Abstract
A recursive rulebase system is proposed to automate, under fixed and/or free boundary conditions, fault tree (FT) generations for systems with loops such as controls, return currents, and emergency shutdown features. A system for which FTs are generated is uniquely modeled as a semantic network via a manually constructed block diagram which is similar to and more general than a GO chart. Each block represents a piece of basic equipment controling a particular attribute of a flow appearing in the system. Several typical pieces are catalogued to facilitate the block diagram representation. With each piece a mini-semantic network is associated to uniquely create the system semantic network. Events are classified into flow-triple, equipment-suspected, and equipment-failure, where the flow-triple is a triple, (flow, attribute, value). Event development rules are classified into four types accordingly, and typical rules are obtained systematically from truth tables. Procedural aspects of a manual FT generation are clarified as a recursive algorithm consisting of two modules: “rule addition and removal” and “event addition and removal”. Three-valued logic is used in the algorithm to remove the added rules and the events from the FT, thus enabling FT simplifications so as to reflect boundary conditions, loops, obvious events, etc. These logic values are propagated upwards to the top event.
