Multiobjective Optimization of Pressure Dependent Dynamic Design for Water Distribution Networks

Optimal design and rehabilitation scheduling of water distribution networks (WDNs) have been often dealt separately over the past few decades. However initial design (which is named as static design in this paper) has indubitable influence on the operational condition and rehabilitation scheduling of network. This paper introduces an approach for simultaneous optimization of initial design and rehabilitation scheduling of WDNs during their life cycle. In this approach which is named as dynamic design, pipe diameters in the first year and their rehabilitation/replacement in the next years of the expected life of the network are determined considering the nodal demands growth and increase in pipes’ roughness. The proposed model consists of a multiobjective ant colony optimization engine linked to a pressure dependent analysis model and a pipe break prediction model. This paper introduces the following contributions: (1) it implements dynamic design based on the pressure dependent analysis with considering leakage; (2) a support vector machine based sub model is used for pipe break prediction. Then pipe breaks and their repair costs are considered in dynamic design process; (3) a new reliability index is used as one of the objective functions. Two networks are used to investigate the impact of static and dynamic designs on the reliability and total cost of design and rehabilitation of WDNs during their life cycle. The results show that the dynamic design produces more reliable and lower cost networks in comparison to the ones resulted from either static design or rehabilitation scheduling separately.