An integer nonlinear programming model for a facility fortification of two-level facility location problems under disruptions

Two-level facility location problem (TFLP) is a facility location problem that mainly considers the products shipped between two consecutive levels. There are two variants classified by the facility's capacity: two-level uncapacitated facility location problem (TUFLP) and two-level capacitated facility location problem (TCFLP). Nowadays, in some situations, the main facilities can be at risk of disruptions affecting their failure that may lead to a higher cost to backup products or use the backup facility. Preventing this situation can be done by fortifying the main facilities. In this thesis, we propose integer nonlinear programming models for TUFLP and TCFLP that the main facilities are addressed to fortify under the risk of disruption. Then, the linearization technique and a heuristic are used to reduce the algorithm’s complexity for solving it. Moreover, a case study is illustrated, and the results of solving the simulated problems by the Gurobi optimizer are compared with a heuristic method. The results show that the proposed heuristics could solve the problems in a reasonable time for small and large-scale problems.