Numerical Simulation Of Sediment Transport Research Articles

Numerical Simulation of Sediment Transport in Unsteady Open Channel Flow

This paper presented a two-dimensional, well-balanced hydrodynamic and sediment transport model based on the solutions of variable-density shallow-water equations (VDSWEs) and the Exner equation for bed change for simulating sediment transport in unsteady flows. Those equations are solved in a coupled way by the first-order Godunov-type finite volume method. The Harten–Lax–van Leer–Contact (HLLC) Riemann solver is extended to find the local Riemann fluxes to maintain the exact balance between the momentum term and the bed slope term. A well-balanced scheme is superior to an unbalanced scheme to minimize numerical dispersion as demonstrated by the synthetic standing contact-discontinuity test case. Following this, the model is employed to simulate two laboratory experiments and a field case, the 1996 Lake Ha! Ha! flood event in Canada. The results of water surface elevations and bed surface profiles agree well with the measurements. The accuracy and robustness of the numerical schemes make the model a good candidate for practical engineering applications.

Effect of input-target datasets on sediment transport modelling in alluvial rivers using artificial neural network

ABSTRACT Numerical simulation of sediment transport in alluvial rivers often becomes untenable due to the absence of requisite data. Over the years, artificial neural network (ANN) models have been successfully employed for tackling such scenarios. However, the effect of input and target datasets on the simulation of sediment transport using ANN has not yet been adequately addressed in the literature so far. To study the effect of input-target dataset on the performance of ANN models, the present study employs seven input-target datasets for the development of several ANN models and assessment of their performance. The limited study carried out reveals that there are multiple ANN models – having different combinations of training algorithms, transfer functions and input/target datasets – that can reliably be employed to estimate bed elevation changes in alluvial rivers.

Impact of shape: DNS of sediment transport with non-spherical particles

Abstract

Numerical simulation of sediment transport, phytoplankton biomass and salinity recovery processes in Lake Pontchartrain due to Bonnet Carré Spillway flood release

The Bonnet Carré Spillway (BCS) was constructed from 1929 to 1936 to protect the city of New Orleans from the Mississippi River floods. When the water stage of the Mississippi River is over 5.18 m of flood stage, BCS will be opened to divert the excessive flood water into the Gulf of Mexico through Lake Pontchartrain. During these flood release events, large amounts of freshwater, sediment and nutrients were discharged into the lake and significantly affected its water quality and aquatic environment. A numerical model (CCHE2D) developed at the National Center for Computational Hydroscience and Engineering (NCCHE), the University of Mississippi, was applied to simulate the dynamic process of hydrodynamics and associated temporal and spatial distributions of sediment, salinity and phytoplankton in Lake Pontchartrain due to the BCS flood release events. Three events occurred in 1997, 2008 and 2011, representing the median, low, and high flood discharge cases, were selected for this study. The simulated results were compared with field measured data and satellite imageries obtained from USGS, US Army Crop of Engineers and NOAA, and good agreements were obtained. The effects of nutrients and suspended sediment on the growth of phytoplankton as well as the occurrence of algal bloom in the lake were analyzed. The processes of salinity recovery in the lake were also discussed. The results obtained from this research provide useful information for analyzing the impacts of flood release event on the aquatic ecosystems in Lake Pontchartrain.

Reduction effect of tsunami sediment transport by a coastal forest: Numerical simulation of the 2011 Tohoku tsunami on the Sendai Plain, Japan

We examined the effect of the coastal forest on tsunami sediment movement on the Sendai Plain, Japan, during the 2011 Tohoku tsunami using a numerical simulation of sediment transport. To account for the variable roughness coefficient in the coastal forest, a composite equivalent roughness coefficient was adopted. The simulated mean concentration of suspended sediment, wave height, flow velocity, and inundation limit were significantly reduced by the coastal forest. For fine to medium sand, the volumes of maximum deposition and erosion were reduced to 57–83% of those in the simulation without the coastal forest; these reductions were particularly notable for fine sand. The maximum extent and thickness of the sand layer were also reduced. The simulated sediment thickness and extent with the coastal forest for finer grain sizes roughly agreed with the observations, while the simulated results for coarser sand underestimated the observations. The reduction of sediment transport due to the coastal forest suggests that land use conditions and the vegetation environment at the time of a tsunami should be considered when studying historical and paleo-tsunamis using the geological evidence.

