Dissertations / Theses on the topic 'Curved panels'

This thesis considers active control of the vibration of doubly-curved panels. Such panels are widely used in vehicles such as cars and aircraft, whose vibration is becoming more problematic as the weight of these vehicles is reduced to control their CO2 emissions. The dynamic properties of doubly-curved panels are first considered and an analytic model which includes in-plane inertia is introduced. The results of this analytical model are compared with those from numerical modelling. Of particular note is the clustering of lower-order modes as the curvature becomes more significant. The influence of these changes in dynamics is then studied by simulating the performance of a velocity feedback controller using an inertial actuator. The feasibility of implementing such an active control system on a car roof panel is then assessed. Experiments and simulations are also conducted on a panel, mounted on one side of a rigid enclosure, which is curved by pressurising the enclosure. The active control of vibration on this panel is then implemented using compensated velocity feedback control and novel inertial actuators. It is found that the performance of the feedback control initially improves as the curvature increases, since the fundamental natural frequency of the panel becomes larger compared with the actuator resonance frequency, but then the performance is significantly degraded for higher levels of curvature, since the natural frequencies of many of the panel modes cluster together. Finally, the integration of a compensator filter in the control system ensures the robustness of the system, despite changes in curvature, which makes it a good candidate for future multi-channel implementations.

Curved panels constructed of laminated graphite-epoxy composite material are of potential interest in airframe fuselage applications. An understanding of structural response at elevated temperatures is required for anticipated future high speed aircraft applications. This study concentrates on the response of unstiffened, curved composite panels subjected to combinations of thermal and mechanical loading conditions. Mechanical loading is due to compressive end-shortening and thermal loading is due to a uniform temperature increase. Thermal stresses, which are induced by mechanical restraints against thermal expansions or contractions, cause buckling and postbuckling panel responses. Panels with three different lamination sequences are considered, including a quasi-isotropic laminate, an axially soft laminate, and an axially stiff laminate. These panels were chosen because they exhibit a range of stiffnesses and a wide variation in laminate coefficients of thermal expansion. The panels have dimensions of 10 in. by 10 in. with a base radius of 60 in. The base boundary conditions are clamped along the curved ends, and simply supported along the straight edges. Three methods are employed to study the panel response, including a geometrically nonlinear Rayleigh-Ritz solution, a finite element solution using the commercially available code STAGS, and an experimental program. The effects of inplane boundary conditions and radius of curvature are studied analytically, along with consideration of order of application in combined loading. A substantial difference is noted in the nonlinear load vs. axial strain responses of panels loaded in end-shortening and panels loaded with uniform temperature change, depending on the specific lamination sequence, boundary conditions, and radius of curvature. Experiments are conducted and results are presented for both room temperature end-shortening tests and elevated temperature tests with accompanying end-shortening. The base finite element model is modified to include measured panel thicknesses, boundary conditions representative of the experimental apparatus, measured initial geometric imperfections, and measured temperature gradients. With these modifications, and including an inherent end displacement of the panel present during thermal loading, good correlation is obtained between the experimental and numerically predicted load vs. axial strain responses from initial loading through postbuckling.
Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999.
Includes bibliographical references (p. 129-133).
Numerical and experimental work was conducted to investigate the use of composites within the Wide Area Surveillance Projectile (WASP) wing system by specifically studying the buckling behavior of curved composite panels under high-g loading. A finite element model was developed as a design tool to model the original WASP wing as a constant thickness curved panel and to predict the buckling response of the panels. The model predicted the critical buckling loads and mode shapes of the composite panels. Experimentally, controlled axial compression tests and high-g tests were performed to determine the buckling response of the panels. The buckling response, including critical loads and mode shapes, was obtained for the controlled axial compression tests. The high-g tests demonstrated that composite panels are a viable option for structures in a high-g environment. All of the samples tested showed no signs of damage and no loss in load carrying capability. The results were used to study the effect of lay-up, curvature, aspect ratio (width to height), and height on the buckling response. The results of the finite element model and the controlled axial compression tests showed good agreement. However, they do not accurately capture the buckling response of the composite panels in the high-g environment.
by Staci Nicole Jenkins.
S.M.

This thesis considered the design of new and improved foldcore sandwich panels suitable for high-performance energy absorption applications. This was achieved by utilising origami geometry design techniques to alter foldcore structures such that they possessed different mechanical behaviours and failure modes. The major findings of this thesis were in three areas as follows. First, a modified planar foldcore geometry was developed by introducing sub-folds into a standard foldcore pattern. The new geometry, deemed the indented foldcore, successfully triggered a high-order failure mode known as a travelling hinge line failure mode. This was found to have a much higher energy absorption than the plate buckling failure mode seen in an unmodified foldcore structure. A comprehensive numerical, theoretical, and experimental analysis was conducted on the indented core, which included the development of a new foldcore prototyping method that utilised 3D printed moulds. It was shown that compared to available commercial honeycomb cores, the indented foldcore had an improved uniformity of energy absorption, but weaker overall peak and crushing stresses. Second, rigid origami design principles were used to develop extended foldcore geometries. New parametrisations were presented for three patterns, to complete a set of Miura-derivative geometries termed first-level derivatives. The first-level derivative parametrisations were then combined to create complex, piecewise geometries, with compatible faceted sandwich face geometry also developed. Finally, a method to generate rigid-foldable, curved-crease geometry from Miura-derivative straight-crease geometry was presented. All geometry was validated with physical prototypes and was compiled into a MATLAB Toolbox. Third, the performance of these extended foldcore geometries under impact loadings was investigated. An investigation of curved-crease foldcores showed that they were stronger than straight-crease foldcores, and at certain configurations can potentially match the strength, energy-absorption under quasi-static impact loads, and out-of-plane stiffness of a honeycomb core. A brief investigation of foldcores under low-velocity impact loadings showed that curved-crease foldcores, unlike straight-crease foldcores, strengthened under dynamic loadings, however not to the same extent as honeycomb. Finally, an investigation of single-curved foldcore sandwich shells was conducted. It was seen that foldcore shells could not match the energy-absorption capability of an over-expanded honeycomb shell, but certain core types did exhibit other attributes that might be exploitable with future research, including superior initial strength and superior uniformity of response.

Sandwich structures constitute basic components of advanced supersonic/hypersonic flight and launch vehicles. These advanced flight vehicles operate in hostile environments consisting of high temperature, moisture, and pressure fields. As a result, these structures are exposed to large lateral pressures, large compressive edge loads, and high temperature gradients which can create large stresses and strains within the structure and can produce the instability of the structure. This creates the need for a better understanding of the behavior of these structures under these complex loading conditions. Moreover, a better understanding of the load carrying capacity of sandwich structures constitutes an essential step towards a more rational design and exploitation of these constructions. In order to address these issues, a comprehensive geometrically non-linear theory of doubly curved sandwich structures constructed of anisotropic laminated face sheets with an orthotropic core under various loadings for simply supported edge conditions is developed. The effects of the radii of curvature, initial geometric imperfections, pressure, uniaxial compressive edge loads, biaxial edge loading consisting of compressive/tensile edge loads, and thermal loads will be analyzed. The effect of the structural tailoring of the facesheets upon the load carrying capacity of the structure under these various loading conditions are analyzed. In addition, the movability/immovability of the unloaded edges and the end-shortening are examined. To pursue this study, two different formulations of the theory are developed. One of these formulations is referred to as the mixed formulation, While the second formulation is referred to as the displacement formulation. Several results are presented encompassing buckling, postbuckling, and stress/strain analysis in conjunction with the application of the structural tailoring technique. The great effects of this technique are explored. Moreover, comparisons with the available theoretical and experimental results are presented and good agreements are reported.
Ph. D.

