Most of the manufacturing industries have a certain amount of stock, i.e., material, unfinished product, finished product and so on, in various location in the production process. By this reason, even in production stop due to an earthquake, it is possible to supply products to the market by consuming the stock. On the other hand, for the reason that it is economically disadvantageous to have a stock, there is a necessity for a rational measure in deciding the amount of stock to be kept. Based on above-mentioned circumstances, the authors introduced stock in a production process, and evaluated effect of improving the recovery curve by stock consumption by means of probability theory in the previous paper (Matsumoto and Nakamura 2016). However, the study of required stock amount and simultaneous consumption of multiple stock have been left as a future study.
In this paper, firstly we show the definition and evaluation method of the recovery curve and then propose a method that can be more simply evaluates recovery curve by decomposing a production process into series systems. Finally we propose a method that can consider the effect of the stock by applying stand-by redundant system. Amount of required stock in addition to the simultaneous consumption and priority in the case of the multiple stock in a production process are discussed. Furthermore, applicability of the proposed method is examined by example of a production process.
Assuming a production process of a chemical plant which produces six products, amount of the stock consumption and improving effect to the recovery curve by stock were evaluated. The following results were obtained:
· Stock can be modeled as a stand-by redundant system.
· On series system, if the stock is inexhaustible, effect of stock is determined by the stock which located in the most downstream of the production process and does not depend on upstream-side-stock.
· In the evaluation of the recovery curve, effect of stock is obtained by adding the stock consumption to the amount of production without stock. And the stock consumption is obtained by subtracting the amount of production without stock from that with stock.
· If there are multiple stock in the series system, the upstream-side-stock consumption event is a subset of the downstream-side-stock consumption event.
· By consuming the upstream-side-stock preferentially, balanced (It does not concentrate consumption to a particular stock) stock consumption can be achievable.
The proposed method can be applied to the case that stock performs an important function such as water and gas supply system, water supply and drainage system of the building in addition to the manufacturing industry. Future study is to enhance the versatility of the proposed method. In addition, in this article, it does not mention the problems such as cost by having the stock and the damage correlation between components. Therefore, they are also a topic for future study.