Interface-resolved direct numerical simulations of sediment transport in a turbulent oscillatory boundary layer

The flow within an oscillatory boundary layer, which approximates the flow generated by propagating sea waves of small amplitude close to the bottom, is simulated numerically by integrating Navier-Stokes and continuity equations. The bottom is made up of spherical particles, free to move, which mimic sediment grains. The approach allows to fully-resolve the flow around the particles and to evaluate the forces and torques that the fluid exerts on their surface. Then, the dynamics of sediments is explicitly computed by means of Newton-Euler equations. For the smallest value of the flow Reynolds number presently simulated, the flow regime turns out to fall in the intermittently turbulent regime such that turbulence appears when the free stream velocity is close to its largest values but the flow recovers a laminar like behaviour during the remaining phases of the cycle. For the largest value of the Reynolds number turbulence is significant almost during the whole flow cycle. The evaluation of the sediment transport rate allows to estimate the reliability of the empirical predictors commonly used to estimate the amount of sediments transported by the sea waves. For large values of the Shields parameter, the sediment flow rate during the accelerating phases does not differ from that observed during the decelerating phases. However, for relatively small values of the Shields parameter, the amount of moving particles depends not only on the bottom shear stress but also on flow acceleration. Moreover, the numerical results provide information on the role that turbulent eddies have on sediment dynamics.

Two-dimensional numerical simulation of sediment transport using improved critical shear stress methods

Research on the critical shear stresses for erosion and deposition for cohesive sediment has attracted substantial attention from both engineering and theoretical viewpoints due to their importance in sediment transport theory. Previous studies have proposed a large number of empirical and semi-empirical methods to estimate the critical erosion and deposition shear stress, but comparative analyses and validation of the existing methods are still lacking, leaving questions regarding the applicability ranges of the methods. The current paper evaluates the performance and applicability range of five critical erosion shear stress methods derived from different hypotheses on sediment transport for flume experiments and natural tidal rivers using a process-based model. In addition, the effect of the critical deposition shear stress on sediment transport is investigated. The results show that the different critical erosion shear stress methods yield distinctly different prediction results, and their performance and applicability ranges are discussed by comparing their predictions with measured sediment concentrations from the Shenzhen River and measured geometric changes from the Partheniades' flume experiment. The hiding and exposure effect has been recognized as a crucial factor in the incipient motion of sediment on nonuniform beds. A sensitivity analysis of selective deposition and continuous deposition justifies the existence of the critical deposition shear stress. The current study highlights the performance and applicability ranges of the existing critical shear stress methods in sediment transport modeling for uniform and nonuniform beds, which will enrich understanding of the underlying mechanisms of erosion and deposition of cohesive sediment.

Advance of research on the numerical simulation of sediment transport in the Yellow River estuary

The numerical simulation of sediment transport in the Yellow River estuary is an important method to quantitative analyze the problems by water and sediment movement, including sediment deposition and river bed evolution, beach deposition and development, the formation and development of the delta, and so on. Making an intensive study of the problems is useful to study the principles of sediment movement and the evolution law of the estuary bed, and it is also important significance to scientific demonstrate of the estuary sediment deposition, sea water intrusion prevention treatment scheme and solve the problems of engineering. Based on the mathematical modeling of sediment transport and our research work, this paper analyzes the research statement, the unsolved issues and the developed trend of this kind problem, to provide the theoretical reference on more accurate numerical simulation of sediment transport in the Yellow River estuary and the scientific reference on the demonstration and decision of estuarine regulation scheme.

Numerical simulation of sediment transport in a U-shaped channel with lateral intake: Effects of intake position and diversion angle

