My practice explores phenomenal poetic truths that exist in fissures between the sensual and physical qualities of material constructs. Magnifying this confounding interspace, my work activates specific instruments within mutable, relational systems of installation, movement, and documentation. The tools I fabricate function within variable orientations and are implemented as both physical barriers and thresholds into alternate, virtual domains. Intersecting fragments of sound and moving image build a nexus of superimposed spatialities, while material constructions are enveloped in ephemeral intensities. Within this compounded environment, both mind and body are charged as active sites through which durational, contemplative experiences can pass. Reverberation, the ghostly refrain of a sound calling back to our ears from a distant plane, can intensify our emotional experience of place. My project Planar Refrains utilizes four electro-mechanical reverb plates, analog audio filters designed to simulate expansive acoustic arenas. Historically these devices have provided emotive voicings to popular studio recordings, dislocating the performer from the commercial studio and into a simulated reverberant territory of mythic proportions. The material resonance of steel is used to filter a recorded signal, shaping the sound of a human performance into something more transformative, a sound embodying otherworldly dynamics. In subverting the designed utility of reverb plates, I am exploring their value as active surfaces extending across different spatial realities. The background of ephemeral sonic residue is collapsed into the foreground, a filter becomes sculpture, and this sculpture becomes an instrument in an evolving soundscape.

No description available.

Structural health monitoring (SHM) is a quickly advancing field of study in civil engineering and recent advances in the field are in stark contrast to where the field started. For example modern technology of wireless sensing systems allowed for easier monitoring of structures, but the challenge of limiting the number of instrumented locations has not been overcome with traditional methods. The potential of alternative methods has only been realized in recent years with the increase of model based approaches. In particular, the use of limited measurements to estimate structural response at all locations is appealing. To accomplish this goal, this work approaches SHM by using a numerical model combined with a linear recursive state estimation algorithm, known as the Kalman Filter, to update the model-based prediction with a limited number of real time measurements taken on the structure. A thorough overview of the contents is given here. The first section introduces the topic of SHM and the goal of SHM. Then the challenges and limitation that face SHM are discussed along with the recent advances that can be used to overcome them. In Section 2, the proposed framework, a Kalman filter approach, is established. First, a finite element model is formulated for plate structures using the Mindlin-Reissner plate theory and then this finite element code is verified by a comparison with a commercial FEA software. Then the state space model of the system is defined for use with the Augmented Kalman Filter (AKF); the AKF approach overcomes the intrinsic challenge of unknown excitations for civil structures. The AKF is then formulated and discussed. For Section 3, using the AKF in numerical simulations are conducted for 5 different cases. The first three cases study the advantages of multi-metric measurements, i.e. strain and acceleration measurements combined, versus single metric measurement, i.e. strain measurement only or acceleration measurement only. Following that, the next two cases explore the question of whether multi-metric measurements will always provide the best results. Based on the conclusions from the previous section, Section 4 investigates the application of a genetic algorithm, a search algorithm based of Darwinian principles, to find the optimal sensor placement to use as the input to the AKF. Here the developed search algorithm is used in two cases, the first is to find the optimal placement for the strain measurement only case. Next, the improvements in accuracy that are gained by placing taking more measurements is investigated to determine if the gain in accuracy per added measurement decreases for large numbers of measurements. Section 5 contains the final conclusions about the use of the AKF for SHM of plate structures then the potential opportunities of future work regarding plate structures are discussed.

