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Dissertations / Theses on the topic 'Discrete-Event models'
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Kuljis, Jasminka. "User interfaces and discrete event simulation models." Thesis, London School of Economics and Political Science (University of London), 1995. http://etheses.lse.ac.uk/1380/.
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A user interface is critical to the success of any computer-based system. Numerous studies have shown that interface design has a significant influence on factors such as learning time, performance speed, error rates, and user satisfaction. Computer-based simulation modelling is one of the domains that is particularly demanding in terms of user interfaces. It is also an area that often pioneers new technologies that are not necessarily previously researched in terms of human-computer interaction. The dissertation describes research into user interfaces for discrete event simulation. Issues that influence the 'usability' of such systems are examined. Several representative systems were investigated in order to generate some general assumptions with respect to those characteristics of user interfaces employed in simulation systems. A case study was carried out to gain practical experience and to identify possible problems that can be encountered in user interface development. There is a need for simulation systems that can support the developments of simulation models in many domains, which are not supported by contemporary simulation software. Many user interface deficiencies are discovered and reported. On the basis of findings in this research, proposals are made on how user interfaces for simulation systems can be enhanced to match better the needs specific to the domain of simulation modelling, and on how better to support users in simulation model developments. Such improvements in user interfaces that better support users in simulation model developments could achieve a reduction in the amount of time needed to learn simulation systems, support retention of learned concepts over time, reduce the number of errors during interaction, reduce the amount of time and effort needed for model development, and provide greater user satisfaction.
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Domingo, Lizza Tandoc. "Formal methods in specifying discrete event simulation models." Thesis, London School of Economics and Political Science (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263339.
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Derrick, Emory Joseph. "Conceptual frameworks for discrete event simulation modeling." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43840.
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Elgmati, Entisar. "Additive intensity models for discrete time recurrent event data." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556142.
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The thesis considers the Aalen additive regression model for recurrent event data. The model itself, estimation of the cumulative regression functions, testing procedures, checking goodness of fit and inclusion of dynamic covariates in the model are reviewed. A disadvantage of this model is that estimates of the conditional probabilities are not constrained to lie between zero and one, therefore a model with logistic intensity is considered. Results under the logistic model are shown to be qualitatively similar to those under the additive model. The additive model is extended to incorporate the possibility of spatial or spatio-temporal clustering, possibly caused by unobserved environmental factors or infectivity. Various tests for the presence of clustering are described and implemented. The issue of frailty modelling and its connection to dynamic modelling is presented and examined. We show that frailty and dynamic models are almost indistinguishable in terms of residual summary plots. A graphical procedure based on the property that the covariance between martingale residuals at time to and t > to is independent of t is proposed and supplemented by a formal test statistic to investigate the adequacy of the fitted models. The results can be used to compare models and to check the validity of the model being tested. Also we investigate properties under various types of model misspecification. All our works are illustrated using two sets of data measuring daily prevalence and incidence of infant diarrhoea in Salvador, Brazil. Significant clustering is identified in the data. We investigate risk factors for diarrhoea and there is strong evidence of dynamic effects being important, implying heterogeneity between individuals not explained by measured socio- economic and environmental factors.
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Soueidan, Hayssam. "Discrete event modeling and analysis for systems biology models." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13916/document.
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Les travaux effectués durant cette thèse portent sur la spécification, l'analyse et l'application de systèmes a événements discrets pour la modélisation de processus biologiques stochastiques en biologie des systèmes. Le point de départ de cette thèse est le langage de modélisation AltaRica, que nous étendons afin de permettre de décrire des événements temporisés selon des distributions de probabilités quelconques (dégénérées, discrètes et continues). Nous définissons ensuite la sémantique de ce langage en terme d'automates de mode stochastiques et présentons trois opérations de compositions permettant de modéliser des systèmes hiérarchiques avec événements synchronisés et partage de valeurs via un mécanisme de connexion. Nous donnons ensuite au automates de mode stochastiques une sémantique en termes de systèmes de transitions dont les transitions sont étiquetées par des distributions de probabilités et des probabilités de transitions instantanées. Nous caractérisons ensuite 6 sous classes de ces systèmes de transitions et donnons pour chacune de ces classes un algorithme de simulation ainsi qu'une mesure de probabilité sur les chemins finis. Nous montrons que pour certaines de ces classes, notre sémantique est conforme avec les mesures de probabilité de chemin usuellement associées aux chaînes de Markov a temps discret, a temps continu et aux processus semi-Markoviens généralisés. Nous abordons ensuite le problème de la réutilisation de modèles continus existant dans un système discret. Nous donnons une méthode d'abstraction permettant de représenter un ensemble de trajectoires bornées ou non d'un modèle continu sous forme d'un système de transition stochastique fini. A travers des exemples tirés de la littérature, nous montrons que notre abstraction préserve les propriétés "qualitatives" (par exemple oscillations, hystérie) des modèles continus et qu'une comparaison entre trajectoires basée sur leurs représentations en termes de systèmes de transitions permet de regrouper les trajectoires en fonction de comportements qualitatifs plus fins que ceux permis par la théorie des bifurcations. Finalement, nous étudions a l'aide de ces modèles des processus liés a la division cellulaire chez les levures. En particulier, nous définissons un modèle pour le vieillissement cellulaire dans une population de levure où le comportement individuel d'une cellule est régi par une équation différentielle ordinaire et où le processus de division est régi par un système de transition. Nous montrons a l'aide de ce modèle que la survie d'une population de levure de type Schizosaccharomyces Pombe, qui se divisent par une fission médiane, n'est possible que grâce a un mécanisme de distribution non symétrique des dégâts oxydatifs entre la progéniture et la cellule souche. Cette hypothèse fut validée expérimentalement lors d'une collaboration avec le laboratoire de micro-biologie de GöteborgA general goal of systems biology is to acquire a detailed understanding of the dynamics of living systems by relating functional properties of whole systems with the interactions of their constituents. Often this goal is tackled through computer simulation. A number of different formalisms are currently used to construct numerical representations of biological systems, and a certain wealth of models is proposed using ad hoc methods. There arises an interesting question of to what extent these models can be reused and composed, together or in a larger framework. In this thesis, we propose BioRica as a means to circumvent the difficulty of incorporating disparate approaches in the same modeling study. BioRica is an extension of the AltaRica specification language to describe hierarchical non-deterministic General Semi-Markov processes. We first extend the syntax and automata semantics of AltaRica in order to account for stochastic labeling. We then provide a semantics to BioRica programs in terms of stochastic transition systems, that are transition systems with stochastic labeling. We then develop numerical methods to symbolically compute the probability of a given finite path in a stochastic transition systems. We then define algorithms and rules to compile a BioRica system into a stand alone C++ simulator that simulates the underlying stochastic process. We also present language extensions that enables the modeler to include into a BioRica hierarchical systems nodes that use numerical libraries (e.g. Mathematica, Matlab, GSL). Such nodes can be used to perform numerical integration or flux balance analysis during discrete event simulation. We then consider the problem of using models with uncertain parameter values. Quantitative models in Systems Biology depend on a large number of free parameters, whose values completely determine behavior of models. Some range of parameter values produce similar system dynamics, making it possible to define general trends for trajectories of the system (e.g. oscillating behavior) for some parameter values. In this work, we defined an automata-based formalism to describe the qualitative behavior of systems’ dynamics. Qualitative behaviors are represented by finite transition systems whose states contain predicate valuation and whose transitions are labeled by probabilistic delays. We provide algorithms to automatically build such automata representation by using random sampling over the parameter space and algorithms to compare and cluster the resulting qualitative transition system. Finally, we validate our approach by studying a rejuvenation effect in yeasts cells population by using a hierarchical population model defined in BioRica. Models of ageing for yeast cells aim to provide insight into the general biological processes of ageing. For this study, we used the BioRica framework to generate a hierarchical simulation tool that allows dynamic creation of entities during simulation. The predictions of our hierarchical mathematical model has been validated experimentally by the micro-biology laboratory of Gothenburg
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Foong, Yew Chong. "Airlift operations modeling using Discrete Event Simulation (DES)." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FFoong.pdf.
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Thesis (M.S. in Modeling, Virtual Environments, and Simulation (MOVES))--Naval Postgraduate School, December 2009.Thesis Advisor(s): Buss, Arnold. Second Reader: Meyer, David. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Discrete Event Simulation, airlift operation. Includes bibliographical references (p. 145-147). Also available in print.
