Orientador: Renato Pavanello / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-10T00:52:29Z (GMT). No. of bitstreams: 1 Moura_MarciodaSilva_M.pdf: 3205928 bytes, checksum: a8344d0c36acf072569df75478f33b23 (MD5) Previous issue date: 2007 / Resumo: o modelo poro elástico é aplicado na representação do comportamento físico de um meio contínuo composto por duas fases distintas, uma sólida e outra fluida. A fase sólida está envolta em um domínio fluídico saturado. A matéria fluida presente no sistema pode ser líquida, gasosa ou uma mistura em função do meio a que se pretende estudar. Estruturas ósseas são um bom exemplo de material poroso, pois são constituídas de uma porção sólida, formada por uma estrutura calcificada e outra fluida, formada pelo sangue, gorduras e fluidos ósseos. Neste trabalho propõem-se elaborar uma ferramenta para simulação computacional da poroelasticidade aplicada em ossos, considerando solicitações estáticas e respostas transientes. Da mesma forma esta ferramenta permite a análise sobre próteses inseridas em ossos e sua interação elástica com uma estrutura poroelástica. O modelo utilizado é baseado no trabalho precursor de Maurice A. Biot, que submeteu uma porção de solo em água saturada a cargas de compressão, analisando suas respostas e o comportamento poroso do sistema. A ferramenta computacional foi desenvolvida em ambiente Fortran90. As análises foram realizadas em termos de tensão, deformação, deslocamentos e pressão e as condições submetidas foram baseadas em situações de solicitação disponíveis na literatura. Os resultados proporcionaram o mapeamento das regiões sujeitas a tensões elevadas avaliando o comportamento da interface osso prótese. Esses estudos possibilitam um melhor entendimento do comportamento dinâmico da fase fluida do osso, permitindo que análises mais precisam próteses implantadas possam ser realizadas / Abstract: The poroelastic model is applied in the representation of the physical behavior of a continuous medium composed by two separate phases: a solid phase and a fiuid one. The solid phase is wrapped in a fiuidic saturated dominium. The fiuid matter in the system may be liquid, gaseous or else a mixture, depending on the medium one intends to study. Bones structures are a good example of a porous material because they comprise a calcified structure and another fiuid structure formed by blood, fat and bones fiuids. In this paper, it propose to develop a tool for computer simulation of poroelasticity applied to bones, considering static loads and transient responses. Likewise, this tool enables analysis of prostheses inserted in bones and their elastic interaction with a poroelastic structure. The model used is based on the early work of Maurice A. Biot, who submitted a portion of sDil in saturated water to compression loads and analyzed its responses and the porous behavior of the system. The computer tool was developed in Fortran90 environment. Analyses were conducted in terms of stress, strain, displacements and pressure. The boundary conditions submitted were based on situations of stress available in the literature. The results enabled to map areas that are subject to high stress 80 the behavior of the bone / prosthesis interface could be assessed. These studies provided a better understanding of the dynamic behavior of the fiuid phase of the bone so more precise analyses of implanted prostheses can be made / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Orientador: Renato Pavanello / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T13:01:53Z (GMT). No. of bitstreams: 1 SilvaJunior_FranciscoIlsonda_D.pdf: 14371994 bytes, checksum: 62ec5e37c9e4a7e588b3e344df5a1542 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho, estudam-se os fenômenos de propagação de ondas elásticas e acústicas em meios poroelásticos acoplados e se propõe uma metodologia de projeto de isolação acústica em baixas freqüências, utilizando-se de técnicas de otimização topológica. Duas formulações para o método de elementos finitos são utilizadas, baseadas nas equações clássicas de Biot modificadas, escritas em termos do deslocamento estrutural (u) e da pressão acústica (p) nos interstícios preenchidos pelo fluido. O problema físico consiste em um material poroelástico absorvedor presente em um tubo de Kundt acoplado a um guia de onda no domínio das baixas freqüências. A célula representativa é composta por dois sub-domínios: Acústico e Poroelástico. Dois métodos para a maximização da absorção acústica são propostos. O primeiro método é uma seqüência evolucionaria baseada no número de sensibilidade determinado a partir dos valores de absorção elementar acústica. O segundo método é baseado na técnica SIMP (¿Simple Isotropic Material with Penalization¿) e envolve uma análise de sensibilidade e métodos de programação matemática. A análise de sensibilidade do sistema acoplado é feita através de três metodologias distintas. Um Método de Programação Linear Seqüencial, o SLP (¿Sequential Linear Programming¿) é utilizado na solução do problema de otimização para validar a metodologia