Includes bibliographical references.
This report presents results from a study on the response of singly curved fibre reinforced polymer (FRP) sandwich and laminate panels subjected to localised blast loads. The aim of the project was to investigate and compare the blast mitigation potential of each panel type and the influence of curvature on the response. Three radii of curvature were examined for both panel types, namely infinite (flat), 1000mm and 500mm. The FRP laminate panels were designed to consist of 1-5 layers of Eglass fibre reinforced epoxy sheets. The FRP sandwich panels consisted of a PVC foam core with 6 layers of FRP sheets on either side. Vacuum infusion, with the aid of three moulds, was used to manufacture the panels. The average thicknesses and areal densities of the FRP sandwich and laminate panels were 18.7mm and 4.9mm; and 862-8g/1m2 and 8458-g/m2 respectively. Three point quasi-static flexural tests were conducted on FRP sandwich and laminate specimens where the localised compression failure beneath the central loading bar was evident on both types of structures. The presence of the core reduced the damage observed on the back face of the FRP sandwich specimens. Blast tests were conducted on a horizontal ballistic pendulum at the Blast Impact and Survivability Research Unit (BISRU), University of Cape Town. Localised blasts were generated by detonating circular cylinder PE4 plastic explosives, placed at a constant standoff distance of 10mm. The charge mass ranged from 10g to 32.5g across all the panels. The failure modes of the blast loaded panels were identified by a post-test inspection. The failure mode initiation charts for the F RP sandwich panels revealed that failure modes were initially observed on the front face sheet and core material with slight appearance of delamination on the back face sheet. Increasing the charge mass resulted in the rupture of the front face sheet and penetration of the core. Additional failure of the back face sheet was also evident as the charge mass increased. The failure mode initiation charts of the FRP laminate panels exhibited less severe failure modes across a greater charge mass range that eventually lead to complete fibre rupture at higher charge masses. Delamination of the front face sheet of the flat FRP sandwich panels was initially observed in the centre of the panel and spread into the exterior region for increasing charge mass. The failure of the core material initially reduced the delaminated area of the back face sheet, however once the rupture of the front face sheet occurred, the delaminated area of the front face sheet reduced and the delaminated area of the back face sheet increased. This was similar for the curved FRP sandwich panels except that the delaminated area was predominately parallel to the axis of curvature prior to rupture and perpendicular to the axis of curvature subsequent to rupture. Delamination in the flat FRP laminate panels was initially observed in the centre of the panel and along the clamped boundary. Increasing charge mass resulted in the delaminated region spreading across the panel. As with the FRP sandwich panels, the delaminated area of the curved FRP laminate panels was initially observed parallel to the axis of curvature prior to rupture. Debonding of the FRP sandwich panels was initially observed at both of the front and back interfaces. For the front interface, the debonded lengths were observed in the centre and in exterior test area of the panel, but only in exterior test area for the back interface. With the rupture of the front face sheet, the debonded length of the front interface decreased and the back interface increased and spread across the entire test area. The blast rupture threshold of the two panel types were compared in terms of largest charge mass resisted. For each radii category, the FRP laminate panels outperformed the FRP sandwich panels, namely by 5g for the flat panels (25g vs 20g) and 9g for the 1000mm curved panels (27.5g vs 18.5g). However, for the 500mm curved panels the FRP laminate and sandwich panels ruptured at identical charge masses of 27.5g.

Two structural models which can be used to predict the buckling, post buckling and vibration behavior of flat and curved composite panels under thermomechanical loadings are developed in this work. Both models are based on higher-order transverse shear deformation theories of shallow shells that include the effects of geometric nonlinearities and initial geometric imperfections. Within the first model (Model I), the kinematic continuity at the contact surfaces between the contiguous layers and the free shear traction condition on the outer bounding surfaces are satisfied, whereas in the second model (Model II), in addition to these conditions, the static interlaminae continuity requirement is also fulfilled. Based on the two models, results which cover a variety of problems concerning the postbuckling behaviors of flat and curved composite panels are obtained and displayed. These problems include: i) buckling and postbuckling behavior of flat and curved laminated structures subjected to mechanical and thermal loadings; ii)frequency-load/temperature interaction in laminated structures in both pre-buckling and post buckling range; iii) the influence of a linear/nonlinear elastic foundation on static and dynamic post buckling behavior of flat/curved laminated structures exposed to mechanical and temperature fields; iv) implication of edge constraints upon the temperature/load carrying capacity and frequencyload/ temperature interaction of flat/curved structures; v) elaboration of a number of methodologies enabling one to attenuate the intensity of the snap-through buckling and even to suppress it as well as of appropriate ways enabling one to enhance the load/temperature carrying capacity of structures.
Ph. D.

Composite materials are increasingly being used in a wide range of structural applications. These applications range from bicycle frames and building facades to hulls of marine ships. Their popularity is due to the high specific strength and stiffness properties, corrosion resistance, and the ability to tailor their properties to a required application. With the increasing use of composites, there is a need to better understand the material and damage behaviour of these structures. In recent years, the increased frequency of wars and terror attacks have prompted investigations into composite failure processes resulting from air-blast. Most of the research has been focused on flat panels, whereas there is relatively little on curved structures. This dissertation reports on the effect of air-blast loading on concave, singly curved fibre reinforced sandwich and composite panels. Sandwich panels and equivalent mass glass fibre laminates were manufactured and tested. Three types of curvature namely a flat panel (with infinite curvature), a curvature of 1000 mm radius and a curvature of 500 mm radius were produced, to determine the influence of curvature on panel response. The laminates were made from 16 layers of 400 g/m² plain weave glass fibre infused with Prime 20 LV epoxy resin. The sandwich panels consisted of a 15 mm thick Airex C70:75 core sandwiched between the 12 layers of 400 g/m² plain weave glass fibre and infused with Prime 20 LV epoxy resin. This arrangement produced a balanced sandwich panel with 6 layers of glass fibre on the front and back respectively. For all panels, vacuum infusion was used to manufacture in a single shot process. Mechanical properties of samples were tested for consistency in manufacturing. It was found that mechanical properties of the samples tested were consistent with low standard deviations on tensile and flexural strength. The panels were tested in the blast chamber flat the University of Cape Town. Blast specimens were clamped onto a pendulum to facilitate impulse measurement. Discs of plastic explosive, with charge masses ranging from 10 g to 25 g, were detonated. After blast testing, a post-mortem analysis of the damaged panels was conducted. Post-mortem analysis revealed that the failure progression was the same irrespective of curvature for both the sandwich panels and the laminates. Sandwich panels exhibited the following failure progression: delamination, matrix failure, core crushing, core shear, core fragmentation, core penetration and fibre fracture. The laminates displayed the following progression: delamination, matrix failure and fibre fracture. Curved panels exhibited failure initiation at lower charge masses than the flat panels. As the curvature increased, the failure modes initiated at lower charge masses. For example, as the charge mass was increased to 12.5 g the front face sheets of the flat and the 1000 mm radius sandwich panels exhibited fibre fracture, but the 500 mm radius sandwich panel exhibited fibre fracture and rupture through the thickness of the front face sheet. The 500 mm radius laminate exhibited front face failure earlier (15 g) than the 1000 mm radius (22.5 g) and flat panel (20 g). Curved laminates exhibited a favoured delamination pattern along the curved edges of the panel for both 1000 mm and 500 mm radii laminates. As the curvature increased, more delamination was evident on the curved edges. The curved panels displayed more severe damage than flat panels at identical charge masses. Curved sandwich panels experienced through thickness rupture at 20 g charge mass whereas the curved laminates did not exhibit rupture at 25 g charge mass. The flat laminates were the most blast resistant, showing no through-thickness penetration at 25 g (the highest charge mass tested) and initiated failure modes at higher charge masses when compared to the other configurations.

This thesis analyzes the design and performance of a photovoltaic (PV) emulator. With increasing interest in renewable energies, large amounts of money and effort are being put into research and development for photovoltaic systems. The larger interest in PV systems has increased demand for appropriate equipment with which to test PV systems. A photovoltaic emulator is a power supply with similar current and voltage characteristics as a PV panel. This work uses an existing power supply which is manipulated via Labview to emulate a photovoltaic panel. The emulator calculates a current-voltage (I-V) curve based on the user specified parameters of panel model, irradiance and temperature. When a load change occurs, the power supply changes its current and voltage to track the calculated I-V curve, so as to mimic a solar panel. Over 250 different solar panels at varying irradiances and temperatures are able to be accurately emulated. A PV emulator provides a controlled environment that is not affected by external factors such as temperature and weather. This allows repeatable conditions on which to test PV equipment, such as inverters, and provides a controlled environment to test an overall PV system.

This thesis describes the design of the active load for adjusting the maximum power point of PV module and the module loaded with the defined parameters for measuring the effectiveness and identifying the characteristics of the PV module.

