Effects of surface waves on hyporheic exchange over a permeable gravel bed

2020 ◽  
Author(s):  
WuRong Shih ◽  
Fu-Chun Wu
Keyword(s):  
Surface Waves ◽  
Hydrodynamic Pressure ◽  
Global Scale ◽  
Hyporheic Exchange ◽  
Navier Stokes ◽  
Driving Mechanism ◽  
Contributing Factors ◽  
Sufficient Detail ◽  
Advective Flows ◽  
Diffusive Processes

<p>Hyporheic exchange represents the interactions between surface and subsurface flows occurring at various geophysical scales. Its importance to the riverine ecological health and the fate of contaminants has long been recognized. Traditionally, the behaviors of hyporheic exchange are explained by the emergence of geomorphological features, such as dune-shaped bedforms, that usually introduce significant pressure differences along the channel bed and, therefore, facilitate exchanges by pumping the flow inward and outward the bed. In addition to this advective mechanism, near-bed turbulence has also been identified as another driver of flow exchange through the turbulent diffusive processes. This study, on the other hand, highlights the decisive control of surface waves on the hyporheic exchange at depth-limited flow conditions, especially for those unbroken standing waves commonly encountered in river riffle areas. It is hypothesized that the presence of surface waves will reshape the distribution of near-bed hydrodynamic pressures, thus altering the properties of advective flows along the channel bed. The validity of this hypothesis is carefully examined through the laboratory experiments using Refractive-Index-Matched (RIM) liquid and solid materials and Particle Tracking Velocimetry (PTV) techniques. This experimental setting helps to simultaneously resolve the surface and subsurface flow patterns to a sufficient detail; the hydrodynamic pressure field can then be derived from the obtained flow velocity fields. Further analysis in a Double-Averaged Navier-Stokes framework indicates that, among different contributing factors, pressure gradient is found to be the most dominant driver of interface exchange. The variations of this driving mechanism, interestingly, can be further decomposed into two parts, namely, the surface wave associated (global-scale) and the bed grain associated (local-scale) components, respectively.</p>

scholarly journals Experimental and Simulation Study on Validating a Numerical Model for CO2 Density-Driven Dissolution in Water

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 738
Author(s):  
Holger Class ◽  
Kilian Weishaupt ◽  
Oliver Trötschler
Keyword(s):  
Carbon Dioxide ◽  
Numerical Model ◽  
Stokes Equations ◽  
Onset Time ◽  
Navier Stokes ◽  
Grid Refinement ◽  
Navier Stokes Equations ◽  
Laboratory Flume ◽  
Diffusive Processes ◽  
Color Indicator

Carbon dioxide density-driven dissolution in a water-filled laboratory flume of the dimensions 60 cm length, 40 cm height, 1 cm thickness, was visualized using a pH-sensitive color indicator. We focus on atmospheric pressure conditions, like in caves where CO2 concentrations are typically higher. Varying concentrations of carbon dioxide were applied as boundary conditions at the top of the experimental setup, leading to the onset of convective fingering at differing times. The data were used to validate a numerical model implemented in the numerical simulator DuMux. The model solves the Navier–Stokes equations for density-induced water flow with concentration-dependent fluid density and a transport equation, including advective and diffusive processes for the carbon dioxide dissolved in water. The model was run in 2D, 3D, and pseudo-3D on two different grids. Without any calibration or fitting of parameters, the results of the comparison between experiment and simulation show satisfactory agreement with respect to the onset time of convective fingering, and the number and the dynamics of the fingers. Grid refinement matters, in particular, in the uppermost part where fingers develop. The 2D simulations consistently overestimated the fingering dynamics. This successful validation of the model is the prerequisite for employing it in situations with background flow and for a future study of karstification mechanisms related to CO2-induced fingering in caves.

scholarly journals Pattern formation in weakly damped parametric surface waves driven by two frequency components

1997 ◽  
Vol 341 ◽  
pp. 225-244 ◽  
Author(s):  
WENBIN ZHANG ◽  
JORGE VIÑALS
Keyword(s):  
Pattern Formation ◽  
Surface Waves ◽  
Frequency Ratio ◽  
Navier Stokes ◽  
Parametric Surface ◽  
Navier Stokes Equation ◽  
Low Viscosity ◽  
Frequency Components ◽  
Subharmonic Response ◽  
Arbitrary Frequency

A quasi-potential approximation to the Navier–Stokes equation for low-viscosity fluids is developed to study pattern formation in parametric surface waves driven by a force that has two frequency components. A bicritical line separating regions of instability to either of the driving frequencies is explicitly obtained, and compared with experiments involving a frequency ratio of 1/2. The procedure for deriving standing wave amplitude equations valid near onset is outlined for an arbitrary frequency ratio following a multiscale asymptotic expansion of the quasi-potential equations. Explicit results are presented for subharmonic response to a driving force of frequency ratio 1/2, and used to study pattern selection. Even though quadratic terms are prohibited in this case, hexagonal or triangular patterns are found to be stable in a relatively large parameter region, in qualitative agreement with experimental results.

