Discrete event simulation is an important tool for modeling and analysis. Some of the simulation applications such as telecommunication network performance, VLSI logic circuits design, battlefield simulation, require enormous amount of computing resources. One way to satisfy this demand for computing power is to decompose the simulation system into several logical processes (Ip) and run them concurrently. In any parallel discrete event simulation (PDES) system, the events are ordered according to their time of occurrence. In order for the simulation to be correct, this ordering has to be preserved. There are three approaches to maintain this ordering. In a conservative system, no lp executes an event unless it is certain that all events with earlier time-stamps have been executed. Such systems are prone to deadlock. In an optimistic system on the other hand, simulation progresses disregarding this ordering and saves the system states regularly. Whenever a causality violation is detected, the system rolls back to a state saved earlier and restarts processing after correcting the error. There is another approach in which all the lps participate in the computation of a safe time-window and all events with time-stamps within this window are processed concurrently. In optimistic simulation systems, there is a global virtual time (GVT), which is the minimum of the time-stamps of all the events existing in the system. The system can not rollback to a state prior to GVT and hence all such states can be discarded. GVT is used for memory management, load balancing, termination detection and committing of events. However, GVT computation introduces additional overhead. In optimistic systems, large number of rollbacks can degrade the system performance considerably. We have studied the effect of load balancing in reducing the number of rollbacks in such systems. We have designed three load balancing algorithms and implemented two of them on a network of workstations. The other algorithm has been analyzed probabilistically. The reason for choosing network of workstations is their low cost and the availability of efficient message passing softwares like PVM and MPI. All of these load balancing algorithms piggyback on the existing GVT computation algorithms and try to balance the speed of simulation in different lps. We have also designed an optimal GVT computation algorithm for the hypercubes and studied its performance with respect to the other GVT computation algorithms by simulating a hypercube in our network cluster. We use the topological properties of a star network in order to design an algorithm for computing a safe time-window for parallel discrete event simulation. We have analyzed and simulated the behavior of an open queuing network resembling such an architecture. Our algorithm is also extended for hierarchical stars and for recursive window computation.

Dans cette thèse, nous nous intéressons à l'étude des courbes discrètes et ses applications en analyse d'images. Nous avons proposé une amélioration de l'estimation de courbure reposant sur le cercle circonscrit. Celle-ci repose sur la notion de segment flou maximal d'épaisseur [nu] et sur la décomposition d'une courbe discrète en sa séquence de segments flous maximaux. Par la suite, nousavons appliqué cette idée en 3D afin d'estimer la courbure et la torsion discrète en chaque point d'une courbe 3D. Au niveau de l'application, nous avons développé une méthode rapide et fiable pour détecter les points dominants dans une courbe 2D. Un point dominant est un point dont la courbure est localement maximale. Les points dominants jouent un rôle très important dans la reconnaissance de formes. Notre méthode utilise un paramètre qui est l'épaisseur des segments flous maximaux. Reposant sur cette nouvelle méthode de détection des points dominants, nous avons développé des méthodes sans paramètres de détection des points dominants. Celles-ci se basent sur une approche multi-épaisseur. D'autre part, nous nous intéressons particulièrement au cercles et arcs discrets. Une méthode linéaire a été développé pour reconnaître des cercles et arcs discrets. Puisnous avons fait évoluer cette méthode afin de travailler avec des courbes bruitées en utilisant une méthode de détection du bruit. Nous proposons aussi une mesure de circularité. Une méthode linéaire qui utilise cette mesure a été aussi développée pour mesurer la circularité des courbes fermées. Par ailleurs, nous avons proposé une méthode rapide pour décomposer des courbes discrètes en arcs et en segments de droite. / In this thesis, we are interested in the study of discrete curves and its applications in image analysis. We have proposed an amelioration of curvature estimation based on circumcircle. This method is based on the notion of blurred segment of width [nu] and on the decomposition of a curve into the sequence of maximal blurred segment of width [nu]. Afterwards, we have applied this idea in 3D to estimate the discrete curvature and torsion at each point of a 3D curve. Concerning the applications, we have developed a rapid et reliable method to detect dominant points of a 2D curve. A dominant point is a point whose the curvature value is locally maximum. The dominant points play an important role in pattern recognition. Our method uses a parameter: the width of maximal blurred segments. Based on this novel method of dominant point detection, we proposed free-parameter methods for polygonal representation. They are based on a multi-width approach. Otherwise, we are interested in discrete arcs and circles. A linear method has been proposed for the recognition of arcs and circles. We then develop a new method for segmentation of noisy curves into arcs based on a method of noise detection. We also proposed a linear method to measure the circularity of closed curves. In addition, we have proposed a robust method to decompose a curve into arcs and line segments

