The "Operating Requirements" portion of the dialog allows you to define a logic tree (in the form of a Requirements-tree or Fault-tree) providing the conditions necessary for the component to operate. These logic trees are defined using a number of different types of nodes (e.g., AND gates, OR gates). In order for a reliability element to be operable, all of its defined requirements must be met. By default, no external requirements (External_Req) are defined, and all of the element’s failure modes are added as internal requirements (Internal_Req).
The Internal_Req and External_Req elements have identical requirements trees, but the Internal_Req element references child elements, and the External_Req element references peer elements. Both require that either another reliability element (Internal_RL and External_RL respectively) with a simple failure rate of 1/3yr is operating or operable, or that a Status element is true (the Status_Int and Status_Ext elements become true at 2.5 years).
If you run the model, you'll see that both elements produce the same results over 1000 realizations.
Logic-tree Built with Internal Requirements
Logic-tree Built with External Requirements
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