Discrete-Event System SimulationRequired TextModelingSimulationModeling & SimulationSystemSystem EnvironmentSystem ComponentsActivities & EventsSystem Component ExamplesSimulation as the Appropriate ToolSimulation as the Appropriate Tool (cont’d.)When Simulation is Not AppropriateWhen Simulation is Not Appropriate (cont’d.)Advantages of SimulationAdvantages (Pegden, et al. 1995)Advantages #2Disadvantages of SimulationDisadvantages (Pegden et al. 1995)Offsetting DisadvantagesWhy Simulate?Why is simulation not used more?Areas of ApplicationCurrent General TrendsSlide 25Activities / EventsClassifications of SystemsModelClassification of ModelsCharacteristics of a Good ModelSteps in a Simulation Study (Figure 1.3)Steps in a Simulation Study (cont’d.)Slide 33Slide 34Slide 35Ten Reasons for Failure (notes)Failure (cont.)Stochastic BehaviorProblem: Simulate a major traffic intersection with objective of improving traffic flow.First IterationSecond IterationThird IterationHomeworkDo Examples from Ch. 21Discrete-Event System SimulationAn Introduction to the Basic Principles of Simulation2Required Text“Discrete-Event System Simulation”5th EditionBanks/Carson/Nelson/NicolOther editions are probably adequate, but not exactly as the 5th.ModelingModeling involves observing a system, noting the various components, then developing a representation of the system that will allow for further study of or experimentation on the systemFocus – computer modelData Structures & ImplementationInteraction of the components34 SimulationThe process of running a (computer) model of a real system to study or conduct experimentsFor understanding the model or its behaviorTo evaluate strategies for operation of the systemInvolves generation of an artificial history, used to draw conclusions about the real systemModeling & SimulationOften described as one processShould distinguish between the two56SystemA set of inputs which pass through certain processes to produce outputsA set of related components which work together toward a given goalA group of objects joined in regular interactions or interdependence for the accomplishment of some purposeHelpful if a system is observable, measurable, systematic7System Environment“World” in which the system existsSystem is affected by elements outside the system – the system environmentBoundary – “line” between the system & its environmentDecision on boundary is dependent upon simulation purpose8System ComponentsConsists of objects called ENTITIESEntities have a set of properties called ATTRIBUTES that describe them There exist interactions called ACTIVITIES and or EVENTS that occur between the entities that cause them to changeThe STATE OF A SYSTEM is a snapshot of the system at a given time i.e. variables necessary to describe systemThe model starts in its INITIAL STATE9Activities & EventsCause changes in the attributes of the entities, and, therefore, the state of the systemEvent: instantaneousActivity: has a length of time10System Component ExamplesBankComputer NetworkHospital Emergency Room(Homework)11Simulation as the Appropriate ToolEnables study and experimentationChanges simulated & results observedGain knowledge of system Determining importance of variables and how variables interactExperiment before implementationVerify analytic solutions12Simulation as the Appropriate Tool (cont’d.)Try different capabilities (of a machine)TrainingAnimation (graphics)Complexity of modern systems almost require simulation13When Simulation is Not AppropriateIf can be solved by Common sense or simple calculationsAnalytical methodsDirect experimentsIf simulation costs exceed savingsIf resources & time are not available14When Simulation is Not Appropriate (cont’d.)If Data is not availableIf verification & validation are not practical due to limited resourcesIf users have unreasonable expectationsIf system behavior is too complex15Advantages of Simulation1. Control2. Time compression3. Sensitivity Analysis4. Training tool5. Doesn’t disturb real system16Advantages(Pegden, et al. 1995) New policies, operating procedures, decision rules, information flows, organizational procedures, etc. can be explored w/o disrupting ongoing operationsNew hardware designs, physical layouts, transportation systems, etc. can be tested w/o committing resources for their acquisitionHypotheses about how or why certain phenomena occur can be tested for feasibility17Advantages #2Time can be compressed or expanded allowing for speedup or slowdown of the phenomena under considerationInsight about the interaction of variables or the importance of variables on performance of the systemBottleneck analysis can be performed indicating where processes are being delayed“What if?” questions can be answered – particularly for a new system18Disadvantages of Simulation1. Expensive2. Extensive time needed3. Lack of experienced personnel19Disadvantages(Pegden et al. 1995)Model building requires special training and experienceResults may be difficult to interpretTime consuming and expensiveUse of simulation when analytical models are available and preferable, particularly for closed-form models20Offsetting DisadvantagesSimulation Software Provides templatesAnalysis capabilitiesFaster simulations Most systems do not fit closed-form models21Why Simulate?To save moneyTo do things you could not physically or morally do within the actual system22Why is simulation not used more?CostLack of familiarityPeople think their judgment or experience is good enough23Areas of ApplicationManufacturing, Semiconductor Mfg.Construction & Project ManagementMilitaryLogistics, Supply Chain, DistributionTransportation & TrafficBusiness ProcessesHealth Care24Current General TrendsRisk AnalysisInsurance, options pricing, portfolio analysisCall Center AnalysisLarge Scale SystemsInternet backbones, wireless networks, supply chainsAutomated Materials Handling (AMHS)Control system sw - emulator25Activities & Events2 types of Events or ActivitiesEndogenous: variables affecting the system which are (can be) manipulated within the systemExogenous: variable which affect the system but cannot be manipulated by the system because they are outside the