The urgent need for a clean and sustainable power supply for wireless sensor nodes and low-power electronics in various monitoring systems and the Internet of Things has led to an explosion of research in substitute energy technologies. Traditional batteries are still the most widely used power source for these applications currently but have been blamed for chemical pollution, high maintenance cost, bulky volume, and limited energy capacity. Ambient energy in different forms such as vibration, movement, heat, wind, and waves otherwise wasted can be converted into usable electricity using proper transduction mechanisms to power sensors and low-power devices or charge rechargeable batteries. This dissertation focuses on the design, modeling, optimization, prototype, and testing of novel piezoelectric energy harvesters for extracting energy from human walking, bio-inspired bi-stable motion, and torsional vibration as an alternative power supply for wireless monitoring systems. To provide a sustainable power supply for health care monitoring systems, a piezoelectric footwear harvester is developed and embedded inside a shoe heel for scavenging energy from human walking. The harvester comprises of multiple 33-mode piezoelectric stacks within single-stage force amplification frames sandwiched between two heel-shaped aluminum plates taking and reallocating the dynamic force at the heel. The single-stage force amplification frame is designed and optimized to transmit, redirect, and amplify the heel-strike force to the inner piezoelectric stack. An analytical model is developed and validated to predict precisely the electromechanical coupling behavior of the harvester. A symmetric finite element model is established to facilitate the mesh of the transducer unit based on a material equivalent model that simplifies the multilayered piezoelectric stack into a bulk. The symmetric FE model is experimentally validated and used for parametric analysis of the single-stage force amplification frame for a large force amplification factor and power output. The results show that an average power output of 9.3 mW/shoe and a peak power output of 84.8 mW are experimentally achieved at the walking speed of 3.0 mph (4.8 km/h). To further improve the power output, a two-stage force amplification compliant mechanism is designed and incorporated into the footwear energy harvester, which could amplify the dynamic force at the heel twice before applied to the inner piezoelectric stacks. An average power of 34.3 mW and a peak power of 110.2 mW were obtained under the dynamic force with the amplitude of 500 N and frequency of 3 Hz. A comparison study demonstrated that the proposed two-stage piezoelectric harvester has a much larger power output than the state-of-the-art results in the literature. A novel bi-stable piezoelectric energy harvester inspired by the rapid shape transition of the Venus flytrap leaves is proposed, modeled and experimentally tested for the purpose of energy harvesting from broadband frequency vibrations. The harvester consists of a piezoelectric macro fiber composite (MFC) transducer, a tip mass, and two sub-beams with bending and twisting deformations created by in-plane pre-displacement constraints using rigid tip-mass blocks. Different from traditional ways to realize bi-stability using nonlinear magnetic forces or residual stress in laminate composites, the proposed bio-inspired bi-stable piezoelectric energy harvester takes advantage of the mutual self-constraint at the free ends of the two cantilever sub-beams with a pre-displacement. This mutual pre-displacement constraint bi-directionally curves the two sub-beams in two directions inducing higher mechanical potential energy. The nonlinear dynamics of the bio-inspired bi-stable piezoelectric energy harvester is investigated under sweeping frequency and harmonic excitations. The results show that the sub-beams of the harvester experience local vibrations, including broadband frequency components during the snap-through, which is desirable for large power output. An average power output of 0.193 mW for a load resistance of 8.2 kΩ is harvested at the excitation frequency of 10 Hz and amplitude of 4.0 g. Torsional vibration widely exists in mechanical engineering but has not yet been well exploited for energy harvesting to provide a sustainable power supply for structural health monitoring systems. A torsional vibration energy harvesting system comprised of a shaft and a shear mode piezoelectric transducer is developed in this dissertation to look into the feasibility of harvesting energy from oil drilling shaft for powering downhole sensors. A theoretical model of the torsional vibration piezoelectric energy harvester is derived and experimentally verified to be capable of characterizing the electromechanical coupling system and predicting the electrical responses. The position of the piezoelectric transducer on the surface of the shaft is parameterized by two variables that are optimized to maximize the power output. Approximate expressions of the voltage and power are derived by simplifying the theoretical model, which gives predictions in good agreement with analytical solutions. Based on the derived approximate expression, physical interpretations of the implicit relationship between the power output and the position parameters of the piezoelectric transducer are given. / Doctor of Philosophy / Wireless monitoring systems with