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Modeler's
Corner
An introduction to
Resources
Eina Ooka
GoldSim Technology Group
eooka@goldsim.com
GoldSim Version 10.1 includes a powerful
new feature called Resources that can be used to model stocks of items
and material that are required for elements to operate or carry out
certain actions. This new feature enables you to easily keep track of
things like money, equipment, spares and personnel that are needed for
various operations. In this Modeler’s Corner, we’ll take a look at a
model that uses some basic Resource functionality. The model
discussed in this edition of Modeler’s Corner is actually installed with
GoldSim Version 10.1 and can be accessed by opening Version 10.1, going
to File|Open Examples…in the main menu and opening the
RL_Resources.gsm example in the Reliability Examples folder.
This example contains 3 reliability elements
representing identical machines which fail approximately twice a month
according to an exponential distribution. When a machine fails, a spare
and a technician are required in order for it to be repaired. The repair
takes 5 days and cannot begin until both a spare and a technician are
available.
Resources are defined and edited through
the Resource Manager dialog that can be accessed by selecting Model|
Resources… in the main menu. The dialog allows you to add, remove and
edit Resource Stores. The properties of existing Stores can
be viewed by double-clicking their entry in the dialog. In this model,
spares are defined as item-type and there are five of them at the
beginning of the simulation. They are replenished by a
Discrete Change element called Add. The model also has a Technician
Resource, which is also item-type. One technician is
available to execute repairs on the three machines.
Now let’s look at reliability elements.
Since we are using Resources to repair failures, Resource requirements
are defined on the Failure Modes tab. If you select the
Exponential/Poisson mode and then click on the Resource button at the
bottom of the tab, you can see Resource requirements for repair of that
mode. One spare is “spent” and one technician is “borrowed.” This means
that the total quantity of spares goes down by one during a repair, and
the number of available technicians is reduced by one for the duration of
the repair.
Resource
requirements for the other two reliability elements are identical.
Because spares are consumed, they need to be resupplied regularly. This
is simulated with the elements in the bottom left of the
model. When a machine is repaired, the availability of spares
is checked. If there are less than 2 spares left in the shop and no order
has been yet made, 5 extra spares are ordered. There is a delivery delay
after the order is placed, after which the spares are added to the
Resource Store.
If
we plot the status of the machines over the duration of the simulation we
get the following time history graph:
Note
that a value of 0 means that machines are functioning and a value of 2
means that they are failed and have not yet been repaired. Look at the
circled region. Right before the failure of Element_2, Element_3 fails.
As a consequence, the technician begins work on repairing Element_3, and
she doesn’t start work on Element_2 until she’s done repairing
Element_3. If Resources were not used, both of the elements would
be repaired 5 days after failure regardless of the status of the other
elements.
In
this example, we’ve looked at Resource usage in reliability elements.
However Resources can be accessed through other elements such as
conditional Containers, Triggered Event elements, Event Delays and
Discrete Change Delays. To learn more about Resources, you can read
the Version 10.10 Summary document, sign up for a Webinar, read the
detailed description in the User’s Guide, and download other Resource
examples from the Model Library.
Suggestions?
Do you have any suggestions for future
Modeler's Corner articles? If so, we'd love to hear from you. Please
contact us at support@goldsim.com.
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