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O presente trabalho investigou a hipÃtese da Curva de Kuznets com o intuito de verificar se existe uma relaÃÃo de âU invertidoâ entre a desigualdade de renda e crescimento econÃmico no Brasil no perÃodo de 1981 a 2009. Por meio da econometria de dados em painel (efeitos fixos, efeitos aleatÃrios e primeira diferenÃa) e com a utilizaÃÃo da forma linear da renda domiciliar per capitamÃdia, como medida de crescimento econÃmico, e dos indicadores de Gini e Theil, para a mensuraÃÃo da desigualdade de renda, foram estimados dois modelos: a forma quadrÃtica usual de Ahluwalia (1976 b) e uma modificaÃÃo da forma cÃbica, de List e Gallet (1999). Para uma melhor compreensÃo acerca do vÃnculo entre estas duas variÃveis, a anÃlise foi subdividida em perÃodos e em regiÃes geogrÃficas brasileiras. As evidÃncias empÃricas revelaram, de uma forma geral, que a hipÃtese de Kuznets nÃo à corroborada. A partir de uma anÃlise teÃrica sobre o contexto polÃtico, econÃmico e social vivenciado pelo Brasil na contemporaneidade, acredita-se que polÃticas pÃblicas efetivas que ofereÃam serviÃos sociais bÃsicos de qualidade sÃo fundamentais para que um novo ciclo de ascensÃo da desigualdade nÃo se verifique.
The present study investigated the hypothesis of the Kuznets Curve in order to check if there is a"U Inverted" relationship between the income inequality and economic growth in Brazil in the period since 1981 to 2009. Through the econometrics of panel data (fixed effects, random effects and first difference), and using the linear form of average household income per capita, as a measure of economic growth, and the Gini and Theil indicators, for the measurement of income inequality, were estimated two models: the usual quadratic form,by Ahluwalia (1976 b), and a modification of the cubic form,by List and Gallet (1999). For a better understanding of the relationship between these two variables, the analysis was divided into periods and geographical regions. Empirical evidence showed that, in general, the Kuznets hypothesis isnât corroborated. From a theoretical analysis of the political, economic and social context experienced by Brazil in contemporaneity, it is believed that effective public policies that providequality in basic socialservices are essential to avoid a new cycle of rising inequality.

Flat panel displays (FPDs) are microfabricated devices that are often fabricated on specialized glass substrates known as display glass. The surface chemistry of the outer few nanometers of display glass can have an important influence on FPD performance and yield. Dsiplay glass surface characterization is difficult because (i) display glass surface composition varies significantly from its bulk composition; (ii) high-surface area forms of glass, such as fibers and powders, may not have the same surface composition as melt-formed planar surfaces, and (iii) the surface composition of display glass may be altered through exposure to chemical treatments commonly used during flat panel display production, including acids, bases, etchants, detergents, and plasmas. We have performed a detailed surface composition of Eagle XG®, a widely used commercial display glass substrate, using a range of surface analytical techniques including time-of-flight secondary ion mass spectrometry (ToF-SIMS), angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and low energy ion scattering (LEIS). The information from these techniques has given us a detailed understanding of the elemental surface composition and surface hydroxylation of Eagle XG® at length scales ranging from ca. 10 nm from the surface to the outermost atomic layer. These analyses reveal that the surface composition of Eagle XG® varies significantly from its bulk composition, having generally lower concentrations of Al, B, Mg, Ca, and Sr, and higher concentrations of Si. Treatment with an industrial alkaline detergent results in significant recovery of aluminum concentration at the Eagle XG® surface, while treatment with hydrochloric and hydrofluoric acid result in further depletion of Al, B, Mg, Ca, and Sr at the sample surface.We used ToF-SIMS to quantify surface hydroxyls at the sample surface of this material. The SiOH+/Si+ peak area ratio was a useful metric of surface hydroxylation. We studied the effects of adventitious surface contamination on the measurements by analyzing samples dosed with perdeuterated triacontane, a model alkane, prior to analysis. Thick triacontane overlayers suppressed the SiOH+ signal, indicating that this approach gives inaccurately low estimates of surface hydroxylation for samples with high degrees of surface contamination, and accurate measurements are only possible for very-clean surfaces. The number of of hydroxyls on Eagle XG® surfaces varied as the surfaces were exposed to different chemical treatments. HF- and HCl- treated surfaces had the highest degree of hydroxylation, while detergent-treated surfaces had the lowest.

The literature addressing the resource curse has been extensive. Many studies have put forth theories to explain the curse, but these theories are often refuted by new studies. Recently, there has been a theory that natural resource abundance leads to decreased economic freedom, which causes slower economic growth. Many of these studies have using frequentist testing to arrive at their conclusions. Although frequentist testing is widely used, there are several drawbacks. In particular, there is no way of addressing model uncertainty. Unless a study is able to incorporate every significant explanatory variable, the results will suffer from omitted variable bias. Recently, researchers have been applying Bayesian statistics to address the problem of model uncertainty. In this study, we apply Bayesian Model Averaging (BMA) to build a growth model, and see if natural resources have a negative effect on growth. We take the implementation of BMA a step further to see if there is an indirect negative effect of natural resources on economic freedom. However, contrary to previous studies, we were not able to find a negative relationship between resource abundance and economic freedom.

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As questões sobre o meio ambiente, ano após ano, vêm desempenhando um destacado papel no debate global sobre o futuro do planeta. Devido à liberação de enormes quantidades de CO2 na combustão de energias fósseis, as suas emissões são classificadas como uma das forças motrizes por trás do fenômeno do aquecimento global. Em todo o mundo, as emissões dos gases de “efeito estufa” (GEE) estão aumentando, apesar dos esforços comuns para implementar acordos internacionais, como o Protocolo de Quioto. Nesse contexto, esta dissertação visa investigar a hipótese da Curva de Kuznets Ambiental (CKA) global e a sua relação com o Protocolo de Quioto. Portanto, um de seus objetivos é verificar se existe uma relação na forma de U invertido entre um índice de degradação ambiental global (emissões de CO2 per capita) e o crescimento econômico (medido pelo PIB per capita) para uma amostra de 167 países durante o período de 2000-2004, utilizando um modelo de efeitos fixos com dependência espacial. Outro objetivo desta dissertação é avaliar o papel do Protocolo de Quioto como uma política global, a fim de reduzir as emissões. Para isso, uma variável dummy, representando os países que ratificaram o Protocolo, é adicionada do lado direito da regressão. Além disso, mais três variáveis são colocadas no lado direito da regressão: nível de comércio, consumo de energia e densidade populacional. Os resultados da Análise Exploratória de Dados Espaciais (AEDE) revelaram que as emissões de CO2 per capita não são distribuídas aleatoriamente, bem como identificou uma série de países que emitem mais do que os outros países: Estados Unidos, Canadá, Austrália, Barein, Brunei, Kuwait, Luxemburgo, Emirados Árabes Unidos, Trinidad e Tobago e Aruba. A AEDE encontrou a existência de clusters, mostrando que o padrão Baixo-Baixo ocorre principalmente nos países mais pobres africanos e asiáticos, enquanto o padrão Alto-Alto aparece essencialmente nos países europeus e países do sudoeste asiático. Os resultados econométricos, a princípio, sugerem a existência de uma CKA na forma de “N” e não de “U” invertido, encontrando os seguintes “pontos de inflexão”: US$ 12.262,44 e US$ 27.083,33. As demais variáveis explicativas também apresentaram os sinais esperados e todas exibiram um coeficiente altamente significativo. Cerca de 80% da amostra não possuem renda acima do ponto de inflexão calculado, ou seja, a grande maioria dos países se encontraria na primeira parte ascendente da curva, revelando que no intervalo de renda observado para os 167 países, muitos exibem uma curva monotonicamente crescente. Isso parece confirmar e ilustrar a natureza global do impacto do dióxido de carbono, revelando que há pouco incentivo para as nações tomarem ações unilaterais para reduzir suas emissões, e que ações multilaterais estão sendo desenvolvidas lentamente. Outra questão importante é o coeficiente negativo e estatisticamente significativo para a variável dummy dos países que ratificaram o Protocolo de Quioto, revelando a importância de acordos internacionais na redução do montante global das emissões de carbono per capita. Portanto, o crescimento econômico sozinho não pode substituir políticas que aspirem a redução das emissões de CO2. Este resultado sugere que políticas internacionais podem ajudar a reduzir as emissões de GEE, mas é preciso que mais países se comprometam nessa redução. Portanto, crescimento econômico por si só não garante a cura para os problemas relacionados ao meio ambiente. As políticas ambientais têm papel fundamental na inversão da trajetória dos poluentes que seguem a CKA.
Over the years environmental issues have been playing a remarkable role in the global debate about the Earth future. Due to the release of huge amounts of CO2 in the combustion of fossil fuels, its emissions are classified as one of the driving forces behind the global warming phenomenon. Worldwide, emissions of the "greenhouse effect" gases (GHG) are increasing, despite the joint efforts to implement international agreements like the Kyoto Protocol. In this context, the present dissertation is aimed at investigating the Global Environmental Kuznets Curve (EKC) hypothesis and its relationship with the Kyoto Protocol. Therefore, one of its objectives is to verify whether there is an inverted U shaped relationship between an index of global environmental degradation (per capita CO2 emissions) and economic growth (measured by per capita GDP) for a sample of 167 countries over the period 2000-2004, using a fixed effect model with spatial dependence. Another objective of this dissertation is to evaluate the role of the Kyoto Protocol as a global policy in order to reduce emissions. To do so, a dummy variable, representing the countries that have ratified the Protocol, is put in right hand of the regression. Besides, another three variables are inserted in the right hand of regression: the trade level, energy consumption and population density. The findings from Exploratory Spatial Data Analysis (ESDA) revealed that per capita CO2 emissions are not randomly distributed, as well as identified a number of countries that emit more than the other countries, namely, United States, Canada, Australia, Bahrain, Brunei, Kuwait, Luxembourg, United Arab Emirates, Trinidad and Tobago and Aruba. The ESDA analysis found the existence of clusters, showing that the low-low pattern occurs mainly in the poorest countries Asian and African, whereas the High High pattern appears mainly in European countries and countries in Southeast Asia. The econometric results, in principle, suggest the existence of a CKA in the form of "N" rather than "U" inverted, finding the following "turning points": US$ 12,262.44 and US$ 27,083.33. The other explanatory variables also showed the expected signs and all exhibited a highly significant coefficient. Around 80% of the sample did not have income above the “turning point” calculated, that is, the vast majority of countries are in the first upward part curve, revealing that in the range of income observed for the 167 countries, many have a curve monotonically increasing. This seems to confirm and illustrate the global nature of the carbon dioxide impact, revealing that there is little incentive for nations takes unilateral actions to reduce their emissions, as well as multilateral actions are being developed slowly. Another important issue is the negative coefficient, and statistically significant, for the dummy variables of the countries that have ratified the Kyoto Protocol, showing the importance of international agreements on reducing the overall amount of per capita carbon emission. Therefore, economic growth alone cannot replace policies that aspire to reducing CO2 emissions. This result suggests that international policies can help reduce GHG emissions, but we need more countries to commit such reduction. Therefore, economic growth alone does not guarantee a cure for the problems related to the environment. Environmental policies have key role in reversing the trajectory of pollutants that follow the CKA.

