Dissertations / Theses on the topic 'Multi-model systems'
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Raimondi, Franco. "Model checking multi-agent systems." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/5627/.
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A multi-agent system (MAS) is usually understood as a system composed of interacting autonomous agents. In this sense, MAS have been employed successfully as a modelling paradigm in a number of scenarios, especially in Computer Science. However, the process of modelling complex and heterogeneous systems is intrinsically prone to errors: for this reason, computer scientists are typically concerned with the issue of verifying that a system actually behaves as it is supposed to, especially when a system is complex. Techniques have been developed to perform this task: testing is the most common technique, but in many circumstances a formal proof of correctness is needed. Techniques for formal verification include theorem proving and model checking. Model checking techniques, in particular, have been successfully employed in the formal verification of distributed systems, including hardware components, communication protocols, security protocols. In contrast to traditional distributed systems, formal verification techniques for MAS are still in their infancy, due to the more complex nature of agents, their autonomy, and the richer language used in the specification of properties. This thesis aims at making a contribution in the formal verification of properties of MAS via model checking. In particular, the following points are addressed: • Theoretical results about model checking methodologies for MAS, obtained by extending traditional methodologies based on Ordered Binary Decision Diagrams (OBDDS) for temporal logics to multi-modal logics for time, knowledge, correct behaviour, and strategies of agents. Complexity results for model checking these logics (and their symbolic representations). • Development of a software tool (MCMAS) that permits the specification and verification of MAS described in the formalism of interpreted systems. • Examples of application of MCMAS to various MAS scenarios (communication, anonymity, games, hardware diagnosability), including experimental results, and comparison with other tools available.
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Gonzalez, Pavel. "Model checking GSM-based multi-agent systems." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/39038.
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Business artifacts are a growing topic in service oriented computing. Artifact systems include both data and process descriptions at interface level thereby providing more sophisticated and powerful service inter-operation capabilities. The Guard-Stage-Milestone (GSM) language provides a novel framework for specifying artifact systems that features declarative descriptions of the intended behaviour without requiring an explicit specification of the control flow. While much of the research is focused on the design, deployment and maintenance of GSM programs, the verification of this formalism has received less attention. This thesis aims to contribute to the topic. We put forward a holistic methodology for the practical verification of GSM-based multi-agent systems via model checking. The formal verification faces several challenges: the declarative nature of GSM programs; the mechanisms for data hiding and access control; and the infinite state spaces inherent in the underlying data. We address them in stages. First, we develop a symbolic representation of GSM programs, which makes them amenable to model checking. We then extend GSM to multi-agent systems and map it into a variant of artifact-centric multi-agent systems (AC-MAS), a paradigm based on interpreted systems. This allows us to reason about the knowledge the agents have about the artifact system. Lastly, we investigate predicate abstraction as a key technique to overcome the difficulty of verifying infinite state spaces. We present a technique that lifts 3-valued abstraction to epistemic logic and makes GSM programs amenable to model checking against specifications written in a quantified version of temporal-epistemic logic. The theory serves as a basis for developing a symbolic model checker that implements SMT-based, 3-valued abstraction for GSM-based multi-agent systems. The feasibility of the implementation is demonstrated by verifying GSM programs for concrete applications from the service community.
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Lu, Gehao. "Neural trust model for multi-agent systems." Thesis, University of Huddersfield, 2011. http://eprints.hud.ac.uk/id/eprint/17817/.
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Introducing trust and reputation into multi-agent systems can significantly improve the quality and efficiency of the systems. The computational trust and reputation also creates an environment of survival of the fittest to help agents recognize and eliminate malevolent agents in the virtual society. The thesis redefines the computational trust and analyzes its features from different aspects. A systematic model called Neural Trust Model for Multi-agent Systems is proposed to support trust learning, trust estimating, reputation generation, and reputation propagation. In this model, the thesis innovates the traditional Self Organizing Map (SOM) and creates a SOM based Trust Learning (STL) algorithm and SOM based Trust Estimation (STE) algorithm. The STL algorithm solves the problem of learning trust from agents' past interactions and the STE solve the problem of estimating the trustworthiness with the help of the previous patterns. The thesis also proposes a multi-agent reputation mechanism for generating and propagating the reputations. The mechanism exploits the patterns learned from STL algorithm and generates the reputation of the specific agent. Three propagation methods are also designed as part of the mechanism to guide path selection of the reputation. For evaluation, the thesis designs and implements a test bed to evaluate the model in a simulated electronic commerce scenario. The proposed model is compared with a traditional arithmetic based trust model and it is also compared to itself in situations where there is no reputation mechanism. The results state that the model can significantly improve the quality and efficacy of the test bed based scenario. Some design considerations and rationale behind the algorithms are also discussed based on the results.
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Russo, Francesco. "Abstraction in model checking multi-agent systems." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9294.
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This thesis presents existential abstraction techniques for multi-agent systems preserving temporal-epistemic specifications. Multi-agent systems, defined in the interpreted system frameworks, are abstracted by collapsing the local states and actions of each agent. The goal of abstraction is to reduce the state space of the system under investigation in order to cope with the state explosion problem that impedes the verification of very large state space systems. Theoretical results show that the resulting abstract system simulates the concrete one. Preservation and correctness theorems are proved in this thesis. These theorems assure that if a temporal-epistemic formula holds on the abstract system, then the formula also holds on the concrete one. These results permit to verify temporal-epistemic formulas in abstract systems instead of the concrete ones, therefore saving time and space in the verification process. In order to test the applicability, usefulness, suitability, power and effectiveness of the abstraction method presented, two different implementations are presented: a tool for data-abstraction and one for variable-abstraction. The first technique achieves a state space reduction by collapsing the values of the domains of the system variables. The second technique performs a reduction on the size of the model by collapsing groups of two or more variables. Therefore, the abstract system has a reduced number of variables. Each new variable in the abstract system takes values belonging to a new domain built automatically by the tool. Both implementations perform abstraction in a fully automatic way. They operate on multi agents models specified in a formal language, called ISPL (Interpreted System Programming Language). This is the input language for MCMAS, a model checker for multi-agent systems. The output is an ISPL file as well (with a reduced state space). This thesis also presents several suitable temporal-epistemic examples to evaluate both techniques. The experiments show good results and point to the attractiveness of the temporal-epistemic abstraction techniques developed in this thesis. In particular, the contributions of the thesis are the following ones: • We produced correctness and preservation theoretical results for existential abstraction. • We introduced two algorithms to perform data-abstraction and variable-abstraction on multi-agent systems. • We developed two software toolkits for automatic abstraction on multi-agent scenarios: one tool performing data-abstraction and the second performing variable-abstraction. • We evaluated the methodologies introduced in this thesis by running experiments on several multi-agent system examples.
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Kwon, Ky-Sang. "Multi-layer syntactical model transformation for model based systems engineering." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42835.
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This dissertation develops a new model transformation approach that supports engineering model integration, which is essential to support contemporary interdisciplinary system design processes. We extend traditional model transformation, which has been primarily used for software engineering, to enable model-based systems engineering (MBSE) so that the model transformation can handle more general engineering models.
We identify two issues that arise when applying the traditional model transformation to general engineering modeling domains. The first is instance data integration: the traditional model transformation theory does not deal with instance data, which is essential for executing engineering models in engineering tools. The second is syntactical inconsistency: various engineering tools represent engineering models in a proprietary syntax. However, the traditional model transformation cannot handle this syntactic diversity.
In order to address these two issues, we propose a new multi-layer syntactical model transformation approach. For the instance integration issue, this approach generates model transformation rules for instance data from the result of a model transformation that is developed for user model integration, which is the normal purpose of traditional model transformation. For the syntactical inconsistency issue, we introduce the concept of the complete meta-model for defining how to represent a model syntactically as well as semantically. Our approach addresses the syntactical inconsistency issue by generating necessary complete meta-models using a special type of model transformation.
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Rajhans, Akshay H. "Multi-Model Heterogeneous Verification of Cyber-Physical Systems." Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/251.
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Complex systems are designed using the model-based design paradigm in which mathematical models of systems are created and checked against specifications. Cyber-physical systems (CPS) are complex systems in which the physical environment is sensed and controlled by computational or cyber elements possibly distributed over communication networks. Various aspects of CPS design such as physical dynamics, software, control, and communication networking must interoperate correctly for correct functioning of the systems. Modeling formalisms, analysis techniques and tools for designing these different aspects have evolved independently, and remain dissimilar and disparate. There is no unifying formalism in which one can model all these aspects equally well. Therefore, model-based design of CPS must make use of a collection of models in several different formalisms and use respective analysis methods and tools together to ensure correct system design. To enable doing this in a formal manner, this thesis develops a framework for multi-model verification of cyber-physical systems based on behavioral semantics.
Heterogeneity arising from the different interacting aspects of CPS design must be addressed in order to enable system-level verification. In current practice, there is no principled approach that deals with this modeling heterogeneity within a formal framework. We develop behavioral semantics to address heterogeneity in a general yet formal manner. Our framework makes no assumptions about the specifics of any particular formalism, therefore it readily supports various formalisms, techniques and tools. Models can be analyzed independently in isolation, supporting separation of concerns. Mappings across heterogeneous semantic domains enable associations between analysis results. Interdependencies across different models and specifications can be formally represented as constraints over parameters and verification can be carried out in a semantically consistent manner. Composition of analysis results is supported both hierarchically across different levels of abstraction and structurally into interacting component models at a given level of abstraction. The theoretical concepts developed in the thesis are illustrated using a case study on the hierarchical heterogeneous verification of an automotive intersection collision avoidance system.
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Koetje, Thabo. "Multi-objectives model predictive control of multivariable systems." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11426.
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Valera, Silvia. "PELDOR in multi-spin systems : from model systems synthesis to biological applications." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/16960.
