Lecture 6: Process-interaction approach for discrete-event simulation

18 Pages·2012·0.63 MB·English

2WB05 Simulation
Lecture 6: Process-interaction
approach
Marko Boon
http://www.win.tue.nl/courses/2WB05
December6,2012
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This approach focusses on describing processes;
In the event-scheduling approach one regards a simulation as executing a sequence of events ordered in time;
but no time elapses within an event.
The process-interaction approach provides a process for each entity in the system; and time elapses during a
process.
In production systems we have processes for:
• Arrivals
• Buffers
• Machines
• Exit
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Example: Single-stage production system
Buffer
Arrivals Exit
Machine
A single machine processes jobs in order of arrival. The interarrival times and processing times are exponential
λ µ λ < µ
with parameters and (with ).
• What is the mean waiting time?
• What is the mean queue length?
• What is the mean length of a busy period?
• How does the performance change if we speed up the machine?
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Arrival process
Generate arrival after random (exponential) time units
arrival
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Buffer process
Add job to buffer and remove job from buffer (if there is any)
0 1 n n+1
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Machine process
Process job (if there is any)
busy
idle
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Exit process
Accept completed job and do accounting
departure accounting
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χ
The specification language :
Modelling and simulation tool for the design of manufacturing systems
χ
The language has been developed by the Systems Engineering group
For documentation, see http://se.wtb.tue.nl/sewiki/chi
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χ
Implementation in
a b c
G
B M E
Processes: G, B, M, E.
, ,
Channels: a b c.
Jobs are generated in G, then they are sent over channel a to B. When M is idle, the first job is sent over channel
b to M. After a delay, the job is sent over channel c to exit process E.
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1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0 10 20 30 40 50 60 70 80 90 100
Mean sojourn time as a function of the number of jobs processed for λ = 1 and µ = 2
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