Vehicle routing problem under safe separation distance for multiple unmanned aerial vehicle operation

In this work, we present a variant of the vehicle routing problem for multiple unmanned aerial vehicle operation. The problem was described as a multi-depot vehicle routing problem with separation distance constraints, and two mathematical models were developed to find the best routes under capacity, maximum traveling time, and intervehicle separation constraints. In the first model, the separation distance constraint was proposed using a discrete time window based on previous studies, while the second model restricts the relative difference of departure time between every two arcs within the safety distance. Although the second model was designed using the mixed-integer linear programming model, finding acceptable solutions within a limited computation time was a challenge. Therefore, a decomposition heuristic, which divides the second model into a routing step followed by a scheduling step, and a hybrid tabu search algorithm with constructive initial solution generation were suggested. The performance of the suggested algorithms was evaluated for randomly generated graphs in two-dimensional space, and computational experiments showed that the proposed algorithms can be applied to practical cases with enhanced computational efficiency.