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Study on the physics of sediment particle movement in micro scale is essential for better understanding sediment transport phenomenon and estimating the rate of sediment transport in rivers and marine environment. Sediment particles basically transport in two modes of bed and suspended load. Bed load takes place through sliding, rolling and saltation. Many parameters influence on this process, which their effects are not fully understood. In this research the influence of the affecting parameters on movement of sediment particles in saltation under unidirectional steady flow are investigated. First, a numerical model is developed to simulate the particle motion in bed load saltation. Then the influencing parameters such as particle shape and its position between other particles, upon the jump length and average velocity of the particles are studied. The result of the study improves our understanding and results in better estimation of sediment transport rate for engineering application.

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Study on the physics of sediment particle movement at grain scale is essential for better understanding sediment transport phenomenon and estimating the rate of sediment transport in rivers and marine environment. Sediment particles basically transport in two modes of bed and suspended load. Bed load takes place through sliding, rolling and saltation, from which the latter is dominant. Many parameters influence on saltation phenomenon, which their effects are not fully understood. These influencing parameters make the saltation a stochastic phenomenon. In the present article the influence of the affecting parameters on movement of sediment particles at saltation mode of transport under unidirectional steady flow are investigated. A numerical model is developed to simulate the particle motion in bed load saltation with considering the main contributor forces. Then the influencing parameters that effect on the jump length and average velocity of the particles are studied. Among them are the initial condition, the particle position between other particles and the shape of particles. The influence of the velocity profile on the jump length and average velocity of the particles are also studied. In summary, the change in the initial condition including the initial velocity and angle produces less than 10% variation on the particle jump length and velocity. On the other hand the position of the grain between the other particles is considerably influential with 40% change in the jump length and average velocity. The particle shape is most important parameter in term of the influence on the jump length and average velocity; there is a 50% difference between the jump length of spherical particles and flake-shape particles, for average velocity it is about 10%. The result of the study improves our understanding of particle motion at grain scale and ultimately results in the better estimation of sediment transport rate. 

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Two incompressible SPH numerical solvers, including a modified explicit method and a new implicit method have been developed to simulate the sediment-laden free surface flow problems. Using, consistent discretization schemes, the proposed explicit method improves somewhat the accuracy of the usual explicit ISPH methods. The implicit method additionally guarantees the incompressibility condition completely. In the presented methods, the liquid phase is modeled using Navier-Stokes equations and to predict the non-Newtonian behavior of the sediment phase, the Bingham plastic rheological model is used. The accuracy and capabilities of the developed incompressible SPH methods is first validated in comparison with available experimental and numerical results of a single-phase water-sediment mixture flow generated by unsteady dam break problem. Then, they are applied to simulate an eroding dam break problem with a two-phase flow sediment transport. Comparing the obtained results with the available results in the literature shows that the developed methods particularly the implicit one, are very powerful tools for simulation of the problems including sediment transport induced by violent free surface flow, with interactions between flow and sediment and morphological changes in bed.

