]       (SJR: 0.317, h-index: 15) J. of Ichthyology       (Followers: 4, SJR: 0.28, h-index: 7) J. of Immigrant and Minority Health       (Followers: 8, SJR: 0.573, h-index: 29) J. of Inclusion Phenomena and Macrocyclic Chemistry       (Followers: 1, SJR: 0.459, h-index: 41) J. of Indian Philosophy       (Followers: 10, SJR: 0.179, h-index: 7) J. of Indian Prosthodontic Society       (SJR: 0.165, h-index: 5) J. of Industrial Microbiology and Biotechnology       (Followers: 10, SJR: 1.064, h-index: 68) J. of Industry, Competition and Trade       (Followers: 7, SJR: 0.411, h-index: 11) J. of Infection and Chemotherapy       (Followers: 1, SJR: 0.65, h-index: 39) J. of Information Technology       (Followers: 44, SJR: 1.659, h-index: 43) J. of Information Technology Teaching Cases       (Followers: 4) J. of Infrared, Millimeter and Terahertz Waves       (Followers: 1, SJR: 0.902, h-index: 31) J. of Inherited Metabolic Disease       (Followers: 2, SJR: 1.182, h-index: 66) J. of Inorganic and Organometallic Polymers and Materials       (Followers: 6, SJR: 0.316, h-index: 27) J. of Insect Behavior       (Followers: 8, SJR: 0.537, h-index: 36) J. of Insect Conservation       (Followers: 9, SJR: 0.775, h-index: 36) J. of Intelligent and Robotic Systems       (Followers: 2, SJR: 0.501, h-index: 36) J. of Intelligent Information Systems       (Followers: 1, SJR: 0.427, h-index: 39) J. of Intelligent Manufacturing       (Followers: 4, SJR: 1.095, h-index: 44) J. of Interventional Cardiac Electrophysiology       (SJR: 1.073, h-index: 38) J. of Intl. 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1.042, h-index: 14) J. of Maxillofacial and Oral Surgery       (Followers: 2) J. of Mechanical Science and Technology       (Followers: 4, SJR: 0.589, h-index: 20) J. of Medical and Biological Engineering       (SJR: 0.434, h-index: 13) J. of Medical Humanities       (Followers: 18, SJR: 0.251, h-index: 13) J. of Medical Systems       (Followers: 2, SJR: 0.604, h-index: 32) J. of Medical Toxicology       (Followers: 6, SJR: 0.765, h-index: 21) J. of Medical Ultrasonics       (Followers: 2, SJR: 0.209, h-index: 11) J. of Medicine and the Person J. of Membrane Biology       (Followers: 1, SJR: 0.971, h-index: 75) J. of Micro-Bio Robotics J. of Microbiology       (Followers: 7, SJR: 0.641, h-index: 35) J. of Mining Science       (Followers: 5, SJR: 0.296, h-index: 11) J. of Molecular Evolution       (Followers: 11, SJR: 1.07, h-index: 99) J. of Molecular Histology       (Followers: 2, SJR: 0.791, h-index: 43) J. of Molecular Medicine       (Followers: 15, SJR: 2.452, h-index: 100) J. of 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h-index: 22) J. of Nonlinear Science       (Followers: 1, SJR: 1.772, h-index: 36) J. of Nonverbal Behavior       (Followers: 3, SJR: 1.122, h-index: 38) J. of Nuclear Cardiology       (SJR: 1.456, h-index: 60) J. of Nutrition, Health and Aging       (Followers: 18, SJR: 0.886, h-index: 50) J. of Obstetrics and Gynecology of India       (Followers: 7, SJR: 0.174, h-index: 3) J. of Occupational Rehabilitation       (Followers: 11, SJR: 1.166, h-index: 43) J. of Ocean Engineering and Marine Energy       (Followers: 1) J. of Ocean University of China (English Edition)       (SJR: 0.144, h-index: 8) J. of Oceanography       (Followers: 7, SJR: 1.031, h-index: 46) J. of Ocular Biology, Diseases, and Informatics       (SJR: 0.228, h-index: 8) J. of Optical and Fiber Communications Reports       (Followers: 2, SJR: 0.831, h-index: 2) J. of Optics       (Followers: 4) J. of Optimization Theory and Applications       (Followers: 2, SJR: 0.928, h-index: 55) J. of Ornithology       (Followers: 21) J. of Orofacial Orthopedics / Fortschritte der Kieferorthopädie       (SJR: 0.667, h-index: 27) J. of Orthopaedic Science       (Followers: 5, SJR: 0.684, h-index: 42) J. of Paleolimnology       (Followers: 5, SJR: 1.284, h-index: 58) J. of Parasitic Diseases       (Followers: 2, SJR: 0.272, h-index: 5) J. of Pediatric Neuropsychology J. of Pest Science       (Followers: 2, SJR: 1.002, h-index: 21) J. of Pharmaceutical Health Care and Sciences J. of Pharmaceutical Innovation       (Followers: 8, SJR: 0.617, h-index: 14) J. of Pharmaceutical Investigation       (Followers: 1, SJR: 0.16, h-index: 2) J. of Pharmacokinetics and Pharmacodynamics       (Followers: 22, SJR: 0.567, h-index: 41) J. of Phase Equilibria and Diffusion       (Followers: 19, SJR: 0.367, h-index: 31)
 Environmental Fluid Mechanics   [SJR: 0.437]   [H-I: 24]   [3 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1573-1510 - ISSN (Online) 1567-7419    Published by Springer-Verlag  [2335 journals]
• Flow structure and turbulence characteristics downstream of a spanwise
suspended linear array
• Abstract: Abstract Laboratory experiments are conducted to quantify the mean flow structure and turbulence properties downstream of a spanwise suspended linear array in a uniform ambient water flow using Particle Tracking Velocimetry. Eighteen experimental scenarios, with four depth ratios (array depth to water column depth) of 0.35, 0.52, 0.78, and 0.95 and bulk Reynolds number (length scale is the array depth) from 11,600 to 68,170, are investigated. Three sub-layers form downstream of the array: (1) an internal wake zone, where the time-averaged velocity decreases with increasing distance downstream, (2) a shear layer which increases in vertical extent with increasing distance downstream of the array, and the rate of the increase is independent of the bulk Reynolds number or the depth ratio, and (3) an external wake layer with enhanced velocity under the array. The location of the shear layer is dependent on the depth ratio. The spatially averaged and normalized TKE of the wake has a short production region, followed by a decay region which is comparable to grid turbulence decay and is dependent on the depth ratio. The results suggest that the shear layer increases the transfer of horizontal momentum into the internal wake zone from the fluid outside of the array and that the turbulence in the internal wake zone can be modeled similarly to that of grid turbulence.
PubDate: 2016-06-22

