Otherwise, to end the session

CLICK ON The X-Upper Right of Main Window.

8. TEXTILE.GPS

Simulation of a textile factory.

Problem Statement

A textile factory produces fine mohair yarn in three departments. The first department draws and blends the raw material, in sliver form, and reduces it to a suitable thickness for spinning, in 5 reducer frames. The second department spins the yarn in one of 40 spinning frames. The final process is in the winding department, where the yarn is wound from spinning bobbins onto cones for dispatch. There are 8 winding frames, to perform the winding operation.

The factory works 8 hours per day. The unit of production is 10 kilograms of yarn. Reducing frames produce one unit every 38±2 minutes, while the spinning frames and winding frames produce one unit in 320±20 minutes and 64±4 minutes, respectively.

The initial inventory of reduced material is 50 units (in Savevalue Reduced), spun material is 25 units (in Savevalue Spun) and finished yarn is 25 units (in Savevalue Wound). The finished material is dispatched, in a container of capacity 200 units, every two days.

1.Simulate the production process in the textile factory for 5 days.

2.Find the distribution of the in-process inventories.

3.Determine the utilization of each of the three types of machines.

Listing

;GPSS World Sample File - TEXTILE.GPS, by Gerard F. Cummings

***********************************************************************

* *

* Production System in a Textile Factory *

* *

***********************************************************************

Reducers STORAGE 5 ;Represents 5 reducer

;frames

Spinners STORAGE 40 ;Represents 40 spinning ; frames

Winders STORAGE 8 ;Represents 8 winding

; frames

Reducing TABLE X$Reduced,20,20,20 ;Inventory reduced material Spinning TABLE X$Spun,20,20,20 ;Inventory spun material Winding TABLE X$Wound,20,20,20 ;Inventory wound material INITIAL X$Reduced,50

INITIAL X$Spun,25

INITIAL X$Wound,25

**********************************************************************

GENERATE 0.334,,1 ;Time unit is one hour QUEUE One ;Enter queue for reducing ENTER Reducers ;Get a machine

DEPART One ;Depart the queue ADVANCE 0.634,0.334 ;Process time LEAVE Reducers ;Leave the machine

**********************************************************************

SAVEVALUE Reduced+,1 ;Reduced inventory up by 1 QUEUE Two ;Queue for spinning process

ENTER Spinners ;Get a spinning machine DEPART Two ;Depart the queue

ADVANCE 5.334,0.334 ;Process time LEAVE Spinners ;Free a machine

SAVEVALUE Reduced-,1 ;Reduced inventory down 1

**********************************************************************

SAVEVALUE Spun+,1 ;Spun inventory up by one QUEUE Three ;Queue for winding process ENTER Winders ;Get a winding machine

DEPART Three ;Depart the queue ADVANCE 1.067,0.067 ;Process time LEAVE Winders ;Free a winding machine

SAVEVALUE Spun-,1 ;Spun inventory down by 1

**********************************************************************

SAVEVALUE Wound+,1 ;Wound inventory up by 1 TERMINATE ;Xact is finished

**********************************************************************

GENERATE 8 ;One xact every day TABULATE Reducing ;Record inventory of ; process

TABULATE Spinning ;Record inventory of spun ; material

TABULATE Winding ;Record inventory of wound ; material

TERMINATE 1 ;One day has passed

***********************************************************************

GENERATE 16 ;A xact every 2 days

TEST GE X$Wound,200,Notthere ;If not done don’t dispatch SAVEVALUE Wound-,200 ;200 Kgs produce delivered TERMINATE ;Xact is finished

Notthere TERMINATE ;Xact is finished

***********************************************************************

The model is organized into several segments. After the Storage Entities are defined and Savevalues initialized, there are three more model segments. Transactions in the top segment represent batches of yarn which pass through the reducing, spinning, and winding operations. Transactions in the middle segment tabulate daily inventories, and the transactions in the bottom segment dispatch a 200 kilogram lot of yarn, if a complete lot is available.