Neste trabalho utiliza-se a formulação direta do Método dos Elementos de Contorno aplicada ao problema de flexão de placas com vinculação interna. Através da utilização da teoria baseada nas hipóteses de Reissner é possível atender em cada ponto, a três condições físicas de contorno. Admite-se a aplicação de cargas transversais distribuídas e concentradas, além de momentos distribuídos em linha. Os elementos de contorno apresentam geometria linear com aproximação quadrática para as variáveis de contorno. As equações integrais dos deslocamentos são escritas para pontos de colocação dispostos fora do domínio, evitando-se assim problemas de singularidades. O sistema de equações algébricas originado da análise de placas via MEC é modificado para incorporar o enrijecimento produzido pela vinculação interna. Primeiramente é analisado o enrijecimento produzido por apoios internos pontuais ou distribuídos em áreas pequenas e, em seguida, é estudada a associação da placa com uma estrutura qualquer, formada por barras. O enrijecimento produzido por esta estrutura é obtido utilizando-se o Método dos Elementos Finitos. Finalmente, são apresentados alguns exemplos simples que mostram a boa precisão da técnica utilizada. / The direct formulation of the Boundary Element Method is applied to the analysis of internally restrained plates in bending. By employing Reissner\'s theory, the three boundary conditions are satisfied at each point. Loading conditions include concentrated or uniformly distributed loads as well as linearly distributed moments. The boundary elements are geometrically linear with quadratic approximation for the boundary variables. The displacement integral equations are written for collocation points outside the domain thus avoiding any singularity problem. The resulting system of algebraic equations is modified to include the stiffening effects. Plates with internal point restraints and restrained over small areas are analyzed as well as plates connected to others structures made up of bars. In this last case, the stiffening effect is calculated through the Finite Element Method. The results obtained in simple problems indicate the accuracy of the procedure.

Digitized by Kansas Correctional Industries / Department: Civil Engineering.

O alto índice de emissões gasosas tem impulsionado cada vez mais pesquisas com células a combustível com membrana trocadora de prótons (PEMFC), dispositivo eletroquímico capaz de produzir energia gerando apenas vapor de água como resíduo. Atualmente, entre os desafios que impossibilitam a popularização deste tipo de dispositivo estão o aperfeiçoamento da gestão da água e a diminuição dos índices de crossover de reagentes do ânodo para o cátodo. Este trabalho teve como meta utilizar a biomimética como ferramenta para criar novos designs de canais em placas de distribuição de reagentes, para melhor gestão da água e minimização do crossover do combustível em PEMFCs. Foram realizados experimentos em laboratório utilizando-se protótipos de PEMFC e experimentos computacionais de modelagem fluidodinâmica utilizando software SolidWorks. Pelos resultados constatou-se que a variação sincronizada da profundidade dos canais de fluxo em ambos os lados da placa bipolar possibilita minimizar a queda de pressão dos reagentes, sem a necessidade de aumento da espessura desta mantendo-se a densidade de potência do stack. Verificou-se que placas de distribuição de reagentes parcialmente interdigitadas são uma ferramenta eficaz no controle da umidade da célula durante a operação, evitando o uso de dispositivos periféricos para umidificação, e maior transferência de energia térmica entre placas e reagente. Numa célula a combustível alimentada com etanol sem periféricos para melhor balanço do decréscimo do crossover de etanol e remoção eficiente da água produzida no cátodo, a melhor combinação de placas de distribuição de reagentes foi obtida quando usado no ânodo uma placa com canais de distribuição de reagentes contínuos, e no cátodo uma placa com canais parcialmente interdigitados. Para melhor gestão da água, transferência de energia térmica e crossover em função do design dos canais de distribuição de reagentes nas placas bipolares, neste trabalho, foram propostas placas com canais de distribuição bioinspirados. O uso da biomimética mostrou ser uma abordagem diferenciada em busca da melhora de desempenho de PEMFCs. A biomimética possibilitou a criação de múltiplos subsistemas com características de autossimilaridade dentro de uma mesma estrutura física, e permitiu ampliar a proporção de área ativa do MEA, mantendo-se as mesmas dimensões das placas bipolares, através do uso de canais em fractais. As placas bipolares bioinspiradas propostas, tendo canais com configurações em fractais padronizadas, mostraram através de ensaios simulados serem altamente eficientes na gestão da água e do crossover. / The high gas emissions content has driving more attention on proton exchange membrane fuel cells (PEMFC), an electrochemical device that generates energy producing only water vapor as waste. Among the challenges that reduces the use of this type of device are a better water management and the fuel crossover reduction. The aim of this work is the use of biomimetics as a tool to create new flow field plate designs for improving water management and minimizing fuel crossover in a PEMFC. A serie of lab experiments were carried out in a single PEMFC prototype and others computational fluid dynamic using SolidWorks. The results have shown that a synchronized variation in the depth of the flow field channels on both sides of a bipolar plate allows minimize the reagent pressure loss without increasing the plate thickness or decreasing the stack power density. The baffle flow field plates have shown be an effective tool for controlling the cell humidification operated without periphericals or humidifiers devices and for a better transferring thermal energy between the plate and reagent. For a better balance between ethanol crossover and efficient removal of water produced in a direct ethanol proton exchange membrane fuel cell without peripherals, the best flow field plate combination obtained was a continuous channels plate at the anode side, and partially discontinuous channels plate at the cathode. For a better water management, thermal energy transfer management and crossover management in this work, flow field plates with designs bioinspired were investigated. The biomimetic was a strong tool to optimizing the performance of PEMFC. The biomimetic has enabled the creation of numerous similar self-subsystems optimizing the MEA active area by using fractals channels without changing the bipolar plate dimensions. The bipolar plate’s bioinspired having configured channels in fractal standard showed through SolidWorks simulated experiments be highly efficient in controlling water or ethanol crossover in a PEMFC.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / Microfiche copy available in Archives and Engineering. / Includes bibliographical references. / M.S.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / Includes bibliographical references. / M.S.