• Comparison of specific sediment transport rates obtained from empirical
formulae and dam breaching experiments
• Abstract: Abstract Sediment transport rate determination plays an essential role in mathematical models of embankment dam breaching. The sediment transport formulae commonly used today were mostly determined under considerably different conditions than those existing during the breaching of embankment dams, i.e. in connection with relatively mild longitudinal slopes. However, due to the scarceness of sediment transport relations for sediment transport rates on steep slopes, these traditional formulae are frequently used in dam breach modelling. This paper contains a description of a physical model of a 0.86 m high sandy dike constructed and breached at an outdoor laboratory operated by the Faculty of Civil Engineering, Brno University of Technology, Czech Republic. The dike shape and material were the same for all experiments. The used material was homogeneous non-cohesive medium-uniform sand. The results of the experimental breaching of the sandy dike were discussed and compared with sediment transport rates obtained from various empirical formulae. The comparison shows differences between experimental and calculated sediment transport rates which in all analysed cases indicate overestimation of the breaching rate calculated by empirical formulae.
PubDate: 2016-06-14

• Modeling and experiments of polydisperse particle clouds
• Abstract: Abstract A model for polydisperse particle clouds has been developed in this study. We extended the monodisperse particle cloud model of Lai et al. (Environ Fluid Mech 13(5):435–463, 2013) to the case of polydisperse particles. The particle cloud is first considered to be a thermal or buoyant vortex ring, with the thermal induced velocity field modeled by an expanding spherical Hill’s vortex. The buoyancy of the composite thermal is assumed to be the sum of buoyancy contributed by the all particles inside the thermal. Individual particles (of different particle properties) in the cloud are then tracked by the particle tracking equation using the computed induced velocity field. The turbulent dispersion effect is also accounted for by using a random walk model. Experiments of polydisperse particle clouds were carried out to validate the model. The agreement between model predictions and experiments was reasonable. We further validate our model by comparing it with the LES study of Wang et al. (J Hydraul Eng ASCE 141(7):06015006, 2014). The limitations of our model are then discussed with reference to the comparison. Overall, although some flow details are not captured by our model, the simplicity and generality of the model makes it useful in engineering applications.
PubDate: 2016-06-02

• Diffusional mass transfer coefficient at the water–sediment
interface for wind-induced flow in very shallow lagoons
• Abstract: Abstract Very shallow lagoons that are a few centimeters deep are common in the arid Andes of Northern Chile, Argentina, Bolivia and Perú. The dynamics of these lagoons are dominated by the water–sediment interface (WSI) and strong afternoon winds. Although many studies have examined the diffusional mass transfer coefficients (k t ) of open channel flows, estimates for wind-induced flows are still unknown. The aim of this article is to propose and validate an analytical expression for computing k t at the WSI for wind-induced flow. The laboratory measurements were conducted in a wind tunnel with a water tank of variable depth located at its downwind end. Natural muddy sediments were placed in the middle of the tank so that the dissolved oxygen (DO) was consumed in the sediments. The diffusional mass transfer coefficient that characterizes the DO uptake in the sediment was obtained from DO micro-profiles measured with an OX-25 Unisense microelectrode. Water velocity profiles were measured with a 2D side-view Sontek acoustic doppler velocimetry (ADV), and the wind shear velocity was computed based on wind velocity profiles that were measured with an Extech hot-wire anemometer. A total of 16 experiments were conducted with different water depths and wind shear stresses. The constants required by the model were determined from these experiments, and the analytical expression was successfully validated by the laboratory observations. The analytical expression obtained for computing k t was also validated with field observations that were conducted in October, 2012, in Salar del Huasco, Northern Chile (20.274° S, 68.883° W, 3800 m above sea level). The comparison between the observed and predicted values of k t provides a determination coefficient of r 2 = 0.48 and a p value < 0.01. The results show that the value of k t for wind-induced flow is proportional to the wind shear velocity and the inverse of the Reynolds number of the wind-induced current.
PubDate: 2016-06-01

• Prediction of mass and momentum transport in turbulent plane wall jets
over smooth and transitionally rough surfaces
• Abstract: Abstract This paper is concerned with the prediction of mass and momentum transport in turbulent wall jets developing over smooth and transitionally rough plane walls. The ability to accurately predict the resulting wall shear stresses and vertical profiles of the Reynolds stresses in these flows is prerequisite to the accurate prediction of bed scour, sediment re-suspension and transport by turbulent diffusion. The computations were performed by solving the Reynolds-averaged forms of the equations describing conservation of mass, momentum and concentration. The unknown correlations that arise from the averaging process (the Reynolds stresses in the case of the momentum equation, and the turbulent mass fluxes in the case of concentration) were obtained from the solution of modeled differential equations that describe their conservation. Since these models are somewhat more complex than those typically used in practice, their benefits are demonstrated by comparisons with results obtained from simpler, eddy-viscosity based closures. Comparisons with experimental data show that results of acceptable accuracy can be obtained only by using the appropriate combination of models for the turbulent fluxes of mass and momentum that properly account for the reduction of the Reynolds stresses due to wall damping effects, and for the modification of the mass transfer rates due to interactions with the mean rates of strain.
PubDate: 2016-06-01

