scholarly journals Collisional transport model for intense bed load

2020 ◽  
Vol 68 (1) ◽  
pp. 60-69
Author(s):  
Václav Matoušek ◽  
Štěpán Zrostlík
Keyword(s):  
Internal Structure ◽  
Open Channel ◽  
Transport Model ◽  
Plane Surface ◽  
Experimental Testing ◽  
Constitutive Relations ◽  
Water Layer ◽  
Transport Layer ◽  
Bed Load ◽  
Dense Layer

AbstractIn an open channel with a mobile bed, intense transport of bed load is associated with high-concentrated sediment-laden flow over a plane surface of the eroded bed due to high bed shear. Typically, the flow exhibits a layered internal structure in which virtually all sediment grains are transported through a collisional layer above the bed. Our investigation focuses on steady uniform turbulent open-channel flow with a developed collisional transport layer and combines modelling and experiment to relate integral quantities, as the discharge of solids, discharge of mixture, and flow depth with the longitudinal slope of the bed and the internal structure of the flow above the bed.A transport model is presented which considers flow with the internal structure described by linear vertical distributions of granular velocity and concentration across the collisional layer. The model employs constitutive relations based on the classical kinetic theory of granular flows selected by our previous experimental testing as appropriate for the flow and transport conditions under consideration. For given slope and depth of the flow, the model predicts the total discharge and the discharge of sediment. The model also predicts the layered structure of the flow, giving the thickness of the dense layer, collisional layer, and water layer. Model predictions are compared with results of intense bed-load experiment carried out for lightweight sediment in our laboratory tilting flume.

Solids Distribution in Sediment-Laden Open-Channel Flow: Experiment and Prediction

2020 ◽  
Author(s):  
Václav Matoušek ◽  
Jan Krupička ◽  
Tomáš Picek ◽  
Štěpán Zrostlik
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Transport Model ◽  
Plane Surface ◽  
Open Channel Flow ◽  
Solid Particles ◽  
Experimental Results ◽  
Transport Layer ◽  
Experimental Investigations ◽  
Solids Concentration

Abstract Solid-liquid flow is studied in an open channel with a mobile bed at the condition of intense transport of solids. It is flow of high-concentrated mixture of coarse sediment and water over a plane surface of the bed eroded due to high bed shear. In the flow, solid particles are non-uniformly distributed across the flow depth. The flow develops a transport layer, adjacent to the the top of the bed, in which transported particles interact with each other. Results are presented of experimental investigations of the sediment-laden open-channel flow in a recirculating titling flume. The experiments included measurements (using ultrasonic techniques) of the distribution of solids velocity across the transport layer. The related distribution of solids concentration was deduced from the measured distribution of velocity and from other measured flow quantities. Since recently, a direct measurement of the solids distribution across the transport layer has been added to the experiments using a measuring technique svideo camera and a laser sheet. This work discusses results of combined measurements of the distributions of solids concentration and velocity in steady uniform turbulent flow for two lightweight solids fractions and various flow conditions (a broad range of the bed Shields parameter, discharge of solids, discharge of mixture, and the longitudinal slope of the bed). Furthermore, the camera-based measuring method and the deducing method for a determination of solids distribution are discussed and their results compared to show a good agreement in a majority of the test runs. The experimental results are compared with predictions of a recently developed bed-load transport model. Among other outputs, the model predicts the position of the top of the transport layer and the local velocity of sediment particles at this position. The presented model predictions agree well with experimental results based on the measured distibutions.

scholarly journals Bed Load Transport Modelling Using Kinetic Theory

2018 ◽  
Vol 40 ◽  
pp. 05072
Author(s):  
Václav Matoušek ◽  
Štěpán Zrostlík
Keyword(s):  
Kinetic Theory ◽  
Internal Structure ◽  
Transport Layer ◽  
Bed Load ◽  
Dense Layer ◽  
Flow Depth ◽  
Transport Modelling ◽  
Vertical Distributions ◽  
Longitudinal Slope ◽  
Load Transport