proposta. Finalmente, as principais conclusões são apresentadas e algumas sugestões de investigações futuras são propostas / Abstract: This work aims to study the coupled poroelasticity and build a design methodology based on Evolutionary and Topological optimization techniques. Two version of the classical Biot equations are written in terms of solid phase structural displacements (u) and interstitial acoustic pressure (p). The problem is solved using a Kundt tube model coupled to an acoustic wave guide in the low frequency domain. Two methods for the maximization of the acoustic absorption at a specific frequency are proposed. The first method is an evolutionary sequence, based on a sensitivity number and obtained by acoustic elementary absorption determination. The second method is based on a SIMP technique (Simple Isotropic Material With Penalization). It involves a sensitivity analysis and mathematical programming methods. A sensitivity analysis of the coupled system is done by three different methodologies. A Sequential Linear Programming Method (SLP) is used to solve the optimization problem. Bidimensional and Tridimensional examples have been implemented and optimized to validate the proposed methodology investigations are proposed. Finally, the main conclusions are presented and some suggestions about future investigations are proposed. / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica

Tissue engineering offers a paradigm shift in the treatment of back pain. Engineered intervertebral discs could replace degenerated tissue and overcome the limitations of current treatments that disrupt the biomechanics of the spine. New materials, which exhibit sophisticated mechanical responses, are needed to provide templates for tissue regeneration. These behaviours include time-dependent deformation---facilitating shock absorption and nutrient transfer---and strong material anisotropy and tensile-compressive nonlinearities---providing flexibility in controlled directions. In this work, frameworks for the design of materials with controllable structure-property relationships are developed. The time-dependent mechanical properties of composites of agar, alginate and gelatin hydrogels are investigated. It is shown that the time-dependent responses of the composites can be tuned over a wide range. It is then demonstrated that materials mimicking the fibre-reinforced nature of natural tissues can be developed by infiltrating thick electrospun fibre networks with alginate. These fibre-reinforced hydrogels have tensile and compressive properties that can be separately altered. To better understand the mechanical behaviour of these hydrogel-based materials, improved methods for characterising poroelastic and poroviscoelastic time-dependent material properties using indentation are developed. It is shown that poroviscoelastic relaxation is the product of separate poroelastic and viscoelastic relaxation responses. The techniques developed here provide a methodology to rapidly characterise the properties of time-dependent materials and to create materials with complex structure-property relationships similar to those found in natural tissues; they present a framework for biomimetic materials design. The work in this thesis can be used to inform the design of clinically relevant tissue engineering treatments and help the quarter of a million people each year who undergo spinal surgery to reduce back pain.

Geotechnical structures under realistic field conditions are usually influenced with complex interactions of coupled hydromechanical behavior of porous materials. In many geotechnical applications, however, these important coupled interactions are ignored in their constitutive models. Under coupled hydromechanical behavior, stress in porous materials causes volumetric change in strain, which causes fluid diffusion; consequently, pore pressure dissipates through the pores that results in the consolidation of porous material. The objective of this research wasto demonstrate the advantages of using hydromechanical models to estimate deformation and pore water pressure of porous materials by comparing with mechanical-only models. Firstly, extensive literature survey was conducted about hydromechanical models based on Biot’s poroelastic concept. Derivations of Biot’s poroelastic equations will be presented. To demonstrate the hydromechanical effects, a numerical model of poroelastic rock materials was developed using COMSOL, a commercialized multiphysics finite element software package, and compared with the analytical model developed by Wang (2000). Secondly, a series of sensitivity analyses was conducted to correlate the effect of poroelastic parameters on the behavior of porous material. The results of the sensitivity analysis show that porosity and Biot’s coefficient has dominant contribution to porous material behavior. Thirdly, a coupled hydromechanical finite element model was developed for a real-world example of embankment consolidation. The simulation results show excellent agreement to field measurements of embankment settlement data.