• Study of flow formed by three coplanar impinging pipe jets at inclination
angles of 30° and 45°
• Abstract: Abstract This paper presents an experimental study of the interactions of three fully-submerged, coplanar impinging jets issued from long pipes. The jets were neutrally buoyant and were arranged symmetrically about the axis of a central jet, with two side jets set to intersect with the central jet at two inclination angles (30° and 45°) and three Reynolds numbers (4240, 6400 and 8000). Measurements of the flow fields were performed using particle image velocimetry to examine the flow structures in various planes, i.e., the jet axis plane (X–Y), the jet normal plane (X–Z) and the cross-sectional plane (Y–Z). This flow configuration results in pronounced interactions among the three jets, and hence better mixing than that of a canonical single pipe jet as illustrated by augmented centreline velocity decay, spreading rate and turbulence level. The jets at the inclination angle of 45° impinge and mix more rapidly than those at 30°. For each case, the flow is highly 3-dimensional, and jet development displayed several distinct regions (converging, merging and combining) along the streamwise direction. The expansion of flow in the X–Y plane is similar to the shape of a hyperbola with necking formed immediately downstream of the impinging point, whereas that in the X–Z plane assumes the shape of a parabola with an open rim exhibiting a pronounced velocity deficit in the central part of the combining flow. Self-similarity of streamwise mean velocity is explored in the combining region of the flow on the two planes of symmetry (X–Y and X–Z). Flow development in the combining region is dominated by large-scale vortical structures, including von Kárman-like spanwise vortices in the X–Y plane and secondary circulation in the form of two pairs of counter-rotating streamwise vortices in the Y–Z plane.
PubDate: 2016-06-01

• Embedded large eddy simulation approach for pollutant dispersion around a
model building in atmospheric boundary layer
• Abstract: Abstract In the present article, the potential of embedded large eddy simulation (ELES) approach to reliably predict pollutant dispersion around a model building in atmospheric boundary layer is assessed. The performance of ELES in comparison with large eddy simulation (LES) is evaluated in several ways. These include a number of qualitative and quantitative comparisons of time-averaged and instantaneous results with wind tunnel measurements supplemented by statistical data analyses using scatter plots and standard evaluation metrics. Results obtained by both LES and ELES approaches show very good agreement with the experiment. However, addition of turbulence to mean flow at Reynolds averaged Navier–Stokes (RANS)–LES interface in ELES approach not only increases the turbulence intensity, it also results in larger values of turbulent kinetic energy (TKE) as well as a shorter reattachment length in the wake region. Accordingly, higher levels of TKE predicted by ELES increase the local intensity of concentration leading to shorter plume shapes as compared with LES. In general, ELES shows better agreement with experiment on the surfaces of model building and also in the downstream wake region. In terms of computational costs, the CPU time required to obtain statistical values in ELES is about 49 % lower than that of LES and the number of iterations per time step is also reduced by 55 % as compared with LES.
PubDate: 2016-06-01

• Velocity measurements in inclined negatively buoyant jets
• Abstract: Abstract Experiments were performed with a particle tracking velocimetry system to investigate the behaviour of inclined negatively buoyant jets with source angles of 15°, 30°, 45°, 60°, 65°, 70°, and 75° in stationary ambient conditions. Velocities were measured in a plane aligned with the central axis of the flow and the experiments were designed such that the flow did not interact with boundaries in the region were the flow behaviour was measured. The results of this study complement previous research, which has largely focused on the mean geometric characteristics and the mean dilution of the discharged fluid. Geometric characteristics, spreading rates, and time-averaged (mean) centreline velocity results are compared with relevant experimental results from previous studies and integral model predictions. Axial and transverse mean velocity profiles at maximum height and the return point provide additional insights into the detrainment of discharged fluid due to the unstable density gradient on the inner side of the flow.
PubDate: 2016-06-01

• Estimation method to identify scalar point source in turbulent flow based
on Taylor’s diffusion theory
• Abstract: Abstract We introduce a new approach to diffusion-source estimation for quick identification of the unknown source, based on Taylor’s diffusion theory for turbulent transport of passive scalar from a fixed point source. In order to evaluate the method, we used planar laser-induced fluorescence to measure the concentration field of fluorescent dye in water flowing in a channel. We considered two kinds of datasets: basis data and observed data. The former is used to determine the basis functions characterizing the streamwise dependence of variances for three statistics: the mean concentration, root-mean-square (RMS) of fluctuations in the concentration, and RMS of the temporal gradient of the fluctuating concentration. Consistent with Taylor’s theory, we found that the lateral distribution of each statistic was basically Gaussian, and their standard deviations increased as a function of the square root of the distance from the emitted point. Based on these facts, a basis function can be formulated and expected to be valid for estimation of unknown sources. Source estimation was performed with the observed data, which corresponded to limited available information about the concentration from an unknown point source. We confirmed a good prediction accuracy of the proposed method with an averaged bias as small as the turbulent integral scale. Better precision was achieved by employing several statistics simultaneously. In this case, the standard deviation of the estimated source position was assessed at 14 % of the mean distance between the source and measurement points, after 100 source-estimate trials with different datasets. The methodology tested in this paper is expected to be applicable more general and complex environmental diffusion issues involving anisotropic turbulent dispersion, and space–time variable mainstream systems; but its versatility in such systems is currently under investigation.
PubDate: 2016-06-01

