As technological advances occur, many conventional materials are incapable of providing the unique multi-functional characteristics demanded thus driving an accelerated focus to create new material systems such as carbon and graphite foams. The improvement of their mechanical stiffness and strength, and tailoring of thermal and electrical conductivities are two areas of multi-functionality with active interest and investment by researchers. The present research focuses on developing models to facilitate and assess multi-functional carbon foams in an effort to expand knowledge. The foundation of the models relies on a unique approach to finite element meshing which captures the morphology of carbon foams. The developed models also include ligament anisotropy and coatings to provide comprehensive information to guide processing researchers in their pursuit of tailorable performance. Several illustrations are undertaken at multiple scales to explore the response of multi-functional carbon foams under coupled field environments providing valuable insight for design engineers in emerging technologies. The illustrations highlight the importance of individual moduli in the anisotropic stiffness matrix as well as the impact of common processing defects when tailoring the bulk stiffness. Furthermore, complete coating coverage and quality interface conditions are critical when utilizing copper to improve thermal and electrical conductivity of carbon foams.

As technological advances occur, many conventional materials are incapable of providing the unique multi-functional characteristics demanded thus driving an accelerated focus to create new material systems such as carbon and graphite foams. The improvement of their mechanical stiffness and strength, and tailoring of thermal and electrical conductivities are two areas of multi-functionality with active interest and investment by researchers. The present research focuses on developing models to facilitate and assess multi-functional carbon foams in an effort to expand knowledge. The foundation of the models relies on a unique approach to finite element meshing which captures the morphology of carbon foams. The developed models also include ligament anisotropy and coatings to provide comprehensive information to guide processing researchers in their pursuit of tailorable performance. Several illustrations are undertaken at multiple scales to explore the response of multi-functional carbon foams under coupled field environments providing valuable insight for design engineers in emerging technologies. The illustrations highlight the importance of individual moduli in the anisotropic stiffness matrix as well as the impact of common processing defects when tailoring the bulk stiffness. Furthermore, complete coating coverage and quality interface conditions are critical when utilizing copper to improve thermal and electrical conductivity of carbon foams.

Vibration energy harvesters, or energy scavengers, recover mechanical energy from their surrounding environment and convert it into useable electricity as sustainable self-sufficient power sources to drive micro-to milli-Watt scale power electronics in small, autonomous, wireless devices and sensors. Using semiconducting, organic piezoelectric nanomaterials are attractive in low-cost, high resistance to fatigue, and environmentally friendly applications. Significantly, the deposition processes of sputtering ZnO (zinc oxide) thin films with high c-axis preferred orientation and electrospun PVDF (polyvinylidene fluoride) nanofibers with high piezoelectric £]-phase crystallisation are controlled at room temperature. Thus they don¡¦t have the necessity of post-annealed and electrical repoling process to obtain an excellent piezoelectricity, and are suitable for all flexible substrates such as PET (polyethylene terephthalate) and PI (polyimide). These works are divided into two parts. Part 1: Flexible piezoelectric harvesters based on ZnO thin films for self-powering and broad bandwidth applications. A new design of Al (aluminum)/PET-based flexible energy harvester was proposed. It consists of flexible Al/PET conductive substrate, piezoelectric ZnO thin film, selectively deposited UV (ultraviolet)-curable resin lump structures and Cu (copper) foil electrode. The design and simulation of a piezoelectric cantilever plate was described by using commercial software ANSYS FEA (finite element analysis) to determine the optimum thickness of PET substrate, internal stress distribution, operation frequency and electric potential. With the optimum thickness predicted by developed accurate analytical formula analysis, the one-way mechanical strain that is efficient to enhance the induced electric potential can be controlled within the piezoelectric ZnO layer. In addition, the relationship among the model solution of piezoelectric cantilever plate equation, vibration