In this thesis, the feasibility of deploying RFID technologies in the case of &ldquo / lowvolume high-value&rdquo / products is considered by focusing on the production processes of a real company. First, the processes of the company are examined and associated problems are determined. Accordingly, a simulation of the current situation is constructed by using the discrete event simulation technique, in order to obtain an accurate model. In addition to modeling the current situation, this simulation model provides a flexible platform to analyze different scenarios and their effects on the company production. Next, various scenarios including RFID technology deployment are examined, and their results are compared with respect to profitanalysis which takes into consideration the changes in the production, work in process (WIP) inventory, stockouts, transportation and initial investment. Finally, the analysis of the results and conclusions are given in order to provide guidance for companies with &ldquo / low-volume high-value&rdquo / product portfolios.

Federated approach for the distributed simulation of a network, is an alternative method that aims to combine existing simulation models and software together using a Run Time Infrastructure (RTI), rather than building the whole simulation from scratch. In this study, an approach that significantly reduces the inter-federate communication load in federated simulation of communication networks is proposed. Rather than communicating packet-level information among federates, characteristics of packet flows in individual federates are dynamically identified and communicated. Flow characterization is done with the Gaussian Mixtures Algorithm (GMA) using a Self Organizing Mixture Network (SOMN) technique. In simulations of a network partitioned into eight federates in space parallel manner, it is shown that significant speedups are achieved with the proposed approach without unduly compromising accuracy.

Limited asset visibility is a key problem in the management of returnable transport items (RTIs) like reusable containers, pallets and kegs. One tool to increase asset visibility is radio frequency identification (RFID) technology. However, RFID requires high investment cost and intensive efforts for implementation. In this study, we investigate the added value of using RFID technology for the management of the RTI pool in a closed-loop supply chain setting considering both costs and benefits. We have conducted a case study in a company which has recently started an RFID application in its closed-loop supply chain of RTIs. The aim of this case study is to identify and understand how an existing RTI pool is managed and the impact of using RFID technology on the management of such an RTI pool. In order to quantify the added value of RFID technology in RTI pool management, we search for the minimum cost solutions both without and with the use of RFID technology in a problem environment similar to that of our case study using the simulation optimization method. We also analyze the impact of using RFID technology on RTI pool management in terms of several performance measures, including RTI pool size, RTI lifetime, RTI trippage and the cycle time for RTIs to complete one trip in the closed-loop supply chain. In our study, we develop a number of discrete event simulation models of the identified closed-loop supply chain of RTIs operating with our predetermined decision rules for the RTI pool management using the simulation software Arena. We then develop our simulation optimization model in OptQuest for Arena in which the discrete event simulation models are embedded. The results from the simulation optimization method show that the added value of using RFID technology is mostly positive and it depends on the severity of the problematic issues in the closed-loop supply chain, as well as on the extent of improvements that RFID brings about.