• Simulations of the flow in the Mahakam river–lake–delta
system, Indonesia
• Abstract: Abstract Large rivers often present a river–lake–delta system, with a wide range of temporal and spatial scales of the flow due to the combined effects of human activities and various natural factors, e.g., river discharge, tides, climatic variability, droughts, floods. Numerical models that allow for simulating the flow in these river–lake–delta systems are essential to study them and predict their evolution under the impact of various forcings. This is because they provide information that cannot be easily measured with sufficient temporal and spatial detail. In this study, we combine one-dimensional sectional-averaged (1D) and two-dimensional depth-averaged (2D) models, in the framework of the finite element model SLIM, to simulate the flow in the Mahakam river–lake–delta system (Indonesia). The 1D model representing the Mahakam River and four tributaries is coupled to the 2D unstructured mesh model implemented on the Mahakam Delta, the adjacent Makassar Strait, and three lakes in the central part of the river catchment. Using observations of water elevation at five stations, the bottom friction for river and tributaries, lakes, delta, and adjacent coastal zone is calibrated. Next, the model is validated using another period of observations of water elevation, flow velocity, and water discharge at various stations. Several criteria are implemented to assess the quality of the simulations, and a good agreement between simulations and observations is achieved in both calibration and validation stages. Different aspects of the flow, i.e., the division of water at two bifurcations in the delta, the effects of the lakes on the flow in the lower part of the system, the area of tidal propagation, are also quantified and discussed.
PubDate: 2016-06-01

• Near-boundary velocity and turbulence in depth-varying stream flows
• Abstract: Abstract This research examined the temporal distribution of turbulent structure near a streambank toe through the progression of a flood wave in West Run (Morgantown, WV, USA). Three-dimensional velocities and water depths were measured through a 17-h flood event. Turbulence characteristics were examined: Reynolds stresses, turbulent kinetic energy, and turbulence intensities. On average, near-boundary velocity during the rising stage was less than the falling stage, likely due to the measurement location and local roughness. The velocity vectors shifted from towards bed before the flood wave to toward the streambank during progression of the flood wave. Turbulent kinetic energy increased with increasing water depth during the rising stage. Reynolds stress, τxz, increased with increasing water depth during the rising stage, but the majority of the stresses were negative through the storm event. Reynolds stress, τxy, was positive throughout the event and did not vary with depth. This work is among the first to evaluate turbulence during depth-varying flows in the field.
PubDate: 2016-06-01

• A numerical model of periodically forced circulation near the shore of a
lake
• Abstract: Abstract Numerical calculations for a model of the near-shore circulation in a lake subject to two diurnal forcing mechanisms are presented. The first mechanism is a heating/cooling term in the heat equation representing the daytime heating and nighttime cooling of the diurnal cycle. The second is a periodic surface stress modelling a sea-breeze/gully wind system typical of some coastal regions. The two forcing mechanisms can either act together or against each other depending on their relative phase. The numerical solutions are compared with previously published analytical solutions and used to explore the extra dynamics associated with non-linear effects (specifically advection). The latter dynamics include the formation of gravity currents and unstable density profiles leading to secondary circulation.
PubDate: 2016-05-28

