Complex Groups [Image: complexGroup.png]

A complex group represents a collection of items which cannot be decomposed into a

combination of distinct series or parallel groups for analysis. The complex group

consists of items arranged horizontally, with the key item in a functioning state shown

with a key symbol. A built-in exclusion group is used to disregard items specified by

the user.

[Image: complex.png]

One approach to dealing with complex groups is to conduct simulations to approximate

the group reliability. For a RBD analysis, the analytical approach is to define a

reliability group with a key element. This Complex RBD group shall have the following

characteristics:

• Two distinct States: (1) Key element functioning (ON) and (2) Key element not functioning (OFF)
• Group reliability when key element is functioning by replacing key element with unbroken reliability connection, R=1
• Group reliability when the key element is not functioning by replacing key element with a broken reliability connection
• Overall reliability of the complex group calculated using the reliabilities of the two scenarios combined with the relative probability of each scenario occurring - this is based on reliability of the key element

Expressed mathematically for the Exponential Distribution Type:

[Image: complexexpeq.png]

Where λke is the part failure rate of the key item,

t is duration of operation, λGroupoff

failure rate of the complex group without the key element, and

λGroupon is the failure rate of the complex group

with the key element.

Expressed mathematically for the Weibull Distribution Type:

[Image: complexweibeq.png]

Where β is the Weibull slope and ηke is the

Weibull characteristic life of the key element.

To create a Complex Group:

1. Right-click an the item in the Project explorer or System Model
2. Select 'RBD Model' Note: The RBD editor will show all items under the currently

selected item.

3. In the RBD editor, select items (hold SHIFT and left-click) to include in the Complex group
4. Right-clicking the RBD diagram and selecting "Group → Complex Group" from the right-click menu Note: An alternative method is to select the complex icon

[Image: complexGroup.png]

from the icon menu to create

the complex group.

5. Select the key item from the Key Element dialog
6. Verify that all selected items have been included in the complex group

[Image: createcomplex.gif]

Toggling Key Element State

To define whether a complex group has a functioning/non-functioning key item:

1. Open the RBD editor for an item containing a complex group
2. Select the complex group and view the Properties viewer
3. In the General tab select the radio button for either 'key element functioning' or 'key element failed'
4. Review the change in reliability for the complex RBD group or the RBD analysis
5. Save changes

[Image: togglekeyitem.gif]