Les tôles courbes sont de plus en plus fréquemment utilisées dans le domaine des ouvrages d'art à la fois pour raisons esthétiques et pour leurs performances mécaniques. Leur dimensionnement est cependant difficile du fait de l'absence de méthode dédiée dans les normes européennes, en particulier en ce qui concerne le voilement de l'Eurocode 3. Le recours à la modélisation par éléments finis est donc nécessaire mais bien souvent coûteux. La présente étude vise ainsi à développer une méthode simplifiée pour le dimensionnement des panneaux cylindriques soumis à une compression uniaxiale. La méthodologie utilisée est basée sur la démarche générale de l'Eurocode 3 pour tous les types de vérifications de stabilité. L'expression analytique obtenue est en bon accord avec les standards des recommandations de l'Eurocode. Cependant, cette démarche peut être difficile à reproduire dans la pratique quotidienne des ingénieurs face à un nouveau problème tel qu'une combinaison de chargements par exemple. Une méthode alternative basée sur la méthode des plans d'expérience numérique a donc été développée. Basée sur des outils statistiques, l'application de cette méthode permet facilement d'obtenir un résultat avec une bonne précision tout en nécessitant que peu simulations

L’émergence des systèmes embarqués a permis le développement des réseaux de capteurs sans fil dans de nombreux domaines différents. Cependant, la sécurité reste un problème ouvert. La vulnérabilité des nœuds est principalement liée au manque de ressources. En effet, l’unité de traitement ne dispose pas d’assez de puissance et de mémoire pour gérer des mécanismes de sécurité très complexes.La cryptographie est une solution qui est largement utilisée pour sécuriser les réseaux. Par rapport à la cryptographie symétrique, la cryptographie asymétrique nécessite des calculs plus compliqués,mais elle offre une distribution de clés plus sophistiquée et la signature numérique. Dans cette thèse, nous essayons d’optimiser la performance d’ECC (Elliptic Curve Cryptography), un cryptosystème asymétrique qui est connu pour sa robustesse et son utilisation de clé plus courte par rapport à RSA. Nous proposons d’utiliser le parallélisme pour accélérer le calcul de la multiplication scalaire, qui est reconnue comme l’opération la plus coûteuse sur les courbes elliptiques. Les résultats de tests ont montré que notre solution offre un gain intéressant malgré une augmentation de la consommation d’énergie.La deuxième partie de la contribution concerne l’application de la tolérance aux pannes dans notre architecture de parallélisation. Nous utilisons les nœuds redondants pour la détection des pannes et la restauration du calcul. Ainsi, en utilisant l’ECC et la tolérance aux pannes, nous proposons une solution de sécurité efficace et sûre pour les systèmes embarqués
The emergence of embedded systems has enabled the development of wireless sensor networks indifferent domains. However, the security remains an open problem. The vulnerability of sensor nodesis mainly due to the lack of resources. In fact, the processing unit doesn’t have enough power ormemory to handle complex security mechanisms.Cryptography is a widely used solution to secure networks. Compared with symmetric cryptography,the asymmetric cryptography requires more complicated computations, but it offers moresophisticated key distribution schemes and digital signature.In this thesis, we try to optimize the performance of ECC. An asymmetric cryptosystem which isknown for its robustness and the use of shorter keys than RSA. We propose to use parallelismtechniques to accelerate the computation of scalar multiplications, which is recognized as the mostcomputationally expensive operation on elliptic curves. The test results have shown that our solutionprovides a significant gain despite an increase in energy consumption.The 2nd part of our contribution is the application of fault tolerance in our parallelism architecture.We use redundant nodes for fault detection and computation recovery. Thus, by using ECC and faulttolerance, we propose an efficient and reliable security solution for embedded systems