Distributed Discrete Event Simulation (DDES) has received much attention in recent years, owing to the fact that uniprocessor based serial simulations may require excessive amount of simulation time and computational resources. It is therefore natural to attempt to use multiple processors to exploit the inherent parallelism in discrete event simulations in order to speed up the simulation process. In this dissertation we study the performance of distributed simulation of queueing networks, by analysing queueing models of message flows in distributed discrete event simulators. Most of the prior work in distributed discrete event simulation can be catego­rized as either empirical studies or analytic (or formal) models. In the empirical studies, specific experiments are run on both conservative and optimistic simulators to see which strategy results in a faster simulation. There has also been increasing activity in analytic models either to better understand a single strategy or to compare two strategies. Little attention seems to have been paid to the behaviour of the interprocessor message queues in distributed discrete event simulators. To begin with, we study how to model distributed simulators of queueing networks. We view each logical process in a distributed simulation as comprising a message sequencer with associated message queues, followed by an event processor. A major contribution in this dissertation is the introduction of the maximum lookahead sequencing protocol. In maximum lookahead sequencing, the sequencer knows the time-stamp of the next message to arrive in the empty queue. Maximum lookahead is an unachievable algorithm, but is expected to yield the best throughput compared to any realisable sequencing technique. The analysis of maximum lookahead, therefore, should lead to fundamental limits on the performance of any sequencing algorithm We show that, for feed forward type simulators, with standard stochastic assump-tions for message arrival and time-stamp processes, the message queues are unstable for conservative sequencing, and for conservative sequencing with maximum lookahead and hence for optimistic resequencing, and for any resequencing algorithm that does not employ interprocessor "flow control". It follows that the resequencing problem is fundamentally unstable and some form of interprocessor flow control is necessary in order to make the message queues stable (without message loss). We obtain some generalizations of the insta­bility results to time-stamped message arrival processes with certain ergodicity properties. For feedforward type distributed simulators, we study the throughput of the event sequencer without any interprocessor flow control. We then incorporate flow control and study the throughput of the event sequencer. We analyse various flow control mechanisms. For example, we can bound the buffers of the message queues, or various logical processes can be prevented from getting too far apart in virtual time by means of a mechanism like Moving Time Windows or Bounded Lag. While such mechanisms will serve to stabilize buffers, our approach, of modelling and analysing the message flow processes in the simulator, points towards certain fundamental limits of efficiency of distributed simulation, imposed by the synchronization mechanism. Next we turn to the distributed simulation of more general queueing networks. We find an upper bound to the throughput of distributed simulators of open and closed queueing networks. The upper bound is derived by using flow balance relations in the queueing network and in the simulator, processing speed constraints, and synchronization constraints in the simulator. The upper bound is in terms of parameters of the queueing network, the simulator processor speeds, and the way the queueing network is partitioned or mapped over the simulator processors. We consider the problem of choosing a mapping that maximizes the upper bound. We then study good solutions o! this problem as possible heuristics for the problem of partitioning the queueing network over the simulator processors. We also derive a lower bound to the throughput of the distributed simulator for a simple queueing network with feedback. We then study various properties of the maximum lookahead algorithm. We show that the maximum lookahead algorithm does not deadlock. Further, since there are no syn­chronization overheads, maximum lookahead is a simple algorithm to study. We prove that maximum lookahead sequencing (though unrealisable) yields the best throughput compared to any realisable sequencing technique. These properties make maximum lookahead a very useful algorithm in the study of distributed simulators of queueing networks. To investigate the efficacy of the partitioning heuristic, we perform a study of queue­ing network simulators. Since it is important to study the benefits of distributed simula­tion, we characterise the speedup in distributed simulation, and find an upper bound to the speedup for a given mapping of the queues to the simulator processors. We simulate distributed simulation with maximum lookahead sequencing, with various mappings of the queues to the processors. We also present throughput results foT the same mappings but using a distributed simulation with the optimistic sequencing algorithm. We present a num­ber of sufficiently complex examples of queueing networks, and compare the throughputs obtained from simulations with the upper bounds obtained analytically. Finally, we study message flow processes in distributed simulators of open queueing networks with feedback. We develop and study queueing models for distributed simulators with maximum lookahead sequencing. We characterize the "external" arrival process, and the message feedback process in the simulator of a simple queueing network with feedback. We show that a certain "natural" modelling construct for the arrival process is exactly correct, whereas an "obvious" model for the feedback process is wrong; we then show how to develop the correct model. Our analysis throws light on the stability of distributed simulators of queueing networks with feedback. We show how the stability of such simulators depends on the parameters of the queueing network.

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.

No description available.

Simulation has been used extensively for addressing probabilistic uncertainty in range estimating for construction projects. However, subjective and linguistically expressed information results in added non-probabilistic uncertainty in construction management. Fuzzy logic has been used successfully for representing such uncertainties in construction projects. In practice, an approach that can handle both random and fuzzy uncertainties in a risk assessment model is necessary. In this thesis, first, a Fuzzy Monte Carlo Simulation (FMCS) framework is proposed for risk analysis of construction projects. To verify the feasibility of the FMCS framework and demonstrate its main features, a cost range estimating template is developed and employed to estimate the cost of a highway overpass project. Second, a hybrid framework that considers both fuzzy and probabilistic uncertainty for discrete event simulation of construction projects is suggested. The application of the proposed framework is discussed using a real case study of a pipe spool fabrication shop. / Construction Engineering and Management

Network emulation has been widely used to aid in the development and evaluation of real-time applications. Many of today s applications and protocols need to be tested and evaluated in large scale network environments such as the Internet, which requires emulation tools that meet the requirements of scale, accuracy, timeliness. Due to physical resource constraints in network emulators, existing emulation tools fail to meet these requirements as they are either limited to small and static networks, use simplified network models, or fail to deliver timely emulation results. If more physical resources are devoted to network emulation by utilizing high performance computing facilities, the accuracy and scalability of network emulation can be greatly improved. However, for many users, high performance computing facilities may not be readily available in a local laboratory environment, and co-locating application code with a remote high performance computing facility may be cumbersome and inconvenient. This thesis proposes a network emulation approach called ROSENET (RemOte SErver-based Network EmulaTion) that utilizes a distributed server-based architecture in which local low-fidelity emulators provide real-time QoS predictions to distributed applications, coupled with a remote large scale high-fidelity simulator that continuously updates and calibrates the local low-fidelity emulators. A library-based modeling approach based on online simulation data collection is proposed and a system identification modeling technique is presented. Experimental results examining emulation end-to-end delay and loss show that ROSENET provides a promising approach to network emulation supporting accuracy and scale while meeting real-time constraints. Challenges faced in applying ROSENET to real world applications are addressed through two case studies including applying synthetic workload on DARPA s NMS network topology for large scale network simulation and a contemporary real-time distributed VoIP application Skype.