A porous-wavemaker theory

1983 ◽  
Vol 132 ◽  
pp. 395-406 ◽  
Author(s):  
Allen T. Chwang
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Small Amplitude ◽  
Vertical Plate ◽  
Hydrodynamic Pressure ◽  
Finite Depth ◽  
Wave Profile ◽  
Total Force ◽  
Wave Effect ◽  
Effect Parameter

A porous-wavemaker theory is developed to analyse small-amplitude surface waves on water of finite depth, produced by horizontal oscillations of a porous vertical plate. Analytical solutions in closed forms are obtained for the surface-wave profile, the hydrodynamic-pressure distribution and the total force on the wavemaker. The influence of the wave-effect parameter C and the porous-effect parameter G, both being dimensionless, on the surface waves and on the hydrodynamic pressures is discussed in detail.

scholarly journals A review of methods for measuring groundwater–surface water exchange in braided rivers

2019 ◽  
Vol 23 (10) ◽  
pp. 4397-4417 ◽  
Author(s):  
Katie Coluccio ◽  
Leanne Kaye Morgan
Keyword(s):  
Surface Water ◽  
Water Exchange ◽  
Global Scale ◽  
Low Flow ◽  
Hyporheic Exchange ◽  
European Alps ◽  
Braided Rivers ◽  
River Bed ◽  
Multi Method Approach ◽  
Remote Sensing Techniques

Abstract. Braided rivers, while uncommon internationally, are significant in terms of their unique ecosystems and as vital freshwater resources at locations where they occur. With an increasing awareness of the connected nature of surface water and groundwater, there have been many studies examining groundwater–surface water exchange in various types of waterbodies, but significantly less research has been conducted in braided rivers. Thus, there is currently limited understanding of how characteristics unique to braided rivers, such as channel shifting, expanding and narrowing margins, and a high degree of heterogeneity affect groundwater–surface water flow paths. This article provides an overview of characteristics specific to braided rivers, including a map showing the regions where braided rivers are mainly found at the global scale: Alaska, Canada, the Japanese and European Alps, the Himalayas, Russia, and New Zealand. To the authors' knowledge, this is the first map of its kind. This is followed by a review of prior studies that have investigated groundwater–surface water interactions in braided rivers and their associated aquifers. The various methods used to characterise these processes are discussed with emphasis on their effectiveness in achieving the studies' objectives and their applicability in braided rivers. We also discuss additional methods that appear promising to apply in braided river settings. The aim is to provide guidance on methodologies most suitable for future work in braided rivers. In many cases, previous studies found a multi-method approach useful to produce more robust results and compare data collected at various scales. Given the challenges of working directly in braided rivers, there is considerable scope for the increased use of remote sensing techniques. There is also opportunity for new approaches to modelling braided rivers using integrated techniques that incorporate the complex river bed terrain and geomorphology of braided rivers explicitly. We also identify a critical need to improve the conceptual understanding of hyporheic exchange in braided rivers, rates of recharge to and from braided rivers, and historical patterns of dry and low-flow periods in these rivers.

Numerical Simulation of Flows Past Partially-Submerged Horizontal Circular Cylinders in Free Surface Waves

2013 ◽  
Author(s):  
Hans Bihs ◽  
Muk Chen Ong
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Wave Theory ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Wave Forces ◽  
Linear Wave ◽  
Numerical Wave Tank ◽  
Linear Wave Theory ◽  
Free Surface Waves

Two-dimensional (2D) numerical simulations are performed to investigate the flows past partially-submerged circular cylinders in free surface waves. The 2D simulations are carried out by solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the k-ω turbulence model. The level set method is employed to model the free-surface waves. Validation studies of a numerical wave tank have been performed by comparing the numerical results with the analytical results obtained from the linear-wave theory. Wave forces on the partially-submerged cylinders have been calculated numerically and compared with the published theoretical and experimental data under regular-wave conditions. The free-surface elevations around the cylinders have been investigated and discussed.

