scholarly journals Revisiting slope influence in turbulent bedload transport: consequences for vertical flow structure and transport rate scaling

2018 ◽  
Vol 839 ◽  
pp. 135-156 ◽  
Author(s):  
Raphael Maurin ◽  
Julien Chauchat ◽  
Philippe Frey
Keyword(s):  
Granular Flow ◽  
Morphological Evolution ◽  
Scaling Law ◽  
Bedload Transport ◽  
Transport Rate ◽  
Past Century ◽  
Granular Bed ◽  
Present Contribution ◽  
Wide Range ◽  
Gravity Driven

Gravity-driven turbulent bedload transport has been extensively studied over the past century in regard to its importance for Earth surface processes such as natural riverbed morphological evolution. In the present contribution, the influence of the longitudinal channel inclination angle on gravity-driven turbulent bedload transport is studied in an idealised framework considering steady and uniform flow conditions. From an analytical analysis based on the two-phase continuous equations, it is shown that: (i) the classical slope correction of the critical Shields number is based on an erroneous formulation of the buoyancy force, (ii) the influence of the slope is not restricted to the critical Shields number but affects the whole transport formula and (iii) pressure-driven and gravity-driven turbulent bedload transport are not equivalent from the slope influence standpoint. Analysing further the granular flow driving mechanisms, the longitudinal slope is shown to not only influence the fluid bed shear stress and the resistance of the granular bed, but also to affect the fluid flow inside the granular bed – responsible for the transition from bedload transport to debris flow. The relative influence of these coupled mechanisms allows us to understand the evolution of the vertical structure of the granular flow and to predict the transport rate scaling law as a function of a rescaled Shields number. The theoretical analysis is validated with coupled fluid–discrete element simulations of idealised gravity-driven turbulent bedload transport, performed over a wide range of Shields number values, density ratios and channel inclination angles. In particular, all the data are shown to collapse onto a master curve when considering the sediment transport rate as a function of the proposed rescaled Shields number.

Discrete simulations of an armoured sediment bed during bedload transport

2020 ◽  
Author(s):  
Rémi Chassagne ◽  
Raphaël Maurin ◽  
Julien Chauchat ◽  
Philippe Frey
Keyword(s):  
Numerical Experiments ◽  
Element Model ◽  
Discrete Element ◽  
Bedload Transport ◽  
Transport Rate ◽  
Discrete Element Model ◽  
Small Particles ◽  
Flowing Fluid ◽  
Wide Range ◽  
Large Particles

<p><span><span>Bedload transport (transport of particles by a flowing fluid along the bed by rolling, sliding and/or saltating) has major consequences for public safety, water resources and environmental sustainabilty. In mountains, steep slopes drive an intense transport of a wide range of grain sizes implying size sorting or segregation largely responsible for our limited ability to predict sediment flux and river morphology. Size segregation can lead to very complex and varied morphologies of bed surface and subsurface, including armouring, and can drastically modify the fluvial morphology equilibrium. In this work, the transport rate of an armoured bed, made of large particles on top of a small particles bed, is studied. </span></span></p><p align="justify"> </p><p><span><span>In order to gain understanding of this process, bedload transport numerical experiments of two-size particle mixtures were carried out, using a coupled Eulerian-Lagrangian fluid-discrete element model validated with experiments (Maurin et al. 2015, 2016). It is composed of a 3D discrete element model (based on the open source code Yade), describing each individual particle, coupled with a one dimensional Reynolds Average Navier Stokes model (Chauchat 2017). A 3D 10% steep domain (angle of 5.71°) is considered. Three different configurations are compared: 2 layers or 4 layers of 6mm particles deposited on top of a bed composed of 3mm particles, and a monodisperse case with only 6mm large particles. The bed is then submitted to a turbulent, hydraulically rough and supercritical water flow until steady transport rate. Shields numbers ranging from 0.1 to 0.5 are considered.</span></span></p><p> </p><p><span><span>The numerical experiments show that in all three configurations, the transport law, relating the dimensionless transport rate to the shields number, is a power law. In addition, it is observed that for the same Shields number, the transport rate is higher in the bidisperse cases than in the monodisperse case. This result can be explained by the rheological properties of bidisperse granular media. Finally, we show that the particles at the interface between large and small particles should be in motion in order to have an increase of particle mobility.</span></span></p><p align="justify"><br><br></p><p><span><span>Chauchat J. 2017. A comprehensive two-phase flow model for unidirectional sheet-flows. </span></span><span><span><em>Journal of Hydraulic Research</em></span></span><span><span>: 10.1080/00221686.2017.1289260.</span></span></p><p><span><span>Maurin R, Chauchat J, Chareyre B, Frey P. 2015. A minimal coupled fluid-discrete element model for bedload transport. </span></span><span><span><em>Physics of Fluids</em></span></span> <span><span><strong>27</strong></span></span><span><span>(11): 113302.</span></span></p><p><span><span>Maurin R, Chauchat J, Frey P. 2016. Dense granular flow rheology in turbulent bedload transport. </span></span><span><span><em>Journal of Fluid Mechanics</em></span></span> <span><span><strong>804</strong></span></span><span><span>: 490-512.</span></span></p>

scholarly journals Exploring shear-induced segregation in controlled-velocity granular flows