Thesis (MScEng (Industrial Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The purpose of this study is to investigate the capacity of a proposed bus rapid transit (BRT) station in Cape Town. A bus rapid transit system is a high-capacity public transportation system that carries passengers from one point to another, providing a service that is faster and more efficient than an ordinary bus line. The implementation of these systems is increasing rapidly worldwide, serving as a solution to decrease traffic congestion. The capacity of the proposed bus station, known as the Thibault Station, is investigated in the study by developing a simulation model. The aim is to develop a stochastic simulation model, which represents the flow of passengers throughout the station so that the station capacity can be investigated. By developing a stochastic model as opposed to a deterministic model, elements of uncertainty can be included into the model, thereby representing a system that is closer to the real-life situation under investigation. The majority of BRT systems, as well as past studies undertaken on the Thibault Station, are designed using deterministic calculations. The study commences by researching literature on BRT systems and focuses on the current methods used to calculate station capacity requirements. Thereafter, the concept of simulation is introduced. Simulation is the method chosen to model and evaluate the passenger and bus operations at the Thibault Station. The study presents the methods used to build and verify the simulation model. This is done to familiarise the user with a number of aspects of the model. The model can then be used as a tool to investigate capacity parameters and alternative designs or scenarios. Using the results of these investigations, decisions can ultimately be made regarding the planning and design components of any bus rapid transit station given that the model is adapted. Scenario results, as well as interpretations of performance measurements, are presented at the end of the study. The results can be used for more realistic design of BRT stations using stochastic modelling. / AFRIKAANSE OPSOMMING: Die doel van die studie is om ondersoek in te stel na die kapasiteit van „n hoëspoed bus vervoer stelsel (BRT). Die ondersoek is gebaseer op „n voorgestelde bus stelsel vir Kaapstad. „n BRT-stelsel is „n hoë-kapasiteit publieke vervoerstelsel wat passasiers van een punt na „n ander vervoer, deur „n diens te verskaf wat vinniger en meer doeltreffend is as „n gewone bus stelsel. Die implementering van hierdie tipe stelsels neem wêreldwyd toe en dien as „n oplossing om verkeersopeenhopings te verminder. Die spesifieke busstasie wat ondersoek word staan bekend as die Thibault Stasie van Kaapstad se BRT-stelsel. Die kapasiteit van die stasie word ondersoek deur middel van simulasiemodellering. Die doel is om „n stogastiese simulasiemodel wat die vloei van passasiers modelleer te ontwikkel ten einde die kapasiteit van die stasie te ondersoek. Deur „n stogastiese model in plaas van „n deterministiese model te gebruik, kan elemente van onsekerheid ingesluit word. Dit verteenwoordig dus „n stelsel wat nader aan die werklikheid is. Tans word meeste BRT-stelsels ontwerpe gebaseer op deterministiese berekeninge, asook historiese studies wat onderneem is oor die Thibault Stasie. Die studie begin deur literatuur oor BRT-stelsels te bestudeer en fokus daarna op die huidige metodes wat gebruik word om die vereiste kapasiteit van „n busstasie te bepaal. Die konsep van simulasie word daarna voorgestel. Simulasie is die metode wat in die studie gebruik word om die passasier- en busaktiwiteite van die Thibault Stasie te modelleer en te evalueer. Die studie verskaf die metodes wat gebruik word vir die ontwikkeling en geldigmaak van die simulasiemodel. Gebruikers word op dié manier blootgestel aan die verskillende aspekte van die model. Nadat die gebruikers vertroud is met sekere aspekte van die model, word die model verder uiteengesit en word daar verduidelik hoe dit as „n instrument om kapasiteit parameters en alternatiewe ontwerpe van busstasies te ondersoek kan dien. Die resultate van die model kan gebruik word om beplannings- en ontwerpbesluite van enige busstasie te neem. Aan die einde van die studie word scenarioresultate bekendgestel, asook die interpretasie daarvan. Die resultate kan gebruik word vir meer realistiese ontwerp van BRT-stasies met behulp van stogastiese simulasie modellering.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O gerenciamento do tempo nos projetos de construção civil usualmente utiliza algoritmos determinísticos para o cálculo dos prazos de finalização e algoritmos PERT para avaliação da probabilidade de o mesmo terminar até uma determinada data. Os resultados calculados pelos algoritmos tradicionais possuem defasagens nos prazos se comparados aos encontrados na realidade o que vem fazendo com que a simulação venha se tornando uma ferramenta cada vez mais utilizada no gerenciamento de projetos. O objetivo da dissertação é estudar o problema dos prazos de finalização dos projetos desenvolvendo novas técnicas de cálculo que reflitam melhor os prazos encontrados na vida real. A partir disso é criada uma ferramenta prática de gerenciamento do tempo de atividades de projetos de construção enxuta baseada em planilha eletrônica onde serão utilizadas técnicas de simulação a eventos discretos, com base em distribuições de probabilidade como, por exemplo, a distribuição beta. / Time management in construction projects usually use deterministic algorithms to calculate the time of fulfillment, and PERT algorithms to evaluate the probability of such project ending by a certain date. The results achieved by traditional algorithms are not accurate when compared to those found in the field, which is increasing the use of simulation as a tool in project management. The aim of this dissertation is to study the deadline fulfillment problems of projects, developing new calculation techniques that better represent the deadlines found in real life. For such study is developed a practical tool for time management of lean construction projects based on spreadsheet which will be used discrete event simulation techniques based in probability distributions, such as, the beta distribution.