Simulation and Analysis of Abrasive Jet Machining with Wheel Restriction in Grinding

2008 ◽  
Vol 389-390 ◽  
pp. 387-391
Author(s):  
Wan Shan Wang ◽  
L.D. Zhu ◽  
Tian Biao Yu ◽  
Jian Yu Yang ◽  
L. Tang
Keyword(s):  
Finite Element Method ◽  
Hydrodynamic Pressure ◽  
Navier Stokes ◽  
Grinding Wheel ◽  
Continuity Equations ◽  
Abrasive Jet Machining ◽  
Simulation Based ◽  
Simulation Results ◽  
Precision Finishing ◽  
Feed Condition

Abrasive jet precision finishing is a new machining method, which injects slurry of abrasive and liquid solvent to grinding zone under without feed condition. The machining is simulated by Finite Element Method (FEM) in the paper. Hydrodynamic pressure on modeling of wedge-like grinding zone between wheel and workpiece on abrasive jet finishing with wheel as restraint was established and simulation, based on Navier-Stokes and continuity equations. The liquid hydrodynamic pressure distributing principle and affecting factor were investigated. The relation hydronamic pressure with grinding wheel velocity was stimulated and verified experimentally. The experiment results show that the simulation results are agreement with experiment, so the simulation model can well forecast hydrodynamic pressure distribution at contact zone.

scholarly journals VOF/Navier-Stokes numerical modeling of surface waves generated by subaerial landslides

2008 ◽  
pp. 21-26 ◽  
Author(s):  
Stéphane Abadie ◽  
Denis Morichon ◽  
Stéphan Grilli ◽  
Stéphane Glockner
Keyword(s):  
Numerical Modeling ◽  
Surface Waves ◽  
Navier Stokes

scholarly journals Quarterdiurnal signature in sporadic E occurrence rates and comparison with neutral wind shear

2018 ◽  
Author(s):  
Christoph Jacobi ◽  
Christina Arras ◽  
Christoph Geißler ◽  
Friederike Lilienthal
Keyword(s):  
Zonal Wind ◽  
Wind Shear ◽  
Lower Thermosphere ◽  
Vertical Wind Shear ◽  
Global Scale ◽  
Maximum Deviation ◽  
Driving Mechanism ◽  
Earth Magnetic Field ◽  
Sporadic E ◽  
Wind Shears

Abstract. The GPS radio occultation (RO) technique is used to study sporadic E (ES) layer plasma irregularities of the Earth’s ionosphere on a global scale using GPS signal-to-noise ratio (SNR) profiles from the COSMIC/FORMOSAT-3 satellite. The maximum deviation from the mean SNR can be attributed to the height of the ES layer. ES are generally accepted to be produced by ion convergence due to vertical wind shear in the presence of a horizontal component of the Earth magnetic field, while the wind shear is provided mainly by solar tides. Here we present analyses of quarterdiurnal (QDT) signatures in ES occurrence rates. We find from a local comparison with mesosphere/lower thermosphere wind shear obtained with a meteor radar at Collm (51:3°N, 13:0°E), that the phases of the QDT in ES agree well with those of negative wind shear for all seasons except for summer, when the QDT amplitudes are small. We also compare the global QDT ES signal with numerical model results. The global distribution of ES occurrence rates qualitatively agrees with the modeled zonal wind shears. The results indicate that zonal wind shear is indeed an important driving mechanism for the QDT seen in ES.

scholarly journals It Will Take a Global Movement to Curb Corruption in Health Systems Comment on "We Need to Talk About Corruption in Health Systems"

2019 ◽  
Vol 8 (11) ◽  
pp. 662-664
Author(s):  
Margot I. Witvliet
Keyword(s):  
Public Health ◽  
Health Systems ◽  
Health Professionals ◽  
General Public ◽  
Global Scale ◽  
Medical Professionals ◽  
Contributing Factors ◽  
Public Health Professionals ◽  
The World ◽  
Global Movement

Corruption in health systems is a problem around the world. Prior research consistently shows that corruption is detrimental to population health. Yet public health professionals are slow to address this complicated issue on a global scale. In the editorial entitled "We Need to Talk About Corruption in Health Systems" concern with the general lack of discourse on this topic amongst health professionals is highlighted. In this invited commentary three contributing factors that hamper public dialogue on corruption are discussed. These include (i) corrupt acts are often not illegal, (ii) government and medical professionals continued acceptance of corruption in the health systems, and (iii) lack of awareness within the general public on the extent of the problem. It is advocated that a global movement that is fully inclusive needs to occur to eradicate corruption.

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