Os materiais compostos de fibras longas vêm se destacando entre o conjunto de novos materiais em desenvolvimento, com larga aplicação na indústria e também na construção civil. Elabora. se aqui um texto introdutório no campo das placas laminadas constituídas de lâminas em compostos de fibras longas. A partir das propriedades dos materiais constituintes, fibra e matriz, são apresentadas as teorias para a determinação das propriedades equivalentes das lâminas. A teoria da anisotropia elástica é formulada e a teoria dos laminados em flexão é desenvolvida. Conclusões com respeito ao acoplamento de esforços em tais estruturas são mostradas. Os modos básicos de ruptura da fibra, matriz e da interface entre ambas são apresentados, bem como os modos básicos de delaminação. Alguns critérios de ruptura são mostrados, assim como um critério de escoamento. Ao fim alguns exemplos ilustram a análise pelo método dos elementos finitos de tais estruturas feita por programa disponível em literatura, com a implementação de subrotina para análise da temperatura. / Long fiber composite materials have been standing out among the group of new materials in development with wide industrial application and also in civil construccion. Here is elaborated an introductory text in laminated plates field constituted of long fiber composite laminae. Starting from constituent materials properties, fiber and matrix, the theories for determination of laminae equivalent properties are presented. Elastic anisotropy theory is formulated and the bending laminated theory is developed. Conclusions about the coupling efforts in such structures are showed. Fiber, matrix and the interface between both failure basic modes are presented, as well as delamination basic modes. Some failure criteria are showed, as well as a yielding criteria. At the end some examples illustrate the finite element method analysis of such structures made by available literature programme with temperature analysis subroutine implementation.

