Michal Tzur’s List of Recent Abstracts

The Transshipment Fund Mechanism: Coordinating the Decentralized Multi-Location Transshipment Problem

The multi-location replenishment and transshipment problem is concerned with several retailers facing random demand for the same item at distinct markets, that may use transshipments to eliminate excess inventory/shortages after demand realization. When the system is decentralized so that each retailer operates to maximize their own profit, there are incentive problems that prevent coordination. These problems arise even with two retailers who may pay each other for transshipped units. We propose a new mechanism based on a transshipment fund which is the first to coordinate the system, in a fully non-cooperative setting, for all instances of two retailers as well as all instances of any number of retailers. The computation and information requirements of this mechanism are realistic and relatively modest. We also present necessary and sufficient conditions for coordination and prove they are always satisfied with our mechanism. Numerical examples illustrate some of the properties underlying this mechanism for two retailers.

Joint work with E. Hanany and A. Levran.

Efficient and Robust Design for Transshipment Networks

Transshipment, the sharing of inventory among parties at the same echelon level, can be used to reduce costs in a supply chain. The effectiveness of transshipment is in part determined by the configuration of the transshipment network. We introduce chain configurations in transshipment settings, where every party is connected to two other parties to form a loop in which each party has the flexibility to transship in either direction. In the case where transshipment costs are homogeneous, we show that the chain configuration is superior to those suggested in the literature. In addition, we demonstrate the efficiency and robustness of chain configurations for more general scenarios and provide managerial insights regarding preferred configurations for different problem parameters.

Joint work with R. Lien, S. Iravani and K. Smilowitz.

The Repositioning Problem in a Bike-Sharing System

Bike-sharing systems allow people to rent a bicycle at one of many automatic rental stations scattered in the city, use them for a short journey and return them at any other station in the city. Recently many cities around the world deployed such systems in order to encourage their citizens to use bicycles as an environmentally sustainable, socially equitable mode of transportation, and as a good complementary to other modes of mass transit transportation systems. A crucial factor for the success of a bike sharing system is its ability to meet the fluctuating demand for bicycles and for vacant lockers at each station. This is performed through a repositioning operation which consists of removing bicycles from stations with high return rates and transferring them to stations with higher demand rates, using a dedicated fleet of trucks. Operating such a fleet in a large bike sharing system is an intricate problem consisting of decisions on routes that the trucks should follow, and the number of bicycles that should be removed or placed in each station at each visit of the truck. In this research we model several versions of the repositioning problem, formulate them as MILPs, and develop methods to solve problems of realistic size.

Joint work I. Forma and T. Raviv.

Last modified: February 2010.