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Pulsed electron-electron double resonance (PELDOR) is an emerging technique for nanometre distance measurements in nano-sized assemblies and between specific sites of molecules. Most commonly nitroxide radicals are used as probes for EPR distance measurements because they are easy to introduce in biological systems such as soluble and membrane proteins or nucleic acids. PELDOR distance measurements currently rely on data processing software which has been proven to accurately extract inter-spin distances from the dipolar coupling between two paramagnetic centres. However, when the dipolar coupling is affected by contributions from other close-by unpaired electrons inaccuracies as broadening effects and artefacts are introduced in the distance distributions derived. This challenge, commonly referred as multi-spin effects, has been affecting the extraction of accurate distance information from PELDOR measurements in chemical and biological systems with multiple spin labels. The aim of this project is to approach, identify and suppress inaccuracies introduced in PELDOR-based distance distributions by multi-spin effects. This is achieved through the synthesis of multiply labelled model systems which would allow for assessment of the impact of multi-spin effects on distance measurements of simple geometries whose behaviour can be easily predicted and modelled. In this work existing methods for suppression of multi-spin effects are tested, together with their efficiency and limitations. The results are used to devise better sets of parameters including alternative settings for extraction of accurate distances from multi-spin systems and to explore their efficiency and limitations. Additional effects influencing distance measurements by pulsed EPR are also examined; in particular the effects of orientation selection and their interplay with multi-spin effects is studied in depth. Studies on rigid symmetric and asymmetric chemical model systems together with heptameric channel membrane proteins allow for outlining of recommendations for PELDOR distance measurements settings on systems presenting similar structural features, including symmetries and inter-spin distances.
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Sun, Congcong. "Multi-layer model predictive control of complex water systems." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/326739.
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This thesis is devoted to design a multi-layer MPC controller applied to the complex water network taking into account that the different layers with different time scales and control objectives have their own controller. A two-layer temporal hierarchy coordinating scheme has been applied to coordinate the MPC controllers for the supply and transportation layers. An integrated real-time simulation-optimization approach which contributes to consider the effect of more complex dynamics, better represented by the simulation model, has been developed for regional water networks. The use of the combined approach of optimization and simulation coordination between simulator and optimizer allows to test the proposed multi-layer MPC in a feedback scheme using a realistic simulator of the regional network.
The second part of this thesis is focused on the design of a control scheme which uses the combination of linear MPC with a constraint satisfaction problem (CSP) to optimize the non-linear operational control of DWNs. The network aggregation method (NAM) is used to simplify a complex water network into an equivalent conceptual one for the bidirectional network before the use of CSP. The proposed approach is simulated using Epanet to represent the real DWN. Non-linear MPC is used for validation using a generic operational tool for controlling water networks named PLIO. A two-layer scheduling scheme for pump stations in a water distribution network has also been designed in the second part of this thesis. The tuning parameters of such algorithm are the lower layer control sampling period and the number of parallel pumps in the pump station.Aquesta tesi està dedicada a dissenyar un controlador MPC multicapa que s'aplica a una complexa xarxa regional emprant com a principal idea el fet de què les diferents capes treballen amb diferents escales de temps i objectius de control s'aconseguiran amb el seu propi controlador. Un esquema jeràrquic de coordinació temporal de dues capes s'ha aplicat per a coordinar als controladors MPC per a les xarxes de captació i transport. Un enfocament integrat de simulació-optimizació que contribueix a asegurar que l'efecte de les dinàmiques complexes, millor representades pel model de simulació s'hagin tingut en compte, s'ha propostat per la gestió operacional temps real de les xarxes regionals. La segona part d'aquesta tesi es centra en el disseny d'un esquema de control que utilitza la combinació del control MPC lineal amb una problema de satisfacció de restriccions (CSP) per optimitzar el control operacional no-lineal de les xarxes d'aigua potable. El mètode d'agregació de xarxes (NAM) s'utilitza per simplificar una xarxa d'aigua complexa en una xarxa conceptual bidireccional equivalent abans d'utilitzar el CSP. L'enfocament proposat es simula utilitzant Epanet per representar el comportament hidràulic de la xarxa d'aigua potable. Finalment, el MPC no lineal s'utilitza per a la validació fent ús de l'eina PLIO per a la seva implementació. I també, un esquema de planificació de dues capes per a estacions de bombament en una aigua xarxa de distribució ha estat proposat en la segona part d'aquesta tesi. Els paràmetres d'ajust d'aquest algorisme són el período de mostreig de control de la capa inferior i el número de bombes en paral·lel en la estació de bombament.
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Jennings, Joel Nicholas. "A new computational model for multi-cellular biological systems." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245334.
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The early development of an animal results from a highly complex sequence of interactions within and between cells to transform a fertilised egg into a functional embryo. A major challenge in the field of morphogenesis is explaining how coordinated cell shape change, growth and movement create the structures that we are familiar with, and what drives the processes that pattern and control this behaviour. Embryos are complicated mechanical systems for which we have a wealth of morphological data about the shapes and movements of cells but it is diffcult to understand how these movements emerge as a result of force-generating mechanisms within the embryo. A new, force-based modelling technique designed to test hypotheses about dynamic processes within an embryo is presented. The model focusses on how the mechanical properties of a cell and inter-cellular forces affect the movements we see within a tissue. It is designed to probe the relationships between cellular and tissue behaviours; such as how forces propagate through a system or the response of a tissue to applied forces. The novel features of the model are discussed along with analysis of tissue and cellular behaviours for different idealised systems, describing how the parameters of the model affect experimental observables. The model is applied to two real world systems. Firstly examining the role of boundary conditions on the patterning seen in the formation of the zebrafish forebrain neural plate. Secondly, two proposed hypotheses for the formation of the primitive streak in the chick embryo are investigated and compared. These applications demonstrate how the model can be used to complement experimental studies and help to tease out the mechanical processes driving morphogenesis.
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McDonald, Mercedes Terre. "OCR: A STATISTICAL MODEL OF MULTI-ENGINE OCR SYSTEMS." Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4459.
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This thesis is a benchmark performed on three commercial Optical Character Recognition (OCR) engines. The purpose of this benchmark is to characterize the performance of the OCR engines with emphasis on the correlation of errors between each engine. The benchmarks are performed for the evaluation of the effect of a multi-OCR system employing a voting scheme to increase overall recognition accuracy. This is desirable since currently OCR systems are still unable to recognize characters with 100% accuracy. The existing error rates of OCR engines pose a major problem for applications where a single error can possibly effect significant outcomes, such as in legal applications. The results obtained from this benchmark are the primary determining factor in the decision of implementing a voting scheme. The experiment performed displayed a very high accuracy rate for each of these commercial OCR engines. The average accuracy rate found for each engine was near 99.5% based on a less than 6,000 word document. While these error rates are very low, the goal is 100% accuracy in legal applications. Based on the work in this thesis, it has been determined that a simple voting scheme will help to improve the accuracy rate.M.S.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical and Computer Engineering
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Howell, Deborah Jane 1979. "Multi-configuration model tuning for precision opto-mechanical systems." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16659.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004.Includes bibliographical references (p. 141-146).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
It is important for the design of future space-based observatories that simulation models physically represent the designed system and are able to track along configuration changes. This thesis outlines a three-step procedure for model tuning of complex opto-mechanical systems in the presence of measured experimental data. It is the hypothesis of this thesis that this procedure will produce a model that effectively tracks along configuration changes. The first step, engineering insight, applies model heuristics to the simulation model in an effort to produce a simulation model that includes all physical effects in the experiment. The next step, model updating, is an automated procedure whereby an optimization problem is formed in order to set uncertain model parameters. The final step is model tracking across configurations. Configuration changes include, but are not limited to, changes in mass, input/output locations, changes in geometric properties and relative placements. A new metric is provided which helps to gauge the level of experimental/model mismatch in the new configuration (using the updated model) by using the objective function from the optimization in Step 2. Using this metric, one can determine how the model changes with respect to specific configuration changes. Finally, this three-step tuning procedure is compared against traditional model tuning on a testbed at the MIT Space Systems Lab (SSL) in order to gauge its usefulness. The traditional model tuning will be performed by a colleague in the SSL who will use such methods as trial-and-error parameter updating to match the simulation model to the experimental data.
(cont.) Using the multi-configuration metric presented in this thesis, it is shown that the model produced using the three step method does track configurations better than the model produced using traditional model tuning.
by Deborah Jane Howell.
S.M.
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Titman, Andrew Charles. "Model diagnostics in multi-state models of biological systems." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612189.
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Jones, Andrew Vaughan. "Model checking and compositional reasoning for multi-agent systems." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/32695.
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Multi-agent systems are distributed systems containing interacting autonomous agents designed to achieve shared and private goals. For safety-critical systems where we wish to replace a human role with an autonomous entity, we need to make assurances about the correctness of the autonomous delegate. Specialised techniques have been proposed recently for the verification of agents against mentalistic logics. Problematically, these approaches treat the system in a monolithic way. When verifying a property against a single agent, the approaches examine all behaviours of every component in the system. This is both inefficient and can lead to intractability: the so-called state-space explosion problem. In this thesis, we consider techniques to support the verification of agents in isolation. We avoid the state-space explosion problem by verifying an individual agent in the context of a specification of the rest of the system, rather than the system itself. We show that it is possible to verify an agent against its desired properties without needing to consider the behaviours of the remaining components. We first introduce a novel approach for verifying a system as a whole against specifications expressed in a logic of time and knowledge. The technique, based on automata over trees, supports an efficient procedure to verify systems in an automata-theoretic way using language containment. We show how the automata-theoretic approach can be used as an underpinning for assume-guarantee reasoning for multi-agent systems. We use a temporal logic of actions to specify the expected behaviour of the other components in the system. When performing modular verification, this specification is used to exclude behaviours that are inconsistent with the concrete system. We implement both approaches within the open-source model checker MCMAS and show that, for the relevant properties, the assume-guarantee approach can significantly increase the tractability of individual agent verification.
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Archila, Daniel. "Development and evaluation of a multi-objective optimization model for multi-reservoir systems." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/51894.