Cette thèse aborde l'un des sujets les plus discutés et en vogue dans le domaine de l'économie, à savoir le lien entre le développement économique et la qualité environnementale. En particulier, on met l’accent sur les effets du développement économique—tant dans ses dimensions économique, sociale que politique—sur la qualité de l'environnement pour les économies en développement et en transition. Le chapitre I, divisé en trois phases clés, à savoir la revue de la littérature théorique, la partie empirique et la revue de la littérature empirique, contribue à la littérature en donnant diverses informations sur le lien entre la croissance économique et la pollution de l'environnement dans les économies en développement et en transition. Globalement, les résultats révèlent que des études empiriques récentes, parvenant à réduire certaines lacunes suggérées par la théorie, pourraient en effet indiquer un certain consensus sur la relation entre la croissance et la pollution, à savoir la validité de l'hypothèse de la Courbe de Kuznets Environnementale (CKE). Le chapitre II examine le lien pollution-croissance dans les pays d'Europe Centrale et Orientale (PECO), en ajoutant à la littérature empirique l’utilisation de l'hypothèse étendue de l'CKE comme cadre théorique. D'une part, il révèle un lien de croissance non linéaire entre le PIB et le CO2 agrégé, qui est fortement robuste pour différents estimateurs et variables de contrôle. En revanche, l'analyse au niveau des pays révèle que la relation entre le PIB et le CO2 se caractérise par une grande diversité dans les PECO. Ainsi, malgré une tendance globale à la hausse, certains PECO ont réussi à assurer à la fois un PIB plus élevé et une réduction des émissions de CO2. Du point de vue politique, les décideurs de l'UE pourraient accorder plus d'attention à ces pays, c'est-à-dire envisager une intégration plus rigoureuse des hétérogénéités des pays et, en même temps, soutenir la croissance économique sans nuire à l'environnement. Le chapitre III étudie la réponse des émissions de CO2 agrégées et sectorielles résultant des perturbations externes du PIB et de l'urbanisation, en supposant un canal de transmission qui intègre deux des éléments clés utilisés dans la lutte contre la dégradation de l'environnement—les énergies renouvelables et l'efficacité énergétique. Les résultats, robustes à plusieurs spécifications alternatives, indiquent que la production globale, l'urbanisation et l'intensité énergétique augmentent les émissions totales de CO2, tandis que les énergies renouvelables ont l'effet inverse. Par ailleurs, en ce qui concerne la réponse du CO2 aux chocs de production et d'urbanisation, le modèle suggère que ces pays atteindront le seuil maximum qui conduirait à un changement de la tendance des émissions à la baisse. Cependant, les résultats varient en fonction du niveau de revenu et du statut des pays sur la ratification/l'adhésion au Protocole de Kyoto. Ensuite, l'analyse sectorielle montre que les transports, les bâtiments et les secteurs non-combustion sont plus susceptibles de contribuer à l'augmentation des niveaux futurs de CO2. En général, ce chapitre peut fournir des informations précieuses sur les perspectives de durabilité environnementale dans les pays en développement. Le chapitre IV explore les effets de la stabilité politique sur la dégradation de l'environnement, donnant une perspective renouvelée sur ce sujet dans les pays en développement. Il montre qu'une évolution non linéaire en forme de cloche décrit la relation entre les variables au niveau agrégé. De plus, bien que ce résultat reste stable pour plusieurs spécifications alternatives, nous identifions des hétérogénéités significatives dans les caractéristiques distinctes des pays et les mesures alternatives de pollution. En outre, des estimations désagrégées révèlent des schémas contrastés pour la relation entre le CO2 et la stabilité politique. (...)
This thesis tackles one of the most debatable and in vogue topics in economics, namely the economic development and environmental quality nexus. Notably, it studies the economic development's effects—in terms of its economic, social, and political dimensions—on the environmental quality for developing and transition economies. Chapter I, which is divided into three key phases, namely theoretical review, empirical exercise, and empirical review, contributes to the literature by giving various insights regarding the link between economic growth and environmental pollution in developing and transition economies. Overall, it reveals that the recent empirical studies, indeed, succeeding to curtail some of the deficiencies suggested by theoretical contributions, might indicate a certain consensus regarding pollution-growth nexus and Environmental Kuznets Curve (EKC) hypothesis validity. Chapter II examines the pollution-growth nexus in Central and Eastern European (CEE) countries, adding to the related empirical literature using the extended EKC hypothesis as a theoretical background. On the one hand, it unveils an increasing nonlinear link between GDP and CO2 at the aggregate level, which is powerfully robust to different estimators and control variables. On the other hand, the country-level analysis reveals that the relationship between GDP and CO2 is characterized by much diversity among CEE countries. Thus, despite an aggregated upward trend, some CEE countries managed to secure both higher GDP and lower CO2 emissions. From a policy perspective, EU policymakers could pay more attention to these countries and amend the current unique environmental policy to account for country-heterogeneities to support economic growth without damaging the environment. Chapter III investigates the aggregated and sector-specific CO2 emissions' responsiveness following exogenous shocks to growth and urbanization, considering a transmission scheme that incorporates two of the widely used instruments in mitigating environmental degradation—renewables and energy efficiency. First, robust to several alternative specifications, the results indicate that output, urbanization, and energy intensity increase the aggregated CO2 emissions, while renewable energy exhibits an opposite effect. Moreover, regarding the CO2 responsiveness in the aftermath of output and urbanization shocks, the pattern may suggest that these countries are likely to attain the threshold that would trigger a decline in CO2 emissions. However, the findings are sensitive to both countries' economic development and Kyoto Protocol ratification/ascension status. Second, the sector-specific analysis unveils that the transportation, buildings, and non-combustion sector exhibits a higher propensity to increase the future CO2 levels. Generally, this chapter may provide useful insights concerning environmental sustainability prospects in developing states. Chapter IV explores the effects of political stability on environmental degradation, giving a renewed perspective on this topic in developing states. It shows that a nonlinear, bell-shaped pattern characterizes the relationship between variables at the aggregate level. Moreover, while this result is robust to a broad set of alternative specifications, significant heterogeneities are found regarding countries' distinct characteristics and alternative pollution measures. Besides, the country-specific estimates unveil contrasting patterns regarding the relationship between CO2 and political stability. Broadly speaking, the findings suggest that both the formal and informal sides of political stability play a vital role in mitigating CO2 pollution in developing countries, and may provide meaningful insights for policymakers. (...)

Der Vortrag beschreibt wie sich mittels der unterschiedlichen Berechnungsverfahren zur Lösung dynamischer Strukturpobleme der Einschlag eines idealisierten Bruchstücks in eine Schutzwand berechnen lässt. Dies wird mittels zweier kommerzieller FEM-Programme beschrieben: a.) Creo Simulate nutzt zur Lösung die Methode der modalen Superposition, d.h., es können nur lineare dynamische Systeme mit rein modaler Dämpfung berechnet werden. Kontakt zwischen zwei Bauteilen lässt sich damit nicht erfassen. Die unbekannte Kraft-Zeit-Funktion des Einschlagvorganges muss also geeignet abgeschätzt und als äußere Last auf die Schutzwand aufgebracht werden. Je dynamischer der Einschlagvorgang, desto eher wird der Gültigkeitsbereich des zugrunde liegenden linearen Modells verlassen. b.) Abaqus/Explicit nutzt ein direktes Zeitintegrationsverfahren zur schrittweisen Lösung der zugrunde liegenden Differentialgleichung, die keine tangentiale Steifigkeitsmatrix benötigt. Damit können sowohl Materialnichtlinearitäten als auch Kontakt geeignet erfasst und damit die Kraft-Zeit-Funktion des Einschlages ermittelt werden. Auch bei extrem hochdynamischen Vorgängen liefert diese Methode ein gutes Ergebnis. Es müssen dafür jedoch weit mehr Werkstoffdaten bekannt sein, um das nichtlineare elasto-plastische Materialverhalten mit Schädigungseffekten korrekt zu beschreiben. Die Schwierigkeiten der Werkstoffdatenbestimmung werden in den Grundlagen erläutert
The presentation describes how to analyze the impact of an idealized fragment into a stell protective panel with different dynamic analysis methods. Two different commercial Finite Element codes are used for this: a.) Creo Simulate: This code uses the method of modal superposition for analyzing the dynamic response of linear dynamic systems. Therefore, only modal damping and no contact can be used. The unknown force-vs.-time curve of the impact event cannot be computed, but must be assumed and applied as external force to the steel protective panel. As more dynamic the impact, as sooner the range of validity of the underlying linear model is left. b.) Abaqus/Explicit: This code uses a direct integration method for an incremental (step by step) solution of the underlying differential equation, which does not need a tangential stiffness matrix. In this way, matieral nonlinearities as well as contact can be obtained as one result of the FEM analysis. Even for extremely high-dynamic impacts, good results can be obtained. But, the nonlinear elasto-plastic material behavior with damage initiation and damage evolution must be characterized with a lot of effort. The principal difficulties of the material characterization are described

Tese de doutoramento em Engenharia Civil, na área de Construção Metálica e Mista, apresentada ao Departamento de Engenharia Civil da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
The objective of this work is to analyse the stability behaviour of cylindrically curved steel panels under generalised in‐plane compressive stresses and to develop design rules which overcome some limitations of current European Standards. For the simplest case of pure compressive axial stresses, the most relevant works have been revisited and analysed. In what concerns the elastic critical stress of cylindrically curved panels, it was concluded that the expressions which are currently available return non‑negligible errors. Relying on the finite element method and, at the same time, on an analytical formulation based on energy methods, new expressions presenting significant improvements and allowing obtaining the elastic critical stress also for panels under non‑uniform in-­plane loading are presented. Concerning the ultimate resistance, the proposed method also shows improvements, but its main contribution is that it allows obtaining the ultimate resistance also for panels under pure in-­plane bending and a direct application to cross‑sections. Finally, it is worth mentioning that, albeit it is not proposed any new method to compute the ultimate load of cylindrically curved panels under biaxial loading, the behaviour of curved panels under this type of loading is analysed relying exclusively on numerical methods.
O objectivo do presente trabalho é a análise da estabilidade de painéis cilín-dricos metálicos sujeitos a tensões de compressão no seu plano médio e o desenvolvimento de regras de dimensionamento que colmatem as limitações que as normas europeias actualmente apresentam. Para o caso mais simples, o da compressão uniaxial uniforme, os principais estudos foram reanalisados tendo-se concluindo que, no que respeita a tensão crítica elástica de painéis cilíndricos metálicos, as expressões disponíveis apresentam erros consideráveis. Recorrendo ao método dos elementos finitos e, paralelamente, a uma formulação analítica baseada em métodos energéticos, foram desenvolvidas novas expressões que melhoram significativamente os valores obtidos para tensão crítica e que permitem, também, calcular a mesma para painéis sujeitos a carregamentos de compressão não uniforme. Em relação à tensão última, o método agora proposto apresenta também melhorias significativas, mas é o primeiro a incluir a possibilidade de calcular a tensão última de painéis cilíndricos metálicos sujeitos a flexão pura no seu plano médio e a permitir uma aplicação directa a secções. Finalmente deve referir-se que, apesar de não se propor nenhum método para a obtenção da tensão última, o comportamento último de painéis cilíndricos sujeitos a compressão uniforme biaxial é caracterizado recorrendo a métodos exclusivamente numéricos.
FCT - SFRH/BD/70424/2010

碩士
國立臺灣大學
工程科學及海洋工程學研究所
105
With the rapid development of technological science, the manufactured techniques of liquid crystal (LC) panel becomes more innovative and more creative. The curved liquid crystal display is one of the product during these innovations. However, it faces a lot of challenge in curved liquid crystal display. One of the major issue is the bending shift between the top and the bottom thin glass panels during manufacturing. This problem causes the light leakage and non-uniform color. In this thesis, we study the situation of the bending shift between two thin glass panels in curved liquid crystal display. A macro photography is set up for our measurement system. Through the finite element method software, we simulate the bending shift between two glass panels based on several models for curved display. The glass structure parameters and the optical properties of liquid crystal are considered in our simulation model. The difference error between the simulation result and the experiment result are investigated and discussed. The purpose in this study is trying to understand the affected parameters and to establish the physical model of the bending shift between two glass panels. Our results can be used as the basis for further study to eliminate the defect of the curved liquid crystal display.

