Systems Reliability/Safety Analysis Using System Behavior Model

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The main of the research is to develop a method of obtaining information on the system failure based on the system behavior model to prevent analysis errors caused by the subjective judgment and experience of system analysts.In the first year of the project, the applicability of bond graphs is examined for obtaining a system behavior model from the system design assumptions. Bond graphs can represent a system composed of mechanical, electrical and hydraulic components in a unified way from the viewpoint of energy flow. The system dynamical behavior can be represented as system state equations in terms of system state variables denoting energy storage, input variables denoting energy supply and characteristic functions denoting elements. Since component characteristic functions can be represented only qualitatively at the early stage of design, a method is developed for the qualitative evaluation of deviation in process variables caused under a component failure condition using the stea … More dy state condition.In the second year, a method is developed for making the qualitative evaluation more efficient. Firstly, system state equations obtained from a system bond graph are represented using the tree graph. A tree graph is composed of nodes and branches : the former represent bond graph elements, input variables and system state variables, while the latter represent input-output relations and between nodes and has the output value of their source node. By propagating a deviation caused by a component failure assumption along the tree graph, all the deviations at nodes can be evaluated. Multiple failure conditions can be dealt with. Since a node corresponds to a system state, all system states can be evaluated from the node values of a tree graph. As long as the assumptions on the system behavior are correct, the validation of the evaluation result from the tree graph is guaranteed. Further, application of the analysis result to the system failure daignosis is considered. However, the failure identification using the tree graph remains a subject to be solved in the near future because an efficient method cannot be obtained to reduce the number of possible candidates which can explain the observed system condition. Less