GoldSim includes a powerful 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 model, some basic Resource functionality is used to provide spare parts for operating equipment.
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.