Intro to Arena A Second Simulation

Model 2 We now consider a more complex simulation, from Ch. 5 of Simulation with Arena. We consider an assembly plant which receives two types of items, prepares them, checks them, attempts to repair the faulty ones, and ships the good finished parts, while scrapping the unfixable ones. Part A prep Part A EXPO(5) Rework 20% Scrapped Sealer 9% TRIA(1,4,8) 80% Salvaged And Shipped EXPO(45) Part B prep 91% Part B Batches of 4 EXPO(30) Part A TRIA(1,3,4) Part B NORM(2.4, 0.5) Shipped TRIA(3,5,10)

Model 2 The arrival and preparation segments of the process to be modeled are no different from the arrival and processing segments of Model1. The “Sealer” and “Rework” modules are new - and require an “Inspector” entity for their implementation, since they will determine whether a part is faulty or not. We will also need to model different processing times (different distributions of processing times) depending on the part being processed. A further change appears because we introduce a “transfer time” from one station to another (parts don’t move instantaneously) - which we had not done before. We will use the “Route” rather than the “Connect” option.

Model 2 We start, as before, with File/New, click on Attach… and choose Common.tpo. Then lay down the two arrival modules, the two servers, the two inspectors, the three departure modules, and a simulate one. You may have to “zoom in” to be able to see the whole layout. Notice we have not added any information or connections, yet.

Model 2 We will introduce the notions of Stations, Station Transfers and Pictures. A “Station” is simply a location where something occurs. Each station has a unique name. The Station Transfer is where the notion of Route will come in. We start by double-clicking on the “Arrive” modules and filling in the details. Enter Data Station: Part A Arrive Arrival Data Time Between EXPO(5) Mark Time Attribute Arrival Time Leave Data Station Part A Prep Route Time 2

Model 2 Click on Assign… to bring up a new dialog box. Click on Add…, to bring up a third one. In this last one Attribute Sealer Time Value TRIA(1,3,4) Check the next slide to see all the dialog boxes and their contents. Make sure you exit each dialog box by clicking OK… otherwise the changes will not occur. If you forget, just re-open and go through it again.

Model 2 The dialog boxes for the arrival of Part A: when you click OK in the Assignments dialog, the list in Assign will change…

Model 2 Double-click on the second Arrival station, and fill in: Enter Data Station Part B Arrive Arrival Data Batch Size 4 Time Between EXPO(30) Mark Time Attribute Arrival Time Leave Data Station Part B Prep Route Time 2 Assignments Attribute Sealer Time Value NORM(2.4, 0.5)

Model 2 The dialog boxes for the arrival of Part B… When done (all Ok), double-click on the upper of the two Servers. You will see the dialog in the next slide.

Model 2 The dialog box has a default station name (Server 1) and a list of all the known station names - including the ones you have typed but not yet assigned to any station. Drop the drop list and pick the Part A Prep name. You could type it in, but you would have to make absolutely sure that what you type matches the name already there…

Model 2 Right before you hit OK, the dialog box should look like this. You will then need to open the dialog box for the second server, and choose Part B Prep as Station; TRIA(1,4,8) for the Server Data Process Time; Sealer as the Station in the Leave Data area; with a Route Time of 2.

Model 2 The Sealer dialog should be filled as indicated. Note that we have a Failure Probability, a station to go to on passing, and another one to go to on failing. Notice that we have not specified the Sealer Time distribution, since each type of part has a different distribution, which has already been assigned, under that name, in “Arrive”.

Model 2 The Rework module comes next, with appropriate entries. Notice the Process Time, the Failure Probability and the two Leave Data areas, both with Route Times of 2, and next station names.

Model 2 We choose the lowest “Depart” module as the “Shipping” module, and fill in as indicated on this slide. Click OK to complete it. The second Depart from the bottom becomes the “Salvaged” module, while the top one is the “Scrap”. All three are filled in the same way, except for choosing the three different names from the drop-down list for “Station”.

Model 2 Fill in the dialog box for the “Simulate” module - 2000 minutes of model run. Now click on the Route button in the “Animate” toolbar at the right of the model design area. You’ll se the dialog:

Model 2 Once you have clicked OK, the cursor changes to a “cross-hair”, and you can click, starting in a station, clicking placement corners, and ending in another station. You may have to repeat the Route button choice for each route segment you want to set up. Right-click (repeat action) might work, too.

Model 2 You are now ready to run the model - use the “tape player” buttons, and try out “single-step”, “fast-forward”, “pause”, etc. At the end you will be asked whether you want to see the data collected - say Yes and look at the results, which have to be interpreted. There is little of significance in a single replication: the results are only “plausible” and “obtainable”. In order to be able to make statistical validity claims you will need many replications - with different random number streams. You will see two sets of variables: Tally Variables and Discrete Change Variables, and various statistics derived from the single run, plus some Counters. Let’s go through them.

Model 2 Tally Variables and Discrete Change Variables give average, 95% confidence-interval half-width, and minimum and maximum observed values. The half-width interval is not given unless at least 320 observations have been taken for the Tallies and at least 5 time units have elapsed for the Discrete Changes. If this is not the case, Arena will report (Insuf). If this test is passed, then a check for data correlation is carried out. If independence is violated, then (Corr) will appear. If all tests are passed, then a half-interval is computed. No such appeared on our report… The only meaningful conclusion relates to the capacity of the Rework station: what is it?

Model 2 Exercises. (From K. S. & S., Ch. 5) Travelers arrive at the main airline door of an airline terminal according to an exponential interarrival-time distribution with mean 1.6 minutes. The travel time between the entrance and the check-in is distributed uniformly between 2 and 3 minutes. At the check-in counter travelers wait in a single line until one of five agents is available to serve them. The check-in time follows a normal distribution with mean of seven minutes and standard deviation of 2 minutes. Upon completion of the check-in, they are free to travel to their gates. Create a simulation model, with animation, of this system. Run the simulation for 16 hours, to determine the average time in system, number of passegers completing check-in, and the average length of the check-in queue. 2) Develop a model of a simple serial two-process system. Items arrive at the system with a mean time between arrivals of 10 minutes. They are immediately sent to Process 1, which has an

Model 2 unlimited queue and a single resource with a mean service time of 9 minutes. Upon completion, they are sent to Process 2, which is identical to Process 1. Items depart the system upon completion of Process 2. Performance measures of interest are the average numbers in queue at each process and the system cycle time. Using a replication length of 10,000 minutes, make the following four runs and compare the results: Run 1: exponential inter-arrival times and exponential service times. Run 2: constant inter-arrival times and exponential service times. Run 3: exponential inter-arrival times and constant service times. Run 4: constant inter-arrival times and constant service times.