Thesis (Ph.D.)--Aerospace Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Erian Armanios; Committee Member: D. Stefan Dancila; Committee Member: Juan R. Cruz; Committee Member: Massimo Ruzzene; Committee Member: Rami Haj-Ali

Thesis (Ph.D.)--Aberdeen University, 2008. / Title from web page (viewed on July 1, 2009). Includes bibliographical references.

Thesis (M. Sc.)--University of Hong Kong, 2006.

Submitted by Ronan Felipe Jorge null (ronan.jorge@hotmail.com) on 2016-04-07T21:29:57Z No. of bitstreams: 1 RonanFelipeJorgeVersaoFinal.pdf: 3551394 bytes, checksum: 30b15e5d6519d49164a37bcb6b0946c8 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-08T13:07:08Z (GMT) No. of bitstreams: 1 jorge_rf_me_sjrp.pdf: 3551394 bytes, checksum: 30b15e5d6519d49164a37bcb6b0946c8 (MD5) / Made available in DSpace on 2016-04-08T13:07:08Z (GMT). No. of bitstreams: 1 jorge_rf_me_sjrp.pdf: 3551394 bytes, checksum: 30b15e5d6519d49164a37bcb6b0946c8 (MD5) Previous issue date: 2016-03-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O conceito de estabilidade estrutural foi introduzido aos estudos de sistemas dinâmicos contínuos por Andronov e Pontryagin (1937). Em 1988, após investigar osciladores com atrito de Coulomb e apresentar equações diferenciais com lado direito descontínuo, Filippov desenvolveu em sua obra uma nomenclatura para o estudo de sistemas dinâmicos descontínuos. Desde então, estudiosos da área vêm tentando analisar a estabilidade estrutural de sistemas dinâmicos descontínuos por diferentes métodos. Um dos métodos é transformar, sem alterar a estrutura dos campos de vetores, estes sistemas descontínuos em sistemas contínuos onde o estudo da estabilidade estrutural já é conhecido. Esta transformação, também conhecida como regularização, pode ser desenvolvida de diversas formas. Este trabalho tem por objetivo a apresentação de um método de regularização através do uso de uma função de transição de campos de vetores Z do plano com um conjunto de descontinuidade S baseando-se no método de regularização apresentado por Sotomayor e Teixeira (1996) em seu artigo, e realizar um breve estudo sobre estabilidade estrutural em campos de vetores regularizados utilizando tal método. / The concept of structural stability was introduced into the studies of continuous dynamical systems by Andronov and Pontryagin (1937). In 1988, after investigating oscillators with Coulomb friction and differential equations with discontinuous right-hand sides, Filippov developed a nomenclature to the study of discontinuous dynamical systems. Since then, researches have been trying to analyze the structural stability of discontinuous dynamical systems by different methods. One of these methods is to transform, without changing the structure of vector fields, these discontinuous systems in continuous systems where the study of structural stability is already known. This transformation, also known as regularization, can be developed in various ways. This work aims at presenting a regularization method using a transition function of vector fields Z in the plane with a discontinuous set S basing in regularization method presented by Sotomayor and Teixeira (1996) in their article, and, also to do a short study about structural stability in regularized vector fields using this method.

