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some optimization problems in crossdocking

Cross-docking is a logistics technique used in the retail and trucking industries to rapidly consolidate shipments from disparate sources and realize economies of scale in outbound transportation.  Cross-docking essentially eliminates the costly inventory-holding functions of a warehouse, while still allowing it to serve its consolidation and shipping functions.  The idea is to transfer shipments directly from incoming to outgoing truck trailers, without in between storage.  Goods typically spend less than 24 hours in a cross-dock, sometimes less than an hour.  With the process of moving shipments from the receiving dock (strip door) to the shipping dock (stack door), bypassing storage, cross-docking reduces inventory carrying cost, transportation cost, and other costs associated with material handling. 

A team of engineering students at Penn addressed for their senior design project worked on Intelligent Transportation Systems (ITS) � integrated packages of hardware and software which perform IT functions that are applicable to transportation. They studied information transfer between dispatching station, computer information group, cross-dock manager and floor workers, and proposed an improvement system that will be studied by a transportation cimpany in NJ.

Another issue we are studying is the cost inside a cross-dock. In a cross-dock facility, goods are moved by forklift from incoming truck platforms (strip doors) to temporary holding areas and then to outgoing truck platforms (stack doors) or directly from strip doors to stack doors.  Costs within the cross-dock may be minimized by appropriate assignment of strip doors to incoming trucks and stack doors to outgoing trucks, thus minimizing the distances that forklifts must travel.  Optimizing strip and stack door assignments given the shape of the cross-dock and the origin-destination volumes of goods is known as the Cross-dock Door Assignment Problem (CDAP).  We will present a formulation of the CDAP as a Generalized Quadratic 3-dimensional Assignment Problem.  We will then compare one approximate and two exact solution methods for optimizing door assignments at a small and a medium cross-dock, for artificially generated but realistic origin-destination volumes of trucked goods.

We will also present pictures and a video of the cross-docks of the NJ company with whom we are working.

Joint research with:
Peter Hahn and Eric Bruun, University of Pennsylvania, USA
Artur Alves Pessoa and Guilherme Henrique Ismael de Azevedo, U. Federal Fluminense, Brazil
Graduate students:
Ying Liu, U. Pennsylvania, now at NYU
Yu-Rong Zhu, Univ. of Pennsylvania, then Elder Research, VA, USA.
Engineering seniors:
Jacci Jeffries, Ciara Kennedy, and Lisa Zheng, University of Pennsylvania, USA