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Goodman, Daniel. "Enhancing discrete event modelling by interfacing expert systems and simulation models." Thesis, London School of Economics and Political Science (University of London), 1993. http://etheses.lse.ac.uk/3050/.
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This thesis investigates the representation of operational decision makers within simulation modelling. Artificial Intelligence concepts, such as expert systems focus on the problem of representing, in high-level code, complex real-world decision making problems. The author therefore proposes that the use of expert system technology may provide an improved means of representing operational decision tasks and that as a consequence, apriori possibilities may exist in the context of model experimentation based on alternative operational policies. The thesis further investigates the nature of operational decision making and the potential need to represent within a model, inter-dependencies between decision makers. A prototype system called ESSIM is developed which comprises of two interlinked components, a discrete event simulation module and expert system module. The benefits of the proposed approach are then assessed by comparing the functionally of ESSIM with conventional modelling techniques. The comparison is carried out by developing three alternative models of an automated container port, one of these using ESSIM. Experiments were then devised and executed which seek to draw conclusions on the thesis proposal.
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Alt, Aaron J. "Profile Driven Partitioning Of Parallel Simulation Models." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1407406955.
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Razavi, Behnam. "Decision analysis models for aircraft engine maintenance planning using discrete event simulation." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52466.
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With stringent standards for materials, manufacturing, operation, and quality control, jet engines in use on commercial aircraft are very reliable. It is not uncommon for engines to operate for thousands of hours before being scheduled for inspection, service or repair. However, due to required maintenance and unexpected failures aircraft must be periodically grounded and their engines attended to. The tasks of maintenance and repair without optimal planning can be costly and result in prolonged maintenance times, reduced availability and possible flight delays. These factors have a negative impact on both the airline operators and the passengers alike. Aircraft manufacturers and maintainers, who provide after sale services, see significant benefits in constantly improving health management and maintenance practices by deploying the most effective maintenance strategies. Maintenance is seen as an imposed cost that ought to be minimized. Airlines must evaluate new technologies and their possible role in reducing the long term expenditure for operating a fleet of aircraft throughout its life cycle. A significant share of these expenses goes towards maintenance of these aircraft, especially their engines.
This study presents a model-based integrated decision making system for aircraft engine maintenance planning. The goal is to determine the optimum number of engines on an aircraft for maintenance based on logged engine operation data in order to maximize the use of estimated remaining time to the next service as well as to minimize the duration of downtime. To achieve this, engine condition is used in a set of preliminary Discrete Event Simulation (DES) models to evaluate and provide the most effective maintenance policies for the aircraft engines. To assess options for making decisions, a comprehensive model is developed based on the integration of the smaller preliminary maintenance models for one, two, three and four engine maintenance cases. Results from these analyses determine the optimal number of engines tagged for maintenance on any aircraft in the fleet that arrives at the service facility. Since the materials, technicians and other costs are proprietary information, this study is time-based but allowance is made for the user to include associated costs and thus perform cost-based decision making.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Sevinc, Suleyman. "Automatic simplification of models in a hierarchical, modular discrete event simulation environment." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184409.
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This research is concerned with the simplification of discrete event simulation models. Specifically, the necessary concepts and tools are investigated for the automatic generation of simplified versions of a discrete event model. The simplification process developed utilizes observations of model behavior. It is based on Zeigler's DEVS formalism developed in his book "Multifacetted Modelling and Discrete Event Simulation". Therefore, the simplified models that are generated adhere to all the canons of this formalism. The implementation is designed as an extension to DEVS-Scheme, a hierarchical modular discrete event modelling and simulation environment. It consists of two layers: the lower layer observes the model behavior and the higher layer generates the code from the observation data obtained at the lower layer. The resulting system allows one to generate simplified models at any level of the model structure hierarchy. A local area network model base is developed and used to demonstrate the validity and complexity reduction of the simplified models relative to the models from which they are extracted.
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Smith, Christopher Rand. "The Programmatic Generation of Discrete-Event Simulation Models from Production Tracking Data." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5829.
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Discrete-event simulation can be a useful tool in analyzing complex system dynamics in various industries. However, it is difficult for entry-level users of discrete-event simulation software to both collect the appropriate data to create a model and to actually generate the base-case simulation model. These difficulties decrease the usefulness of simulation software and limit its application in areas in which it could be potentially useful. This research proposes and evaluates a data collection and analysis methodology that would allow for the programmatic generation of simulation models using production tracking data. It uses data collected from a GPS device that follows products as they move through a system. The data is then analyzed by identifying accelerations in movement as the products travel and then using those accelerations to determine discrete events of the system. The data is also used to identify flow paths, pseudo-capacities, and to characterize the discrete events. Using the results of this analysis, it is possible to then generate a base-case discrete event simulation. The research finds that discrete event simulations can be programmatically generated within certain limitations. It was found that, within these limitations, the data collection and analysis method could be used to build and characterize a representative simulation model. A test scenario found that a model could be generated with 2.1% error on the average total throughput time of a product in the system, and less than 8% error on the average throughput time of a product through any particular process in the system. The research also found that the time to build a model under the proposed method is likely significantly less, as it took an experienced simulation modeler .4% of the time to build a simple model based off a real-world scenario programmatically than it did to build the model manually.
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de, Toro A. Alfredo. "Assessment of field machinery performance in variable weather conditions using discrete event simulation /." Uppsala : Dept. of Biometry and Engineering, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/a462.pdf.
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San, Jose Angel. "Analysis, design, implementation and evaluation of graphical design tool to develop discrete event simulation models using event graphs and SIMKIT." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA397405.
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Thesis (M.S. in Operations Research) Naval Postgraduate School, Sept. 2001.Thesis advisor(s): Buss, Arnold; Miller, Nita. "September 2001." Includes bibliographical references (p. 109-110). Also available in print.
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Kesaraju, Vishnu Sharma. "An Integrated Simulation Environment Combining Process-Driven and Event-Driven Models." Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1238779995.
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Egger, Peter Johann. "Event history analysis : discrete-time models including unobserved heterogeneity, with applications to birth history data." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386202.
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Goeree, Barry Boudewijin. "On synthesizing discrete event controllers for robotic assembly by automatic construction of qualitative contact models." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284194.
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This dissertation focuses on methods for automatic synthesis of discrete event controllers (DEC's) for robotic assembly of polyhedral parts. A DEC reacts to contact transitions and issues desired transitions to the underlying continuous system. A DEC can be implemented by an augmented adjacency graph. Each node represents a qualitative configuration state of the objects. Spatially adjacent states are connected by arcs. Each node is augmented with a desired transition. The graph can be constructed while searching backwards. A state is expanded by generating hypotheses about spatially adjacent states and subsequently rejecting the infeasible hypotheses. This paradigm requires a representation with the following properties: (i) the representation must contain all information about contacts; (ii) spatial adjacency must be easy to verify and, (iii) a necessary condition for spatial adjacency suitable for hypothesis generation must exist. Two representations have been considered: sets of elementary contacts; and feature interaction matrices (FIM's). Spatial adjacency is difficult to verify for sets of elementary contacts. Hypothesis generation is complicated by the lack of a suitable necessary condition for spatial adjacency. These problems make sets of elementary contacts ill-suited as a representation for automatic synthesis of DEC's. A FIM encodes besides contact information about the relative configuration. An important advantage of using FIM's representation is that spatial adjacency can be verified easily using convex cone techniques. Furthermore, there exists a simple necessary condition for spatial adjacency that can be used for hypothesis generation. Complete algorithms for hypothesis generation are presented. An optimization-based approach is presented to verify the geometric feasibility of hypothetical feature interaction matrices. Some hypothetical FIM's constrain the relative configuration such that the objects necessarily penetrate each other. An algorithm has been presented that can falsify some of these hypotheses by simple processing of the FIM's.
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Verma, Poonam Santosh. "Non-equilibrium surface growth for competitive growth models and applications to conservative parallel discrete event simulations." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-11092007-141815.
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Bell, Mark. "Methods for enhancing system dynamics modelling : state-space models, data-driven structural validation & discrete-event simulation." Thesis, Lancaster University, 2015. http://eprints.lancs.ac.uk/86867/.