induced electric potential and electric power was realized. ZnO thin film of high (002) c-axis preferred orientation with an excellent piezoelectricity was deposited on the Al/PET by RF (radio-frequency) magnetron sputtering in room temperature. Al was sputtered on the PET substrate as the bottom electrode because of its low sheet resistance, superior adhesion with PET, and lattice constants matching with ZnO thin film. The selectively deposited UV-curable resin lump structures as proof mass were directly constructed on flexible piezoelectric plate using electrospinning with a stereolithography technique. One individual harvester achieves a maximum OCV (open-circuit voltage) up to 4V with power density of 1.247 £gW/cm2. This self-powered storage system can drive the warning signal of the LED (light emitting diode) module in both resonant and non-resonant conditions. We also succeeded in accomplishing a broad bandwidth harvesting system with operating frequency range within 100 Hz to 400 Hz to enhance powering efficiency. This system comprises four units of individual ZnO piezoelectric harvester in the form of a cantilever structure connected in parallel, and rectifying circuit with storage module. In addition, a modified design of a flexible piezoelectric energy-harvesting system with a serial bimorph of ZnO piezoelectric thin film was presented to enhance significantly higher power generation. This high-output system was examined at 15 Hz. The maximum DC (direct current) voltage output voltage with loading was 3.18 V, and the maximum DC power remained at 2.89 £gW/cm2. Furthermore, in order to examine the deformation between interfaces and the adhesion mechanism of multi-layer flexible electronics composites (e.g., ITO (indium tin oxide)/PET, Al/PET, ZnO/ITO/PET, and ZnO/Al/PET), nanoscratching and nano-indention testing (nanoindenter XP system) were conducted to analyze the adhesion before and after the vibration test. The plastic deformation between the ductile Al film and PET substrate is observed using SEM (scanning electron microscopy). Delamination between the ZnO and Al/PET substrate was not observed. This indicates that Al film provides excellent adhesion between the ZnO thin film and PET substrate. Part 2: Pre-strained piezoelectric PVDF nanofiber array fabricated by near-field electrospining on cylindrical process for flexible energy conversion. In various methodologies of energy harvesting from ambient sources, one-dimensional nanoharvesters have been gaining more attention recently. However, these nanofibers fabricated by micro-forming technologies may not easily control their structural diameter and length. This study originally presented the HCNFES (hollow cylindrical near-field electrospining) process to fabricate permanent piezoelectricity of PVDF piezoelectric nanofibers. Under high in-situ electric poling and strong mechanical stretching effect during HCNFES process, large PVDF nanofiber array with high piezoelectric £]-phase crystallisation was demonstrated. These pre-strained piezoelectric PVDF nanofibers fabricated by HCNFES with high process flexibility at low cost, availability in ultra-long lengths, various thicknesses and shapes can be applied at power scavenge, sensing and actuation. Firstly, PVDF nanofibers lay on a PET substrate, silver paste was applied at both ends of fibers to fix their two ends tightly on a Cu foil electrode pair. The entire structure was packaged inside a thin flexible polymer to maintain its physical stability. Repeatedly stretching and releasing the nanoharvester (NH 1) with a strain of 0.05% at 5 Hz vibration created a maximum peak voltage and current of -50 mV and -10 nA in forward connection, respectively. Secondly, a total of 44 parallel nanofibers have been fabricated and transferred onto an IDT (interdigital) electrode with 64 electrode pairs as a nanohavester (NH 2) to amplify current outputs under repeated mechanical vibration and impact tests. Under a repeated maximum strain of 0.14% at 6 Hz vibration, a peak current of 39 nA and peak voltage of 20.2 mV have been measured. Impact testing at 15 Hz, peak current of 130 nA has been collected with a voltage of 24.4 mV. Finally, the single PVDF fiber as nanoharvester (NH 3) with a strain of 0.05-0.1% at 5 Hz vibration created a maximum peak voltage and current of -45 mV and -3.9 nA, respectively. The maximum power remained at 18.45 pW/cm2 with a load resistor of 6.8 M£[. Based on the mechanism of converes piezoelectric effect, ANSYS software with coupled field analysis was used to realize piezoelectric actuation behavior of the PVDF fibers. From the observation of actuation property, a fixed-fixed single nanofiber was tested under different DC voltage supply. Comparing the polarized fiber with non-polarized fibers, the measurement of the center displacements as a function of electric field was conducted and characterized.

