Simulation and Modelling - Old Questions

3.  Why is GPSS called transaction flow oriented language? A machine tool in a manufacturing shop is turning out parts at the rate of every 5 minutes. When they are finished, the parts are sent to an inspector, who takes 4±3 minutes to examine each one and rejects 15% of the parts. Draw and explain a block diagram and write a GPSS program to simulate using the concept of facility.

GPSS (General Purpose Simulation System) is a highly structured and special purpose simulation language based on process interaction approach and oriented toward queuing systems. The system being simulated is described by the block diagram using various GPSS blocks. Each block represents events, delays or other actions that affect the transaction flow. Therefore GPPS is called transaction flow oriented language.

The block diagram for given problem using GPSS is given below:

A GENERATE block is used to represent the output of the machine by creating one transaction every five units of time. A QUEUE block places the transaction in the queue and SEIZE block allows a transaction to engage a facility if it is available. If more than one inspector is available, the transaction leaves the queue which is denoted by DEPART block and enters into ADVANCE block. An ADVANCE block with a mean of 4 and modifier of 3 is used to represent inspection. The time spent on inspection will therefore be any one of the values 1, 2, 3, 4, 5, 6 or 7, with equal probability given to each value. Upon completion of the inspection, RELEASE block allows a transaction to disengage the facility and transaction go to a TRANSFER block with a selection factor of 0.15, so that 85 % of the parts go to the next location called ACC, to represent accepted parts and 15 % go to another location called REJ to represent rejects. Both locations reached from the TRANSFER block are TERMINATE blocks.

Now,

Code for simulating the given problem using GPSS:

        GENERATE     5, 0        
        QUEUE     1    
        SEIZE     1
        DEPART     1
        ADVANCE     4, 3
        RELEASE     1
        TRANSFER  0.15  ACC   REJ
ACC TERMINATE     1

REJ TERMINATE     1