embedded wireless sensor nodes have been widely applied in human health care, structural health monitoring, home security, environment assessment, and wild animal tracking. One distinctive advantage of wireless monitoring systems is to provide unremitting, wireless monitoring of interesting parameters, and data transmission for timely decision making. However, most of these systems are powered by traditional batteries with finite energy capacity, which need periodic replacement or recharge, resulting in high maintenance costs, interruption of service, and potential environmental pollution. On the other hand, abundant energy in different forms such as solar, wind, heat, and vibrations, diffusely exists in ambient environments surrounding wireless monitoring systems which would be otherwise wasted could be converted into usable electricity by proper energy transduction mechanisms. Energy harvesting, also referred to as energy scavenging and energy conversion, is a technology that uses different energy transduction mechanisms, including electromagnetic, photovoltaic, piezoelectric, electrostatic, triboelectric, and thermoelectric, to convert ambient energy into electricity. Compared with traditional batteries, energy harvesting could provide a continuous and sustainable power supply or directly recharge storage devices like batteries and capacitors without interrupting operation. Among these energy transduction mechanisms, piezoelectric materials have been extensively explored for small-size and low-power generation due to their merits of easy shaping, high energy density, flexible design, and low maintenance cost. Piezoelectric transducers convert mechanical energy induced by dynamic strain into electrical charges through the piezoelectric effect. This dissertation presents novel piezoelectric energy harvesters, including design, modeling, prototyping, and experimental tests for energy harvesting from human walking, broadband bi-stable nonlinear vibrations, and torsional vibrations for powering wireless monitoring systems. A piezoelectric footwear energy harvester is developed and embedded inside a shoe heel for scavenging energy from heel striking during human walking to provide a power supply for wearable sensors embedded in health monitoring systems. The footwear energy harvester consists of multiple piezoelectric stacks, force amplifiers, and two heel-shaped metal plates taking dynamic forces at the heel. The force amplifiers are designed and optimized to redirect and amplify the dynamic force transferred from the heel-shaped plates and then applied to the inner piezoelectric stacks for large power output. An analytical model and a finite model were developed to simulate the electromechanical responses of the harvester. The footwear harvester was tested on a treadmill under different walking speeds to validate the numerical models and evaluate the energy generation performance. An average power output of 9.3 mW/shoe and a peak power output of 84.8 mW are experimentally achieved at the walking speed of 3.0 mph (4.8 km/h). A two-stage force amplifier is designed later to improve the power output further. The dynamic force at the heel is amplified twice by the two-stage force amplifiers before applied to the piezoelectric stacks. An average power output of 34.3 mW and a peak power output of 110.2 mW were obtained from the harvester with the two-stage force amplifiers. A bio-inspired bi-stable piezoelectric energy harvester is designed, prototyped, and tested to harvest energy from broadband vibrations induced by animal motions and fluid flowing for the potential applications of self-powered fish telemetry tags and bird tags. The harvester consists of a piezoelectric macro fiber composite (MFC) transducer, a tip mass, and two sub-beams constrained at the free ends by in-plane pre-displacement, which bends and twists the two sub-beams and consequently creates curvatures in both length and width directions. The bi-direction curvature design makes the cantilever beam have two stable states and one unstable state, which is inspired by the Venus flytrap that could rapidly change its leaves from the open state to the close state to trap agile insects. This rapid shape transition of the Venus flytrap, similar to the vibration of the harvester from one stable state to the other, is accompanied by a large energy release that could be harvested. Detailed design steps and principles are introduced, and a prototype is fabricated to demonstrate and validate the concept. The energy harvesting performance of the harvester is evaluated at different excitation levels. Finally, a piezoelectric energy harvester is developed, analytically modeled, and validated for harvesting energy from the rotation of an oil drilling shaft to seek a continuous power supply for downhole sensors in oil drilling monitoring systems. The position of the piezoelectric transducer on the surface of the shaft is parameterized by two variables that are optimized to obtain the maximum power output. Approximate expressions of voltage and power of the torsional vibration piezoelectric energy harvester are derived from the theoretical model. The implicit relationship between the power output and the two position parameters of the transducer is revealed and physically interpreted based on the approximate power expression. Those findings offer a good reference for the practical design of the torsional vibration energy harvesting system.