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System dynamics (SD) simulation models are differential equation models that often contain a complex network of relationships between variables. These models are widely used, but have a number of limitations. SD models cannot represent individual entities, or model the stochastic behaviour of these individuals. In addition, model parameters are often not observable and so values of these are based on expert opinion, rather than being derived directly from historical data. This thesis aims to address these limitations and hence enhance system dynamics modelling. This research is undertaken in the context of SD models from a major telecommunications provider. In the first part of the thesis we investigate the advantages of adding a discreteevent simulation model to an existing SD model, to form a hybrid model. There are few examples of previous attempts to build models of this type and we therefore provide an account of the approach used and its potential for larger models. Results demonstrate the advantages of the hybrid’s ability to track individuals and represent stochastic variation. In the second part of the thesis we investigate data-driven methods to validate model assumptions and estimate model parameters from historical data. This commences with use of regression based methods to assess core structural assumptions of the organisation’s SD model. This is a complex, highly nonlinear model used by the organisation for service delivery. We then attempt to estimate the parameters of this model, using a modified version of an existing approach based on state-space modelling and Kalman filtering, known as FIMLOF. One such modification, is the use of the unscented Kalman filter for nonlinear systems. After successfully estimating parameters in simulation studies, we attempt to calibrate the model for 59 geographical regions. Results demonstrate the success of our estimated parameters compared to the organisation’s default parameters in replicating historical data.
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Venkateswaran, Jayendran. "PRODUCTION AND DISTRIBUTION PLANNING FOR DYNAMIC SUPPLY CHAINS USING MULTI-RESOLUTION HYBRID MODELS." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1185%5F1%5Fm.pdf&type=application/pdf.
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Tako, Antuela Anthi. "Development and use of simulation models in Operational Research : a comparison of discrete-event simulation and system dynamics." Thesis, University of Warwick, 2008. http://wrap.warwick.ac.uk/2984/.
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The thesis presents a comparison study of the two most established simulation approaches in Operational Research, Discrete-Event Simulation (DES) and System Dynamics (SD). The aim of the research implemented is to provide an empirical view of the differences and similarities between DES and SD, in terms of model building and model use. More specifically, the main objectives of this work are: 1. To determine how different the modelling process followed by DES and SD modellers is. 2. To establish the differences and similarities in the modelling approach taken by DES and SD modellers in each stage of simulation modelling. 3. To assess how different DES and SD models of an equivalent problem are from the users’ point of view. In line with the 3 research objectives, two separate studies are implemented: a model building study based on the first and second research objectives and a model use study, dealing with the third research objective. In the former study, Verbal Protocol Analysis is used, where expert DES and SD modellers are asked to ‘think aloud’ while developing simulation models. In the model use study a questionnaire survey with managers (executive MBA students) is implemented, where participants are requested to provide opinions about two equivalent DES and SD models. The model building study suggests that DES and SD modelling are different regarding the model building process and the stages followed. Considering the approach taken to modelling, some similarities are found in DES and SD modellers’ approach to problem structuring, data inputs, validation & verification. Meanwhile, the modellers’ approach to conceptual modelling, model coding, data inputs and model results is considered different. The model use study does not identify many significant differences in the users’ opinions regarding the specific DES and SD models used, implying that from the user’s point of view the type of simulation approach used makes little difference if any. The work described in this thesis is the first of its kind. It provides an understanding of the DES and SD simulation approaches in terms of the differences and similarities involved. The key contribution of this study is that it provides empirical evidence on the differences and similarities between DES and SD from the model building and model use point of view. Albeit the study does not provide a comprehensive comparison of the two simulation approaches, the findings of the study, provide new insights about the comparison of the two simulation approaches and contribute to the limited existing comparison literature.
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Griffith, Edward Shane. "The Effect of Heterogeneous Servers on the Service Level Predicted by Erlang-A." NSUWorks, 2011. http://nsuworks.nova.edu/hsbe_etd/38.
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Thousands of call centers operate in the United States employing millions of people. Since personnel costs represent as much as 80% of the total operating expense of these centers, it is important for call center managers to determine an appropriate staffing level required to maintain the desired operating performance. Historically, queueing models serve an important role in this regard. The one most commonly used is the Erlang-C model.
The Erlang-C model has several assumptions, however, which are required for the predicted performance measures to be valid. One assumption that has received significant attention from researchers is that callers have infinite patience and will not terminate a call until the service is complete regardless of the wait time. Since this assumption is not likely to occur in reality, researchers have suggested using Erlang-A instead.
Erlang-A does consider caller patience and allows for calls to be abandoned prior to receiving service. However, the use of Erlang-A still requires an assumption that is very unlikely to occur in practice - the assumption that all agents provide service at the same rate. Discrete event simulation is used to examine the effects of agent heterogeneity on the operating performance of a call center compared to the theoretical performance measures obtained from Erlang-A.
Based on the simulation results, it is concluded that variability in agent service rate does not materially affect call center performance except to the extent that the variability changes the average handle time of the call center weighted by the number of calls handled and not weighted by agent. This is true regardless of call center size, the degree of agent heterogeneity, and the distribution shape of agent variability.
The implication for researchers is that it is unnecessary to search for an analytic solution to relax the Erlang-A assumption that agents provide service at the same rate. Several implications for managers are discussed including the reliability of using Erlang-A to determine staffing levels, the importance of considering the service rates of the agents rather than the average handle time, and the unintended consequence of call routing schemes which route calls to faster rather than slower agents.
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Karnon, J. D. "Economic evaluation of health care technologies : a comparison of alternative decision modelling techniques." Thesis, Brunel University, 2001. http://bura.brunel.ac.uk/handle/2438/4806.
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The focus of this thesis is on the application of decision models to the economic evaluation of health care technologies. The primary objective addresses the correct choice of modelling technique, as the attributes of the chosen technique could have a significant impact on the process, as well as the results, of an evaluation. Separate decision models, a Markov process and a discrete event simulation (DES) model are applied to a case study evaluation comparing alternative adjuvant therapies for early breast cancer. The case study models are built and analysed as stochastic models: whereby probability distributions are specified to represent the uncertainty about the true values of the model input parameters. Three secondary objectives are also specified. Firstly, the empirical application of the alternative decision models requires the specification of a 'modelling process' that is not well defined in the health economics literature. Secondly, a comparison of alternative methods for specifying probability distributions to describe the uncertainty in the model's input parameters is undertaken. The final secondary objective covers the application of methods for valuing the collection of additional information to inform the resource allocation decision. The empirical application of the two relevant modelling techniques clarifies the potential advantages derived from the increased flexibility provided by DES over Markov models. The thesis concludes that the use of DES should be strongly considered if either of the following issues appear relevant: model parameters are a function of the time spent in particular states, or the data describing the timing of events are not in the form of transition probabilities. The full description of the modelling process provides a resource for health economists wanting to use decision models. No definitive process is established, however, as there exist competing methods for various stages of the modelling process. The main conclusion from the comparison of methods for specifying probability distributions around the input parameters is that the theoretically specified distributions are most likely to provide a common baseline for comparisons between evaluations. The central question that remains to be addressed is which method is the most theoretically correct? The application of a Vol analysis provides useful insights into the methods employed and leads to the identification of particular methodological issues requiring future research in this area.
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Plan, Elodie L. "Pharmacometric Methods and Novel Models for Discrete Data." Doctoral thesis, Uppsala universitet, Institutionen för farmaceutisk biovetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-150929.
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Pharmacodynamic processes and disease progression are increasingly characterized with pharmacometric models. However, modelling options for discrete-type responses remain limited, although these response variables are commonly encountered clinical endpoints. Types of data defined as discrete data are generally ordinal, e.g. symptom severity, count, i.e. event frequency, and time-to-event, i.e. event occurrence. Underlying assumptions accompanying discrete data models need investigation and possibly adaptations in order to expand their use. Moreover, because these models are highly non-linear, estimation with linearization-based maximum likelihood methods may be biased. The aim of this thesis was to explore pharmacometric methods and novel models for discrete data through (i) the investigation of benefits of treating discrete data with different modelling approaches, (ii) evaluations of the performance of several estimation methods for discrete models, and (iii) the development of novel models for the handling of complex discrete data recorded during (pre-)clinical studies. A simulation study indicated that approaches such as a truncated Poisson model and a logit-transformed continuous model were adequate for treating ordinal data ranked on a 0-10 scale. Features that handled serial correlation and underdispersion were developed for the models to subsequently fit real pain scores. The performance of nine estimation methods was studied for dose-response continuous models. Other types of serially correlated count models were studied for the analysis of overdispersed data represented by the number of epilepsy seizures per day. For these types of models, the commonly used Laplace estimation method presented a bias, whereas the adaptive Gaussian quadrature method did not. Count models were also compared to repeated time-to-event models when the exact time of gastroesophageal symptom occurrence was known. Two new model structures handling repeated time-to-categorical events, i.e. events with an ordinal severity aspect, were introduced. Laplace and two expectation-maximisation estimation methods were found to be performing well for frequent repeated time-to-event models. In conclusion, this thesis presents approaches, estimation methods, and diagnostics adapted for treating discrete data. Novel models and diagnostics were developed when lacking and applied to biological observations.