The fierce competition among the manufacturers all over the world as a result of globalisation and the dynamic atmosphere of the market has brought a new era to the production world. Shorter lead times, faster takt-times, variety of demand and products by customers, optimized inventory level, new rules and regulations legislated by governments and organizations plus efficiency of the supply chain are examples of challenges which urge companies to seek for any feasible tool which help can help to overcome the upcoming complex problems. Recent advancements in the IT world have caused emergence of contemporary methods and tools for companies to use when confronting intricate situations to be able to handle such incidents and stay competitive in the market. Today, more companies realize the significance of change in their production system. Discrete-event simulation is one of the virtual tools used more and more recently in different areas. It is undoubtedly one of the most functional tools which could be used for different purposes in such as: System learning System prediction Scenario planning   The application scope of discrete-event simulation is both in micro and macro levels as it can be used in a partial study of a specific process in a manufacturing company for optimization or in a higher level, to help a company to analyze its strategic plans by simulating them ahead of time. In the current study it has been tried to investigate the application and implementation of discrete-event simulation in production. For reaching that goal, the project has been divided into two main parts; first of all a discrete event simulation has been conducted regarding a real-world potential problem. Later, by gaining the experience from the first part plus doing research around discrete simulation, it has been tried to develop a framework for industrial companies to ease the use of discrete-event simulation project process in a standardized manner. A future prospective of the current project could be the implementation of the results and provided framework on further real-world cases and explore more innovative uses of discrete-event tool in industry. Obviously, discrete-event could be a great decision-making or analysis tool for production development if being used in the proper context. / Simulering är en verktyg  som möjliggör system analys billigt och lätt. När man ska simulera ett system så bygger man en model baserad på verklighet med en viss nivå of abstraktion, beroende på syftet av simuleringen. De företag som har komplicerade processer kan använda simulering som en beslutsstöd verktyg. Genom simulering av ett komplicerat system så kan man uppnå olika saker: Lära om systemet Förutsäga e systemets beteende Scenarioplanering När det gäller simulering så krävs två olika saker som har varit grunden för detta projektet; förmågor inom systemet som kan simuleras, kunskaper inom simuleringsteknik. Båda faktorer spelar stor roll för att ett simuleringprojekt blir framgångsrik. Simulering har bred applikation och kan användas i olika områden exempelvis flyg simulatorer mm. Produktion är ett område där finns potential av att utnyttja simulering framförallt ’discrete-event’ typ av simulering som för det mesta passar produktionsanalyser på grund av diskret natur av produktions verksamhet. Genom att simulera produktion eller tillverkningssystem kan man i en virtuell miljö prova kapacitet, flödet och mm. Detta projekt har haft som mål att skapa ett standardiserat arbetssätt för användning av simulering (med fokus på DES) i produktionsutveckling. Projektet har genomförts inom Volvo CE, i Härdverket i Eskilstuna. Dessutom, det beskriver om utmaningar som dyker upp när man utför ett simuleringsprojekt genom en analys av det genomförde projektet. / <p>The project has been done with cooperation of Volvo Construction Equipments</p>

