A simple transport rate relation that unifies aeolian and fluvial nonsuspended sediment transport

2020 ◽  
Author(s):  
Thomas Pähtz ◽  
Orencio Duran
Keyword(s):  
Sediment Transport ◽  
Fluid Shear Stress ◽  
Field Measurements ◽  
Viscous Sublayer ◽  
Transport Layer ◽  
Transport Rate ◽  
Fluid Shear ◽  
Sublayer Thickness ◽  
Fluvial Environments ◽  
Rate Relation

<p>Nonsuspended sediment transport driven by streams of liquid or air is an important driver of the morphodynamics of planetary landscapes, seascapes, and riverscapes. Laboratory and field measurements of the sediment transport rate as a function of the fluid shear stress have enabled us to predict such processes with reasonable accuracy on Earth. However, sediment transport is also ubiquitous in extraterrestrial environments, such as on Venus, Mars, Titan, and occurs possibly even on Pluto. This raises the question of whether we can extrapolate transport rate expressions validated with measurements on Earth to extraterrestrial environments. The answer is probably, yes, but only if the used expressions capture the essential physics. Here, using coupled DEM/RANS numerical sediment transport simulations, we show that nonsuspended sediment transport in a large range of aeolian and fluvial environments has a conceptually simple common physical underpinning that allows treating these different transport regimes in a universal manner. That is, a conceptually simple universal model captures simulated and measured transport thresholds and transport rates. In particular, when the transport layer thickness substantially exceeds the viscous sublayer thickness (true for many environments), this model yields a mathematically simple transport rate expression that agrees, simultaneously, with existing measurements in air and water.</p>

Unified model of sediment transport threshold and rate across subaqueous bedload, windblown sand, and windblown snow

2021 ◽  
Author(s):  
Thomas Pähtz ◽  
Yonghui Liu ◽  
Yuezhang Xia ◽  
Peng Hu ◽  
Zhiguo He ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Numerical Simulations ◽  
Deterministic Model ◽  
Field Measurements ◽  
Model Parameters ◽  
Data Sets ◽  
Windblown Sand ◽  
Grain Size And Shape ◽  
Snow Conditions ◽  
Fluvial Environments

<p>Nonsuspended sediment transport (NST) refers to the sediment transport regime in which the flow turbulence is unable to support the weight of transported grains. It occurs in fluvial environments (i.e., driven by a stream of liquid) and in aeolian environments (i.e., wind-blown) and plays a key role in shaping sedimentary landscapes of planetary bodies. NST is a highly fluctuating physical process because of turbulence, surface inhomogeneities, and variations of grain size and shape and packing geometry. Furthermore, the energy of transported grains varies strongly due to variations of their flow exposure duration since their entrainment from the bed. In spite of such variability, we here propose a deterministic model that represents the entire grain motion, including grains that roll and/or slide along the bed, by a periodic saltation motion with rebound laws that describe an average rebound of a grain after colliding with the bed. The model simultaneously captures laboratory and field measurements and discrete element method (DEM)-based numerical simulations of the threshold and rate of equilibrium NST within a factor of about 2, unifying weak and intense transport conditions in oil, water, and air (oil only for threshold). The model parameters have not been adjusted to these measurements but determined from independent data sets. Recent DEM-based numerical simulations (Comola, Gaume, et al., 2019, https://doi.org/10.1029/2019GL082195) suggest that equilibrium aeolian NST on Earth is insensitive to the strength of cohesive bonds between bed grains. Consistently, the model captures cohesive windblown sand and windblown snow conditions despite not explicitly accounting for cohesion.</p>

scholarly journals SUSPENDED SEDIMENT AND LONGSHORE SEDIMENT TRANSPORT DATA REVIEW

1972 ◽  
Vol 1 (13) ◽  
pp. 51 ◽  
Author(s):  
M.M. Das
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Field Measurements ◽  
Field Studies ◽  
Volume Transport ◽  
Transport Rate ◽  
General Validity ◽  
Average Percentage ◽  
Longshore Sediment Transport ◽  
Semi Empirical

