Browsing by Subject "Inventory Policy"
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Item Open Access Age and lifetime based policies for perishable items(2018-10) Poormoaied, SaeedMany inventory systems hold items which perish after a specific time. Upon perishing, the inventory level falls down to zero which may incur irreparable costs to the system. Therefore, developing a genius control policy for managing such inventories is a crucial task. Since the lifetime of items are now affecting the inventory level, applying the traditional inventory policies which are based only on the stock level causes some shortcomings. The traditional inventory policies lack the information regarding the lifetime of items. On the other hand, the optimal policy for perishable items is known to be a periodic review policy keeping the complete information regarding the remaining lead times of orders, inventory onhand, and lifetimes of items. Optimal control policy class for continuous review is still an open question. In this regard, we attempt to contribute the remaining lifetime of items into the inventory policy for perishable items with positive lead time and fixed lifetime under a continuous review with a service level constraint. We develop a class of hybrid control policies which utilize the remaining lifetimes of items in addition to stock levels. We study a stochastic single item inventory system where demand follows a Poisson process and unmet demand is lost. The aging process of a new batch starts when it joins the inventories. We provide an exact analytic model by using an embedded Markov chain process to derive the stationary distribution of the effective lifetimes in the presence of both one and more than one outstanding orders assumptions. Operating characteristics of the system are derived using the renewal reward theorem. Additionally, we propose some control policies based on only the remaining lifetime of items. Our results reveal that the hybrid policies consistently outperform the stock level and remaining lifetime-based polices, especially when demand during the lifetime is sufficiently small and unit perishing cost is high. It is observed that the dominance relations among these two policy classes depend on the particular parameter setting. In particular, when the lifetime of items is long enough, the stock level based policy performs very well. Finally, we present our methodology for finding the optimal solution thorough a heuristic algorithm derived by considering the structure of the objective function and service level constraint, and a sensitivity analysis is performed to evaluate the impact of the key input parameters.Item Open Access Product rollover strategy and inventory policy of a monopoly manufacturing substitutable products(2010) Koca, EsmaIn many industries, effective management of product rollovers is extremely important for being able to survive. In management of product rollovers, timing decision; i.e., time to introduce of a secondary product and time to phase out a primal product is critical. Inventory policy is another factor that affects management of rollovers. In this study, we analyze primary rollover strategy of a monopoly manufacturing two substitute products together with its contingency strategies over a two period planning term. Specifically, we consider four different primary rollover strategies, namely Base Strategy, IS Strategy, ISES Strategy and IFES Strategy, derived with existence/non-existence of the products. Base Strategy is associated with the case where we decide to introduce and sell only the primary product. On the other hand, IS Strategy brings introduction of a newer (secondary) product in the second period. If monopoly chooses to make its move with IFES Strategy, it introduces both of the products simultaneously in the first period while phasing out the primary product in the beginning of the next period. Another alternative strategy, ISES Strategy, would be selling products in different periods, primary product first and secondary product next. When a primary strategy is selected, there is a commitment to this strategy. In this study, to reflect market conditions, we consider two alternative demand forms; multiplicative and additive forms and there is an adjustment to market through inventory policy. Firm replenishes its stocks with an order-up-to policy in each period where demands for these substitute products are assumed to be correlated and these products assumed to be substitutable; i.e., there exists stockout-induced substitution between the products.In the analysis, we determine the optimal inventory levels when a specified rollover strategy is executed. Moreover, we explore the conditions, which play important role in making rollover strategies. Furthermore, factors that affect early and late introduction of a new product into the market are investigated. We also discuss the factors that motivate a monopoly to introduce a new product.