In this work, the mechanism of sediment transport in a U-shaped channel with a lateral intake is investigated experimentally and numerically, together with the processes of sediment entry into the intake itself and formation of bed topography. Dry sediment is injected into a steady flow in a rigid channel with a bend and sediment particles are traced in time. In order to validate the numerical model, the three components of the flow velocity, as well as the sediment path in time and the diverted sediment ratios, are measured experimentally. A numerical Discrete Phase Model (DPM) is then applied to study the effect of the intake position and diversion angle on the sediment transport mechanism in the bend. The DPM has, in fact, the capability of specifying for each particle its position relative to a reference time and space and, thereby, it is used in this study to analyze the phenomenon evolution and determine the sediment particles diverted into the intake. The comparison between the experimental data and the DPM numerical results shows a good agreement. In order to investigate the mechanism of sediment transport and to evaluate the percentage of the diverted sediments, a parametric study is then conducted through the numerical model, with different positions of the outer bend of the channel, diversion angles of the lateral intake and diversion discharge ratios. The results show that the mechanism of sediment entry into the lateral intake is affected by the diversion discharge ratio. For low discharge ratios, the mechanism of sediment entry to the lateral intake only consists of continuous entrance from the upstream edge of the intake. With the increase of the discharge ratio, it consists of a continuous entrance from the downstream edge and a periodic entrance from the upstream edge of the intake. The DPM results show that, for all diversion discharge ratios, the minimum percentage of sediment entered into the lateral intake corresponds to the position of 120∘ and diversion angle equal to 50∘.

Study on setting of saturation concentration of suspended sediment in numerical simulation of sediment transport associated with tsunami for off Takahama Bay

Study on setting of saturation concentration of suspended sediment in numerical simulation of sediment transport associated with tsunami for off Takahama Bay

A semi-Lagrangian splitting method for the numerical simulation of sediment transport with free surface flows

We present a numerical model for the simulation of 3D poly-dispersed sediment transport in a Newtonian flow with free surfaces. The physical model is based on a mixture model for multiphase flows. The Navier–Stokes equations are coupled with the transport and deposition of the particle concentrations, and a volume-of-fluid approach to track the free surface between water and air. The numerical algorithm relies on operator-splitting to decouple advection and diffusion phenomena. Two grids are used, based on unstructured finite elements for diffusion and an appropriate combination of the characteristics method with Godunov’s method for advection on a structured grid. The numerical model is validated through numerical experiments. Simulation results are compared with experimental results in various situations for mono-disperse and bi-disperse sediments, and the calibration of the model is performed using, in particular, erosion experiments.

Element-free Galerkin method for numerical simulation of sediment transport equations on regular and irregular distribution of nodes

In this paper, the numerical simulation of the bed-load sediment transport using Element-Free Galerkin (EFG) method is presented. The governing equations of this model include shallow water equations for the hydraulic behaviour, Exner equation for morphodynamic variations, and Grass model for solid discharge. The governing equations are formulated for the coupled approach. The problem is solved using EFG meshfree method, in which the problem domain is represented by a set of arbitrarily distributed nodes; there is no need to use meshes, elements, or any other node connectivity information for field variable interpolation. The EFG method is based on moving least-squares (MLS) shape functions originated in scattered data fitting. Finally, to assess the ability and the efficiency of the EFG method, several benchmark examples on regular and irregular distribution of nodes are investigated and the results are compared with those of previously published works.

A collision model for grain-resolving simulations of flows over dense, mobile, polydisperse granular sediment beds

We present a collision model for phase-resolved Direct Numerical Simulations of sediment transport that couple the fluid and particles by the Immersed Boundary Method. Typically, a contact model for these types of simulations comprises a lubrication force for particles in close proximity to another solid object, a normal contact force to prevent particles from overlapping, and a tangential contact force to account for friction. Our model extends the work of previous authors to improve upon the time integration scheme to obtain consistent results for particle–wall collisions. Furthermore, we account for polydisperse spherical particles and introduce new criteria to account for enduring contact, which occurs in many sediment transport situations. This is done without using arbitrary values for physically-defined parameters and by maintaining the full momentum balance of a particle in enduring contact. We validate our model against several test cases for binary particle–wall collisions as well as the collective motion of a sediment bed sheared by a viscous flow, yielding satisfactory agreement with experimental data by various authors.

Numerical Simulation of Sediment Transport along a Channel with Underwater Sill

Sediment prevention structures such as underwater sill (UWS) may be used to divert the sediment movement, and prevent it to enter the port basin or navigation channel. In this study, a quasi 3D-numerical model called multilayered model based on the Method of Characteristics was utilized to simulate the flow, and a particle tracking method was developed to simulate the sediment transport around an UWS. A straight channel with an UWS approximately a half way between upstream and downstream boundaries was simulated. The height of the UWS was varied to observe the effectiveness of such structure against sedimentation. The influence of UWS on flow and sedimentation pattern, vertical distribution of suspended sediment concentration, and the implication of effectiveness of underwater sill structures to control the flow and reduce sedimentation were analyzed. The numerical simulations indicated that the UWS significantly altered the flow/current pattern. It presence contributes in reducing the sediment transport that cause siltation problem in port basin.