As estruturas, particularmente na engenharia civil, podem apresentar ruína quando atingem sua capacidade resistente ou quando perdem sua estabilidade, sendo, portanto atribuição básica do engenheiro de estruturas o estudo de ambas as situações. A instabilidade de uma estrutura pode surgir de dois modos, a saber: por ocorrência de uma bifurcação de equilíbrio ou por ocorrência de um ponto limite, também conhecido por snap-through, onde o aumento do carregamento provoca uma diminuição da rigidez da estrutura, até que esta se anula no ponto limite (REIS; CAMOTIM, 2012). Estruturas como arcos, treliças e calotas esféricas abatidas, presentes em grandes coberturas, são tipos de estruturas que podem apresentar esta instabilidade, em que há a passagem dinâmica da estrutura para uma configuração de equilíbrio afastada e estável, saltando para essa configuração pós-crítica envolvendo grandes deslocamentos e inversão da curvatura. Se, no entanto, o carregamento é dinâmico, como, por exemplo, harmônico, a resposta do sistema adquire uma grande riqueza de possíveis comportamentos, em função da amplitude e frequência desse carregamento. As respostas podem resultar vibrações periódicas de vários períodos diferentes, quase periódicas, caóticas etc. Este trabalho tem como objetivo fazer um estudo da estabilidade estática e dinâmica do problema da treliça simples de duas barras (treliça de Von Mises) e do arco abatido senoidal, de comportamento elástico linear, com o estabelecimento das equações de equilíbrio na configuração deformada, i.e., levando em conta a não linearidade geométrica. A avaliação da resposta, bem como a caracterização de sua estabilidade, se dará pela apresentação das cargas críticas de instabilidade do sistema perfeito, exibição do comportamento de pós-instabilidade e, com a integração numérica do modelo matemático, o estudo geométrico dado pelos planos de fase, mapas de Poincaré, diagramas de bifurcação e fronteira de estabilidade. / Structures, particularly in civil engineering, can ruin when they reach their strength capacity or when they lose their stability. So, it is the basic assignment of the structural engineer to study both situations. The instability of a structure can arise in two ways, namely: by the occurrence of bifurcation of equilibrium or by the occurrence of a snap-through, where an increase of the loading causes a decrease in structure stiffness, until the stiffness is annulled in the limit point (REIS, CAMOTIM, 2012). Structures such as arches, trusses and domes, present in large roofs, are types of structures that may present this kind of instability, in which there is the dynamic passage of the structure to a far away stable equilibrium configuration, jumping to this post-critical configuration involving large displacements and reversal of the curvature. If, however, the load is dynamic, such as harmonic, the response of the system acquires a great wealth of possible behaviors, depending on the amplitude and frequency of this loading. The responses may result in periodic vibrations of several different periods, almost periodic, chaotic, etc. This work intends to study the static and the dynamic stability of the Von Mises truss and the shallow arc of linear elastic behavior, with the establishment of the equilibrium equations in the deformed configuration, i.e., taking into account the geometric non-linearity. The evaluation of the response, as well as the characterization of its stability, will be done by numerical integration of the mathematical model and geometric study of the phase planes, Poincaré maps, bifurcation diagrams and stability border.

The scanning Laser Doppler Vibrometer (LDV) has developed into a useful tool for rapidly acquiring spatially dense structural dynamic response information in a noncontacting manner. The research presented in this paper is part of a larger project at the Structural Imaging and Modal Analysis Laboratory in the Department of Mechanical Engineering at Virginia Polytechnic Institute and State University, Blacksburg, VA, to develop a six-degree-of-freedom (6-DOF) structural response model based on experimental data. This paper represents a portion of the research for the 6-DOF structural imaging project. A method for creating a functionalized description of a discreetly sampled 2-D data field containing response measurements evenly spaced in laser scan angie coordinates is presented. A filtering process involving a median and edge-median filter algorithm followed by a Discrete Fourier Transform/low-pass spatial frequency domain filter/Inverse Discrete Fourier Transform algorithm is used to reduce the effect of errant data recorded by the LDV data acquisition system. A means of evaluating the performance of this process is developed. Finally, an experiment to determine the relationship between structural response stability and ambient temperature and relative humidity is presented. The response of a lightly damped structure was studied over a twenty-six hour period. A direct relationship between temperature and the dynamic response of the structure was found. This study is important to the overall 6-DOF project since structural stability is assumed in merging the various scans of the structure to obtain 6-DOF information. Recommendations are given for further research of topics discussed in this thesis. / Master of Science

This study developed a general methodology for probabilistic service life prediction of a composite viscoelastic cylindrical structure under random outdoor environment. The analysis emphasized both the statistical variations of environmental thermal loads and of material properties. The daily probability of failure was calculated considering failures due to both the excessive stress and strain. The probabilistic service life was then obtained via the evaluation of cumulative hazard function. Models for the deterministic and random variations of environmental thermal loads- ambient temperature, sky radiation, wind convection, and solar radiation, were developed and were considered in obtaining the structure's surface temperature. The statistical characteristics such as the mean and variance of the induced stresses and-strains were calculated via the uses of complex frequency response functions. Methods for statistical characterization of time and temperature dependent viscoelastic material properties were presented. Five statistical distributions- Normal, Log-Normal, Beta, Gamma, and Weibull, were considered for the goodness of fit. Two forms of material deterioration- time and temperature dependent aging and cumulative damage due to loading were also recognized. Three statistical distributions- Normal, Log-Normal, and Weibull, were used to represent the variations of induced daily maximum stress and strain. The daily probabilities of failure due to the maximum stress and strain were calculated based on the concept of load and resistance interference. The effects of these failure modes were then combined to define daily probability of failure of the structure. / Doctor of Philosophy