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The BC Hydro and Power Authority is the largest electric utility in the province of British Columbia, Canada. With a generating capacity of more than 12,000 MW, it serves almost 2 million customers in the province. It operates 31 hydroelectric facilities, most of them located in multi-reservoir systems. In order to facilitate the operation of these reservoirs, BC Hydro developed an in-house application called the Operations Planning Tool (OPT), a deterministic Linear Programming (LP) model that provides the optimal operation of the multi-reservoir systems considering multiple purposes. The objective of this research was to investigate, develop, incorporate and test additional modeling features that would expand the current capabilities of the OPT. This included developing a formulation for the analysis of units’ maintenance outages and changing the optimization model to consider inflow uncertainty and avoid the use of weight coefficients and penalty functions. The formulation developed for the analysis of units’ maintenance outages is based on a two-stage algorithm. In the first stage, a pre-processor defines all the possible outage solutions given some initial configurations. In the second stage, a modified OPT model is run to find an outage solution that optimizes the objectives using a Mixed-Integer Linear Programming (MILP) algorithm. The formulation was tested using the Bridge River system in British Columbia, Canada. An alternative OPT model was also developed to consider the uncertainty in the reservoir’s inflow and modify the formulation of the objective function. It was desired to avoid the use of weight coefficients and penalty functions due to the limitations that they present. The proposed alternative was based on the development of a linear decision rule and the use of chance constraints. The linear decision rule is an operating rule that defines the spillway releases and forebay elevation as a linear function of the inflow, the turbine releases and a deterministic decision variable. The chance constraints were used to consider the probability of the spillway releases and forebay elevation not being within a preferred range of values established by the user. The developed formulation was tested using the Stave Falls system.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Hashimoto, Kazumune. "Distributed Aperiodic Model Predictive Control for perturbed multi-agent systems." Thesis, KTH, Reglerteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-138441.
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In this master thesis we propose an aperiodic formulation of Model Predictive Control for distributed agents with additive bounded disturbances. In this control method, each agent solves an optimal control problem only when certain control performances are not guaranteed according to several triggering rules. This may lead not only to the dramatic reduction of energy expenditures but also to the alleviation of communication loads among them. The problem will be considered to be general and practical; it handles the non-linearity of the each agent which is perturbed by additive bounded disturbances, where the triggering rule is derived from several robust stability criterion. The triggering rule will be addressed for event-based control and self-triggered control, which are the two main different aperiodic control approaches. Finally some simulation results verify our proposal.
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Droge, Greg Nathanael. "Behavior-based model predictive control for networked multi-agent systems." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51864.
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We present a motion control framework which allows a group of robots to work together to decide upon their motions by minimizing a collective cost without any central computing component or any one agent performing a large portion of the computation. When developing distributed control algorithms, care must be taken to respect the limited computational capacity of each agent as well as respect the information and communication constraints of the network. To address these issues, we develop a distributed, behavior-based model predictive control (MPC) framework which alleviates the computational difficulties present in many distributed MPC frameworks, while respecting the communication and information constraints of the network. In developing the multi-agent control framework, we make three contributions. First, we develop a distributed optimization technique which respects the dynamic communication restraints of the network, converges to a collective minimum of the cost, and has transients suitable for robot motion control. Second, we develop a behavior-based MPC framework to control the motion of a single-agent and apply the framework to robot navigation. The third contribution is to combine the concepts of distributed optimization and behavior-based MPC to develop the mentioned multi-agent behavior-based MPC algorithm suitable for multi-robot motion control.
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Mian, Zhibao. "Model transformation for multi-objective architecture optimisation for dependable systems." Thesis, University of Hull, 2014. http://hydra.hull.ac.uk/resources/hull:10519.
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Model-based engineering (MBE) promises a number of advantages for the development of embedded systems. Model-based engineering depends on a common model of the system, which is refined as the system is developed. The use of a common model promises a consistent and systematic analysis of dependability, correctness, timing and performance properties. These benefits are potentially available early and throughout the development life cycle. An important part of model-based engineering is the use of analysis and design languages. The Architecture Analysis and Design Language (AADL) is a new modelling language which is increasingly being used for high dependability embedded systems development. AADL is ideally suited to model-based engineering but the use of new language threatens to isolate existing tools which use different languages. This is a particular problem when these tools provide an important development or analysis function, for example system optimisation. System designers seek an optimal trade-off between high dependability and low cost. For large systems, the design space of alternatives with respect to both dependability and cost is enormous and too large to investigate manually. For this reason automation is required to produce optimal or near optimal designs. There is, however, a lack of analysis techniques and tools that can perform a dependability analysis and optimisation of AADL models. Some analysis tools are available in the literature but they are not able to accept AADL models since they use a different modelling language. A cost effective way of adding system dependability analysis and optimisation to models expressed in AADL is to exploit the capabilities of existing tools. Model transformation is a useful technique to maximise the utility of model-based engineering approaches because it provides a route for the exploitation of mature and tested tools in a new model-based engineering context. By using model transformation techniques, one can automatically translate between AADL models and other models. The advantage of this model transformation approach is that it opens a path by which AADL models may exploit existing non-AADL tools. There is little published work which gives a comprehensive description of a method for transforming AADL models. Although transformations from AADL into other models have been reported only one comprehensive description has been published, a transformation of AADL to petri net models. There is a lack of detailed guidance for the transformation of AADL models. This thesis investigates the transformation of AADL models into the HiP-HOPS modelling language, in order to provide dependability analysis and optimisation. HiP-HOPS is a mature, state of the art, dependability analysis and optimisation tool but it has its own model. A model transformation is defined from the AADL model to the HiP-HOPS model. In addition to the model-to-model transformation, it is necessary to extend the AADL modelling attributes. For cost and dependability optimisation, a new AADL property set is developed for modelling component and system variability. This solves the problem of describing, within an AADL model, the design space of alternative designs. The transformation (with transformation rules written in ATLAS Transformation Language (ATL)) has been implemented as a plug-in for the AADL model development tool OSATE (Open-source AADL Tool Environment). To illustrate the method, the plug-in is used to transform some AADL model case-studies.
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Freitas, Artur Luiz Silva da Cunha. "Model-driven engineering of multi-agent systems based on ontology." Pontifícia Universidade Católica do Rio Grande do Sul, 2017. http://hdl.handle.net/10923/11737.
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Previous issue date: 2017Model-driven engineering provides abstractions and notations for improving the understanding and for supporting the modelling, coding, and verification of applications for specific domains. Ontologies, on the other hand, provide formal and explicit definitions of shared conceptualisations and enable the use of semantic reasoning. Although these areas have been developed by different communities, important synergies can be achieved when both are combined. These advantages can be explored in the development of multi-agent systems, given their complexity and the need for integrating several components that are often addressed from different angles. This work investigates how to apply ontologies for agentoriented software engineering. Initially, we present a new modelling approach where multiagent systems are designed using the proposed OntoMAS ontology. Then, we describe techniques, implemented in a tool, to help programmers bring their concepts into code and also generate code automatically from instantiated ontology models. Several advantages can be obtained from these new approaches to model and code multi-agent systems, such as semantic reasoning to carry out inferences and verification mechanisms. But the main advantage is the unified high (knowledge) level specification language that allows modelling the three dimensions that are united in the JaCaMo framework so that systems specifications can be better communicated across developing teams. The evaluations of these proposals indicate that they contribute with the different aspects of agent-oriented software engineering, such as the specification, verification, and programming of these systems.
A engenharia orientada a modelos fornece abstrações e notações para melhorar a compreensão e para apoiar a modelagem, codificação e verificação de aplicações em domínios específicos. As ontologias, por outro lado, fornecem definições formais e explícitas de conceitualizações compartilhadas e permitem o uso de raciocínio semântico. Embora essas áreas tenham sido desenvolvidas por diferentes comunidades, sinergias importantes podem ser alcançadas quando ambas são combinadas. Essas vantagens podem ser exploradas no desenvolvimento de sistemas multiagentes, dada a sua complexidade e a necessidade de integrar vários componentes que são frequentemente abordados de diferentes ângulos. Este trabalho investiga como aplicar ontologias para engenharia de software orientada a agentes. Inicialmente, apresentamos uma nova abordagem de modelagem onde os sistemas multiagentes são projetados usando a ontologia OntoMAS proposta. Então, descrevemos técnicas, implementadas em uma ferramenta, para ajudar os programadores a trazer seus conceitos em código e também gerar código automaticamente a partir de modelos instanciados da ontologia. Várias vantagens podem ser obtidas a partir dessas novas abordagens para modelar e codificar sistemas multiagentes, como o raciocínio semântico para realizar inferências e mecanismos de verificação. Mas a principal vantagem é a linguagem de especificação unificada de alto nível (conhecimento) que permite modelar as três dimensões que estão unidas em JaCaMo para que as especificações dos sistemas possam ser melhor comunicadas entre equipes em desenvolvimento. As avaliações dessas propostas indicam que elas contribuem com os diferentes aspectos da engenharia de software orientada a agentes, como a especificação, verificação e programação desses sistemas.
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Jansson, Jens, Alexandar Vukosavljevic, and Ismet Catovic. "Performance comparison between multi-model, key-value and documental NoSQL database management systems." Thesis, Högskolan i Skövde, Institutionen för informationsteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-19857.
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This study conducted an experiment that compares the multi-model NoSQL DBMS ArangoDB with other NoSQL DBMS, in terms of the average response time of queries. The DBMS compared in this experiment are the following: Redis, MongoDB, Couchbase, and OrientDB. The hypothesis that is answered in this study is the following: “There is a significant difference between ArangoDB, OrientDB, Couchbase, Redis, MongoDB in terms of the average response time of queries”. This is examined by comparing the average response time of 1 000, 100 000, and 1 000 000 queries between these database systems. The results show that ArangoDB performs worse compared to the other DBMS. Examples of future work include using additional DBMS in the same experiment and replacing ArangoDB with another multi-model DBMS to decide whether such a DBMS, in general, performs worse than single-model DBMS.
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Zhou, Di. "A model driven architecture based approach for developing multi-agent systems." Thesis, University of Canterbury. Computer Science and Software Engineering, 2008. http://hdl.handle.net/10092/2104.
