435 research outputs found

    Modelling & analysis of hybrid dynamic systems using a bond graph approach

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    Hybrid models are those containing continuous and discontinuous behaviour. In constructing dynamic systems models, it is frequently desirable to abstract rapidly changing, highly nonlinear behaviour to a discontinuity. Bond graphs lend themselves to systems modelling by being multi-disciplinary and reflecting the physics of the system. One advantage is that they can produce a mathematical model in a form that simulates quickly and efficiently. Hybrid bond graphs are a logical development which could further improve speed and efficiency. A range of hybrid bond graph forms have been proposed which are suitable for either simulation or further analysis, but not both. None have reached common usage. A Hybrid bond graph method is proposed here which is suitable for simulation as well as providing engineering insight through analysis. This new method features a distinction between structural and parametric switching. The controlled junction is used for the former, and gives rise to dynamic causality. A controlled element is developed for the latter. Dynamic causality is unconstrained so as to aid insight, and a new notation is proposed. The junction structure matrix for the hybrid bond graph features Boolean terms to reflect the controlled junctions in the graph structure. This hybrid JSM is used to generate a mixed-Boolean state equation. When storage elements are in dynamic causality, the resulting system equation is implicit. The focus of this thesis is the exploitation of the model. The implicit form enables application of matrix-rank criteria from control theory, and control properties can be seen in the structure and causal assignment. An impulsive mode may occur when storage elements are in dynamic causality, but otherwise there are no energy losses associated with commutation because this method dictates the way discontinuities are abstracted. The main contribution is therefore a Hybrid Bond Graph which reflects the physics of commutating systems and offers engineering insight through the choice of controlled elements and dynamic causality. It generates a unique, implicit, mixed-Boolean system equation, describing all modes of operation. This form is suitable for both simulation and analysis

    A formal ontology for industrial maintenance

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    International audienceThe rapid advancement of information and communication technologies has resulted in a variety of maintenance support systems and tools covering all sub-domains of maintenance. Most of these systems are based on different models that are sometimes redundant or incoherent and always heterogeneous. This problem has lead to the development of maintenance platforms integrating all of these support systems. The main problem confronted by these integration platforms is to provide semantic interoperability between different applications within the same environment. In this aim, we have developed an ontology for the field of industrial maintenance, adopting the METHONTOLOGY approach to manage the life cycle development of this ontology, that we have called IMAMO (Industrial MAintenance Management Ontology). This ontology can be used not only to ensure semantic interoperability but also to generate new knowledge that supports decision making in the maintenance process. This paper provides and discusses some tests so as to evaluate the ontology and to show how it can ensure semantic interoperability and generate new knowledge within the platform

    Development of Multi-Agent Control Systems using UML/SysML

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    Engineering and Information Technologies Handbook 2011

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    A Bayesian learning approach to inconsistency identification in model-based systems engineering

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    Designing and developing complex engineering systems is a collaborative effort. In Model-Based Systems Engineering (MBSE), this collaboration is supported through the use of formal, computer-interpretable models, allowing stakeholders to address concerns using well-defined modeling languages. However, because concerns cannot be separated completely, implicit relationships and dependencies among the various models describing a system are unavoidable. Given that models are typically co-evolved and only weakly integrated, inconsistencies in the agglomeration of the information and knowledge encoded in the various models are frequently observed. The challenge is to identify such inconsistencies in an automated fashion. In this research, a probabilistic (Bayesian) approach to abductive reasoning about the existence of specific types of inconsistencies and, in the process, semantic overlaps (relationships and dependencies) in sets of heterogeneous models is presented. A prior belief about the manifestation of a particular type of inconsistency is updated with evidence, which is collected by extracting specific features from the models by means of pattern matching. Inference results are then utilized to improve future predictions by means of automated learning. The effectiveness and efficiency of the approach is evaluated through a theoretical complexity analysis of the underlying algorithms, and through application to a case study. Insights gained from the experiments conducted, as well as the results from a comparison to the state-of-the-art have demonstrated that the proposed method is a significant improvement over the status quo of inconsistency identification in MBSE.Ph.D

    Modeling and Simulation in Engineering

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    This book provides an open platform to establish and share knowledge developed by scholars, scientists, and engineers from all over the world, about various applications of the modeling and simulation in the design process of products, in various engineering fields. The book consists of 12 chapters arranged in two sections (3D Modeling and Virtual Prototyping), reflecting the multidimensionality of applications related to modeling and simulation. Some of the most recent modeling and simulation techniques, as well as some of the most accurate and sophisticated software in treating complex systems, are applied. All the original contributions in this book are jointed by the basic principle of a successful modeling and simulation process: as complex as necessary, and as simple as possible. The idea is to manipulate the simplifying assumptions in a way that reduces the complexity of the model (in order to make a real-time simulation), but without altering the precision of the results

    On Falsification of Large-Scale Cyber-Physical Systems

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    In the development of modern Cyber-Physical Systems, Model-Based Testingof the closed-loop system is an approach for finding potential faults andincreasing quality of developed products. Testing is done on many differentabstraction levels, and for large-scale industrial systems, there are severalchallenges. Executing tests on the systems can be time-consuming and largenumbers of complex specifications need to be thoroughly tested, while manyof the popular academic benchmarks do not necessarily reflect on this complexity.This thesis proposes new methods for analyzing and generating test casesas a means for being more certain that proper testing has been performed onthe system under test. For analysis, the proposed approach can automaticallyfind out how much of the physical parts of the system that the test suite hasexecuted.For test case generation, an approach to find errors is optimization-basedfalsification. This thesis attempts to close the gap between academia and industryby applying falsification techniques to real-world models from VolvoCar Corporation and adapting the falsification procedure where it has shortcomingsfor certain classes of systems. Specifically, the main contributionsof this thesis are (i) a method for automatically transforming a signal-basedspecification into a formal specification allowing an optimization-based falsificationapproach, (ii) a new collection of specifications inspired by large-scalespecifications from industry, (iii) an algorithm to perform optimization-basedfalsification for such a large set of specifications, and (iv) a new type of coveragecriterion for Cyber-Physical Systems that can help to assess when testingcan be concluded.The proposed methods have been evaluated for both academic benchmarkexamples and real-world industrial models. One of the main conclusions isthat the proposed additions and changes to the analysis and generation oftests can be useful, given that one has enough information about the systemunder test. The methods presented in this thesis have been applied to realworldmodels in a way that allows for higher-quality products by finding morefaults in early phases of development

    Defining Interactions and Interfaces in Engineering Design

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