when should i use simulation?
Post on 22-Nov-2014
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When should I use
simulation?
Prof. Brian Harrington
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Agenda
• Common Manufacturing issues
• Intro to different types of simulation
• Using maths to analyze a Queuing System
• Using Excel/Monte Carlo simulation
• Using Discrete Event Simulation to look at
system design
• Six Sigma simulations
• A case study.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Manufacturing Dilemma
• Any product development process
involves extensive prototyping;
• Yet, costly manufacturing production
systems are typically not prototyped
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Simulation in Manufacturing
• System Design
• Operational Procedures
• Performance Evaluation
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System Design
• Plant Layout
• Effects of introducing new equipment
• Location and sizing of inventory buffers
• Location of inspection stations
• Optimal number of carriers, pallets
• Resource planning
• Protective capacity planning
Biggest Bang for the Dollar!
Contains Operational Procedures &
Performance Metrics.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Operational Procedures
• Production Scheduling - Choice of scheduling
and dispatching rules
• Control strategies for material handling
equipment
• Shift patterns and planned downtime
• Impact of product variety and mix
• Inventory Analysis
• Preventative maintenance on equipment
availability
Continuous Improvement
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Performance Evaluation
• Throughput Analysis (capacity of the
system, identification of bottlenecks); Jobs
per Hour
• Time-in-System Analysis
• Assessment of Work-in-process (WIP)
levels
• Setting performance measure standards;
OEE
If you can measure it, you can manage it!
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Agenda
• Common Manufacturing issues
• Intro to different types of simulation
• Using maths to analyze a Queuing System
• Using Excel/Monte Carlo simulation
• Using Discrete Event Simulation to look at
system design
• Six Sigma simulations
• A case study.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Why Simulation?
• Competition drives the following:
• Leaner production environment
• Shorter product development cycles
• Narrower profit margins
• Flexible Manufacturing (1 Facility, 1
Process, Multiple Models)
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Types of Simulation
• Mathematical Modeling
– e.g. Queuing Theory
• Monte Carlo Simulation
– e.g. Excel based models
• Discrete Event Simulation
– e.g. SIMUL8
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Simulation Overview
System Model
Deterministic Stochastic
Static Dynamic Static Dynamic
Continuous Continuous Discrete Discrete
DES
Monte Carlo
Differential equations
Queuing Theory
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Agenda
• Common Manufacturing issues
• Intro to different types of simulation
• Using maths to analyze a Queuing System
• Using Excel/Monte Carlo simulation
• Using Discrete Event Simulation to look at
system design
• Six Sigma simulations
• A case study.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
A Queuing System
Jockeying
Queue
Queue
Reneging
Service
Mechanism
Queue Structure Service Process
Arrival
Process
Balking
Serv
ed
Cu
sto
mers
Input Source
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Queuing Concepts Relationships for M/M/C
P = o
1
S n=0
C-1 (l/m) n
n!
c + (l/m)
c! ( )
cm
cm - l
L = q
(l/m)
2
c (l m) o P
(c – 1)! (cm – l)
l = mean arrival rate
m= mean service rate
C = number of parallel servers
These are messy to calculate by
hand, but are very easy with
appropriate software or a table.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Queuing Concepts A Comparison of Single Server Models
L = q
2(1 - l/m)
2 l s + (l/m)
2 2
L = q
2(1 - l/m)
2 (l/m)
L = q
(1 - l/m)
(l/m) 2
M/G/1
M/D/1
M/M/1
Note that
M/D/1 is
½ of M/M/1
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Limitations on Queuing Models
• What if:
– we don’t have one of these basic models?
– we have a complex system that has segments
of these basic models and has other
segments that do not conform to these basic
models?
• Then – simulate!
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Excel Based Simulations
• Uses Data Table functions
• Each Row might be one iteration of a simulation
• Each Col is a random variable generated in the
simulation
• RAND(), VLOOKUP(), COUNTIF(), NORMINV()
• Calculation & Iteration
• >>> Using VBA to bring in Probability functions
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Monte Carlo Simulation
• Named after the gaming tables of Monte Carlo
• Also referred to as a Static Simulation Model in
that it is a representation of a system at a
particular point in time
• In contrast, a Dynamic Simulation is a
representation of a system as it evolves over
time
• Might be accomplished using Excel and the
Random()
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Monte Carlo Simulation A Simple Example
Day RN Deman
d
Units
Sold
Units
Unsold
Units
Short
Sale
s
Rev
Return
s
Rev
Unit
Cost
Good
Will
Profit
$
1 10 16 16 2 0 4.80 0.16 2.70 0.00 2.26
2 22 16 16 2 0 4.80 0.16 2.70 0.00 2.26
3 24 17 17 1 0 5.10 0.08 2.70 0.00 2.48
4 42 17 17 1 0 5.10 0.08 2.70 0.00 2.48
5 37 17 17 1 0 5.10 0.08 2.70 0.00 2.48
6 77 18 18 0 0 5.40 0.00 2.70 0.00 2.70
7 99 20 18 0 2 5.40 0.00 2.70 0.14 2.56
8 96 20 18 0 2 5.40 0.00 2.70 0.14 2.56
9 89 19 18 0 1 5.40 0.00 2.70 0.07 2.63
10 85 19 18 0 1 5.40 0.00 2.70 0.07 2.63
Avg 2.50
Where do this numbers come from?
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Limitations & Disadvantages
• Stochastic, but static! Usually the time
evolution of a manufacturing system is
significant!
• Excel based models, soon start to use
VBA, and become very complicated
• Might require 1000’s of iterations; Data
Tables become slow
• Difficult to communicate results to
management.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Agenda
• Common Manufacturing issues
• Intro to different types of simulation
• Using maths to analyze a Queuing System
• Using Excel/Monte Carlo simulation
• Using Discrete Event Simulation to look at
system design
• Six Sigma simulations
• A case study.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Benefits of using DES Simulation
• Mathematical & Excel based models only go so
far
• Less difficult than mathematical methods
• Adds lot of “realism” to the model. Easy to
communicate to end users and decision makers
• Time compression
• Easy to “scale” the system and study the effects
• User involvement results in a sense of
“ownership” and facilitates implementation
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
SIMUL8 Common Building Blocks
The 8 Common Building Blocks: Start Point, Queue, Activity, Conveyor,
Resource, and End Point. Then the Logical aspect Labels & Conditional
Statements.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
8 is all you Need
1. Work Item Types: Can represent parts,
carriers, signals, phone calls, just about
anything that requires a “Label Profile”.
2. Activities: Work Centers, machines, tasks,
process steps, anything that requires a “Cycle
Time”.
3. Storage Areas: Buffers, de-couplers, banks,
magazines, anything that requires a finite space
to occupy over time.
4. Conveyors: Moving parts from pt A to pt B;
Number of parts & Speed of conveyor.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
…8 is all you Need…
5. Resources: Manpower, crews, forklifts, tugs;
anything that require a certain resource to be
present.
6. End Pt: Keep track of statistics and free
memory!
7. Labels: The attributes of a Work Item.
8. Visual Logic: The ability to create conditional
statements; variables, loops, commands &
functions.
SIMUL8 Corporation | SIMUL8.com | info@SIMUL8.com
Less is More using 6-Sigma
DMAIC or DMADV steps: • Define, Measure, Analyze, Improve, Control
• Define, Measure, Analyze, Design, Verify
DES Steps: • Objective, Assumptions, Data Collection, Build Model,
Verify, Validate, Experimentation, Results
Very similar steps!
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