Assist. Prof. Dr. Özlem Türker Bayrak

Assist. Prof. Dr. Özlem Türker Bayrak

09.12.2014 1Çankaya University, Industrial Engineering Dept.

Özlem Türker Bayrak

Dept. of Industrial Eng.

L-318, 233 1365

[email protected]

http://ie.cankaya.edu.tr/otbayrak_en.html

209.12.2014Çankaya University, Industrial Engineering Dept.

mailto:[email protected]

http://ie.cankaya.edu.tr/otbayrak_en.html

ó Definition of Simulationó Application Areasó Advantages & Disadvantagesó Demosó Questions????


“Simulation is the process of designing a model of a real system and conducting experiments with this model for the purpose of either understanding the behavior of the system and/or evaluating various strategies for the operation of the system.”

Introduction to Simulation Using SIMAN (2nd Edition)



ó What’s being simulated is the system.


ó System: A collection of entities (people, parts, messages, machines, servers, …) that act and interact together toward some end (Schmidt and Taylor, 1970).

ó Examples:ó A manufacturing system with its machine centers,

inventories, conveyor belts, production schedule, items produced.

ó A telecommunication system with its messages, communication network servers.

ó A theme park with rides, workers, …


REAL WORLD SYSTEMS OF INTEREST ARE HIGHLY COMPLEX!!!

ó What are the ways to study a system?


System

Experiment with actual system

Experiment with a model of actual system

Physical model Mathematical model

Analytical solution Simulation



ó Often make assumptions/approximations, both logical and mathematical, about how the system works. ó These assumptions form a model of the system.ó Definition: A model is an abstraction of the real system.


ó If model structure is simple enough, could use mathematical methods to get exact information on questions of interest —analytical solution (QueueingTheory, Linear Programming, Differential Equations etc.)

ó But most complex systems require models that are also complex (to be valid)ó Must be studied via simulation

— evaluate model numerically and collect data to estimate model characteristics.


System

Experiment with actual system

Experiment with a model of actual system

Physical model Mathematical model

Analytical solution Simulation



ó Describing how the modelled system operates;ó Developing a computer programme that realises this

algorithm, i.e. simulation model;ó Experiment with the developed computer programme,

as you would like to experiment with a real system, i.e.simulate;ó Analyse and interpret the results of simulation

experiments, make related decisions and implementthem.


ó Better understanding of system behaviour.ó Analysis of system operation in different situations

("what - if" analysis).ó Analysis and removal of bottlenecks.ó Optimisation of system parameters.ó Comparison of alternative scenarios.ó Personnel training (e.g., managerial personnel).

09.12.2014Çankaya University, Industrial Engineering Dept. 13

SIMULATION

Programming

Analysis Modeling

Probability & Statistics


ó Ability to compress time, expand timeó Ability to control sources of variationó Avoids errors in measurementó Ability to stop and reviewó Ability to restore system stateó Facilitates replicationó Modeler can control level of detail

*Discrete-Event Simulation: Modeling, Programming, and Analysis by G. Fishman, 2001, pp. 26-27


ó By handó Spreadsheetsó Programming in General Purpose Languagesó Java, C++ etc.

ó Simulation Languagesó SIMAN, SIMSCRIPT, SLAM etc.

ó Simulation Packagesó Arena, Simul8, FlexSim etc.

Issue: Modeling Flexibility vs. Ease of Use


ó service systemsó manufacturing systemsó transport systemsó inventory systemsó logistics systemsó communication systems


ó A support tool for:ó designing a new production system (optimisation of

investments)ó modernisation of already existing production (meeting

market demands)ó scheduling a production process (maximising

throughput, minimizing performance time)ó reliability and maintanence analysisó inventory controló personnel training (getting managerial skills)


ó Sample application areas:ó as a design and analysis aid for factory layouts,ó equipment decisions, operating policies, etc.ó as a scheduling aid for production processesó as a part of a real-time, on-line control system (e.g.,

generating a new schedule when a piece of equipmenthas broken down).


ó Typical questions, to be answered by simulation in a design mode:ó What will be the throughput of a particular design?ó Where are the bottlenecks? How can we remove them?ó How does the system performance change in a function

of number and type of machines, number of workers,in-process storage and transportation, etc.?

ó How will breakdowns affect the throughput?


ó Sample application areas:ó facility location decisions (comparison of alternative

locations)ó transportation planning (evaluation of different routes)ó inventory management (evaluation of inventory policies,

tuning their parameters)ó supply chain management (evaluation of customer

service, minimization of total inventories, minimizationof lead times, analysis of supply chain dynamics)


ó Simulation’s greatest strength is its ability to answer “what if” questions…ó Can be used to study existing systems without

disrupting the ongoing operations.ó Proposed systems can be “tested” before

committing resources.ó Allows us to control time.ó Allows us to identify bottlenecks.ó Allows us to gain insight into which variables are

most important to system performance.


Simulation is notwithout its drawbacks...


ó Model building is an art as well as a science. The quality of the analysis depends on the quality of the model and the skill of the modeler (Remember: GIGO).ó Simulation results are sometimes hard to

interpret.ó Simulation analysis can be time consuming and

expensive.ó Should not be used when an analytical method

would provide for quicker results.


Simulation is one of the most widely used techniques in operations research and management science…


ó http://www.pwc.com/us/en/healthcare/simulation-optimization/#

ó http://www.youtube.com/watch?v=JsV6DEKItk8

ó http://www.youtube.com/watch?v=M0iZ52kUOiQ

ANY QUESTIONS ????


http://www.pwc.com/us/en/healthcare/simulation

http://www.youtube.com/watch?v=JsV6DEKItk8

http://www.youtube.com/watch?v=M0iZ52kUOiQ

Documents

Assist. Prof. Dr. Özlem Türker Bayrak