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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Dynamic Adaptive Multimesh Refinement for Coupled Physics Equations Applicable to Nuclear Engineering

Dugan, Kevin 16 December 2013 (has links)
The processes studied by nuclear engineers generally include coupled physics phenomena (Thermal-Hydraulics, Neutronics, Material Mechanics, etc.) and modeling such multiphysics processes numerically can be computationally intensive. A way to reduce the computational burden is to use spatial meshes that are optimally suited for a specific solution; such meshes are obtained through a process known as Adaptive Mesh Refinement (AMR). AMR can be especially useful for modeling multiphysics phenomena by allowing each solution component to be computed on an independent mesh (Multimesh AMR). Using AMR on time dependent problems requires the spatial mesh to change in time as the solution changes in time. Current algorithms presented in the literature address this concern by adapting the spatial mesh at every time step, which can be inefficient. This Thesis proposes an algorithm for saving computational resources by using a spatially adapted mesh for multiple time steps, and only adapting the spatial mesh when the solution has changed significantly. This Thesis explores the mechanisms used to determine when and where to spatially adapt for time dependent, coupled physics problems. The algorithm is implemented using the Deal.ii fiinite element library [1, 2], in 2D and 3D, and is tested on a coupled neutronics and heat conduction problem in 2D. The algorithm is shown to perform better than a uniformly refined static mesh and, in some cases, a mesh that is spatially adapted at every time step.
2

Timing of fuzzy membership functions from data

Frantti, T. (Tapio) 20 June 2001 (has links)
Abstract In this dissertation the generation and tuning of fuzzy membership function parameters are considered as a part of the fuzzy model development process. The automatic generation and tuning of fuzzy membership function parameters are needed for the fast adaptation and tuning of fuzzy models of various nonlinear dynamical systems. The developed methods are especially useful in automatic fuzzy membership function generation and tuning when dynamic of application area is fast enough to exclude manual tuning. The fuzzy model development process and development methods, modelling environment and nature of application area as well as algorithm development parameters are extensively discussed, because each of them sets their own restrictions on the design parts and parameters used in the modelling. The developed methods have been applied in different kinds of applications (in forecasting the demand of signal transmission products, power control and code tracking of cellular phone system, fuzzy reasoning in radio resource functions of cellular phone systems), where other approaches are either very difficult or too time consuming to implement. The professional areas of the thesis are fuzzy modelling and control in telecommunications.
3

On goal-oriented error estimation and adaptivity for nonlinear systems with uncertain data and application to flow problems

Bryant, Corey Michael 09 February 2015 (has links)
The objective of this work is to develop a posteriori error estimates and adaptive strategies for the numerical solution to nonlinear systems of partial differential equations with uncertain data. Areas of application cover problems in fluid mechanics including a Bayesian model selection study of turbulence comparing different uncertainty models. Accounting for uncertainties in model parameters may significantly increase the computational time when simulating complex problems. The premise is that using error estimates and adaptively refining the solution process can reduce the cost of such simulations while preserving their accuracy within some tolerance. New insights for goal-oriented error estimation for deterministic nonlinear problems are first presented. Linearization of the adjoint problems and quantities of interest introduces higher-order terms in the error representation that are generally neglected. Their effects on goal-oriented adaptive strategies are investigated in detail here. Contributions on that subject include extensions of well-known theoretical results for linear problems to the nonlinear setting, computational studies in support of these results, and an extensive comparative study of goal-oriented adaptive schemes that do, and do not, include the higher-order terms. Approaches for goal-oriented error estimation for PDEs with uncertain coefficients have already been presented, but lack the capability of distinguishing between the different sources of error. A novel approach is proposed here, that decomposes the error estimate into contributions from the physical discretization and the uncertainty approximation. Theoretical bounds are proven and numerical examples are presented to verify that the approach identifies the predominant source of the error in a surrogate model. Adaptive strategies, that use this error decomposition and refine the approximation space accordingly, are designed and tested. All methodologies are demonstrated on benchmark flow problems: Stokes lid-driven cavity, 1D Burger’s equation, 2D incompressible flows at low Reynolds numbers. The procedure is also applied to an uncertainty quantification study of RANS turbulence models in channel flows. Adaptive surrogate models are constructed to make parameter uncertainty propagation more efficient. Using surrogate models and adaptivity in a Bayesian model selection procedure, it is shown that significant computational savings can be gained over the full RANS model while maintaining similar accuracy in the predictions. / text
4

Software adaptativo: método de projeto, representação gráfica e implementação de linguagem de programação. / Adaptive software: project method, graphical representation and programming language implementation.

