Dissertations / Theses on the topic 'Discrete approach'
To see the other types of publications on this topic, follow the link: Discrete approach.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Discrete approach.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Graham, Justin W. "School choice : a discrete optimization approach." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127294.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, May, 2020Cataloged from PDF version of thesis.
Includes bibliographical references (pages 32-34).
An equitable and flexible mechanism for assigning students to schools is a major concern for many school districts. The school a student attends dramatically impacts the quality of education, access to resources, family and neighborhood cohesion, and transportation costs. Facing this intricate optimization problem, school districts often utilize to stable-matching techniques which only produce stable matchings that do not incorporate these different objectives; this can be expensive and inequitable. We present a new optimization model for the Stable Matching (SM) school choice problem which relies on an algorithm we call Price-Costs-Flexibility-and- Fairness (PCF2). Our model leverages techniques to balance competing objectives using mixed-integer optimization methods. We explore the trade-offs between stability, costs, and preferences and show that, surprisingly, there are stable solutions that decrease transportation costs by 8-17% over the Gale-Shapley solution.
by Justin W. Graham.
S.M.
S.M. Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center
2
Villa, Cristiano. "An objective Bayesian approach for discrete scenarios." Thesis, University of Kent, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633699.
Full textAbstract:
Objective prior distributions represent a fundamental part of Bayesian inference. Although several approaches for continuous parameter spaces have been developed, Bayesian theory lacks of a general method that allows to obtain priors for the discrete case. In the present work we propose a novel idea, based on losses, to derive objective priors for discrete parameter spaces. We objectively measure the worth of each parameter values, and link it to the prior probability by means of the self information loss function. The worth is measured by taking into consideration the surroundings of each element of the parameter space. Bayes theorem is then re-interpreted, where prior and posterior beliefs are not expressed as probabilities, but as losses. The approach allows to retain meaning from the beginning to the end of the Bayesian updating process. The prior distribution obtained with the above approach is identified as the t-Walker prior. We illustrate the approach by applyi~t.,to various scenarios. We derive objective priors for five specific models: a population size model, the Hypergeometric and multivariate Hypergeometric models, the Binomial-Beta model, and the Binomial model. We also derive the Villa- Walker prior for the number of degrees of freedom of a t distribution. An important result in this last case, is that the objective prior has to be truncated.
3
Pillay, Samara. "Modelling angiogenesis : a discrete to continuum approach." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:a6f3f5a2-5f47-480d-8500-e560d46d9157.
Full textAbstract:
Angiogenesis is the process by which new blood vessels develop from existing vessels. Angiogenesis is important in a number of conditions such as embryogenesis, wound healing and cancer. It has been modelled phenomenologically at the macroscale, using the well-known 'snail-trail' approach in which trailing endothelial cells follow the paths of other, leading endothelial cells. In this thesis, we systematically determine the collective behaviour of endothelial cells from their behaviour at the cell-level during corneal angiogenesis. We formulate an agent-based model, based on the snail-trail process, to describe the behaviour of individual cells. We incorporate cell motility through biased random walks, and include processes which produce (branching) and annihilate (anastomosis) cells to represent sprout and loop formation. We use the transition probabilities associated with the discrete model and a mean-field approximation to systematically derive a system of non-linear partial differential equations (PDEs) of population behaviour that impose physically realistic density restrictions, and are structurally different from existing snail-trail models. We use this framework to evaluate the validity of a classical snail-trail model and elucidate implicit assumptions. We then extend our framework to explicitly account for cell volume. This generates non-linear PDE models which vary in complexity depending on the extent of volume exclusion incorporated on the microscale. By comparing discrete and continuum models, we assess the extent to which continuum models, including the classical snail-trail model, account for single and multi-species exclusion processes. We also distinguish macroscale exclusion effects introduced by each cell species. Finally, we compare the predictive power of different continuum models. In summary, we develop a microscale to macroscale framework for angiogenesis based on the snail-trail process, which provides a systematic way of deriving population behaviour from individual cell behaviour and can be extended to account for more realistic and/or detailed cell interactions.
4
Simpson, Andrew E. "A Discrete Model Approach to Biofilm Growth." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1342790784.
Full text
5
Logue, James K. "The discrete, orthogonal wavelet transform, a projective approach." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA304330.
Full text
6
Ren, Mingming. "An incremental approach for hardware discrete controller synthesis." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00679296.
Full textAbstract:
The Discrete Controller Synthesis (DCS) technique is used for automatic generation of correct-by-construction hardware controllers. For a given plant (a state-based model), and an associated control specification (a behavioral requirement), DCS generates a controller which, composed with the plant, guarantees the satisfaction of the specification. The DCS technique used relies on binary decision diagrams (BDDs). The controllers generated must be compliant with standard RTL hardware synthesis tools. Two main issues have been investigated: the combinational explosion, and the actual generation of the hardware controller. To address combinational explosion, common approaches follow the "divide and conquer" philosophy, producing modular control and/or decentralized control. Most of these approaches do not consider explicit communication between different components of a plant. Synchronization is mostly achieved by sharing of input events, and outputs are abstracted away. We propose an incremental DCS technique which also applies to communicating systems. An initial modular abstraction is followed by a sequence of progressive refinements and computations of approximate control solutions. The last step of this sequence computes an exact controller. This technique is shown to have an improved time/memory efficiency with respect to the traditional global DCS approach. The hardware controller generation addresses the control non-determinism problem in a specific way. A partially closed-loop control architecture is proposed, in order to preserve the applicability of hierarchical design. A systematic technique is proposed and illustrated, for transforming the automatically generated control equation into a vector of control functions. An application of the DCS technique to the correction of certain design errors in a real design is illustrated. To prove the efficiency of the incremental synthesis and controller implementation, a number of examples have been studied.
7
Ahlbach, Connor Thomas. "A Discrete Approach to the Poincare-Miranda Theorem." Scholarship @ Claremont, 2013. http://scholarship.claremont.edu/hmc_theses/47.
Full textAbstract:
The Poincare-Miranda Theorem is a topological result about the existence of a zero of a function under particular boundary conditions. In this thesis, we explore proofs of the Poincare-Miranda Theorem that are discrete in nature - that is, they prove a continuous result using an intermediate lemma about discrete objects. We explain a proof by Tkacz and Turzanski that proves the Poincare-Miranda theorem via the Steinhaus Chessboard Theorem, involving colorings of partitions of n-dimensional cubes. Then, we develop a new proof of the Poincare-Miranda Theorem that relies on a polytopal generalization of Sperner's Lemma of Deloera - Peterson - Su. Finally, we extend these discrete ideas to attempt to prove the existence of a zero with the boundary condition of Morales.
8
Liu, Xuecheng 1963. "Nonparametric estimation with censored data : a discrete approach." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85570.
Full textAbstract:
This dissertation principally addresses nonparametric maximal likelihood (NPML) estimation of the cumulative distribution function (CDF) given multivariate (arbitrarily) censored data (herein abbreviated MCD).The CDF nonparametric maximal likelihood estimate (NPMLE) given MCD has support on the union of all maximal intersections of the data. The CDF NPMLE can be computed numerically using the clique matrix of the intersection graph of the data; these NPMLEs can be nonunique in both a representational and a mixture sense (see Peto 1973, Turnbull 1976, Gentleman & Vandal 2001 and Gentleman & Vandal 2002).
