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O presente trabalho consiste no uso do Método dos Elementos Finitos (MEF) para a análise de interação fluido-estruturas de barras com foco em problemas transientes envolvendo explosões ou outras ações com propagação de ondas de choque. Para isso é necessário o estudo de três diferentes aspectos: a dinâmica das estruturas computacional, a dinâmica dos fluidos computacional e o problema do acoplamento. No caso da dinâmica das estruturas computacional deve-se identificar em função da cinemática de deformações, quais são os requisitos para que um elemento seja adequado para analisar tais problemas, tendo em vista que a formulação deve admitir grandes deslocamentos. Para evitar problemas relacionados com aproximações de rotações finitas, opta-se por empregar uma formulação descrita em termos de posições e que leva em consideração os efeitos de empenamento da seção transversal. No caso da dinâmica dos fluidos computacional, busca-se uma formulação para escoamentos compressíveis que seja estável e ao mesmo tempo sensível ao movimento da estrutura, sendo empregado um algoritmo de integração temporal explícito baseado em características com as equações governantes descritas na forma Lagrangeana-Euleriana Arbitrária (ALE). No que se refere ao acoplamento, busca-se modularidade e versatilidade, empregando-se um modelo particionado fraco (explícito) de acoplamento e técnicas de transferência das condições de contorno (Dirichlet-Neummann), sendo estudados os efeitos de utilizar transferência bidirecional ou unidirecional dessas condições de contorno. / This work consists in the use of the Finite Element Method (FEM) for numerical analysis of fluid-bar structures, focusing on transient problems involving explosions or other actions with shock waves propagation. For this purpose, one needs to study three different aspects: the computational structural dynamics, the computational fluid dynamics and the coupling problem. Regarding computational structural dynamics, one need firstly to identify the requirements for an element to be adequate to analyze such problems, taking into account the fact that such element should admit large displacements. In order to avoid problems related to finite rotation approximations and to give a realist representation of a 3D bar structure, we chose a formulation defined in terms of positions and that considers the cross-section warping effects. Regarding computational fluid dynamics, we seek for a stable formulation for compressible flows, and at same time, sensitive to the movement of the structure, leading to an explicit time integration algorithm based on characteristics with governing equations described in the Arbitrary Lagrangian-Eulerian (ALE) form. Regarding to coupling, we chose to use a weak (explicit) partitioning coupling model in order to ensure modularity and versatility. The developed coupling scheme is bases on boundary conditions transfer techniques (Dirichlet-Neummann), and we study the effects of using bidirectional or unidirectional boundary conditions transfers.

Au cours des dernières décennies, l’astronomie infrarouge a changé notre point de vue au sujet de l’évolution des galaxies, en particulier à de grandes distances. Nous avons accès à une grande variété d’informations physiques grâce au domaine spectral infrarouge. Toutefois, les limites de diffraction des instruments infrarouges et l’existence d’un grand nombre de sources font de l’identification individuelle des galaxies une tâché difficile. La première partie de cette thèse est consacrée à Résoudre le fond extragalactique infrarouge avec l’observatoire spatial Herschel, à, l’aide de simulations réalistes, correspondant aux images les plus profondes jusqu’ici obtenues en infrarouge lointain. Nous avons étudié l’origine du bruit de confusion dans les images GOODS-Herschel et résolu une partie de fond cosmique infrarouge en galaxies individuelles. De nouvelles techniques ont été développées pour prédire les flux en infrarouge lointain à partir de la connaissance préalable des positions, décalages spectraux et densités de flux des sources dans l’infrarouge moyen. Les images simulées ont été construites en utilisant les flux prédits afin d’évaluer le rôle du bruit local de confusion et d’identifier des sources individuelles. La deuxième partie de la thèse concerne l’étude de la Destruction de grains de poussières par des jets vus en radio. Nous avons étudié les effets des noyaux actifs de galaxies dans le milieu interstellaire, en particulier le mécanisme qui donne lieu à la région des raies étroites dans les galaxies de type Seyfert. Des spectres en infrarouge proche à fente longue a ont été enregistrés sur un ensemble de galaxies Seyfert de type 2 afin de mesurer les raies d’émission de ([Fe II], [P II] et Paβ) qui révèlent la destruction de poussières par les ondes de choc produites par les jets radio. Nous avons