Dynamic behavior of flexural-torsional coupled vibration of rotating beams using the Rayleigh-Ritz method with orthogonal polynomials as basis functions is studied. The present work starts from a review of the development and analysis of four basic types of beam theories: the Euler-Bernoulli, Rayleigh, Shear and Timoshenko and goes over to a study of flexural-torsional coupled vibration analysis using basic beam theories. In obtaining natural frequencies, orthogonal polynomials used in the Rayleigh-Ritz method are studied as an efficient way of getting results. The study is also performed for both non-rotating and rotating beams. Orthogonal polynomials and functions studied in the present work are : Legendre, Chebyshev, integrated Legendre, modified Duncan polynomials, the eigenfunctions of a pinned-free uniform beam, and the special trigonometric functions used in conjunction with Hermite cubics. Studied cases are non-rotating and rotating Timoshenko beams, bending-torsion coupled beam with free-free boundary conditions, a cantilever beam, and a rotating cantilever beam. The obtained natural frequencies and mode shapes are compared to those available in various references and results for coupled flexural-torsional vibrations are compared to both previously available references and with those obtained using NASTRAN finite element package. / Master of Science

The aim of this thesis is to design crankshaft for in-line six-cylinder diesel engine and to design viscous torsional vibration damper for the cranktrain of specified parameters. The thesis includes the creation of a dynamic torsional model of cranktrain and calculation of forced vibrations of mechanism with and without damper. Part of this thesis is also strength analysis of the designed crankshaft with damper using the Finite Element Method (FEM).

No description available.

El presente trabajo, consiste en la implementación de estos disipadores fluido-viscosos en una edificación con predominación de muros estructurales de 5 niveles que presenta un comportamiento torsional. El diseño de estos disipadores, parten con el objetivo de diseño de daño moderado y bajo un sismo de 475 años de periodo de retorno, es decir que la deriva objetivo necesario para el diseño es 0.58%. Se analiza bajo la colocación en diagonal para amortiguadores lineales y no lineales. La colocación se hace de manera uniforme, y de manera que compense el movimiento torsional. Se colocaron un total de 40 disipadores en todo el edificio. Entre los principales resultados, la fuerza fuerzas en los disipadores fueron en un orden de 213 ton-f y comportamiento torsional debido a zonas frágiles de la estructura fueran reducidas en 80%. La implementación de los disipadores fluido-viscosos permiten reducir la deriva en 60% y todas las derivas se mantienen por debajo de 0.58%, en teoría. En un futuro, en el Perú, será necesario implementar una normativa para el diseño y el aporte de amortiguamiento en el edificio. / The present work consists of the implementation of these fluid-viscous dissipators in a building with a predominance of structural walls, of 5 levels that presents a torsional behavior, as well as fails to comply with the permissible drift limit established by Norma Técnica E.030. The design of these dissipators starts with the design objective of moderate damage and under an earthquake of 475 years of return period, whose corresponding objective drift assumes a value of 0.58%. It is discussed under diagonal placement for linear and nonlinear dampers. The placement is done uniformly, and in a way that compensates for torsional movement. A total of 40 heatsinks were placed throughout the building, 8 per floor. Among the main results, the forces in the dissipators were in the order of 200 ton-f and torsional behavior due to flexible areas of the structure were reduced by 80%. The implementation of fluid-viscous heatsinks allows the drift to be reduced by 60%, and all drifts are kept below 0.58%, that is, both linear and non-linear devices meet the target drift, even though the latter have a higher drift, given their lower C, therefore, lower force, less drift control, even so, they are efficient, both structurally and economically, given their lower strength. In the future, in Peru, it will be necessary to implement a regulation for the design and the cushioning contribution in the building. / Trabajo de investigación

Transition metal oxides (TMO) have proven to exhibit novel properties such as high temperature superconductivity, magnetic ordering, charge and spin density waves, metal to insulator transitions and colossal magnetoresistance. Among these are a spin-orbit coupling (SOC) induced Mott insulator Sr2IrO4. The electric transport properties of this material remain finite even at cryogenic temperatures enabling its complex electronic structure to be investigated by a scanning tunneling microscope. At T = 77 K, we observed two features which represent the Mott gap with a value of 2D ~ 615 meV. Additionally an inelastic loss feature was observed inside this gap due to a single magnon excitation at an energy of ~ 125 meV. These features are consistent with similar measurements with other probes. In addition to these features, at T = 4.2 K lower energy features appear which are believed to be due to additional magnetic ordering. Another material that exhibits a unique physical behavior is the sliding charge density wave (CDW) material TaS3. It is a quasi-one dimensional material that forms long narrow ribbon shaped crystals. It exhibits anomalies including non-ohmic conductivity, a decrease in the Young’s modulus, a decrease in the shear modulus and voltage induced changes in the crystal’s overall length. In addition, we have observed the torsional piezo-like response, voltage induced torsional strain (VITS), in TaS3 which was first discovered by Pokrovskii et. al. in 2007. Our measurements were conducted with a helical resonator. The VITS response has a huge effective piezoelectric coefficient of ~ 104 cm/V. In addition we have concluded that the VITS is a very slow response with time constants of ~ 1 s near the CDW depinning threshold, that these time constants are dependent on the CDW current, and we suggest that the VITS is due to residual twists being initially present in the crystal.