Running the Simulation

To run the simulation and create a Standard Report,

CHOOSE File / Open

and in the dialog box

SELECT TEXTILE

and then

SELECT Open

Next, we must create the simulation.

CHOOSE Command / Create Simulation

then

CHOOSE Command / START and in the dialog box, replace the 1

TYPE 5

and

SELECT OK

The simulation will end when 5 transactions have entered the TERMINATE 1 Block. This represents 5 days of operation.

When the simulation ends, GPSS World writes a report to the default report file, Textile.1.1. As discussed in Chapter 1, the Report extension will vary depending on saved simulations and previously existing reports. For our purposes, we will assume that this is the first time the simulation has been created and run giving an extension of 1.1.

This report will be automatically displayed in a window. If you close the window, you can reopen it by using the GPSS World File / Open in the Main Menu. Then

you should choose Report in the "Files of type" drop down box at the bottom of the window. GPSS World reports are written in a special format. If you wish to edit the report, you will have to copy its contents to the clipboard and from there into a word processor. You will not be able to open the file directly in a word processor.

Discussion of Results

The distribution of the in-process inventories is given by the Tables Reduced, Spun, and Wound. The utilization of reducers was about 39%, and that of the spinners 36%, and winders about 32%.

Inside the Simulation

Let’s now explore the ending condition of the simulation which generated the Standard Report above. If you are not at the end of the simulation, please Retranslate the model and run it again.

Let’s use the Expression Window to look at some System Numeric Attributes. First, look at the units of reduced material on hand.

CHOOSE Window / Simulation Window / Expressions Window

The Edit Expressions Window opens. When you enter the value in the second box in this dialog box, you should place the mouse pointer in the small box and

click once. Do not press e to go from the first to the second box as GPSS World

then assumes that all values have been entered. Now, in the dialog box for the Label field

TYPE Reduced Material

and in the Expression field

TYPE X$Reduced

CLICK ON View

and

CLICK ON Memorize

If we memorize all the expressions, we'll be able to close the window and open it again later with easy retrieval of all the values. Also if you save the simulation the values in the Expressions Window will be saved with the simulation if they have been memorized. We're going to close this window and reopen it later so please memorize this expression and the ones that follow.

In the dialog box for the Label field replace the current value

TYPE Spun Material

and in the Expression field, replace the current value

TYPE X$Spun

CLICK ON View

CLICK ON Memorize

Finally, let’s keep track of the Wound material.

In the dialog box for the Label field, replace the current value

TYPE Wound Material

and in the Expression field, replace the current value

TYPE X$Wound

CLICK ON View

CLICK ON Memorize

SELECT OK

This shows the inventory of each of the products. If this window is open while the simulation runs, the values are updated on-line. Next, let’s also open some graphics windows.

CHOOSE Window / Simulation Window / Storages Window

This window gives information on machine usage. There are 1 reducer, 17 spinners, and 2 winders busy. The utilizations are between 30% and 40%. The Reduced, Spun, and Wound Tables can be easily viewed.

CHOOSE Window / Simulation Window / Table

and in the drop-down box Reducing is already showing for the Table name

SELECT OK

and expand the window to viewable size.

Figure 8—1. The Reducing Table Window.

You can open the next two Tables as well using the same method but selecting the names Spinning and Winding from the drop-down box.

Finally, let’s take a look at where transactions are.

CHOOSE Window / Simulation Window / Blocks Window

Notice, that we can tell how many machines are busy by how many transactions are in the ADVANCE Blocks. This is consistent with the information in the Storages Window.

Now look at the history of transactions in the simulation. You will see this in the Total Entry column of this window. Scroll down to the last Block in the model that is labeled Nothere, using the scroll bar on the right side of the window. Notice that this Block was entered twice. This means that on two occasions there was not enough finished yarn for the dispatcher. Clearly, the production of the factory needs to be increased. All the capital equipment is under utilized, and the production quotas are not being met. We should increase the rate that jobs are begun. Also, we could schedule a second shift of operation every work day.

Please feel free to modify the parameters and Blocks of this simulation.