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Mueller, Ralph. "Specification and Automatic Generation of Simulation Models with Applications in Semiconductor Manufacturing." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16147.
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The creation of large-scale simulation models is a difficult and time-consuming task. Yet simulation is one of the techniques most frequently used by practitioners in Operations Research and Industrial Engineering, as it is less limited by modeling assumptions than many analytical methods. The effective generation of simulation models is an important challenge. Due to the rapid increase in computing power, it is possible to simulate significantly larger systems than in the past. However, the verification and validation of these large-scale simulations is typically a very challenging task.
This thesis introduces a simulation framework that can generate a large variety of manufacturing simulation models. These models have to be described with a simulation data specification. This specification is then used to generate a simulation model which is described as a Petri net. This approach reduces the effort of model verification.
The proposed Petri net data structure has extensions for time and token priorities. Since it builds on existing theory for classical Petri nets, it is possible to make certain assertions about the behavior of the generated simulation model.
The elements of the proposed framework and the simulation execution mechanism are described in detail. Measures of complexity for simulation models that are built with the framework are also developed.
The applicability of the framework to real-world systems is demonstrated by means of a semiconductor manufacturing system simulation model.
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Arata, Wilson Munemassa. "Representação computacional de Sistemas a Eventos Discretos considerando a heterogeneidade e a integração dos modelos." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-09012006-105116/.
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Para estudar os chamados Sistemas a Eventos Discretos (SEDs), existe uma variedade de tipos de modelos, mas, entretanto, estes acabam tratando de aspectos sistêmicos específicos, da mesma forma que suas análises. Para ter uma visão mais completa de tais sistemas, é importante lidar com esses tipos heterogêneos de modelos e com as técnicas desenvolvidas para sua integração. Este trabalho foca na questão da representação computacional desses modelos e de como adequá-la à heterogeneidade e à integração desses modelos. No que diz respeito à heterogeneidade, é proposta uma descrição matemática das ferramentas computacionais de modelagem e análise de SEDs, com a qual se pode visualizar as interações entre a heterogeneidade dos modelos, o poder de expressão e de montagem de representações de modelos e os processamentos de análise. Baseado nesta descrição e considerando-se os diversos custos envolvidos, diversas características são analisadas, de modo que, ao final, determina-se quais aquelas que são favoráveis para o caso de heterogeneidade e integração de modelos. Porém, existe ainda a heterogeneidade inerente aos modelos que não pode ser eliminada e isso constitui um obstáculo no caso de ter de lidar com modelos heterogêneos, representando um custo adicional para o aproveitamento de sua integração. Em relação a este caso, a proposta deste trabalho é de representar as informações semânticas associadas aos diversos modelos como forma de obter uma descrição integrada da dinâmica sendo modelada. Desde que as condições de consistência dessas representações sejam atendidas, com tal descrição, é possível visualizar os relacionamentos entre os diversos modelos e realizar análises sem ter que lidar com as diferenças estruturais dos vários tipos de modelos. Além disso, tais informações são úteis na construção de representações de modelos de SEDs e no estabelecimento de relacionamentos entre modelos de dinâmicas diferentes. Dessa discussão fica claro que tais representações têm papel fundamental para um efetivo processamento computacional das informações que a modelagem e análise oferecem.Discrete Event Dynamic Systems (DEDS) can be approached by a variety of types of models, but each one deals with specific system aspects and whose analysis provides a limited set of information.For a more comprehensive understanding of DEDS, it is important to deal with these heterogeneous types of models and with techniques that integrate them. This work focus on the issue of computational representation of such models and of how to handle their heterogeneity and integration. In the case of the heterogeneity, a mathematical description of computational tools for modeling and analysis of DEDS is developed, based on which it is possible to visualize the interactions involving model heterogeneity, the capability of expressing and building model representations, and analysis processing. Based on this description and considering the various costs involved in the adoption of such tools, several characteristics are assessed, so that guidelines for configurations favourable to heterogeneity and integration of models are established. However, handling the heterogeneity of models does not eliminate it, remaining as a major obstacle when dealing with models of different types, representing an additional cost in their integration. Related with this issue, an approach based on the representation of the semantic information associated to the models as a means to generate an integrated description of the dynamics being modeled is introduced. As long as this representation presents consistency features, it is possible to visualize the various relationships between models and execute analysis without dealing, directly, with the structural differences observed in models of different types. Besides, the information being represented is helpful in the construction of representations of DEDS models and in establishing relationships between models referring to different dynamics. From all this discussion, it is clear that the proposed computational representation of information plays a fundamental role in the effective processing of the information provided by modeling and analysis.
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Sotiropoulos, Pesiridis Konstantinos. "Parallel Simulation of SystemC Loosely-Timed Transaction Level Models." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-227806.
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Parallelizing the development cycles of hardware and software is becoming the industry’s norm for reducing time to market for electronic devices. In the absence of hardware, software development is based on a virtual platform; a fully functional software model of a system under development, able to execute unmodified code. A Transaction Level Model, expressed with the SystemC TLM 2.0 language, is one of the many possible ways for constructing a virtual platform. Under SystemC’s simulation engine, hardware and software is being co-simulated. However, the sequential nature of the reference implementation of the SystemC’s simulation kernel, is a limiting factor. Poor simulation performance often constrains the scope and depth of the design decisions that can be evaluated. It is the main objective of this thesis’ project to demonstrate the feasibility of parallelizing the co-simulation of hardware and software using Transaction Level Models, outside SystemC’s reference simulation environment. The major obstacle identified is the preservation of causal relations between simulation events. The solution is obtained by using the process synchronization mechanism known as the Chandy/Misra/Bryantt algorithm. To demonstrate our approach and evaluate under which conditions a speedup can be achieved, we use the model of a cache-coherent, symmetric multiprocessor executing a synthetic application. Two versions of the model are used for the comparison; the parallel version, based on the Message Passing Interface 3.0, which incorporates the synchronization algorithm and an equivalent sequential model based on SystemC TLM 2.0. Our results indicate that by adjusting the parameters of the synthetic application, a certain threshold is reached, above which a significant speedup against the sequential SystemC simulation is observed. Although performed manually, the transformation of a SystemC TLM 2.0 model into a parallel MPI application is deemed feasible.
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Rea, David J. "Surviving the Surge: Real-time Analytics in the Emergency Department." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1624914727282486.
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Patel, Hiren Dhanji. "HEMLOCK: HEterogeneous ModeL Of Computation Kernel for SystemC." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/9632.
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As SystemC gains popularity as a System Level Design Language (SLDL) for System-On-Chip (SOC) designs, heterogeneous modelling and efficient simulation become increasingly important. The key in making an SLDL heterogeneous is the facility to express different Models Of Computation (MOC). Currently, all SystemC models employ a Discrete-Event simulation kernel making it difficult to express most MOCs without specific designer guidelines. This often makes it unnatural to express different MOCs in SystemC. For the simulation framework, this sometimes results in unnecessary delta cycles for models away from the Discrete-Event MOC, hindering the simulation performance of the model. Our goal is to extend SystemC's simulation framework to allow for better modelling expressiveness and efficiency for the Synchronous Data Flow (SDF) MOC. The SDF MOC follows a paradigm where the production and consumption rates of data by a function block are known a priori. These systems are common in Digital Signal Processing applications where relative sample rates are specified for every component. Knowledge of these rates enables the use of static scheduling. When compared to dynamic scheduling of SDF models, we experience a noticeable improvement in simulation efficiency. We implement an extension to the SystemC kernel that exploits such static scheduling for SDF models and propose designer style guidelines for modelers to use this extension. The modelling paradigm becomes more natural to SDF which results to better simulation efficiency. We will distribute our implementation to the SystemC community to demonstrate that SystemC can be a heterogeneous SLDL.Master of Science
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García, Martín Rafael Adrián, and Sánchez José Manuel Gaspar. "Screening for important factors in large-scale simulation models: some industrial experiments." Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-11484.