Transient modelling of heat fluxes and temperatures in structures was conducted to examine the effect of various characteristics on the temperature response during unusual operating and extreme weather conditions. The analytical model was validated using published experimental data and numerical results from well-known computer codes. The effect of including radiation heat transfer between interior surfaces, using the Mean Radiative Temperature method, on the temperature response was investigated and found to be negligible for a typical commercial building and a house during winter and summer power outages. The effect of thermal mass in the interior and exterior walls on the inside temperature drift after an HVAC system cutoff or a power outage was presented. The inside air temperature response curve is presented for different wall (exterior or interior) constructions of buildings. The effect of insulation position in exterior walls was also shown for several R values. The effect of exterior wall emissivity, sky temperature, outside vertical convective coefficient, furnishings, and ground temperature on the interior temperature response during winter and summer power outages were examined for buildings. The effect of infiltration on the temperature drift in buildings was investigated during winter and summer power outages. Restarting the HVAC after the power outage was examined during both seasons for typical buildings. Outside temperature profiles exceeding the 97.5 design temperature criterion were used to study the effect of extreme weather on the interior temperature of buildings with the HVAC system operating. / Ph. D.

The focus of the current research is to investigate the potential of using bistable unsymmetric cross-ply laminated composites as a means for achieving structures with morphed characteristics. To this end, an investigation of the design space for laminated composites exhibiting bistable behavior is undertaken and the key parameters controlling their behavior are identified. For this purpose a nonlinear Finite Element methodology using ABAQUS code is developed to predict both the cured shapes and the stability characteristics of unsymmetric cross-ply laminates. In addition, an experimental program is developed to validate the analytically predicted results through comparison with test data. A new method is proposed for attaching piezoelectric actuators to a bistable panel in order to preserve its favorable stability characteristics as well as optimizing the actuators performance. The developed nonlinear FE methodology is extended to predict the actuation requirements of bistable panels. Actuator requirements, predicted using the nonlinear FE analysis, are found to be in agreement with the test results. The current research also explores the potential for implementing bistable panels for Uninhabited Aerial Vehicle (UAV) wing configuration. To this end, a set of bistable panels is manufactured by combining symmetric and unsymmetric balanced and unbalanced stacking sequence and their stability characteristics are predicted. A preliminary analysis of the aerodynamic characteristics of the manufactured panels is carried out and the aerodynamic benefits of manufactured bistable panel are noted.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Metabolic systems are open systems continually subject to changes in the surrounding environment that cause uctuations in the state variables and perturbations in the system parameters. However, metabolic systems have mechanisms to keep them dynamically and structurally stable in the face of these changes. In addition, metabolic systems also cope with large changes in the uxes through the pathways, not letting metabolite concentrations vary wildly. Quantitative measures have previously been proposed for "metabolic regulation", using the quantitative framework of Metabolic Control Analysis. However, the term "regulation" is so loosely used so that its content is mostly lost. These di erent measures of regulation have also not been applied to a model and comparably investigated prior to this study. Hence, this study analyses the usefulness of the di erent quantitative measures in answering di erent types of regulatory questions. Thus, the aim of this study was to distinguish the above mentioned aspects of metabolic regulation and to nd appropriate quantitative measures for each, namely dynamic stability, structurally stability, and homeostasis. Dynamic stability is the property of a steady state to return to its original state after a perturbation in a metabolite in the system, and can be analysed in terms of self and internal-response coe cients. Structural stability is concerned with the