constaté que le mécanisme dominant l’ionisation près du noyau des galaxies Seyfert est le champ de rayonnement produit par l’activité du trou noir. Dans la partie extérieure de la région des raies étroites, des ondes de choc induites par des jets de radio contribuent également au budget énergétique du milieu interstellaire et à la destruction des grains de poussière. Cette thèse s’est déroulée en co-encadrement au Service d’Astrophysique du CEA-Saclay et au Département d’Astronomie de l’Université de Concepción, au Chili. / During the last decades, infrared astronomy has changed our view about the evolution of galaxies, especially at large distances. We have access to large variety of physical information in the infrared bands. However, diffraction limits of the infrared instruments and the existence of a large number of sources makes individualization of galaxies a difficult task. The first part of this thesis is entitled Resolving the Cosmic Infrared Background with the Herschel Space Observatory where, by the use of far-infrared realistic simulations of the deepest infrared images of the Universe, we have studied the origin of the confusion noise in the GOODS-Herschel images and resolved a substantive part of the Cosmic Infrared Background into individual galaxies. New techniques were developed to predict the fluxes in the far-infrared from prior knowledge in the mid-infrared. Mock images were built using those predicted fluxes to evaluate the role of local confusion noise and identify individual sources. The second part of the thesis concerns the study of the Destruction of dust grains by radio jets. We study the effects of active galactic nuclei in the insterstellar medium, in particular in the mechanism that gives rise to the narrow-line region in Seyfert galaxies. Long-slit near-Infrared spectra of a set of type-2 Seyfert galaxies were taken to measure diagnostic emission lines ([Fe II], [P II] and Paβ) that reveal the destruction of dust grains due to the shock waves produced by the radio jets. We found that the dominant mechanism of ionization close to the nuclei of the Seyfert galaxies is the radiation field produced by the back hole activity. In the outer part of the narrow-line region, shock waves induced by the radio jets also contribute to the energy budget of the interstellar medium and sputter the dust grains. This was a co-advising thesis performed in the Service d’Astrophysique CEA-Saclay and the Astronomy Department of the University of Concepción, Chile. / Durante las últimas décadas, la astronomía infrarroja ha cambiado nuestra visión sobre la evolución de galaxias, en especial revelando que a grandes distancias (z >1) las galaxias individuales son típicamente Galaxias Infrarrojas Ultraluminosas (cuyas siglas en inglés son ULIRGs por Ultraluminous Infrared Galaxies, 1012 < Lbol < 1013 L⊙). Actualmente tenemos acceso a una gran variedad de información física basada en la emisión en bandas espectrales infrarrojas (IR), radiación que en el caso de las galaxias es producida en su mayoría por granos de polvo. Sin embargo, el límite de difracción de los instrumentos infrarrojos junto con el gran número de fuentes de emisión hace de la individualización de galaxias una tarea difícil. La primera parte de esta tesis se titula Resolviendo el Fondo Cósmico Infrarrojo con el Observatorio Espacial Herschel donde, con el uso de simulaciones realistas de las imágenes más profundas del Universo, hemos estudiado el origen del ruido de confusión en las imágenes GOODS-Herschel y resuelto en galaxias individuales una parte sustantiva del Fondo Cósmico Infrarrojo. Nuevas técnicas fueron desarrolladas para predecir los flujos en el infrarrojo lejano a partir del conocimiento a priori en el infrarrojo medio. Las imágenes simuladas fueron construidas usando esos flujos predichos y con ellos evaluar el rol del ruido de confusión local así como identificar fuentes individuales. La segunda parte de la tesis trata del estudio sobre la Destrucción de granos de polvo por chorros en ondas de radio. Este proyecto que se concentró en la observación de galaxias Seyfert y ULIRGS y apunta a entender mejor el ciclo de vida del polvo al estudiar la destrucción de granos en galaxias con nucleos activos y los efectos de la actividad de estas últimas en el medio interestelar, en particular en el mecanismo que da origen a la región de líneas de emisión angostas en las galaxias Seyfert. Se obtuvo espectros infrarrojos de rendija larga de galaxias Seyfert del tipo 2 para medir líneas de emisión ([Fe II], [P II] y Paβ) las cuales revelan la destrucción de granos de polvo debido a las perturbaciones de las ondas de choque producidas por chorros detectados en ondas de radio. Hemos encontrado que el mecanismo dominante de la ionización cerca de los núcleos de las galaxias Seyfers es el campo de radiación producido por la actividad del agujero negro central. En la parte externa de la región de líneas de angostas, las ondas de choque inducidas por los chorros en radio también contribuyen al balance energético del medio interestelar y desintegran los granos de polvo. Esta fue una tesis de co-tutela llevada a cabo en el Departamento de Astronomía de la Universidad de Concepción y en el Service d’Astrophysique del Commissariat á l’Énergie Atomique (CEA), Francia