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The research described in this thesis is an attempt to utilize the Model Driven Architecture for semi-automatically developing a prototype Multi-Agent System to support the management of a real container terminal. Agent technology has been increasingly applied in Transport Logistics and seems to be a viable solution to support the container terminal management. Thus, from the user point of view, the focus of this research is to investigate the applicability of Multi-Agent Systems to assist the container terminal's decision makers in improving the container terminal productivity, which is often measured in terms of the productivity of cranes. A prototype Multi-Agent System has been developed to evaluate and compare a set of proposed vehicle dispatching strategies, which are a collection of rules that a vehicle (e.g. straddle carrier) uses to decide the priority of serving the working cranes. Employing an appropriate dispatching strategy may greatly improve the efficiency of vehicle allocation to the working cranes, so as to increase the utilization of cranes which directly enhance the container terminal productivity. In order to investigate the applicability of the Multi-Agent System for supporting the container terminal management, experiments have been conducted in a variety of real-world scenarios. The experiment results have revealed that Multi-Agent Systems are applicable to assist container terminal decision makers in evaluating operating strategies. On the other hand, from the developer point of view, the author investigates how to apply the Model Driven Architecture to agent technologies, providing a partially automated support for the derivation of Multi-Agent System implementation from the agent-oriented design, independently from the target implementation platforms. The Model Driven Architecture approach studied in this research is a model-driven software development process that explicitly separates models at three different levels of abstraction: platform independent models, platform specific models, and implementation models. In contrast to the conventional code-centric software development, the Model Driven Architecture based software development uses models as the primary engineering artifacts. The adopted development approach is to take a high-level abstraction model of a system and transform it into a set of platform specific models, each of which is in turn transformed into the corresponding implementation. Transformations between models are automatically carried out by a set of transformation tools. The experience of using the Model Driven Architecture for the development of the prototype Multi-Agent System has revealed the following benefits: (a) automated transformations between models increase software productivity; (b) separating the high-level specification of the system from the underlying implementation technology improves the portability of the system's high-level abstraction model; (c) strong separation of concerns, guaranteed consistency between models, and automatic generation of source code minimize future software maintenance effort.
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Xu, Hao. "A semi-partitioned model for scheduling mixed criticality multi-core systems." Thesis, University of York, 2017. http://etheses.whiterose.ac.uk/18709/.
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Many Mixed Criticality scheduling algorithms have been developed with an assumption that lower criticality level tasks may be abandoned to guarantee the schedulability of higher criticality tasks when the criticality level of the system changes. But it is valuable to explore means by which all of the tasks remain schedulable throughout criticality level changes. This thesis introduces a semi-partitioned model which allows all of the tasks to remain schedulable if only a bounded number of cores increase their criticality levels. In such a model, some lower criticality tasks are allowed to migrate instead of being abandoned. Different possible semi-partitioned approaches are proposed and analysed in this thesis. It is concluded from the experiments results that the semi-partitioned algorithm provides improved schedulability and performance of multi-core mixed criticality systems while enables all tasks to keep executing in the majority of scenarios.
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Rivotti, Pedro. "Multi-parametric programming and explicit model predictive control of hybrid systems." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24432.
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This thesis is concerned with different topics in multi-parametric programming and explicit model predictive control, with particular emphasis on hybrid systems. The main goal is to extend the applicability of these concepts to a wider range of problems of practical interest, and to propose algorithmic solutions to challenging problems such as constrained dynamic programming of hybrid linear systems and nonlinear explicit model predictive control. The concepts of multi-parametric programming and explicit model predictive control are presented in detail, and it is shown how the solution to explicit model predictive control may be efficiently computed using a combination of multi-parametric programming and dynamic programming. A novel algorithm for constrained dynamic programming of mixed-integer linear problems is proposed and illustrated with a numerical example that arises in the context of inventory scheduling. Based on the developments on constrained dynamic programming of mixed-integer linear problems, an algorithm for explicit model predictive control of hybrid systems with linear cost function is presented. This method is further extended to the design of robust explicit controllers for hybrid linear systems for the case when uncertainty is present in the model. The final part of the thesis is concerned with developments in nonlinear explicit model predictive control. By using suitable model reduction techniques, the model captures the essential nonlinear dynamics of the system, while the achieved reduction in dimensionality allows the use of nonlinear multi-parametric programming methods.
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Choi, J. "Model checking for decision making behaviour of heterogeneous multi-agent autonomous system." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8031.
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An autonomous system has been widely applied for various civil/military research because of its versatile capability of understanding high-level intent and direction of a surrounding environment and targets of interest. However, as autonomous systems can be out of control to cause serious loss, injury, or death in the worst case, the verification of their functionalities has got increasing attention. For that reason, this study is focused on the verification of a heterogeneous multi-agent autonomous system. The thesis first presents an overview of formal methods, especially focuses on model checking for autonomous systems verification. Then, six case studies are presented to verify the decision making behaviours of multi-agent system using two basic scenarios: surveillance and convoy. The initial system considered in the surveillance mission consists of a ground control system and a micro aerial vehicle. Their decision-making behaviours are represented by means of Kripke model and computational tree logic is used to specify the properties of this system. For automatic verification, MCMAS (Model Checker for Multi-Agent Systems) is adopted due to its novel capability to accommodate the multi-agent system. After that, the initial system is extended to include a substitute micro aerial vehicle. These initial case studies are then further extended based on SEAS DTC exemplar 2 dealing with behaviours of convoy protection. This case study includes now a ground control system, an unmanned aerial vehicle, and an unmanned ground vehicle. The MCMAS successfully verifies the targeting behaviours of the team-level unmanned systems. Reversely, these verification results help retrospectively improve the design of decision-making algorithms by considering additional agents and behaviours during four steps of scenario modification. Consequently, the last scenario deals with the system composed of a ground control system, two unmanned aerial vehicles, and four unmanned ground vehicles with fault-tolerant and communications relay capabilities. In conclusion, this study demonstrates the feasibility of model checking algorithms as a verification tool of a multi-agent system in an initial design stage. Moreover, this research can be an important first step of the certification of multi-agent autonomous systems for the domains of robotics, aerospace and aeronautics.
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Shaw, David. "Development of a model for smart card based access control in multi-user, multi-resource, multi-level access systems." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 1999. https://ro.ecu.edu.au/theses/1229.
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The primary focus of this research is an examination of the issues involved in the granting of access in an environment characterised by multiple users, multiple resources and multiple levels of access permission. Increasing levels of complexity in automotive systems provides opportunities for improving the integration and efficiency of the services provided to the operator. The vehicle lease / hire environment provided a basis for evaluating conditional access to distributed, mobile assets where the principal medium for operating in this environment is the Smart Card. The application of Smart Cards to existing vehicle management systems requires control of access to motor vehicles, control of vehicle operating parameters and secure storage of operating information. The issues addressed include examination of the characteristics of the operating environment, development of a model and design, simulation and evaluation of a multiple application Smart Card. The functions provided by the card include identification and authentication, secure hash and encryption functions which may be applied, in general, to a wide range of access problems. Evaluation of the algorithms implemented indicate that the Smart Card design may be provably secure under single use conditions and conditionally secure under multiple use conditions. The simulation of the card design provided data to support further research and shows the design is practical and able to be implemented on current Smart Card types.
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Yang, Ang Information Technology & Electrical Engineering Australian Defence Force Academy UNSW. "A networked multi-agent combat model : emergence explained." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Information Technology and Electrical Engineering, 2007. http://handle.unsw.edu.au/1959.4/38823.
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Simulation has been used to model combat for a long time. Recently, it has been accepted that combat is a complex adaptive system (CAS). Multi-agent systems (MAS) are also considered as a powerful modelling and development environment to simulate combat. Agent-based distillations (ABD) - proposed by the US Marine Corp - are a type of MAS used mainly by the military for exploring large scenario spaces. ABDs that facilitated the analysis and understanding of combat include: ISAAC, EINSTein, MANA, CROCADILE and BactoWars. With new concepts such as networked forces, previous ABDs can implicitly simulate a networked force. However, the architectures of these systems limit the potential advantages gained from the use of networks. In this thesis, a novel network centric multi-agent architecture (NCMAA) is pro-posed, based purely on network theory and CAS. In NCMAA, each relationship and interaction is modelled as a network, with the entities or agents as the nodes. NCMAA offers the following advantages: 1. An explicit model of interactions/relationships: it facilitates the analysis of the role of interactions/relationships in simulations; 2. A mechanism to capture the interaction or influence between networks; 3. A formal real-time reasoning framework at the network level in ABDs: it interprets the emergent behaviours online. For a long time, it has been believed that it is hard in CAS to reason about emerging phenomena. In this thesis, I show that despite being almost impossible to reason about the behaviour of the system by looking at the components alone because of high nonlinearity, it is possible to reason about emerging phenomena by looking at the network level. This is undertaken through analysing network dynamics, where I provide an English-like reasoning log to explain the simulation. Two implementations of a new land-combat system called the Warfare Intelligent System for Dynamic Optimization of Missions (WISDOM) are presented. WISDOM-I is built based on the same principles as those in existing ABDs while WISDOM-II is built based on NCMAA. The unique features of WISDOM-II include: 1. A real-time network analysis toolbox: it captures patterns while interaction is evolving during the simulation; 2. Flexible C3 (command, control and communication) models; I 3. Integration of tactics with strategies: the tactical decisions are guided by the strategic planning; 4. A model of recovery: it allows users to study the role of recovery capability and resources; 5. Real-time visualization of all possible information: it allows users to intervene during the simulation to steer it differently in human-in-the-loop simulations. A comparison between the fitness landscapes of WISDOM-I and II reveals similarities and differences, which emphasise the importance and role of the networked architecture and the addition of strategic planning. Lastly but not least, WISDOM-II is used in an experiment with two setups, with and without strategic planning in different urban terrains. When the strategic planning was removed, conclusions were similar to traditional ABDs but were very different when the system ran with strategic planning. As such, I show that results obtained from traditional ABDs - where rational group planning is not considered - can be misleading. Finally, the thesis tests and demonstrates the role of communication in urban ter-rains. As future warfighting concepts tend to focus on asymmetric warfare in urban environments, it was vital to test the role of networked forces in these environments. I demonstrate that there is a phase transition in a number of situations where highly dense urban terrains may lead to similar outcomes as open terrains, while medium to light dense urban terrains have different dynamics
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Cordeiro, Lucas. "SMT-based bounded model checking of multi-threaded software in embedded systems." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/186011/.
