Value of information and supply uncertainty in supply chains
Cheong, Tae Su
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This dissertation focuses on topics related to the value of real-time information and/or to supply uncertainties due to uncertain lead-times and yields in supply chains. The first two of these topics address issues associated with freight transportation, while the remaining two topics are concerned with inventory replenishment. We first assess the value of dynamic tour determination for the traveling salesman problem (TSP). Given a network with traffic dynamics that can be modeled as a Markov chain, we present a policy determination procedure that optimally builds a tour dynamically. We then explore the potential for expected total travel cost reduction due to dynamic tour determination, relative to two a priori tour determination procedures. Second, we consider the situation where the decision to continue or abort transporting perishable freight from an origin to a destination can be made at intermediate locations, based on real-time freight status monitoring. We model the problem as a partially observed Markov decision process (POMDP) and develop an efficient procedure for determining an optimal policy. We determine structural characteristics of an optimal policy and upper and lower bounds on the optimal reward function. Third, we analyze a periodic review inventory control problem with lost sales and random yields and present conditions that guarantee the existence of an optimal policy having a so-called staircase structure. We make use of this structure to accelerate both value iteration and policy evaluation. Lastly, we examine a model of inventory replenishment where both lead time and supply qualities are uncertain. We model this problem as an MDP and show that the weighted sum of inventory in transit and inventory at the destination is a sufficient statistic, assuming that random shrinkage can occur from the origin to the supply system or destination, shrinkage is deterministic within the supply system and from the supply system to the destination, and no shrinkage occurs once goods reach the destination.