A recently emerging engineering design approach entails studying the brilliant design solutions found in nature with an aim to develop design strategies that mimic the remarkable efficiency found in biological systems. This novel engineering approach is referred to as bio-inspired design. In this context, the present study quantifies the structure-property relations in bighorn sheep (Ovis canadensis) horn keratin, qualitatively characterizes the effects of a tapered spiral geometry (the same form as in a ram’s horn) on pressure wave and impulse mitigation, describes the stress attenuation capabilities and features of a ram’s head, and compares the structures and mechanical properties of some energy absorbent natural materials. The results and ideas presented herein can be used in the development of lightweight, energy absorbent, bio-inspired material designs. Among the most notable conclusions garnered from this research include: Horn keratin behaves in an anisotropic manner similar to a long fiber composite. Moisture content dominates the material behavior of horn keratin more than anisotropy, age, and stress-state. This makes moisture content the most influential parameter on the mechanical behavior of horn keratin. Tapered geometries mitigate the impulse generated by a stress wave due to the convergent boundary and a continually decreasing cross sectional area such that greater uniaxial stresses and subsequent axial deformation arises. Furthermore, the tapered geometry introduces small shear stresses that further decrease the impulse. Spiral geometries attenuate the impulse generated by a stress wave by the introduction of shear stresses along the length of the spiral. These shear stresses introduce transverse displacements that function to lessen the impulse. When both a taper and spiral geometry are used in a design, their synergistic effects multiplicatively reduce the impulse Tough natural materials have a high porosity, which makes them light-weight, while increasing their compressive energy absorption ability. Biomaterials whose functions include protection and energy absorption feature a multiscale, hierarchical, composite structure. The constituent materials are arranged in such ways to achieve a synergistic effect, where the properties of the composite exceed the properties of its constituents. Biological materials are therefore not confined to the law of mixtures.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis concentrates on the study of hybrid gas journal bearings (bearings with externally pressurized mass addition). It differs from most work in that it goes back to “basics” to explore the hydrodynamic phenomena in the bearing gap. The thesis compares geometrically identical bearings with 2 configurations of external pressurization, porous liners where mass-addition compensation is varied by varying the liner’s permeability, and bushings with 2 rows of 6 feedholes where the mass-addition compensation is varied by the feedhole diameter. Experimentally, prototype bearings with mass-addition compensation that spans 2 orders of magnitude with differing clearances are built and their aerostatic properties and mass addition characteristics are thoroughly tested. The fundamental equations for compressible, laminar, Poiseuille flow are used to suggest how the mass flow “compensation” should be mathematically modeled. This is back-checked against the experimental mass flow measurements and is used to determine a mass-addition compensation parameter (called Kmeas) for each prototype bushing. In so doing, the methodology of modeling and measuring the mass addition in a hybrid gas bearing is re-examined and an innovative, practical, and simple method is found that makes it possible to make an “apples-to-apples” comparison between different configurations of external pressurization. This mass addition model is used in conjunction with the Reynolds equation to perform theory-based numerical analysis of virtual hybrid gas journal bearings (CFD experiments). The first CFD experiments performed use virtual bearings modeled to be identical to the experimental prototypes and replicate the experimental work. The results are compared and the CFD model is validated. The ontological significance of appropriate dimensionless similitude parameters is re-examined and a, previously lacking, complete set of similitude factors is found for hybrid bearings. A new practical method is developed to study in unprecedented detail the aerostatic component of the hybrid bearings. It is used to