Amgad Elansary

A mathematical model to stimulate overland and channel flow using the finite element technique was adapted and applied to a small semiarid rangeland watershed (2035 acres) in the USDA Walnut Gulch experimental watershed in the southwestern United States. The Holtan equation was used to estimate precipitation excess, and with the precipitation excess as input, the finite-element technique was used to route overland and channel flow. The program was structured with sufficient flexibility so that the effect of land use changes, either gradual or sudden, on the runoff hydrograph could be estimated. Abstraction losses in the stream channel are accounted for. The simulation model predictions are compared with field data for several storms, and the comparisons are satisfactory; however, improvements could be made with additional data on antecedent moisture content and better estimates of abstraction losses. Based on these comparisons, it is felt that the model can be used to estimate runoff hydrographs from ungaged watersheds in semiarid regions.

A mathematical model to simulate overland and channel flow using the finite element technique was adapted and applied to a small semi-arid rangeland watershed (2,035 acres) in the USDA Walnut Gulch experimental watershed in the Southwestern United States. The Holtan equation was used to estimate precipitation excess, and with the precipitation excess as input, the finite-element technique was used to route overland and channel flow. The program was structured with sufficient flexibility so that effect of land use changes either gradual or sudden, on runoff hydrograph could be estimated. Abstraction losses in the stream channel are accounted for. The simulation model predictions are compared with field data for several storms and the comparisons are satisfactory; however, improvements could be made with additional data on antecedent moisture content and better estimates of abstraction losses. Based on these comparisons, it is felt that the model can be used to estimate runoff hydrographs from ungaged watersheds in semi-arid regions.

A numerical method to calculate the load-settlement of an axially loaded pile is presented. The method is based on an iterative scheme that tests the global equilibrium conditions and the load transfer (t-z) equations. The scheme is both accurate and computationally very economical.

The control of axial stresses and liquid pressure surges in pipes is an important problem in the design of hydraulic pipe networks. The method of characteristics has been used to solve the transient stresses and pressures in liquid-filled piping systems. Friction is included in the equation of motion. The HZim pressure and maximum stress at any point along the length of the pipe are evaluated for the entire simulation tine. A nonlinear search technique has been developed using the simplex method. The optimal valve closure is sought, that will minimize the maximum pressure and/or stresses. A continuous optimal valve closure policy is specified using spline functions. Numerical examples are presented showing the reduction of the dynamic stress and the dynamic pressure from linear valve closure to optimal valve closure.

The control of stresses and liquid pressure surges in pipes is an important problem in the design of hydraulic pipe networks. The method of characteristics has been used to solve the transient stresses and pressures in liquid-filled piping systems. The friction force is included in the equations of motion for the fluid and the pipe wall. The maximum pressure and maximum stress at any point along the length of the pipe are evaluated for the entire simulation time. A nonlinear search technique has been developed using the simplex method. The optimal valve closure is sought, that will minimize the maximum pressure and/or stresses. A continuous optimal valve closure policy is specified using spline functions. Numerical examples are presented showing the reduction of the dynamic pressure and the dynamic stress from linear valve closure to optimal valve closure for a simple pipeline and a complex pipeline. Also, a method for choosing the shortest time of closure which will keep the stresses below specified allowable stresses is presented.

The control of stresses and liquid pressure surges in pipes is an important problem in the design of hydraulic pipe networks. The method of characteristics has been used to solve the transient stresses and pressures in liquid-filled piping systems. The friction force is included in the equation of motion for the fluid and the pipe wall. The maximum pressure and maximum stress at any point along the length of the pipe are evaluated for the entire simulation time. The Von Mises criterion is used for the stress calculation. A nonlinear search technique has been developed using the simplex method. The optimal valve closure is sought, that will minimize the maximum pressure and/or stresses. A continuous optimal valve closure policy is specified using spline functions. Numerical examples are presented showing the reduction of the dynamic stress and the dynamic pressure from linear valve closure to optimal valve closure.

One of the objectives of this study was to reduce the undesirable dynamic pressure oscillation in a simple pipeline due to valve closure and to prevent the occurence of column separation. The second objective was to minimize the maximum dynamic pressure and estimate the best (minimum) time of closure, T*, that results in a pipe stress equal to the maximum allowable stress. The method of characteristics with the time-line interpolation technique was used to solve the transient stresses and pressures in liquid-filled piping system. Frequency-dependent friction was used in the equation of motion for the fluid and the pipe wall. A non-linear optimization technique was utilized to generate the optimum valve closure policy. Maximum and minimum pressure heads resulting from the optimal policy were calculated and compared with those resulting from a uniform valve closure. Plots of the pressure variation at the valve for these two valve closure policies were also generated. Examples are presented to demonstrate the advantage of the optimum valve closure policy over the uniform valve closure policy. The reduction in the maximum dynamic pressure and stress at the valve for different Tc is also presented.