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A large number of flows encountered in nature and technology are a mixture of phases. Advances in computational fluid mechanics have provided the basis for further insight into the dynamics of multiphase flows. Currently there are two approaches for the numerical calculation of multiphase flows: the Euler-Euler approach and the Euler-Lagrange approach
In the Euler-Euler approach, the different phases are treated mathematically as interpenetrating continua. In FLUENT, three different Euler-Euler multiphase models are available: the volume of fluid (VOF) model, the mixture model, and the Eulerian model. For sedimentation, we must use the Eulerian model. The Eulerian multiphase model in FLUENT allows for the modeling of multiple separate, yet interacting phases. The phases can be liquids, gases, or solids in nearly any combination. The Lagrangian discrete phase model (DPM) in FLUENT follows the Euler-Lagrange approach. The fluid phase is treated as a continuum by solving the time-averaged Navier-Stokes equations, while the dispersed phase is solved by tracking a large number of particles through the calculated flow field.
Sediment transport by fluid flow is one of the most important two phase flow in the nature. Due to existence of secondary current in channel bends, the mechanism of flow and sediment transport in these channels is much complex and locationg lateral intake at outer bank of the bens decreases this compelexity.
In this paper, mechanisms of sediments transport into the intake in a 180 degree bend channel with lateral intake have been simulated whit the Eulerian and Discrete phases models in fluent software. The intake is located at the outer bank of an 180o bend at position 115° with 45° diversion angle. The effect of diversion discharge rate and diversion angle on mechanism of sediment entry to the intake was considered.
The turbulence model is k-ε model. Model҆s in different time has performed and the result compared with laboratory result.The results show in Qr=40%, the mechanism of sediment entry was consist of continues entrance from downstream edge of intake and periodic entrance from upstream of the intake, however in Qr=25%, the mechanism of sediment entry was only consist of continues entrance from downstream edge of intake. The two models (Eulerian and Discrete phases) have shown good results. The rout mean square errors for outer boundary of the path of the particle at the channel ҆s bed for two discharges (25% and 40%) have measured.
The number of particle in discrete phases is limited; therefore this model cannot be display the depth of sediment. The Eulerian model displays the bed topography very well. Measuring mean square errors show that the model operation for topography simulation is very well. This model shows the location of intermittent dune and location of sediment accumulation very well. The discrete phase model can be shown the particle trapped place better than the Eulerian model.
Due to increase in intake discharge, dimension of sediment accumulation is decrease. the mechanism of sediment entry to lateral intake is affected by diversion angle of intake. the minimum sediment is entered to lateral intake at diversion angle equal to 50 degree.

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In this paper a Godunov-type finite volume method is used for the solution of bedload sediment transport dynamics. The utilised equations for this modelling comprise the shallow water equations used for the hydrodynamic phase and also the Exner equation applied for the morphodynamic variations. These set of equations are then solved using a weakly-coupled scheme based on an augmented Riemann solver. In this approach the morphodynamic equation is first solved and the updated bedload changes with the same Riemann structure are used as a source term within the shallow water equations. The proposed numerical model is first used for the simulation of the parabolic sediment layer and the obtained numerical results are validated with the exact solution. Then, a bedload hump propagation with an initial subcritical condition which is able to create both mild and strong sediment and free-surface interactions is considered and the computed results are compared with the reference solution. These numerical results indicate that the defined weakly coupled method developed based on an augmented Riemann technique is able to be used for modelling bedload sediment transport for all flow regimes and exhibits a very good agreement with analytical or reference solutions for the given test cases.

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Turbidity currents account for transporting sediments into reservoirs, seas, and oceans. Therefore, understanding dynamics of these currents for sedimentation and erosion is very important. In this paper, the effects of two obstacles on the behaviour of turbidity currents investigated experimentally. An 11 m long rectangular channel (11 m×0.6 m×1.0 m) with the bottom slope of 0.25% was used to run the experiments and a 3 m3 tank along with a constant head tank were served as the turbid water supplier. Two triangular obstacles were installed at predefined locations from the sluicegate. Then the experiments were carried out and the results compared with those from without obstacle condition. Velocity and concentration profiles at the upstream of first obstacle and between the first and second obstacles are measured by Vectrino at quasi-steady conditions and compared to those of without obstacle conditions showing a significant decrease of velosity in the presence of the two obstacles specially between the two obstacles and also at the downstream of the second obstacle. Fluid volume discharge per unit width and suspended sediment transport rate are calculated based on measured velocity and concentration. Also, the effects of inlet Froud number on the fluid volume discharge per unit width and suspended sediment transport rate was investigated. The results show that presence of obstacles introduces new regions to velocity profiles and two ponds of turbidity currents are formed at the upstream of the first obstacle and between the two obstacles. The hydraulic conditions at these ponds make a suitable condition for the suspended particles to be trapped and hence the sedimentation. Variation of the suspended sediment transport rate and the fluid volume discharge per unit width depend on obstacle location. These parameters at the upstream of the first obstacle are directly in proportion to the inlet Froud number while at the downstream the second obstacle and between the obstacles are inversely proportional. By decreasing the inlet Froud number, the volume discharge per unit width increases at the upstream of the first obstacle wheras, the amount decreases between the obstacles. Also, as the inlet Froud number decreases, the suspended sediment transport rate increases at the the upstream of the first obstacle but the value decreases between the obstacles and downstream of the second obstacle resulting the increase of the trap efficiency. The obstacles become more effective in controlling the turbidity currents when the inlet Froud number decreases. The first obstacle is 1.8 times more effective on reduction of local sedimentation rate than the second obstacle. These parameters at the upstream of the first obstacle are directly in proportion to the inlet Froud number while at the downstream the second obstacle and between the obstacles are inversely proportional. By decreasing the inlet Froud number, the volume discharge per unit width increases at the upstream of the first obstacle wheras, the amount decreases between the obstacles. Also, as the inlet Froud number decreases, the suspended sediment transport rate increases at the the upstream of the first obstacle but the value decreases between the obstacles and downstream of the second obstacle resulting the increase of the trap efficiency. The obstacles become more effective in controlling the turbidity currents when the inlet Froud number decreases. The first obstacle is 1.8 times more effective on reduction of local sedimentation rate than the second obstacle.