The fundamental methodology used in this dissertation consists in applying graph theory to the intersection graph of censored data and discrete mathematics to its linear algebraic representation. An optimal algorithm to determine the maximal intersections of MCD is proposed. A full discussion of measures of NPMLE mixture nonuniqueness and their computational implementations for the measures is provided. The iterative convex minorant (ICM) algorithm to obtain the NPMLE is extended to the case of MCD. The nonparametric likelihood maximization given MCD is simplified via the use of a reduction tree. The EM/X Algorithm is introduced to compute the NPMLE for large MCD set. Bounds on self-consistent estimates of the CDF (a class to which the CDF NPMLE belongs) given MCD are used to assess the degree of consistency of the CDF NPMLE. Constrained estimation and likelihood intervals computation given univariate censored data are discussed. The empirical likelihood method is also applied to construct CDF likelihood sets for MCD. An unbiased and consistent estimate is proposed for MCD with fixed censoring times.
9
Sze, Chuen-kan, and 施泉根. "On framelets and their applications: a discrete approach." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29803937.
Full text
10
CARVALHO, LUCIANA CRUZ ALVES DE. "A DISCRETE TIME APPROACH OF REAL OPTIONS THEORY." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=7829@1.
Full textAbstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROOs métodos tradicionais de avaliação de projetos vem sendo questionados por não considerarem possíveis incertezas associadas ao investimento. Neste contexto, a Teoria das Opções Reais busca aplicar o conceito de opções a ativos reais, com a finalidade de agregar o valor da flexibilidade gerencial aos métodos tradicionais de avaliação de investimentos. A avaliação por Opções Reais é considerada complexa devido à difícil modelagem de incertezas e das flexibilidades, além da necessidade de se ter mercados completos. Este estudo busca incorporar a flexibilidade gerencial à avaliação de projetos através do uso de Árvores Binomiais de Decisão, com probabilidades neutras ao risco, para a avaliação por Opções Reais em Tempo Discreto. Utilizamos programação dinâmica para a aplicação desta metodologia, a qual é computacionalmente intensa, porém de solução simples e intuitiva. A aplicação prática foi realizada através da valoração da opção de expandir e da opção de abandonar enfrentada por uma empresa de Tecnologia.
The traditional methods of Valuation are being questioned as they do not consider possible uncertainties related to investment decisions. In this scenario, Real Options Theory applies option`s concept to real assets, aiming to add the value of managerial flexibility to traditional Valuation techniques. The evaluation for Real Options is considered complex due to the difficulty of modeling uncertainties and flexibilities, beyond the need to have complete markets. This work aims to add the managerial flexibility to Valuation by binomial lattice and decision tree techniques, with risk neutral probabilities, in a discrete time approach to evaluation for Real Options. Using dynamic programming to apply this method, which is computationally intense, but simple and intuitive. The practical application consists in valuing an option to expand and to abandon faced by an IT company.
11
Demir, Ramazan. "An approximate dynamic programming approach to discrete optimization." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9137.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2000.Includes bibliographical references (leaves 181-189).
We develop Approximate Dynamic Programming (ADP) methods to integer programming problems. We describe and investigate parametric, nonparametric and base-heuristic learning approaches to approximate the value function in order to break the curse of dimensionality. Through an extensive computational study we illustrate that our ADP approach to integer programming competes successfully with existing methodologies including state of art commercial packages like CPLEX. Our benchmarks for comparison are solution quality, running time and robustness (i.e., small deviations in the computational resources such as running time for varying instances of same size). In this thesis, we particularly focus on knapsack problems and the binary integer programming problem. We explore an integrated approach to solve discrete optimization problems by unifying optimization techniques with statistical learning. Overall, this research illustrates that the ADP is a promising technique by providing near-optimal solutions within reasonable amount of computation time especially for large scale problems with thousands of variables and constraints. Thus, Approximate Dynamic Programming can be considered as a new alternative to existing approximate methods for discrete optimization problems.
by Ramazan Demir.
Ph.D.
12
Au, Grace. "A graphics driven approach to discrete event simulation." Thesis, London School of Economics and Political Science (University of London), 1990. http://etheses.lse.ac.uk/1226/.
Full textAbstract:
This thesis investigates the potential of computer graphics in providing for a graphics driven specification system that gives sufficient structure and content to form the simulation model itself. The nature of discrete event simulation modelling, the diagramming method of activity cycle diagrams which underpinned this research, the three phase simulation model structure, and the trend of visual simulation modelling are discussed as the basis for the research. Some current existing simulation languages and packages are reviewed, which gives insight into the essential features of an ideal computer simulation environment. The basic research method adopted was to build systems that exemplified the state of thinking at the time. The purpose of this method was to enable ideas to be developed, discarded and enhanced, and for new ideas to emerge. The research has undergone a series of application developments on the Apple Macintosh to examine the advantages and limitations of such systems. The first system developed during the research, MacACD, provides the basis for proposals concerning the enhancement of the ACD diagramming method in a computer-aided environment. However, MacACD demonstrated the limitations of an ACD interface and the need for a more flexible specification system. HyperSim, a simulation system developed using HyperCard, has all the power of interconnectivity demonstrated as a need by MacACD, but has severe limitations both in terms of security of system development, and an inability to provide a running model directly due to lack of speed. However, the power of an icon-based interconnected textual and diagrammatic based system were demonstrated by the construction of this system during this research, and led to the development of the final system described in this thesis : MacGraSE. The development of this system during this research incorporates many innovations. The main input device is a picture representing the problem, including a background display. This system allows for dynamic icon based visual model running, as well as code generation for complete model embellishments, interactive report writing, and representational graphics outputs.
13
Bradford, Alexander. "Automated Conjecturing Approach to the Discrete Riemann Hypothesis." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4470.
Full textAbstract:
This paper is a study on some upper bounds of the Mertens function, which is often considered somewhat of a ``mysterious" function in mathematics and is closely related to the Riemann Hypothesis. We discuss some known bounds of the Mertens function, and also seek new bounds with the help of an automated conjecture-making program named CONJECTURING, which was created by C. Larson and N. Van Cleemput, and inspired by Fajtowicz's Dalmatian Heuristic. By utilizing this powerful program, we were able to form, validate, and disprove hypotheses regarding the Mertens function and how it is bounded.
14
Cardoso, Nungaray Víctor Eduardo. "Discrete volume method : a variational approach for brittle fracture." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/565906.
Full textAbstract:
This thesis presents a proposal to simulate mechanics and dynamics of brittle fracture. A variational formulation is used to describe Lagrangian mechanics, by minimizing the difference between potential and kinetic energy of the system, obtaining a pair of partial differential equations; the solution of these equations corresponds to the displacement field and damage phase-field respectively. Such an equations are coupled in the sense that the damage field is used in the first equation and the displacement field is used in the second one.
In this work we propose a numerical method based on control volumes to solve the differential equations, extending the formulation to support the separation of control volumes, processing these volumes as discrete entities. This treatment results in accurate calculations of stress field and the nucleation of new internal fractures that can be propagated through domain creating multiple bifurcations.
To integrate equations inside control volumes we introduce a family of polynomial splines that we refer as homeostatic splines, since its derivatives are null at vertices with a smooth function variation between adjacent volumes. Furthermore, we propose a shape function with trigonometric components for dynamic analysis, allowing bigger time steps that with traditional approaches.
