Ali Khosronejad

Simulation-Based Approach for Stream Restoration Structure Design: Model Development and Validation

AbstractWe develop, validate, and demonstrate the potential of Virtual StreamLab (VSL3D), a novel three-dimensional hydromorphodynamics computational model capable of simulating turbulent flow and sediment transport in natural waterways with embedded and arbitrarily complex hydraulic structures under live-bed conditions. The numerical model is based on the curvilinear immersed boundary (CURVIB) approach and can solve the unsteady Reynolds-averaged Navier-Stokes (URANS) equations closed with the k−ω turbulence model in arbitrarily complex waterways with mobile sediment beds. Bed material transport is simulated by solving the nonequilibrium Exner equation for the bed surface elevation coupled with a transport equation for suspended load. Field-scale measurements obtained from experiments carried out in the St. Anthony Falls Laboratory Outdoor StreamLab are employed to validate the predictive capabilities of the numerical model. The VSL3D is used to develop a virtual testing environment of unprecedented reso...

Sand waves in environmental flows: Insights gained by coupling large-eddy simulation with morphodynamics

Sand waves arise in subaqueous and Aeolian environments as the result of the complex interaction between turbulent flows and mobile sand beds. They occur across a wide range of spatial scales, evolve at temporal scales much slower than the integral scale of the transporting turbulent flow, dominate river morphodynamics, undermine streambank stability and infrastructure during flooding, and sculpt terrestrial and extraterrestrial landscapes. In this paper, we present the vision for our work over the last ten years, which has sought to develop computational tools capable of simulating the coupled interactions of sand waves with turbulence across the broad range of relevant scales: from small-scale ripples in laboratory flumes to mega-dunes in large rivers. We review the computational advances that have enabled us to simulate the genesis and long-term evolution of arbitrarily large and complex sand dunes in turbulent flows using large-eddy simulation and summarize numerous novel physical insights derived fro...

Optimization of the Sefid-Roud Dam desiltation process using a sophisticated one-dimensional numerical model

Abstract Although water and soil conservation activities reduce reservoir sedimentation, it is inevitable that reservoirs fed by rivers transporting high amounts of sediment will experience sedimentation. The Ghezel-Ozan and Shah-Roud rivers, which flow to the Sefid-Roud reservoir dam, are both highly sediment-laden and transport significant amounts of sediment in both bed load and suspended load forms to the reservoir. Hence, it seems that the only practical way to remove the sediment from the reservoir is to flush it out using the Chasse method. In the present paper, field measurements of Chasse operation characteristics taken in previous years are presented, and a numerical model that simulates this process is introduced. After calibrating the model using field measured data, the calculated results (for reservoir pressure flushing and released sediment volume) of the numerical model were compared with other measured data for the same Chasse operation and the results agree well. Finally, using the numerical simulation results, the best approaches to ensure highly effective flushing while conserving reservoir water are presented (at least for the Sefid-Roud dam). The operation of the bottom outlet gates, the shape of the output hydrograph, and the reservoir water level variation during flushing were optimized. In addition, the numerical model and related parameters, which need to be calibrated, are discussed.

Simulation-based optimization of in-stream structures design: J-hook vanes

ABSTRACT J-hook vanes are geometrically complex rock structures that are used extensively in stream and river restoration. We employ the St Anthony Falls Laboratory Virtual StreamLab (VSL3D) code to elucidate the flow and transport phenomena induced by such structures in large rivers and develop design guidelines based on this physical understanding. The unsteady Reynolds averaged Navier–Stokes module of the VSL3D model with the k – ω closure is used to carry out coupled hydro-morphodynamic simulations in waterways with complex hydraulic structures. We construct two virtual river geometries, representative of gravel and sand-bed rivers in nature, and employ them for developing design guidelines for J-hook vanes. We systematically simulate numerous arrangements of J-hook vanes to understand physical mechanisms via which such structures modify turbulent flow and sediment transport processes depending on river environment and structure layout. The resulting physical insights are then distilled into a set of physics-based design guidelines for optimal structure design and placement in large rivers.

Simulation-based optimization of in–stream structures design: bendway weirs

Bendway weirs are one of the most practical in–stream rock structures utilized to protect the outer bend of meandering streams and rivers from erosion. We present development of a simulation-based paradigm for effective design of bendway weir structures to enhance meandering stream bank stability and control lateral migration. To do so, we employ the St. Anthony Falls Laboratory Virtual StreamLab (VSL3D) code to elucidate the flow and sediment transport phenomena induced by interaction of flow, mobile bed, and in–stream structures in large rivers under prototype conditions. We carried out numerous numerical experiments to systematically simulate various arrangements of bendway weir in two river test-beds and gaining insights into the physical mechanisms via which such bendway weirs modify turbulent flow, sediment transport and scour processes. The so-gained physical insights are then taken into account to develop a set of practical physics-based design criteria for optimal placement of bendway weirs in large rivers.

Three-dimensional numerical modeling of unconfined and confined wall-jet flow with two different turbulence models

Wall-jet flow is an important flow field in hydraulic engineering, and its applications include flow from the bottom outlet of dams and sluice gates. An in-house three-dimensional (3-D) finite-volume Reynolds-averaged-Navier-Stokes (RANS) numerical model predicts the hydrodynamic characteristics of wall jets with square and rectangular source geometry. Either the low-turbulence Reynolds number k–ω or the standard k–e turbulence closure models are applied. The calculated results for velocity profile and bed shear stress in both longitudinal and vertical directions compare favourably with both the published experimental results and the FLUENT® finite volume model. The two closure models are compared with the k–ω model, displaying 4% greater average accuracy than the k–e model. Finally, the influence of lateral confinement of the receiving channel on wall-jet hydrodynamics is investigated, with decreased longitudinal deceleration and decreased bed shear stress observed in a confined jet. This has important i...

Simulation-based optimization of in-stream structures design: rock vanes

We employ a three-dimensional coupled hydro-morphodynamic model, the Virtual Flow Simulator (VFS-Geophysics) in its Unsteady Reynolds Averaged Navier–Stokes mode closed with

3D Numerical Modeling of Flow and Sediment Transport in Laboratory Channel Bends

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