2021 ◽  
Vol 249 ◽  
pp. 03012
Author(s):  
Lu Jing ◽  
Julio M. Ottino ◽  
Richard M. Lueptow ◽  
Paul B. Umbanhowar
Keyword(s):  
Shear Rate ◽  
Scaling Law ◽  
Granular Flows ◽  
Particle Segregation ◽  
Shear Rates ◽  
Wide Range ◽  
Gravity Driven ◽  
Rate Gradient

Particle segregation in geophysical and industrial granular flows is typically driven by gravity and shear. While gravity-induced segregation is relatively well understood, shear-induced segregation is not. In particular, what controls segregation in the absence of gravity and the interplay between shearand gravity-driven segregation remain unclear. Here, we explore the shear-induced segregation force on an intruder particle in controlled-velocity granular flows where the shear profile is systematically varied. The shear-induced segregation force is found to be proportional to the shear rate gradient, which effectively pushes the large intruder from lower to higher shear rate regions. A scaling law is developed for the segregation force that is accurate over a wide range of overburden pressures and shear rates, and hence inertial numbers.

Taking into account granular bed resistance in turbulent bedload transport with arbitrary slope and particle shape

2020 ◽  
Author(s):  
Raphaël Maurin ◽  
Remi Monthiller ◽  
Laurent Lacaze
Keyword(s):  
Sediment Transport ◽  
Particle Shape ◽  
Granular Media ◽  
Element Model ◽  
Bedload Transport ◽  
Transport Rate ◽  
Major Influence ◽  
Granular Bed ◽  
Sediment Transport Rate ◽  
Shape Influence

<p>Turbulent bedload transport has a major influence for riverbed evolution and is still lacking a general understanding for realistic configurations with arbitrary slopes and sediments shapes. In this contribution, we explore the importance of the granular bed resistance to the fluid flow. Based on the work of Maurin et al (2018), we show that a generalized version of the repose angle of the granular material can be defined, and is able to characterize the slope influence on sediment transport rate for particle scale simulations (Maurin et al, 2015) over a large range of slopes and fluid forcing (i.e. Shields number). Extending the configuration to arbitrary particle shapes, the sediment transport rate is shown to be correlated to the variation of the granular media repose angle (Monthiller 2019), and the relevance of the latter is discussed.</p><p>Maurin, R., Chauchat, J., Chareyre B. & Frey, P. (2015). A minimal coupled fluid-discrete element model for bedload transport, Physics of Fluids, 27, 113302<br>Maurin, R., Chauchat, J., & Frey, P. (2018). Revisiting slope influence in turbulent bedload transport: Consequences for vertical flow structure and transport rate scaling. Journal of Fluid Mechanics, 839, 135-156. doi:10.1017/jfm.2017.903<br>Monthiller, R. (2019), Particle shape influence on turbulent bedload transport, Master thesis ENSEEIHT/Toulouse Univ.</p>

scholarly journals Dense granular flow rheology in turbulent bedload transport

2016 ◽  
Vol 804 ◽  
pp. 490-512 ◽  
Author(s):  
Raphael Maurin ◽  
Julien Chauchat ◽  
Philippe Frey
Keyword(s):  
Granular Flow ◽  
Large Scale ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Particle Diameter ◽  
Bedload Transport ◽  
Spherical Particles ◽  
Granular Rheology ◽  
Wide Range ◽  
Dense Granular Flow

The local granular rheology is investigated numerically in turbulent bedload transport. Considering spherical particles, steady uniform configurations are simulated using a coupled fluid–discrete-element model. The stress tensor is computed as a function of the depth for a series of simulations varying the Shields number, the specific density and the particle diameter. The results are analysed in the framework of the $\unicode[STIX]{x1D707}(I)$ rheology and exhibit a collapse of both the shear to normal stress ratio and the solid volume fraction over a wide range of inertial numbers. Contrary to expectations, the effect of the interstitial fluid on the granular rheology is shown to be negligible, supporting recent work suggesting the absence of a clear transition between the free-fall and turbulent regimes. In addition, data collapse is observed up to unexpectedly high inertial numbers $I\sim 2$, challenging the existing conceptions and parametrisation of the $\unicode[STIX]{x1D707}(I)$ rheology. Focusing upon bedload transport modelling, the results are pragmatically analysed in the $\unicode[STIX]{x1D707}(I)$ framework in order to propose a granular rheology for bedload transport. The proposed rheology is tested using a 1D volume-averaged two-phase continuous model, and is shown to accurately reproduce the dense granular flow profiles and the sediment transport rate over a wide range of Shields numbers. The present contribution represents a step in the upscaling process from particle-scale simulations towards large-scale applications involving complex flow geometry.