Finally, we perform ten numerical experiments to show the effectiveness of the method and to compare our results with those published by other authors.La tesis presenta una propuesta para simular la mecánica y dinámica del fenómeno de fractura frágil. Se plantea una formulación variacional que consiste en minimizar la diferencia entre la energía potencial y la energía cinética del sistema, obteniendo así un par de ecuaciones diferenciales parciales, cuya solución corresponden al campo de desplazamientos y al campo de daño respectivamente. Estas ecuaciones están acopladas en el sentido de que el campo de daño se usa en la primera ecuación y el de desplazamientos en la segunda. En este trabajo se propone un método numérico basado en volúmenes de control para resolver las ecuaciones diferenciales, además el modelo se extiende para soportar la separación de los volúmenes de control, tratándolos posteriormente como entidades discretas, esto permite calcular con precisión el campo de esfuerzos y la aparición de fracturas internas que pueden propagarse a través del dominio y crear múltiples bifurcaciones. Para integrar las ecuaciones dentro de los volúmenes de control se introducen una familia de splines polinomiales, que se les refiere como splines homeostáticos, ya que sus derivadas son nulas en los vértices y el cambio de la función entre dos volúmenes contiguos es suave. Además, se propone una función de forma con componentes trigonométricas para el análisis dinámico, permitiendo pasos de tiempo más grandes que con enfoques tradicionales. Finalmente se realizan diez experimentos numéricos para mostrar la eficacia del método y contrastar los resultados con aquéllos publicados por otros autores.
15
Nunes, Letícia Faria de Carvalho. "Practice location of physicians: a discrete choice model approach." reponame:Repositório Institucional do FGV, 2015. http://hdl.handle.net/10438/13827.
Full textAbstract:
Submitted by Letícia Nunes (leticiafcnunes@gmail.com) on 2015-06-11T16:44:52Z
No. of bitstreams: 1
Dissertação - Leticia Nunes - Practice Location of Physicians.pdf: 569206 bytes, checksum: bde07c17bc4ab59a76a947e9fa27f35e (MD5)Approved for entry into archive by BRUNA BARROS (bruna.barros@fgv.br) on 2015-06-18T13:46:34Z (GMT) No. of bitstreams: 1 Dissertação - Leticia Nunes - Practice Location of Physicians.pdf: 569206 bytes, checksum: bde07c17bc4ab59a76a947e9fa27f35e (MD5)
Approved for entry into archive by Marcia Bacha (marcia.bacha@fgv.br) on 2015-06-29T12:13:05Z (GMT) No. of bitstreams: 1 Dissertação - Leticia Nunes - Practice Location of Physicians.pdf: 569206 bytes, checksum: bde07c17bc4ab59a76a947e9fa27f35e (MD5)
Made available in DSpace on 2015-06-29T12:13:22Z (GMT). No. of bitstreams: 1 Dissertação - Leticia Nunes - Practice Location of Physicians.pdf: 569206 bytes, checksum: bde07c17bc4ab59a76a947e9fa27f35e (MD5) Previous issue date: 2015-04-07
Economists and policymakers have long been concerned with increasing the supply of health professionals in rural and remote areas. This work seeks to understand which factors influence physicians’ choice of practice location right after completing residency. Differently from previous papers, we analyse the Brazilian missalocation and assess the particularities of developing countries. We use a discrete choice model approach with a multinomial logit specification. Two rich databases are employed containing the location and wage of formally employed physicians as well as details from their post-graduation. Our main findings are that amenities matter, physicians have a strong tendency to remain in the region they completed residency and salaries are significant in the choice of urban, but not rural, communities. We conjecture this is due to attachments built during training and infrastructure concerns.
16
Muncy, David. "Automated Conjecturing Approach for Benzenoids." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4608.
Full textAbstract:
Benzenoids are graphs representing the carbon structure of molecules, defined by a closed path in the hexagonal lattice. These compounds are of interest to chemists studying existing and potential carbon structures. The goal of this study is to conjecture and prove relations between graph theoretic properties among benzenoids. First, we generate conjectures on upper bounds for the domination number in benzenoids using invariant-defined functions. This work is an extension of the ideas to be presented in a forthcoming paper. Next, we generate conjectures using property-defined functions. As the title indicates, the conjectures we prove are not thought of on our own, rather generated by a process of automated conjecture-making. This program, named Cᴏɴᴊᴇᴄᴛᴜʀɪɴɢ, is developed by Craig Larson and Nico Van Cleemput.
17
Chao, Daphne (Yu Fen). "MDRIP: A Hybrid Approach to Parallelisation of Discrete Event Simulation." Thesis, University of Canterbury. Computer Science and Software Engineering, 2006. http://hdl.handle.net/10092/1076.
Full textAbstract:
The research project reported in this thesis considers Multiple Distributed Replications in Parallel (MDRIP), a hybrid approach to parallelisation of quantitative stochastic discrete-event simulation. Parallel Discrete-Event Simulation (PDES) generally covers distributed simulation or simulation with replicated trials. Distributed simulation requires model partitioning and synchronisation among submodels. Simulation with replicated trials can be executed on-line by applying Multiple Replications in Parallel (MRIP). MDRIP has been proposed for overcoming problems related to the large size of simulated models and their complexity, as well as with the problem of controlling the accuracy of the final simulation results. A survey of PDES investigates several primary issues which are directly related to the parallelisation of DES. A secondary issue related to implementation efficiency is also covered. Statistical analysis as a supporting issue is described. The AKAROA2 package is an implementation of making such supporting issue effortless. Existing solutions proposed for PDES have exclusively focused on collecting of output data during simulation and conducting analysis of these data when simulation is finished. Such off-line statistical analysis of output data offers no control of statistical errors of the final estimates. On-line control of statistical errors during simulation has been successfully implemented in AKAROA2, an automated controller of output data analysis during simulation executed in MRIP. However, AKAROA2 cannot be applied directly to distributed simulation. This thesis reports results of a research project aimed at employing AKAROA2 for launching multiple replications of distributed simulation models and for on-line sequential control of statistical errors associated with a distributed performance measure; i.e. with a performance measure which depends on output data being generated by a number of submodels of distributed simulation. We report changes required in the architecture of AKAROA2 to make MDRIP possible. A new MDRIP-related component of AKAROA2, a distributed simulation engine mdrip engine, is introduced. Stochastic simulation in its MDRIP version, as implemented in AKAROA2, has been tested in a number of simulation scenarios. We discuss two specific simulation models employed in our tests: (i) a model consisting of independent queues, and (ii) a queueing network consisting of tandem connection of queueing systems. In the first case, we look at the correctness of message orderings from the distributed messages. In the second case, we look at the correctness of output data analysis when the analysed performance measures require data from all submodels of a given (distributed) simulation model. Our tests confirm correctness of our mdrip engine design in the cases considered; i.e. in models in which causality errors do not occur. However, we argue that the same design principles should be applicable in the case of distributed simulation models with (potential) causality errors.
18
McCarragher, Brenan Joseph. "A discrete event dynamic systems approach to robotic assembly tasks." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12887.
Full text
19
Miller, Russell. "A geometric approach to three-dimensional discrete electrical impedance tomography." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/a-geometric-approach-to-threedimensional-discrete-electrical-impedance-tomography(37264580-d227-4797-9ff0-ae63e406ee7c).html.