• Numerical study of wave–current–vegetation interaction in
coastal waters
• Abstract: Abstract Research on interactions among wave, current, and vegetation has received increasing attention. An explicit depth-averaged hydrodynamic model coupled with a wave spectral model (CMS-wave) was proposed in this study in order to simulate the wave and wave-induced current in coastal waters. The hydrodynamic model was based on the finite volume method while the intercell flux was computed by employing the Harten–Lax–van Leer approximate Riemann solver to investigate the dry-to-wet interface, and the drag force of vegetation was modeled as the sink terms in the momentum equations. The CMS-wave model was used to investigate the non-breaking and the breaking random waves propagation in vegetation fields. Afterwards, an empirical wave energy dissipation term with plant effect was derived to represent the resistance induced by aquatic vegetation in the wave-action balance equation. The established model was calibrated and validated with both the experimental and field data. The results showed that the wave height decreased significantly along the wave propagation direction in the presence of vegetations. The sensitivity analysis for the plant density, the wave height, and the water depth were performed by comparing the numerical results for the wave height attenuation. In addition, wave and wave-induced current through a finite patch of vegetation in the surf zone were investigated as well. The strong radiation stress gradient could be produced due to the variation of the energy dissipation by vegetation effect in the nearshore zone, which impacted the direction and amplitude of the longshore current. The calculated results showed that the coupling model had good performance in predicting wave propagation and the current over vegetated water regions.
PubDate: 2016-05-27

• Scale dependency of dynamic relative permeability–satuartion curves
in relation with fluid viscosity and dynamic capillary pressure effect
• Abstract: Abstract Capillary pressure–saturation-relative permeability relationships (Pc–Sw–Kr) are functions of importance in modeling and simulations of the hydrodynamics of two-phase flow in porous media. These relationships are found to be affected by porous medium and fluid properties but the manner in which they are affected is a topic of intense discussion. For example, reported trends in fluid viscosity and boundary conditions effects have been found to be contrary to each other in different studies. In this work, we determine the dependency of dynamic Kr–Sw relationships (averaged data) on domain scale in addition to investigating the effects of fluid viscosity and boundary pressure using silicone oil (i.e. 200 and 1000 cSt) and water as the respective non-wetting and wetting fluids with a view to eliminating some of the uncertainties reported in the literature. Water relative permeability, Krw, was found to increase with increasing wetting phase saturation but decreases with the increase in viscosity ratio. On the other hand, the oil relative permeability, Krnw, was found to increase with the increasing non-wetting phase saturation in addition to the increase in viscosity ratio. Also, it was found that with the increasing boundary pressure Krw decreases while Krnw increases. The influence of scale on relative permeability was slightly indicated in the non-wetting phase with Krnw decreasing as domain size increases. Effect of measurement location on dynamic relative permeability was explored which is rarely found in the literature. Comparison was also made between Kr–Sw relationships obtained under static and dynamic condition. Finally, mobility ratio (m) and dynamic coefficient (τ) were plotted as a function of water saturation (Sw), which showed that m decreases as τ increases at a given saturation, or vice versa.
PubDate: 2016-05-10

• Influence of planform geometry and momentum ratio on thermal mixing at a
stream confluence with a concordant bed
• Abstract: Abstract The effects of planform geometry and momentum flux ratio on thermal mixing at a stream confluence with concordant bed morphology are investigated based on numerical simulations that can capture the dynamics of large-scale turbulence. In two simulations, the bathymetry and asymmetrical planform geometry are obtained from field experiments and the momentum flux ratio is set at values of one and four. These two conditions provide the basis for studying differences in thermal mixing processes at this confluence when the wake mode and the Kelvin–Helmholtz mode dominate the development of coherent structures within the mixing interface (MI). The effects of channel curvature and angle between the two incoming streams on thermal mixing processes are investigated based on simulations conducted with modified planform geometries. Two additional simulations are conducted for the case where the upstream channels are parallel but not aligned with the downstream channel and for the zero-curvature case where the upstream channels are parallel and aligned with the downstream channel. The simulations highlight the influence of large-scale coherent structures within the MI and of streamwise-oriented vortical (SOV) cells on thermal mixing processes within the confluence hydrodynamics zone. Simulation results demonstrate the critical role played by the SOV cells in promoting large-scale thermal mixing for cases when such cells form in the immediate vicinity of the MI and in modifying the shape of the thermal MI within cross sections of the downstream channel—predictions consistent with empirical measurements of thermal mixing at the confluence. The set of numerical simulations reveal that the degree of thermal mixing occurring within the confluence hydrodynamic zone varies dramatically with planform geometry and incoming flow conditions. In some cases thermal mixing at the downstream end of the confluence hydrodynamic zone is limited to the MI and its immediate vicinity, whereas in others substantial thermal mixing has occurred over most of the cross-sectional area of the flow. Overall, the simulations highlight the flow conditions and the controls of these conditions that influence mixing within the immediate vicinity of a confluence.
PubDate: 2016-05-05

