Search

Numerical algorithms are presented for modeling bank failures during reservoir flushing. The algorithms are based on geotechnical theory and the limit equilibrium approach to find the location and the depth of the slides. The actual movements of the slides are based on the solution of the Navier-Stokes equations for laminar flow with high viscosity. The models are implemented in the SSIIM computer program, which also can be used for modelling erosion of sediments from reservoirs. The bank failure algorithms are tested on the Bodendorf hydropower reservoir in Austria. Comparisons with measurements show that the resulting slides were in the same order of magnitude as the observed ones. However, some scatter on the locations were observed. The algorithms were stable for thick sediment layers, but instabilities were observed for thin sediment layers.

A three-dimensional numerical model was used for calculating the velocity and bed level changes over time in a 90[degrees] bended channel. The numerical model solved the Reynolds-averaged Navier-Stokes equations in three dimensions to compute the water flow and used the finite-volume method as the discretization scheme. The k-[epsilon] model predicted the turbulence, and the SIMPLE method computed the pressure. The suspended sediment transport was calculated by solving the convection diffusion equation and the bed load transport quantity was determined with an empirical formula. The model was enhanced with relations for the movement of sediment particles on steep side slopes in river bends. Located on a transversally sloping bed, a sediment particle has a lower critical shear stress than on a flat bed. Also, the direction of its movement deviates from the direction of the shear stress near the bed. These phenomenona are considered to play an important role in the morphodynamic process in sharp channel bends. The calculated velocities as well as the bed changes over time were compared with data from a physical model study and good agreement was found. CE Database subject headings: Numerical models; Sediment transport; Bed Load; Suspended load; Erosion; Channel beds; Secondary flow; Three-dimensional models.

A three-dimensional CFD model was used to compute the formation of the meandering pattern in an initially straight alluvial channel. The numerical model was based on the finite volume method using an unstructured grid with dominantly hexahedral cells. The k-[epsilon] model was used to predict turbulence and the SIMPLE method was used to compute the pressure. The sediment transport was computed as bed load in addition to solving the convection-diffusion equation for suspended sediment transport. The bed changes were calculated and the grid was altered during the computation as channel erosion and deposition caused wetting and drying. The model was tested by comparing with results from physical model studies carried out at Colorado State Univ., Fort Collins, Colo. The results showed successfully the replication of many of the meander characteristics, including secondary currents, cross-sectional profiles, meander planform, meander wavelength, downstream meander migration, and chute formation. DOI: 10.1061/(ASCE)0733-9429(2003) 129:5(366) CE Database subject headings: Fluid dynamics; Sediment transport; Numerical models; Grid systems; Meandering streams; Computational fluid dynamics technique.

A 3D computational fluid dynamics program was used to calculate the wind-induced accumulation of phytoplankton in Eglwys Nynydd, a water supply reservoir in Wales. The computational fluid dynamics model solved the Navier-Stokes equations for the water velocities using the SIMPLE method to calculate the pressure. Two turbulence models were tested: a zero-equation model and the (kappa-epsilon) model. An unstructured nonorthogonal 3D grid with hexahedral cells was used. The distribution of the blue-green algae Microcystis was calculated by solving the transient convection-diffusion equation for phytoplankton concentration, based on the modeled flow field. The numerical model included algorithms for calculating the growth rate of phytoplankton and simulating the response of the algae to changes in underwater light intensity. The model was validated by comparing the horizontal distribution patterns produced by simulation with those recorded during a field survey of surface concentrations. The results demonstrated reasonable agreement, particularly when using the (kappa-epsilon) turbulence model. The main parameter affecting the results was the effective diameter of the Microcystis colonies.

The stage-discharge curve for a complex spillway geometry has been computed with a three-dimensional numerical model. The model solved the Reynolds-averaged Navier-Stokes equations using the k-ε turbulence model. An orthogonal fixed grid was used, where the cells could be wet, dry or partially wet. A volume-of-fluid method was used to compute the location of the free surface in the grid. The spillway consisted of four partly separated free overflow chambers, with tunnel outlets. The four tunnels joined in a collection tunnel where free surface occurred in some sections and filled the tunnel in others. The resulting stage-discharge curve, therefore, showed two parts: one for low discharges with dominantly free surface flow in the tunnels and another part when the tunnels were filled. The results were compared with a physical model study. The deviation between the computed and measured values of the rating curve were under 2% for most of the curve, but rose to a maximum value of 10% where the flow was most complex. The findings indicate that a three-dimensional numerical model can be an accurate, inexpensive and rapid tool to predict the stage-discharge curve for complex spillways. [ABSTRACT FROM AUTHOR]