Full textAbstract:
Electrical impedance tomography (EIT) is an imaging modality with many possible practical applications. It is mainly used for geophysical applications, for which it is called electrical resistivity tomography. There have also been many proposed medical applications such as respiratory monitoring and breast tumour screening. Although there have been many uniqueness and stability results published over the last few decades, most of the results are in the context of the theoretical continuous problem. In practice however, we almost always have to solve a discretised problem for which very few theoretical results exist. In this thesis we aim to bridge the gap between the continuous and discrete problems. The first problem we solve is the three-dimensional triangulation problem of uniquely embedding a tetrahedral mesh in R3. We parameterise the problem in terms of dihedral angles and we provide a constructive procedure for identifying the independent angles and the independent set of constraints that the dependent angles must satisfy. We then use the implicit function theorem to prove that the embedding is locally unique. We also present a numerical example to illustrate that the result works in practice. Without the understanding of the geometric constraints involved in embedding a three-dimensional triangulation, we cannot solve more complex problems involving embeddings of finite element meshes. We next investigate the discrete EIT problem for anisotropic conductivity. It is well known that the entries of the finite element system matrix for piecewise linear potential and piecewise constant conductivity are equivalent to conductance values of resistors defined on the edges of the finite element mesh. We attempt to tackle the problem of embedding a finite element mesh in R3, such that it is consistent with some known edge conductance values. It is a well known result that for the anisotropic conductivity problem, the boundary data is invariant under diffeomorphisms that fix the boundary. Before investigating this effect on the discrete case, we define the linear map from conductivities to edge conductances and investigate the injectivity of this map for a simplistic example. This provides an illustrative example of how a poor choice of finite element mesh can result in a non-unique solution to the discrete inverse problem of EIT. We then extend the investigation to finding interior vertex positions and conductivity distributions that are consistent with the known edge conductances. The results show that if the total number of interior vertex coordinates and anisotropic conductivity variables is larger than the number of edges in the mesh, then there exist discrete diffeomorphisms that perturb the vertices and conductivities such that no change in the edge conductances is observed. We also show that the non-uniqueness caused by the non-injectivity of the linear map has a larger effect than the non-uniqueness caused by diffeomorphism invariance.
20
King, Matthew Lee. "A CAD-centric Approach to CFD Analysis With Discrete Features." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd570.pdf.
Full text
21
Åkerlind, Amanda. "Elastic properties of the Singö zone from a discrete approach." Thesis, KTH, Skolan för arkitektur och samhällsbyggnad (ABE), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-268640.
Full textAbstract:
A rock mass is characterised by the properties of the intact rock and the fractures. Considering the impact of both constituents is of vital importance for assessing the behaviour of the rock mass. In particular in the case of complex or heterogeneous rock mass compositions. A discrete approach, by using the Discrete Fracture Network (DFN) methodology, enables for the consideration of these aspects.This master’s thesis concerns the evaluation of elastic properties of the Singö deformation zone. A discrete approach has been applied by three-dimensional discrete fracture network modelling, using previously evaluated DFN parameters. The elastic properties have then been obtained by analytical means by using the methodology developed by Davy et al. (2018).The results show that in comparison to earlier evaluations of the elastic properties of the Singö zone, the respective Young’s moduli and Poisson’s ratios obtained by this thesis may indicate a weaker material. However, this study differs from the earlier evaluation by more extensive DFN modelling and the application of a state of stress which is more representative of the surroundings of the zone in Forsmark. The analysis indicates that theadequate model size is slightly larger than the maximum studied DFN model size. A suggested future improvement would be a re-evaluation and updating of the DFN parameters. As a concluding remark, the methodology of Davy et al. (2018) may prove successful in the future for the application to deformation zones.En bergmassa karakteriseras av egenskaperna hos det intakta berget och dess sprickor. Det är därmed av vikt att båda dessa beståndsdelar beaktas vid utvärdering av bergmassans beteende, speciellt vid komplexa eller heterogena bergartssammansättningar.Detta examensarbete syftar till att utvärdera deformationsegenskaper för den så kallade Singözonen. Ett diskret angreppsätt har tillämpats genom modellering av tredimensionella diskreta spricknätverk med hjälp av tidigare utvärderade DFN-parametrar. Deformationsegenskaperna har sedan utvärderats med hjälp av metodiken som presenteras i Davy et al. (2018).Jämfört med tidigare utvärderade deformationsegenskaper hos Singözonen så indikerar resultaten av denna masteruppsats en svagare bergmassa, med hänsyn till uppskattade värden på E-moduler och tvärkontraktionstal. Däremot skiljer sig modelleringsprocessen i detta arbete mot de som utförts i de tidigare studierna. Detta med hänsyn till omfattningen av DFN-modelleringen samt tillämpandet i detta arbete av en spänningsansats som är mer representativ för Forsmarksområdet. Vidare indikerar resultaten att den representativa modellvolymen är något större än den största modellvolym som tillämpats i detta arbete. Förslagsvis kan en utvärdering och eventuell uppdatering av de använda DFN-parametrarna utgöra en möjlig utveckling eller förbättring av det arbete som utförts i detta mastersarbete. Slutligen kan det konstateras att framtida tillämpningar av den metodik som tagits fram av Davy et al. (2018) verkar lämplig att applicera på deformationszoner.
22
McLaughlin, Bryce. "An Incidence Approach to the Distinct Distances Problem." Scholarship @ Claremont, 2018. https://scholarship.claremont.edu/hmc_theses/118.
Full textAbstract:
In 1946, Erdös posed the distinct distances problem, which asks for the minimum number of distinct distances that any set of n points in the real plane must realize. Erdös showed that any point set must realize at least &Omega(n1/2) distances, but could only provide a construction which offered &Omega(n/&radic(log(n)))$ distances. He conjectured that the actual minimum number of distances was &Omega(n1-&epsilon) for any &epsilon > 0, but that sublinear constructions were possible. This lower bound has been improved over the years, but Erdös' conjecture seemed to hold until in 2010 Larry Guth and Nets Hawk Katz used an incidence theory approach to show any point set must realize at least &Omega(n/log(n)) distances. In this thesis we will explore how incidence theory played a roll in this process and expand upon recent work by Adam Sheffer and Cosmin Pohoata, using geometric incidences to achieve bounds on the bipartite variant of this problem. A consequence of our extensions on their work is that the theoretical upper bound on the original distinct distances problem of &Omega(n/&radic(log(n))) holds for any point set which is structured such that half of the n points lies on an algebraic curve of arbitrary degree.
23
Gram, Annika. "Numerical Modelling of Self-Compacting Concrete Flow : Discrete and Continuous Approach." Licentiate thesis, KTH, Civil and Architectural Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10288.
Full textAbstract:
With the advent of Self-Compacting Concrete (SCC) that flows freely, under the soleinfluence of gravity, the wish for hassle-free and predictable castings even in complexcases, spurged the simulation of concrete flow as a means to model and predictconcrete workability. To achieve complete and reliable form filling with smoothsurfaces of the concrete, the reinforced formwork geometry must be compatible withthe rheology of the fresh SCC. Predicting flow behavior in the formwork and linkingthe required rheological parameters to flow tests performed on the site will ensurean optimization of the casting process.In this thesis, numerical simulation of concrete flow is investigated, using both discreteas well as continuous approaches.The discrete particle model here serves as a means to simulate details and phenomenaconcerning aggregates modeled as individual objects. The here presented cases aresimulated with spherical particles. However, it is possible to make use of nonsphericalparticles as well. Aggregate surface roughness, size and aspect ratio maybe modeles by particle friction, size and clumping several spheres into forming thedesired particle shape.The continuous approach has been used to simulate large volumes of concrete. Theconcrete is modeled as a homogeneous material, particular effects of aggregates,such as blocking or segregation are not accounted for. Good correspondence wasachieved with a Bingham material model used to simulate concrete laboratory tests(e.g. slump flow, L-box) and form filling. Flow of concrete in a particularly congestedsection of a double-tee slab as well as two lifts of a multi-layered full scale wall castingwere simulated sucessfully.A large scale quantitative analysis is performed rather smoothly with the continuousapproach. Smaller scale details and phenomena are better captured qualitativelywith the discrete particle approach. As computer speed and capacity constantlyevolves, simulation detail and sample volume will be allowed to increase.A future merging of the homogeneous fluid model with the particle approach to formparticles in the fluid will feature the flow of concrete as the physical suspension thatit represents. One single ellipsoidal particle falling in a Newtonian fluid was studiedas a first step.
