Simulation Modeling And Optimization Using ProModel

Simulation Modeling and Optimization Using ProModelOther uses include modeling high-rate, discrete partmanufacturing systems.589resources such as empty and full speeds, acceleration,deceleration, pickup and delivery time can also bespecified.2.2 Entities (or parts)2.5 Processing (or routing)Parts or entities refer to the items being processed in thesystem. These include raw materials, piece parts,assemblies, loads, WIP, finished products, etc. Entitiesof the same type or of different types may be consolidated into a single entity, separated into two or moreadditional entities or converted to one or more new entitytypes.Entities may be assigned attributes that can be testedin making decisions or for gathering specialized statistics. The graphic of an entity can be changed as a resultof an operation to show the physical change during theanimation.2.3 Path NetworksPath networks are optional and define the possible pathsthat entities and resources may travel when movingthrough the system. Path networks consist of nodesconnected by path segments and are defined graphicallywith simple mouse clicks. Multiple path networks maybe defined and one or more resources and/or entities mayshare the same network. Movement along a path networkmay be defined in terms of distance and speed or bytime. Path distances are automatically computed basedon the layout scale defined by the user.There are three types of path networks: passing, nonpassing, and crane. A passing network is used for openpath movement where entities and resources are free toovertake one another. Non-passing networks consist ofsingle-file tracks or guide paths such as those used forAGVs where vehicles are not able to pass. Cranenetworks define the operating envelope and interfacepoints for bridge cranes.2.4 ResourcesA resource may be a person, tool, vehicle or other objectthat may be used to: Transport material between routing locations. Perform an operation on material at a location Perform maintenance on a location or other resourcethat is down.Resources may be either static or assigned to a pathnetwork for dynamic movement. A special type ofdynamic resource is a crane. Built-in decision rules canbe used for allocation of resources and for prioritizationof part pick-up and delivery. Motion characteristics ofThis element defines the processing sequence and flowlogic of entities between routing locations. The operationor service times at locations, resource requirements,processing logic, input/output relationship, routingconditions, and move times or requirements can bedescribed using the Processing element.Operation times can be defined by constants, distributions, functions, attributes, subroutines, etc. or anexpression containing any combination of these. Operation logic can include IF-THEN-ELSE statements, loops,nested statement blocks and subroutine calls. Resourcerelated statements such as GET, USE, and JOINTLYGET with Boolean expressions and built-in operationstatements such as ACCUM, JOIN, and GROUP greatlysimplify otherwise complex logic in describing theprocessing requirements. Built-in and user-definedrouting rules provide flexibility for modeling all types ofrouting conditions.2.6 Arrivals (or production schedule)Deterministic, conditional, or stochastic arrivals can bemodeled using this element. External files includingproduction schedules or arrival data can be read intoProModel in the Arrivals element. Built-in or user defined distributions or spreadsheet created data can beused to define inter arrival times and quantities.2.7 Shifts (or work schedules)A powerful feature is the ability to define custom workand break schedules through ProModel's Shifts module.Work and break schedules are defined graphically bytime of day and day of the week. Resources or locationsare then assigned to a specific shift schedule. Inaddition, you can define shift and break logic thatcontrols location and resource behavior when they gooff-line and what happens once they are off-line.3 ADDITIONAL MODELING ELEMENTSProModel provides additional modeling elements used instatements and expressions to define special decision andoperating logic in a model. These elements distributions, and costing.There are several types of logic elements that may bedefined by the user. Like model elements, names given

590Bensonto these elements may be up to 80 characters in length.Figure 2 shows the menu for accessing these additionalelements. Some of these elements will be discussed inthis section.3.5 SubroutinesA subroutine is a user-defined block of statements thatcan be passed values when called and optionally returnvalues when completed. Subroutines may be referencedin the place of any value or logic. A complex operationperformed several places in a model may beappropriately defined by a single subroutine.3.6 Arrival Cycles, Table Functions and UserDefined DistributionsArrival patterns, table functions or user distributions maybe defined. For example, a user defined distributionwhich returns an operation time of 5 minutes 30 percentof the time and an operation time of 8 minutes 70 percentof the time can be expressed in the User Distributionselement.3.7 External FilesFigure 2: More Elements Menu3.1 AttributesAttributes for entities and locations can be defined. Theymay contain real or integer values. Location, resourceand entity names may also be assigned to attributes.3.2 VariablesVariables are used for decision making and statisticalreporting. The value of a variable may be monitored overtime and displayed at the end of the simulation as a timeseries plot or histogram. Variables may hold integer orreal values. Local variables may also be used for quickconvenience when defining logic.3.3 ArraysAn array is a matrix of variables representing multiplevalues. An array may be one dimensional or multidimensional.3.4 MacrosA macro is a complex expression or set of expressionsthat can be defined once and used multiple times as partof a logic statement (i.e. processing, scheduling,downtime logic). Macros can be helpful in situationswhere the same bit of logic is repeated in many places inthe model.One of the powerful features of ProModel is the abilityto read data from external text or spreadsheet files orwrite data to external files. For example, operation times(even in the form of expressions) from an EXCELspreadsheet file can be read into ProModel using thiselement.4 COSTINGWith ProModel’s new Costing feature, you can nowmake decisions about your system on a cost basis. Newdialogs allow you to monitor costs associated withlocations, entities, and resources during a model run. Inaddition, the General Statistics Report now includesCosting statistics, automatically generated at runtime.For locations, you can find the cost of operating alocation. For resources, the total cost includes the usagecost as well as the cost of not using the resource. Forentities, the total cost includes the costs incurred at alllocations the entity passed through, the costs incurred byuse of resources, and the initial cost of the entity.5 GRAPHICSGraphics in ProModel are realistic and easy to create.Visually realistic animation helps simulation to becomean effective communication vehicle between engineersand managers. ProModel comes with an extensive libraryof graphics with provision to create and add othergraphics to the library. ProModel's Graphic Editorcomes with a complete set of drawing tools and a fullspectrum of color selections. Scaling, rotating, copyingand many other editing features are available. You can