Using the AdS/CFT correspondence, we study the anisotropic transport properties of both supersymmetric and non-supersymmetric matter fields on (2+1)-dimensional defects coupled to a (3+1)-dimensional N=4 SYM "heat bath". We address on the one hand the purely conformal defect where the only non-vanishing background field that we turn on is a "topological", parameter parametrizing the impact on the bulk. On the other hand we also address the case of a finite external background magnetic field, finite net charge density and finite mass. We find in the purely conformal limit that the system possesses a conduction threshold given by the wave number of the perturbation and that the charge transport arises from a quasiparticle spectrum which is consistent with an intuitive picture where the defect acquires a finite width in the direction of the SYM bulk. We also examine finite-coupling modifications arising from higher derivative interactions in the probe brane action. In the case of finite density, mass and magnetic field, our results generalize the conformal case. We discover at high frequencies a spectrum of quasiparticle resonances due to the magnetic field and finite density and at small frequencies a Drude-like expansion around the DC limit. Both of these regimes display many generic features and some features that we attribute to strong coupling, such as a minimum DC conductivity and an unusual behavior of the "cyclotron" and plasmon frequencies, which become correlated to the resonances found in the conformal case. We further study the hydrodynamic regime and the relaxation properties, in which the system displays a set of different possible transitions to the collisionless regime. The mass dependence can be cast in two regimes: a generic relativistic behavior dominated by the UV and a non-linear hydrodynamic behavior dominated by the IR. In the massless case, we also extend earlier results to find an interesting duality under the transformation of the conductivity and the exchange of density and magnetic field. Furthermore, we look at the thermodynamics and the phase diagram, which reproduces general features found earlier in 3+1 dimensional systems and demonstrates stability in the relevant phase.

Using the AdS/CFT correspondence, we study the anisotropic transport properties of both supersymmetric and non-supersymmetric matter fields on (2+1)-dimensional defects coupled to a (3+1)-dimensional N=4 SYM "heat bath". We address on the one hand the purely conformal defect where the only non-vanishing background field that we turn on is a "topological", parameter parametrizing the impact on the bulk. On the other hand we also address the case of a finite external background magnetic field, finite net charge density and finite mass. We find in the purely conformal limit that the system possesses a conduction threshold given by the wave number of the perturbation and that the charge transport arises from a quasiparticle spectrum which is consistent with an intuitive picture where the defect acquires a finite width in the direction of the SYM bulk. We also examine finite-coupling modifications arising from higher derivative interactions in the probe brane action. In the case of finite density, mass and magnetic field, our results generalize the conformal case. We discover at high frequencies a spectrum of quasiparticle resonances due to the magnetic field and finite density and at small frequencies a Drude-like expansion around the DC limit. Both of these regimes display many generic features and some features that we attribute to strong coupling, such as a minimum DC conductivity and an unusual behavior of the "cyclotron" and plasmon frequencies, which become correlated to the resonances found in the conformal case. We further study the hydrodynamic regime and the relaxation properties, in which the system displays a set of different possible transitions to the collisionless regime. The mass dependence can be cast in two regimes: a generic relativistic behavior dominated by the UV and a non-linear hydrodynamic behavior dominated by the IR. In the massless case, we also extend earlier results to find an interesting duality under the transformation of the conductivity and the exchange of density and magnetic field. Furthermore, we look at the thermodynamics and the phase diagram, which reproduces general features found earlier in 3+1 dimensional systems and demonstrates stability in the relevant phase.