Call number: LD2668 .T4 1961 H62

In a market environment that is subject to continuous changes, companies need to adapttheir production systems in order to maintain the competitive edge. Current literatureshows that with a successful production system design, higher levels of output, eciencyand quality can be achieved.However, designing a production system is done infrequently and therefore tends tolack experience. As a result, design decisions have to be made under uncertainty due toa lack of information, structure and knowledge. In fact, the success of a design process isdirectly linked to the level of uncertainty.The purpose of this thesis is to reduce uncertainty in production system design throughDiscrete Event Simulation before an assembly system is implemented. Therefore, a theoreticalstudy was carried out dening types and sources of uncertainty in productionsystem design. Parallel to the theoretical study, a case study in Volvo ConstructionEquipment Operations Hallsberg was conducted. Discrete Event Simulation was testedas a tool to reduce uncertainty in production system design.The analysis illustrates the observed sources of uncertainty in production systemdesign cover a process, organizational, corporate, market and cultural context.The relevant uncertainty types identied in the case study in Volvo ConstructionEquipment Operations Hallsberg were environmental, system, technical, structural,temporal, lack of knowledge and lack of information. The information providedby the Discrete Event Simulation in order to reduce uncertainty are in form ofKPIs, process structure and visualization. The provided information had a positiveimpact on the degree of technical uncertainties, the lack of knowledge and thelack of information. As a result, the level of uncertainty in the Volvo ConstructionEquipment Operations Hallsberg future line designing process was reduced.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Multiple discrete antennas distributed around the circumference of a large missile and driven by one transmitter are sometimes used to radiate telemetry omnidirectionally. But driving discrete antennas separated by several wavelengths around the missile body with a single transmitter can result in an antenna pattern with deep nulls in the roll plane. Varying the relative signal phase or amplitude among the signals driving the antennas as well as the polarization of the antennas can be used to change the nulls in an attempt to decrease the null depth. In this paper the effects of phase, amplitude, and polarization on the roll-plane pattern are examined and measurement data presented.

Solar power systems are becoming increasingly popular due to the fact that solar power can offer time and money saving solutions for off-grid and grid-connected homes, cabins, and businesses with clean and affordable energy. However, there are still significant opportunities to reduce the cost of solar power systems by optimizing system design. This paper presents a methodology for evaluating the lifecycle labor costs of solar power systems. This methodology can help optimize system designs relative to cost. It can also support solar power system selection decisions based on a holistic lifecycle view. The methodology accomplishes this by first presenting a method to evaluate the modularity of competing systems, or design variants. It then describes a method of gathering data and modeling the systems so that it can be communicated to relevant stakeholders. Finally, it uses discrete event simulation to generate an estimate of relative lifecycle labor cost performance. Verification and validation of the methods described are presented through a case study of the MegaModule residential solar power system, designed by the team at GTRI. The paper concludes with a review of limitations and proposed future work.

published_or_final_version / Statistics and Actuarial Science / Doctoral / Doctor of Philosophy

The purpose of this experiment was to implement an alternative mapping realization of the hierarchical abstract simulator on the Intel Multibus 1 microprocessor system. Utilizing three 286/10 single board computers, integration of the M286 monitor with the hierarchical abstract simulator algorithm and execution of the distributed simulator system (DSS) was studied. Seven experiments were done on the DSS showing that the DSS correctly executes the algorithm of the hierarchical abstract simulator. An additional benefit is that parallelism is achieved even without external input: one simulator executes the internal transition function, with other executing the external transition function. This system has demonstrated that the hierarchical abstract simulator concept can be implemented on present-day, available hardware.

A new discrete ordinates method designed for use on modern, large memory, vector and/or parallel processing super computers has been developed. The method is similar to conventional SN techniques in that the medium is divided into spatial mesh cells and that discrete directions are used. However, in place of an approximate differencing scheme, a nearly exact matrix representation of the streaming operator is determined. Although extremely large, this matrix can be stored on today's computers for repeated use in the source iteration. Since the source iteration is cast in matrix form it benefits enormously from vector and/or parallel processing, if available. Several test results are presented demonstrating the reduction in numerical diffusion and elimination of ray effects.