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Issues in Eulerian-Lagrangian modeling of sediment transport under saltation regime

International Journal of Sediment Research 2018年第4期33卷 441-461页

作者： Reza Barati Seyed ali akbar salehi neyshabouri Goodarz Ahmadi Faculty of Civil and Environmental Engineering Tarbiat Modares University Water Engineering Research Center Department of Civil Engineering Tarbiat Modares University Department of Mechanical and Aeronautical Engineering Clarkson University

The saltation regime is very important for understanding the sediment transport mechanism. However,there is no consensus on a model for the saltation regime. This study answers several questions raised with respect to the Eulerian-Lagrangian modeling of sediment transport. The first question is why the previous saltation models that use different combinations of hydrodynamic forces yielded acceptable results? The second question is which shear lift model(i.e. a shear lift expression and its coefficient) is more appropriate? Another important question is which hydrodynamic forces have greater contributions to the saltation characteristics of a sediment particle? The last question is what are the contributions of the turbulence fluctuations as well as effects of using two-and three-dimensional(2 D and 3 D) models on the simulation results? In order to fairly answer these questions, a systematic study was done by considering different scenarios. The current study is the first attempt to clearly discuss these issues. A comprehensive 3 D saltation model for non-cohesive sediment was developed that includes all the hydrodynamic forces acting on the particle. The random nature of sediment transport was included using turbulent flow and bed-particle collision models. The eddy interaction model was applied to generate a3 D turbulent flow field. Bed-particle collisions were considered using the concept of a contact zone and a corresponding contact point. The validation of the model was done using the available experimental data for a wide range of sediment size(0.03 to 4.8 cm). For the first question, the results indicated that some of the hydrodynamic effects show opposing trends and some have negligible effects. With these opposing effects it is possible to adjust the coefficients of different models to achieve acceptable agreement with the same experimental data while omitting some aspects of the physics of the process. A suitable model for the shear lift force was develop

关键词： Two-phase model Turbulent flow Sediment transport Saltation Hydrodynamic forces

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Scour and flow field around a spur dike in a 90° bend

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International Journal of Sediment Research 2008年第1期23卷 56-68页

作者： Majid FAZLI Masoud GHODSIAN Seyed ali akbar salehi neyshabouri Department of Civil Engineering Tarbiat Modares University Water Engineering Research Center Department of Civil Engineering Tarbiat Modares University Water Engineering Research Center Department of civil Engineering Tarbiat Modares University

Spur dike is an important element in river training that creates rapid variations in flow field, sediment transport and bed topography. The mechanism of flow and sediment transport in a channel bend is very complex, especially when a spur dike is constructed in a bend. Most of previous investigations on flow behavior and scour around spur dike were carried out in straight channels. In this paper results of experiments on flow field and scour around a spur dike in a 90 degree channel bend are presented. Sand with uniform grain size was used as the bed material. Experiments were conducted for different locations and different lengths of spur dikes at the bend with different values of discharge. The three dimensional flow fields around a spur dike were investigated. The maximum depth of scour was correlated to the Froude numbers, lengths and the locations of spur dike in the bend.

关键词： Spur dike Scouring 90° channel bend Bed topography Movable bed Flow pattern

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Numerical simulation of incipient particle motion

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International Journal of Sediment Research 2020年第1期35卷 1-14页

作者： ali Nasrollahi ali akbar salehi neyshabouri Goodarz Ahmadi Masoud Montazeri Namin Civil Engineering Department Tarbiat Modares University Department of Mechanical and Aeronautical Engineering Clarkson University Civil Engineering Department University of Tehran

A two-dimensional(2 D) computational model for simulation of incipient sediment motion for noncohesive uniform and non-uniform particles on a horizontal bed was developed using the Discrete Element Method(DEM).The model was calibrated and verified using various experimental data reported in the literature and compared with different theories of incipient particle *** analysis was done and the effects of relevant parameters were *** addition to hydrodynamic forces such as drag,shear lift and Magnus force,the particle-particle interaction effects were included in the *** asymptotic critical mobility number was evaluated for various critical particle Reynolds numbers(R*) in the range of very small and very large R*.The obtained curve is classified into four *** was found that in the linear region,the drag force has the principal role on the initiation of ***,the critical mobility number is independent of particle diameter.A procedure for estimating the critical shear velocity directly from the information on particle diameter and roughness height was ***,the mechanism of incipient motion for the different regions was studied and the effect of different forces on the incipient particle motion was *** was found that the maximum effects of lift and Magnus forces were,respectively,less than ten and twenty percent of the total *** drag force,however,was typically the dominant force accounting for majority of the net hydrodynamic force acting on sediment particles at the onset of incipient motion.

关键词： Incipient motion Shields curve Numerical simulation Drag force Lift force Magnus force Discrete Element Method

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EXPERIMENTAL AND FIELD STUDY ON MINING-PIT MIGRATION

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International Journal of Sediment Research 2002年第4期17卷 323-331页

作者： S.ali akbar salehi neyshabouri,ali FARHADZADEH,Ata AMINI Civil Engineering Dept. University of Tarbiat Modarres University of Tarbiat Modarres University of Tarbiat Modarres Assistant Professor P.O.Box14115-143 Tehran Iran Ph.D.Student Msc.Student

Rivers are one of the most essential sources of sand and gravel supply for civil works. However, undesirable effects of irregular in-stream mining have been reported on natural sources, environment and infrastructures close to rivers. Therefore, it is necessary to find the effects of mining on rivers in more details. This research concentrates on mining-pit migration phenomenon and its effects on the channel bed. This paper reports an experimental study on the migration of rectangular mining pits and variation of longitudinal profile in the channel bed composed of rather uniform sediments. Different values of widths and lengths were used for pit while pit depths and flow variables were kept constant. The results show that the migration speed changes with the length/width ratio of the pit. The migration speed in convection period is higher than that in diffusion period. In addition, by increasing the length or width, filling rate of pit increases, where the effect of width is more important than the effect of the length. Also is reported in this paper a field study on the changes of three pits excavated at different locations of a river. Some similarities between the pit migration in the straight reach of the river and that of the experimental work is realized and presented.

关键词： Pit migration Sand and gravel mining Experiment Field study

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