scholarly journals Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4672
Author(s):  
Mohamed H. Hassan ◽  
Cian Vyas ◽  
Bruce Grieve ◽  
Paulo Bartolo
Keyword(s):  
Noble Metals ◽  
Direct Electrochemistry ◽  
Glucose Sensing ◽  
Glucose Sensors ◽  
Diabetic Patients ◽  
Past Century ◽  
Industrial Sectors ◽  
Recent Advances ◽  
Wide Range ◽  
Sensitivity And Selectivity

The detection of glucose is crucial in the management of diabetes and other medical conditions but also crucial in a wide range of industries such as food and beverages. The development of glucose sensors in the past century has allowed diabetic patients to effectively manage their disease and has saved lives. First-generation glucose sensors have considerable limitations in sensitivity and selectivity which has spurred the development of more advanced approaches for both the medical and industrial sectors. The wide range of application areas has resulted in a range of materials and fabrication techniques to produce novel glucose sensors that have higher sensitivity and selectivity, lower cost, and are simpler to use. A major focus has been on the development of enzymatic electrochemical sensors, typically using glucose oxidase. However, non-enzymatic approaches using direct electrochemistry of glucose on noble metals are now a viable approach in glucose biosensor design. This review discusses the mechanisms of electrochemical glucose sensing with a focus on the different generations of enzymatic-based sensors, their recent advances, and provides an overview of the next generation of non-enzymatic sensors. Advancements in manufacturing techniques and materials are key in propelling the field of glucose sensing, however, significant limitations remain which are highlighted in this review and requires addressing to obtain a more stable, sensitive, selective, cost efficient, and real-time glucose sensor.

Allometric heterochrony in the Pliocene-Pleistocene planktic foraminiferal clade Globoconella

Paleobiology ◽  
1994 ◽  
Vol 20 (1) ◽  
pp. 66-84 ◽  
Author(s):  
Kuo-Yen Wei
Keyword(s):  
Opposite Direction ◽  
Morphological Evolution ◽  
Evolutionary Stage ◽  
Allometric Growth ◽  
Displacement Mode ◽  
Ancestral Lineage ◽  
Wide Range ◽  
Allometric Analysis ◽  
Acceleration Mode ◽  
Evolutionary Stasis

Allometric analysis of the size-shape relationships in the Pliocene-Pleistocene planktic foraminiferal Globorotalia (Globoconella) puncticulata-inflata plexus reveals several heterochronic modes underlying the morphological evolution of the clade. The ancestral lineage, G. puncticulata, is a peramorphocline, showing a pre-displacement mode of heterochrony between 3.5 Ma and 3.0 Ma and an acceleration mode from 3.0 to 2.7 Ma. A different peramorphosis process, isometric giantism (hypermorphosis), in the ontogeny of the ancestral stocks of Globoconella occurred at about 3.5 Ma and gave rise to the G. inflata lineage. The descendant lineage, G. inflata, appears to have adopted a paedomorphosis trend by delaying the onset of the neanic stage in ontogeny during the period of 3.5 to 2.35 Ma, resulting in a series of transposition allometries. During the interval of 2.4 to 1.73 Ma, the allometries shifted to the opposite direction, signifying a pre-displacement trend. Evolutionary stasis marks the evolution during 1.73 to 0.25 Ma. Neoteny concluded the final evolutionary stage of the G. inflata lineage during the latest Quaternary (0.26 to 0.05 Ma). The enormous plasticity and fluctuations in morphology of G. inflata are attributed to the highly positive allometric growth during the ontogeny and the wide-range transposing allometries in the phyletic history. The major changes in heterochronic mode coincide with paleoceanographic events, suggesting that the morphological evolution in the Globoconella clade has been modulated by changes in paleoceanographic conditions.

scholarly journals Two-Dimensional Convection Induced by Gravity and Centrifugal Forces in a Rotating Porous Layer Far Away from the Axis of Rotation

