Date

2021-5-26

Author

Atashi Khoei, Arsham

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Green logistics encompasses the efforts to observe and reduce the environmental impacts of logistics activities. This thesis studies different problems in two subdivisions of green logistics that are green transportation and green warehousing. To address green transportation, we introduce different problems in the context of the planar facility location problem. We first consider an extension of the classical Weber problem, named as the green Weber problem (GWP). The GWP decides on the location of a single facility in the plane and the speeds of the vehicles serving the customers from the facility within the customers’ deadlines so as to minimize the total amount of carbon dioxide emitted in the whole distribution system. We also introduce time-dependent congestion on roads which limits the vehicle speeds in different time periods and call the resulting problem as the time-dependent green Weber problem (TD-GWP). We formulate the GWP and TD-GWP as second order cone programming problems both of which can be efficiently solved to optimality. Computational results compare the resulting carbon dioxide emissions of the classical Weber problem with those of the GWP and compare the GWP with the TD-GWP in terms of carbon dioxide emissions in different traffic congestion patterns. Then, we study the multi-facility green Weber problem (MF-GWP), an extension of the classical multi-facility Weber problem, that determines the locations of p facilities on the plane, p>1, allocations of customers to the facilities, and the speeds of the distribution vehicles so as to minimize the total amount of carbon dioxide emitted from the vehicles. We formulate this problem as a mixed-integer second order cone programming (MISOCP) problem. This formulation turns out to be weak and therefore only small size instances can be solved to optimality within four hours. For larger size instances, a local search heuristic is proposed and some well-known heuristics developed for the multi-facility Weber problem, namely "location-allocation", "transfer follow-up", and "decomposition" are adapted for the MF-GWP. The experimental results compare the proposed solution methods for the MF-GWP in terms of solution quality and time. We also investigate how the total amount of carbon dioxide emitted by distribution vehicles changes with respect to the number of facilities located. To address green warehousing, we concentrate on energy efficiency in the material handling systems of warehouses. The order picker forklifts, in recent applications of the material handling systems, provide efficient utilization of the limited storage space by their ability to move in narrow aisles and pick items from high level racks in warehouses. Routing the order picker forklifts to pick ordered items belongs to the operational decision making level and is done in high frequency. We introduce and study the energy minimizing order picker forklift routing problem (EMFRP) which aims to find an energy-efficient route for an order picker forklift to pick a given list of items. A mixed-integer programming formulation and a dynamic programming approach are developed to solve the EMFRP exactly. Since the exact solution approaches are able to solve only small size instances to optimality within a given time limit, we provide some tour construction and tour improvement heuristics for the problem and integrate them into a single solution approach. Computational results show that the proposed solution approach for the EMFRP finds high quality solutions. Moreover, it is observed that significant energy savings can be achieved by solving the EMFRP instead of the classical distance minimization problems.

Subject Keywords

Green transportation, Green warehousing, Continuous location, Order picking problem, Second order cone programming, Time-dependent congestion

URI

https://hdl.handle.net/11511/91118

Collections

Graduate School of Natural and Applied Sciences, Thesis