在存貨系統中，最常使用傳統EOQ模式，但是傳統EOQ模式，未考慮退化性因素，與一般現實狀況不合。關於退化性產品的存貨系統模式之探討，最早是由Ghare和Schrader在1963年提出來的，他們建立了一個退化率與需求率為常數的存貨模式。事實上，對於很多的產品或複雜的系統而言，大部分的產品或系統的壽命都是具有浴缸型退化率函數。此外，在傳統EOQ模式中，我們經常假設需求率為固定已知的常數。然而，在Ouyang et al. (2003)和Teng et al. (2005)中我們可以觀察到需求率通常與存貨水準有關。因此，基於上述理由，本研究考慮在有限的計畫期間內，分別建構產品壽命為Xie等人(2002)、Hjorth (1980)與Mudholkar 和 Srivastava (1993)所定義的浴缸型退化率及隨著存貨水準變動的需求率之存貨模式。
最後，本文將建立三個含有持有成本、退化成本、訂購成本、缺貨成本及產品銷售損失成本的浴缸型退化性之存貨模式。並且利用數值範例來說明求解的程序，以決定最佳訂購策略。 Classical EOQ model is used most frequently in the inventory system, but it is not considered deteriorated factor. It is not conformed with the general realistic state. First, Ghare and Schrader (1963) suggest an inventory model for deteriorating items with fixed deteriorated rate and demand rate. In fact, most products or system life all have bathtub-shaped distributed deterioration for many products or complicated system. In addition, it is generally assumed that the demand rate is constant in the classical EOQ model. However, we could observe that the demand rate usually depends on inventory-level in Ouyang et al. (2003) and Teng et al. (2005). So, in this thesis, we will consider product life with bathtub-shaped distributed deterioration by Xie et al. (2002), Hjorth (1980), Mudholdar and Srivastava (1993) defined and inventory model with stock-dependent demand rate over a fixed planning horizon, respectively. Finally, we construct three bathtub-shaped distributed deterioration inventory models with holding cost, deteriorating cost, ordering cost, shortage cost, and sale loss cost. We give some numerical examples to illustrate solution procedure and decide the optimal replenishment policy.