碩士
國立成功大學
土木工程學系碩博士班
97
Because the composite laminated plates possess excellent characteristics such as lightweight, high stiffness and low thermal conductivity, has been widely used in advanced industrial engineering structures. To avoid structures produce resonance phenomenon, making materials exceeding the limits allowed to break, the structures analysis of natural frequencies become guidelines on structural design. In this thesis, ABAQUS finite element software is used to analyze that arc angle, boundary conditions, fiber, geometric shapes and axial pressure, have influence on maximization of the fundamental frequencies of symmetric composite laminated curved panel. And the golden section method is applied to find the angle of the best arrange fiber and its corresponding maximization of the fundamental frequency in the composite laminated curved panel. Analysis result displayed, maximization of the fundamental frequency of the composite laminated curved panel reduces along with increase of the axial pressure. And it can improve the fundamental frequency to choose from laminates fiber angle, boundary conditions and geometry suitably. In the future, the widespread use of composite plates is of help.

碩士
國立成功大學
土木工程學系碩博士班
98
Because of the composite laminated plates possess excellent characteristics such as high strength, high stiffness, lightweight, and low thermal conductivity, they have been widely used in advanced industrial engineering structures. To avoid structures producing resonance phenomenon and to make materials exceeding the limits allowed, structural analysis of natural frequency becomes the standard on structural design. In this thesis, ABAQUS finite element software is used to analyze the influence of arc angle, hole size, fiber orientations, geometric shapes and axial pressure on the maximum fundamental frequencies of composite laminated curved panel. The Fibonacci search is employed to find the optimal fiber orientations and its corresponding maximum fundamental frequency in the composite laminated curved panel. The results of the analyses show that the maximum fundamental frequency not only reduces with the increase of the axial pressure and the panel aspect ratio but also increases with the increase of hole size and arc angle. Therefore, choosing laminates fiber angle and suitable geometry can improve the fundamental frequency. So, it is useful in the design of composite curved panels in the future.

abstract: The focus of this investigation is on the renewed assessment of nonlinear reduced order models (ROM) for the accurate prediction of the geometrically nonlinear response of a curved beam. In light of difficulties encountered in an earlier modeling effort, the various steps involved in the construction of the reduced order model are carefully reassessed. The selection of the basis functions is first addressed by comparison with the results of proper orthogonal decomposition (POD) analysis. The normal basis functions suggested earlier, i.e. the transverse linear modes of the corresponding flat beam, are shown in fact to be very close to the POD eigenvectors of the normal displacements and thus retained in the present effort. A strong connection is similarly established between the POD eigenvectors of the tangential displacements and the dual modes which are accordingly selected to complement the normal basis functions. The identification of the parameters of the reduced order model is revisited next and it is observed that the standard approach for their identification does not capture well the occurrence of snap-throughs. On this basis, a revised approach is proposed which is assessed first on the static, symmetric response of the beam to a uniform load. A very good to excellent matching between full finite element and ROM predicted responses validates the new identification procedure and motivates its application to the dynamic response of the beam which exhibits both symmetric and antisymmetric motions. While not quite as accurate as in the static case, the reduced order model predictions match well their full Nastran counterparts and support the reduced order model development strategy.
Dissertation/Thesis
M.S. Mechanical Engineering 2011

PhD thesis in Steel and Composite Construction submitted to the Faculty of Sciences and Technology of the University of Coimbra
Despite being increasingly used in several engineering fields, design provisions to predict the strength of steel curved panels are mostly empirical and with a small range of application. Consequently, the main aim of this thesis is to predict the nonlinear behaviour and ultimate strength of stiffened and unstiffened cylindrically curved steel panels under in-plane and out-of-plane loading based on a physically robust approach, through semi-analytical methods (SAM). The main advantage of this approach, in comparison to the usual approaches, like the Finite Element Method (FEM), is allowing to identify the key parameters that influence the behaviour of the curved panels and to develop expressions purely based on the physical background of the problem, which have a large practical interest. However, the FEM is also used for two reasons: i) to characterize thoroughly and realistically the behaviour of the panels through a wide parametric study; in this case, an innovative way to model imperfections is developed, being more unfavourable than the default approach in shell structures, in a large part of the cases; and ii) to validate the semi-analytical formulation developed for the curved panels. The analysed parameters are found to change dramatically the behaviour of the panels, which, in some cases, may lead to unexpected results. For example, it may be quite unsafe to design a curved panel as if it was a flat plate. In contrast, in other cases, significant gains in resistance are obtained with the increase in curvature. This shows that the design of curved panels has to be performed with a deep knowledge of this complex behaviour. Although only uniaxial in-plane compression (the key aspect in the stability of thin walled structures) and out-of-plane pressure are studied in this thesis, the formulation is developed to account for generalized loading. A large deflection formulation with a multi degree-of-freedom (MDOF) solution and imperfections is implemented. Additionally, the SAM accounts for in-plane constrained and unconstrained simply supported boundary conditions. This requires a rigorous solution of boundary value problem of the fourth order nonlinear partial differential equations. Despite the complex behaviour identified for the curved panels, the SAM is able to account accurately for all the geometric parameters, boundary and loading conditions. Although the panels with larger curvatures benefit from the implemented MDOF solution, closed-form expressions, based on a SDOF approximation, are able to provide accurate results for the equilibrium paths of unstiffened and stiffened curved panels with practical significance under in-plane and out-of-plane loading. The SAM is then used, with a yield criterion, to predict the resistance of unstiffened curved panels under compression. Expressions are derived to calculate the ultimate load of these panels, showing good agreement with the FEM.
Apesar de serem cada vez mais usados em vários campos da engenharia, as provisões para prever a resistência de painéis curvos são maioritariamente empíricas e com reduzida gama de aplicação. Consequentemente, o principal objetivo desta tese é prever o comportamento não-linear e carga última de painéis curvos cilíndricos não reforçados e reforçados com base numa abordagem fisicamente robusta, através de métodos semi-analíticos (MSA). A principal vantagem desta abordagem, comparativamente às abordagens usuais, como o método dos elementos finitos (MEF), é permitir identificar os parâmetros-chave que influenciam o comportamento dos painéis curvos e desenvolver expressões puramente baseadas no contexto físico do problema, as quais têm um enorme interesse prático. Contudo, o MEF é também usado por duas razões: i) para caracterizar detalhada e realisticamente o comportamento dos painéis curvos através de um estudo paramétrico alargado; neste caso, é desenvolvida uma forma inovadora de modelar as imperfeições, sendo esta mais desfavorável, numa grande parte dos casos, que a abordagem padrão utilizada em estruturas de casca; e ii) para validar a formulação semi-analítica desenvolvida para os painéis curvos. Os parâmetros analisados mostram-se capazes de alterar drasticamente o comportamento dos painéis, os quais, em alguns casos, podem conduzir a resultados inesperados. Por exemplo, pode ser bastante inseguro dimensionar um painel curvo como se fosse uma placa plana. Contrariamente, em outros casos, são obtidos ganhos significativos da resistência com o aumento da curvatura. Isto mostra que o dimensionamento de painéis curvos deve ser realizado com um profundo conhecimento deste complexo comportamento. Embora apenas compressão uniaxial no plano (o especto-chave na estabilidade de estruturas de parede fina) e pressão fora do plano sejam estudadas, a formulação é desenvolvida para ter em conta carregamento generalizado. É implementada uma formulação de grandes deslocamentos com uma solução de multi-graus de liberdade (MGDL) e imperfeições. Adicionalmente, o MSA tem em conta condições de fronteira simplesmente apoiadas restringidas e não restringidas no plano. Isto requer uma solução rigorosa do problema de valor de fronteira das equações diferenciais parciais não-lineares de quarta ordem. Apesar do complexo comportamento identificado para os painéis curvos, o MSA é capaz de ter em conta, de forma precisa, todos os parâmetros geométricos, condições de fronteira e carregamento. Embora os painéis com maiores curvaturas beneficiem da solução MGDL implementada, expressões de forma fechada, baseadas numa aproximação de um único grau de liberdade (UGDL), são capazes de fornecer resultados precisos para as trajetórias de equilíbrio de painéis curvos não reforçados e reforçados com significância prática, sob carregamento no plano e fora do plano. O MSA é seguidamente usado com um critério de cedência para prever a resistência de painéis curvos não reforçados sob compressão. São derivadas expressões para calcular a carga última destes painéis, mostrando bom acordo com o MEF.