1998 ◽  
Vol 4 (2) ◽  
pp. 73-90 ◽  
Author(s):  
Peter Vadasz ◽  
Saneshan Govender
Keyword(s):  
Rayleigh Number ◽  
Porous Layer ◽  
Temperature Fields ◽  
Wave Number ◽  
Marginal Stability ◽  
Two Dimensional ◽  
Wide Range ◽  
Gravity Driven ◽  
Gravity Driven Flow ◽  
The Stability

The stability and onset of two-dimensional convection in a rotating fluid saturated porous layer subject to gravity and centrifugal body forces is investigated analytically. The problem corresponding to a layer placed far away from the centre of rotation was identified as a distinct case and therefore justifying special attention. The stability of a basic gravity driven convection is analysed. The marginal stability criterion is established in terms of a critical centrifugal Rayleigh number and a critical wave number for different values of the gravity related Rayleigh number. For any given value of the gravity related Rayleigh number there is a transitional value of the wave number, beyond which the basic gravity driven flow is stable. The results provide the stability map for a wide range of values of the gravity related Rayleigh number, as well as the corresponding flow and temperature fields.

Temporal variations in bedload transport rates and sediment storage in gravel-bed rivers

1992 ◽  
Vol 16 (3) ◽  
pp. 319-338 ◽  
Author(s):  
Trevor Hoey
Keyword(s):  
Three Dimensional ◽  
Temporal Variations ◽  
Sampling Interval ◽  
Bedload Transport ◽  
Sediment Storage ◽  
Data Set ◽  
Gravel Bed ◽  
Wide Range ◽  
Gravel Bed Rivers ◽  
Bed Waves

Temporal variability in bedload transport rates and spatial variability in sediment storage have been reported with increasing frequency in recent years. A spatial and temporal classification for these features is suggested based on the gravel bedform classification of Church and Jones (1982). The identified scales, meso-, macro-, and mega- are each broad, and within each there is a wide range of processes acting to produce bedload fluctuations. Sampling the same data set with different sampling intervals yields a near linear relationship between sampling interval and pulse period. A range of modelling strategies has been applied to bed waves. The most successful have been those which allow for the three-dimensional nature of sediment storage processes, and which allow changes in the width and depth of stored sediment. The existence of bed waves makes equilibrium in gravel-bed rivers necessarily dynamic. Bedload pulses and bed waves can be regarded as equilibrium forms at sufficiently long timescales.

scholarly journals Morphological evolution of Cuban super heavyweight boxers, 1976-2014

2021 ◽  
Vol 38 (5) ◽  
pp. 312-318
Author(s):  
Wiliam Carvajal Veitía ◽  
Sofía Alberta León Pérez ◽  
María Elena González Revuelta ◽  
Yanel Deturnel Campo
Keyword(s):  
Body Composition ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Skinfold Thickness ◽  
The Body ◽  
Morphological Attributes ◽  
International Trends ◽  
Sitting Height ◽  
Wide Range ◽  
Scientific Value

Objective: To evaluate the morphological changes of Cuban super heavyweight boxers, more and less successful, through the period 1976-2014. Material and method: Thirty super heavy boxers, who were members of the Cuban national teams in the period 1976-2014, were compared; The strategy consisted of separating the group in the periods 1976-1989, 1990-1999, 2000-2009 and 2010-2014. Sixteen anthropometric dimensions were recorded (weight, height, sitting height, six skinfold thickness, five girths and two breadths), from which the body composition and the somatotype were obtained. The data were analyzed applying the Analysis of variance (ANOVA). The conglomerate analysis based on the Euclidean distance was used in order to evaluate the correspondence between physical development and sports performance. A discriminant analysis was carried out in order to analyze the contribution of the anthropometrical variables to the variance of different clusters. Results: Most of the anthropometric dimensions and indicators showed significant differences, having an impact on the increase in adiposity, body fat and endomorphy (p <0.05), as well as the decrease in the indicators dependent on height (p <0.05). The analysis by conglomerates, as well as the study of the Migratory Distances of the somatotype, showed that the Olympic medalist boxers differed in terms of the characteristics of body composition and in terms of the intensity of the somatotype changes in the period 1976-2014. Conclusions: The Cuban boxer of the super heavyweight category showed a wide range of morphological demands, but these were framed within the international trends of professional boxers. The morphological attributes of the Olympic medalists differed from each other, and from the rest of the boxers investigated over time. These results provide anthropometric data of high scientific value, both for selection and for medical control of training.

scholarly journals Study on Scaling Law of Impact Cratering on Granular Bed

2020 ◽  
Vol 27 (0) ◽  
pp. 106-109
Author(s):  
Yu MATSUDA
Keyword(s):  
Scaling Law ◽  
Granular Bed ◽  
Impact Cratering
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