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The present project discusses the application of screening techniques in large-scale simulation models with the purpose of determining whether this kind of procedures could be a substitute for or a complement to simulation-based optimization for bottleneck identification and improvement. Based on sensitivity analysis, the screening techniques consist in finding the most important factors in simulation models where there are many factors, in which presumably only a few or some of these factors are important. The screening technique selected to be studied in this project is Sequential Bifurcation. This method consists in grouping the potentially important factors, dividing the groups continuously depending on the response generated from the model of the system under study. The results confirm that the application of the Sequential Bifurcation method can considerably reduce the simulation time because of the number of simulations needed, which decreased compared with the optimization study. Furthermore, by introducing two-factor interactions in the metamodel, the results are more accurate and may even be as accurate as the results from optimization. On the other hand, it has been found that the application of Sequential Bifurcation could become a problem in terms of accuracy when there are many storage buffers in the decision variables list. Due to all of these reasons, the screening techniques cannot be a complete alternative to simulation-based optimization. However, as shown in some initial results, the combination of these two methods could yield a promising roadmap for future research, which is highly recommended by the authors of this project.
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Azasoo, Makafui. "Data Science and the Ice-Cream Vendor Problem." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3957.
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Newsvendor problems in Operations Research predict the optimal inventory levels necessary to meet uncertain demands. This thesis examines an extended version of a single period multi-product newsvendor problem known as the ice cream vendor problem. In the ice cream vendor problem, there are two products – ice cream and hot chocolate – which may be substituted for one another if the outside temperature is no too hot or not too cold. In particular, the ice cream vendor problem is a data-driven extension of the conventional newsvendor problem which does not require the assumption of a specific demand distribution, thus allowing the demand for ice cream and hot chocolate respectively to be temperature dependent. Using Discrete Event Simulation, we first simulate a real-world scenario of an ice cream vendor problem via a demand whose expected value is a function of temperature. A sample average approximation technique is subsequently used to transform the stochastic newsvendor program into a feature-driven linear program based on the exogenous factors of probability of rainfall and temperature. The resulting problem is a multi-product newsvendor linear program with L1-regularization. The solution to this problem yields the expected cost to the ice cream vendor as well as the optimal order quantities for ice cream and hot chocolate, respectively.
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Allamkota, Vijayaprasad Venkhat Abhishek. "Discrete Event Simulation of Cabinet Assembly at ABB Robotics and Discrete Automation." Thesis, KTH, Industriell produktion, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302482.
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Planning of the optimised production system is an intricate task. The reason behind this is changing demand, variations, and other disturbances. The main purpose of this study the current performance in the existing production system and provide recommendations for optimising the production in order to accommodate a new product. Since, the addition of new products may lead to bottlenecks in the flow which affects the output performance. The bottlenecks would lead to ineffective results, while tying up the capital in the production downstream as inventory gets stagnated in the assembly lines. The performance evaluation is a tedious process however, the study probes into the use of flow simulation tool to analyse the production performance. In this thesis work, Discrete Event Simulation (DES) is utilised as a tool to examine the performance of the production systems and to determine the cost consuming areas. To achieve that, the production system is replicated as a functional model into the DES system with the appropriate logics and parameters, with the thorough understanding of the existing workflows. To supplement it, the data from the orders, resources, and parts are charted.In the later part, production flow is analysed with the additions of determined improvisations to understand the impact on the output. Later, investigations are performed to identify the challenges and applicable changes required to meet future output. As an outcome, the production system is restructured and optimised, thus getting an overview of the future production set up as a digital factory layout.Planering av det optimerade produktionssystemet är en invecklad uppgift. Orsaken bakom detta är förändrad efterfrågan, variationer och andra störningar. Huvudsyftet med denna studie är den nuvarande prestandan i det befintliga produktionssystemet och ger rekommendationer för att optimera produktionen för att rymma en ny produkt. Eftersom tillägg av nya produkter kan leda till flaskhalsar i flödet som påverkar uteffekten. Flaskhalsarna skulle leda till ineffektiva resultat, samtidigt som kapitalet i produktionen binds nedströms när lagret stagnerar i löpande band. Prestationsutvärderingen är en tråkig process, men studien undersöker användningen av flödessimuleringsverktyg för att analysera produktionsprestanda. I detta avhandlingsarbete används Discrete Event Simulation (DES) som ett verktyg för att undersöka produktionssystemens prestanda och bestämma de kostnadskrävande områdena. För att uppnå det replikeras produktionssystemet som en funktionell modell i DES -systemet med lämpliga logiker och parametrar, med en grundlig förståelse av de befintliga arbetsflödena. För att komplettera det kartläggs data från order, resurser och delar. I den senare delen analyseras produktionsflödet med tillägg av bestämda improvisationer för att förstå effekten på produktionen. Senare utförs undersökningar för att identifiera de utmaningar och tillämpliga förändringar som krävs för att möta framtida produktion. Som ett resultat omstruktureras och optimeras produktionssystemet och får därmed en överblick över den framtida produktionsuppsättningen som en digital fabrikslayout.
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Svensson, Harari Natalia. "Manufacturing systems model interoperability in discrete event simulation." Thesis, KTH, Industriell produktion, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91591.
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The use of simulation has been said to be a useful tool to analyze manufacturing systems, Discrete Event Simulation - DES for instance under the occurrence of different events. Information management in Manufacturing Systems is an important issue and so it is insimulation studies because some of the difficulties in building, reusing and integratingsimulation models with other applications used in manufacturing systems are related withthe data. In this context different efforts have been made to facilitate the use of simulationand overcome interoperability problems through improving the information management,one of this is the Core Manufacturing Simulation Data Information Model - CMSDIMdeveloped by The National Institute of Standards and Technology - NIST. The objective of this thesis is to contribute to the use of the CMSDIM in ExtendSim V8. A method to import databases structured based on the CMSDIM into the Simulation softwareExtendSim V8 is developed and applied in a case study in a production line of SCANIA.
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Alghwiri, Alaa Ali. "Parking System Analysis Using Discrete Event Simulation." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1405364577.
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Huang, Chien-Chung. "Discrete event system modeling using SysML and model transformation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45830.
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The objective of this dissertation is to introduce a unified framework for modeling and simulating discrete event logistics systems (DELS) by using a formal language, the System Modeling Language (SysML), for conceptual modeling and a corresponding methodology for translating the conceptual model into a simulation model. There are three parts in this research: plant modeling, control modeling, and simulation generation.
Part 1:Plant Modeling of Discrete Event Logistics Systems.
Contemporary DELS are complex and challenging to design. One challenge is to describe the system in a formal language. We propose a unified framework for modeling DELS using SysML. A SysML subset for plant modeling is identified in this research. We show that any system can be described by using the proposed subset if the system can be modeled using finite state machines or finite state automata. Furthermore, the system modeled by the proposed subset can avoid the state explosion problem, i.e., the number of the system states grows exponentially when the number of the components increases. We also compare this approach to other existing modeling languages.
Part 2:Control Modeling of Discrete Event Logistics Systems.
The development of contemporary manufacturing control systems is an extremely complex process. One approach for modeling control systems uses activity diagrams from SysML, providing a standard object-oriented graphical notation and enhancing reusability. However, SysML activity diagrams do not directly support the kind of analysis needed to verify the control model, such as might be available with a Petri net (PN) model. We show that a control model represented by UML/SysML activity diagrams can be transformed into an equivalent PN, so the analysis capability of PN can be used and the results applied back in the activity diagram model. We define a formal mathematical notation for activity diagrams, show the mapping rules between PN and activity diagrams, and propose a formal transformation algorithm.
Part 3:Discrete Event Simulation Generation.
The challenge of cost-effectively creating discrete event simulation models is well-known. One approach to alleviate this issue is to describe a system using a descriptive modeling language and then transform the system model to a simulation model. Some researchers have tried to realize this idea using a transformation script. However, most of the transformation approaches depend on a domain specific language, so extending the domain specific language may require modifying the transformation script. We propose a transformation approach from SysML to a simulation language. We show that a transformation script can be independent of the associated domain specific language if the domain specific language is implemented as domain libraries using a proposed SysML subset. In this case, both the domain library and the system model can be transformed to a target simulation language. We demonstrate a proof-of-concept example using AnyLogic as the target simulation language.
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Marin, Mauricio. "Discrete-event simulation on the bulk-synchronous parallel model." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298626.
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Qianwen, Xu. "OUTPATIENT PHYSICIAN OFFICE STAFFING MODEL USING DISCRETE EVENT SIMULATION." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1466970867.
