Este trabalho objetiva o estudo específico, teórico e numérico, da determinação dos diferentes modos de colapso, elásticos e elastoplásticos, de uma estrutura tubular sujeita a esforços: pressão externa, flexão e flexo-pressurização. Entre os mais importantes elementos estruturais básicos, analisaremos inicialmente o modelo de um anel comprimido por uma carga radial. Isso significa determinar as pressões de instabilidade, elástica e elastoplástica, e de colapso, com os correspondentes modos, para anéis com diferentes relações diâmetro-espessura, D/t , submetidos a uma série gradual de pressões externas. A Estabilidade estrutural é computada utilizando uma formulação variacional, com discretização por elementos finitos. O modelo material pressupõe comportamento elastoplástico, com pequenas deformações. A análise não linear envolve a aplicação de pressurização externa aos anéis, de forma incremental, para a obtenção da resposta, tomando em conta a falta de circularidade inicial dos mesmos. Casos específicos envolvendo anéis de paredes finas e grossas serão considerados. Será analisado depois o estudo da resposta e da estabilidade de tubos de metal de parede fina e relativamente grossa sob flexão e flexo-pressurização através do método dos elementos finitos. Durante as últimas décadas este problema tem muito sido estudado através de métodos analíticos e experimentais. A maioria das soluções, entretanto, referem-se ao comportamento destas estruturas sob condições elásticas. No entanto, uma experiência de um elemento tubular é um problema inerentemente não linear com flambagem ou colapso do cilindro tomando lugar. Ás vezes com localização. Confrontaremos no final principalmente os resultados numéricos com aqueles da literatura, Kyriakides et al (1987), (1991) e (1992). / This work looks first at the determination of instability pressures as well as elastoplastic collapse, with the corresponding modes of rings with different diameter/thickness ratios under incremental external pressure loading and . Structural stability is computed by a variational formulation with discretization by finite elements. Material modeling considers elastoplastic behaviour with small deformations. Non Linear analysis produces the response curves considering lack of initial out-of-roundness. .After the response and stability of long and relatively thick wall metal tubes under bending and combined bending and external pressure were studied through experimental and analytical methods during the last decades. Most of the solutions, however, refered to the behavior under elastic conditions. In these cases we used the Finite Element Method with several discretizations. Nonetheless these experiments of a tube element is an inherently nonlinear problem with cylinder buckling or collapse taking place. Sometimes with localization. At the end numerical results are mainly compared to experimental measurements of Kyriakides et al (1987), (1991) e (1992).