Silva, Salvador Ramos Bernardino da 02 September 2011 (has links)
Linguagem para programação adaptativa se apresenta como um tema relativo às tecnologias adaptativas que suscita muitas pesquisas, até que venha a se constituir em mais uma ferramenta disponível ao programador. Nessa perspectiva, esta dissertação apresenta uma linguagem de alto nível, básica, que permita a geração de código adaptativo, bem como os requisitos e características de uma linguagem dessa natureza, recomendações sobre como projetar um software nessa linguagem e a representação gráfica do mesmo, o respectivo compilador e o ambiente de run-time no qual os programas serão executados. Apresenta, ainda, um exemplo de um programa fonte escrito na linguagem proposta. / Programming Languages for coding adaptive programs constitute a very rich research subject in the field of adaptive technology. It aims to offer a tool for programmers to express adaptive programs in a user-friendly, high-level, machine- readable, abstract notation. This MSc thesis presents the specification of requirements and desirable attributes for high-level languages allowing the automatic generation of adaptive code, and recommends a design methodology for conceiving and implementing adaptive programs using such languages as well. A graphical notation is suggested for that purpose, a compiler and a run-time environment are also considered and described. An example is given of the design and semi-formal specification of an adaptive software with the help of the suggested graphical notation, and finally the corresponding source program is encoded in the proposed language and executed.
5

Software adaptativo: método de projeto, representação gráfica e implementação de linguagem de programação. / Adaptive software: project method, graphical representation and programming language implementation.

Salvador Ramos Bernardino da Silva 02 September 2011 (has links)
Linguagem para programação adaptativa se apresenta como um tema relativo às tecnologias adaptativas que suscita muitas pesquisas, até que venha a se constituir em mais uma ferramenta disponível ao programador. Nessa perspectiva, esta dissertação apresenta uma linguagem de alto nível, básica, que permita a geração de código adaptativo, bem como os requisitos e características de uma linguagem dessa natureza, recomendações sobre como projetar um software nessa linguagem e a representação gráfica do mesmo, o respectivo compilador e o ambiente de run-time no qual os programas serão executados. Apresenta, ainda, um exemplo de um programa fonte escrito na linguagem proposta. / Programming Languages for coding adaptive programs constitute a very rich research subject in the field of adaptive technology. It aims to offer a tool for programmers to express adaptive programs in a user-friendly, high-level, machine- readable, abstract notation. This MSc thesis presents the specification of requirements and desirable attributes for high-level languages allowing the automatic generation of adaptive code, and recommends a design methodology for conceiving and implementing adaptive programs using such languages as well. A graphical notation is suggested for that purpose, a compiler and a run-time environment are also considered and described. An example is given of the design and semi-formal specification of an adaptive software with the help of the suggested graphical notation, and finally the corresponding source program is encoded in the proposed language and executed.
6

Model sistema elektronskog učenja za poboljšanje kognitivnog postignuća studenata / The model of e-learning systems used for the improvement of students’ cognitive achievements

Ristić Igor 25 June 2020 (has links)
<p>U dana&scaron;nje vreme sve vi&scaron;e obrazovnih institucija kao &scaron;to su fakulteti koji nude e-obrazovanje. U nekim slučajevima učenje na daljinu je ukombinovano sa tradicionalnim oblicima učenja, dok se u drugim ono odvija u potpunosti samostalno putem internata. U svakom slučaju da bi učenje na daljinu moglo da se realizuje i da bi njime moglo da se upravlja potrebno je da postoji posebno okruženje u kom će se ono organizovati. U većini slučajeva Sistemi za obrazovanje na daljinu &ndash; (Learning management system &ndash; LMS) obavljaju ovaj zadatak. LMS obezbeđuje raznovrsne alate za podr&scaron;ku profesorima u kreiranju, administriraju i upravljanju online kursevima. S druge strane oni uglavnom ne uzimaju u obzir individualne razlike studenata i tretiraju sve studente na isti način bez obzira na njihove lične potrebe i karakteristike. U na&scaron;oj literaturi ne postoji puno radova koji se bave temom adaptivnog elektronskog obrazovanja, naročito ne sa aspekta izrade i implementacije modela adaptivnog elektronskog obrazovanja. Predmet ove doktorske disertacije je implementacija sistema za elektronsko obrazovanje koji je kreiran po modelu adaptivnog elektronskog obrazovanja i koji obezbeđuje za isto vreme veće neposredno znanje korisnika i pozitivno utiče na trajnost znanja, nego standardni neadaptivni sistem za elektronsko obrazovanje. U radu su kombinovane prednosti LMS-a sa adaptivnim sistemima i na taj način je pro&scaron;irena funkcija LMS-a tako &scaron;to su integrisani stilovi učenja i obezbeđena je adaptivnost sistema. Adaptivni model elektronskog obrazovanja koji je razvijen u radu je implementiran i procenjivan kori&scaron;ćenjem Moodle sistema. Ova doktorska disertacija imala je za cilj da na osnovu kreiranja, implementacije i kori&scaron;ćenja modela adaptivnog elektronskog obrazovanja ukaže na statistički značajnu mogućnost podizanja sveobuhvatnog nivoa i kvaliteta obrazovnog procesa.</p> / <p>Nowadays the majority of universities offer e-learning to their students. Sometimes distance learning is combined with traditional education, while in other cases it functions on its own by using the Internet. However, distance learning requires special surroundings where it can be organized. Learning management systems &ndash; LMSs are used in most of the cases for distance learning. LMS provides professors with various tools for creation, administration, and management of online courses. On the other hand, LMSs don&rsquo;t usually consider individual differences of students and treat all students in the same way, disregarding their personal needs and characteristics. In our literature, there are very few studies that analyze adaptive e-learning systems, especially the creation and implementation of adaptive e-learning models. The goal of this doctoral thesis has been creation and implementation of an adaptive model of the e-learning system which provides students with wider knowledge that lasts a longer period of time comparing to the knowledge acquired with standard (non-adaptive) systems of e-learning. The thesis has expanded the function of LMS by combining LMS with adaptive systems and incorporating students&rsquo; learning styles into it. The adaptive model that is developed in the thesis has been implemented and evaluated by using Moodle system. The aim of the doctoral thesis has been to point out at statistically significant probability of improving the level and quality of the educational process by creating, implementing and using the adaptive model of e-learning.</p>
7

