Inclass - OPIM 301 In-class Exercise Instructions December...

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OPIM 301 In-class Exercise Instructions December 4, 2009 In this exercise, you will develop a basic simulation model in Excel. You will use Excel’s random number generator to simulate production of 30 items on a two-workstation assembly line with no buffer space between the two workstations. The objective is to understand the basic concepts behind simulation and also why Excel is not that suitable for simulating complex manufacturing or service processes. Instructions for the Exercise 1. Log on to SUCourse OPIM 301 website, go to Assignments section and click Week 10 In-class Simulation Exercise . Download the attachment inclass.xls . The file inclass.pdf includes the instructions you are reading now. 2. Open the inclass.xls Excel file. The contents of the file should be seen as in the picture below. You will enter the necessary formulae to complete the Excel model. 3. An important aspect of simulation models is about probability distributions (to represent values that are not deterministic or certain) and random numbers that are used to generate values from these distributions. The values are used to repeat the simulation a number of times to obtain statistical results. In this exercise, Workstation 1 and Workstation 2 operator performance times are not constant and they come from discrete probability distributions listed below. The performance times are in seconds. Workstation 1 Performance Time Probability Workstation 2 Performance Time Probability 10 0.04 10 0.08 20 0.06 20 0.10 30 0.10 30 0.12 40 0.20 40 0.14 50 0.40 50 0.20 60 0.11 60 0.16 70 0.05 70 0.12 80 0.04 80 0.08 A Random Number is a number generated by the computer. The number is typically between 0 and 1, and it is converted to another meaningful value for simulation purposes. For instance, if service time is uniformly distributed between 2 minutes and 8 minutes, random number 0.5 is converted to 5.
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The range P3:R11 contains this information, but the probabilities are multiplied by 100 and listed cumulatively . The first two columns contain the probability values for Workstation 1 and 2, respectively, and the third column contains the performance times. The table is arranged (i.e. cumulative probabilities) such that when the random numbers are generated, the corresponding performance times can be extracted from this table using the VLOOKUP function (see Step 6). 4. Starting filling in the formula to create your simulation model. Since you will be simulating production of 30 items, start by filling in Column A (starting in row 3) with numbers 1 to 30. No formula needed here. 5. Next, you must enter a formula in columns B and H for random number (RN) generation. Enter formula =INT(RAND()*100) in cell B3 , and copy this formula over to range B4:B32 . Enter the same formula in cell H3 , and copy this formula over to range H4:H32 . Here, the RAND function returns a floating value between 0 and 1, and the INT function takes the integer portion of its input value. The result is a random number between 0 and 99. Note:
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Inclass - OPIM 301 In-class Exercise Instructions December...

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