Intense transport of bed load is associated with highconcentrated sediment-laden flow over a plane mobile bed at high bed shear. Typically, the flow exhibits a layered internal structure in which a vast majority of sediment grains is transported through a collisional layer above the bed. Our investigation focuses on steady uniform open-channel flow with a developed collisional transport layer and combines modelling and experiment to relate integral quantities, as the discharge of solids, discharge of mixture, and flow depth with the longitudinal slope of the bed and the internal structure of the flow above the bed. In the paper, flow with the internal structure described by linear vertical distributions of granular velocity and concentration across the collisional layer is analyzed by a model based on the classical kinetic theory of granular flows. The model predicts the total discharge, the discharge of sediment, and the flow depth for given (experimentally determined) bed slope and thickness of collisional layer. The model also predicts whether the intefacial dense layer develops between the bed and the collisional layer and how thick it is. Model predictions are compared with results of intense bed-load experiment carried out for lightweight sediment in our laboratory tilting flume.

scholarly journals THREE-DIMENSIONAL STABILITY ANALYSIS OF OPEN CHANNEL FLOW OVER AN ERODIBLE BED

1971 ◽  
Vol 2 (2) ◽  
pp. 93-108 ◽  
Author(s):  
FRANK ENGELUND ◽  
JØRGEN FREDSØE
Keyword(s):  
Open Channel ◽  
Three Dimensional ◽  
Open Channel Flow ◽  
Present Theory ◽  
Bed Load ◽  
Lower Range ◽  
First Order ◽  
Stability And Instability ◽  
Regions Of Stability ◽  
Bed Waves

The formation of ripples and dunes (lower range bed waves) is assumed to be related to the transport of sediment as bed load. From the present theory it is concluded that the formation of the upper range bed configurations (standing waves, antidunes) may be explained on the assumption that the predominant part of the sediment transport is in suspension. The paper presents a mathematical model of the formation of double-periodic antidunes, first-order potential flow theory being applied. It differs from previous models in taking account of the non-uniform distribution of the suspended load. The theory predicts regions of stability and instability. Results are compared with measurements made by different observers.

Modeling Dislocation-Mediated Hydrogen Transport and Trapping in Fcc Metals

2021 ◽  
pp. 1-54
Author(s):  
Theodore Zirkle ◽  
Luke Costello ◽  
Ting Zhu ◽  
David L. McDowell
Keyword(s):  
Transport Model ◽  
Constitutive Relations ◽  
Crack Tip ◽  
Lattice Diffusion ◽  
Hydrogen Transport ◽  
Crack Tip Field ◽  
Coupled Diffusion ◽  
Crystal Plasticity Model ◽  
Physically Based ◽  
Material Ductility

Abstract The diffusion of hydrogen in metals is of interest due to the deleterious influence of hydrogen on material ductility and fracture resistance. It is becoming increasingly clear that hydrogen transport couples significantly with dislocation activity. In this work, we employ a coupled diffusion-crystal plasticity model to incorporate hydrogen transport associated with dislocation sweeping and pipe diffusion in addition to standard lattice diffusion. Moreover, we consider generation of vacancies via plastic deformation and stabilization of vacancies via trapping of hydrogen. The proposed hydrogen transport model is implemented in a physically-based crystal viscoplasticity framework to model the interaction of dislocation substructure and hydrogen migration. In this study, focus is placed on hydrogen transport and trapping within the intense deformation field of a crack tip plastic zone. We discuss the implications of the model results in terms of constitutive relations that incorporate hydrogen effects on crack tip field behavior and enable exploration of hydrogen embrittlement mechanisms.

scholarly journals Evaluation of an acoustic Doppler technique for bed-load transport measurements in sand-bed Rivers

2018 ◽  
Vol 40 ◽  
pp. 02053 ◽  
Author(s):  
S. Conevski ◽  
A. Winterscheid ◽  
N. Ruther ◽  
M. Guerrero ◽  
C. Rennie
Keyword(s):  
Transport Model ◽  
Transport Rate ◽  
Qualitative Assessment ◽  
Bed Load ◽  
Apparent Velocity ◽  
Digital Cameras ◽  
Statistical Correlations ◽  
Hydraulic Conditions ◽  
Load Transport ◽  
Bed Load Transport

