at new ones, just close up the Storages and Facilities Windows and the two

Windows for the Tables in this model should be visible. Usually, it is a good idea to only keep open the windows that you are actively viewing.

CLICK ON The X-Upper Right of Each Window

Let’s see what happens when the mean truck arrival rate is doubled. Make the following change to your model in the Model Window.

Using the Editor, in the Model Window, change operand A of the first GENERATE Block from 18 to 9. Editing is described in Lesson 4 of the first chapter of this manual.

Next, Retranslate the model.

CHOOSE Command / Retranslate

As you run the next simulation, open the Storages Window, Facilities Window, and Table Windows, occasionally returning to the Blocks Window to observe the distribution of transactions. We’ll run the simulation a little longer so you’ll have time to move from window to window.

CHOOSE Command / START

and in the dialog box replace the 1

TYPE 1000,NP

and

SELECT OK

Things aren’t going very well, are they? Pumps 1 & 3 are busy almost all the time, and a waiting line of trucks is building up outside the depot. At this traffic load, we need to carefully evaluate our alternatives. Would we need more pumps?

Please feel free to modify the parameters and Blocks of this simulation, as we did in the first 7 examples of this chapter. Don’t forget that you can interrupt the simulation, and make changes on the spot to named values, make more extensive changes followed by a almost instantaneous retranslating of the model or redirect transactions with Manual Simulation.

You may stop here or choose to go on to the next model.

If you wish to go on to the next lesson, close all windows related to this model.

CLICK ON The X-Upper Right of Each Window

Otherwise, to end the session

CLICK ON The X-Upper Right of Main Window.

10. ASSEMBLY.GPS

Simulation of a pump assembly process.

Problem Statement

A manufacturer makes centrifugal pump units which are assembled to customer orders. The orders arrive on average, every 5 hours, exponentially distributed. When the order arrives, two copies are made. The original order is used to obtain a motor from stock and prepare it for assembly (200±100 minutes). The first copy is used to order and adapt a pump (180±120 minutes), and the second copy is used to initiate the manufacture of the baseplate (80±20 minutes).

When the pump and the baseplate are ready, a test fitting is carried out (50±10 minutes). All three components are assembled, when they are available. The unit is then dismantled, and the pump and motor are painted, and the baseplate is galvanized. Final assembly then takes place (150±30 minutes).

1.Investigate the utilization of the manufacturing facilities.

2.Determine the transit times and delays, of customers’ orders.

3.What Facility will be a bottleneck, if orders increase significantly?

4.Simulate the assembly of 50 motor-pump units.

Listing

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

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

*Assembly of Motor Pump and Baseplate *

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

Transit TABLE M1,200,200,20

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

GENERATE (Exponential(1,0,300)) ;New order arrives SPLIT 2,Factory,1 ;Make 2 copies of order

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

*Purchase Motor Original Transaction Goes Here, P1=1

QUEUE Motor ;Queue for motor SEIZE Motor ;Get a Facility DEPART Motor ;Depart the queue

ADVANCE 200,100 ;Take motor from stock RELEASE Motor ;Free the Facility TRANSFER ,Tryout ;Send to trial assembly

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

Factory TEST E P1,2,Baseplate ;Is P1=2 ? QUEUE Pumps ;Join the Queue (P1=2) SEIZE Pumps ;Get a Facility

DEPART Pumps ;Depart the Queue ADVANCE 180,120 ;Prepare the Pump Pump MATCH Plate ;Wait for baseplate ADVANCE 50,10 ;Check pump on baseplate RELEASE Pumps ;Free the Facility

TRANSFER ,Tryout ;Send for a tryout

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

Baseplate QUEUE Base ;Join Queue P1 must=3 SEIZE Base ;Get a Facility

DEPART Base ;Depart the Queue ADVANCE 80,20 ;Make the baseplate

Plate MATCH Pump ;Wait for the pump unit ADVANCE 50,10 ;Check the pump on

; baseplate

RELEASE Base ;Free the Facility

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

Tryout GATHER 3 ;Gather 3 units to tryout ADVANCE 60 ;Trial assembly

TEST E P1,1,Finish ;Is it the motor?(P1=1)

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

SEIZE Paint1 ;Get first paint Facility ADVANCE 100,20 ;Paint the motor RELEASE Paint1 ;Free paint Facility 1 TRANSFER ,Build ;Send for assembly

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

Finish TEST E P1,2,Basplate ;Is it the pump?(P1=2) SEIZE Paint2 ;Get paint Facility 2

ADVANCE 120,30 ;Paint the Pump RELEASE Paint2 ;Free paint Facility 2 TRANSFER ,Build ;Send for assembly