碩士
逢甲大學
智能製造與工程管理碩士在職學位學程
107
This study investigates the difference in strength under different geometric conditions of curve glasses. With two widely known practical testing, the strength comparisons are obtained by several experiments. In this study, two radii of curvature glass samples were produced. Their surfaces are chemically strengthened. And the strength tests were performed in the direction of convex and concave surface upward. And the unbent or flat samples were tested as using for results comparisons. The four-point bending test and the steel ball drop impact test were used as strength testing method. The maximum destructive reactions of each group of samples can be analyzed and compared. It is found from the experimental results that the strength of the convex surface upward is higher than the concave surface upward. And the curve glasses with smaller radius of curvature will have larger strength. From the results of the four-point bending test, it is found that the strength of glass with convex surface upward is about 10% higher than that of the flat sample. But the concave surface upward glasses have a little smaller strength that the flat samples. For the falling test of the steel ball results, it is found that the strength of convex surface upward glass increased about 50% that flat samples. And the glasses with smaller radius of curvature have better strength. It is found that concave surface upward samples have obvious worse strength that flat samples.

碩士
國立臺灣科技大學
電機工程系
100
Photovoltaic (PV) panels are subject to problems such as hot spots and reduced output power when operating in partially shaded conditions. Although bypass diodes are utilized to alleviate these problems, the diodes cause multiple-peak characteristics. Tracking the maximum output power point in partially shaded conditions is difficult using conventional software-based maximum power point tracking (MPPT) techniques. Current-voltage (I-V) curve tracers can assist software-based MPPT to track the true maximum power point (MPP) by scanning several potential MPP areas. Therefore, a software-based MPPT with an I-V curve tracer is a preferred solution. This study investigates the advantages and disadvantages of several I-V curve tracers and proposes a load self-adaptive PV panel characteristic curve tracer by applying a hysteretic self-controlled duty-modulated load resistor (DMLR) to a boost converter I-V curve tracer. Several advantages are achieved, such as simple structure, cost-efficient implementation, and no tracing limitation near the Voc. A circuit for a 120 W PV panel is simulated and implemented to verify the feasibility of the proposed curve tracer.

碩士
國立臺灣科技大學
電子工程系
101
This research is to create a comprehensive and robust set of measurement approaches making for accurately evaluating the quality and accuracy of displays happen. To help users better understand the LCD monitor and better evaluate, select, use, and adjust the product even when display is in different settings. The experiments were conducted to verify the color characteristics and tone reproduction curves of the flat panel display in 4 measurement items including color gamut, tone reproduction curve (TRC), correlated color temperature (CCT) and color difference under designed 12 matrix simulated conditions: 4 different CCTs in 5000 K, 6500 K, 9300 K and 10000 K independently the display is adjusted to 3 different luminance in 200 cd/m&;sup2;, 100 cd/m&;sup2; and 60 cd/m&;sup2; respectively. These 12 situations are dependent to general users but are overlooked in making display measurements and evaluations. According to the experimental conclusion, the display shows stable statistics significant characteristics in all test items when CCTs changed from low value to high value no matter how the display luminance is in high luminance, medium or low luminance.

碩士
國立臺灣科技大學
電機工程系
100
To trace I-V characteristic of PV panels, several I-V curve tracer are proposed including variable resistors, electronic loads, DC-DC converters, bipolar power amplifiers, four-quadrant power supplies and capacitive load I-V curve tracers. Among them, the capacitive I-V curve tracer has several advantages over the others: simple circuit, fast measurement speed, automatic sweep, low heat dissipation, compact size, and low cost. However, it sweeps too quickly to collect the data in lacking of insufficient sampling resolution around the MPP operating regions. To increase the sampling resolution, a capacitive-type high-resolution characteristic curve tracer for PV panel is proposed to extend the sweep time around the MPP regions by adding a charging-current shunt sub-circuit with simple control. Consequently, more I-V sampling points can be captured by the analog to digital (ADC) device. To confirm the function of the capacitive-type high-resolution characteristic curve tracer for PV panel, the simlution and the experimental results are also proveded. Further, additional modification of the proposed curve tracer is made to measure the I-V curve with multiple-peak power points under partial shading condition.

碩士
國立臺北大學
經濟學系
97
In this thesis we discuss important econometric problems with the estimation of Environmental Kuznets Curve, which we exemplify with the particular example of the Carbon Kuznets Curve(CKC). The Carbon Kuznets hypothesis postulates an inverse U-shaped relationship between per capita GDP and per capita CO2 emissions. It suggests that environmental degradation increases in the early stages of economic growth but eventually decreases as income over a certain level. However, there are several important issues in EKC estimations by the current econometric methods. First, there is a potential risk of spurious regression if we estimate EKC relationship without testing the present of unit roots in pollution and income data beforehand. Second, if we investigate EKC relationship with single country data, we would ignore the fact that CO2 has accumulated and widely dispersed feature. It will cause some problems of low power when performing conventional unit root tests. Third, traditional panel data estimation methods used in the EKC literature rely on the cross-sectional independence assumption, i.e. the individual countries' GDP and emissions series are independent across countries. This simplified assumption may cause bias and lose power in estimation and testing of panel data. For solving all these problems in EKC estimation, we apply panel unit root tests proposed by Pesaran (2007) in regional panel data. With an application of factor model based methods for cross-sectional dependence, we show that both pollution and income data are stationary. The EKC without cross-sectional dependence and without cross-sectional dependence and common trend are derived and estimated. It is shown that the former still have inverted U-shape curves, while the latter have arc-like shapes that increase with GDP gradually. We try to interpret above results, and consider that researchers should have drawn a conclusion with more caution than commonly done, especially in the case of the cross-sectional independence assumption.

碩士
國立交通大學
機械工程學系
101
In this thesis, the effects of several system parameters on the sound pressure level (SPL) curves of panel-speakers made of different materials are studied via both theoretical and experimental approaches. For the panel-speakers, it is not uncommon to have SPL drops termed as sound valleys on the SPL curves, which can affect the sound quality of the speakers. This research offers a way to eliminate the sound valleys by adjusting the system parameters using the finite element model established on the basis of the simulation software “ANSYS”. In the first place, the experimental results are used to prove the correctness of the ANSYS model which can be used for the following investigation. Then we make changes in the system parameters such as plate material, diameter of coil, lamination arrangement of plate, and properties of elastic support to study the effects of the parameters on the SPL curves of the speakers. Finally, the appropriate system parameters are used to fabricate a panel-speaker to demonstrate the practicability of the design.

碩士
國立中興大學
應用經濟學研究所
93
The Environmental Kuznets Curve (EKC) hypothesis suggests that an inverted U relationship exists between environmental degradation and income per capita. In the past decade, numerous studies have been focused on testing the EKC hypothesis but they were not paid attention to the greenhouse gas emissions (GHGES). Since GHGS are special pollutants that create global, not local. This paper analyzes the relationship between GDP per capita and GHGES from the global point of view. Our major estimated results show that the EKC for each gas are consistent with an inverted-U shaped in 28 Annex I country’s samples. However, such hypothesis for the global environmental Kuznets curve is not proved. Furthermore, the change of strength and occurrence probabilities of the El Ni o and La Ni a from increasing carbon dioxide emission is also tested and estimated. The strength of the El Ni o (or La Ni a) and the probabilities of occurrence of the El Ni o and La Ni a will be increased if the carbon dioxide emission increases.