Simulation Modeling and Optimization Using ProModeleven import drawings from other graphics packages.With little effort you can develop quick and simple 2Dlayouts, or, with little extra effort, 3D perspectivelayouts. CAD layout drawings (e.g. AutoCAD) can alsobe brought in to use as the model background. TheGraphic Editor is shown in figure 3.591During the simulation, you can query the status ofresources or the current value of any logic element.Source level debugging allows you to trace each actionwith the option to display the actual source statement thattriggered the action. Trace statements may be confined toa single area of a model. Status lights for locationschange colors to help you see various states such asbusy, idle, down, etc.The animation screen is a virtual screen that means theanimation layout is limited only by memory in yourcomputer. By turning off the animation, you can speedup the simulation, run for a while and turn the animationback on. The simulation clock resolution can beexpressed in terms of hours, minutes, or seconds with aclock resolution of .00001 a second.8 OUTPUT REPORTSFigure 3: ProModel's Graphic Editor6 SCENARIOS AND RUNTIME INTERFACEBy choosing the statistics for resources, locations,entities, variables, etc., users can customize the outputreports. The statistics are written to a results databasewhich can be exported to spreadsheets. Additionally,graphical reports of the outputs can be displayed, printedor plotted. These graphs can be individual orcomparative pie charts, histograms, time-series plots, etc.See Figure 4 for a sample location state graph.The runtime interface (RTI) is a convenient andcontrolled environment for modifying selected modelparameters (capacities, operation times, etc.) withouthaving to change the model data directly. It alsoprovides an experimental environment, which permitsmultiple scenarios to be defined and simulated. The RTIcan be accessed at the beginning of a simulation run formaking modifications for a single run or for savingalternative modifications as scenarios for doing multiplescenario analysis.7 RUNNING THE SIMULATION & ANIMATIONModels can be run for specified lengths of time or untilall entities have been processed. Multiple replicationsmay also be specified. Models may be run with orwithout animation. The animation is very smooth and itmaintains great resolution at any zoom factor.The Views feature allows you to define and thenquickly and easily access specific areas of the modellayout. Selecting a view scrolls the layout window andadjusts the zoom so you see a specific region of thelayout regardless of the layout window’s size. Once aview is defined, you can select it while running thesimulation or change the view from within the logic.Figure 4: A Location State Graph9 OPTIONSOne of the most accommodating features of ProModel isthe provision for customizing the modeling environmentto suit the preferences of the user. Under the View menu,you can zoom in or out, display a grid, refresh thescreen, set default directories for model files, icon libraryfiles, or model output files. You can set and save defaultsettings (i.e. window sizes, appearance).

