User's guide chapter 5

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Chapter 5 – Model Simulation

5.1 – Simulation Options

Accessed from the Simulation menu, the Options dialog contains the settings and information you will use to run your model. Be sure to review these settings before running the simulation of the model. Once you are familiar with these options and have set them according to your objectives, you can run the simulation.

 If the first entity arrives in the model at 8:00am the simulation clock will jump ahead to that event. This happens when there is a daily pattern or scheduled arrival of entities to occur at 8:00am. If no events are occurring in the simulation, the clock jumps ahead to a point when some action is taking place.

  Each ProcessModel simulation begins at 12:00 a.m. (midnight) on Monday morning (of the first week).

5.1.1 – Run Tab

simulation menu of processmodelRun length The length of time for running the simulation. You may use any constant or expression to indicate the length of time the simulation will run.

  The longest a model can run a simulation for is 71,582 hours or 2,982.6 days or 8.17 years approximately. The smallest time allowed is.06 seconds, .001 minutes, or .000017 hours.

Warmup length The length of time to run the simulation before collecting statistics. Many systems require a time to warm up before they are running at a steady state, and if you collected statistics during this warm-up period, your results would likely be skewed. This option allows you to define that time to allow your model to warm up before you begin collecting statistics. Again, any constant or expression may be used in this field. The scoreboard values will reset after the warmup period ends. This is the designed purpose of the warm up length.

The longest warm-up length allowed is 2,270 hours.

Replications The number of replications to run for increasing the statistical significance of output results. If your model has any random behavior defined using one or more probability distributions, the simulation results will also be random. Running multiple replications allows you to use a meaningful sample size when interpreting the results since each replication uses a different seed to generate random numbers.

Report time units Allows you to select the default time units to use when you run the model.

Show Animation If checked, the process will be animated during the simulation. Disabling the animation enables the simulation to run faster and consumes less memory.

Show Scoreboard Check to display basic performance measures (entities processed, value-added time, etc.) during the simulation.

Scoreboard Time units Allows you to select the time unit displayed in the scoreboard at the time of simulation.

Disable subprocesses Causes the simulation to be run the main model only (no submodels are executed). Individual submodels can be disabled in the Activity dialog.

 The ProcessModel simulation clock runs straight time using 24 hour days, 7 days per week. If there is a need to avoid the shift files to compensate for evenings and weekends, just run straight work time (not being concerned with the “day of week”), it can reduce the simulation run length to 40 hours per week. For example, a normal 7 day work week is 168 hours (7 x 24). To run a model without shift files for 4 weeks, using a 5 day workweek at 40 hours per week, reduce the run length from 672 hours (4 x 168) to 160 hours (4 x 40). Caution: Daily Pattern or Scheduled arrivals can not be used with this technique because the clock is no longer tracking 24 hour days. Continuous, Periodic, or Ordered arrivals will need to be used.

5.1.2 – Files Tab

simulation menu files tab in processmodel

External Files This option allows you to include shift files for activities and resources.

Create shift file Allows you to create a shift file for the model.

Interrupt activity to go off shift or on break When you check this option, ProcessModel will interrupt an activity or resource (whether or not it is currently busy) to cause it to go off shift or on break. Use this only for activities or resources you can interrupt.

5.1.3 – Graphics Tab

ProcessModel version 5.6.2 and above do not support this feature. The Graphics tab allowed you to use a custom graphics library in the model and was provided primarily for compatibility with earlier versions of ProcessModel. If you have models built in version 2.1 or earlier and you don’t want to add any custom entity icons to the models, uncheck the “Use custom graphics library for simulation” box. This will conserve the disk space required to generate a custom graphics library.

5.1.4 – Output Tab

simulation output files tab in processmodel

Show standard deviation When you check this option, ProcessModel will show standard deviation in the cycle time calculation of the Output Summary.

Number of cycle time Allows you to choose the size of the cycle in which the standard deviation is sampled. Larger samples use more processing memory.

Statistics Allows you to choose if resource stats will be shown by unit or in a summary of all units.

5.2 – The Simulation Window

From the Simulation menu, select Simulate Chart (or Run Scenarios) to run a ProcessModel flowchart. When you run the simulation, the Simulation Window appears and ProcessModel compiles the model into simulation code for execution. Your model then starts running according to the options you have selected.

 The simulation window is set to run maximized and does not allow switching to other programs running on your system. The simulation window can either be minimized or re-sized. As long as it is not running maximized, you will be able to switch between it and other programs currently running. There is no method of programmatically changing the size or priority of the simulation window. It must be changed manually. However, the status and location of the window will be saved when you end the simulation. So the next time you run a simulation, it will use the same window settings it used previously.

5.2.1 – Scoreboard

In addition to your flowchart, a scoreboard appears on the Simulation Window to illustrate performance measures if the scoreboard option is selected in the Options dialog.scoreboard during processmodel simulation

Entity1, Entity2,… Entities for which statistics are gathered are displayed across the top of the scoreboard.

Qty Processed The number of entities of this particular type that have been processed, meaning those that have exited the system.

Avg. Cycle Time (time unit) The average time the entity type spent in the system. Expressed in terms of the time unit selected in the Simulation/Options dialog.

Avg. VA Time (time unit) The average value added time—time the entity type spent in activity time. Expressed in terms of the time unit selected in the Simulation/ Options dialog.

Cost per Unit The average cost of the entity type.

 Since entity names can be changed during a simulation, statistics are collected based on the name assigned to the entity when it exits the system.

 Variables may also be shown on the Scoreboard (see variables).

The decimal places shown in the simulation when displaying a real variable using a Label is fixed at 2 decimal places and can not be changed.

5.2.2 – Run-time Menus

Once a simulation begins, a new menu bar appears at the top of the screen with selections for controlling the animation and for interacting with the simulation. As shown below, these menu items appear above the animation speed control bar and simulation clock.

The Simulation Window has a menu of its own, with selections for controlling many simulation parameters such as the run speed. You can also control the animation through panning, zooming and pausing.

run time menus during simulation in processmodel

The screen above shows the speed control bar, along with the clock selection button for controlling the format of the clock readout. In addition, each resource has a status light which changes throughout the simulation to reflect the current operational state of each resource (a maximum of 12 status lights will be shown for multi-unit resources).

 Slow simulation is typically caused by a large number of entities arriving, or being moved from one location to another simultaneously. If possible, space out the arrivals so not so many entities are entering the model at the same time, the simulation speed will increase dramatically. Many calculations need to occur for every entity when it moves in the model. So the more entities moving at the same time, the longer it takes to process the required information. If there are long routing times and many entities moving on those routes, the simulation will slow dramatically. In this instance, consider using an activity (with no input queue and no output queue, and infinite capacity and a time that corresponds to the movement time. The routes that goes into and out of the activity can then be set to zero time. This should increase the simulation speed.

Run-Time Simulation Menu

The Run-Time Simulation menu has two options: End Simulation and Pause/Resume Simulation. Each of these functions is defined below.simulaiton menu during simulation in processmodel

End Simulation Choose this option to end the simulation. You will then be prompted to collect statistics or return to the model editor without collecting statistics. If running m