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Our reliance on the correct functioning of embedded systems is growing rapidly. Such systems are used in a wide range of applications such as airbag control systems, mobile phones, and high-end television sets. These systems are becoming more and more complex and require multi-core processors with scalable shared memory to meet the increasing computational power demands. The reliability of the embedded (distributed) software is thus a key issue in the system development. In this thesis we describe and evaluate an approach to reason accurately and effectively about large embedded software using bounded model checking (BMC) based on Satisfiability Modulo Theories (SMT) techniques. We present three major novel contributions. First, we extend the encodings from previous SMT-based bounded model checkers to provide more accurate support for variables of finite bit width, bit-vector operations, arrays, structures, unions and pointers and thus making our approach suitable to reason about embedded software. We then provide new encodings into existing SMT theories and we show that our translations from ANSI-C programs to SMT formulas are as precise as bit-accurate procedures based on Boolean Satisfiability. Second, we develop three related approaches for model checking multi-threaded software in embedded systems. In the lazy approach, we generate all possible interleavings and call the SMT solver on each of them individually, until we either find a bug, or have systematically explored all interleavings. In the schedule recording approach, we encode all possible interleavings into one single formula and then exploit the high speed of the SMT solvers. In the underapproximation and widening approach, we reduce the state space by abstracting the number of interleavings from the proofs of unsatisfiability generated by the SMT solvers. Finally, we describe and evaluate an approach to integrate our SMT-based BMC into the software engineering process by making the verification process incremental. In particular, our approach looks at the modifications suffered by the software system since its last verification, and submits them to a partly static and dynamic verification process, which is thus guided by a set of test cases for coverage. Experiments show that our SMT-based BMC can analyze larger problems and reduce the verification time compared to state-of-the-art techniques that use BMC, iterative context-bounding or counterexample-guided abstraction refinement
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Chevet, Thomas. "Robust model predictive control for deployment and reconfiguration of multi-agent systems." Electronic Thesis or Diss., université Paris-Saclay, 2020. http://www.theses.fr/2020UPASG007.
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Cette thèse porte sur le développement de techniques de commande prédictive pour le déploiement et la reconfiguration d'un système multi-agents dans une zone convexe et bornée en deux dimensions. Un nouvel algorithme de commande prédictive décentralisé, fondé sur une partition de Voronoï de l'espace pour le déploiement d'une flotte de drones quadrirotor, est construit. La loi de commande prédictive décentralisée est d'abord rendue plus robuste pour supporter des perturbations déterministes bornées s'appliquant sur les agents, introduisant une nouvelle partition de Voronoï garantie fondée sur des boîtes pour assurer la sécurité du déploiement. Dans ce cas, un nouveau correcteur prédictif fondé sur des tubes avec observateur est conçu en résolvant des problèmes d'optimisation sous contraintes d'inégalités matricielles linéaires/bilinéaires. Ensuite, pour supporter des perturbations stochastiques non bornées, un nouvel algorithme de commande prédictive sous contraintes probabilistes est proposé, rendu résoluble par la transformation des contraintes probabilistes apparaissant dans le problème d'optimisation en contraintes algébriques. Enfin, une stratégie de reconfiguration fondée sur un correcteur prédictif décentralisé est conçue pour permettre à des agents de rejoindre ou de quitter le système multi-agents durant son déploiement. Des résultats de simulation sur une flotte de drones quadrirotor valident l'efficacité des stratégies de commande proposéesThis thesis presents Model Predictive Control (MPC) techniques for the deployment and the reconfiguration of a dynamical Multi-Agent System (MAS) in a bounded convex two-dimensional area. A novel decentralized predictive control law for the Voronoi-based deployment of a fleet of quadrotor Unmanned Aerial Vehicles (UAVs) is derived. The proposed decentralized MPC is firstly robustified to deal with bounded deterministic perturbations acting on the agents, introducing a new box-based guaranteed Voronoi tessellation to ensure a safe deployment. In this case, a new output-feedback tube-based MPC is designed by solving constrained optimization procedures relying on linear/bilinear matrix inequalities. Secondly, to deal with unbounded stochastic perturbations, a new output-feedback chance-constrained MPC algorithm is proposed, solved by mean of a relaxation of the considered probabilistic constraints into algebraic constraints. Finally, a decentralized MPC-based reconfiguration strategy is designed to deal with the case of agents joining or leaving the multi-agent system during the deployment. Illustrative simulation results on a fleet of quadrotor UAVs validate the effectiveness of the proposed control strategies
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Tinsley, Carl Terrie III. "Modeling of Multi-Pulse Transformer/Rectifier Units in Power Distribution Systems." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/34655.
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Multi-pulse transformer/rectifier systems are becoming increasingly popular in power distribution systems. These topologies can be found in aircraft power systems, motor drives, and other applications that require low total harmonic distortion (THD) of the input line current. This increase in the use of multi-pulse transformer topologies has led to the need to study large systems composed of said units and their interactions within the system. There is also an interest in developing small-signal models so that stability issues can be studied.
This thesis presents a procedure for the average model of multi-pulse transformer/rectifier topologies. The dq rotating reference frame was used to develop the average model and parameter estimation is incorporated through the use of polynomial fits. The average model is composed of nonlinear dependent sources and linear passive components. A direct benefit from this approach is a reduction in simulation time by two orders of magnitude. The average model concept demonstrates that it accurately predicts the dynamics of the system being studied. In particular, two specific topologies are studied, the 12-pulse hexagon transformer/rectifier (hex t/r) and the 18-pulse autotransformer rectifier unit (ATRU). In both cases, detailed switching model results are used to verify the operation of the average model. In the case of the hex t/r, the average model is further validated with experimental data from an 11 kVA prototype. The hex t/r output impedance, obtained from the linearized average model, has also been verified experimentally.Master of Science
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Jobe, Jonathan Michael. "Multi-aspect component models enabling the reuse of engineering analysis models in SysML /." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24810.
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Hodge, Philip J. (Philip James), and Joshua D. Lemaitre. "A multi-echelon supply chain model for strategic inventory assessment through the deployment of kanbans." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45228.
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Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.Includes bibliographical references (leaves 100-102).
As global competition in the manufacturing space grows, so do corporations' needs for sophisticated and optimized management systems to enable continuous flows of information and materials across the many tiers within their supply chains. With the complexities introduced by the variability in the demand for finished goods as well as by the variability in lead-time of transportation, procurement, production and administrative activities, corporations have turned to quantitative modeling of their supply chains to address these issues. Based on the data of a heavy machinery manufacturer headquartered in the US, this research introduces a robust model for the deployment of strategic inventory buffers across a multi-echelon manufacturing system. Specifically, this study establishes a replenishment policy for inventory using a multiple bin, or Kanban, system for each part number in the assembly of products from our sponsors tractor line. We employ a numerical simulation to evaluate and optimize the various inventory deployment scenarios. Utilizing several thousand runs of the simulation, we derive a generalized treatment for each part number based on an econometric function of the parameters associated with lead-time, order frequency, inventory value and order costing. The pilot for the simulation focuses on the parts data for three earthmoving products across eight echelons, but scales to n products across m echelons. Our results show that this approach predicted the optimal quantities of Kanbans for 95% of parts to a level of accuracy +/- 3 bins.
by Philip J. Hodge and Joshua D. Lemaitre.
M.Eng.in Logistics
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Pimenta, Paulo. "Application of model-driven engineering to multi-agent systems : a language to model behaviors of reactive agents." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS031/document.
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Des nombreux utilisateurs des systèmes multi-agents (SMA) sont très souvent découragés de modéliser et simuler dans les plates-formes actuelles SMA. Plus précisément, modéliser la dynamique d'un système (en particulier les comportements de l'agent) est très souvent vu comme un défi pour les utilisateurs de SMA. Dans le domaine des systèmes socio-écologiques (SES), cet inconvénient est plus souvent observé une fois que les experts de domaine en SES sont rarement des programmeurs. De plus, la majorité des plateformes SMA n'a pas été conçue en prenant en considérant le fait que les experts de domaines ne sont pas des programmeurs. On constate que la majeure partie des outils MAS ne sont pas dédiés à SES, ou qu'ils ne possèdent pas un formalisme compréhensible pour représenter les comportements de SMA. En outre, comme ces outils sont dépendant des plateformes, un modèle réalisé dans une plateforme SMA ne peut pas être correctement utilisé dans une autre plate-forme en raison de l'incompatibilité entre ces plateformes SMA. Afin de surpasser ces limitations, nous proposons un langage dédié au domaine SES pour décrire les comportements des agents réactifs, quelle que soit la plate-forme utilisée pour la simulation des SMA. Pour ce faire, nous avons appliqué l’approche de l’ingénierie dirigée par les modèles (IDM), une approche qui fournit des outils pour développer des langages dédiés à partir d'un méta-modèle (syntaxe abstraite), des éditeurs textuels avec coloration syntaxique (pour la syntaxe concrète) et des outils des générateurs de code (pour la génération de source code à partir d'un modèle). En conséquence, nous avons mis en œuvre un langage et un éditeur de texte qui permet à des experts du domaine SES de décrire les comportements de trois manières différentes qui sont fermées à leur expression naturelle : sous forme d'équations quand ils sont familiers avec celles-ci, en tant que séquence d'activités proche du langage naturel ou comme un diagramme d'activité pour représenter les décisions et une séquence de comportements en utilisant un formalisme graphique. Pour montrer la généralité, nous avons également développé des générateurs de code ciblant deux plates-formes différentes SMA (Cormas et Netlogo). Nous avons testé les générateurs de code en mettant en œuvre deux modèles SES avec le langage dédié développé. Le code généré obtenu a été généré pour les deux plates-formes SMA Cormas et NetLogo, et simulé avec succès dans un des deux plateformes. Nous avons conclu que l'approche IDM fournit des outils adéquats à développer des langages dédiés et des générateurs de code pour faciliter la modélisation et la simulation SMA par des non-programmeurs. En ce qui concerne le langage développé, bien que l’aspect comportemental de la simulation MAS fasse partie de la complexité de la modélisation en SMA, il y a encore d'autres aspects essentiels du modèle et de la simulation de SMA qui sont encore à être explorés, tels que l'initialisation et les points de vue sur un le monde simulé d’un modèleMany users of multi-agent systems (MAS) are very commonly discouraged to model and simulate using current MAS platforms. More specifically, modeling the dynamics of a system (in particular the agent's behaviors) is very often a challenge to users of MAS. That issue is more often observed in the domain of socio-ecological systems (SES), because SES domain experts are rarely programmers. Indeed,the majority of MAS platforms were not conceived taking into consideration domain-experts that are non-programmers. Most of the current MAS tools are not dedicated to SES, or they do not possess an easily understandable formalism to represent behaviors of agents. Moreover, because it is platform-dependent, a model realized in a MAS platform cannot be properly used in another platform due to incompatibility between MAS platforms. To overcome these limitations, we propose a domain-specific language (DSL) to describe the behaviors of reactive agents, regardless of the MAS platform used for simulation. To achieve that, we applied model-driven engineering (MDE), an approach that provides tools to develop DSLs from a meta-model (abstract syntax), textual editors with syntax highlighting (for the concrete syntax) and code generation capabilities (for source-code generation of a model). As a result, we implemented a language and a textual editor that allows SES domain experts to describe behaviors in three different ways that are closed to their natural expression: as equations when they are familiar to those, as a sequence of activities close to natural language or as an activity diagram to represent decisions and a sequence of behaviors using a graphic formalism. To show the generality we also developed code generators targeting two different MAS platforms (Cormas and Netlogo). We tested the code generators by implementing two SES models with the developed DSL. The generated code was targeted for both MAS platforms (Cormas and Netlogo), and successfully simulated in one of them.We conclude that the MDE approach provides adequate tools to develop DSL and code generators to facilitate MAS modeling and simulation by non-programmers. Concerning the developed DSL, although the behavioral aspect of MAS simulation is part of the complexity of modeling in MAS, there are still other essential aspects of model and simulation of MAS that are yet to be explored, such as model's initialization and points of view on the model's simulated world
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ZHU, Peihu. "An improved model for trust-aware recommender systems based on multi-faceted trust." Digital Commons @ Lingnan University, 2016. https://commons.ln.edu.hk/cds_etd/15.
