en تحقیق در عملیات Operations Research پژوهشي Research Considering the high costs of the implementation and maintenance of gas distribution networks in urban areas, optimal design of such networks is vital. Today, urban gas networks are implemented within a tree structure. These networks receive gas from City Gate Stations (CGS) and deliver it to the consumers. This study presents a comprehensive model based on Mixed Integer Nonlinear Programming (MINLP) for the design of urban gas networks taking into account topological limitations, gas pressure and velocity limitations and environmental limitations. An Ant Colony Optimization (ACO) algorithm is presented for solving the problem and the results obtained by an implementation of ACO algorithm are compared with the ones obtained through an iterative method to demonstrate the efficiency of ACO algorithm. A case study of a real situation (gas distribution in Kelardasht, Iran) affirms the efficacy of the proposed approach.<br> &nbsp; Designing urban networks, optimization, tree structure, ant colony algorithm, pressure, velocity, metaheuristic algorithms. 441 460 http://ijiepr.iust.ac.ir/browse.php?a_code=A-10-116-13&slc_lang=en&sid=1 Mojtaba Torkinejad mtorkinejad@yahoo.com 180031947532846004523 180031947532846004523 No Mazandaran University of Science and Technology Iraj Mahdavi irajarash@rediffmail.com 180031947532846004524 180031947532846004524 Yes Mazandaran University of Science and Technology Nezam Mahdavi-Amiri nezamm@sharif.edu 180031947532846004525 180031947532846004525 No Sharif University of Technology Mirmehdi Seyed Esfahani zramiri@gmail.com 180031947532846004526 180031947532846004526 No Amirkabir University of Technology