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Boussif, Abderraouf. "Contributions to model-based diagnosis of discrete-event systems." Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10144/document.
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L’objet de cette thèse porte sur le diagnostic des systèmes à évènements discrets modélisés par des automates à états finis, avec une extension vers les réseaux de Petri bornés et étiquetés. Les différentes contributions de ce travail peuvent être présentées selon deux volets, au regard des approches pionnières existantes dans la littérature: le diagnostic à base de diagnostiqueur, et le diagnostic à base de twin-plant.Sur le premier volet, i.e., le diagnostic à base de diagnostiqueur, nous proposons :- Une variante du diagnostiqueur avec une nouvelle structure qui nous permet de : (i) formuler une nouvelle condition nécessaire et suffisante pour l'analyse de la diagnosticabilité des fautes permanentes, (ii) développer une procédure systématique pour l'analyse de la diagnosticabilité (iii) établir un algorithme à-la-volée pour construire le diagnostiqueur et analyser la diagnosticabilité en parallèle.- Une extension de notre diagnostiqueur pour traiter des fautes intermittentes. - Une version hybride de notre diagnostiqueur, pour analyser la diagnosticabilité des réseaux de Petri bornés et étiquetés.Sur le deuxième volet, i.e., le diagnostic à base de twin-plant, nous proposons de nouvelles techniques pour l’analyse de diagnosticabilité de fautes permanentes et intermittentes dans le cadre de vérification par model-checking. Ainsi, la performance des techniques de model-checking et des outils associés peut être exploitée pour traiter des questions de diagnosticThis PhD thesis deals with fault diagnosis of discrete-event systems modeled as finite state automata with some extensions to bounded Petri net models. The developed contributions can be classified regarding two pioneering approaches from the literature: the diagnoser-based technique and the twin-plant based technique. Regarding the diagnoser-based technique, we propose a new diagnoser variant with some interesting features that allow us to reformulate a necessary and sufficient condition for diagnosability of permanent faults and propose a systematic procedure for checking such a condition without building any intermediate model. An on-the-fly algorithm, for simultaneously constructing the diagnoser and verifying diagnosability is then developed. The established diagnoser is then extended to deal with fault diagnosis of intermittent faults. A Hybrid version (in the sense of combining enumerative and symbolic representations) of our diagnoser is also established in order to deal with fault diagnosis of labeled bounded Petri nets. The developed approaches are implemented in dedicated tools and evaluated through benchmarks with respect to the reference approaches in the domain.Regarding twin-plant based technique, our contribution consists in elaborating a model-checking framework that extends the Cimatti’s work for the actual verification of various diagnosability concepts pertaining to permanent and intermittent failures based on the twin-plant structure. The main idea is to reformulate and express the diagnosability issues as temporal logics and then to tackle them using the model-checking engines
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Wang, Yan. "An integrative process mining approach to mine discrete event simulation model from event data." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0183/document.
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L'inférence d’un système, par la reconstruction de la structure à partir de l’analyse de son comportement, est reconnue comme un problème critique. Dans la théorie des systèmes, la structure et le comportement se situent aux extrémités de la hiérarchie qui définit la connaissance du système. L'inférence d’un système peut être également considérée comme l’escalade de la hiérarchie depuis la connaissance de bas niveau vers la connaissance de plus haut niveau. Ceci n'est possible que sous des conditions maitrisées et justifiées. Dans cette thèse, une nouvelle méthode d'inférence de système est proposée. La méthode proposée étend la technique Process Mining pour extraire des connaissances depuis les données des événements du système. Les aspects de modularité, de fréquence et de synchronisation peuvent être extraits des données. Ils sont intégrés ensemble pour construire un modèle Fuzzy-Discrete Event System Specification (Fuzzy-DEVS). La méthode proposée, également appelée méthode D2FD (Data to Fuzzy-DEVS), comprend trois étapes: (1) l’extraction depuis des journaux d’évènements (registres) obtenus à partir des données générées par le système en utilisant une approche conceptuelle; (2) la découverte d'un système de transition, en utilisant des techniques de découverte de processus; (3) l'intégration de méthodes Fuzzy pour générer automatiquement un modèle Fuzzy-DEVS à partir du système de transition. La dernière étape est de l’implémenter cette contribution en tant que plugin dans l'environnement Process Mining Framework (ProM). Afin de valider les modèles construits, une approximation de modèle basée sur le morphisme et une méthode prédictive intégrée à Granger Causality sont proposées. Deux études de cas sont présentées dans lesquelles le modèle Fuzzy-DEVS est déduit à partir de données réelles, où l'outil SimStudio est utilisé pour sa simulation. Les modèles ainsi construits et les résultats de simulation sont validés par comparaison à d'autres modèlesSystem inference, i.e., the building of system structure from system behavior, is widely recognized as a critical challenging issue. In System Theory, structure and behavior are at the extreme sides of the hierarchy that defines knowledge about the system. System inference is known as climbing the hierarchy from less to more knowledge. In addition, it is possible only under justifying conditions. In this thesis, a new system inference method is proposed. The proposed method extends the process mining technique to extract knowledge from event data and to represent complex systems. The modularity, frequency and timing aspects can be extracted from the data. They are integrated together to construct the Fuzzy Discrete Event System Specification (Fuzzy-DEVS) model. The proposed method is also called D2FD (Data to Fuzzy-DEVS) method, and consists of three stages: (1) extraction of event logs from event data by using the conceptual structure; (2) discovery of a transition system, using process discovery techniques; (3) integration of fuzzy methods to automatically generate a Fuzzy-DEVS model from the transition system. The last stage is implemented as a plugin in the Process Mining Framework (ProM) environment. In order to validate constructed models, morphism-based model approximation and predictive method integrated with Granger Causality are proposed. Two case studies are presented in which Fuzzy-DEVS model is inferred from real life data, and the SimStudio tool is used for its simulation. The constructed models and simulation results are validated by comparing to other models
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Puthoff, Frederick Anthony. "The model analyzer : prototyping the diagnosis of discrete-event simulation model specifications /." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10102009-020137/.
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Cosme, Maximilien. "Modélisation qualitative à événements discrets des dynamiques d'écosystèmes." Thesis, Université de Montpellier (2022-….), 2022. http://www.theses.fr/2022UMONG013.