This study aims to investigate the behaviour of low-order beam and plate elements especially for their application to laminated structures. The merits and dements of the existing elements are brought out and new low-order elements with better interpolation polynomials are proposed. Two new beam elements are proposed for laminated composite beams that yield better representation of twist due to material coupling. Out of the two elements developed, one is based on the conventional formulation and the other on the coupled-field formulation, both capturing material induced coupling. The beam developed using coupled field formulation shows a novel way of obtaining a fully coupled interpolation function for field variables using the complete set of equilibrium equations for the composite beams. The element has shown a superior coarse mesh performance. These elements can practically capture plate behaviour in beam elements for a wide range of plate thickness. The locking problems in conventional 4-node quadrilateral elements, such as shear locking and geometric locking are studied. Various techniques available in literature to remedy these problems are also studied. A suite of QUAD4 with conventional techniques such as. Reduced Integration, Field Consistency, Mixed Interpolation of Tensorial strain Components, Assumed Natural Strain, Discrete Shear Gap, Incompatible modes Q6 and QM6 is developed. An effort is made to combine these techniques to develop new element that yields improved performance. The element is shown to exhibit improved performance for certain cases. Several four-node rectangular elements are developed based on the coupled-field techniques. First two new-coupled elements are formulated that employ Sabir's [101] plane bending formulation with drilling degree of freedom, and the plate bending rotations are generated using equilibrium equations. However, since Sabir's plane bending interpolation polynomials yielded inaccurate performance for composites, it led to development of elements with fully coupled field formulations. Finally, two new 4-node rectangular elements are developed using coupled-field formulations with six and seven dof freedom per node respectively. Here the interpolation polynomials are derived using the complete equilibrium equations. The elements are extensively tested for static deflection, dynamics and buckling of isotropic and laminated plates/beams. The elements show superior coarse mesh convergence. Several problems pertaining to vibration and buckling of composite plates/beams are solved using the elements developed in this work.

Orientador: Renato Pavanello / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia mecanica / Made available in DSpace on 2018-08-04T08:49:46Z (GMT). No. of bitstreams: 1 PoelFilho_CornelisJoannesvander_D.pdf: 8296875 bytes, checksum: 048da8ba9cfe029f98229ac0b593f989 (MD5) Previous issue date: 2005 / Resumo: Microsistemas eletromecânicos geralmente têm seu princípio de funcionamento baseado na interação entre dois ou mais campos físicos. Para seu projeto são necessárias ferramentas de simulação multi-domínios. Este trabalho visa estudar o fenômeno de acoplamento eletromecânico em microsistemas e construir uma ferramenta de simulação numérica para este tipo de problema. São apresentados métodos de análise estática, modal e transiente baseados em modelos de elementos finitos e de ordem reduzida. Na análise estática cada domínio é resolvido separadamente. Foi mostrado um método de transferência das forças eletrostáticas para o domínio mecânico e proposto e testado um esquema de atualização da malha elétrica. Para a análise dinâmica transiente foi implementado um método de Newmark adaptado de forma a considerar os efeitos do acoplamento eletromecânico. Outro método de análise dinâmica apresentado é baseado numa estratégia de perturbação do sistema em equilíbrio em conjunto com a resolução de um problema de autovalor / autovetor. O método de perturbação fornece diretamente as freqüências naturais de vibração do sistema acoplado. A técnica de redução de ordem apresentada é baseada numa projeção de Galerkin da equação diferencial governante utilizando como funções de base os modos empíricos do sistema dinâmico. Um programa computacional para modelagem numérica multi-domínios com solução particionada para o acoplamento eletromecânico foi proposto e implementado. O código computacional, denominado MefLab, onde os métodos numéricos