Med uppkomsten av självkompakterande betong (SKB) och dess möjligheter att flyta ut under inverkan av endast gravitation uppstod ett behov av att kunna förutsäga och kontrollera även mer komplicerade gjutningar. Numerisk simulering av SKBs flöde kan kommma att utgöra ett kraftfullt verktyg för att optimera gjutprocessen, ge möjlighet att förutsäga nödbvändig arbetbarhet och säkerställa kompatibilitet mellan den armerade formen och betongens reologi. I föreliggande avhandling undersöks betongens flöde med både diskreta och kontinuumbaserade simuleringsmetoder. Den diskreta partikelmodellen används för att simulera detaljer och fenomen hos t.ex. ballast i betong. I de här presenterade simuleringarna används sfäriska partiklar, men det är även möjligt att skapa ballastkorn av olika form. Ballastens ytråhet och storlek kan modelleras med parametrar för friktion och storlek medan sammanfogning av ett flertal partiklar kan ge ekvivalent form. Den kontinuumbaserade ansatsen används för att simulera större flödesmängder. Betongen modelleras som ett homogent material, eventuella effekter av ballastens inverkan, till exempel blockering eller separation, ingår ej. God överensstämmelse har uppnåtts med Binghams materialmodell som applicerats på några av SKBs provningsmetoder (bl a flytsättmått och L-låda) liksom även för större gjutningar. Formfyllnad av en hårt armerad sektion av ett STT-element, liksom två pumpade betongleveranser till en hög vägg, har framgångsrikt simulerats. En kvantitativ övergripande analys av betongflödet i formen kan göras med den kontinuumbaserade ansatsen för att upptäcka zoner med eventuella svårigheter. En högupplöst detaljstudie kompletterar sedan analysen på valda delar av och kring dessa zoner för att fånga partikelfenomen kvalitativt med hjälv av den diskreta modellen. Då datorkapaciteten ökar kommer även större volymer med högre detaljrikedom att kunna simuleras. En framtida modell simulerar med stor sannolikhet partiklar i flöde, vilket till fullo kan fånga betongens egenskaper som suspension. Som ett första steg på vägen har en fallande ellipsoid i en newtonsk vätska simulerats.
24
Fahy, Caroline. "A discrete transport-mechanical approach for modelling the durability of concrete." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5761/.
Full textAbstract:
Reinforced concrete is one of the most commonly used structural materials in the world and is used for buildings and many different types of civil engineering structures, such as bridges, tunnels and airports. The majority of these structures are required to remain in service for at least 50 years while some are expected to last well over 100 years. Fracture of these structures leads to an increase in the permeability of the concrete which in turn can result in increased ingress of water and other aggressive agents, such as chlorides or carbon dioxide, that accelerate the deterioration of these structures. Likewise, the mechanical properties of the concrete can be affected by the transport of moisture into the structure. The increase in moisture can lead to a reduction of the strength and the stiffness of the material. The costs arising from structural failure are extremely high and in practice repair work tends to be implemented even when it is not entirely necessary. Therefore reliable approaches that can describe the interaction between the transport and mechanical properties of concrete and predict resulting structural degradation are of great benefit for practising engineers. Numerical models, such as the one proposed in this work, could be used for predicting when a repair is really necessary. In this work, a transport-mechanical lattice approach to modelling the durability of concrete is proposed. The discretisation of the specimen domain is based on a dual Delaunay and Voronoi tessellation in which the edges of the Delaunay triangles form the mechanical elements and the transport elements are placed along the edges of the Voronoi polygons. The mechanical response of the concrete is described using an isotropic damage constitutive law, while the transport of moisture through the specimen is described using constitutive laws developed for mass transport through porous materials. Both the mechanical and the transport models are assessed individually before the coupling ii between the two models is implemented. The accuracy of the proposed coupled approach is validated through the analysis of an elastic thick-walled cylinder, in which the numerical results are compared with an analytical solution derived as part of this work. The proposed coupled approach is then applied to the case of corrosion-induced cracking of reinforced concrete structures. In this approach, the corrosion products are assumed to behave as a fluid and therefore values of fluid properties are required. A value of viscosity is determined based on the analysis of a concrete specimen containing a single reinforcement bar. Finally, the proposed approach is applied to a concrete specimen containing four reinforcement bars to assess the approach as a predictive model. As expected with the concrete specimen containing a single reinforcement bar, very good agreement between numerical and experimental results is obtained. In the case of a specimen containing four reinforcement bars, it is observed that for small attack penetration depths the proposed approach is in very good agreement with experimental results. As the analysis continued, however, the numerical approach under-estimated the crack width when compared to experimental results.
25
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.
Full text
26
Neidig, Jörg. "An automata theoretic approach to modular diagnosis of discrete-event systems /." Norderstedt : Books on Demand, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016571312&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
Full text
27
Miclo, Romain. "Challenging the "Demand Driven MRP" Promises : a Discrete Event Simulation Approach." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2016. http://www.theses.fr/2016EMAC0016/document.
Full textAbstract:
Les principaux enjeux des supply chain d’aujourd’hui concernent l’adaptation à des environnements instables. Demand Driven Material Requirements Planning (DDMRP) est une méthode récente et prometteuse de gestion des flux qui a été conçue pour faire face aux problématiques actuelles. Le travail de recherche réalisé détaille et positionne DDMRP par rapport aux autres méthodes connues de pilotage de flux. Le but de ce travail est de challenger les principales promesses de DDMRP. Pour cela, un plan d’expériences a été réalisé sur un cas d’étude pour évaluer le comportement de MRP II, Kanban et DDMRP face à différentes sources de variabilité. Le dimensionnement des buffers DDMRP est un sujet majeur pour la méthode. Il a été traité sur un cas d’étude avec un travail d’optimisation. Toutes les contributions ont été expérimentées avec l’implémentation de DDMRP sur un cas réel. La thèse permet ainsi de valider certains atouts de DDMRP, tels que l’adaptation du système à différentes formes de variabilités, mais elle permet également de souligner des perspectives majeures de recherche sur ce sujetThe main Supply Chain current issues concern the adaptation to unstable environments. Demand Driven Material Requirements Planning (DDMRP) is a recent and promising material management method that is designed to tackle these current issues. The research work details and classifies DDMRP compared to the other material management methods known. The goal of this work is to challenge the main DDMRP promises. This is why a design of experiments was realised on a case study in order to assess MRP II, Kanban and DDMRP behaviours with different variability sources. The DDMRP buffer sizing is a major issue. It was dealt with an optimisation work on a case study. All the contributions were experimented with a DDMRP implementation on a real case. The research work enables several DDMRP advantages to be validated, such as the system adjustment to different variability sources, however this work also allows research perspectives to be underlined
28
Chegenizadeh, Amin. "Experimental approach to investigate reinforced clay." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/2288.
