Routing and scheduling decisions in the hierarchical hub location problem
Kara, Bahar Y.
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Hubs are facilities that consolidate and disseminate flow in many-to-many distribution systems. The hub location problem considers decisions including the locations of hubs on a network and also the allocations of the demand (non-hub) nodes to these hubs. In this study, a hierarchical multimodal hub network is proposed. Based on this network, a hub covering problem with a service time bound is defined. The hierarchical network consists of three layers. In this study, two different structures, which are ring(s)-star-star (R-S-S) and ring(s)-ring(s)-star (R-R-S), are considered. The multimodal network has three different types of vehicles at each layer, which are airplanes, big trucks and pickup trucks. For the proposed problems (R-S-S and R-R-S), two mathematical models are presented and strengthened with some valid inequalities. The computational analysis is conducted over Turkish and CAB data sets. Finally, we propose a heuristic algorithm in order to solve large-sized problems and also test the performance of this heuristic approach on Turkish network data set.