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Les écosystèmes se déploient dans le temps au rythme des événements successifs qui modifient ses composants. Ces événements, qu'ils soient aléatoires ou non, sont les phénomènes par lesquels les écosystèmes s'assemblent et se désassemblent. Chaque séquence d'états – ou trajectoire – est une histoire possible de l'écosystème. Mais si ces événements, ou leur ordre, avait été différent, l'état futur aurait pu l'être également. Or, l'ordre des événements, du fait des limites de notre connaissance, est souvent incertain. Lorsque cette incertitude est grande, il est donc raisonnable de concevoir la dynamique de l'écosystème comme un ensemble de trajectoires possibles. Si l'ensemble des trajectoires possibles était connu, il pourrait notamment se révéler utile pour savoir si un état souhaitable est atteignable, et si oui, par quel(s) chemin(s). Dans cette thèse, nous proposons une approche de modélisation nommée EDEN (pour Ecological Discrete-Event Networks) permettant de répondre à cette question. Elle se présente sous la forme d'un formalisme dont les variables sont qualitatives et dont les valeurs sont modifiées par des règles "si-alors" représentant les événements de l'écosystème. Celles-ci sont tirées une à une, de façon non-déterministe et sans aucune probabilité. Cette approche non-déterministe et non-probabiliste a donc été qualifiée de possibiliste. Les dynamiques se présentent alors sous la forme d'un graphe états-transitions dont on peut vérifier l'existence de propriétés dynamiques (comme le fait qu'une espèce puisse persister).Dans un premier temps, une brève histoire de la modélisation en écologie des écosystèmes est présentée, avec une attention particulière aux approches de modélisation qualitatives, dont l'approche EDEN fait partie. Prenant appui sur les limites des approches existantes pour répondre à certaines questions, nous proposons l'approche EDEN et justifions la pertinence de ses propriétés par des exemples simples.Dans un second temps, l'approche EDEN est illustrée sur des écosystèmes semi-arides d'Afrique de l'Est et de l'Ouest dans le but de savoir si certains états d'intérêt sont atteignables (comme le maintien de la végétation en savane, ou de la fertilité dans un agroécosystème). Pour ce faire, nous présentons et utilisons des outils jusqu'ici peu utilisés en écologie, comme les summary graphs et les logiques temporelles. Pour un scénario donné, ces outils rendent possible de définir (1) les transitions possibles entre les états d'intérêt, (2) les conditions dans lesquelles elles peuvent advenir et (3) les événements responsables de ces transitions. En Afrique de l'Est, l'approche EDEN a permis de déterminer les effets à long terme sur la végétation et les activités humaines d'une réduction/accroissement de la disponibilité en eau de surface, indiquant une forte influence indirecte de cette dernière sur la végétation ligneuse. En Afrique de l'Ouest, en utilisant EDEN, il a été possible de déterminer les conditions permettant à de petits producteurs du sud-ouest du Burkina Faso de développer un agropastoralisme persistant, ainsi que les événements nécessaires pour atteindre un tel état.Nous discutons enfin des apports de l'ensemble des modèles EDEN à divers champs de l'écologie, ainsi que des améliorations possibles et des ponts à dresser entre l'écologie, la biologie des systèmes et l'informatique théoriqueEcosystems unfold over time in response to successive events that modify their components. These events, whether random or not, are the phenomena by which ecosystems assemble and disassemble. Each sequence of states - or trajectory - is a possible history of the ecosystem. Yet, if these events, or their order, had been different, the future state could have been different. However, the order of events, due to the limits of our knowledge, is often uncertain. When this uncertainty is important, it is therefore reasonable to conceive the dynamics of the ecosystem as a set of possible trajectories. If the set of possible trajectories were known, it could be useful to know if a desirable state is attainable, and if so, by which path(s).In this thesis, we propose a modelling approach named EDEN (for Ecological Discrete-Event Networks) to answer this question. It is presented in the form of a formalism whose variables are qualitative and whose values are modified by "if-then" rules representing the events of the ecosystem. These rules are executed one by one, in a non-deterministic way and without any probability. This non-deterministic and non-probabilistic approach has therefore been called possibilistic. The dynamics are then presented in the form of a state-transition graph whose dynamic properties (such as the fact that a species can persist) can be verified.First, a brief history of dynamical modelling in ecosystem ecology is presented, with a particular focus on qualitative modelling approaches, to which EDEN belongs to. Based on the limitations of existing approaches to answer certain questions, we propose the EDEN approach and justify the relevance of its properties with simple examples.Then, the EDEN approach is illustrated on semi-arid ecosystems in East and West Africa in order to know if certain states of interest are reachable (such as the maintenance of vegetation in savanna, or soil fertility in an agroecosystem). To do this, we present and use tools that have not been used much in ecology until now, such as summary graphs and temporal logics. For a given scenario, these tools enable to define (1) the possible transitions between the states of interest, (2) the conditions under which they can occur and (3) the events responsible for these transitions. In East Africa, the EDEN approach was able to determine the long-term effects on vegetation and human activities of reduced/increased surface water availability, indicating a strong indirect influence of the latter on woody vegetation. In West Africa, using EDEN, it was possible to determine the conditions that allowed small-scale producers in southwestern Burkina Faso to develop persistent agropastoralism, as well as the events necessary to achieve such a state.Finally, we discuss the contributions of the EDEN set of models to various fields of ecology, as well as possible improvements and bridges to be built between ecology, systems biology and theoretical computer science
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Wu, Tai-Chi. "Definition, analysis, and an approach for discrete-event simulation model interoperability." Diss., Mississippi State : Mississippi State University, 2005. http://sun.library.msstate.edu/ETD-db/ETD-browse/browse.
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Smith, Simon D. "Productivity estimation of earthmoving operations using a discrete-event simulation model." Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/12143.
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The earthmoving industry in the UK is described with reference to the major changes in emphasis over the past few decades. The sites that were chosen for study are described and the method of data collection outlined. A determinate model is developed. This is solved using a spreadsheet and the term match factor, indicating the efficiency of an earthmoving operation, is introduced. The disadvantages of the determinate model are discussed with the main conclusion that the variability in the earthmoving plant's working rates means that the production cannot be calculated accurately by determinate methods. A model is then developed based on the discrete-event models used to evaluate queuing systems. This model was initially tested on a computer spreadsheet but a dedicated program, in C, was later written. Discrete-event simulation requires the generation of random numbers and emphasis is placed on the determination of the probability distributions that accurately represent the real distributions of plant cycle times. A three stage validation process was used which involved both the acceptance from 'experts' of the modelled system (which was obtained both in the UK and the United States) and also the ability of the model to determine accurately the production of observed operations. The simulation model could then, once validated, be used as an experimental platform. Experiments on actual operations have indicated which of the input factors to an operation the output is most sensitive to. They have shown that the correct number of trucks and maximisation of the loader working rate is essential of efficient earthmoving.
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Huang, Zhongdong. "RULES BASED MODELING OF DISCRETE EVENT SYSTEMS WITH FAULTS AND THEIR DIAGNOSIS." UKnowledge, 2003. http://uknowledge.uky.edu/gradschool_diss/340.
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Failure diagnosis in large and complex systems is a critical task. In the realm of discrete event systems, Sampath et al. proposed a language based failure diagnosis approach. They introduced the diagnosability for discrete event systems and gave a method for testing the diagnosability by first constructing a diagnoser for the system. The complexity of this method of testing diagnosability is exponential in the number of states of the system and doubly exponential in the number of failure types. In this thesis, we give an algorithm for testing diagnosability that does not construct a diagnoser for the system, and its complexity is of 4th order in the number of states of the system and linear in the number of the failure types. In this dissertation we also study diagnosis of discrete event systems (DESs) modeled in the rule-based modeling formalism introduced in [12] to model failure-prone systems. The results have been represented in [43]. An attractive feature of rule-based model is it's compactness (size is polynomial in number of signals). A motivation for the work presented is to develop failure diagnosis techniques that are able to exploit this compactness. In this regard, we develop symbolic techniques for testing diagnosability and computing a diagnoser. Diagnosability test is shown to be an instance of 1st order temporal logic model-checking. An on-line algorithm for diagnosersynthesis is obtained by using predicates and predicate transformers. We demonstrate our approach by applying it to modeling and diagnosis of a part of the assembly-line. When the system is found to be not diagnosable, we use sensor refinement and sensor augmentation to make the system diagnosable. In this dissertation, a controller is also extracted from the maximally permissive supervisor for the purpose of implementing the control by selecting, when possible, only one controllable event from among the ones allowed by the supervisor for the assembly line in automaton models.
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Sprock, Timothy A. "A metamodel of operational control for discrete event logistics systems." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54946.
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Discrete Event Logistics Systems (DELS) are a class of dynamic systems that are defined by the transformation of discrete flows through a network of interconnected subsystems. The DELS domain includes systems such as supply chains, manufacturing systems, transportation networks, warehouses, and health care delivery systems. Advancements in computer integrated manufacturing and intelligent devices have spurred a revolution in manufacturing. These smart manufacturing systems utilize technical interoperability and plant-wide integration at the device-level to drive production agility and efficiency. Extending these successes to enterprise-wide integration and decision-making will require the definitions of control and device to be extended and supported at the operations management and the business planning levels as well. In the future, smart operational control mechanisms must not only integrate real-time data from system operations, but also formulate and solve a wide variety of optimization analyses quickly and efficiently and then translate the results into executable commands. However in contemporary DELS practice, these optimization analyses, and analyses in general, are often purpose-built to answer specific questions, with an implicit system model and many possible analysis implementations depending on the question, the instance data, and the solver. Also because of the semantic gap between operations research analysis models such as job-shop scheduling algorithms and IT-based models such as MES, there is little integration between control analysis methods and control execution tools. Automated and cost-effective access to multiple analyses from a single conceptual model of the target system would broaden the usage and implementation of analysis-based decision support and system optimization. The fundamental contribution of this dissertation is concerned with interoperability and bridging the gap between operations research analysis models and practical applications of the results. This dissertation closes this gap by constructing a standard domain-specific language, standard problem definitions, and a standard analysis methodology to answer the control questions and execute the prescribed control actions. The domain specific language meets a broader requirement for facilitating interoperability for DELS, including system integration, plug-and-play analysis methods and tools, and system design methodologies. The domain-specific language formalizes a recurring product, process, resource, and facility description of the DELS domain. It provides a common language to discuss our systems, including the questions that we want to ask about our systems, the problems that we need to solve in order to answer those questions, and the mechanisms to deploy the solution.