Induced seismicity (earthquakes caused by injection or extraction of fluids in Earth's subsurface) is a major, new hazard in the United States, the Netherlands, and other countries, with vast economic consequences if not properly managed. Addressing this problem requires development of predictive simulations of how fluid-saturated solids containing frictional faults respond to fluid injection/extraction. Here we present a numerical method for linear poroelasticity with rate-and-state friction faults. A numerical method for approximating the fully coupled linear poroelastic equations is derived using the summation-by-parts-simultaneous-approximation-term (SBP-SAT) framework. Well-posedness is shown for a set of physical boundary conditions in 1D and in 2D. The SBP-SAT technique is used to discretize the governing equations and show semi-discrete stability and the correctness of the implementation is verified by rigorous convergence tests using the method of manufactured solutions, which shows that the expected convergence rates are obtained for a problem with spatially variable material parameters. Mandel's problem and a line source problem are studied, where simulation results and convergence studies show satisfactory numerical properties. Furthermore, two problem setups involving fault dynamics and slip on faults triggered by fluid injection are studied, where the simulation results show that fluid injection can trigger earthquakes, having implications for induced seismicity. In addition, the results show that the scheme used for solving the fully coupled problem, captures dynamics that would not be seen in an uncoupled model. Future improvements involve imposing Dirichlet boundary conditions using a different technique, extending the scheme to handle curvilinear coordinates and three spatial dimensions, as well as improving the high-performance code and extending the study of the fault dynamics.

The world population is expected to increase to approximately 11 billion by 2100. The ageing population (aged 60 and over) is projected to exceed the number of children in 2047. This will be a situation without precedent. The number of citizens with disorders of old age like Dementia will rise to 115 million worldwide by 2050. The estimated cost of Dementia will also increase, from $604 billion in 2010, to $1,117 billion by 2030. At the same time, medical expertise, evidence-driven policymaking and commissioning of services are increasingly evolving the definitive architecture of comprehensive long-term care to account for these changes. Technological advances, such as those provided by computational science and biomedical engineering, will allow for an expansion in our ability to model and simulate an almost limitless variety of complex problems that have long defied traditional methods of medical practice. Numerical methods and simulation offer the prospect of improved clinically relevant predictive information, and of course optimisation, enabling more efficient use of resources for designing treatment protocols, risk assessment and urgently needed management of a long term care system for a wide spectrum of brain disorders. Within this paradigm, the importance of the relationship of senescence of cerebrospinal fluid transport to dementia in the elderly make the cerebral environment notably worthy of investigation through numerical and computational modelling. Hydrocephalus can be succinctly described as the abnormal accumulation (imbalance between production and circulation) of cerebrospinal fluid (CSF) within the brain. Using hydrocephalus as a test bed, one is able to account for the necessary mechanisms involved in the interaction between cerebral fluid production, transport and drainage. The current state of knowledge about hydrocephalus, and more broadly integrative cerebral dynamics and its associated constitutive requirements, advocates that poroelastic theory provides a suitable framework to better understand the disease. In this work, Multiple-network poroelastic Theory (MPET) is used to develop a novel spatio-temporal model of fluid regulation and tissue displacement in various scales within the cerebral environment. The model is discretised in a variety of formats, through the established finite difference method, finite difference – finite volume coupling and also the finite element method. Both chronic and acute hydrocephalus was investigated in a variety of settings, and accompanied by emerging surgical techniques where appropriate. In the coupled finite difference – finite volume model, a key novelty was the amalgamation of anatomically accurate choroid plexuses with their feeding arteries and a simple relationship relaxing the constraint of a unique permeability for the CSF compartment. This was done in order to account for Aquaporin-4 sensitisation. This model is used to demonstrate the impact of aqueductal stenosis and fourth ventricle outlet obstruction. The implications of treating such a clinical condition with the aid of endoscopic third (ETV) and endoscopic fourth ventriculostomy (EFV) are considered. It was observed that CSF velocity in the aqueduct, along with ventricular displacement, CSF pressure, wall shear stress and pressure difference between lateral and fourth ventricles