Orientador: José Mario De Martino / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T22:55:53Z (GMT). No. of bitstreams: 1 Santos_RodrigoMologniGoncalvesdos_M.pdf: 13617752 bytes, checksum: 7a0f3cc2f97bbc5f0bb170014d19861b (MD5) Previous issue date: 2011 / Resumo: Nas últimas décadas, o estudo dos fenômenos de propagação de ondas mecânicas e de suas conseqüências tem recebido crescente atenção de grupos de pesquisa de variados ramos da engenharia, sobretudo daqueles dedicados ao desenvolvimento de métodos computacionais para resolução de problemas complexos na área da Mecânica dos Meios Contínuos (MMC). Os métodos computacionais desenvolvidos por estes grupos geralmente são constituídos de modelagem matemática e simulação computacional de problemas físicos, que substituem a necessidade do uso de protótipos ou infraestrutura de laboratórios, mas que em contrapartida produzem uma volumosa quantidade de dados numéricos que pode dificultar ou inviabilizar uma análise mais eficiente dos resultados sem o suporte de técnicas específicas para o mapeamento destes dados em representações visuais. Esta dissertação apresenta um trabalho científico-tecnológico na área de Visualização Científica, cujas técnicas foram empregadas em MMC para a visualização dos fenômenos de propagação de ondas mecânicas, especificamente em meios materiais sólidos. Os objetivos principais do trabalho foram possibilitar que os especialistas pudessem validar mais rapidamente os seus métodos computacionais voltados ao estudo dos fenômenos de propagação de ondas mecânicas e, principalmente, que eles pudessem entender com mais facilidade os resultados gerados pela simulação computacional, ampliando assim a eficiência da análise de problemas complexos. Os estudos de casos realizados e apresentados no trabalho permitem afirmar que estes objetivos foram alcançados e os resultados foram satisfatórios. As principais contribuições deste trabalho são: identificação de um conjunto de informações derivadas dos dados brutos gerados pela simulação computacional que podem ser empregados para análise dos fenômenos de propagação de ondas mecânicas; metodologias e respectivas formulações matemáticas para cálculo destas informações; desenvolvimento de um protótipo de ambiente de visualização dos dados que descrevem o comportamento das ondas mecânicas; e estudo e definição de diretrizes de como as técnicas de visualização de dados escalares e vetoriais podem ser aplicadas para favorecer a análise das informações disponíveis. É importante observar que o trabalho é limitado à visualização de ondas mecânicas bi ou tridimensionais geradas sobre grades de dimensão bidimensional / Abstract: In recent decades, the study of the mechanical wave propagation phenomena and their consequences has been receiving increasing attention from research groups in engineering, principally those dedicated to the development of computational methods for solving complex problems in the area of Continuum Mechanics (CM). The computational methods developed by these groups usually consist of mathematical modeling and computer simulation of physical problems, which replace the need for prototypes or laboratory infrastructure. But in opposition, produces a large amount of numerical data that can hinder a more efficient analysis of the results without the support of specific techniques for mapping these data into visual representations. This master's dissertation presents a scientific-technological work in the area of Scientific Visualization, whose techniques were applied in the area of CM for visualization of the mechanical wave propagation phenomena, specifically in solid material media. The main objectives of the work were to allow MCM experts to validate more quickly their computational methods for the study of the mechanical wave propagation phenomena and, especially, that they could more easily understand the results generated by computer simulation, increasing the efficiency of analysis of complex problems. The case studies analyzed and presented in the dissertation allow to state that these objectives were attained and the results were satisfactory. The main contributions of the work are: identification of a set of implicit information, derived from raw data generated by computer simulation, that can be used to analyze the mechanical wave propagation phenomena; methodologies and their mathematical formulations to calculate these information; development of a visualization environment prototype of the data that describe the behavior of mechanical waves; and study and guideline definition of how to apply the visualization techniques of scalar and vector data for expand the analysis the available information. It is important to mention that the work is limited to visualization of two or three-dimensional mechanical waves generated on two-dimensional grids / Mestrado / Engenharia de Computação / Mestre em Engenharia Elétrica

The development of adaptive finite element procedures for the solution of geometrically and physically nonlinear problems in structural mechanics is very important for the augmentation of the efficiency of FE-codes. In this contribution methods of mesh refinement as well as mesh coarsening are presented for a material model considering finite elasto-plastic deformations. For newly generated elements stresses, strains and internal variables have to be calculated. This implies the determination of the nodal values as well as the Gaussian point values of the new elements based on the transfer of data from the former mesh. Analogously, the coarsening of less important elements necessitates the determination of these values for the newly created father elements.

The boundary value problems (BVPs) of geomechanics are challenging due to the complexity in modeling soil behavior and difficulties in modeling large deformations. While traditional numerical schemes have struggled in realistically simulating geomechanical BVPs, new numerical methods –such as the material point method (MPM)–are increasingly being used to tackle these problems. However, algorithms in MPM have not yet been sufficiently developed, scrutinized, and validated. This thesis focuses on the development, verification, and validation of MPM for use in geomechanical BVPs. In particular, the thesis focuses on simulation of cone penetration tests in both controlled environments and in field conditions.<div><br></div><div>To efficiently simulate cone penetration, a silent boundary scheme, known as a cone boundary, was proposed in the generalized interpolation material point method (GIMP), a variant of MPM. The implementation of the cone boundary in GIMP was discussed, and the boundaries were validated by comparison against several benchmark problems. The cone boundaries were shown to be suitable in transmitting energy at the boundary. In addition, the implementation of traction boundaries in GIMP was analyzed. In GIMP, traction boundaries may be implemented either at the centroid of the material point, or at the edge of the material point domain. It was shown that the implementation of traction boundaries at the edge of the domain led to stress oscillations near the boundary, which were minimized when the traction boundaries were implemented at the edge of the domain.<br></div><div><br></div><div>During cone penetration, the soil near the cone-soil interface is pushed to large strains. At large strains, soils reach critical state, a state in which the soil shears at constant volume. Simulation of incompressible materials using low-order shape functions commonly used in GIMP leads to stiffer solutions and stress oscillations. To mitigate the constraints imposed by incompressibility, the non-linear B-bar method was implemented in GIMP. The modifications required for the implementation of the B-bar method in GIMP were discussed, and the efficacy of the method in mitigating incompressibility was demonstrated by analyzing several benchmark problems.<br></div><div><br></div><div>To simulate cone penetration in saturated soil, a coupled formulation was proposed in GIMP.A single material point was used to represent both the soil matrix and water. The governing equations were solved using an explicit scheme with the velocity of the soil matrix and the velocity of water as the primary variables. The formulation was validated through problems for which analytical or numerical solutions are available.<br></div><div><br></div><div>Finally, cone penetration analyses were performed both in dry sand and saturated clays. Two bounding surface models –one for sand and one for clay –were used for accurately capturing the soil response. Cone penetration tests were performed on Ottawa 20-30 sand under a variety of loading conditions at a large calibration chamber. The penetration resistances were measured, and the displacement fields were captured using the digital image correlation technique(DIC). The cone penetration resistances predicted by MPM were within 25% of the measured values, and the displacement fields computed using MPM were similar to those captured using DIC. For saturated clays, cone penetration test results reported in the literature for a Boston Blue Clay (BBC) test site were used. The simulated cone resistance of 650 kPa lied within the CPT resistance range of 580-730 kPa reported in the field. The results demonstrate the capability of MPM in simulating cone penetration in both sands and clays provided that sufficiently accurate algorithms and advanced constitutive models capable of reproducing realistic soil behavior are used in the analyses.<br></div>