Two mathematical formulations for the computation of transient flow in piping systems are compared with experimental data. The formulations are: a four-equations fluid structure interaction model (FSI) that includes Poisson coupling, and a two-equations model for the fluid. Both models are solved numericaly using the method of characteristics. A partial-closure of a valve located at an intermediate point in a pipeline is used to create transient flow. The two-equations model computed the maximum pressure peak satisfactorily but the FSI model gave an overall better simulation. An unsteady-friction model, added to the FSI model, did not influence the final results significantly. The experimental procedures followed to obtain the valve characteristics and the pressure history along the pipeline are explained in detail. Excellent numerical results at the valve are obtained when experimental data is used to simulate the time …

One of the objectives of this study was to reduce the undesirable dynamic pressure oscillation that occurs in a simple pipeline due to valve closure and to prevent the occurrence of column separation. This is accomplished by maximizing the minimum pressure in the pipeline. The second objective was to minimize the maximum dynamic pressure, and the third objective was to estimate the best (minimum) time of closure, T* c, that results in a pipe stress equal to the maximum allowable stress. The method of characteristics with the time-line interpolation technique was used to solve the transient stresses and pressures in a liquid-filled piping system. Frequency-dependent friction was used in the equation of motion for the fluid and the pipe wall. A nonlinear optimization technique was utilized to generate the optimum valve closure policy. Maximum and minimum pressure heads resulting from the optimal policy were …

Groundwater is one of the most important sources of freshwater in Egypt, with specific reference to cities located away from the River Nile. Unlike surface water, groundwater is not directly subject to pollution. However, owing to its generally very low velocity, groundwater once contaminated will often remain so for many generations to come. Because the process of groundwater pollution is generally lengthy and also due to the low velocities of groundwater, contamination is more likely to be discovered after twenty or thirty years from its initiation so numerical models are vital to predict and study the behavior of contaminant movements under different conditions. In the Sadaat city, various natural and waste or sewage water are stored and spread on, or beneath land surface through oxidation ponds, where they are susceptible to percolation. This study presents the effect of the oxidation ponds on groundwater quality …

Freshwater is a vital commodity. With the ever increasing population and the limited water resources around the world, groundwater is considered one of the strategic supplies of freshwater for agricultural, domestic and industrial uses. Groundwater contamination presents a major environmental hazard. Contamination sources include leaching of agricultural fertilizers and pesticides, leakage from sewers and sewage systems, and spills from underground storage tanks (USTs). Some of these pollutants are biodegradable, such that natural filtration and adsorption may remove part of unsuitable present organisms. On the other hand, chemical contaminants are of persisting nature, and thus more hazardous. One of these is gasoline contamination from USTs, which poses severe contamination problems to the groundwater aquifers. A mathematical and numerical model is developed to simulate the transport and fate of …

The Southern Valley Development Project (Toshka) is a major project located 1,000 km south of Cairo, Egypt. The project involves pouring Nile water out off Lake Naser into the desert in order to reclaim parts of it for agricultural use. The Toshka project is considered one of the largest projects in the world with its unique pumping station that delivers 25 x 106 m3/day (∼300 m3/sec). As a result, safety is a major concern and maximum protection measures against waterhammer should be incorporated into the project's design. Waterhammer analysis will provide the required protection that is needed for both pump and pipeline. This paper contains numerical model that simulates pump power failure followed by a valve closure for a pumping system drawing liquid through a single pipeline and discharging it into a reservoir. The method of characteristics was used to solve the transient pressures in a liquid-filled piping …

The Southern Valley Development Project (Toshka) is a major project located 1,000 km south of Cairo, Egypt. The project involves pouring Nile water out off Lake Naser into the desert in order to reclaim parts of it for agricultural use. The Toshka project is considered one of the largest projects in the world with its unique pumping station that delivers 25 x 106 m3/day (∼300 m3/sec). As a result, safety is a major concern and maximum protection measures against Waterhammer should be incorporated into the project's design. Waterhammer analysis will provide the required protection that is needed for both pump and pipeline. This paper contains numerical model that simulates pump power failure followed by a valve closure for a pumping system drawing liquid through a single pipeline and discharging it into a reservoir. The method of characteristics was used to solve the transient pressures in a liquid-filled piping …

This paper introduces an approach for solving coupled flow and transports equations in a variable density flow system and presents a numerical model for pollutant transport and flow pattern in layered aquifer system. This formulation is general, flexible and capable of taking full advantage of the nature of flow in such multi-layer systems. Governing equations are discussed for the flow and solute solution with significant variations of density through a porous medium. Equations for mass conservation and solute conversation are formulated in terms of mass fraction hydraulic head and the mass fraction concentrated solute solution. These equations are combined into two nonlinear-coupled partial differential equations. The non-linearity arising from the density variation and from a velocity dependent dispersion tensor made the problem very hard. Therefore, special techniques including mixed interpolation finite …

The Egyptian government is replacing the existing Naga Hammadi barrage, located across the Nile River some 450 km south of Cairo, with the New Naga Hammadi barrage (NNHB) to incorporate a hydropower plant and to improve conditions for river traffic. The new structure will lead to an increase in river water levels, both locally near the new barrage and upstream. The rise in river water levels will in turn result in changes in groundwater levels in the aquifer system up and downstream of the barrages. In this paper, an area is chosen, which is expected to suffer from a high groundwater table after the construction of the NNHB, to investigate the problem and propose alternatives for lowering the groundwater levels. The study area is a village called Bakhaness, with an area of 588 ha. It is located some 1.5 km upstream of the NNHB. A computer model (MicroFEM) has been used to simulate the groundwater …