increased with applied stenosis. The application of ETV reduced the aqueductal velocity, ventricular displacement, CSF pressure, wall shear stress and pressure difference within nominal levels. The greatest reversal of the effects of atresia come by opting for ETV rather than the more complicated procedure of EFV. For the finite difference model incorporating nonlinear permeability, qualitatively similar results were obtained in comparison to the pertinent literature, however, there was an overall amplification of ventriculomegaly and transparenchymal pressure difference using this model. A quantitative and qualitative assessment is made of hydrocephalus cases involving aqueductal stenosis, along with the effects to CSF reabsorption in the parenchyma and subarachnoid space. The finite element discretisation template produced for the n^th- dimensional transient MPET system allowed for novel insight into hydrocephalus. In the 1D formulation, imposing the breakdown of the blood-CSF barrier responsible for clearance resulted in an increase in ventricular displacement, transparenchymal venous pressure gradient and transparenchymal CSF pressure gradient, whilst altering the compliance proved to markedly alter the rate of change of displacement and CSF pressure gradient. The influence of Poisson's ratio was investigated through the use of the dual-grid solver in order to distinguish between possible over or under prediction of the ventricular displacement. In the 2D model based on linear triangles, the importance of the MPET boundary conditions is acknowledged, along with the quality of the underlying mesh. Interesting results include that the fluid content is highest in the periventricular region and the skull, whilst after longer time scales, the peak CSF content becomes limited to the periventricular region. Venous fluid content is heavily influenced by the Biot-Willis constant, whilst both the venous and CSF/ISF compartments show to be strongly influenced by breakdown in the blood-CSF barrier. Increasing the venous compliance effects the arterial, capillary and venous compartments. Decreasing the venous compliance shows an accumulation of fluid, possibly helping to explain why the ventricles can be induced to compress rather than expand under decreased compliance. Finally, a successful application of the 3D-MPET template is shown for simple geometries. It is envisaged that future observations into the biology of cerebral fluid flow (such as perivascular CSF-ISF fluid exchange) and its interaction with the surrounding parenchyma, will demand the evolution of the MPET model to reach a level of complexity that could allow for an experimentally guided exploration of areas that would otherwise prove too intricate and intertwined under conventional settings.

Etudier le séchage est un moyen original de caractériser les propriétés de fluides complexes. Cette technique permet de concentrer continûment des fluides : d'un état dilué à un état sec. A l'échelle microfluidique, la manipulation, les observations et les processus qui entrent en jeu sont simplifiés. Ce travail de thèse s'attache à décrire le séchage de ces fluides et plus particulièrement le cas de dispersions colloïdales. Ces travaux présentent deux méthodes pour étudier l'extraction du solvant d'un fluide à l'échelle microfluidique : la micropervaporation et la goutte confinée. Ces techniques ont notamment permis de réaliser des estimations précises de coefficients de diffusion collective sur toute la gamme de concentrations pour un mélange eau/glycérol et pour une dispersion colloïdale de nanoparticules de silice chargées. Par ailleurs, le séchage induit des contraintes mécaniques conséquentes. Ces contraintes peuvent générer des déformations importantes, des phénomènes de délamination ou de fracturation du matériau solidifié. Une méthode originale de mesure in situ de contraintes a été mise en place pendant ces travaux. Les mesures réalisées avec une dispersion colloïdale modèle permettent de mettre en évidence expérimentalement l'apparition de contraintes mécaniques au moment de la transition sol/gel de la dispersion. L'augmentation de la contrainte est ensuite associée au séchage d'un gel poroélastique. / Drying complex fluids is an original technique to study their properties. Solvent extraction enables the continuous concentration of fluids from a dilute to a solid state. The use of the microfluidic scale allows one to limit side effects and simplify experiments, observations and modeling. This project mainly describes the drying of colloidal dispersions in two confined geometries: microfluidic channels and confined droplets between two plates. With these two techniques, we estimate collective diffusion for a water/glycerol mixture and a model dispersion of charged silica nanoparticles over the whole concentration range. Moreover, the drying of complex fluids often induces mechanical stresses which are the root for deformation, delamination phenomena and cracks. We developed an original technique to measure these stresses in situ. For a model colloidal dispersion, we evidenced experimentally that these forces arise from a liquid to solid state transition. The increase of these stresses is then associated with the drying of a poroelastic gel.