Hybrid Adaptive Multilevel Monte Carlo Algorithm for Non-Smooth Observables of Itô Stochastic Differential Equations

Rached, Nadhir B. 12 1900 (has links)
The Monte Carlo forward Euler method with uniform time stepping is the standard technique to compute an approximation of the expected payoff of a solution of an Itô SDE. For a given accuracy requirement TOL, the complexity of this technique for well behaved problems, that is the amount of computational work to solve the problem, is O(TOL-3). A new hybrid adaptive Monte Carlo forward Euler algorithm for SDEs with non-smooth coefficients and low regular observables is developed in this thesis. This adaptive method is based on the derivation of a new error expansion with computable leading-order terms. The basic idea of the new expansion is the use of a mixture of prior information to determine the weight functions and posterior information to compute the local error. In a number of numerical examples the superior efficiency of the hybrid adaptive algorithm over the standard uniform time stepping technique is verified. When a non-smooth binary payoff with either GBM or drift singularity type of SDEs is considered, the new adaptive method achieves the same complexity as the uniform discretization with smooth problems. Moreover, the new developed algorithm is extended to the MLMC forward Euler setting which reduces the complexity from O(TOL-3) to O(TOL-2(log(TOL))2). For the binary option case with the same type of Itô SDEs, the hybrid adaptive MLMC forward Euler recovers the standard multilevel computational cost O(TOL-2(log(TOL))2). When considering a higher order Milstein scheme, a similar complexity result was obtained by Giles using the uniform time stepping for one dimensional SDEs. The difficulty to extend Giles' Milstein MLMC method to the multidimensional case is an argument for the flexibility of our new constructed adaptive MLMC forward Euler method which can be easily adapted to this setting. Similarly, the expected complexity O(TOL-2(log(TOL))2) is reached for the multidimensional case and verified numerically.
8

Localized Coarsening of Conforming All-Hexahedral Meshes

Woodbury, Adam C. 28 July 2008 (has links) (PDF)
Finite element mesh adaptation methods can be used to improve the efficiency and accuracy of solutions to computational modeling problems. For many finite element modeling applications, a conforming all-hexahedral mesh is preferred. When adapting a hexahedral mesh, localized modifications that preserve topologic conformity are often desired. Effective hexahedral refinement methods that satisfy these criteria have recently become available. However, due to hexahedral mesh topology constraints, little progress has been made in the area of hexahedral coarsening. This thesis presents a new method to locally coarsen conforming all-hexahedral meshes. The method works on both structured and unstructured meshes and is not based on undoing previous refinement. Building upon recent developments in quadrilateral coarsening, the method utilizes hexahedral sheet and column operations, including pillowing, column collapsing, and sheet extraction. A general algorithm for automated coarsening is presented and examples of models that have been coarsened are shown. While results are promising, further work is needed to improve the automated process.
9