The Formula SAE is a student based competition organised by SAE International where engineering students from a university design, develop and test a formula-style race car prototype to compete against other universities. The competition car needs to satisfy the competition rules set out by the organisers. The competition strives to stimulate original, creative problem solving together with innovative engineering design practices. In any race environment, the primary goal is always to be as competitive as possible. Due to the competitive nature of motor sport, vehicle components need to withstand various and severe stresses. The components of a race car vehicle are responsible for the vehicle’s handling characteristics and reliability. The chassis is a crucial and integral component of a Formula SAE competition car, primarily responsible for the vehicle’s performance characteristics. The chassis is the structural component that accommodates all the other components. A Formula SAE chassis is a structure that requires high torsional stiffness, low weight as well as the necessary strength properties. In this study, multiple Formula SAE chassis were designed and developed using computer aided design software. Each concept’s torsional stiffness, weight and strength properties were tested using finite element analysis software. The different concepts consisted of different design techniques and applications. All the concepts were analysed and assessed, leading to the identification of an acceptable prototype. The prototype was manufactured for experimental tests. The designed chassis complied with the Formula SAE rules and regulations. The weight, torsional stiffness and strength characteristics of the designed chassis frame were also favourable compared to accepted standards for Formula SAE chassis frames. The manufactured chassis was prepared for experimental tests in order to validate the simulation results produced by the finite element analysis. The torsional stiffness, weight and strength were experimentally determined and the results were compared with the corresponding simulations results. The comparison of the experimental and simulated results enabled the validation of the finite element analysis software. The study draws conclusions about the use of computer aided design and finite element analysis software as a design tool for the development of a Formula SAE chassis. Closure about the study is provided with general conclusions, recommendations and research possibilities for future studies. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

Les maladies à expansion de triplets nucléotidiques situés dans la région codante, telles que la maladie de Huntington, sont des maladies où les gènes en questions possèdent un nombre de répétitions trinucléotidiques anormalement élevé et inversement corrélé avec l'âge d‟apparition des symptômes. Plusieurs de ces maladies démontrent une anticipation paternelle, où un ajout de répétitions trinucléotidiques a lieu pendant la spermiogenèse, mais les étapes et les mécanismes impliqués sont encore mal compris. Or, la spermiogenèse est caractérisée par un remodelage drastique de la chromatine, où les histones sont ultimement remplacées par les protamines afin de compacter et protéger davantage le matériel génétique. Cette transition implique aussi un changement topologique majeur qui mène à une accumulation de superenroulement négatif qui est éliminé par la topoisomérase 2[beta]. Pour identifier les étapes précises où l'extension trinucléotidique a lieu, j'ai développé une stratégie de séparation des spermatides en utilisant la cytométrie en flux, ce qui m'a permis d'obtenir quatre populations, soit les spermatides aux étapes 1 à 9, 10 à 12, 13-14 et 15-16. J'ai appliqué cette stratégie sur un modèle de souris transgéniques pour la maladie de Huntington, ce qui a permis de démontrer par PCR que l'extension trinucléotidique des répétitions CAG a lieu à la fin du remodelage de la chromatine, soit à l'étape 14. Afin d‟élucider le mécanisme d‟extension trinucléotidique, j'ai utilisé une stratégie in vitro, basée sur l'incubation d‟extraits nucléaires actifs de spermatides avec un plasmide contenant des répétitions CAG. Cette stratégie a démontré que le superenroulement négatif libre, tel que retrouvé pendant le remodelage de la chromatine, est capable d'induire des structures secondaires dans les répétitions CAG, ce qui entraîne une cascade d‟événements menant à l'extension trinucléotidique. J'ai validé ce processus en inhibant aussi les topoisomérases de type 2 qui sont responsables d'éliminer le superenroulement. Finalement, j‟ai démontré que la protamination de l‟ADN, telle qu'observée dans les spermatides, accentue l'accumulation de stress torsionnel aux répétitions CAG, ce qui favorise leur extension. Mes travaux sur le stress torsionnel lors de la protamination suggèrent une nouvelle source potentielle d'instabilité trinucléotidique, nécessitant une caractérisation additionnelle. Cette source d'instabilité, qui est spécifique au mâle, jouerait un rôle majeur dans l'anticipation paternelle des maladies trinucléotiditiques. / Abstract : Trinucleotidic diseases, such as the Huntington disease, are genetic diseases characterized by abnormally long trinucleotidic repeats within a specific gene, which are inversely correlated with the age of onset of symptoms when within exons. Many trinucleotidic diseases display paternal anticipation, where trinucleotidic repeats are added during spermiogenesis, without any details on the mechanism or the steps involved. Interestingly, spermiogenesis is characterized by a drastic chromatin remodeling, where histones are ultimately replaced by protamines in order to achieve greater compaction and protection of DNA. This transition also involves major topological changes, where accumulation of negative supercoils are eliminated by the topoisomerase 2[beta]. In order to identify the specific steps where trinucleotidic extension occurs, I have developed a strategy to separate spermatids from mice, using flow cytrometry. This allowed me to purify four distinct spermatids population, consisting of steps 1-9, 10-12, 13-14 and 15-16 spermatids. The sorting strategy was used on a transgenic mouse model of the Huntington disease, which allowed me to determine, using PCR, that CAG extension occurs at the end of chromatin remodeling, more specifically at step 14. The mechanism of extension was investigated using an in vitro approach, based on the incubation of active nuclear extracts from spermatids with a plasmid containing CAG repeats. Using this strategy, I showed that free negative supercoils, as observed during chromatin remodeling, may lead to secondary structures, and more specifically hairpins in trinucleotidic repeats, which ultimately result in trinucleotidic extension. This hypothesis was validated by inhibiting enzymes such as type 2 topoisomerases, since they are responsible for negative supercoils removal. Moreover, I showed that DNA protamination, as observed in spermatids, may increase torsional stress at CAG repeats and leads to expansion. In conclusion, this work suggest that torsional stress induced by protamination of DNA could be a new potential source of trinucleotidic instability. Moreover, this male specific source of trinucleotidic instability could play a major role in paternal anticipation of trinucleotidic diseases.

