A finite volume shock-capturing solver of the fully coupled shallow water-sediment equations

This paper describes a numerical solver of well-balanced, 2D depth-averaged shallow water-sediment equations. The equations permit variable variable horizontal fluid density and are designed to model watersediment flow over a mobile bed. A Godunov-type, HLLC finite volume scheme is used to solve the fully coupled system of hyperbolic conservation laws which describe flow hydrodynamics, suspended sediment transport, bedload transport and bed morphological change. Dependent variables are specially selected to handle the presence of the variable density property in the mathematical formulation. The model is verified against analytical and semi-analytical solutions for bedload transport and suspended sediment transport, respectively. The well-balanced property of the equations is verified for a variable-density dam break flow over discontinuous bathymetry. Simulations of an idealised dam-break flow over an erodible bed are in excellent agreement with previously published results ([1]), validating the ability of the model to capture the complex interaction between rapidly varying flow and an erodible bed and validating the eigenstructure of the system of variable-density governing equations. Flow hydrodynamics and final bed topography of a laboratory-based 2D partial dam breach over a mobile bed are satisfactorily reproduced by the numerical model. Comparison of the final bed topographies, computed for two distinct sediment transport methods, highlights the sensitivity of shallow water-sediment models to the choice of closure relationships

Variable density shallow flow model for flood simulation

Flood inundation is a major natural hazard that can have very severe socio-economic consequences. This thesis presents an enhanced numerical model for flood simulation. After setting the context by examining recent large-scale flood events, a literature review is provided on shallow flow numerical models. A new version of the hyperbolic horizontal variable density shallow water equations with source terms in balanced form is used, designed for flows over complicated terrains, suitable for wetting and drying fronts and erodible bed problems. Bed morphodynamics are included in the model by solving a conservation of bed mass equation in conjunction with the variable density shallow water equations. The resulting numerical scheme is based on a Godunov-type finite volume HLLC approximate Riemann solver combined with MUSCL-Hancock time integration and a non-linear slope limiter and is shock-capturing. The model can simulate trans-critical, steep-fronted flows, connecting bodies of water at different elevations.The model is validated for constant density shallow flows using idealised benchmark tests, such as unidirectional and circular dam breaks, damped sloshing in a parabolic tank, dam break flow over a triangular obstacle, and dam break flow over three islands. The simulation results are in excellent agreement with available analytical solutions, alternative numerical predictions, and experimental data. The model is also validated for variable density shallow flows, and a parameter study is undertaken to examine the effects of different density ratios of two adjacent liquids and different hydraulic thrust ratios of species and liquid in mixed flows. The results confirm the ability of the model to simulate shallow water-sediment flows that are of horizontally variable density, while being intensely mixed in the vertical direction. Further validation is undertaken for certain erodible bed cases, including deposition and entrainment of dilute suspended sediment in a flat-bottomed tank with intense mixing, and the results compared against semi-analytical solutions derived by the author.To demonstrate the effectiveness of the model in simulating a complicated variable density shallow flow, the validated numerical model is used to simulate a partial dam-breach flow in an erodible channel. The calibrated model predictions are very similar to experimental data from tests carried out at Tsinghua University. It is believed that the present numerical solver could be useful at describing local horizontal density gradients in sediment laden and debris flows that characterise certain extreme flood events, where sediment deposition is important.</p

Risk-adjusted Earned Value and Earned Duration Management models for project performance forecasting

Project control is essential to ensure that the investment on a project is providing the intended benefits and is valuable to the customers. Previous methods offer project performance monitoring and forecasting tools, but they lack accuracy and the associated techniques omit the project financial risk (any unplanned event that has an impact on schedule and budget); the main factor of project failure. Poor project execution, and particularly failure to control and accurately forecast the project performance, may lead to increased costs, upset customers and eventually loss of market share. These gaps have been filled in this study by the development of novel models that use statistical analysis of the previous project performance, including risk evaluation techniques. The proposed models succeeded in providing remarkably improved forecasts in three project dimensions: duration, cost and resources. The robustness of the models has been verified by testing them on real projects. The results show superiority in terms of accuracy and easy application compared to any existing method, proving that the risk inclusion provides improvement compared to previous studies. The most important features of the models are: risk-based adjustment of the forecasted values, periodic and completion forecasts, statistical processing and holistic approach. The greatest advancements have been made in the cost forecast, for which the risk adjustment inclusion is examined for the first time. The resources (man-hours) forecast is another pioneer element of the proposed models. All the above provide a complete image of the project status and paint the picture of future performance. The models results are fed in a Decision Support System, which highlights the overperforming and underperforming areas of the project. This confirms the proposition that the model results can be used to initiate restorative action. The contribution of this study to the project management field is easy-to-use and accurate models, which include the financial risk and facilitate the project manager’s decisions and actions. Anticipation of the project performance, by considering the risk, can result to significant time and cost savings, crucial for project success.  