Basplate SEIZE Galvanize ;Get a Facility ADVANCE 120,30 ;Galvanize baseplate RELEASE Galvanize ;Free the Facility

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

Build ASSEMBLE 3 ;Collect 3 units ADVANCE 150,30 ;Assemble unit TABULATE Transit ;Record transit time TERMINATE 1 ;One unit completed

Transactions represent orders. When an order is received, 2 offspring transactions are created by a SPLIT Block. This allows individual orders for the motor, pump, and baseplate to proceed at the same time. Orders representing the pump and the baseplate wait for each other at the MATCH Blocks labeled Pump and Plate. When both have arrived, an initial assembly delay is simulated. After all three orders have arrived at the GATHER Block an ADVANCE Block represents the trial assembly. Then the three orders are again separated for finishing. The ASSEMBLE Block labeled Build causes final assembly to be delayed until all components are ready.

The Table Transit represents the distribution of order completion times.

Running the Simulation

To run the simulation and create a Standard Report,

CHOOSE File / Open

SELECT ASSEMBLY

and then

SELECT Open

Next, create the simulation.

CHOOSE Command / Create Simulation

then

CHOOSE Command / START

and in the dialog box, replace the 1

TYPE 50

and

SELECT OK

The simulation will end when 50 order completion times have been tabulated.

When the simulation ends, GPSS World writes a report to the default report file, Assembly.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

From the Standard Report, we see that the Facilities representing capital equipment have utilizations from 31% to 73%. The order completion times are represented in the Table Transit. The mean was 877.79 minutes, with a standard deviation of around 256.86.

The Facilities representing the pump station and the base station have the highest utilizations. If all activity is increased proportionately, they will be the first to saturate.

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.

Now let’s open some graphics windows.

CHOOSE Window / Simulation Window / Table Window

and in the drop-down box, Transit is already selected.

SELECT OK

Expand the Table to a comfortable viewing size. This is the Transit Table, a histogram of order completion times. The mean order completion time was 877.79 minutes.

Figure 10—1. The Transit Table Window

Next, look at the Facilities.

CHOOSE Window / Simulation Window / Facilities Window

To see all of the Facilities, open the window to a larger size or use the scroll bar on the side of the window to move up and down in the window.

Look at the Facility utilization listing on the right side of the window. The Pump and Base Facilities were highest at 72% and 73% respectively and are currently busy (red icon). Painting and Galvanizing have much lower usage and are currently not in use (gray icon).

Let’s take a look at how transactions travel inside the simulation. First, close the windows we no longer wish to observe. Make sure to keep the Journal / Simulation Window open. If you close this window, you can no longer run the simulation.

CLICK ON The X-Upper Right of Each Window

then

CHOOSE Window / Simulation Window / Blocks Window

Now, select the first GENERATE Block with your mouse by positioning the mouse over the Block and clicking once. Then,

CLICK ON The Place Icon in the Debug Toolbar

This will cause the next simulation to stop just before any transaction attempts to enter the Block. Now, let’s start the simulation running after you have sized the Blocks Window to a comfortable viewing size.

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

TYPE 10,NP

and

SELECT OK

The simulation is ready to start an order. Other orders may be unfinished, and still in the simulation.

PRESS m

several times. The simulation will stop each time just before another order enters the simulation. However, each time you continue, you may see parts of two different orders circulating in the simulation. Often, just after one transaction enters an ADVANCE Block, a new one will become active.

Now, when the simulation stops, turn on the trace indicator of the active transaction.

CHOOSE Command / Custom

and in the dialog box

TYPE Trace

SELECT OK

Put the focus on the Journal Window and open it to a comfortable size for viewing.

PRESS m

several times until all the trace messages cease. Since offspring transactions get a copy of the parent transaction’s trace indicator, the trace messages have all the Block entry information pertaining to the processing of a single order.

Let’s explore a specific order in detail. Set the window focus on the Blocks Window. The simulation should currently be stopped at the GENERATE Block. Let’s Step through it and watch the progress of the order. First turn on the trace flag in this Transaction.

CHOOSE Command / Custom

and in the dialog box

TYPE Trace

SELECT OK

Make sure you can see both the Blocks and Journal Windows.

PRESS p

repeatedly Watch the new offspring transactions which represent component orders. MATCH, ASSEMBLE, and GATHER Blocks cause related transactions to wait for each other.

Please feel free to modify the parameters and Blocks of this simulation. You may stop here or choose to go on to the next model.

If you wish to go on to the next lesson, close all windows related to this model.

CLICK ON The X-Upper Right of Each Window

Otherwise, to end the session

CLICK ON The X-Upper Right of Main Window.