Une grande partie de la structure des avions modernes est fabriquée à partir des dernières générations de matériaux composites. Le principal défi des constructeurs d’avions réside dans la taille importante des pièces en composites. D’où la nécessité de développer de nouvelles technologies de fabrication telle que la dépose automatique de préimprégné. La qualité des pièces fabriquées dépend de nombreux facteurs dont notamment la maîtrise de la rhéologie de la résine du préimprégné. Cette dernière évolue fortement avec les conditions environnementales et les conditions de fabrication. Elle détermine pour partie, les instabilités de la matière particulièrement le long des trajectoires curvilignes. Ces instabilités, qui se présentent sous forme de cloques, engendrent après cuisson des pièces avec des défauts de repliement des couches dans les stratifiés. L’objectif principal de cette thèse de doctorat est l’étude du comportement mécanique d’un ruban de préimprégné prenant en compte la rhéologie de la matière ainsi que sa pégosité dans le but de mieux comprendre les conditions d’apparition des cloques en trajectoire curviligne. Une partie de mes travaux est consacrée à la caractérisation des propriétés physico-chimiques et mécaniques de la matière. Une seconde partie, complémentaire à la première, est dédiée au développement d’un modèle de comportement mécanique d’une plaque sur fondation élastique représentant le ruban de préimprégné et soumise à une rotation imposée. La méthode de Ritz a été utilisée pour l'obtention de solutions explicites des charges critiques de flambement. Il a été montré que les plus faibles rayons de courbure sans formation de cloques en trajectoire curviligne dans le plan sont obtenus avec un faible écrasement du rouleau et un niveau de collant élevé. / The evolution of composite materials in aerospace has been spectacular over the last thirty years. The main advantage provided by composites is weight gain compared to other materials. However, new aluminum lithium alloys may slow this trend because of their specific properties and exceptional manufacturing costs lower than those of composites. Much parts of the structure of the A380 are made from the latest generation of composite materials with organic matrix. The Airbus A380 is the first plane of the manufacturer composed by a center wing box made by composite reinforced with carbon fibers and organic matrix. And like the devices that preceded it, the center wing box, rudder, horizontal stabilizer and the elevators were designed with composites reinforced with carbon fibers and organic matrix. But the main challenge with the new aircraft is the size of parts ; the size of the horizontal stabilizer of the A380 for example, is similar to the wing of the A310. Hence the need to develop the intensive use of automatic prepreg lay up technology. The use of semi-finished prepregs for the manufacture of parts allows standardizing production. Indeed, these products exhibit with the desired rate of reinforcement on the final parts, all the delicate operations of pumping excess resin during the implementation of parts, as the case in the RTM process (Resin Transfer Molding) are eliminated. The quality of parts produced using automatic lay up depends on many factors including the accuracy of trajectory lay up, the control of rheology of the resin contained in the prepreg and behavior at the interface of the material and tooling. The rheology of the resin is changing considerably with environmental conditions (temperature, humidity) and processing conditions (speed of removal, compaction strength). It determines in part and in combination with the tackiness of the prepreg, the instabilities of the material particularly along curved trajectories. In curvilinear lay up, the rotation of the tow placement head imposes to this portion of slit tape, a curvature generating a circular bending phenomenon.The outer portion of the tape is then stretched while the inside is compressed. When the radius of curvature of the tow placement head is low, the result is a phenomenon of local buckling of the slit tape. The corresponding layer waviness (See figure 1) is visible after the passage of the roller so instantly or delayed, depending on the conditions of lay up (speed lay up,compaction strength, temperature, humidity) and the tackiness of the material. Thus, the formation of the layer waviness is a local phenomenon that appears in the material between the tow placement head and tools. It is this area of the material defined by the form of plate, and the extent of which depends on the compaction strength and flexibility of the roller which will be the model proposed in this communication. It is supposed that this plate is based on elastic foundation in order to reflect the tack of the material. The formation mechanism of ply waviness is very few studied and remains unclear since these defects appear at different steps in the manufacturing process. Some studies recommend, without justification, to not exceed some radius of curvature to avoid buckling [1]. Interactions between tooling and material in relation with lay up conditions were studied [2]. In this paper we study the mechanical behavior of a slit tape taking into account the rheology of the material so that his tack in order to better understand the conditions of appearance of layer waviness during circular trajectories. At first, we will present some results from the identification of physico-chemical and mechanical properties of prepreg carbon / epoxy and then we will explain the evolutions observed. A second part, complements the first,will be dedicated to the development of a model of mechanical behavior of a plate based onelastic foundation, representing the slit tape which is subjected to a rotation imposed. The mechanical model of the slit tape will be based on the theory of plate under the hypotheses of Kirchhoff-Love and Von-Karman. Determining the critical buckling load is carried by the Ritz method. The simulation results using different boundary conditions will be analyzed and compared to real cases.