The bottom tracking (BT) feature of the acoustic Doppler current profilers (ADCP) have emerged as a promising technique in evaluating the bed load. Strong statistical correlations are reported between the ADCP BT velocity and the transport rate obtained by physical sampling or dune tracking; however, these relations are strictly site-specific and a local calibration is necessary. The direct physical sampling is very labor intensive and it is prone to high instrument uncertainty. The aim of this work is to develop a methodology for evaluating the bed load transport using commercial ADCPs without calibration with physical samples. Relatively long stationary measurements were performed in a sand-bed and sand gravel rivers, using three different ADCPs working at 3MHz, 1.2MHz and 0.6MHz. Simultaneously, bed load samples were collected with physical samplers, and the riverbed was closely observed with digital cameras mounted on the samplers. It is demonstrated that the kinematic transport model can yield a relatively good estimate of the transport rate by directly using filtered apparent velocity, the knowledge of the hydraulic conditions and instrument-related calibration coefficients. Additionally, the ADCP data can help in qualitative assessment of the physical sampling. Future investigation of the backscattering echo and further confirmation of the BT apparent velocity should be performed in laboratory-controlled conditions.

Development and Validation of a Porous Medium Computational Fluid Dynamics Model for a Jet

2008 ◽  
Author(s):  
Timothy J. Drzewiecki ◽  
Brian L. Mount ◽  
Martin Lopez de Bertodano
Keyword(s):  
Porous Medium ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Transport Model ◽  
Constitutive Relations ◽  
Symmetric Domain ◽  
Jet Mixing ◽  
Negative Reactivity ◽  
An Array Of Cylinders ◽  
Development And Validation

The fast boron shutdown injection in a PHWR consists of a jet flowing through a very large moderator tank that contains an array of cylindrical coolant channels. The accurate prediction of the turbulent jet mixing is required to determine an accurate distribution of boron inside the moderator tank to model the insertion of negative reactivity into the reactor during fast shutdown. A CFD code is used to determine the distribution of boron in the moderator tank. The flow is analyzed with a porous medium model based on volume averaged momentum, turbulent kinetic energy, and turbulence dissipation equations. The additional source terms arise due to the averaging must be constituted. The constitutive relations that are implemented in the present model are: (i) the drag force on an array of cylinders for the momentum equations and (ii) the additional mixing effect of the cylinders which results in the sources of turbulent kinetic energy and turbulence dissipation transport model. The CFD analysis is performed on a porous, axis symmetric domain. The CFD results are finally compared with data for the boron concentration distribution obtained in a scaled geometrically similar experiment, demonstrating the validity of the approach.

scholarly journals Flow Structures of the Air-Water Layer in the Free Surface Region of High-Speed Open Channel Flows

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Feng Jiang ◽  
Weilin Xu ◽  
Jun Deng ◽  
Wangru Wei
Keyword(s):  
Free Surface ◽  
Layer Thickness ◽  
High Speed ◽  
Open Channel ◽  
Water Layer ◽  
Channel Flows ◽  
Flow Structures ◽  
Air Velocity ◽  
Open Channel Flows ◽  
The Relationship

In hydraulic engineering, intense free surface breakups have been observed to develop in high-speed open channel flows, resulting in a mixed air-water layer near the free surface that grows with the development of self-aeration. This region is characterized by a substantial number of droplets coexisting with an induced air layer above. Little information about this droplet layer is currently available and no practicable approach has been proposed for predicting the parameters of the induced air layer based on the related flow structures in the droplet layer. In this research, laboratory experiments were accordingly conducted to observe the detailed droplet layer development in terms of layer thickness, droplet size, and frequency distributions under comparative flow conditions. Based on the simplified droplet layer roughness determined using the experimentally measured mean droplet size, the classical power-law of boundary layer theory was applied to provide an analytical solution for the air velocity profile inside the air layer. The relationship of air layer growth to droplet layer thickness, which is a key factor when determining the air velocity distribution, was also established, and the analytical results were proven to be in reasonable agreement with air velocity profiles presented in the literature. By determining the relationship between droplet layer properties and air velocity profiles, the study establishes a basis for the improved modeling of high-speed open channel flows.

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