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As customers enjoy the convenience of online shopping today, they face the problem of selecting from hundreds of thousands of products. Recommender systems, which make recommendations by matching products to customers based on the features of the products and the purchasing history of customers, are increasingly being incorporated into e-commerce websites. Collaborative filtering is a major approach to design algorithms for these systems. Much research has been directed toward enhancing the performance of recommender systems by considering various psychological and behavioural factors affecting the behaviour of users, e.g. trust and emotion.
While e-commerce firms are keen to exploit information on social trust available on social networks to improve their services, conventional trust-aware collaborative filtering does not consider the multi-facets of social trust. In this research, we assume that a consumer tends to trust different people for recommendations on different types of product. For example, a user trusts a certain reviewer on popular items but may not place as much trust on the same reviewer on unpopular items. Furthermore, this thesis postulates that if we, as online shoppers, choose to establish trust on an individual while we ourselves are reviewing certain products, we value this individual’s opinions on these products and we most likely will value his/her opinions on similar products in future.
Based on the above assumptions, this thesis proposes a new collaborative filtering algorithm for deriving multi-faceted trust based on trust establishment time. Experimental results based on historical data from Epinions show that the new algorithm can perform better in terms of accuracy when compared with conventional algorithms.
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Lee, Lik-hang, and 李力恆. "An agent-based model to support multi-issue negotiation in green supply chain." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/197508.
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To implement green supply chain, a company has to consider sustainability impacts in assessing potential suppliers. Thereby, the supplier evaluation and selection criteria would include various key performance indicators such as price, quality, delivery, as well as environmental and corporate social responsibility aspects. Researchers have proposed numerous multi-criteria decision making (MCDM) approaches for evaluating the multiple conflicting criteria in supplier selection. However, most of the existing approaches have ignored some important issues in business environment such as supplier qualification, supplier autonomy, negotiation between manufacturer and supplier, etc.
In this thesis, a multi-agent system (MAS) is proposed for supplier selection in green supply chain. It comprises two types of autonomous agents, namely, buyer agent and seller agents, to represent the interests of manufacturer and suppliers, respectively.
The proposed MAS presents three prominent features. First, the proposed supplier selection criteria incorporate the conventional, environmental and social aspects in the supplier selection process. The criteria are classified into negotiable and non-negotiable criteria. Initially, all criteria are included to evaluate and rank all the candidate suppliers. Subsequently, the top-ranked candidates are invited to participate in the bargaining process. In this regard, the negotiable criteria are used for assessing the quality of an offer, while the non-negotiable criteria, i.e. environmental and social criteria, influence the manufacturer’s negotiation attitude to candidate suppliers. The classification enables the manufacturer to fully utilize the performance values of all criteria.
Secondly, supplier selection is implemented in a two-stage methodology. The TOPSIS method is devised in the first stage to shortlist some suitable candidate suppliers for entering negotiation in the next stage. In the second stage, the agent-based negotiation process is adopted for selecting the final supplier. Representing the manufacturer and the shortlisted suppliers respectively, the buyer and seller agents bargain on a number of negotiable issues in the multi-round negotiation. A multi-issue and multilateral agent interaction protocol, which is an extension of the contract net protocol, is implemented in the MAS. Accordingly, the buyer agent coordinates with the seller agents to exchange offers and counteroffers.
Thirdly, a novel preference-based negotiation strategy is used to govern the behavior of agents during negotiation. A heuristics model with the Particle Swarm Optimization (PSO) algorithm and Adaptive Penalty Function has been designed and implemented to realize the proposed negotiation strategy. The strategy guides the autonomous agents to narrow down the discrepancies in the values of the negotiable criteria (price, delivery days, contract length) in their offers, and simultaneously search a mutually beneficial and acceptable agreement. The negotiation payoffs and negotiation time are improved.
Experimental results indicate that the proposed agent-based model could help the manufacturer to identify the most appropriate supplier and improve the quality of final agreement. In addition, the model successfully integrates supplier qualification and automated negotiation, and promotes supplier autonomy in the supplier selection process.published_or_final_version
Industrial and Manufacturing Systems Engineering
Master
Master of Philosophy
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Ferreira, José Alexandre Pires. "Monitoring morphisms to support sustainable interoperability of enterprise systems." Master's thesis, Faculdade de Ciências e Tecnologia, 2011. http://hdl.handle.net/10362/7527.
Full textAbstract:
Dissertation to obtain the Master degree in Electrical Engineering and Computer ScienceNowadays, organizations are required to be part of a global collaborative world. Sometimes this is the only way they can access new and wider markets, reaching new opportunities, skills and sharing assets, e.g. tools, lessons learnt. However, due to the different sources of enterprise models and semantics, organizations are experiencing difficulties in exchanging vital information via electronic and in a seamlessly way. To solve this issue, most of them try to attain interoperability by establishing peer-to-peer mappings with different business partners, or in optimized networks using neutral data standards to regulate communications. Moreover, the systems are more and more dynamic, changing frequently to answer new customer’s requirements, causing new interoperability problems and a reduction of efficiency. This dissertation proposes a multi-agent system to monitor existing enterprise systems, by being capable of detecting morphism changes. With this, network harmonization breakings are timely detected, and possible solutions are suggested to regain the interoperable status, thus enhancing robustness for reaching sustainability of business networks.
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Jose, Bijoy Antony. "Formal Model Driven Software Synthesis for Embedded Systems." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/28622.
Full textAbstract:
Due to the ever increasing complexity of safety-critical applications, handwritten code is being
replaced by automatically generated code derived from a high level specification. Code generation
from high level specification requires a model of computation with an underlying formalism
and correctness-preserving refinement steps to generate the lower level application code. Such
software synthesis techniques are said to be â correct-by-constructionâ . Synchronous programming
languages such as Esterel, LUSTRE, which are based on a synchronous model of computation
are used for sequential code generation. They work on a synchrony assumption (zero time intraprocess
computation and zero time inter process communication) at the specification level. Early
versions of synchronous languages followed an execution pattern where an iteration of software
was mapped to an interval between ticks of an external reference clock. Since this external reference
tick was unrelated to variables (or signals) within the software, redundant operations such
as reading of ports, computation of guards were performed for each tick. In this dissertation, we
highlight some of these performance issues and missed optimization opportunities. Also we show
how a multi-clock (or polychronous) formalism, where each variable has an independent rate of
execution associated with it, can avoid these problems.
An existing polychronous language named SIGNAL, creates a hierarchy of clocks based on the
rate of execution of individual variables, to form a root clock which acts a reference tick. We
seek to replace the clock analysis with a technique to form a unique order of events without a
reference time line. For this purpose, we present a new polychronous formalism termed Multi-rate
Instantaneous Channel connected Data Flow (MRICDF). Our new synthesis technique inspects
the specification to identify a master trigger at a Boolean equation level to act as the reference
tick. Furthermore, we attempt to make polychronous specification based software synthesis more
accessible to practicing engineers, by constructing a software tool EmCodeSyn, with a visual environment
for specification and a more intuitive analysis technique. Our Boolean approach to
sequential synthesis of embedded software has multiple implementations, each of which utilizes
existing academic software tools. Optimizations are proposed to minimize synthesis time by simplifying
the input to these external tools. Weaknesses in causal loop analysis techniques applied
by existing synthesis tools are highlighted and solutions for performing time efficient loop analysis
are integrated into EmCodeSyn. We have also determined that a part of the non-synthesizable
polychronous specifications can be used to generate correct multi-threaded code. Additionally,
we investigate composition of polychronous modules and propose properties that are necessary to
guarantee agreement on shared signals.Ph. D.
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Hales, Alwin Livingstone. "A model to determine optimal water management procedures for multi-variable irrigation systems." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259483.
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Das, Satyajit. "Architecture and Programming Model Support for Reconfigurable Accelerators in Multi-Core Embedded Systems." Thesis, Lorient, 2018. http://www.theses.fr/2018LORIS490/document.
