An analytical approach for using simulation in real-time decision making in FMSs

This paper presents an analytical approach to determine the suitability of and to adapt discrete-event simulation for real-time decision making in fle xible manufacturing systems (FMSs). First, a formula is developed to predic t the simulation CPU run time for a given manufacturing system, a planning horizon, and a computer system. It is shown that there are only three main factors that affect simulation run time: the planning horizon, the overall system average interarrival time, and the average number of workstations pe r part routing. In light of this, an approach to reduce simulation run time is presented. It is based on aggregating workstations to reduce the averag e number of workstations per part routing. The validity of the approach is justified by comparing the performance measures of example systems with and without aggregation. A theoretical approximation of the error incurred as a result of aggregations is derived. The results show that time savings of up to 400% can be achieved at the expense of only a few percentage points l oss in accuracy of the average flowtime performance measure. The developed concepts have been integrated in an algorithm to serve as a front end for d iscrete-event simulation to adapt simulation models to real-time decision-m aking requirements. The application of this algorithm is illustrated with a n example.