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Transportation needs of entrepreneurs in Wroclaw agglomeration - study results

Yedes Y., Chelbi A., Rezg N.

Logistics and Transport

2011

Vol. 12, No. 1

89-100

This paper deals with the integrated supply chain management problem in the context of a single vendor-single buyer system for which the production unit is assumed to randomly shift from an in-control to an out-of-control state. Two different strategies, integrating production, shipment and maintenance policies, are proposed and compared to satisfy the buyers order at a minimum integrated total cost rate. The first strategy is based on a classical production policy for which the buyer's order of size nQ is manufactured continuously and shipped by lots of size Q. The second strategy suggests that the same buyer's order should be produced and shipped separately by equal sized lots Q. For both strate- gies, a corrective or preventive maintenance action is performed at the end of each production cycle, depending on the state of the production unit, and a new setup is carried out. The total integrated average cost per time unit is consid- ered as the performance criterion allowing choosing the best policy for any given situation.

Repairable systems availability optimization under imperfect maintenance

Samet S., Chelbi A., Hmida F.B.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2009

Vol. 57, nr 3

249-256

This paper deals with the modeling of a preventive maintenance strategy applied to a single-unit system subject to random failures. According to this policy, the system is subjected to imperfect periodic preventive maintenance restoring it to 'as good as new1 with probability p and leaving it at state 'as bad as old' with probability q. Imperfect repairs are performed following failures occurring between consecutive preventive maintenance actions, i.e the times between failures follow a decreasing quasi-renewal process with parameter a. Considering the average durations of the preventive and corrective maintenance actions as well as their respective efficiency extents, a mathematical model is developed in order to study the evolution of the system stationary availability and determine the optimal PM period which maximizes it. The modeling of the imperfection of the corrective maintenance actions requires the knowledge of the quasi-renewal function. A new expression approximating this function is proposed for systems whose times to first failure follow a Gamma distribution. Numerical results arc obtained and discussed.