Full textAbstract:
Soil reinforcement with discrete flexible fibres has always been an issue for further research. In Geotechnical engineering field, the research on sandy soil has considerably been more than the clayey one. The main reason for this lack can be expressed as the complexity of clayey material due to their cohesion and interaction between clay and reinforcement.The present research aims to show possibility of discrete fibre usage in clay. For this purpose, selection of material has been conducted with special care to make the project outcome applicable to industry projects. The fibre which was used for this research prepared by BASF Company in Western Australia and currently is used in fibre reinforced concrete for infrastructure projects. Kaolin has been used as soil part and provided by Prestige Company.Experimental approach was applied to investigate the effect of different parameters on composite soil strength. These tests cover the variety range of soil mechanics tests from compaction tests to triaxial compression tests. The results from all the tests were presented in the thesis.A theoretical model was also developed for clayey material for the first time with the use of modified cam clay model to predict the behaviour of samples precisely. This model is based on the rule of mixture and considers the effect of soil and fibre separately. The model was validated with the results from CD triaxial test.
29
Danancher, Mickaël. "A discrete event approach for model-based location tracking of inhabitants in smart homes." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2013. http://tel.archives-ouvertes.fr/tel-00955543.
Full textAbstract:
Life expectancy has continuously increased in most countries over the last decades and will probably continue to increase in the future. This leads to new challenges relative to the autonomy and the independence of elderly. The development of Smart Homes is a direction to face these challenges and to enable people to live longer in a safe and comfortable environment. Making a home smart consists in placing sensors, actuators and a controller in the house in order to take into account the behavior of their inhabitants and to act on their environment to improve their safety, health and comfort. Most of these approaches are based on the real-time indoor Location Tracking of the inhabitants. In this thesis, a whole new approach for model-based Location Tracking of an a priori unknown number of inhabitants is proposed. This approach is based on Discrete Event Systems paradigms, theory and tools. The usage of Finite Automata (FA) to model the detectable motion of the inhabitants as well as different methods to create such FA models have been developed. Based on these models, algorithms to perform efficient Location Tracking are defined. Finally, several approaches aiming at evaluating the relevance of the instrumentation of a Smart Home with the objective of Location Tracking are proposed. The approach has also been fully implemented and tested. Throughout the thesis, the different contributions are illustrated on case studies.
30
Jayaraman, Gangadhar. "Computational schemes for exact linearization of discrete-time systems using a geometric approach." Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058542922.
Full text
31
Prager, Tobias. "Synchronization in periodically driven and coupled stochastic systems a discrete state approach /." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980110262.
Full text
32
Li, Yufeng. "High precision motion control based on a discrete-time sliding mode approach." Doctoral thesis, KTH, Machine Design, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3293.
Full text
33
Macedo, J. M. P. "An integrated approach to the parallel processing of explicit/discrete element problems." Thesis, Swansea University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637970.
Full textAbstract:
A framework to implement parallel programs able to run on shared and/or distributed memory machines has been developed in the present thesis, using an explicit finite/discrete element code as proof of the principle. A system, termed SMeM, conveniently documented with an interface to web browsers, has been designed and implemented to create an interface to parallel programs using shared memory parallel machines. The system contains a set of libraries to be used by C language and/or FORTRAN programs, providing real time/post mortem event/state log system and debugging facilities, including a mechanism to activate a debugger within the processes of a parallel program. An explicit finite/discrete element code has been parallelised, using the library, able to run on shared and/or distributed memory machines, and to solve large strain elasto-plastic problems using adaptive remeshing techniques. Some specific algorithms have been implemented in order to create an efficient parallel solution, namely: a parallel contact detection algorithm using an alternating digital tree; a more efficient dual graph to be used by domain decomposers and, for contact problems, a fast algorithm to define the boundary of the finite element domain; and a technique to identify the underlining elements of the old mesh associated to the nodal points on the regenerated mesh, when adaptivity is involved.
34
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.
Full textAbstract:
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
35
Özveren, Cüneyt M. "Analysis and control of discrete event dynamic systems : a state space approach." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14183.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1989.GRSN 409176
Includes bibliographical references (leaves 263-267).
by Cüneyt Mehmet Özveren.
Ph.D.
36
Lee, J. "Nonparametric structural analysis of discrete data : the quantile-based control function approach." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/516136/.
Full textAbstract:
The first chapter is introduction and Chapter 2 proposes formal frameworks for identifiability and testability of structural features allowing for set identification. The results in Chapter 2 are used in other chapters. The second section of Chapter 3, Chapter 4 and Chapter 5 contain new results. Chapter 3 has two sections. The first section introduces the quantile-based control function approach (QCFA) proposed by Chesher (2003) to compare and contrast other results in Chapter 4 and 5. The second section contains new findings on the local endogeneity bias and testability of endogeneity. Chapter 4 assumes that the structural relations are differentiable and applies the QCFA to several models for discrete outcomes. Chapter 4 reports point identification results of partial derivatives with respect to a continuously varying endogenous variable. Chapter 5 relaxes differentiability assumptions and apply the QCFA with an ordered discrete endogeneous variable. The model in Chapter 5 set identifies partial differences of a nonseparable structural function.
37
Andersson, Carl. "A bonded discrete element approach to simulate loading with hydraulic mining excavators." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-84845.
Full textAbstract:
When operating hydraulic mining excavators the loading equipment is exposed to harsh conditions which lead to extensive wear of the equipment, especially the bucket and bucket teeth. Simulations are used to better understand the wear development and to evaluate new methods to operate excavators more efficiently. At the Aitik mine, operated by the high-tech metal company Boliden Mines, hydraulic excavators are used when loading the mined ore. One of the hydraulic excavators used at Aitik is the Komatsu PC7000. In this master thesis, a simulation model for the hydraulic excavator Komatsu PC7000 was developed with the simulation software LS-DYNA. This model consists of multi rigid body dynamics to describe the motion of the excavator and a granular material model to describe the rocks loaded into the bucket of the excavator. Simulations with two different types of granular material models have been utilized to study the wear development of the bucket. One of the models (bonded DE model) uses bonded discrete elements to describe the large rocks and single discrete elements are used to describe smaller rocks. This model is compared to the current FE-DE model which is being used today at Boliden. This model uses finite elements (FE) to model the larger rocks and discrete element spheres (DES) for smaller rocks. By using the bonded DE method a 71\% reduction in simulation time could be achieved. This can be partly explained by the reduction of the number of elements included in the rock pile. Archard's wear law was used to numerically describe the wear development of the bucket. When simulating the wear a total of 30 bucket fillings were performed with the excavator. This was done with both the bonded DE method and the FE-DE method. In this wear study, the inside of the bucket was of interest. The resulting simulated wear map was compared to experimental measurements from which the plate thickness of the bucket had been measured two times to obtain the wear depth of some points inside the bucket. The experimental measurements and two 3D scanned point clouds were used to determine the wear depth inside the bucket. Results from the simulation showed that the wear is concentrated to the center of the bucket while less wear is concentrated to the sides of the bucket. With the bonded DE method the wear appeared to be more evenly distributed inside the bucket while the wear from the FE-DE method appeared in spots inside the bucket. The experimental results also showed that the wear was more extensive in the center of the bucket and also in the back of the bucket. Both simulation methods also showed that the wear was concentrated to the back of the bucket. From the simulations, it was also seen that the behavior of the material flow differed between the two methods. In the bonded DE method the material flow had more sliding behavior while the material flow in the FE-DE method had more rolling behavior. This could also be the reason why the bonded DE method captures the wear more evenly. The rolling behavior seen in the FE-DE method leads to more impact wear which is not captured by Archard's wear law. Overall, the bonded DE method leads to a big reduction in simulation time which is favorable when it comes to simulation. The larger rocks will have simpler shapes without sharp corners. However, the method allows for a more complex shape than just an ordinary sphere which is the simplest and most common shape to describe granular material. The bonded DE method also allows for easier configuration of contact definition since fewer contact interfaces must be added to the model. Furthermore, the post-processing of wear in LS-DYNA was facilitated since the wear does not have to be divided into two wear collectors for FE elements and DE elements.