Risk-adjusted Earned Value and Earned Duration Management models for project performance forecasting

Project control is essential to ensure that the investment on a project is providing the intended benefits and is valuable to the customers. Previous methods offer project performance monitoring and forecasting tools, but they lack accuracy and the associated techniques omit the project financial risk (any unplanned event that has an impact on schedule and budget); the main factor of project failure. Poor project execution, and particularly failure to control and accurately forecast the project performance, may lead to increased costs, upset customers and eventually loss of market share. These gaps have been filled in this study by the development of novel models that use statistical analysis of the previous project performance, including risk evaluation techniques. The proposed models succeeded in providing remarkably improved forecasts in three project dimensions: duration, cost and resources. The robustness of the models has been verified by testing them on real projects. The results show superiority in terms of accuracy and easy application compared to any existing method, proving that the risk inclusion provides improvement compared to previous studies. The most important features of the models are: risk-based adjustment of the forecasted values, periodic and completion forecasts, statistical processing and holistic approach. The greatest advancements have been made in the cost forecast, for which the risk adjustment inclusion is examined for the first time. The resources (man-hours) forecast is another pioneer element of the proposed models. All the above provide a complete image of the project status and paint the picture of future performance. The models results are fed in a Decision Support System, which highlights the overperforming and underperforming areas of the project. This confirms the proposition that the model results can be used to initiate restorative action. The contribution of this study to the project management field is easy-to-use and accurate models, which include the financial risk and facilitate the project manager’s decisions and actions. Anticipation of the project performance, by considering the risk, can result to significant time and cost savings, crucial for project success.  

Variable density shallow flow model for flood simulation

Flood inundation is a major natural hazard that can have very severe socio-economic consequences. This thesis presents an enhanced numerical model for flood simulation. After setting the context by examining recent large-scale flood events, a literature review is provided on shallow flow numerical models. A new version of the hyperbolic horizontal variable density shallow water equations with source terms in balanced form is used, designed for flows over complicated terrains, suitable for wetting and drying fronts and erodible bed problems. Bed morphodynamics are included in the model by solving a conservation of bed mass equation in conjunction with the variable density shallow water equations. The resulting numerical scheme is based on a Godunov-type finite volume HLLC approximate Riemann solver combined with MUSCL-Hancock time integration and a non-linear slope limiter and is shock-capturing. The model can simulate trans-critical, steep-fronted flows, connecting bodies of water at different elevations. The model is validated for constant density shallow flows using idealised benchmark tests, such as unidirectional and circular dam breaks, damped sloshing in a parabolic tank, dam break flow over a triangular obstacle, and dam break flow over three islands. The simulation results are in excellent agreement with available analytical solutions, alternative numerical predictions, and experimental data. The model is also validated for variable density shallow flows, and a parameter study is undertaken to examine the effects of different density ratios of two adjacent liquids and different hydraulic thrust ratios of species and liquid in mixed flows. The results confirm the ability of the model to simulate shallow water-sediment flows that are of horizontally variable density, while being intensely mixed in the vertical direction. Further validation is undertaken for certain erodible bed cases, including deposition and entrainment of dilute suspended sediment in a flat-bottomed tank with intense mixing, and the results compared against semi-analytical solutions derived by the author. To demonstrate the effectiveness of the model in simulating a complicated variable density shallow flow, the validated numerical model is used to simulate a partial dam-breach flow in an erodible channel. The calibrated model predictions are very similar to experimental data from tests carried out at Tsinghua University. It is believed that the present numerical solver could be useful at describing local horizontal density gradients in sediment laden and debris flows that characterise certain extreme flood events, where sediment deposition is important.EThOS - Electronic Theses Online ServiceGBUnited Kingdo