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RiskSpectrum^® C-BDD

Relcon Scandpower has been monitoring the development of the Binary Decision Diagram (BDD) methodology for the representation of logic since the beginning of the 1990Žies. So far we have concluded that there are still problems with this solution technique, when used for converting fault trees to BDD.

One way of working around the problems converting fault trees into BDD is to generate cutsets using the classical solution (inclusion/exclusion rules) and then convert the minimal cutsets into a BDD. With the BDD-representation, the top frequency/unavailability and importance/sensitivity measures can be calculated without truncation (based on the generated MCS-list).

Today, Relcon Scandpower have a prototype of such a BDD "hybrid" solution engine RiskSpectrum C-BDD. Using this engine, cutsets are generated using the classic RSAT algorithm, but instead of using Min Cut Upper Bound or first, second and third order approximation for calculating top event frequency/unavailability, the cutsets are converted to a BDD in which the top event can be calculated without truncation.

There are two major advantages using RiskSpectrum C-BDD:

1. Solves the problem with high probabilities using Min Cut Upper Bound, first, second or third order approximation: Top frequency/unavailability and importance/sensitivity measures are calculated without truncation using a BDD. This means that you can use high probability events in your fault tree models and use RS C-BDD for converting your MCS lists (including high probability events) and calculating top event frequency, etc, without truncation.
2. NOT-logic can be included in MCS lists. MCS lists including NOT-logic are converted to RS C-BDD without problems and in BDD, top frequency/unavailability and importance/sensitivity measures are calculated without truncation, also including NOT-logic.

Relcon Scandpower is pursuing the development of a conversion tool going directly from fault trees to BDD.

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