Numerical modeling of unsteady and non-equilibrium sediment transport in rivers

Thesis (Master)--Izmir Institute of Technology, Civil Engineering, Izmir, 2008Includes bibliographical references (leaves: 118-128)Text in English; Abstract: Turkish and Englishxiii, 135 leavesManagement of soil and water resources is one of the most critical environmental issues facing many countries. For that reason, dams, artificial channels and other water structures have been constructed. Management of these structures encounters fundamental problems: one of these problems is sediment transport.Theoretical and numerical modeling of sediment transport has been studied by many researchers. Several empirical formulations of transported suspended load, bed load and total load have been developed for uniform flow conditions. Equilibrium sediment transport under unsteady flow conditions has been just recently numerically studied. The main goal of this study is to develop one dimensional unsteady and nonequilibrium numerical sediment transport models for alluvial channels.Within the scope of this study, first mathematical models based on the kinematic, diffusion and dynamic wave approach are developed under unsteady and equilibrium flow conditions. The transient bed profiles in alluvial channels are simulated for several hypothetical cases involving different particle velocity and particle fall velocity formulations and sediment concentration characteristics. Three bed load formulations are compared under kinematic and diffusion wave models. Kinematic wave model was also successfully tested by laboratory flume data. Secondly, a mathematical model developed based on kinematic wave theory under unsteady and nonequilibrium conditions. The model satisfactorily simulated transient bed forms observed in laboratory experiments. Finally, nonuniform sediment transport model was developed under unsteady and nonequilibrium flow based on diffusion wave approach.The results implied that the sediment with mean particle diameter and the sediments with nonuniform particle diameters gave different solutions under unsteady flow conditions

Numerical modeling of unsteady and non-equilibrium sediment transport in rivers

Thesis (Master)--Izmir Institute of Technology, Civil Engineering, Izmir, 2008Includes bibliographical references (leaves: 118-128)Text in English; Abstract: Turkish and Englishxiii, 135 leavesManagement of soil and water resources is one of the most critical environmental issues facing many countries. For that reason, dams, artificial channels and other water structures have been constructed. Management of these structures encounters fundamental problems: one of these problems is sediment transport.Theoretical and numerical modeling of sediment transport has been studied by many researchers. Several empirical formulations of transported suspended load, bed load and total load have been developed for uniform flow conditions. Equilibrium sediment transport under unsteady flow conditions has been just recently numerically studied. The main goal of this study is to develop one dimensional unsteady and nonequilibrium numerical sediment transport models for alluvial channels.Within the scope of this study, first mathematical models based on the kinematic, diffusion and dynamic wave approach are developed under unsteady and equilibrium flow conditions. The transient bed profiles in alluvial channels are simulated for several hypothetical cases involving different particle velocity and particle fall velocity formulations and sediment concentration characteristics. Three bed load formulations are compared under kinematic and diffusion wave models. Kinematic wave model was also successfully tested by laboratory flume data. Secondly, a mathematical model developed based on kinematic wave theory under unsteady and nonequilibrium conditions. The model satisfactorily simulated transient bed forms observed in laboratory experiments. Finally, nonuniform sediment transport model was developed under unsteady and nonequilibrium flow based on diffusion wave approach.The results implied that the sediment with mean particle diameter and the sediments with nonuniform particle diameters gave different solutions under unsteady flow conditions

Experimental Study of Submerged Vanes in Intakes under Sediment Feeding Conditions

Sediment is transported along the river flow and deposited in the mouth of the intake structure over time and reducing the water intake capacity. Nowadays, many water intake structures lose their function and are closed to operation. To deal with this problem, recently, submerged vane application has offered a practical and economical solution. The aim of this study was to evaluate the efficiency of three vane installations under sediment feeding conditions by comparing the bed topography before and after vanes were installed. For that purpose, experiments were carried out in a laboratory channel running for 90-degree intake angle. Three vanes were installed in one column at near the intake entrance. The vanes dimensions were equal to; 3cm height, 12cm long, 10 mm thick, and aligned with α = 20° angle to flow direction. The tests were run until equilibrium was reached, i.e. when the outgoing solid discharge was equal or larger than 90% of the incoming. Once the bed topography remained stable, bed and water level surfaces were measured. tests were carried out by feeding sediment from upstream of the main channel

Prediction of Local Scour around Bridge Piers Using Hierarchical Clustering and Adaptive Genetic Programming

The physics of local scour around bridge piers is fairly complex because of multiple forces acting on it. Existing empirical formulas cannot cover all scenarios and soft computing methods require ever greater amounts of data to cover all cases with a single formula or a neural network. The approach proposed in this study brings together observations from over 40 studies, grouping similar observations with hierarchical clustering, and using genetic programming with adaptive operators to evolve formulas specific to each cluster to predict the scour depth. The resulting formulas are made available along with a basic web-based user interface that finds the closest cluster for newly presented data and finds the scour depth using the formula for that cluster. All formulas have R2 scores over 0.8 and have been validated with validation and testing sets to reduce overfitting. When compared to existing empirical formulas, the generated formulas consistently record higher R2 scores

