Abstract

International audience; Specific properties emerge from the structure of large networks, such as that of worldwide air traffic, including a highly hierarchical node structure and multi-level small world sub-groups that strongly influence future dynamics. We have developed clustering methods to understand the form of these structures, to identify structural properties, and to evaluate the effects of these properties. Graph clustering methods are often constructed from different components: a metric, a clustering index, and a modularity measure to assess the quality of a clustering method. To understand the impact of each of these components on the clustering method, we explore and compare different combinations. These different combinations are used to compare multilevel clustering methods to delineate the effects of geographical distance, hubs, network densities, and bridges on worldwide air passenger traffic. The ultimate goal of this methodological research is to demonstrate evidence of combined effects in the development of an air traffic network. In fact, the network can be divided into different levels of "cohesion", which can be qualified and measured by comparative studies (Newman, 2002; Guimera et al., 2005; Sales-Pardo et al., 2007).

Abstract

International audience; In this paper, ant colony optimization algorithm (ACOA) is proposed to solve the problem of how to efficiently operate a natural gas pipeline under steady state assumptions. The system is composed by compressing stations linked by pipe-legs. For each station, it is necessary to find the operating turbocompressors optimal values and the discharge pressures ones to minimize the total amount of fuel gas consumed in the system by the compressor stations. In the past, several techniques ranging from classical gradient-based procedures to dynamic programming, for solving this no convex problem have been applied. In this paper, we propose the ant colony optimization metaheuristic. This method was applied to the gas pipeline Hassi R' mell- ARZEW (two cities in Algeria) and the results are compared with those obtained by employing dynamic programming method. From these results, we obtain that the ACO technique is an interesting way for the gas pipeline operations optimization.