foram programados, usa o paradigma de orientação a objetos e a linguagem C++. Resultados com as diversas metodologias são mostrados e analisados / Abstract: Microelectromechanical systems have their working principIes based on the interaction between two or more physical fields. To design them, multi-physics simulation tools are needed. This work aims to study the coupled field effects in microsystems and build a computer code for numerical simulation of this problem. Static, dynamic modal and transient methods are introduced. They are based on finite elements and reduced order models. The static analysis is done by a staggered treatment. A method for transfering electrostatic pressures to the mechanical domain was shown and a mesh updating scheme was proposed and tested. For the transient analysis, in order to consider the electromechanical coupling effects, an adaptation was inserted in the classical Newmark direct integration method. A dynamical modal method based in a perturbation strategy was presented. It involves the staggered static algorithm and the solution of an eigenvalue/eigenvector problem. This method is able to give the natural coupled frequencies of the system with low computational costs. A reduced order modeI was constructed by using a Galekin projection of the governing differential equations in an empirical basis. This basis was obtained through results of transient finite element analysis. A multi-domain project with staggered procedures for the electromechanical coupling was proposed and implemented. It refers to the software MefLab++, a computer code written in C++ where numerical strategies are programmed according to the oriented object paradigm. Numerical results for the static, dynamic modal and transient methodologies are shown / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica

Die Anwenung von Operator-Splitting-Methoden auf gewöhnliche Differentialgleichungen ist gut etabliert. Für Differential-algebraische Gleichungen und partielle Differential-algebraische Gleichungen unterliegt sie jedoch vielen Einschränkungen aufgrund des Vorhandenseins von Nebenbedingungen. Die räumliche Diskretisierung reduziert PDAEs und lenkt unseren Fokus auf das Konzept der DAEs. Um eine reibungslose Übertragung des Operator-Splittings von ODEs auf DAEs durchzuführen, ist es wichtig, eine geeignete entkoppelte Struktur für das gewünschte Differential-algebraische System zu haben. In dieser Arbeit betrachten wir ein Modell, das partielle Differentialgleichungen für elektromagnetische Bauelemente - modelliert durch die Maxwell-Gleichungen - mit Differential-algebraischen Gleichungen koppelt, die die elementaren Schaltungselemente beschreiben. Nach der räumlichen Diskretisierung der klassischen Formulierung der Maxwell-Gleichungen mit Hilfe der finiten Integrationstechnik formulieren wir das resultierende gekoppelte System als Differential-algebraische Gleichung. Um eine geeignete Entkopplung zu bekommen, verwenden wir den zweigorientierten Loop-Cutset-Ansatz für die Schaltungsmodellierung. Daraus folgt, dass wir in der Lage sind, eine geeignete Operatorzerlegung so zu konstruieren, dass wir eine natürliche topologisch entkoppelte Port-Hamiltonsche DAE-Struktur erhalten. Wir schlagen einen Operator-Splitting-Ansatz für die Schaltungs-DAEs und gekoppelten Feld-Schaltungs-DAEs in entkoppelter Form vor und analysieren seine numerischen Eigenschaften. Darüber hinaus nutzen wir das Hamiltonsche Verhalten der inhärenten gewöhnlichen Differentialgleichung durch die Verwendung expliziter und energieerhaltender Zeitintegrations-methoden. Schließlich führen wir numerische Tests, um das mathematische Modell zu illustrieren und die Konvergenzergebnisse für das vorgeschlagene DAE-Operator-Splitting zu demonstrieren. / Le equazioni algebriche differenziali e algebriche alle derivate parziali hanno avuto un enorme successo come modelli di sistemi dinamici vincolati. Nella modellazione matem- atica, spesso si desidera catturare diversi aspetti di una situazione come le leggi di conservazione della fisica, il trasporto convettivo o la diffusione. Queste aspetti si riflettono nel sistema di equazioni del modello come operatori diversi. La tecnica dell’Operator Splitting si è rivelata una strategia di successo per affrontare problemi così complicati. L’applicazione dei metodi di Operator Splitting alle equazioni differenziali ordinarie (ODE) è ormai una tecnologia ben consolidata. Tuttavia, per