As forças devidas ao vento variam espacial e temporalmente e consequentemente provocam esforços de torção em edifícios. A magnitude desses esforços depende basicamente da forma do edifício, de sua altura e estrutura, da influência da vizinhança e da direção do vento. As normas técnicas geralmente negligenciam a importância da torção. A versão atual da norma brasileira de forças devidas ao vento (NBR 6123) não possui uma abordagem aplicável para modos de vibração torcionais. Verificando a falta de recomendações da norma brasileira a respeito dos efeitos dinâmicos da torção em edifícios, este trabalho apresenta uma metodologia para a estimativa do momento torçor devido ao vento, a qual contempla tanto a parcela média quanto a parcela flutuante da solicitação. Para sua calibração utilizaram-se dados de 19 edifícios altos ensaiados no túnel de vento do Laboratório de Aerodinâmica das Construções com o método High Frequency Pressure Integration (HFPI), bem como dados da literatura técnica. A análise dos resultados mostrou que as excentricidades das forças de arrasto para cálculo do momento torçor apresentadas na NBR 6123 são adequadas na estimativa dos efeitos estáticos para edificações com efeitos de vizinhança mas tendem a subestimar a solicitação nos casos sem efeito de vizinhança. Assim, propuseram-se novos valores de excentricidades baseadas na análise da base de dados. Finalmente, apresentou-se uma metodologia para estimativa dos momentos torçores estáticos equivalentes, a qual foi comparada com os valores fornecidos pelo HFPI e constatou-se que a proposta fornece valores adequados. / Wind loads change spatially and temporally consequently they induce torsional moments on buildings. These moments are affected by building shape and structure, by interfering effects of nearby buildings and wind direction. The importance of torsional loads is usually neglected by most codes. Indeed, dynamic torsional response is not presented on current Brazilian Wind Loads Code (NBR 6123). Therefore, a procedure to determine torsional dynamic response of buildings subjected to turbulent wind action is proposed. Experimental data of 19 buildings are used to improve the reliability of proposed procedure. These experimental tests were performed in boundary layer wind tunnel of Aerodynamic Laboratory using the High Frequency Pressure Integration (HFPI) technique. About torsional loads, results have shown that drag forces eccentricities present on the NBR 6123 are reliable when neighboring effects are considered, but they underestimate torsion when neighboring effects are not considered. New eccentricities values are proposed. Finally, a procedure to estimate the torsional static equivalent moment is presented and it agrees well with HFPI results. The average relative error between the results determined by the proposed formulae and the experimental data obtained by the HFPI shows the reliability and applicability of the proposed formulation to the design of isolated and nonisolated buildings.

Tese de mestrado integrado. Engenharia Civil (Área de Especialização de Geotecnia). Faculdade de Engenharia. Universidade do Porto. 2012