38
Roveda, Roberto. "A combined discrete velocity particle based numerical approach for continuum/rarefied flows /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004370.
Full text
39
Banham, Benjamin E. "An Evolutionary Approach to Image Compression in the Discrete Cosine Transform Domain." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/5.
Full textAbstract:
This paper examines the application of genetic programming to image compression while working in the frequency domain. Several methods utilized by JPEG encoding are applied to the image before utilizing a genetic programming system. Specifically, the discrete cosine transform (DCT) is applied to the original image, followed by the zig-zag scanning of DCT coefficients. The genetic programming system is finally applied to the one-dimensional array resulting from the zig-zag scan. The research takes an existing genetic programming system developed for the spatial domain and develops DCT domain functionality. The results from the DCT domain-based genetic programming system are compared with those from the spatial domain-based system, and show improvements to the image quality with a reduction up to half of the evolved image's average error. The results show that working in the frequency domain has advantages over the spatial domain. Several methods to exploit these advantages are proposed and evaluated.
40
Sleimen, Rita. "Coupling ans symmetry breaking in discrete bimanual tasks : a proof of concept approach in stroke." Thesis, Aix-Marseille 2, 2011. http://www.theses.fr/2011AIX22113.
Full textAbstract:
Les objectifs de notre travail étaient : (i) de proposer un nouveau cadre conceptuel pour l’entraînement bimanuel chez les patients hémiplégiques (ii) de concevoir et tester une nouvelle approche de rééducation basée sur l’équilibre entre les différentes contraintes. Afin d’atteindre ces objectifs, nous avons adopté une approche du type preuve-de-concept.La première partie de ce document est consacrée à une revue critique de la littérature. La deuxième partie présente le travail expérimental qui était mené pour explorer ce concept, chez des sujets sains et des patients hémiparétiques. La première étude a exploré le comportement unimanuel dans une tâche de pointage discret pour une large gamme de d’indices de difficulté (ID). Dans la seconde étude, nous avons exploré l’effet de l’asymétrie bimanuelle induite par la tâche sur l’expression du couplage. La troisième étude aborde la problématique des asymétries induites par l’AVC et par la tâche chez des patients soufrant de déficits plus ou moins graves. Globalement, les résultats expérimentaux ont corroboré nos hypothèses initiales. Ainsi, ils nous ont permis de concevoir une nouvelle stratégie de rééducation bimanuelle. Cette stratégie de rééducation, avec le protocole de recherche clinique en cours, ont été présentés dans la troisième partie de la thèse. Notre approche a fourni une preuve de concept sur l’importance de l’équilibre entre couplage et rupture de symétrie dans le comportement bimanuel du patient hémiplégique. Elle a permis également d’envisager la manière dont les asymétries devraient être prises en compte dans la rééducation. Les perspectives futures ont été discutées dans la dernière partie du manuscritIn the present work we aimed at: (i) setting new conceptual foundations for bimanual movement training in stroke, and (ii) providing practical guidelines to appropriately design and test a comprehensive constraint-led bimanual rehabilitation strategy. In order to achieve these stated objectives, we adopted a proof-of-concept approach.The first part of the current manuscript includes a critical review of BMT literature on the basis of the theoretical principles and empirical findings of the dynamical systems approach. The second part reports the experimental work that was conducted to investigate this concept in healthy and in hemiparetic subjects. The first study investigated unimanual discrete rapid aiming, under different task conditions and for a wide range ID values. In the second study, the effect of task-induced inter-limb asymmetry on the expression of bimanual coupling was explored. The third study, addressed the issue of task- and stroke-induced asymmetries in patients with different degrees of impairments. Overall, experimental findings corroborated our initial hypotheses. It permitted the design of a new BMT strategy to (re)train stroke patient. This rehabilitation strategy and the on-going clinical protocol were presented in the third part of the thesis.Though voluntarily qualitative, our approach provided a preliminary proof of concept on how CVA- and task-induced inter-limb asymmetries should be taken into account in rehabilitation. The conclusions of our work along with the opened perspectives were discussed at the end of the manuscript
41
Wasadikar, Amit. "DEVELOPING AN OBJECT-ORIENTED APPROACH FOR OPERATIONS SIMULATION IN SPEEDES." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2126.
Full textAbstract:
Using simulation techniques, performance of any proposed system can be tested for different scenarios with a generated model. However, it is difficult to rapidly create simulation models that will accurately represent the complexity of the system. In recent years, Object-Oriented Discrete-Event Simulation has emerged as the potential technology to implement rapid simulation schemes. A number of software based on programming languages like C++ and Java are available for carrying out Object Oriented Discrete-Event Simulation. These software packages establish a general framework for simulation in computer programs, but need to be further customized for desired end-use applications. In this thesis, a generic simulation library is created for the distributed Synchronous Parallel Environment for Emulation and Discrete-Event Simulation (SPEEDES). This library offers classes to model the functionality of servers, processes, resources, transporters, and decisions. The library is expected to produce efficient simulation models in less time and with a lesser amount of coding. The class hierarchy is modeled using the Unified Modeling Language (UML). To test the library, the existing SPEEDES Space Shuttle Model is enhanced and recreated. This enhanced model is successfully validated against the original Arena model.M.S.
Department of Industrial Engineering and Management Systems
Engineering and Computer Science
Industrial Engineering and Management Systems
42
Ali, Shaukat. "Newton-Euler approach for bio-robotics locomotion dynamics : from discrete to continuous systems." Phd thesis, Ecole des Mines de Nantes, 2011. http://tel.archives-ouvertes.fr/tel-00669588.
Full textAbstract:
This thesis proposes a general and unified methodological framework suitable for studying the locomotion of a wide range of robots, especially bio-inspired. The objective of this thesis is twofold. First, it contributes to the classification of locomotion robots by adopting the mathematical tools developed by the American school of geometric mechanics.Secondly, by taking advantage of the recursive nature of the Newton-Euler formulation, it proposes numerous efficient tools in the form of computational algorithms capable of solving the external direct dynamics and the internal inverse dynamics of any locomotion robot considered as a mobile multi-body system. These generic tools can help the engineers or researchers in the design, control and motion planning of manipulators as well as locomotion robots with a large number of internal degrees of freedom. The efficient algorithms are proposed for discrete and continuous robots. These methodological tools are applied to numerous illustrative examples taken from the bio-inspired robotics such as snake-like robots, caterpillars, and others like snake-board, etc.
43
Lin, Jing-Yue. "A temporal logic approach to the analysis and synthesis of discrete-event systems." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6635.
Full textAbstract:
The analysis and synthesis of discrete event systems (DESs) are addressed in this thesis by a temporal logic approach. This approach provides a temporal logic model and a temporal logic language for the modeling and specification, an algorithm for reachability analysis, and a procedure for the controller design and synthesis of DESs. To handle the probabilistic system where the point probability distributions are known, a temporal logic model is defined and a generalized temporal logic language is formulated to include the certainty operators for specifications and verification. An algorithm is developed for computing the reachability set and constructing the reachability graph. Using a process algebra, the composition and synthesis of processes are investigated through the process homomorphism; and a procedure is proposed for the controller synthesis and configuration. Then the optimization problem of DESs is solved by the $A\sp*$ algorithm via a heuristic search. Based on these results, a software package is developed for the temporal logic evaluation, reasoning and simulating discrete event systems. The software is designed using an object-oriented approach and implemented in Objective-C. The simulation results are reported in terms of the logic evaluation, temporal logic reasoning, and discrete event system simulation. Besides, the examples of applications are also given to convey and motivate the theoretical discussions. The results are compared with related works, particularly, qualitative reasoning, other modeling approaches of DESs, and different temporal logic approaches; and our results are seen more advantageous than them in various aspects.