A canonical set of control questions defines the comprehensive functional specification of all the decision-making mechanisms that a controller needs to be able to provide; i.e. a model of analysis models or a metamodel of operational control. These questions refine the interoperability mechanism between system and analysis models by mapping classes of control analysis models to implementation and execution mechanisms in the system model. A standard representation of each class of control problems is only a partial solution to fully addressing operational control. The final contribution of this dissertation constructs a round-trip analysis methodology that completes the bridge between operations research analysis models and deployable control mechanisms. This contribution formalizes an analysis pathway, from formulating an analysis model to executing a control action, that is grounded in a more fundamental insight into how analysis methods are executed to support operational control decision-making.
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Stoffers, Mirko [Verfasser]. "Automated Optimization of Discrete Event Simulations without Knowing the Model / Mirko Stoffers." Düren : Shaker, 2019. http://d-nb.info/1200808460/34.
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Batarseh, Ola. "AN INTERVAL BASED APPROACH TO MODEL INPUT UNCERTAINTY IN DISCRETE-EVENT SIMULATION." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2540.
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The objective of this research is to increase the robustness of discrete-event simulation (DES) when input uncertainties associated models and parameters are present. Input uncertainties in simulation have different sources, including lack of data, conflicting information and beliefs, lack of introspection, measurement errors, and lack of information about dependency. A reliable solution is obtained from a simulation mechanism that accounts for these uncertainty components in simulation. An interval-based simulation (IBS) mechanism based on imprecise probabilities is proposed, where the statistical distribution parameters in simulation are intervals instead of precise real numbers. This approach incorporates variability and uncertainty in systems. In this research, a standard procedure to estimate interval parameters of probability distributions is developed based on the measurement of simulation robustness. New mechanisms based on the inverse transform to generate interval random variates are proposed. A generic approach to specify the required replication length to achieve a desired level of robustness is derived. Furthermore, three simulation clock advancement approaches in the interval-based simulation are investigated. A library of Java-based IBS toolkits that simulates queueing systems is developed to demonstrate the new proposed reliable simulation. New interval statistics for interval data analysis are proposed to support decision making. To assess the performance of the IBS, we developed an interval-based metamodel for automated material handling systems, which generates interval performance measures that are more reliable and computationally more efficient than traditional DES simulation results.Ph.D.
Department of Industrial Engineering and Management Systems
Engineering and Computer Science
Industrial Engineering PhD
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McDonald, Anthony D. (Anthony Douglas). "A discrete event simulation model for unstructured supervisory control of unmanned vehicles." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59947.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 33).
Most current Unmanned Vehicle (UV) systems consist of teams of operators controlling a single UV. Technological advances will likely lead to the inversion of this ratio, and automation of low level tasking. These advances will also lead to a growth in UV use in large-scale applications such as urban search and rescue, which will require the use of both teams of operators and teams of UVs. This growth will in turn require research and development in the area of team supervisory control of multiple UVs. Human-in-the- loop experimentation is often used during this research but can be time consuming and expensive. The time and cost of experimentation can often be drastically reduced by using predictive models. However there is a lack of such models in the area of multiple-operator supervisory control of multiple- UVs. This problem is addressed in this thesis through the following method: First, current predictive models of human supervisory control of UVs are analyzed, and attributes of systems related to this modeling space are identified. Second, a queuing-based multiple-operator multiple-vehicle discrete event simulation model (MO-MUVDES) is developed which captures these attributes, including the ability to predict performance in situations with low observable exogenous event arrivals. MO-MUVDES also incorporates traditional system variables such as level of vehicle autonomy, vehicle and operator team structure, and operator switching strategy. The accuracy and robustness of the MO-MUVDES model were measured by a two-stage validation process using data from a human-in-the-loop supervisory control experiment, and a Monte Carlo simulation. The first stage of the validation process used data from the experiment as input for the MOMUVDES model which was then used to generate predictions of operator performance. In the second stage of validation, a sensitivity analysis was performed on the MO-MUVDES model. This validation process achieved confidence in the model's ability to predict operator performance and a measurement of the robustness of the model under varying input conditions. Additionally, the process indicated that discrete event simulation is an effective technique for modeling team supervisory control of UVs in a situation where exogenous event arrivals are not clearly observable. As a result, the MO-MUVDES model could be used to reduce development time for systems within its modeled space.
by Anthony D. McDonald.
S.B.
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Uslu, Berk. "Discrete Event Simulation Model for Project Selection Level Pavement Maintenance Policy Analysis." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/77014.
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A pavement investment and management process has a dynamic structure with cause and effect. Better investment decisions for maintenance will increase the condition of the flexible pavement and will end up with a better level of service. Therefore, better investments decisions on pavement maintenance will increase the economic growth and global competition for the area. However, improper allocation of money and resources would end up with further deteriorations of the facilities. So asset management encourages highway maintenance managers to spend their scarce budget for the maintenance that is really needed. A well-developed pavement management simulation model will allow highway maintenance managers to consider the impact of choosing one maintenance policy alternative versus another through what-if analysis and having informed decisions.
Discrete event simulation (DES) is an alternative method of analysis that offers numerous benefits in pavement management. Unlike the models currently in use, a decision support model created by utilizing the DES technique would allow fractionalizing the pavement in smaller proportions and simulating the policies on these smaller segments. Thus, users would see how their decisions would affect these specific segments in the highway network over a period of time. Furthermore, DES technique would better model the multiple resource requirements and dynamic complexity of pavement maintenance processes.
The purpose for this research is to create a decision support tool utilizing discrete event simulation technique where the highway maintenance managers can foresee the outcomes of their what-if scenarios on the specific segments and whole of the highway network evaluated. Thus, can be used for both project and network level decision support. The simulation can also be used as a guiding tool on when, where and why resources are needed on needs basis.
This research relies on the budget allocation results from the linear optimization model (LOM). This model is a tool that creates the optimized budget allocation scheme for a network fitting to a determined scenario. Thus by integrating the LOM and the DES model, the maintenance managers can acquire an optimized budget allocation for their district and evaluate the results in both network and project selection level. Maintenance managers can obtain the best budget allocation plan without performing the repetitive trial and error approach like the previous decision support tools.
There is a vast amount data in many varieties gathered as results from the simulation model. This fact alone demonstrates how powerful the discrete event simulation model is. By the nature of this simulation technique, the resources (highway segments, annual budget) can be traced throughout the simulation and this trait allows the design of the project selection level decision support system. By examining these reports, the maintenance managers can better observe how the scenarios evolve. Thus this tool helps the maintenance managers to have better decisions on the project selection level. The discrete event simulation model established in this research carries the project selection level pavement management from a position where maintenance managers should solely depend on their engineering judgment and experience to a position where maintenance managers can have more effective and justified plans since they can foresee the results of these decisions on the segments that are forming the network.
This simulation engine is created with the discrete event simulation language called STROBOSCOPE. The model consists of two parts which work like a lock and key mechanism. The first part of the model is the data feeding mechanism where information from any network is loaded. The second part is the generic engine which can evaluate any road network data it is fed. The purpose of segregating these two components of the model is to allow the user to evaluate any network regardless of length, number of segments or the location.Master of Science
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Lacy, Lee. "ITERCHANGING DISCRETE EVENT SIMULATIONPROCESS INTERACTION MODELSUSING THE WEB ONTOLOGY LANGUAGE - OWL." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3332.
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Discrete event simulation development requires significant investments in time and resources. Descriptions of discrete event simulation models are associated with world views, including the process interaction orientation. Historically, these models have been encoded using high-level programming languages or special purpose, typically vendor-specific, simulation languages. These approaches complicate simulation model reuse and interchange. The current document-centric World Wide Web is evolving into a Semantic Web that communicates information using ontologies. The Web Ontology Language – OWL, was used to encode a Process Interaction Modeling Ontology for Discrete Event Simulations (PIMODES). The PIMODES ontology was developed using ontology engineering processes. Software was developed to demonstrate the feasibility of interchanging models from commercial simulation packages using PIMODES as an intermediate representation. The purpose of PIMODES is to provide a vendor-neutral open representation to support model interchange. Model interchange enables reuse and provides an opportunity to improve simulation quality, reduce development costs, and reduce development times.Ph.D.
Department of Industrial Engineering and Management Systems
Engineering and Computer Science
Modeling and Simulation
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Gould, Geoffrey Michael. "Signaling and Communication in the Breeding Behavior of the Lesser Prairie-Chicken (Tympanuchus pallidicinctus)." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595442814242732.
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