change in steady state after a perturbation of a parameter in the system, and can be analysed in terms of concentration-response coe cients. Furthermore, it is shown that control patterns are useful in understanding which system properties determine structural stability and to what degree. Homeostasis is de ned as the change in the steady-state concentration of a metabolite relative to the change in the steady-state ux through the metabolite pool following a perturbation in a system parameter, and co-response coe cients are proposed as quantitative measures of homeostasis. More speci cally, metabolite-ux coresponse coe cients allow the de nition of an index that quanti es to which degree a metabolite is homeostatically regulated. A computational model of a simple linear metabolic sequence subject to feedback inhibition with di erent sets of parameters provided a test-bed for the quantitative analysis of metabolic regulation. Log-log rate characteristics and parameter portraits of steady-state variables, as well as response and elasticity coe cients were used to analyse the steady-state behaviour and control properties of the system. This study demonstrates the usefulness of generic models based on proper enzyme kinetics to further our understanding of metabolic behaviour, control and regulation and has laid the groundwork for future studies of metabolic regulation of more complex core models or of models of real systems. / AFRIKAANSE OPSOMMING: Metaboliese sisteme is oop sisteme wat gedurig blootgestel word aan `n uktuerende omgewing. Hierdie uktuasies lei tot veranderinge in beide interne veranderlikes en parameters van metaboliese sisteme. Metaboliese sisteme besit egter meganismes om dinamies en struktureel stabiel te bly. Verder verseker hierdie meganismes ook dat die konsentrasies van interne metaboliete relatief konstant bly ten spyte van groot veranderinge in uksie deur die metaboliese pad waarvan hierdie metaboliete deel vorm. Kwantitatiewe maatstawwe is voorheen voorgestel vir "metaboliese regulering", gebaseer op die raamwerk van Metaboliese Kontrole Analise. Die onkritiese gebruik van die term "regulering" ontneem egter hierdie konsep van sinvolle betekenis. Voor hierdie studie is die voorgestelde maatstawwe van regulering nog nie toegepas op 'n model ten einde hulle met mekaar te vergelyk nie. Die huidige studie ondersoek die toepaslikheid van die verskillende maatstawwe om verskillende tipe vrae oor regulering te beantwoord. Die doelwit van hierdie studie was om aspekte van metaboliese regulering, naamlik dinamiese stabiliteit, strukturele stabiliteit en homeostase, te onderskei, asook om 'n gepaste maatstaf vir elk van die verskillende aspekte te vind. Dinamiese stabiliteit is 'n eienskap van 'n bestendige toestand om terug te keer na die oorspronklike toestand na perturbasie van die konsentrasie van 'n interne metaboliet. Hierdie aspek van regulering kan in terme van interne respons en self-respons koeffi siente geanaliseer word. Strukturele stabiliteit van 'n bestendige toestand beskryf die mate van verandering van die bestendige toestand nadat 'n parameter van die sisteem geperturbeer is, en kan in terme van konsentrasie-responskoeffisiente geanaliseer word. Verder wys hierdie studie dat kontrole patrone van nut is om vas te stel watter eienskappe van 'n sisteem die strukturele stabiliteit bepaal en tot watter mate. Homeostase word gede finieer as die verandering in die konsentrasie van 'n interne metaboliet relatief tot die verandering in die uksie deur daardie metaboliese poel nadat 'n parameter van die sisteem verander het. Vir die analise van hierdie aspek van regulering word ko-responskoe ffisiente as 'n maatstaf voorgestel. Meer spesi ek kan metaboliet- uksie ko-responskoeff siente gebruik word om `n indeks te de nieer wat meet tot watter mate 'n metaboliet homeostaties gereguleer word. 'n Rekenaarmatige model van 'n eenvoudige lineere metaboliese sekwens wat onderhewig is aan terugvoer inhibisie is gebruik om die verskillende aspekte van metaboliese regulering kwantitatief te analiseer met vier verskillende stelle parameters. Dubbel-logaritmiese snelheidskenmerke en parameter portrette van bestendige toestandsveranderlikes, asook van respons- en elastisiteit koeffisente is gebruik om die bestendige toestandsgedrag en kontrole eienskappe van die sisteem te analiseer. Hierdie studie demonstreer die nut van generiese modelle wat op korrekte ensiemkinetika gebaseer is om ons verstaan van metaboliese gedrag, kontrole en regulering te verdiep. Verder dien hierdie studie as grondslag vir toekomstige studies van metaboliese regulering van meer ingewikkelde kernmodelle of modelle van werklike sisteme. / National Research Foundation