<p>Biorefineries which seek to convert biomass into ethanol face many different challenges, and among them, mechanical failure of equipment is common. Unfortunately, the resulting downtime can significantly reduce the profitability and the viability of bioethanol plants. One important piece of mechanical equipment in this setting is the compression screw feeder, which is used both to convey and compress biomass into pressurized chemical reactors. However, due to the variability of feedstock properties, this feeding operation is challenging. An analytical model for predicting the operational steady-state torque of a compression screw feeder can assist the identification of optimal processing conditions, as well as predict and prevent equipment failure.<br></p> <p>Since these models have not yet been proposed, this thesis restricts attention to milled corn stover and investigates the application of the discrete element method (DEM) and analytical techniques to develop predictive models for the stresses and torques developed inside a compression screw feeder. Specifically, DEM simulations are used to identify and study the stresses within the different sections of a representative compression screw feeder for three backpressures, three screw pitches, and three internal friction angles. Using these numerical results, a suite of analytical models is then developed to predict the operational torque required to drive the screw feeder. In this thesis, the DEM results are also used in lieu of experimental data to provide a point of comparison for the models.</p> <p>The analytical models predict stresses on the correct order of magnitude and are not prohibitively sensitive to input properties, but the operational steady-state torque is overpredicted by the model in all cases. The mispredictions of the model are likely due to the assumption of constant material properties along the densification process, and the assumption of hydrostatic conditions throughout the compression screw feeder (especially near the boundaries). Despite these limiting assumptions, the proposed procedure for calculating the torque provides a first-order estimate of the required screw torque, demonstrates the sensitivity of the screw feeder to different inputs, and outlines the necessary steps to improve the model. The DEM simulations proved an invaluable tool in analyzing the behavior of bulk material within a compression screw feeder, but more experiments and simulations (possibly using the finite element method) are needed to further understand the biomass feeding operation.</p>

For a structure designed to interact with the surrounding fluid, structural deformation under loads induced by fluid flows is an important factor to consider, and one which is traditionally difficult to account for analytically. Coupling the finite element method for structural analysis with the finite volume method for the determination of fluid response allows for accurate simulation of the pressure and shearing loads applied by the fluid onto the fluid-structure interface, while also determining localized structural displacements that would cause changes to the geometry of the interface. This work seeks to simulate the behavior of cylinders with varying heights and stiffnesses under external flows with low Reynolds numbers. To address structural deformation accurately in the simulation, a morphing and remapping algorithm is applied to the fluid-structure interface. With additional consideration for anisotropy in the structure's elasticity, these analyses could potentially support the development of flexible components that deform in predetermined ways under anticipated fluid loads, allowing for simpler and more efficient solutions to control flow scenarios that traditionally require moving components and control surfaces.

