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Periodic-review inventory systems with exogenous and endogenous replenishment lead times

Aşcı, Murtaza
In this thesis, two-echelon systems with exogenous and endogenous lead times are studied for the orders placed by the retailer(s) from the supplier. The retailer(s) employ periodic-review base-stock policy, namely (R,S) policy. For the case the demand during review period is i.i.d. and the probability distribution is Normal for each review period, a new method is proposed for exogenous lead time case under stationary policy. The results of the proposed method is then compared with the results of the existing methods in the literature and it is concluded that the proposed method provides service levels sufficiently close to target levels whereas the existing methods do not necessarily provide target levels. We use the simulation to study the endogenous replenishment lead time case. The proposed method is modified when the retailer employs stationary policy and it is seen that the proposed method gives no-stockout probabilities close to target levels. Moreover, the impacts of using adaptive policy on the performance of the retailer are studied for endogenous replenishment lead time case. It is concluded that updating of the order-up-to-level deteriorates the performance of the retailer. Finally, it is questioned whether it is beneficial for a retailer to use adaptive policy in a supply chain with two retailers. Simulation results show that the deterioration in the performance of the retailer handling stationary policy is larger compared to the other retailer handling adaptive policy and the deteriorations get larger in the case of an increase in update frequency or in utilization of the supplier.