Qualification of Hydraulic Analysis Models for Optimal Design of Water Distribution Systems

Young Hwan Choi

doi:10.3390/app11178152

Abstract

The hydraulic analysis of water distribution systems (WDSs) is divided into two approaches, namely, a demand-driven analysis (DDA) and a pressure-driven analysis (PDA). In DDA, the basic assumption is that the nodal demand is fully supplied irrespective of the nodal pressure, which is mainly suitable for normal operating conditions. However, in abnormal conditions, such as pipe failures or unexpected increases in demand, the DDA approach may cause unrealistic results, such as negative pressure. However, despite these realistic hydraulic analysis approaches for WDSs being emphasized in the design process, this consideration was lacking in the design aspect. Therefore, in this study, the designs by the DDA-based design model and PDA-based design model are compared, and their design characteristics are analyzed to identify the efficiency of the WDSs design under abnormal system conditions. The developed PDA model was applied to three networks (a well-known benchmark system and a real-life WDN), and the results showed that the proposed model is superior to other reported models when dealing with negative pressure under abnormal conditions. In addition, the optimal design of WDN considered PDA is presented, and the optimal construction cost is decreased to increase the percentage of PDA.

Highlights

In the hydraulic analysis of water distribution systems (WDSs), there have been several approaches throughout the decades for designing and representing the behavior of these systems more realistically, especially in case of abnormal operating conditions
Based on the characteristic of hydraulic scenarios are applied on three WDSs and derive the difference depending on the hydraulic results, each WDSs performs optimal design using metaheuristic optimization algorithm, methods (i.e., demand-driven analysis (DDA) and pressure-driven analysis (PDA))
The hydraulic analysis of WDSs is categorized into two types of the demand-driven hydraulic analysis, which should be supplied by the fixed demand and the pressure-driven hydraulic analysis, which considers the head–outflow relationship for abnormal conditions

Summary

Introduction

In the hydraulic analysis of water distribution systems (WDSs), there have been several approaches throughout the decades for designing and representing the behavior of these systems more realistically, especially in case of abnormal operating conditions. The risk of an abnormal condition can define a measure with which a hazard or threat resulting either from probable events beyond our control or from the possible consequences of a decision may be assessed [1,2] This abnormal condition can be generated frequently in WDSs fields such as pipe breakage, leakage, extreme demand e.g., fire flow, and for this reason, the realistic quantification of damage via efficient hydraulic analysis approaches is needed. The history of the development of these iterative methods is long and wide; it was Todini and Pilati [3] who suggested the gradient method, an improved version of the Newton–Raphson approach that assumes and obtains unknown values of nodal head and pipe flows simultaneously This approach does not need a balance of equations at the beginning of the method, which is a big improvement compared with previous methods, becoming the most prominent iterative method for simple formulation and computational benefits. The accurate results of this method under normal operation conditions (no leakage, pipe breaks, or unexpected fire demands) were enough reason to implement it in commercial hydraulic solvers, such as EPANET [4] and KYPipe [5]

Methods

Results

Conclusion