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Contribution à l'analyse des systèmes pilotés par calculateurs : extraction de scénarios redoutés et vérification de contraintes temporelles

Abstract : The progressive integration of electronics in the car and avionics fields has lead to improvements in both functions and services. However, this has caused an increased complexity in the design of these systems, typically involving computers (e.g. mecatronic systems, flight computers, etc.), which makes the control of their reliability difficult. In addition, the phase of design must be fast and inexpensive (i.e. less prototypes and at later stages) with a level of guaranteed safety. In more cases for reasons of cost and implementation, material resources are limited and the system designers must avoid component redundancies within the system as much as possible. Reliability studies performed at the design phase have allowed a better control of the risks and reliability of the conceived systems. Indeed, the weak points which are highlighted during the evaluation of the level of safety of the conceived systems make it possible for the designers to specify strategies of piloting, and modes of reconfiguration, before the first tests on a real prototype. Computer-controlled systems that combine mechanical, hydraulic, electronic and data-processing technologies are referred to as hybrid. For these systems, continuous dynamics is applied to the power characteristics, and discrete dynamics is related to the numerical control and the existence of discrete events (for example, failures and thresholds). The study of reliability for such systems must necessarily take into account the existing interactions between their physical parameters (e.g. temperature, pressure, speed, etc.) and the failure of their components. Traditional methods for reliability such as Failures Trees are insufficient for these complex and hybrid systems because of their dynamic nature. Therefore, the time and order of execution of the events must be taken into account to ensure the safety of these systems. The scarcity of these feared scenarios exposes methods based only on simulation to the combinative explosion. There are indeed techniques of acceleration of simulation, largely used successfully, in particular in nuclear engineering. Our research work is placed within the framework of dynamic reliability. The objective is to carry out a qualitative analysis of the reliability of computer-based systems to extract the scenarios leading to feared states. This is a question of characterizing these scenarios as soon as possible in the design phase, which makes it possible to evaluate their probabilities of occurrence in order to validate the architecture of the system. We propose an approach based on linear logic and Predicates Transitions Differential Stochastic Petri Nets model (RdP PTDS), which respects the hybrid nature of these systems. This approach takes into account the continuous aspect of the system, and more particularly the thresholds associated to certain transitions in the Petri Net model. This approach determines more precisely the exact conditions of the occurrence of the feared event, i.e what has led the system to leave its normal operation and to evolve into the feared state. The originality of our approach is that the order of occurrence of the events is taken into account, and impossible scenarios with respect to continuous dynamics of the system are eliminated. Our approach is also directed towards the checking of certain properties of the computer-controlled systems. These properties can be temporal (e.g. maximum duration of a scenario, or duration between two orders), or related to the accessibility between two states. We believe that the automation of all stages of our approach is essential for the cases of complex systems where the risk of human error is very significant. This is why we developed a tool ESA_PetriNet (Extraction & Scenarios Analyser by PetriNet model), which makes it possible to extract the critical scenarios from a temporal Petri Net model, and to check certain properties of these computer-based systems. null null
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Submitted on : Wednesday, June 28, 2006 - 10:58:21 AM
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Malika Medjoudj. Contribution à l'analyse des systèmes pilotés par calculateurs : extraction de scénarios redoutés et vérification de contraintes temporelles. Automatique / Robotique. Université Paul Sabatier - Toulouse III, 2006. Français. ⟨tel-00082568⟩



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