592BensonProModel also allows you to choose editingpreferences for model development. Default fonts andsizes for text and a choice of long or abbreviated menulengths are available. Prompts and added explanationscan also be activated which may assist the novice user.The expert user can benefit from choosing options thatstreamline the editing process.10 OPTIMIZATIONSimRunner Optimization is an add-on capability forProModel simulation software. SimRunner turns yoursimulation model into an answer machine by giving youthe best answer possible while saving you the most time.The optimization process takes an existing ProModelsimulation model and performs sophisticated “what-if”analysis and optimization automatically.For each optimization project, you tell SimRunnerwhich model to analyze/optimize, which input factors tochange, and how you measure system simulationperformance. You can run two types of projects inSimRunner: Stage One Optimization Analysis, and StageTwo Simulation Optimization.A Stage One Optimization Analysis is a factorialdesign of experiments that tells you whether or notchanging a given input factor is affecting the objectivefunction, and the significance of the effects. A StageTwo Simulation Optimization is a multi-variableoptimization that tries various combinations of inputfactors to arrive at the combination that provides the bestobjective function value.The SimRunner Output report generates three types ofdata and reporting for you:1. Data reports - for import into spreadsheets2. Analysis reports - for text and word processingreports3. Charts - for graphical display of results.Each of these can be printed or exported to otherapplications using common clipboard functions.11 SUPPLY CHAIN APPLICATIONSSimulation models have had extreme value in manycompanies, being used as decision making and planningtools by managers in supply chain related areas.ProModel is successful in providing an accuraterepresentation for many players involved in a singleproduct line. The players may consist of suppliers,warehouses, customers, retailers, and transportationvehicles.Such issues facing the players of theorganization are fleet sizing, inventory reduction, andshutdowns and outages. ProModel allows you to createa model, which addresses these issues in a single model.11.1 Fleet SizingIn the effort to correctly size various types of fleets (railcar, truck, ISO, etc.), models may incorporate variabilityin transportation times. Seasonal peaks and dives areeasily modeled in addition to vessel maintenanceoutages. Rail switching issues involving stoppages andcongestion can also be investigated. Demand increasesmay be used in a current state model to determine theneed for more vessels and/or how to meet the need withexisting resources. ProModel has been used to meetspecial seasonal orders without additional resources,reduce current fleet sizes, and manage the currenttransportation resources more effectively.11.2 Inventory reductionEspecially challenging issues in supply chainapplications include capturing the behavior ofcontinuous flow systems with stochastic conditions. Onscreen variables and output statistics modules provideguidance to make decisions on tank sizing, capacityanalysis and impact of variability of supply onmanufacturing units. Benefits include the ability toanalyze complex systems with a holistic perspective,reducing inventory levels by modeling continuous flowsystems at both manufacturing and consumer sites anddetermining the needs of campaigning of differingproducts on the same unit.11.3 Shutdowns and outagesThe long and short-term impacts of planned outages havebeen a problem for managers. Unplanned and randomoutages are much worse. Outage issues not only includemanufacturing or customer outages and their variousimpacts, but also involve shipping and supply outages.ProModel allows you to determine the impact of plannedshutdowns on remote customer sites as well as thepossibility of shutting down production because ofpoorly planned, customer interfaced outages. Modelsprovide flexibility on testing alternate scenarios, movingand shifting the timing of outages as well as thedurations.12 CONCLUSIONSUntil recently, manufacturing companies have not fullybenefited from simulation in making continuousimprovements because of the time, programming expertise, and cost involved in getting useful results.ProModel is designed for manufacturing companies tofully achieve the benefits of simulation technology at anaffordable price. ProModel is directed toward making

Simulation Modeling and Optimization Using ProModelsimulation a standard tool in the hands of engineers,managers and systems analysts just as spreadsheet software is in the hands of accountants and financial analysts.REFERENCESHarrell C. R. 1990. Trends in Manufacturing Simulation.In Proceeding of Autofact Conference, eds. A. Adlard,21-31. Detroit, Michigan.Harrell C. R. and K. Tumay. 1992. ProModel Tutorial.In Proceedings of the Winter Simulation Conference,eds. J. Swain, D. Goldsman, R. Crain, J. Wilson, 405409. Arlington, VAHarrell C. R. and J.J. Leavy. 1993. ProModel Tutorial.In Proceedings of the Winter Simulation Conference,eds. G.W. Evans, M. Mollaghasemi, E.C. Russell,W.E. Biles, 184-189. Los Angeles, CABaird S.P. and J.J. Leavy. 1994. Simulation ModelingUsing ProModel for Windows. In Proceedings of theWinter Simulation Conference, eds. J. D. Tew, S.Manivannan, D. A. Sadowski, A. F. Seila, 527-532.Arlington, VADulgeroglu O. and Gates G.A. 1997. Simulation to theRescue: Stochastic Modeling Applied to Logistics. InIndustrial Engineering SOLUTIONS ’97 ConferenceProceedings, 10-17. Norcross, GA.AUTHOR BIOGRAPHYDEBORAH BENSON is the Director of ProModelSupport Services at PROMODEL Corporation. She hasworked for PROMODEL Corporation since September1992 and has held responsibilities in training, sales, andconsulting.She authored the documentation forProModel software, versions 2.0 and 3.0. She received aB.S. in Industrial Engineering from Arizona StateUniversity and a Master of Engineering Managementfrom Brigham Young University. She currently servesas Treasurer for her local chapter of IIE.593

SIMULATION MODELING AND OPTIMIZATION USING PROMODEL Deborah Benson PROMODEL Corporation 1875 South State St., Suite 3400 Orem, UT 84097, USA ABSTRACT The ProModel Optimization Suite is a powerful yet easy-to-use simulation tool for modeling all types