Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Bibliography: p.R1-R5. / by Joshua D. Borah. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / Microfiche copy available in Archives and Barker / Bibliography: leaves 108-109. / by William Neil McCasland. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Joseph A. Amram. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 157-161. / by Gregory S. Lauer. / Ph.D.

Predictive computational tools to study granular materials are important in fields ranging from the geosciences and civil engineering to computer graphics. The simulation of granular materials, however, presents many challenges. The behavior of a granular medium is fundamentally multi-scale, with pair-wise interactions between discrete granules able to influence the continuum-scale evolution of a bulk material. Computational techniques for studying granular materials must therefore contend with this multi-scale nature. This research first addresses both the question of how to accurately model interactions between grains and the question of how to achieve multi-scale simulations of granular materials. We propose a novel rigid body contact model and a time integration technique that, for the first time, are able to simultaneously capture five key features of rigid body impact. We further validate this new model and time integration method by reproducing computationally challenging phenomena from granular physics. We next propose a technique to couple discrete and continuum models of granular materials to one another. This hybrid model reveals a family of possible discretizations suitable for simulation. We derive an explicit integration technique from this framework that is able to capture phenomena previously reserved for discrete treatments, including frictional jamming, while treating bulk regions of the material with a continuum model. To effectively handle the large plastic deformations inherent in the evolution of a granular medium, we further propose a method to dynamically update which regions are treated with a discrete model and which regions are treated with a continuum model. We demonstrate that hybrid simulations of a dynamically evolving granular material are possible and practical, and lay the foundation for further algorithmic development in this space. Finally, as the the tools used in computational science and engineering become progressively more complex, the ability to effectively train students in the field becomes increasingly important. We address the question of how to train students from a computer science background in numerical computation techniques by proposing a new system to automatically vet and identify problems in numerical simulations. This system has been deployed at the undergraduate and graduate level in a course on physical simulation at Columbia University, and has increased both student retention and student satisfaction with the course.

This thesis deals with the estimation of unobserved variables or states from a time series of noisy observations. Approximate minimum variance filters for a class of discrete time systems with both additive and multiplicative noise, where the measurement might be delayed randomly by one or more sample times, are investigated. The delayed observations are modelled by up to N sample times by using N Bernoulli random variables with values of 0 or 1. We seek to minimize variance over a class of filters which are linear in the current measurement (although potentially nonlinear in past measurements) and present a closed-form solution. An interpretation of the multiplicative noise in both transition and measurement equations in terms of filtering under additive noise and stochastic perturbations in the parameters of the state space system is also provided. This filtering algorithm extends to the case when the system has continuous time state dynamics and discrete time state measurements. The Euler scheme is used to transform the process into a discrete time state space system in which the state dynamics have a smaller sampling time than the measurement sampling time. The number of sample times by which the observation is delayed is considered to be uncertain and a fraction of the measurement sample time. The same problem is considered for nonlinear state space models of discrete time systems, where the measurement might be delayed randomly by one sample time. The linearisation error is modelled as an additional source of noise which is multiplicative in nature. The algorithms developed are demonstrated throughout with simulated examples.

Lan Weiyao. / "December 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 163-172). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

nÃo hà / Este trabalho apresenta a modelagem e o desenvolvimento de um sistema de combustÃo de biomassa de baixo custo para ser utilizado em caldeiras geradoras de vapor ou em outros processos de aquecimento que utilizam biomassa na forma de cavacos de madeira ou pellets como combustÃvel. A qualidade do processo de combustÃo à avaliada pelo teor de oxigÃnio nos gases de escape. A partir dessa informaÃÃo e da necessidade de geraÃÃo de calor do sistema, desenvolveu-se uma estratÃgia de controle para a admissÃo de combustÃvel e de ar no processo. Uma vez que os analisadores de oxigÃnio industriais disponÃveis no mercado possuem custo elevado, projetou-se e desenvolveu-se um analisador de oxigÃnio de baixo custo baseado em sondas lambda de uso veicular. Foi dada atenÃÃo especial ao controle de temperatura desta sonda. O trabalho envolveu a identificaÃÃo de um modelo matemÃtico para a mesma, assim como simulaÃÃes para validaÃÃo e projeto de um controlador digital que garanta um controle efetivo. O instrumento foi testado em um queimador de gÃs liquefeito de petrÃleo e sua resposta foi comparada e ajustada à resposta de um analisador industrial com certificado de calibraÃÃo rastreado pelo Inmetro, obtendo-se resultados bem consistentes. Em um segundo momento desenvolveu-se uma modelagem matemÃtica simplificada de uma caldeira geradora de vapor e de um sistema de controle digital de admissÃo de combustÃvel e ar. O modelo foi simulado com os parÃmetros de uma caldeira real e os resultados indicaram um desempenho bastante satisfatÃrio. / This dissertation presents a mathematical modelling and development of a low cost biomass combustion system for use in industrial boilers or other process that uses biomass as combustible for heating. The system uses the oxygen gas rate on the exhaust gases to verify the quality of the combustion process. With this information and with an information about the needs for energy on the heating process, a control strategy was developed to the biomass and air admission system. Due to the high cost of industrial oxygen analyzers, a new equipment was developed based on a vehicular lambda probe. Especial attention was given to the temperature control, including the modeling, simulation and project of a digital controller. The equipment was tested on a propane burning system and the results were compared with a calibrated and certificated industrial gas analyzer. The response curve was adjusted to improve the precision of the developed instrument. On a second moment, a simplified mathematical model was created for an industrial boiler and for a digital controller for the air and biomass admission. This model was simulated using real boiler parameters and the results achieved indicates a good performance of the system.

Based on a Ph.D. thesis in the Dept. of Electrical Engineering, 1968. / Bibliography: p.125-126.

One of the commonly used simulation approaches is process orientation. This is based on the use of nodes (or blocks) that perform functions in series. In spite of the compactness and ease of learning that characterize process-based simulation, many languages are somewhat complex, primarily the result of the large number of nodes that users have to deal with and the considerable gulf between a user's abstract notion of the model and the details required to implement it. This paper describes a process-based simulation system that integrates object-oriented programming, visual interactive simulation and graphical model specification. Object-oriented programming techniques and simulation seem to be a natural match. The process classes are represented as network blocks or network nodes, and the process as a network diagram or directed graph. Arcs connect the nodes and specify the next step in the process. Each block type has its own icon. Developing an application model requires selecting a set of nodes, connecting them, and specifying the parameters (such as activity durations and random number streams) of the nodes through dialog boxes or inspection panels. Nodes have been designed to accomplish the major requirements in simulation modeling, including creation and termination of entities, attribute assignment, branching, queues and resources, activity specification and statistics collection and display. Additional system features include: statistics manipulation for steady state results, execution trace utilities, and limited animation capabilities. The system has been implemented for the NeXT programming environment using Objective-C. The NeXT includes an extensive object-oriented user interface library, relatively powerful hardware, and a modern multi-tasking and virtual memory operating system. Objective-C allows object-oriented concepts such as inheritance and subclassing while adding only a few constructs to that of the C language. The system modeling environment developed in this research enhances the applicability and usability of high level modeling tools. The program also provides a platform for further work on the distribution of the modeling process over several cooperating, communicating applications. / Graduation date: 1992