Simscript/Data Analysis Assignment

Due Thursday, March 24, 2005

In this assignment you will use Simscript models to answer some questions about systems.

Telephone Problem (#1.29 pages 104-105)

The file phonesAB.sim contains a Simscript program that models the telephone system described in problem 1.29 of the text (and discussed in class). Copy this program to your directory either by saving it from this page or using the cp command (the complete pathname of the file is

~cpsc/public_html/Spring2005/CPSC420A/phonesAB.sim

Notice that the program is written with a loop in main so that it can be run for several different numbers of phone lines between cities A and B (the user enters a min and a max number).

  1. Compile and run the program using the system parameters given in the problem description (note that the problem gives the interarrival times for calls in seconds but the program asks for the arrival rate per minute - so for the interarrival time of 10 seconds, the arrival rate would be 6 per minute). Run the program for between 30 and 35 lines.
  2. You should note that the answers above do not meet the goal of no more than 5% blocked calls. Try other numbers until you seem to get numbers in the right range.
  3. Modify the program by adding an inner loop in main to do replications. Also add code to write the results to a file - you should get a new file for each number of lines (so the results for say 30 lines would all go in one file, for 31 in another, etc.). A model to use is the mmsexp.sim example we did in class (you should have a handout - this simulated a system with one queue but multiple servers).
  4. Run the program for at least 5 different numbers of lines in the range that you think contains the best solution (the smallest number of lines that meets the 5% goal). For each number of lines do at least 10 replications.
  5. Use Minitab to analyze the data from each number of lines.
  6. Use your Minitab analysis to determine the smallest number of lines that meets the 5% goal. Give reasons for your answer.

A Variation on the Machine Problem (#1.22 on page 102)

In this variation, the manufacturing system contains two different types of machines AND the machines have two different types of breakdowns (minor and major). The differences between the two types of machines (Type I and Type II) are as follows: Both types of machines have the same repair characteristics. Both experience both ordinary breakdowns and major breakdowns. A major breakdown requires two repair workers to be working on it simultaneously ( you can request 2 units of a resource - be sure to also relinquish 2). Fifteen percent of the breakdowns are major. The repair times for ordinary breakdowns are exponentially distributed (with a mean to be determined) and the major ones are uniformly distributed (between two numbers).

The SIMSCRIPT program to model this system should be written from the above information (no system parameters such as means or numbers of machines of each type or numbers of repair workers hardcoded - these numbers will be provided later). In the program, have a MACHINE process with an attribute for the machine type. As in the Quarry example, use arrays for the values that depend on the type of machine. (NOTE: Unfortunately Simscript does not let you tally or accumulate on an array variable. You will need to sum your own downtime for each machine type.) For experimental purposes, the program should be written with a loop in main so replications can be automatically performed and data written to a file for easy analysis.

Be sure to document your program appropriately and have clear prompts. The program should compute the following performance measures:

Goal of the Simulation: The current system has 5 Type I machines and 2 Type II machines. The owner plans to purchase 3 new machines and wants to know which types should be purchased (all type I, all type II, or 2 of one and one of the other type) to minimize cost and whether or not he/she needs to hire an additional repair worker (that could also affect the minimum cost).

System Parameters: Click here

HAND IN: Copies of the programs and the data analysis files for each problem. A written analysis for each with your conclusions and justification for those conclusions.