Three dimensional modelling of cohesive sediment transport in estuarine waters

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Details are given herein of the development and application of three-dimensional layer integrated numerical model to predict cohesive sediment transport in estuarine waters. The Finite Volume Method on the staggered grid system was deployed to discretize governing differential equation which consists the mass balance equation for suspended sediments. Three dimensional advection–diffusion equation was solved by the use of splitting algorithm which divided the equation into two-dimensional horizontal and one dimensional vertical part. The layer integrated two-dimensional advection-diffusion equation was solved horizontally using modified ULTIMATE QUICKEST scheme for the advection acceleration while in the vertical part the QUICKEST scheme was deployed. Verification of model was carried out by comparison of model results and analytical solutions. Comparison of these two-set of results represent a reasonable degree of similarity. Model application was carried out by simulating the cohesive sediment transport in Boushehr Bay. Results of developed numerical model were compared with measurements which represents the applicability of the model in real case studies

Application of Bed Load Formulations for Dam Failure and Overtopping

The Enhanced HLLC scheme as a robust approximate Riemann solver is used for numerical modeling of three different test cases of mobile bed and stepped mobile bed in dam failure and dam overtopping conditions. The current research has been done in the frame of the finite volume method using shallow water equations along with the Exner equation for sediment continuity. The Ribberink, Wong and Parker formulations have been used for the modelling of bed load movement. A convenient approach based on the Boussinesq hypothesis is deployed for considering turbulence effects in the second case. The affections of stepped and slope condition for the flow bed are considered through a corrected version of the HLLC flux components. Finally, the model is applied for modelling overtopping in the third case. The results of the present model are relatively reasonable by comparing with the experimental data

Numerical investigation of simultaneous effect of end sills and roughness on flow characteristics in V-shaped stepped spillways

The special configuration of V- shape stepped spillways increases energy dissipation and aeration compared to the smooth spillways due to the creation of many vortices near the steps. In this research, the energy dissipation in different types of stepped spillways with various horizontal face angles has been investigated using numerical modeling. The FLUENT, was used to model the flow over V-shape stepped spillway. The k-ɛ realizable turbulence model was selected to model the turbulent flow. The numerical results were compared with the available experimental data. The results showed a reasonable agreement between two sets of data. Then the effects of horizontal face angle, roughness and the efficiency of the end sill were investigated by numerical modeling. According to the model results, as the horizontal face angle increased, the energy dissipation also increased. Furthermore, the efficiency of end sill on the stepped spillways increased the rate of energy dissipation about 2.8 to 3.99 percent because the end sill acted like a stilling basin. Moreover, the energy dissipation increased slightly about 0.9 to 1.94 percent by increasing the roughness. Also, areas of steps under the negative pressure that could create cavitation were determined to define the minimum negative pressure and its location in all of models. Finally, the simultaneous effect of several parameters was considered to increase the energy dissipation and the minimum negative pressure

Numerical investigation of groundwater balance and artificial recharge in the Kerman-Baghin Aquifer

In the present paper, the behavior of Kerman-Baghin aquifer has been investigated using the MODFLOW program and GMS 10.3 software. The piezometer data during October 2011 are applied for steady state condition of groundwater modeling. Then, the model is calibrated for 66 months for unsteady condition using observational information, and it is validated for 24 months. Finally, the results are compared with the available observed data and show acceptable accuracy in calibration and validation steps. After validating the model, the status of the aquifer is estimated for a period of 5 years. Management scenarios including 10, 20 and 30 percent reduction in groundwater abstraction as well as artificial recharge at eight selected aquifer sites have been investigated. The location of artificial recharge sites is selected based on seven parameters of land slope, distance from waterways, distance from faults, electrical conductivity, hydraulic conductivity, geology of the area and groundwater depth (thickness of unsaturated area). These parameters are combined with the index overlay method by Arc GIS 10.3 software. The results show that by continuing the current situation, the Kerman-Baghin aquifer could face an average annual deficit of more than 52 million cubic meters. It may cause various problems in the near future including abstraction water from groundwater sources and reducing water quality. The results of implementing different scenarios show that, the best scenario can be obtained by 10% reducing water withdrawal with artificial recharge in four zones 1, 2, 10 and 12

Effect of the flow regime on the hydraulic features governing the operation of vortex drop shafts with spiral inlets

If the operation of existing vortex drop shafts should be verified, then it is essential to know the hydraulic performance of these special structures under both subcritical and supercritical flow regimes. The purpose of the present research consisted, then, in providing practical guidelines and recommendations for managing the hydraulic design and verification of subcritical and supercritical vortex drop shafts. The examination of various experimental results from physical model investigations allowed to show that the inlet channel and the spiral inlet behave differently depending on the energy approach flow content. The main dissimilarity lied, however, in the functioning of the vertical shaft and the dissipation chamber. The rotation of the falling flow along the vertical shaft was more evident for approach supercritical flows. Severe flow conditions in terms of water depths and bottom pressures could be observed in the dissipation chamber under a supercritical flow regime. The design of this special component must be carried with prudence compared with the subcritical flow regime because failure events as the chamber submergence and the crash of the bottom surface just under the shaft outlet may occur for approach supercritical flows