La propagation sismique dans les milieux poreux est classiquement associée à des phénomènes de dispersion et d’atténuation des ondes sous l’effet des mouvements fluides. Dans certaines conditions, celle-ci peut également être associée à une conversion d’énergie sismique en énergie électromagnétique dite « sismoélectrique ». La théorie des phénomènes sismoélectriques combinant la théorie de l’électrocinétique à la poroélasticité de Biot, repose en grande partie sur les développements de Pride (1994). Sur la base de ces développements théoriques, Pride et Haartsen (1996) relient le champ électrique cosismique à l’accélération sismique qui le génère par une fonction de transfert. Nous proposons une étude quantitative des couplages sismoélectriques en vue de valider la théorie de Pride et sa généralisation en milieu non saturé. Dans ce but, nous avons développé une expérience en laboratoire sur un sable de quartz non-consolidé, menée dans la gamme du kilohertz sur la base d’un dispositif d’acquisition électrique modulable. Deux méthodes de traitement des signaux sont proposées, l’une temporelle, l’autre spectrale, permettant d’obtenir une analyse complète des vitesses de phase, atténuations et fonctions de transfert. Les expériences réalisées se sont focalisées sur l’étude du rôle de la conductivité du fluide et de la saturation en eau dans le phénomène sismoélectrique cosismique. Une étude time-lapse a ainsi pu être réalisée dans des situations de changements de salinité et de teneur en eau. Dans tous les contextes, l’étude quantitative des rapports d’amplitudes des champs sismoélectriques et sismiques E/ü montre une bonne corrélation avec les prédictions théoriques. Par ailleurs, l’étude des variations de saturation dans une gamme allant de la saturation résiduelle en eau (Sw = 0.3) à la saturation totale, montre que: i) les atténuations et fonctions de transfert ont des comportements reliés à la distribution des fluides qui influencent fortement les propriétés mécaniques du milieu ; ii) une inversion de polarité du champ sismoélectrique peut être observée dans le cas très particulier des milieux non consolidés. / Seismic propagation within porous media is usually associated with wave attenuation and dispersion phenomena related to fluid flow. Under certain circumstances, it may also be correlated to a conversion of seismic into electromagnetic energy known as “seismoelectric”. The understanding of seismoelectric phenomena, combining the theory of electrokinetic to Biot’s poroelasticity, relies mainly on the formulation by Pride (1994). On basis of these theoretical developments, Pride and Haartsen (1996) defined a transfer function expressing the link between the coseismic seismoelectric field and the seismic acceleration at its origin. We propose a quantitative analysis of coseismic seismoelectric couplings with the purpose of validating Pride’s theory and generalizing it to partially saturated media. With this aim in view we developed a laboratory experiment involving an adjustable device for electric acquisitions, conducted within the kilohertz range on unconsolidated quartz sand. Experimental data were subsequently processed in both time and frequency domains, enabling a full analysis that embraces phase velocities, attenuations and transfer functions. The conducted experiments focused on the impact of fluid conductivity and water saturation with regard to the coseismic seismoelectric phenomenon. Time-lapse monitoring were accordingly run under varying salinity or water content. In all scenarios, the quantitative analysis of the electric-to-seismic amplitude ratio E/ü appeared in good agreement with theoretical projections. Moreover, investigations of saturation variations, ranging from the residual water saturation (Sw = 0.3) to full saturation, showed that: i) the behavior of attenuations and transfer functions are directly related to fluid distribution, that greatly impacts the mechanical properties of the medium; ii) in the very peculiar case of unconsolidated media, polarity inversion of the coseismic seismoelectric field may be experienced.

