Jakobus E. van Zyl

Impact of Water Demand Parameters on the Reliability of Municipal Storage Tanks

AbstractMunicipal storage tanks are normally sized according to inherently conservative design guidelines. An alternative way to determine the required size of a tank, on the basis of a stochastic analysis of the system, was proposed in a previous study, in which it was recommended that tanks should be sized for a minimum reliability of one failure in 10 years at the most critical time of the year, typically under seasonal peak demand conditions. In this study, the same method is used to investigate the impact of different user demand parameters on tank reliability. It was concluded that the supply ratio, defined as the ratio of the source capacity to the average demand in the week considered, is the most important demand-related factor affecting tank reliability. It is shown that the reliability of tanks varies greatly throughout the year, and it is recommended that municipalities do everything possible to ensure that their system runs smoothly over the seasonal peak demand period. Several other importan...

Optimal Reliability-Based Design of Bulk Water Supply Systems

AbstractThe hydraulic reliability of bulk water-supply systems can be defined in terms of the failure frequency of the municipal storage tanks they supply: the system fails when the tank runs dry and is functional otherwise. Municipal storage tanks are normally sized according to deterministic guidelines that make allowances for balancing, fire and emergency storage. In this study, genetic algorithm (GA) optimization was used together with stochastic analyses to find the optimal combination of feeder pipe configuration, feeder pipe capacity and tank capacity for a given risk of failure. A sensitivity analysis was conducted to determine the factors that have the greatest impact on the optimal design for an example system. The results showed that the optimal pipe configuration is a single feeder pipe in most cases, but that two parallel pipes are preferable for shorter feeder pipes. It was found that it is often cost-effective to trade off a smaller tank size for a greater feeder pipe capacity. Based on thi...

Extended-period modeling of water pipe networks-a new approach

The extended-period (time-varying or dynamic) equations describing incompressible flow in pipe networks can be classified mathematically as a set of first-order, non-homogenous, non-linear differential equations. Since this set of equations cannot normally be solved analytically, numerical integration or regression methods are typically used. In this paper, a new method for extended-period simulation, called the explicit integration method, is proposed for water pipe networks without demands. The method is based on the premise that a complex water pipe network can be represented by a number of simple base networks. The simple base networks are selected in such a way that their dynamic equations can be solved through explicit integration. In this paper a simple base network consisting of a fixed-head reservoir feeding a tank through a single pipeline is analyzed. It is then illustrated how a complex water pipe network can be decoupled into its constituent simple base networks and its dynamic behavior simulated using a step-wise procedure. The explicit integration method is then compared to the commonly used Euler numerical integration method. It is shown that the accuracy of the explicit integration method is considerably better than that of the Euler method for the same computational effort.

Critical Parameters for the Reliability of Municipal Storage Tanks

A stochastic analysis method for sizing municipal storage tanks based on reliability criteria is discussed. A sensitivity analysis was done to determine the parameters most critical for sizing tanks (and thus for tank reliability). The results show that daily variations in water demand to be the most critical parameter, followed by hourly variations in demand, the supply ratio, and then pipe failures. Further work is required on fire water before conclusions on its impact can be made.