Full textAbstract:
La complexité des systèmes embarqués et des applications impose des besoins croissants en puissance de calcul et de consommation énergétique. Couplé au rendement en baisse de la technologie, le monde académique et industriel est toujours en quête d'accélérateurs matériels efficaces en énergie. L'inconvénient d'un accélérateur matériel est qu'il est non programmable, le rendant ainsi dédié à une fonction particulière. La multiplication des accélérateurs dédiés dans les systèmes sur puce conduit à une faible efficacité en surface et pose des problèmes de passage à l'échelle et d'interconnexion. Les accélérateurs programmables fournissent le bon compromis efficacité et flexibilité. Les architectures reconfigurables à gros grains (CGRA) sont composées d'éléments de calcul au niveau mot et constituent un choix prometteur d'accélérateurs programmables. Cette thèse propose d'exploiter le potentiel des architectures reconfigurables à gros grains et de pousser le matériel aux limites énergétiques dans un flot de conception complet. Les contributions de cette thèse sont une architecture de type CGRA, appelé IPA pour Integrated Programmable Array, sa mise en œuvre et son intégration dans un système sur puce, avec le flot de compilation associé qui permet d'exploiter les caractéristiques uniques du nouveau composant, notamment sa capacité à supporter du flot de contrôle. L'efficacité de l'approche est éprouvée à travers le déploiement de plusieurs applications de traitement intensif. L'accélérateur proposé est enfin intégré à PULP, a Parallel Ultra-Low-Power Processing-Platform, pour explorer le bénéfice de ce genre de plate-forme hétérogène ultra basse consommationEmerging trends in embedded systems and applications need high throughput and low power consumption. Due to the increasing demand for low power computing and diminishing returns from technology scaling, industry and academia are turning with renewed interest toward energy efficient hardware accelerators. The main drawback of hardware accelerators is that they are not programmable. Therefore, their utilization can be low is they perform one specific function and increasing the number of the accelerators in a system on chip (SoC) causes scalability issues. Programmable accelerators provide flexibility and solve the scalability issues. Coarse-Grained Reconfigurable Array (CGRA) architecture consisting of several processing elements with word level granularity is a promising choice for programmable accelerator. Inspired by the promising characteristics of programmable accelerators, potentials of CGRAs in near threshold computing platforms are studied and an end-to-end CGRA research framework is developed in this thesis. The major contributions of this framework are: CGRA design, implementation, integration in a computing system, and compilation for CGRA. First, the design and implementation of a CGRA named Integrated Programmable Array (IPA) is presented. Next, the problem of mapping applications with control and data flow onto CGRA is formulated. From this formulation, several efficient algorithms are developed using internal resources of a CGRA, with a vision for low power acceleration. The algorithms are integrated into an automated compilation flow. Finally, the IPA accelerator is augmented in PULP - a Parallel Ultra-Low-Power Processing-Platform to explore heterogeneous computing
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Shei, Shaun. "A model-driven approach towards designing and analysing secure systems for multi-clouds." Thesis, University of Brighton, 2018. https://research.brighton.ac.uk/en/studentTheses/53c11a93-3d8d-4cbe-82df-deb34be6ab1f.
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Stein, Jacob. "Supporting feature model configuration based on multi-stakeholder preferences." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/117277.
Full textAbstract:
Configuração modelo de features é conhecida por ser uma atividade complexa, demorada e propensa a erros. Esta atividade torna-se ainda mais complicada quando envolve múltiplas partes interessadas no processo de configuração. Trabalhos de pesquisa têm proposto abordagens para ajudar na configuração de modelo de features, mas elas dependem de processos sistemáticos que restringem as decisões de alguns dos stakeholders. Neste trabalho, propomos uma nova abordagem para melhorar o processo de configuração multi-stakeholder, considerando as preferências dos stakeholders expressas através de restrições duras e brandas. Com base em tais preferências, recomendamos diferentes configurações de produto utilizando diferentes estratégias da teoria da escolha social. Nossa abordagem é implementada em uma ferramenta chamada SACRES, que permite criar grupos de stakeholders, especificar preferências dos stakeholders sobre uma configuração e gerar as configurações ideais. Realizamos um estudo empírico para avaliar a eficácia de nossas estratégias no que diz respeito à satisfação individual e justiça entre todos os stakeholders. Os resultados obtidos provem evidência de que estratégias em particular possuem melhor performance em relação à satisfação de grupo, chamadas average e multiplicative considerando as pontuações atribuídas pelos participantes e complexidade computacional. Nossos resultados são relevantes não só no contexto de Linha de Produto de Software, mas também para a Teoria da Escolha Social, dada a instanciação de estratégias de escolha social em um problema prático.Feature model con guration is known to be a hard, error-prone and timeconsuming activity. This activity gets even more complicated when it involves multiple stakeholders in the con guration process. Research work has proposed approaches to aid multi-stakeholder feature model con guration, but they rely on systematic processes that constraint decisions of some of the stakeholders. In this dissertation, we propose a novel approach to improve the multi-stakeholder con guration process, considering stakeholders' preferences expressed through both hard and soft constraints. Based on such preferences, we recommend di erent product con gurations using di erent strategies from the social choice theory. Our approach is implemented in a tool named SACRES, which allows creation of stakeholder groups, speci cation of stakeholder preferences over a con guration and generation of optimal con guration. We conducted an empirical study to evaluate the e ectiveness of our strategies with respect to individual stakeholder satisfaction and fairness among all stakeholders. The obtained results provide evidence that particular strategies perform best with respect to group satisfaction, namely average and multiplicative, considering the scores given by the participants and computational complexity. Our results are relevant not only in the context software product lines, but also in the context of social choice theory, given the instantiation of social choice strategies in a practical problem.
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Van, Broekhoven Scott B. (Scott Bennett). "A simplified multi-zone model for determining the placement of bio-defense sensors in large buildings." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43865.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.Includes bibliographical references (leaves 110-112).
The anthrax mailings of 2001 increased public and government awareness to the threat of bio-terrorism. Particularly vulnerable to a bio-terrorist event are large indoor facilities such as convention centers, office buildings, transportation centers, and sports arenas with their high population densities and limited physical security. Under heightened threat levels deploying bio-aerosol sensors inside these facilities provides added protection to the occupants. The challenge is determining the number and placement of sensors needed to guarantee the detection of a release inside a particular building. The methodology proposed here aims to simplify the analysis of contamination transport within buildings and provide first-order sensing requirements for dose dependant sensors in large facilities. A reduced-order model is developed that allows buildings to be subdivided into larger sections while maintaining a higher degree of accuracy than building analysis models with the same level of granularity. The problem is formulated as a network model with the nodes representing possible sensor locations and the path lengths equal to the reduction in dose as a contaminant travels between sensor locations. Techniques borrowed from network theory are then used to determine the minimum cost set of sensors that provides full building coverage. The reduced-order model estimates sensing requirements in hours or days for problems that would take months to analyze with fine grained multi-zone models and that are too large to be considered with computational fluid dynamics. Models of an office building, a convention center, and an airport terminal are constructed and their underlying network graph is employed to understand how the structure of the indoor environment affects the placement of sensors.
(cont.) Additionally, the equations derived to formulate the network model are used to quantify the optimal tradeoff between sensor sensitivity and cost as a function of building parameters. Future efforts will continue on this path, focusing on how easily discernible building properties such as size, HVAC layout, and air exchange rates can be used to predict the sensing requirements in large indoor spaces.
by Scott B. Van Broekhoven.
S.M.
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Howard, Matthew. "A MULTI-OBJECTIVE NO-REGRET DECISION MAKING MODEL WITH BAYESIAN LEARNING FOR AUTONOMOUS UNMANNED SYSTEMS." Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2376.
Full textAbstract:
The development of a multi-objective decision making and learning model for the use in unmanned systems is the focus of this project. Starting with traditional game theory and psychological learning theories developed in the past, a new model for machine learning is developed. This model incorporates a no-regret decision making model with a Bayesian learning process which has the ability to adapt to errors found in preconceived costs associated with each objective. This learning ability is what sets this model apart from many others. By creating a model based on previously developed human learning models, hundreds of years of experience in these fields can be applied to the recently developing field of machine learning. This also allows for operators to more comfortably adapt to the machine's learning process in order to better understand how to take advantage of its features. One of the main purposes of this system is to incorporate multiple objectives into a decision making process. This feature can better allow its users to clearly define objectives and prioritize these objectives allowing the system to calculate the best approach for completing the mission. For instance, if an operator is given objectives such as obstacle avoidance, safety, and limiting resource usage, the operator would traditionally be required to decide how to meet all of these objectives. The use of a multi-objective decision making process such as the one designed in this project, allows the operator to input the objectives and their priorities and receive an output of the calculated optimal compromise.M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE
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Tlili, Olfa. "Hydrogen systems : what contribution to the energy system? Findings from multiple modelling approaches." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC083/document.
