Jens Wollenweber

A multi-stage facility location problem with staircase costs and splitting of commodities: model, heuristic approach and application

In this paper a multi-stage facility location problem with staircase costs and splitting of commodities is introduced and formulated as a mixed integer program. The problem is motivated by an application in the context of a reverse supply chain for end-of-life vehicles. We propose a two-phase heuristic solution approach: The greedy construction heuristic utilizes the solution obtained by the LP-relaxation of the problem. In the improvement heuristic we combine ADD, DROP and SWAP neighborhoods with a diversification strategy to a Variable Neighborhood Descent (VND) and to a Variable Neighborhood Search (VNS) approach. Computational results show that this approach is able reduce the duality gap provided by state-of-the-art MIP solver CPLEX for small and medium-sized instances and is also able to provide high-quality solutions for large-scale instances with up to 2,900 candidate facilities. The building blocks of the solution approach can easily be rearranged in order to solve other facility location problems.

Application of genetic algorithms for the design of large-scale reverse logistic networks in Europe's automotive industry

After providing a brief overview on Europes legislative situation with regard to the demanded recovering and recycling of end-of-life vehicles the paper characterizes the specifications of a modeling approach describing the design of a recycling network including a large variety of different cooperating actors set at diverse positions on a reverse supply-chain. It advances with a discussion of requirements a suitable optimization approach needs to fulfil. Then it proceeds by addressing the optimization approach that has been chosen and it concludes by providing results for an ideal network design.