• Eddy diffusivity: a single dispersion analysis of high resolution drifters
in a tidal shallow estuary
• Abstract: Abstract In an estuary, mixing and dispersion resulting from turbulence and small scale fluctuation has strong spatio-temporal variability which cannot be resolved in conventional hydrodynamic models while some models employs parameterizations large water bodies. This paper presents small scale diffusivity estimates from high resolution drifters sampled at 10 Hz for periods of about 4 h to resolve turbulence and shear diffusivity within a tidal shallow estuary (depth <3 m). Taylor’s diffusion theorem forms the basis of a first order estimate for the diffusivity scale. Diffusivity varied between 0.001 and 0.02 m2/s during the flood tide experiment. The diffusivity showed strong dependence (R2 > 0.9) on the horizontal mean velocity within the channel. Enhanced diffusivity caused by shear dispersion resulting from the interaction of large scale flow with the boundary geometries was observed. Turbulence within the shallow channel showed some similarities with the boundary layer flow which include consistency with slope of 5/3 predicted by Kolmogorov’s similarity hypothesis within the inertial subrange. The diffusivities scale locally by 4/3 power law following Okubo’s scaling and the length scale scales as 3/2 power law of the time scale. The diffusivity scaling herein suggests that the modelling of small scale mixing within tidal shallow estuaries can be approached from classical turbulence scaling upon identifying pertinent parameters.
PubDate: 2016-05-04

• Vertical oil dispersion profile under non-breaking regular waves
• Abstract: Abstract An experimental program was conducted to investigate vertical oil dispersion of surface oil spills under non-breaking regular waves. The variation in oil concentration caused by oil dispersion in a water column was studied to determine the vertical oil dispersion profile. The experiments were performed using different waves characteristics for different volumes of oil spill to evaluate the variation in oil concentration at three depths at two sampling stations. The correlations between oil concentration and the main parameters of wave characteristics, oil spill volume, sampling depth, and distance of sampling stations to spill location were assessed. The results revealed that the trend of variation in oil concentration versus wave steepness is linear. The results obtained from experimental measurements indicated that the oil concentrations at mid-depth were 44–77 % and the concentrations near the flume bed were 12–33 % of the concentration near the water surface.
PubDate: 2016-05-04

• Numerical simulations of intrusive gravity currents interacting with a
bottom-mounted obstacle in a continuously stratified ambient
• Abstract: Abstract In this study, the flow dynamics of intrusive gravity currents past a bottom-mounted obstacle were investigated using highly resolved numerical simulations. The propagation dynamics of a classic intrusive gravity current was first simulated in order to validate the numerical model with previous laboratory experiments. A bottom-mounted obstacle with a varying non-dimensional height of $$\tilde{D}=D/H$$ , where D is the obstacle height and H is the total flow depth, was then added to the problem in order to study the downstream flow pattern of the intrusive gravity current. For short obstacles, the intrusion re-established itself downstream without much distortion. However, for tall obstacles, the downstream flow was found to be a joint effect of horizontal advection, overshoot-springback phenomenon, and associated Kelvin-Helmholtz instabilities. Analysis of the numerical results show that the relationship between the downstream propagation speed and the obstacle height can be subdivided into three regimes: (1) a retarding regime ( $$\tilde{D}$$ $$\approx$$ 0–0.3) where a 30 % increase in obstacle height leads to a 20 % reduction in propagation speed, simply due to the obstacle’s retarding effect; (2) an impounding regime ( $$\tilde{D}$$ $$\approx$$ 0.3–0.6) where the additional 30 % increase in obstacle height only leads to a further (negligible) 5 % reduction in propagation speed, due to the accelerating effect of upstream impoundment and downstream enhanced mixing; and (3) a choking regime ( $$\tilde{D}$$ $$\approx$$ 0.6–1.0) where the propagation speed is dramatically reduced due to the dominance of the obstacle’s blocking effect. The obstacle thickness was found to be irrelevant in determining the downstream propagation speed at least for the parameter range explored in this study. The present work highlights the significance of topographic effects in stratified flows with horizontal pressure forcing.
PubDate: 2016-05-02