44
Jiang, Shengbing. "SUPERVISORY CONTROL AND FAILURE DIAGNOSIS OF DISCRETE EVENT SYSTEMS: A TEMPORAL LOGIC APPROACH." UKnowledge, 2002. http://uknowledge.uky.edu/gradschool_diss/338.
Full textAbstract:
Discrete event systems (DESs) are systems which involve quantities that take a discrete set of values, called states, and which evolve according to the occurrence of certain discrete qualitative changes, called events. Examples of DESs include many man-made systems such as computer and communication networks, robotics and manufacturing systems, computer programs, and automated trac systems. Supervisory control and failure diagnosis are two important problems in the study of DESs. This dissertation presents a temporal logic approach to the control and failure diagnosis of DESs. For the control of DESs, full branching time temporal logic-CTL* is used to express control specifications. Control problem of DES in the temporal logic setting is formulated; and the controllability of DES is defined. By encoding the system with a CTL formula, the control problem of CTL* is reduced to the decision problem of CTL*. It is further shown that the control problem of CTL* (resp., CTL{computation tree logic) is complete for deterministic double (resp., single) exponential time. A sound and complete supervisor synthesis algorithm for the control of CTL* is provided. Special cases of the control of computation tree logic (CTL) and linear-time temporal logic (LTL) are also studied; and for which algorithms of better complexity are provided. For the failure diagnosis of DESs, LTL is used to express fault specifications. Failure diagnosis problem of DES in the temporal logic setting is formulated; and the diagnosability of DES is defined. The problem of testing the diagnosability is reduced to that of model checking. An algorithm for the test of diagnosability and the synthesis of a diagnoser is obtained. The algorithm has a polynomial complexity in the number of system states and the number of fault specifications. For the diagnosis of repeated failures in DESs, different notions of repeated failure diagnosability, K-diagnosability, [1,K]-diagnosability, and [1,1]-diagnosability, are introduced. Polynomial algorithms for checking these various notions of repeated failure diagnosability are given, and a procedure of polynomial complexity for the on-line diagnosis of repeated failures is also presented.
45
Curram, Stephen Paul. "Representing intelligent decision making in discrete event simulation : a stochastic neural network approach." Thesis, University of Warwick, 1997. http://wrap.warwick.ac.uk/59461/.
Full textAbstract:
The problem of representing decision making behaviour in discrete event simulation was investigated. Of particular interest was modelling variety in the decisions, where different people might make different decisions even where the same circumstances hold. An initial investigation of existing and alternative approaches for representing decision making was carried out. This led to the suggestion of using a neural network to represent the decision making behaviour in the form of a multi-criteria probability distribution based on data of observed decision making. The feasibility of the stochastic neural network approach was investigated. Models were fitted using artificial data from discrete and continuous distributions that included the shape parameters as inputs, and tested against known results from the distributions. Also a bank simulation was used to collect data from volunteers who controlled the queuing decisions of customers inside the bank. Models of their behaviour were created and implemented in the bank simulation to automate the decision making of customers. The investigation established the feasibility of the approach, although it indicated the need for substantial amounts of data showing examples of decision making. A hybrid model that combined the stochastic neural network approach with a rule-based approach allowed the development of more general models of decision making behaviour.
46
Davoren, Mark. "A structural approach to the mapping problem in parallel discrete event logic simulations." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/14748.
Full text
47
Marques, Alexandre Noll. "A unified discrete-time approach to the state space representation of aeroelastic systems." Instituto Tecnológico de Aeronáutica, 2007. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=350.
Full textAbstract:
In complex flow situations, it is common to use numerical tools to evaluate the aerodynamic unsteady behavior. The present work presents an alternate formulation for the state space representation of aeroelastic systems based on digital control theory that is shown to be effective and accurate for the coupling of numerical solutions with such systems. The application of the z transform allows for direct frequency domain representations of the aerodynamic solutions without the need for approximating models, as generally occurs in other state space formulations. This fact makes this new methodology also a more straightforward procedure for aeroelastic analyses. A survey on the numerical calculation of impulsive and indicial unsteady aerodynamic responses with modern CFD solvers is also presented. A brief historical background on this subjected is introduced, and it is shown how new interpretations of CFD solvers as discrete-time systems change the way impulsive and indicial responses can be directly obtained. The objective is to demonstrate that the rigorous relationships theoretically established among the aerodynamic responses to impulsive, indicial, harmonic and smooth inputs can be reproduced numerically with modern CFD solvers. Although the numerical results presented herein are obtained with a single CFD tool, the argument is valid for every numerical solution scheme. The CFD tool in question solves the two-dimensional Euler equations with an explicit time march, using a finite volume discretization which supports fully unstructured grids. The results are compared both in the time and in the frequency domains, which yields a more complete understanding of details of the numerical solutions. Finally, typical section models of a flat plate and a NACA 0012 airfoil at subsonic and transonic speed are used as test-cases in order to assess the correctness and accuracy of the proposed aeroelastic analysis methodology. The present results are compared with data obtained from continuous-time state space formulations and through the direct integration of the structural dynamic and aerodynamic equations.
48
Myers, Douglas Ray. "A knowledge-based approach for diagnosis of discrete processes involving programmable logic controllers /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487685204970728.
Full text
49
Parker, I. "A study of brittle powder compaction using a combined discrete finite element approach." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/12511.
Full textAbstract:
Bibliography: leaves 100-103.The Discrete Element Method (DEM) is a collection of numerical techniques based on a discontinuum idealisation of a physical system. Discrete Element Methods have been successfully applied to the simulation of the dynamic behaviour of granular media. Using the Finite Element Method to model the behaviour of each discrete element has resulted in the Combined Finite Discrete Element Method. This combination allows researchers to investigate the behaviour of assemblies of particles in which each particle need not behave in an entirely elastic mamrer. More importantly, discrete crack constitutive models may now be applied to each discrete element. The purpose of this thesis is to simulate the macroscopic behaviour of an assembly of brittle particles, using the Combined Finite Discrete Element Method. Brittle behaviour is incorporated via the use of a Mode I and Mode II brittle failure constitutive models. The Mode I and Mode II failure models used are the Rankine and Tresca failure models, respectively. The development of a pre-processor to generate the initial configuration of the particle assembly also formed a major component of the thesis. Algorithms to fill a plane with randomly shaped polygons were developed and implemented for the pre-processor. The cold compaction process is idealised as the compaction of a granular medium, in which each particle is a deformable polygon. Two algorithms are proposed and implemented to generate randomly shaped polygons. A further algorithm was developed to fill a simple bounding polygon with smaller polygons. A_commercial CFDEM code, ELFENExplicit, was used to investigate the effect of particle constitutive model and particle interaction on the macroscopic behaviour of the granular assembly. The built-in linear elastic and Mode I Rankine failure models were used in the initial simulations while a Tresca failure model was implemented to investigate the effect of a Mode II failure model.
50
Helal, Magdy. "A hybrid system dynamics-discrete event simulation approach to simulating the manufacturing enterprise." Orlando, Fla. : University of Central Florida, 2008. http://purl.fcla.edu/fcla/etd/CFE0002264.
Full text