Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology / Logistic Engineering
M.A. Schroten Voorraadbeheer met vraagsubstitutie; een simulatiemodel.
Computer program, Report 93.3.LT.4169, Transport Technology, Logistic Engineering.
In this research project an inventory control system is considered in which substitute deliveries are allowed in case of shortages on stock.
The following distribution of demand is assumed: the size of an order has a normal distribution while the interarrival times of the orders are exponentially distributed. This distribution is taken instead of the usual normal distribution because of the fact that in such a way different types of orders can be considered. With the usual normal distribution the composition and the arrivaltimes of the orders are not clear. In advance of the investigation of the inventory control system research is done to determinate the behaviour of the given distribution. By simulation and literature it becomes clear the distribution has characteristics of a compound Poisson distribution.
After the demand distribution is identified, the restrictions and the environment of the simulation model are determinated. Next, the objects are
determinated and the process model is made. The description of the model is to be found in the Booch-notation, a structured method for object oriented design.
Given this fact the simulation model is built. A structured design is made and registered by the Booch notation. With this structure a program is written using Borland Pascal 7.0 and MUST.
The following three situations are considered.
A situation without substitute deliveries. Here the proper values of the parameters are determinated.
A situation where substitute deliveries are allowed. Special interest is taken in the effects on the service levels caused by substitute deliveries. Finally the parameter values determinated in the first situation are manipulated to try to get the servicelevels down to the values wich are reached in the first situation.
The results of the experiments show that the model gives the proper values in case of a situation without substitute deliveries and a rise of total
servicelevels when substitutes are allowed. However, the direct service levels will drop because of the fact that part of the stock is used as substitute for other products.
If the parameters are manipulated the results show that reduction on stocklevels are possible but because of the fact that the parameters are linked the precise effects are not clear. Investigation with independent parameters is needed for this.
Reports on Logistic Engineering (in Dutch)
