Reliability-Based Water Network Optimization for Steady State Flow and Water Hammer

The paper presents the reliability-based water network optimization by selecting the optimal pipe diameters for steady state flow and water hammer under hydraulic reliability. Hydraulic reliability is the probability that a water distribution system can supply consumers’ demands over a specified time interval under specified conditions. Thus, hydraulic reliability refers to the basic function of a water distribution system; conveyance of desired water quantities at desired pressures to desired locations at desired times. The evaluation of the hydraulic reliability of a network is achieved through stochastic simulation. In this study, the Monte Carlo simulation is used. The optimization method used in this study is the Genetic Algorithm (GA) which is a popular optimization choice for solving problems that are difficult for traditional deterministic optimization methods. The main advantage of GA is its ability to find the global optimum by using function values only. The GA is integrated with a hydraulic analysis solver, a Monte Carlo simulation program and a transient analysis program to improve the search for the optimal diameters under certain constraints. These include the minimum allowable pressure head constraints at the nodes for the steady state flow and the minimum and maximum allowable pressure head constraints for the water hammer. The approach was applied on a network and the transient flow is introduced to the water system by the pump power failure. The application of GA optimization tool to the case study demonstrates the capability of the Monte Carlo method and the genetic algorithm to find the optimal pipe. The technique of the optimal pipe diameter selection is very economical as the network design can be achieved without using hydraulic devices for water hammer control. This technique is not only crucial for the design and performance of water networks, but also effective in minimizing costs.