Live, Work, Adapt: Deconstructing Work-Life Balance

Walker, Arielannia Verdella 15 June 2023 (has links)
This thesis is derived from dissatisfaction with the term work–life balance. Definitions of the term imply that we have the ability to separate half of our time between home and work, but it is never this binary. The term is too simple to describe the vast concepts of work and life. Work-life balance is similar to playing a losing game with time, where one aspect is often neglected, may it be time for self, family, or health. The neglect is a product of overwork and financial stress. In The Healthy Workplace Nudge, they note that "work is baking stress into the workforce and that work is the fifth leading cause of death in America," 1 and that work-related stress is associated with a range of health concerns such as poor mental well-being, social isolation, and chronic diseases. 83% of Americans experience the effects of work-related stress.2 Consequently, they carry these feelings home each day. As factors of life pile on coupled with a range of social issues, life becomes harder to balance between home and work. As a response to rapid and unpredictable changes in society, this thesis aims to explore the ways we live and work. How can home and work environments adapt to the changing needs of society? The initial hypothesis was that a proposed shared living complex has the potential to provide social support and strengthen accessibility to programs where the individual can gain a better quality of life. Efforts to deconstruct work-life balance include breaking down the concepts of work, life, and self, causing this thesis to seem immeasurable at times. The study's intent is not to completely redefine the term but to explore how individuals can view the term as a more fluid approach to navigating life. / Master of Architecture / Work-related stress is at an all-time high, with 83% of Americans feeling pressure from work and financial concerns.2 The project acknowledges this, but it is not just concerned with those feeling the blow of burnout. Everyone works, adults, children, and teenagers. Work is an indispensable and necessary part of life, and there are multiple types of work. There is financial work, the job you do to pay the bills, there's hobby work, the things you do outside of the place you work and then there's relationship and self-work, this includes taking time to yourself and loved ones. I selected this thesis topic because it is a topic that I am passionate about and can continue to research throughout my architectural career. It's my fundamental belief that basic conditions of life should not be a struggle. This thesis is intended for people who work endlessly to provide financial support for loved ones, but because of working hours and fatigue are not able to spend time with them. It is also for those who work a demanding job and eventually work themselves into burnout and mental exhaustion, leaving it hard for them to recover. It is also for future workers to highlight the importance of discovering what matters to them. Whatever your occupation or stage of life, we all work and want a prosperous life. This thesis attempts to study how everyday work and living can be supported to give individuals better control of their time to focus on what gives them a purpose. On average, 86.9% of our time is spent indoors (at work and home).3 This thesis aims to explore a new approach to work-life balance by examining the term through the lens of physical space and architecture. In the following pages, I am working to understand how the proposed architecture can support people on a daily basis.
10

Adaptive mesh modelling of the thermally driven annulus

Maddison, James R. January 2011 (has links)
Numerical simulations of atmospheric and oceanic flows are fundamentally limited by a lack of model resolution. This thesis describes the application of unstructured mesh finite element methods to geophysical fluid dynamics simulations. These methods permit the mesh resolution to be concentrated in regions of relatively increased dynamical importance. Dynamic mesh adaptivity can further be used to maintain an optimised mesh even as the flow develops. Hence unstructured dynamic mesh adaptive methods have the potential to enable efficient simulations of high Reynolds number flows in complex geometries. In this thesis, the thermally driven rotating annulus is used to test these numerical methods. This system is a classic laboratory scale analogue for large scale geophysical flows. The thermally driven rotating annulus has a long history of experimental and numerical research, and hence it is ideally suited for the validation of new numerical methods. For geophysical systems there is a leading order balance between the Coriolis and buoyancy accelerations and the pressure gradient acceleration: geostrophic and hydrostatic balance. It is essential that any numerical model for these systems is able to represent these balances accurately. In this thesis a balanced pressure decomposition method is described, whereby the pressure is decomposed into a ``balanced'' component associated with the Coriolis and buoyancy accelerations, and a ``residual'' component associated with other forcings and that enforces incompressibility. It is demonstrated that this method can be used to enable a more accurate representation of geostrophic and hydrostatic balance in finite element modelling. Furthermore, when applying dynamic mesh adaptivity, there is a further potential for imbalance injection by the mesh optimisation procedure. This issue is tested in the context of shallow-water ocean modelling. For the linearised system on an $f$-plane, and with a steady balance permitting numerical discretisation, an interpolant is formulated that guarantees that a steady and balanced state remains steady and in balance after interpolation onto an arbitrary target mesh. The application of unstructured dynamic mesh adaptive methods to the thermally driven rotating annulus is presented. Fixed structured mesh finite element simulations are conducted, and compared against a finite difference model and against experiment. Further dynamic mesh adaptive simulations are then conducted, and compared against the structured mesh simulations. These tests are used to identify weaknesses in the application of dynamic mesh adaptivity to geophysical systems. The simulations are extended to a more challenging system: the thermally driven rotating annulus at high Taylor number and with sloping base and lid topography. Analysis of the high Taylor number simulations reveals a direct energy transfer from the eddies to the mean flow, confirming the results of previous experimental work.

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