<p>Breast cancer affects 12.5\% of women over their life time and tissue expansion (TE) is the most common technique for breast reconstruction after mastectomy. However, the rate of complications with TE can be as high as 15\%. Even though the first documented case of TE happened in 1957, there has yet to be a standardized procedure established due to the variations among patients and the TE protocols are currently designed based on surgeon's experience. There are several studies of computational and theoretical framework modeling skin growth in TE but these tools are not used in the clinical setting. This dissertation focuses on bridging the gap between the already existing skin growth modeling efforts and it's potential application in the clinical setting.</p> <p><br></p> <p>We started with calibrating a skin growth model based on porcine skin expansions data. We built a predictive finite element model of tissue expansion. Two types of model were tested, isotropic and anisotropic models. Calibration was done in a probabilistic framework, allowing us to capture the inherent biological uncertainty of living tissue. We hypothesized that the skin growth rate was proportional to stretch. Indeed, the Bayesian calibration process confirmed that this conceptual model best explained the data. </p> <p><br></p> <p>Although the initial model described the macroscale response, it did not consider any activity on the cellular level. To account for the underlying cellular mechanisms at the microscopic scale, we have established a new system of differential equations that describe the dynamics of key mechanosensing pathways that we observed to be activated in the porcine model. We calibrated the parameters of the new model based on porcine skin data. The refined model is still able to reproduce the observed macroscale changes in tissue growth, but now based on mechanistic knowledge of the cell mechanobiology.  </p> <p><br></p> <p>Lastly, we demonstrated how our skin growth model can be used in a clinical setting. We created TE simulations matching the protocol used in human patients and compared the results with clinical data with good agreement. Then we established a personalized model built from 3D scans of a patient unique geometry. We verified our model by comparing the skin growth area with the area of the skin harvested in the procedure, again with good agreement.</p> <p><br></p> <p>Our work shows that skin growth modeling can be a powerful tool to aid surgeons design TE procedures before they are actually performed. The simulations can help with optimizing the protocol to guarantee the correct amount of skin is growth in the shortest time possible without subjecting the skin to deformations that can compromise the procedure.</p>

<p>The capability of manipulation of the flow of mechanical energy in the form of mechanical waves (including acoustic and elastic waves) has always been a challenge and a critical part in various areas of engineering. The recent advances in topological acoustic/elastic metamaterials certainly open a new pathway to the manipulation of mechanical waves, especially for the novel scattering-immune wave-guiding capability, even in the presence of defects, disorders or sharp bends along the waveguide. In this Dissertation, the theoretical background and experimental evidence of various types of elastic-wave topological metamaterials including analogues to 2D quantum valley Hall effect (QVHE) materials, 2D quantum spin Hall effect (QSHE) topological insulators are presented. First, the formulation the elastic-wave analogue to QVHE materials in a general continuous elastic phononic structure (not limited to local resonant lattices, filling the gap in the literature) is proposed, and a strategy using pressurized cells to actively control the phononic lattice is presented. By finite prestrain and geometric nonlinear effect, the space inversion symmetry of the original hexagonal lattice is broken, resulting in distinct QVHE phases (characterized by valley Chern numbers) in lattice domains with opposite pressurization. With such mechanism, the edge-state path, i.e., the domain wall connecting lattices with distinct QVHE phases, can be real-time configured. Further more, edge states with tunable frequency-wavenumber dispersion can be created at the external boundaries of the lattice by appropriate pressurization of the outermost cells. An aluminum reticular sheet built with water-jet cutting is machined in the pre-deformed pattern with a Z-shape domain wall at the center, which spatially divides the sheet into two domains with opposite QVHE phases. Using piezoelectric transducers and laser Doppler vibrometry, the measured harmonic and transient responses confirm the back-scattering-immunity of the topological edge states, and the frequency-wavenumber dispersion matches the numerical prediction. A strategy is proposed for unidirectionally generating edge states along the domain wall using two off-phase transducers, which is also experimentally demonstrated. For elastic-wave analogue to QSHE topological insulators, we focus on the ``zone-folding'' method and propose a honeycomb 2D elastic beam network with periodically altered thickness with a generalized Kekule distortion pattern. Such framework provides a parametric space with exhaustive control in the topological phase diagram of waves in the lattice compared to earlier works in the literature. The effective Hamiltonian as well as the characterized topological phase are gauge dependent, particularly they change with different reference frames. This lead to ambiguity in the topological phase of such phononic crystal. Based on this argument, it is predicted that edge states could exist at a dislocation interface connecting two piece of phononic structures of the same pattern with relative displacement. Following the same idea, but considering the available fabrication options, a phononic plate with honeycomb groove pattern engraved on both sides is built, which the depth varied according to the Kekule pattern. With proper tuning of the parameters, it realizes an analogue to the QSHE topological insulator. With <em>ab initio</em> calculation of the Berry curvature (without involving any approximations such as the perturbative approach), a new topological invariant <em>local topological charge</em> is defined and evaluated as the counterpart of the Z₂ invariant in the classical-wave-zone-folding analogue. The local topological charge has intrinsic ambiguity and its value depends on the selected reference frame. However, its <em>change </em>according to changes in the parameters, under a consistent reference frame, is well-defined. Given the fact that shifting the reference frame by certain fractions of a lattice constant was equivalent to changing one of the parameters by a certain amount, it also lead to a well-defined change in the local topological charge, which indicates topological phase transition, and one can predict the existence of edge states at the displacement-dislocation interface between two neighboring lattices having the same pattern up to a rigid-body shifting. The phononic plate is machined by a CNC mill, and the experiment is carried out using piezoelectric transducers and laser Doppler vibrometry, which confirms the existence and robustness of the topological edge states at such dislocation interface connecting identical pattern, which was unprecedented in both quantum and classical systems. The final part of this Dissertation focuses on creating classical mechanical analogues to the 1D Kitaev superconducting model and Majorana-like bound states aimed at future acoustic-wave based computation.</p>