definitively compare the feedhole bearings to the porous liner bearings. The hydrostatic bearing efficiency (HBE) is defined and it is determined that the maximum achievable hydrostatic bearing efficiency (MAHBE) is determined solely by the bearing’s mass addition configuration. The MAHBE of the porous liner bearings is determined to be over 5 times that of the feedhole bearings. The method also presents a means to tune the Kmeas to the clearance to achieve the MAHBE as well as giving a complete mapping of the hitherto misunderstood complex shapes of aerostatic load versus radial deflection curves. This method also rediscovers the obscure phenomenon of static instability which is called in this thesis the “near surface effect” and appears to be the first work to present a practical method to predict the range of static instability and quantify its resultant stiffness fall-off. It determines that porous liner type bearings are not subject to the phenomenon which appears for feedhole type bearings when the clearance exceeds a critical value relative to its mass-addition compensation. The standing pressure waves of hydrostatic and hybrid bearings with the 2 configurations of external pressurization as well as a geometrically identical hydrodynamic bearing are studied in detail under the methodology of the “CFD microscope”. This method is used to characterize and identify the development, growth, and movement of the pressure wave extrema with increased hydrodynamic action (either increasing speed or increasing eccentricity). This method is also used to determine the “cause” of the “near surface effect”. A gedanken experiment is performed based on these results which indicates that a bearing with a “stronger aerostatic strength” component should be more stable than one with a low aerostatic strength component. Numerical instability “speed limits” are found that are also related to the hydrostatic strength of the bearing. The local conditions in the standing waves are characterized in terms of their local Mach number, Knudsen number, Reynolds number, and Taylor Number. It is concluded that low eccentricity bearing whirl can be attributed to the off load-line orientation of the bearing load force caused by the overlay of the hydrodynamic bearing standing wave onto the hydrostatic bearing wave of the hybrid bearing, whereas it is hypothesized that aperiodic and random self-excited vibration which occurs at high eccentricity, as reported in the literature, is probably due to shock waves, turbulence, near surface effect, and slip at local areas of the standing wave.

Indiana University-Purdue University Indianapolis (IUPUI) / Ignition of a combustible mixture by a transient jet of hot reactive gas is important for safety of mines, pre-chamber ignition in IC engines, detonation initiation, and in novel constant-volume combustors. The present work is a numerical study of the hot-jet ignition process in a long constant-volume combustor (CVC) that represents a wave-rotor channel. The mixing of hot jet with cold mixture in the main chamber is first studied using non-reacting simulations. The stationary and traversing hot jets of combustion products from a pre-chamber is injected through a converging nozzle into the main CVC chamber containing a premixed fuel-air mixture. Combustion in a two-dimensional analogue of the CVC chamber is modeled using global reaction mechanisms, skeletal mechanisms, and detailed reaction mechanisms for four hydrocarbon fuels: methane, propane, ethylene, and hydrogen. The jet and ignition behavior are compared with high-speed video images from a prior experiment. Hybrid turbulent-kinetic schemes using some skeletal reaction mechanisms and detailed mechanisms are good predictors of the experimental data. Shock-flame interaction is seen to significantly increase the overall reaction rate due to baroclinic vorticity generation, flame area increase, stirring of non-uniform density regions, the resulting mixing, and shock compression. The less easily ignitable methane mixture is found to show higher ignition delay time compared to slower initial reaction and greater dependence on shock interaction than propane and ethylene. The confined jet is observed to behave initially as a wall jet and later as a wall-impinging jet. The jet evolution, vortex structure and mixing behavior are significantly different for traversing jets, stationary centered jets, and near-wall jets. Production of unstable intermediate species like C2H4 and CH3 appears to depend significantly on the initial jet location while relatively stable species like OH are less sensitive. Inclusion of minor radical species in the hot-jet is observed to reduce the ignition delay by 0.2 ms for methane mixture in the main chamber. Reaction pathways analysis shows that ignition delay and combustion progress process are entirely different for hybrid turbulent-kinetic scheme and kinetics-only scheme.