Hamid Demmou

Reliability analysis of discrete event dynamic systems with Petri nets

This paper deals with dynamic reliability of embedded systems. It presents a method for deriving feared scenarios (which might lead the system to a critical situation) in Petri nets. A classical way to obtain scenarios in Petri nets is to generate the reachability graph. However, for complex systems, it leads to the state space explosion. To avoid this problem, in our approach, Petri net reachability is translated into provability of linear logic sequents. Linear logic bases are introduced and used to formally define scenarios and minimality of scenarios. These definitions allow the method to produce only pertinent scenarios. The steps of the method are described and illustrated through a landing-gear system example.

Critical scenarios derivation methodology for mechatronic systems

Abstract This paper deals with safety in design of mechatronic systems. We propose a method based on a qualitative analysis of a Petri net model of the system. It allows deriving feared scenarios by determining the sequences of actions and state changes leading to the feared state in which the passengers safety is no longer guaranteed. The Petri net model of the system takes into account normal behaviour, failures and reconfiguration mechanisms. Our approach uses linear logic as formal framework and is based on a backward and a forward reasoning. It derives feared scenarios as causal relationships between normal states and the feared one.

Petri nets for the evaluation of redundant systems

Abstract This paper gives an overview of the use of Petri nets for the evaluation of redundant systems. After listing modelling criteria for this type of system, we describe the powerful characteristics of Petri nets concerning both representation and performance evaluation: descriptive ability, formal verification procedures, the ability to incorporate time and quantitative analysis. Finally, we discuss the possibilities offered by this theory, as well as certain limitations when it comes to modelling large-scale systems such as those usually encountered in industrial applications.

Engineering dependability requirements for complex systems — A new information model definition

Requirements engineering is an important phase in a systems life cycle. It is important to perform it correctly. The increasing complexity of systems makes requirements engineering activities more difficult. In design of complex system, the system engineering is widely used. Model-driven engineering, in which models are the main artifact during system development, is an emergent approach that tries to address system complexity by the intense use of models. In this context, this paper proposes a new information model based on SysML to properly manage requirements with a special attention to dependability requirements.

Analysing a mechatronic system with coloured Petri nets

Mechatronic subsystems of cars are examples of hybrid systems. Modelling and simulation of the interactions between continuous and discrete parts are essential to perform dependability evaluation. In this paper we show how it is possible to model a concrete mechatronic system with coloured Petri nets, but the methods used are applicable to a wider range of hybrid systems. The constructed models are simulated to obtain a quantitative dependability evaluation. Qualitative evaluations of the model are obtained using state space analysis.

Managing systems engineering processes: A multi-standard approach

Considering that system design becomes more and more complex to manage, systems engineering standards are useful and necessary for the companies. In order to choose the right standard, this paper presents an analysis of and a detailed comparison between the current releases of the main Systems Engineering standards in system design industry, ANSI/EIA-632, ISO/IEC-15288 and IEEE-1220, and illustrates how to choose a standard on the basis of specific characteristics of the project. For cases where no standard completely satisfies the criteria, we suggest a way to extend and adapt a standard.

Minimality of Critical Scenarios in Petri Net Models

The aim of this paper is to define the concept of minimality of scenarios, considering that in our approach a scenario is defined as a partial order between events. For deriving feared scenario (ie: scenario that leads the system to critical situation) Petri nets are used for the modelling of systems. To avoid space state explosion, Petri net reachability is translated into provability of linear logic sequent. It is possible to determine a partial order of transition firings and extract feared scenarios which are represented by sequents. By analogy with the concept of minimal cutsets for the fault trees, we define in this paper the concept of minimal scenario.

Using Self-Recurrent Neurons for Fault Detection and Diagnosis

Abstract A recurrent neural network model for process monitoring is proposed. Fault detection, isolation and diagnosis are introduced in the context of production systems. Sequences and temporal constraints between events are considered as essential for process monitoring. The difficulty that have artificial neural networks to deal with time is highlighted. Self-recurrent connections are proved to be a simple mechanism to treat time and sequences and their basic properties are given. A modular architecture is presented and applied to a flexible assembly cell.

Safety management method in complex system engineering

The main objective of System Engineering is the successful development of complex system. It is based on the application of iterative and recursive processes on each phase or step of the system development. One critical process is the requirement management, particularly when it deals with the safety requirements. These one are non-functional requirements and are related to emergent properties, which come from the integration of the different system components. They must be identified as soon as possible, because they are guards to validate or not the system, which can require changes in system architecture. Moreover, they are formulated at system level and need to be derived at sub-system level. The objective of this paper is to propose a safety management method based on well-known safety methods, in order to organize the different tasks to make the system safe. The method focuses mainly on the definition of the system safety requirements following risk and hazard analysis, and also on their derivation according to a top-down approach. It is based on the well-known Failure Mode, Effects, and Criticality Analysis (FMECA) and the use of Fault Trees and Event Trees.

A safety requirement engineering method and tool

Requirement engineering is one of the most critical system engineering processes, particularly when it deals with the safety requirements which are non-functional requirements and are related to emergent system properties. In fact, safety requirements must be formulated at system level and then be derived at sub-system level. The main objective of this paper is to present a new tool, “SafetyLab”, which implements a method for safety treatment of complex systems. The method allows the definition of the system safety requirements following a risk and hazard analysis, and then their derivation according to a top-down approach. It is based on the famous Failure Mode, Effects, and Criticality Analysis (FMECA) and the use of Fault Trees.