equazioni algebriche differenziali (DAE) e algebriche differenziali parziali (PDAE), l’approccio è soggetto a molte restrizioni dovute alla presenza di vincoli e alla proprietà di indice. La discretizzazione spaziale riduce le PDAE e indirizza la nostra attenzione al concetto di DAE. Le DAE emergono in problemi dinamici vincolati come circuiti elettrici o reti di trasporto di energia. Al fine di generalizzare agevolmente la tecnica dell’Operator Splitting dalle ODE alle DAE, è importante avere una struttura disaccoppiata adeguata per il sistema algebrico differenziale desiderato. In questa tesi, consideriamo un modello che accoppia equazioni differenziali alle derivate parziali per dispositivi elettromagnetici -modellati dalle equazioni di Maxwell- con equazioni algebriche differenziali che descrivono gli elementi base del circuito. Dopo aver discretizzato spazialmente la formulazione classica delle equazioni di Maxwell usando la tecnica di integrazione finita, formuliamo il sistema accoppiato risultante come una equazione algebrica differenziale. Interpretando il dispositivo elettromagnetico come un elemento capacitivo, l’indice dell’intero sistema di circuito e campo accoppiato può essere specificato utilizzando le proprietà topologiche del circuito e non supera il valore di due. Per eseguire un disaccoppiamento appropriato, utilizziamo l’approccio loop-cutset per la modellazione dei circuiti. In tal modo siamo in grado di costruire una opportuna decomposizione dell’operatore tale da ottenere una naturale struttura disaccoppiata port-Hamiltonian DAE. Proponiamo un approccio di suddivisione dell’operatore per i DAE a circuito disaccoppiato e a circuito di campo accoppiato utilizzando gli algoritmi di divisione Lie-Trotter e Strang e per analizzare le proprietà numeriche di questi sistemi. Inoltre, sfruttiamo il comportamento hamiltoniano del sistema di equazioni differenziali ordinarie mediante l’utilizzo di metodi di integrazione temporale con esatta conservazione dell’energia. Poggiando sull’analisi di convergenza del metodo di suddivisione dell’operatore ODE, deriviamo i risultati di convergenza per l’approccio proposto che dipendono dall’indice delsistema e quindi dalla sua struttura topologica. Infine, eseguiamo prove numeriche di sistemi circuitali, nonchè sistemi accoppiati a circuito di campo, per testare il modello matematico e dimostrare i risultati di convergenza per la proposta Operator Splitting DAE. / The application of operator splitting methods to ordinary differential equations (ODEs) is well established. However, for differential-algebraic equations (DAEs) and partial differential-algebraic equations (PDAEs), it is subjected to many restrictions due to the presence of constraints. In constrained dynamical problems as electrical circuits or energy transport networks, DAEs arise. In order to perform a smooth transfer of the operator splitting from ODEs to DAEs, it is important to have a suitable decoupled structure for the desired differential-algebraic system. In this thesis, we consider a model which couples partial differential equations for electro- magnetic devices -modeled by Maxwell’s equations- with differential-algebraic equations describing the basic circuit elements. After spatially discretizing the classical formulation of Maxwell’s equations using the finite integration technique, we formulate the resulting coupled system as a differential-algebraic equation. To perform an appropriate decoupling, we use the branch oriented loop-cutset approach for circuit modeling. It follows that we are able to construct a suitable operator decomposition such that we obtain a natural topologically decoupled port-Hamiltonian DAE structure. We propose an operator splitting approach for the decoupled circuit and coupled field- circuit DAEs using the Lie-Trotter and Strang splitting algorithms and analyze its numerical properties. Furthermore, we exploit the Hamiltonian behavior of the system’s inherent ordinary differential equation by the utilization of explicit and energy-preserving time integration methods. Based on the convergence analysis of the ODE operator splitting method, we derive convergence results for the proposed approach that depends on the index of the system and thus on its topological structure. Finally, we perform numerical tests, to underline the mathematical model and to demonstrate the convergence results for the proposed DAE operator splitting.