• Characteristics of flow structure of free-surface flow in a partly
obstructed open channel with vegetation patch
• Abstract: Abstract Free-surface flows over patchy vegetation are common in aquatic environments. In this study, the hydrodynamics of free-surface flow in a rectangular channel with a bed of rigid vegetation-like cylinders occupying half of the channel bed was investigated and interpreted by means of laboratory experiments and numerical simulations. The channel configurations have low width-to-depth aspect ratio (1.235 and 2.153). Experimental results show that the adjustment length for the flow to be fully developed through the vegetation patch in the present study is shorter than observed for large-aspect-ratio channels in other studies. Outside the lateral edge of the vegetation patch, negative velocity gradient ( $$\partial \overline{u}/\partial z < 0$$ ) and a local velocity maximum are observed in the vertical profile of the longitudinal velocity in the near-bed region, corresponding to the negative Reynolds stress ( $$- \overline{{u^{\prime}w^{\prime}}} < 0$$ ) at the same location. Assuming coherent vortices to be the dominant factor influencing the mean flow field, an improved Spalart–Allmaras turbulence model is developed. The model improvement is based on an enhanced turbulence length scale accounting for coherent vortices due to the effect of the porous vegetation canopy and channel bed. This particular flow characteristic is more profound in the case of high vegetation density due to the stronger momentum exchange of horizontal coherent vortices. Numerical simulations confirmed the local maximum velocity and negative gradient in the velocity profile due to the presence of vegetation and bed friction. This in turn supports the physical interpretation of the flow processes in the partly obstructed channel with vegetation patch. In addition, the vertical profile of the longitudinal velocity can also be explained by the vertical behavior of the horizontal coherent vortices based on a theoretical argument.
PubDate: 2016-04-28

• Variations of bed elevations due to turbulence around submerged cylinder
in sand beds
• Abstract: Abstract This paper presents the spatio-temporal variations in bed elevations and the near-bed turbulence statistics over the deformed bed generated around the submerged cylindrical piers embedded vertically on loose sediment bed at a constant flow discharge. Experiments were carried out in a laboratory flume for three blockage ratios in the range of 0.04–0.06 using three different sizes of submerged cylinders individually placed vertically at the centerline of the flume. Clear-water experimental conditions were maintained over the smooth sediment bed surface with a constant flow discharge ( $$Q = 0.015\,{\rm m}^3/{\rm sec}$$ ), thereby giving three different cylinder Reynolds numbers $$Re_{D_c} = \frac{U_mD_c}{\nu }$$ (=10200, 12750, 15300) away from the cylinder locations, where $$U_m$$ is the maximum mean velocity, $$D_c$$ is the cylinder diameter and $$\nu$$ is the kinematic viscosity of fluid. Instantaneous sand bed elevations around the cylinders were recorded using a SeaTek 5MHz ultrasonic ranging system of net 24 transducers to estimate bed form migration, and the near-bed velocity data at transducer locations over the stable deformed bed around the pier-like structures were collected using down-looking three-dimensional (3D) Micro-acoustic Doppler velocimeter to estimate the bottom Reynolds shear stresses and the contributions of bursting events to the dominant shear stress component. The flow perturbation generated due to relatively lower flow blockage ratio favored to achieve the stable bed condition more rapidly than the others, and larger upstream scour-depth and deformed areas were noticed for greater flow blockage ratio due to larger cylinder diameter. For larger blockage ratio in the upstream of scour-hole near the bed, occurrences of probabilities of both boundary-ward interactions (Q1 and Q3) were the dominant; whereas in the downstream of the scoured region, occurrences of probabilities of second and third quadrant events (Q2 and Q4) were dominant. On the other hand, for the lower blockage ratio, quadrant (Q2) was dominant over Q4 in the downstream of scour-hole, and in the upstream of scour-hole, quadrant Q4 was the dominant.
PubDate: 2016-04-08

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