Numerical simulation of sediment transport in coastal waves and wave-induced currents

Prediction of coastal sediment transport is of particularly importance for analyzing coast erosion accurately and solving the corresponding coast protection engineering problems. The present study provided a numerical scheme for sediment transport in coastal waves and wave-induced currents. In the scheme, the sand transport model was implemented with wave refraction-diffraction model and near-shore current model. Coastal water wave was simulated by using the parabolic mild-slope equation in which wave refraction, diffraction and breaking effects are considered. Wave-induced current was simulated by using the nonlinear shallow water equations in which wave provides radiation stresses for driving current. Then, sediment transport in waves and wave-induced currents was simulated by using the two-dimensional suspended sediment transport equations for suspended sediment and the bed-load transport equation for bed load. The numerical scheme was validated by experiment results from the Large-scale Sediment Transport Facility at the US Army Corps of Engineer Research and Development Center in Vicksburg. The numerical results showed that the present scheme is an effective tool for modeling coastal sediment transport in waves and near-shore currents.

Sediment Transport Modelling with Advanced Hydroinformatic Tool Case study - Modelling on Bega Channel Sector

Understanding of sediment transports related phenomena's (soil erosion, particles entrainment, transport and deposition) is important for predicting sediment and contaminant transport in surface water networks. Sediment transport is a critical process in many environmental and hydrotechnical systems, due to its negative effects (eutrophication and siltation of reservoirs, water courses, channels and harbours, earth dam's failures, decreasing of reservoirs storage capacity, damage and loss of wildlife habitat, flooding, especially flash flooding, damage to public health, increase costs of water treatment for drinking, decreased fertility of agricultural land etc.). The management of most aquatic ecosystems and hydrotechnical arrangements requires a detailed understanding of sediment dynamics, with their environmental and economic implications, especially where there is any anthropogenic involvement. Numerical simulations of sediment transport with advanced hydroinformatic tools are often the most efficient and practical methods for predicting sediment transport in complex hydrotechnical systems. Numerical modelling requires descriptions of the individual processes involved in sediment transport: erosion, entrainment, movement of sediments and deposition in the water column. This paper analyzes the necessity and possibility of sediment transport modelling with advanced hydroinformatic tool.

Numerical simulation of sediment transport and bedmorphology around Gangjeong Weir on Nakdong River

In this study, we modified and applied an open source CFD software package, the TELEMAC, to simulate sediment transport and bed morphology around Gangjeong Weir on Nakdong River in Korea. The simulations have been carried out with the real river bathymetry and the weir geometry, and for different operation scenarios of the weir. The hydrodynamic parameters and bed evolutions obtained from the numerical results have been validated against field observation data. Particularly, the scour depth has been verified against the results obtained from a well-known empirical formula. Agreement between numerical computations, observed data and empirical formulas is judged to be satisfactory on all major comparisons. This study is not only to point out the locations where deposition and erosion taken place due to the weir gate operation, but also to analyze the mechanism of formation and evolution of scour holes after the weir gates.

703 自然風を考慮した底質輸送現象の数値解析(GS-5・9 水環境)

703 自然風を考慮した底質輸送現象の数値解析(GS-5・9 水環境)

1-D numerical simulation of sediment transport in alluvial channel beds

1-D numerical simulation of sediment transport in alluvial channel beds

NUMERICAL SIMULATIONS OF SEDIMENT TRANSPORT INDUCED BY THE 2004 INDIAN OCEAN TSUNAMI NEAR KIRINDA PORT IN SRI LANKA

Numerical simulations of sediment transport induced by the 2004 Indian Ocean tsunami near Kirinda port in southeastern Sri Lanka is carried out and the relationships between the tsunami-induced flow and sediment transport are discussed. The results show two clear relationships. The first one is that the local scour occurs and a large amount of suspended sediment is generated around the head of breakwaters when the tsunami-induced flow passes through there. The second one is that the suspended sediment is deposited near vortex centers due to a secondary flow.