A new approach for implementing the HLL approximate riemann solver for one-dimensional dam-break flows

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Several new techniques are proposed to overcome the deficiencies in the conventional formulation of the approximate Riemann solvers for one-dimensional dam-break flows, which include numerical imbalance and failure to satisfy mass conservation. The former arises in the case of irregular geometry and the latter in the presence of a hydraulic jump. These new techniques include: (1) adopting the form of the Saint Venant equations which include only one source term representing driving forces; (2) using water surface level as one of the primitive variables, in stead of crosssectional area; (3) defining discharge at interface and evaluating it according to the flux obtained by the HLL Riemann solver (Harten et al 1983). The performance of the resulting schemes is evaluated by means of theoretical analysis and various test examples, including ideal dam-break flows with dry bed, hydraulic jump, steady flow over bump with hydraulic jump, and a real-life dam-break flow in natural river valley with complex geometry. It is demonstrated that the scheme has excellent numerical balance and mass conservation property and is capable of satisfactorily reproducing various complicated open channel flows

Flow conveyance and sediment transport capacity in vegetated channels

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732This paper has reviewed the approaches to estimate the roughness of flexible and rigid vegetation under submerged and emergent conditions, and then presented a hydraulic model to compute flow discharge in vegetated channels. The drag effect of vegetation is considered in roughness coefficients in the determination of channel conveyance. The sediment transport capacity in vegetated channels has also been investigated. The bed-load rate is computed using the Wu et al. formula, in which the effective bed shear stress is computed using SRsbγτ=, with S being the channel slope, γ the unit weight of water, and the spacing hydraulic radius defined by Barfield et al. The established models have been tested against experimental and field data. The computed flow discharge and bed-load rate agree well with the measured data

Techniques for mesh density control

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Mesh generation is crucial in computational fluids dynamic (CFD) analysis, which solves a set of partial differential equations (PDE) based on a computational mesh. To a large extent, the success of solving these equations depends on the mesh quality. In addition to the orthogonality and the smoothness, the mesh density distribution is the key to a desirable mesh. The objective of the current research is to develop methods which make the control of mesh density simple and effective. The resulting mesh is near-orthogonal but more desirable for the numerical simulation. In this study, two new techniques for mesh density control are proposed. The first one is a three-parameter stretching function which stretches the nodes along a line in two directions and control their location of the distribution. The second method is a modified RL system (Ryskin and Leal, 1983) in which the distortion function is evaluated by the averaged scale factors and the scale factors which are formulated by weighting functions of desired mesh density distribution

Comparison of 1-d and depth-averaged 2-d fish habitat suitability models

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Habitat evaluation, a state-of-the-art technique for impact assessment and resource management, becomes an important tool for estimating the amount of habitat available for a given fish species within a study reach. This paper presents a comparison of one-dimensional (1-D) and depth-averaged two-dimensional (2-D) fish habitat suitability models. The recently developed CCHE1D and CCHE2Dfvm habitat suitability models as well as the Physical Habitat Simulation System (PHABSIM) are compared in estimation of the weighted usable area and overall suitability index for adult cutthroat trout in the East Fork River in Wyoming at different flow discharges. To enhance the accuracy in determining flow depth and velocity in CCHE1D, a cross section is divided into a suitable number of vertical panels and the flow velocity at each panel is calculated using Manning’s equation. It has been found that 1-D and 2-D models give close estimations for cross sections with simple geometry, but differences exist for those with complex geometry since complex flow features are neglected in the 1-D models

Numerical simulations of channel response to riverine structures in Arkansas River

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Numerical simulation of flows, sediment transport and river channel change in complex geometries of natural environment is a challenge to computational fluid dynamics (CFD). The difficulties include not only the discretization of the physical domain with a computational mesh, but also the capabilities of simulating the short and long term channel morphologic change in response to adjustment of hydraulic structures. Therefore, a robust numerical modeling system consisting of an efficient mesh generator and fluvial process simulator is needed. In this study, the response of the Arkansas River navigation channel to riverine structure modifications was simulated by using a hydrodynamic and sediment transport computational model, CCHE2D. The feasibility of deepening the channel using modified dike fields with more, higher and longer dikes was confirmed with this model. In addition, the new design of the dike fields was further improved by multiple simulations of the computational model