Códigos do JEL: C23, E62, H21./
The current economic and sovereign crisis in the Eurozone led some European governments, due mainly to outside impositions (of the IMF, European Commission, and the ECB, the troika), to increases the tax rates, with the goal of boosting tax revenues, and in that way to decrease excessive deficits, and to fight high public debt, which most countries of the Eurozone, in particular Southern Countries, face. Were these decisions the most correct? What is the relationship between tax rates and tax revenues? What is the tax rate that maximizes the revenue? In the economic literature we find in the concept of the Laffer Curve the answer for the previous questions. Using panel-data, observed between 1995 and 2011 (for direct taxes) and 2000 and 2011 (for indirect taxes), we will estimate Laffer Curves for the Eurozone countries, either for the Eurozone as a whole and also for each individual Eurozone member country. We chose the three taxes that contribute the most to the state revenue, and they are the value added tax (VAT), as an indirect tax; the corporate income tax, and the household income tax. We can conclude for the existence of a Laffer Curve in the Eurozone for VAT and for the individual income tax, but in case of the corporate income tax, we come to the opposite conclusion. In the case of Portugal the optimal tax rate for the individual income tax is 49% and for the corporate income tax is 30%.
A grave crise económica e orçamental que tem vindo a assolar os países da Zona Euro levou alguns governos, maioritariamente devido a imposições externas (FMI, Comissão Europeia e BCE, a troika), a aumentar as taxas de imposto, com o objetivo de aumentar a receita fiscal para evitar a ocorrência de défices excessivos, que se têm verificado continuadamente, e dessa forma combater a elevada divida pública que caracteriza uma parte dos países da Zona Euro (principalmente os Países do Sul). Terá sido esta a decisão mais correta? Qual a relação entre a taxa de um dado imposto e a sua receita? Qual é a taxa de imposto que maximiza a receita desse imposto? A teoria económica encontra na Curva de Laffer a resposta a estas perguntas. Através de estimação econométrica com dados em painel, compreendidos entre 1995-2011 (impostos diretos) e 2000-2011 (imposto indireto), iremos estimar a Curva de Laffer para a Zona Euro, evidenciando possíveis diferenças entre países. Para tal escolhemos os três impostos que mais contribuem para as receitas do estado - o Imposto sobre o Valor Acrescentado (IVA); o Imposto sobre o Rendimento das Pessoas Coletivas (IRC) e, por último, o Imposto sobre o Rendimento das Pessoas Singulares (IRS). Através das nossas estimações concluímos que existe evidência da Curva de Laffer para a Zona Euro para o IVA e para o IRS, enquanto que para o IRC, chegamos à conclusão inversa. Para Portugal a taxa ótima para o IRC é de 30% e para o IRS é de 49%.

Chin, Yu.
Thesis Ph.D. Chinese University of Hong Kong 2015.
Includes bibliographical references (leaves 162-183).
Abstracts also in Chinese; appendixes in Chinese, appendix B6 in English.
Title from PDF title page (viewed on 15, November, 2016).

O trabalho que se apresenta modela as trajectórias do bem-estar psicológico a partir da escala psicométrica do General Health Questionnaire – 12 (GHQ-12), utilizando dados do British Household Panel Survey (BHPS) relativos a quatro anos consecutivos, de 2003 a 2006. Utilizam-se os métodos de estimação desenvolvidos no âmbito do Latent Growth Curve Models, que estimam trajectórias latentes. A aproximação à modelação da escala do GHQ-12 é feita a partir do pressuposto, assente na proposta de Graetz (1991), de que o GHQ-12 é uma escala multidimensional que contém três dimensões distintas. Considera-se que estas três dimensões (ansiedade e depressão, disfunção social e perda de confiança) têm subjacente um factor de segunda ordem. De forma a comparar a trajectória de um indicador único com trajectórias dos três factores, no primeiro passo modelou-se a trajectória dos três factores considerando os scores das respostas dos indivíduos, obtidos a partir das somas das respostas aos respectivos itens. A comparação dos modelos permitiu concluir que o ganho em capacidade explicativa com um modelo considerando três dimensões é reduzido. O mesmo acontece quando modelamos as trajectórias considerando as escalas ordinais das variáveis de input. Inversamente, a estimação dos modelos de trajectória latente condicionada permitiu concluir que o modelo que considera as medidas repetidas ordinais e um factor de segunda ordem tem uma maior capacidade explicativa do que os modelos de LGCM condicionados quer do indicador único de bem-estar subjectivo, quer do factor latente medido pelos scores nas dimensões de ansiedade e depressão, disfunção social e perda de confiança.
This work intends to model the trajectories of psychological well-being based on the psychometric scale of the General Health Questionnaire – 12 (GHQ-12), using four consecutive years’ data from the British Household Panel Survey (BHPS), from 2003 to 2006. In order to achieve this, estimation methods developed in the context of Latent Growth Curve Models – that estimate latent trajectories – were used. The approach to the GHQ-12 scale modelling was carried out based on the assumption, supported by Graetz’s (1991) proposal, that the GHQ-12 is a multidimensional scale containing three distinct dimensions (anxiety and depression, social dysfunction and loss of confidence) which are considered to have an underlying second order factor. In order to compare the trajectory of a single indicator to the trajectories of these three factors, the first step was to model the three factors’ trajectory considering the individuals’ answers scores, obtained by adding the answers to the respective items. The models’ comparison led to the conclusion that the potential explicative gain from a tripartite model is slim. The same occurs when modelling the trajectories considering the ordinal scales of the input variables. On the contrary, the estimation of the conditioned latent growth models led to the conclusion that the model which considers the repeated ordinal measures and a second order factor has a larger explicative ability than both the conditioned LGCM models: one regarding the subjective well-being single indicator and another the latent factor measured by the scores in the anxiety and depression, social dysfunction and loss of confidence dimensions.

MCom (Economics)
Department of Economics
The need to realise steady economic growth, measured in this research by Gross Domestic Product (GDP), has ignited a plethora of studies about the contributors of economic growth and their optimal levels. Government expenditure is one contributor to economic growth. From a theoretical standpoint, optimal government size is depicted by an inverted U-curve known as the Armey curve which is hypothesised between the relationship of government size and economic growth. Empirical literature provides evidence that optimal government size is between 20-30 percent a share of GDP. However, little has been done to investigate the optimal level of isolated components of government spending that maximizes economic growth. One component of government spending that has gained limelight over the past decade is that of social assistance. Defined as public expenditure spent as cash and food transfers to the poor, this research uses social assistance expenditure to assess its optimal level that maximizes growth. This is important because some policymakers are concerned about the ballooning budgets directed at social assistance, and argue that the scarce resources need to be transferred to other social services sectors such as health and education. Basing on the panel-data accessed from the World Bank, this research uses the quadratic equation model to determine the optimal level of social assistance for African and Organisation for Economic Co-Operation and Development (OECD) countries covering the period 2009-15. The finding is that the optimal level of social assistance spending for African and OECD countries is 3.2 percent of GDP and 29.4 percent of GDP respectively. The study also finds that both African and OECD countries operate below the optimal levels and it is suggested that they need to increase social assistance spending in order to realize positive contributions to economic growth.
NRF

Classificação JEL: C33; C63
Com o intuito de modelar longitudinalmente trajetórias de privação material, com dados provenientes do painel rotativo ICOR (Inquérito às Condições de Vida e ao Rendimento), são apresentados resultados de diversos estudos, tendo por base diferentes opções metodológicas no framework dos modelos com equações estruturais, designadamente modelos com trajetória latente. Para lidar com as omissões resultantes da rotatividade do painel são utilizadas as abordagens estatísticas full information maximum likelihood e imputação múltipla, assumindo um mecanismo de omissão de dados ignorável. Porém, neste painel existem não respostas, cujo mecanismo de omissão pode ser considerado não ignorável. Assim, foram também utilizadas as abordagens pattern mixture e selection models. Foi realizado um estudo de simulação, recorrendo ao pacote estatístico Mplus, no sentido de avaliar o efeito da existência de omissões, de desvios face à normalidade da distribuição dos dados, do número de momentos temporais, da dimensão da amostra e do método de estimação, nas estimativas dos parâmetros do modelo. Assim, os principais contributos metodológicos desta tese são a modelação longitudinal de dados provenientes de um painel rotativo com recurso a diferentes abordagens estatísticas para lidar com as omissões, o desenvolvimento de rotinas para implementação de um estudo de simulação em Mplus, e a apresentação de um conjunto de orientações a serem seguidas por um investigador que pretenda usar modelos com trajetória latente em painéis rotativos com dados omissos.
In order to model longitudinal trajectories of material deprivation, with data from the rotating panel ICOR (Statistics on Income and Living Conditions), different studies results are presented, based on distinct methodological options in the framework of structural equation models, namely latent growth curve models. To deal with the non-responses resulting from the rotation of the panel the statistical approaches full information maximum likelihood and multiple imputation are used, if is assumed an ignorable missing data mechanism. However, there is another type of nonresponses in this panel whose missing data mechanism cannot be considered ignorable. Thus the approaches pattern mixture and selection models were also considered. A simulation study was performed using the statistical software Mplus, in order to evaluate the effect of the existence of missing data, the deviations from the normality distribution, the number of time points, the sample size and estimation method, on model parameters estimates. Thus, the main methodological contributions of this thesis are modeling longitudinal data from a rotating panel using different statistical approaches in order to deal with the non-responses, the development of routines for implementing a simulation study in Mplus, and presenting a set of guidelines to be followed by a researcher wishing to use latent growth curve models in rotating panels with missing data.