A review of laboratory and field studies on suspended sediment under waves shows that although about five analytical or semi-empirical approaches have been attempted to predict the vertical distribution of suspended sediment, none of the approaches has had its general validity proven. This is mainly due to the lack of knowledge about the characteristics of turbulence of the wave boundary layer and to the lack of a suitable suspended sediment measuring technique for use in waves. Six different suspended sediment measuring techniques have been used in the studies previewed. Although none of them gives completely reliable laboratory or field measurements, an optical system appears to show promise in obtaining information on the mechanics of suspension under waves. The reanalysis of longshore sediment transport data and tests of the relationships Q = A..E , Q = A,,E , and I = A„E , where Q is volume transport rate in cubic yards per day, E is longshore component of wave energy flux in lbs per day per foot of beach and I is immersed weight transport rate in lbs per day, for different subsets of data and using the method of least squares, showed that a single set of A-, A„ and B does not fit all subsets of data with minimum average percentage deviation of observed values from those predictable by the relationships. The subset of data consisting of all but the observations with light weight sediments can be described by the line of fit, Q =1.93 X 10-4E , with the observed data differing from the predicted ones by 74 percent on the average.

Sediment transport under dry weather conditions in a small sewer system

1998 ◽  
Vol 37 (1) ◽  
pp. 155-162
Author(s):  
Flemming Schlütter ◽  
Kjeld Schaarup-Jensen
Keyword(s):  
Sediment Transport ◽  
Field Data ◽  
Field Measurements ◽  
Weather Conditions ◽  
Sewer System ◽  
Transport Models ◽  
Sewer Systems ◽  
Combined Sewer ◽  
Initial Results

Increased knowledge of the processes which govern the transport of solids in sewers is necessary in order to develop more reliable and applicable sediment transport models for sewer systems. Proper validation of these are essential. For that purpose thorough field measurements are imperative. This paper renders initial results obtained in an ongoing case study of a Danish combined sewer system in Frejlev, a small town southwest of Aalborg, Denmark. Field data are presented concerning estimation of the sediment transport during dry weather. Finally, considerations on how to approach numerical modelling is made based on numerical simulations using MOUSE TRAP (DHI 1993).

scholarly journals Epigenetic Changes During Mechanically Induced Osteogenic Lineage Commitment

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Julia C. Chen ◽  
Mardonn Chua ◽  
Raymond B. Bellon ◽  
Christopher R. Jacobs
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Shear Stress ◽  
Fluid Shear Stress ◽  
Methylation Status ◽  
Lineage Commitment ◽  
Fluid Shear ◽  
Osteogenic Lineage ◽  
Osteogenic Markers ◽  
Heterochromatin Structure

Osteogenic lineage commitment is often evaluated by analyzing gene expression. However, many genes are transiently expressed during differentiation. The availability of genes for expression is influenced by epigenetic state, which affects the heterochromatin structure. DNA methylation, a form of epigenetic regulation, is stable and heritable. Therefore, analyzing methylation status may be less temporally dependent and more informative for evaluating lineage commitment. Here we analyzed the effect of mechanical stimulation on osteogenic differentiation by applying fluid shear stress for 24 hr to osteocytes and then applying the osteocyte-conditioned medium (CM) to progenitor cells. We analyzed gene expression and changes in DNA methylation after 24 hr of exposure to the CM using quantitative real-time polymerase chain reaction and bisulfite sequencing. With fluid shear stress stimulation, methylation decreased for both adipogenic and osteogenic markers, which typically increases availability of genes for expression. After only 24 hr of exposure to CM, we also observed increases in expression of later osteogenic markers that are typically observed to increase after seven days or more with biochemical induction. However, we observed a decrease or no change in early osteogenic markers and decreases in adipogenic gene expression. Treatment of a demethylating agent produced an increase in all genes. The results indicate that fluid shear stress stimulation rapidly promotes the availability of genes for expression, but also specifically increases gene expression of later osteogenic markers.

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