Research Of Two-Step Optimization For Optimal Design Of Water Distribution System

Water distribution system (WDS) is an important part of urban water supply system ,which is not only a bridge linking water treatment plant with customer, but also accounts for 50~80 percent of total investment and 30~50 percent of energy consumption of the total water supply system budget. The investment in rehabilitation is growing with the development of water use. The rationality of network programming, design and operating can affect the investment and reliability of water supply system.This thesis studies optimization of WDS from the view of economy and reliability. A two-step optimization technique is put forward in the study. It includes two parts: optimization of network topology and optimization of pipe size. The study uses Dijkstra arithmetic to get the best network layout, and adopts Genetic Algorithms (GA) to get the optimal combination of pipe size.By analyzing existing WDS design modes, the author presents a multi-objective model based on economy and reliability. In the process of setting up the model, the reliability of WDS is defined as"weighted mean of nodal extrapressure"and"pipe network resilience"in order to make it easy and straight forward to evaluate the reliability of WDS. At the same time, the annual cost is used as the economical characteristic of WDS.The two-step optimization technique is put forward in the study with the combination of optimization of network topology and optimization of pipe size. With this method, I designed a nine loop network. First, a good trunk main network layout is fixed, then GA is used to get a reasonable combination of pipe size. The result shows that two-step optimization technique is better than the traditional design on the aspects of convergence and calculation efficiency. It is very important to the optimal design of WDS.