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Sand and gravel are essential materials for developing purposes in infrastructures and many various purposes. Iran, is a developing country and numerous infrastructure projects all around the country are under construction. This issue, demonstrates the growing demand for sand and gravel harvesting. Irregular and non-technical harvesting of sand and gravel from rivers, plays an important role in unwanted morphological and environmental side-effects. Physical modeling and numerical simulation are two main techniques to investigate this phenomenon. Considering the high cost of constructing physical models, application of numerical tools for simulation of hydrodynamics and sedimentation has made a significant help for understanding the related phenomenon including the effects of sand and gravel removal in different rivers. In this study, the accuracy of the MIKE21 as a two-dimensional numerical tool, in simulation of sand harvesting hole displacement was investigated by comparison with laboratory data. For this purpose, nine experiments with different dimensions of excavation holes were designed in a 10 m long and 0.7 m wide laboratory flume with uniform sand bed materials. (D₅₀=0.71mm). Two types of triangular and trapezoidal excavation holes were tested. Four important point plus depth and area of the excavated hole were considered as base points of comparison between simulated and experimental results. The flow depth was constant during all experiments (12 cm) and clear water condition was considered (v/vc=0.95). Acceptable agreement between numerical and experimental results was observed. However, the accuracy of the model was more in larger holes whereas the maximum error in predicting the migrated hole geometry in trapezoidal holes was about a half of triangular ones. After verifying the numerical model in laboratory, a specific reach in Helleh river was considered as a case study. Initially one-dimensional model of the river was simulated with HEC-RAS. 25 years return period flow hydrograph was introduced as the upstream boundary condition. Normal flow depth at Helleh Lagoon and time series of the water surface elevation changes of the Persian Gulf were introduced as two downstream boundary conditions. The boundary conditions of the selected reach for   two-dimensional modeling were extracted from one-dimensional simulation. After setting up the two-dimensional model, the effect of sand and gravel mining on a bridge in the reach was investigated in two different scenarios. The distance of the sand mining hole to the bridge was selected as 1000 m and 100 m respectively in two scenarios. It should be noted the simulation was conducted only for a 25 years return period within 16 days. More severe floods can leave more significant effects on the river and in-line structures. The results indicated that for a flood event with a return period of 25 years which was considered for simulation, sand and gravel mining had changed the hydraulic parameters and bed profile significantly, so that the flow depth at the vicinity of the excavation hole was raised up to 77% in second scenario. The flow velocity was reduced up to 75% in the first scenario and the bed profile was decreased up to 1.27m at the foundation of the bridge in the second scenario. Initial signs of river meandering were emerged in the second scenario where the flow was deviated to the mining hole.