Although carbonates hold more than 60 percent of the world's oil reserves, they, nevertheless, exhibit much lower average recovery factor values than terrigenous sandstone reservoirs. Thus, utilization of advanced enhanced oil recovery (EOR) techniques such as high pressure CO2 injection may normally be required to recover oil in place in carbonate reservoirs. This study addresses how different rock types can influence the seismic monitoring of CO2 sequestration in carbonates. This research utilizes an elastic parameter, defined in a rock physics model of poroelasticity and so-­called as the frame flexibility factor, to successfully quantify the carbonate pore types in core samples available from the Great Bahama Bank (GBB). This study shows that for carbonate samples of a given porosity the lower the frame flexibility factors the higher is the sonic wave velocity. Generally, samples with frame flexibility values of <4 are either rocks with visible moldic pores or intraframe porosity; whereas, samples with frame flexibility values of >4 are rocks with intercrystalline and microporosity. Hence, different carbonate pore geometries can be quantitatively predicted using the elastic parameters capable of characterizing the porous media with a representation of their internal structure on the basis of the flexibility of the frame and pore connectivity. In this research, different fluid substitution scenarios of liquid and gaseous CO2 saturations are demonstrated to characterize the variations in velocity for carbonate-specific pore types. The results suggest that the elastic response of CO2 flooded rocks is mostly governed by pore pressure conditions and carbonate rock types. Ultrasonic P-­wave velocities in the liquid-­phase CO2 flooded samples show a marked decrease in the order of 0.6 to 16 percent. On the contrary, samples flooded with gaseous-­phase CO2 constitute an increase in P-­wave velocities for moldic and intraframe porosities, while establishing a significant decrease for samples with intercrystalline and micro-­porosities. Such velocity variations are explained by the stronger effect of density versus compressibility, accounting for the profound effect of pore geometries on the acoustic properties in carbonates. The theoretical results from this research could be a useful guide for interpreting the response of time-­lapse seismic monitoring of carbonate formations following CO2 injection at depth. In particular, an effective rock-­physics model can aid in better discrimination of the profound effects of different pore geometries on seismic monitoring of CO2 sequestration in carbonates.

Atherosclerosis is a vascular degenerative disease leading to progressive thickening in the intima of large and medium sized arteries through the formation of plaque that is very rich with cholesterol. The cholesterol is carried by LDL (low density lipoprotein) particles which pass through the endothelium and accumulate in the intima. The passage of LDL is influenced by wall shear stress which activates physiological responses of the endothelium. However, the causal relationship between the physiological responses and their effect on LDL mass transport is not fully understood. To obtain blood flow patterns in human carotid arteries, a fluid structure interaction (FSI) computational approach is employed, based on the in-vivo arterial geometry constructed from black blood magnetic resonance images (BBMRI) and flow rate boundary conditions obtained from phase contrast images (PC). Wall shear stress (WSS) on the luminal surface is computed, and this variable is related to the formation of leaky junctions, which is a major transendothelial pathway for LDL. A model for the fraction of leaky junction at a surface is incorporated into the overall computational scheme for mass transport, along with pore theory. The theoretical model is applied to images from three human carotid arteries in which the degree of disease ranges from mild to moderate. Maximum mass flux is predicted to be in the downstream region of stenoses where WSS is low, and this result is consistent with the clinical observation of plaque progression downstream of the stenosis. The hypothesis that the majority of LDL enters into the intima through leaky junctions is supported by observation of similar distributions between the pattern of volume flux via leaky junctions and mass flux. These studies suggest that mass flux of LDL can be a predictor to indicate areas with potential for plaque formation and progression in human carotid artery disease.