Analyse systémique | EPFL Graph Search

L'analyse systémique est l'analyse faite selon les principes interdisciplinaires de la systémique, étude d'objets complexes par leurs échanges, qu'il s'agisse d'êtres vivants, d'organisations sociales, ou d'objets techniques. Face à ce type de problème, il est nécessaire d'adopter une démarche globale :

en s'attachant davantage aux échanges entre les parties du système qu'à l'analyse de chacune d'elles,
en raisonnant par rapport à l'objectif du système (téléologie),
en établissant les états stables possibles du système. L'analyse systémique « s’appuie sur une approche globale des problèmes ou des systèmes que l’on étudie et se concentre sur le jeu des interactions entre leurs éléments. […] Au précepte cartésien de réductionnisme qui demande une décomposition en autant de parcelles qu’il est possible de le faire et qui constitue la caractéristique essentielle de l’approche analytique, l’approche systémique oppose le précepte du globalisme. Les objets d’études ne sont pas en effe

Optimal Process Design for Power Production from Wet Waste Biomass by Hydrothermal Gasification coupled to a Solid Oxide Fuel Cell

This report presents a system analysis of the production of electricity from wet waste biomass. A system of Hydrothermal Gasification is coupled with a Hybrid Cycle composed by a SOFC and two Gas Turbines, driven in an inverted Brayton--‐Joule cycle. A thermodynamic optimization approach, based on the system energy integration, is used to analyze several configuration options. The influence of the process design on performances is discussed for the most representative scenario that highlights the key aspects of the system. Optimization results prove that a systematic system design may reaches efficiencies higher than 60%.

2011

Object-oriented approach for dynamic system modelling and simulation

Adel Besrour

Software engineering always cares to provide solutions for building applications as close as possible to what they should be, according to the requirements and the final users needs. Systems behavior simulation is a very common application to virtually reproduce and often predict the real-world behavior. Simulation is one of the most operational research tool in a large variety of engineering and scientific domains: Transport, telecommunication, medicine, chemical processes, physics, etc. The complexity of such application is relative to the increasing complexity of the systems. In this context, it is relevant to bring together different tools and formalisms such as markovian chain, Petri nets, etc., to improve the existent approaches and so to answer the simulations performances needs. The principle objective of this thesis is to bring together techniques from software engineering and safety engineering in order to improve the state of the art of modeling and simulation of dynamic systems in the industrial context. In addressing this objective, this work initially involves defining the essential limitations of the used formalisms, methods and tools regarding from one hand the software engineering modeling and simulation techniques and from the other hand the existent risk analysis methodologies. This work is conducted with respect to the problem of danger identification, considering the context of the complex systems behavior and their interaction with the human operator. In software engineering, it is well known that Petri/high-level nets have attractive characteristics to be used in systems simulation and behavior prediction such as the natural graphical representation, and their well-defined semantic. They are well-suited for the description of complex situations with concurrency (interleaving and true concurrency depending on the underlying semantics), conflict and confusion. However, the absence of structuring capabilities has been one of the main criticisms raised against Petri nets/high-level nets. Thus, there have been many attempts to introduce structuring principles in nets of this kind [BCM88] [Kie89] [JR91]. The attractive characteristics of Petri/high-level nets have prompted researchers to enrich these formalisms with object-oriented features. CO-OPN (Concurrent Object-Oriented Petri Net) approach, brings together the power of both Petri/high-level nets and object-orientation techniques, it has been devised so as to offer an adequate framework for the specification and design of large scale concurrent system [BG91]. CO-OPN, as a powerful modeling tool, has been used in a limited way to simulate systems. This work aims to provide a CO-OPN extension to allow a more realistic systems' simulation. Actually, its simulator semantic uses to be a suitable approach for modeling near closed systems and software components, because they need to loose coupling with external world. But, when we model more realistic problems like industrial processes, where human interaction is a relevant event, this approach is not sufficient to catch all system activity attributes. Moreover, the CO-OPN interpretation process does not allow interaction with the object internal states. This work provides a new solution to overcome CO-OPN simulation limitations and a set of prototypes to assist dynamic systems simulations. Furthermore, this work has been conducted in a Risk Analysis (RA) context, a domain where computer-based simulations research are of utmost interest. Actually, classical approaches used to address complex workplace hazard in a limited way, using checklists or sequence models. Moreover, the use of single oriented methods, such as AEA (man-oriented), FMEA (machine oriented) or HAZOP (process oriented), is not satisfactory to overcome the increasing sophistication of industrial processes. The automation of a part of the analysis process as well as the multiple-oriented approach allowed by dynamic modeling may indeed enhance significantly the analysis completeness and reduce the time analyzing time. This work, based on Object Oriented Petri net formalism (CO-OPN), propose an alternative multi-oriented approach where existent methods limitations have been criticized to develop a dynamic model, MORM (Man-machine Occupational Risk Modeling). A real industrial system (metal wire making process) has been specified to implement the different approach steps (system identification, model application, system simulation, system analysis).

EPFL2005

Conception et optimisation multicritère des échappements libres pour montres-bracelets mécaniques

Thierry Conus

The watchmaking crisis of the nineteen-seventies in effect marked an interruption of scientific research into the working of mechanical watches. For the past few years, a revival of interest in these timepieces has given industrialists the financial resources needed to improve the performance of existing systems and create new mechanisms. The escapement is the only subsystem of a watch movement which combines an energy transfer function with a direct mechanical action on the oscillating weight : its role here is therefore fundamental. This thesis describes a design approach leading up to the development of an escapement mechanism which satisfies the requirements of the movement suppliers as effectively as possible ; this procedure is based on four phases : formulation, synthesis, analysis and evaluation. Analysis is divided into a quantitative part and a qualitative part. While the state of the art essentially centres on calculation of the performance of a particular escapement, this thesis highlights on the one hand a synthesis-based method which systematically presents the different solutions that may be adopted to make a free escapement ; and on the other, the development of qualitative analysis tools enabling a choice of interesting solutions to be made among the numerous variants which emerge from the synthesis. With regard to the state of the art, the main contributions of this thesis are: an in-depth study of the different sources of interference with the precision of a mechanical watch movement, as well as the potential for improvement of the escapement, the definition of a functional specification for free escapements, the notion of the geometrical function condition and a clear demonstration of the importance of analysis of tolerances, a method of quantitative energy analysis for free escapements, a qualitative analysis of energy transfer in an escapement, the latter being demonstrated by two interacting masses moving on an axis ; the relationship between the efficiency of an escapement and its inertia as well as the quality factor of the oscillator is established, a synthesis approach based on the breakdown of functions, enabling original escapements to be proposed, the systematic search for new escapements with tangential pulses, a nomenclature of free escapements, energy and chronometric study of alternative methods for the transfer of energy to the oscillator.

EPFL2007