Full textAbstract:
L'hydrogène… Cet élément simple et très abondant pourrait être un contributeur clé à la transition énergétique, mais dans quelles conditions technico-économiques et politiques ? Cette thèse propose une contribution à l'évaluation de la faisabilité de pénétration de l'hydrogène dans le système énergétique, en mettant en oeuvre différents modèles qui permettent des éclairages complémentaires. Elle se concentre sur l’hydrogène bas carbone, obtenu par électrolyse de l’eau.Notre analyse multirégionale qui porte sur le contexte énergétique européen, américain, chinois et japonais (régions qui présentent des défis énergétiques contrastés) montre que les politiques énergétiques actuelles ne facilitent qu’une faible pénétration de l'hydrogène dans le système énergétique, lui permettant de réaliser environ 3% de l’effort à fournir par les quatre régions afin de limiter l’augmentation de la température à 2°C par rapport aux niveaux préindustriels. Nous soulignons dans cette thèse que l’injection d’hydrogène dans les réseaux de gaz naturel qui permet dans une certaine mesure d’éviter des fuites de méthane à fort pouvoir de réchauffement, pourrait jouer un rôle significatif dans la réalisation des objectifs de réduction des émissions de gaz à effet de serre.L'analyse des marchés de l'hydrogène a été menée en deux étapes. Tout d'abord, chaque marché (industriel ou énergétique) a été abordé individuellement afin d’établir des coûts d'entrée sur ce marché (pour les différents contextes énergétiques considérés). Ensuite, les différentes applications de l’hydrogène ont été resituées en interaction avec l’ensemble du système énergétique à travers le modèle TIMES-PT et un cas d’étude portant sur le Portugal, permettant ainsi d’examiner le potentiel de couplage entre les secteurs énergétiques rendu possible par l’hydrogène. Ces travaux ont permis de qualifier l'attractivité des différents marchés, celui de la mobilité apparaissant comme le plus favorable.Nous nous sommes ensuite intéressés aux coûts requis sur l'ensemble de la chaîne d'approvisionnement en hydrogène afin de pénétrer le marché de la mobilité.Pour ce faire, nous avons utilisé des modèles avec une maille géographique et temporelle fine (GLAES, EuroPower et InfraGis), en commençant par l’étape de production. Nous avons étudié le rôle potentiel de l'hydrogène pour la fourniture de flexibilité au système électrique dans un contexte de forte pénétration des énergies renouvelables intermittentes en France. Nos résultats montrent que l’hydrogène pourrait permettre non seulement d’éviter d’écrêter la production d’énergies renouvelables (entre 1,4 et 7,9 TWh en fonction du scénario de capacité d’interconnexion), mais pourrait aussi mettre à profit l’énergie nucléaire disponible (bas carbone donc), évitant par-là d’imposer de fortes rampes de puissances aux centrales. Cependant, une attention particulière doit être accordée au taux d'utilisation de l'électrolyseur afin de maintenir les coûts de production d'hydrogène suffisamment bas.Enfin, nous nous sommes concentrés sur l’approvisionnement de l’hydrogène, depuis les sites de production jusqu’à l’utilisation pour la mobilité, la question de l’infrastructure étant un problème majeur entravant les investissements dans l’hydrogène. Cinq filières d’approvisionnement (transport et distribution) ont été développées à la maille régionale et comparées sur le plan économique pour le cas français. Nos résultats montrent que, lors des toutes premières phases de pénétration du marché (scénario 1%), il est plus intéressant de privilégier la production décentraliséeHydrogen… This simple, very abundant element holds great promise to contribute to the transition towards a cleaner future energy system, but under which techno-economic and political conditions? This thesis is a contribution to the assessment of the hydrogen penetration feasibility into the energy system, using a multi-model approach. The focus is put on low-carbon hydrogen, obtained by electrolysis.Our multi-regional analysis on the European, American, Chinese and Japanese energy context (presenting contrasted energy challenges) show that, with the current energy policies implemented which result in a modest penetration of hydrogen into the energy system, hydrogen may achieve approximately 3% of the effort that needs to be done by the four regions, in order to limit the increase of the temperature to 2°C, compared to preindustrial levels. We highlight in this thesis that blending hydrogen with natural gas, and thereby avoiding methane leakages to a certain extent, may represent a significant contribution in achieving the carbon mitigation goals.The hydrogen market analysis has been carried out following two steps. First, each market (industrial and energy-related) was tackled aside in order to propose market entry costs considering the four energy contexts and investigate the timeframe of the market penetration potential. Then, the different hydrogen applications were examined within the overall energy system through the TIMES-PT model (for a Portugal case study), allowing to investigate the hydrogen potential for energy sector coupling. Based on this work, the markets attractiveness was evaluated: mobility (using fuel cell vehicles) appears to be the most favourable.Then, we tackled the required costs over the whole hydrogen supply chain in order to enter the mobility market.To do so, we used temporally and spatially resolved models (GLAES, EuroPower and InfraGis) starting with the production side where we studied the hydrogen potential role in providing the electricity system with flexibility and the impact of such electrolysis operation on the hydrogen generation costs in the context of high shares of renewable energies in France. Our results show that hydrogen can contribute to improve the flexibility of the electric system by allowing avoiding renewable curtailment (between 1.4 and 7.9 TWh depending on the interconnection capacity scenario) but also by taking advantage of nuclear plant available energy (thereby avoiding nuclear ramping), the latter ensuring a low carbon and low cost electricity provision. However, a special attention needs to be dedicated to the utilisation rate of the electrolyser, to keep the hydrogen production costs low enough.Last but not least, we focused on how to link the hydrogen production sites and its final use for mobility applications, the delivery infrastructure being a major issue hampering the hydrogen investments. Five transport and delivery pathways were geographically designed and economically assessed, for the French case. According to our findings, during the very first market penetration phases (1% scenario), it is more interesting to start with decentralised production that proved to be less expensive for the whole pathway at this stage
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Margetts, Rebecca. "Modelling & analysis of hybrid dynamic systems using a bond graph approach." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.600647.
Full textAbstract:
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.
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Lydiard, John M. IV. "Multi-region capacity planning model with contracts of varying duration under uncertainty : a satellite capacity acquisition case study." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91439.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Engineering Systems Division, 2014.19
"June 2014." Cataloged from PDF version of thesis.
Includes bibliographical references (pages 125-127).
This paper highlights the issues associated with and presents a modeling framework for long-term capacity planning problems constrained in a similar fashion to satellite capacity acquisition. Although ambiguities exist, the satellite capacity planning problem also contains many clearly defined constraints. In the immediate time horizon, universal satellite capacity is fixed, as satellite launches are rare, and each incremental satellite launch only marginally increases capacity. In the world of Commercial Satellite Communications (COMSATCOM), satellites have fixed coverage areas as they are typically in geo-synchronous orbit. Other military applications such as observation and satellite phone require, low-earth orbit and medium-earth orbit satellites. The contracts used to acquire satellite capacity from the commercial sector also clearly define constraints, such as start and end date, bandwidth, price per unit bandwidth and allocated satellite system, which also implies frequency and available capacity. The paper first reviews the issues involved with planning capacity acquisition, and then presents a modeling framework for developing strategies to meet criteria and minimize cost. A simulation environment is developed for testing contracts and satellites of different parameters against varying demand distributions. A dynamic program is used to solve the integer program associated with selecting satellite capacity levels to cover demand.
by John M. Lydiard, IV.
S.M.
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Backer-Meurke, Henrik, and Marcus Polland. "Predicting Road Rut with a Multi-time-series LSTM Model." Thesis, Högskolan Dalarna, Institutionen för information och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:du-37599.
Full textAbstract:
Road ruts are depressions or grooves worn into a road. Increases in rut depth are highly undesirable due to the heightened risk of hydroplaning. Accurately predicting increases in road rut depth is important for maintenance planning within the Swedish Transport Administration. At the time of writing this paper, the agency utilizes a linear regression model and is developing a feed-forward neural network for road rut predictions. The aim of the study was to evaluate the possibility of using a Recurrent Neural Network to predict road rut. Through design science research, an artefact in the form of a LSTM model was designed, developed, and evaluated.The dataset consisted of multiple-multivariate short time series where research was limited. Case studies were conducted which inspired the conceptual design of the model. The baseline LSTM model proposed in this paper utilizes the full dataset in combination with time-series individualization through an added index feature. Additional features thought to correlate with rut depth was also studied through multiple training set variations. The model was evaluated by calculating the Root Mean Squared Error (RMSE) and the Mean Absolute Error (MAE) for each training set variation. The baseline model predicted rut depth with a MAE of 0.8110 (mm) and a RMSE of 1.124 (mm) outperforming a control set without the added index. The feature with the highest correlation to rut depth was curvature with a MAEof 0.8031 and a RMSE of 1.1093. Initial finding shows that there is a possibility of utilizing an LSTM model trained on multiple-multivariate time series to predict rut depth. Time series individualization through an added index feature yielded better results than control, indicating that it had the desired effect on model performance.
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Ozpamukcu, Serkan. "An Assessment Of A Two-echelon Inventory System Againstalternative Systems." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613949/index.pdf.
Full textAbstract:
In this study, we focus on a real life problem that involves a single item which is
used in military operations. The items in use fail according to a Poisson process
and lead times are deterministic. Four alternative inventory control models are
developed. Among these models, a two-echelon system consisting of a depot in
the upper and several bases in the lower echelon is operated currently. This
system is compared to a single-echelon system that consists of several bases. The
comparison reveals the importance of the holding cost incurred for the items intransit
between the depot and the base which is ignored in most of the studies in
literature. Both the two and single-echelon models are also extended to have
repair ability. A continuous-review base-stock policy is used for all models.
Exact models are formulated. The results are obtained under various lead time,
unit costs and demand parameters. Results of four different settings are compared
and the findings are reported.
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Bhonsle, Shailendra K. "Semiorder model for temporal composition of activities from events in multi-sensory information management systems /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9963652.
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May, Jeffrey Lee. "Developing a Multi-Objective Decision Model for Maximizing IS Security within an Organization." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/914.
Full textAbstract:
Numerous IS researchers have argued that IS Security can be more effectively managed if the emphasis goes beyond the technical means of protecting information resources. In an effort to adopt a broader perspective that accounts for issues that transcend technical means alone, Dhillon and Torkzadeh (2006) present an array of 9 fundamental and 16 means objectives that are essential for maximizing IS security in an organization. These objectives were derived using a value-focused thinking approach and are organized into a conceptual framework. This conceptual framework provides a rigorous theoretical base for considering IS security in a manner that accounts for both technical and organizational issues; however, no direction is provided for using these objectives so that informed decisions can be made. As a result, the goal of this dissertation is to develop a decision model using Multiple Objective Decision Analysis (MODA) techniques that seek to provide informed alternatives to decision makers who desire to maximize IS security within an organization.
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Yang, Yuecheng. "Self-organization and Intervention of Nonlinear Multi-agent Systems." Doctoral thesis, KTH, Optimeringslära och systemteori, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-197270.
Full textAbstract:
This dissertation concerns the self-organization behaviors in different types of multi-agent systems, and possible ways to apply interventions on top ofthat to achieve certain goals. A bounded confidence opinion dynamics modelis considered for the first two papers. Theoretical analysis of the model isperformed and modifications of the model are given so that it will have better properties in some aspect. Leader-follower based models are studied in the third to fifth papers where various optimal control problems are considered. Different methods such as Pontryagin minimum principle and dynamic programming are used to solve those optimal control problem. For complex problems, one may only get approximate solutions or suboptimal solutions.In Paper A and Paper B, we consider the continuous-time Hegselmann-Krause (H-K) model and its variations and target the problem of reaching consensus. A sufficient condition on the initial opinion distribution is givento guarantee consensus for the original continuous-time H-K model. A modified model is provided and proven to be able to lead a larger range of initial opinions to synchronization. An H-K model with an exo-system is also studied where sufficient conditions on the exo-system are given for the purpose of consensus.In Paper C and Paper D, optimal control problems with leader-followerbased multi-agent systems are discussed. Analytic solutions are derived if the dynamics is linear by applying Pontryagin minimum principle. For generalnon-linear leader-follower interactions, we provide a method that use sstatistic moments of the follower crowd to approximate the optimal control.The dynamic programming approach is used and certain approximation ofthe Hamilton-Jacobi-Bellman equations is needed. The computational burdenis so heavy that model predictive control method is required in practical applications.In Paper E, we apply a similar method to the approach used in PaperD to target a pollutant elimination problem. It implies that we can use themethod to attack optimal control problem with partial differential equation constraints by discretization in space. The dimension of the discretization is not related to the computational complexity since only the statistic moments are needed.QC 20161201