Using numerical models and acoustic methods to predict reservoir sedimentation

This study draws on drainage basin hydrography, numerical modeling and geographic information system (GIS) techniques in concert with dual frequency echo sounder data to estimate sediment thickness when initial surveys are unavailable or inaccurate. Tahtali Reservoir (Turkey), which provides 40% of water supply to the city of Izmir, was selected as the study site. Deposition patterns within the whole lake were estimated with a 3-D hydrodynamic and sediment transport model applied to Tahtali Reservoir. The numerical model simulated lake response to wind forcing and inflows and/or outflows and was used to describe sediment deposition patterns resulting from the erosion of soils quantified by the implementation of Universal Soil Loss Equation (USLE) to the whole watershed. Surveying of the lake via dual frequency (28/200 kHz) echo sounder system revealed the current bathymetry, and sediment thickness was estimated from the difference of depths measured by the dual frequency sounder along surveyed transects. These results were compared to the modeled sedimentation thicknesses and to preliminary estimates of watershed sediment yield estimated by USLE. Results of this study can be used for further water quality studies and for long term management plans.TÜBİTAK project No: 104Y323 and European Commission project No: 28292 (RESTRAT

Numerical Analysis of Three Vertical Axis Turbine Designs for Improved Water Energy Efficiency

A hydrokinetic turbine with a vertical axis is specifically designed to harvest the kinetic energy from moving water. In this study, three vertical axis water turbines, namely Gorlov, Darrieus, and Savonius turbines, were compared for their efficiency via numerical modeling for steady-state conditions via the ANSYS 2022 R2 Fluent model. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) was implemented with an SST k-ω turbulence model. The dynamic mesh technique, which allows modeling according to changes in angular velocity at each time step, was used to simulate flow around the turbines for six different velocities (from 0.5 to 3 m/s). The efficiency of the turbines was compared and the results were analyzed. The pressure, velocity, and turbulence kinetic energy distributions around the rotor were measured at different rotational angles and results indicated a wider operating range for the Darrieus and Gorlov turbines compared to the Savonius turbine. The highest power coefficient of 0.293 was achieved in the model featuring a Darrieus turbine, corresponding to a TSR value of 1.34, compared to 0.208 for the Gorlov and 0.257 for the Savonius turbine, at TSR values of 1.3 and 1.06, respectively. Numerical modeling results pointed to a significantly higher self-starting capacity for the Savonius turbine compared to the others

Investigation of the Hydroelectric Development Potential of Nonpowered Dams: A Case Study of the Buyuk Menderes River Basin

The adaptation of nonpowered dams (NPDs) to dams with hydroelectric generation units requires only minor interventions compared with the construction of a completely new dam and power plant. Thus, it is both more economical and has a minimal environmental impact, especially during construction. The aim of this study was to determine the environmental, technical, and economic feasibility of hydroelectric retrofitting projects in the Büyük Menderes basin in Turkey. For this purpose, the economic feasibility and retrofitting potential of 11 NPDs in the basin were investigated using Water Evaluation and Planning (WEAP) software. The results from the energy simulation revealed that the annual average hydropower generation potential and installed capacity for the selected 11 NPDs are 38.7 GWh/year and 4.4 MW, respectively. The total estimated capital investment cost of the 11 retrofit projects was found to be $7.9 million with a total NPV of$25.6 million. In addition, in this study, the leveled electricity cost for each retrofitting project was established and compared with the LCOE values of other renewable energy sources. The findings show that retrofitting NPDs may represent an as yet untapped opportunity to support the global energy transition by providing a cheaper and more environmentally friendly option to pioneer rural electrification

Application of Three-Dimensional CFD Model to Determination of the Capacity of Existing Tyrolean Intake

CFD models of intakes in high-head hydropower systems are rare due to the lack of geometric data and cost of modeling. This study tests two different types of software to see how modeling can be performed in a cost-effective way with scarce input data and still have sufficient accuracy. The volume of fluid (VoF) model simulations are conducted using both ANSYS Fluent and OpenFOAM. The geometry is modelled from Google Earth satellite images, drone scanning data, and design drawings from the construction period and supported by field observations for extra quality control. From the model, both capacity parameters and flow pattern are calculated. For capacity, the Cd factor is calculated and compared with the literature. The simulations are conducted for a Tyrolean weir with rectangular bars (flat steel) in the rack. Simulated flow patterns through the rack with ANSYS Fluent and OpenFOAM are compared. OpenFOAM simulations yielded 15% to 20% higher water levels compared to the VOF model applied in Ansys Fluent. Also, when the flow rate was high, the water capture capacity calculated with ANSYS Fluent was 10% higher than that obtained with OpenFOAM. However, considering the total simulation times, modeling with OpenFOAM offered approximately 11% faster results