Hydrates, wax, and other fluids forms in cold subsea pipelines which restrict flow of petroleum products during operation. This thesis analyses the global buckling behaviour of subsea pipelines with Direct Electric Heating cables (DEH) through a combination of analytical and FEM simulations. A subsea pipeline with an attached DEH cable has limited impact on the pipelines initial global buckling behaviour. The DEH cable holds back and reduces the buckle size. Strap distance and cable rotational location has very limited impact on buckling behaviour. Analytical and FEM model has in places low convergence, this is likely due to limitations in the models. / Hydrater, vax, och andra fluider formas i kalla undervattensrörledningar som begränsar flödet av petroleumprodukter i drift. Detta examensarbete analyserar global buckling av undervattensrörledningar med Direct Electric Heating (DEH) kabel med en kombination av analytisk och FEM simuleringar. En undervattensrörledning med tillhörande DEH kabel har begränsad påverkan på en rörlednings initiala globala bucklingsbeteende. DEH kabeln håller tillbaka och reducerar bucklingsstorleken. Avstånd mellan remmar och kabelns läge har mycket begränsad påverkan på bucklingsbeteendet. Den analytiska och FEM‐modellen har i vissa fall låg konvergens, troligen på grund av begränsningar i modellerna.

By using the rotor dynamic capabilities of Simcenter Nastran Rotordynamics, an eigenvalue analysis of 3D-finite element models of the Jeffcott rotor and the overhung rotor were conducted and compared to the results with beam-based, lumped parameter models. The first two critical speeds of the Jeffcott rotor were estimated with variations of 3.9 and 6.4%. The first three critical speeds of the overhung rotor were estimated with 8.5, 6.7 and 6.5% variations, respectively. The Jeffcott rotor was also analysed with different element configurations: Solid elements, axisymmetric Fourier elements, beam/solids and all beam elements. The Fourier elements were the most appropriate option for axisymmetric rotors regarding computational time and accuracy. Tilting pad journal bearings were simulated and validated against data from Vattenfall's facilities in Älvkarleby, where a vertical rotor is connected to two four-pad tilting pad journal bearings. The bearing formulation was defined in a Fortran based subroutine, which acquires the rotor's speed and position to supply a bearing load vector in Simcenter Nastran's transient solver. The experimental rig was also modelled to include the rotor/stator interaction. The force and displacement orbits at the bearings were replicated adequately concerning experimental data, where a maximum deviation of 20.8% and 9.8% were observed for the forces in x and y-directions.  A 3D-finite element model and a beam based finite element model were compared for an actual hydropower unit, which aimed to investigate the mode extraction procedure and how high mass, elastic rotor components influence the system's dynamics. Consistent rotor modes were identified at frequencies within 15% deviation, where the maximum deviation occurred in the upper range frequency pairs. Convergence between the models was observed for the static, lower range frequencies when considering a rigid generator rotor in the 3D finite element model. The outcome is consistent with the model assumptions and underlines that the beam based model cannot capture specific contributions from elastic rotor components. 3D-finite element analysis is a viable option when considering non-axisymmetric and complex rotors. High mass, non-rigid components must be analysed  in this manner as their dynamic contributions may not be captured with other approaches. Intricate and non-rigid supporting structures are also suitable for 3D modelling to properly reflect the stator-rotor interaction. It is a delicate matter to pinpoint when these conditions occur, and modelling decisions must be therefore be substantiated by simulations and experimental validation.