Evaluating the Effects of SARS-CoV-2 Spike Mutation D614G on Transmissibility and Pathogenicity

Global dispersal and increasing frequency of the SARS-CoV-2 spike protein variant D614G are suggestive of a selective advantage but may also be due to a random founder effect. We investigate the hypothesis for positive selection of spike D614G in the United Kingdom using more than 25,000 whole genome SARS-CoV-2 sequences. Despite the availability of a large dataset, well represented by both spike 614 variants, not all approaches showed a conclusive signal of positive selection. Population genetic analysis indicates that 614G increases in frequency relative to 614D in a manner consistent with a selective advantage. We do not find any indication that patients infected with the spike 614G variant have higher COVID-19 mortality or clinical severity, but 614G is associated with higher viral load and younger age of patients. Significant differences in growth and size of 614G phylogenetic clusters indicate a need for continued study of this variant

Optimal control of flood diversion in an open channel and a channel network

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732In the study, the optimization approach is applied to find the optimal lateral outflow hydrograph to control hazardous flood water stages in open channel and channel network in a watershed. By using the internal boundary conditions of the adjoint equations in each confluence of a channel network, the adjoint sensitivity analysis is successfully applied to obtain the optimal solutions of the outflow hydrographs at floodgates. The hypothetical flood control examples demonstrated the applicability and the accuracy of the optimal control methodology to solve the optimal hydrographs of the lateral outflow for control of flood diversion in a channel network and a natural river. In addition, this optimization model based on the nonlinear Saint-Venent equations has been integrated into a general flow model, called CCHE1D, which has been systematically verified and validated. Therefore, this optimization tool is capable of solving realistic flood control problems in natural streams and watersheds

Development of a numerical model for simulating tidal and wave-induced currents in coastal inlets

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732An advanced numerical solution scheme has been developed to solve the two-dimensional shallow water equations for simulating coastal hydrodynamics driven by tides and waves in estuaries and coastal inlets. The shallow water equations are discretized implicitly by the control volume approach, and the resulting linear algebraic equations are solved by a penta-diagonal solver. To confirm the capability and efficiency of the numerical model, the numerical applications in the paper are focused on the simulations of currents induced by tides and spectral waves in coastal inlets. By running the model connected with a wave module steered by the SMS (Surfacewater Modeling System) interface, the obtained numerical results show that this model could run not only with a large time increment, but also stably and robustly in all application simulations

A coupled numerical model for 2-Dimensional surface and 3-Dimensional subsurface flows

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732This paper presents a fully implicit coupled model designed for hydrologic evaluation in wetlands, agricultural fields, etc. In this model, the diffusion wave equation for two-dimensional unsteady surface flow is coupled with the modified Richards equation in the mixed form for three-dimensional unsteady variably saturated subsurface flow. The integration between surface and subsurface flow model components is accomplished by considering the process of infiltration in dynamic equilibrium. The continuity conditions of pressure head and exchange flux are used at the ground surface. The pressure head is assumed to be equal to the surface water depth when surface flow starts to occur, and the water exchange flux is considered in the new surface flow boundary condition. The coupled system of equations governing surface and subsurface flows is discretized using the finite volume method in space and an implicit backward difference scheme in time. To handle the nonlinearity of the system, the modified Picard procedure is used to linearize the surface and subsurface flow equations. The discretized algebraic equation system is then solved using Stone’s Strongly Implicit Procedure (SIP). Accurate numerical solution and mass balance are reached when the convergence criteria of both the Picard iteration loop and SIP solution loop are satisfied at each time step. Component modules and the coupled model have been tested by comparing numerical results with published experimental data and analytical solutions. The results have demonstrated that the established numerical model is capable of simulating 3-D subsurface flow and 2-D surface flow as well as predicting the interactions between them