9,541 research outputs found

    Converging organoids and extracellular matrix::New insights into liver cancer biology

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    Numerical Investigation of Diffusion Flame in Transonic Flow with Large Pressure Gradient

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    A finite-volume method for the steady, compressible, reacting, turbulent Navier-Stokes equations is developed and implemented by using a novel splitting scheme for the stiff source terms in chemical reaction. The laminar and turbulent reacting flows in a mixing layer with large streamwise pressure gradient are studied and compared to the boundary-layer solutions. The influence of chemical reaction on the turbulent transport in the mixing layer is analyzed. The influence of vitiated air on the combustion process and aerodynamic performance is also investigated for the cases of turbulent mixing layer and turbine cascade.Comment: 21 pages, 20 figure

    Study of the behavior of a thermoplastic injection mold and prediction of fatigue failure with numerical simulation

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    Tese de doutoramento em Engenharia MecânicaO objetivo deste trabalho é a criação de uma metodologia de análise da resistência à fadiga de moldes de injeção de termoplásticos. Uma metodologia capaz de satisfazer o mercado atual que exige a diminuição do tempo de entrega e custos de moldes de injeção, sem comprometer a sua fiabilidade. Para o desenvolvimento desta metodologia, foram utilizados modelos digitais. Com estes modelos é possível executar-se várias iterações sem os custos de um modelo físico. Além do menor custo dos modelos digitais, também é possível compreender o comportamento de cada molde no decorrer da fase de projeto. Com o aumento da complexidade dos componentes injetados, o estudo da resistência à fadiga tende a ser cada vez mais importante. Neste trabalho serão apresentados cuidados a ter na preparação dos modelos digitais, de forma a obter-se resultados fiáveis. No desenvolvimento desta metodologia, usaram-se dois softwares de simulação numérica para gerar os modelos digitais. Um deles dedica-se ao estudo reológico de peças termoplásticas e outro ao comportamento estrutural dos moldes de injeção. A execução de simulações numéricas requer uma boa caracterização dos materiais usados. No caso dos termoplásticos, os fabricantes têm uma grande base de dados com a informação necessária para as simulações numéricas. No entanto, para as simulações estruturais, os fabricantes tendem apenas a fornecer os dados das curvas monotónicas, os quais não fornecem qualquer informação sobre o comportamento à fadiga. Portanto, neste trabalho foram estudados modelos empíricos que se adaptam aos aços usados em moldes de injeção, a partir dos quais é possível gerar as curvas S-N e e-N. De modo a avaliar qual o modelo empírico que se adaptaria melhor a esta área, foram realizados ensaios experimentais com provetes feitos em EN 1.2311. A partir destes ensaios, escolheu-se o modelo empírico mais conservador. Com base no modelo empírico escolhido, foi desenvolvida uma aplicação capaz de gerar as curvas S-N e e-N, a partir das informações fornecidas pela aciaria. Além da caracterização dos materiais, também é importante que as condições de carregamento do modelo numérico estrutural sejam o mais aproximadas possível do que irá ocorrer no modelo físico. Como as cargas deste modelo numérico podem ser previstas a partir do modelo numérico reológico, a criação de uma ponte entre estes dois modelos numéricos é imprescindível. Logo, neste trabalho foi construída uma aplicação capaz de converter os dados gerados pelo software comercial Moldflow em ficheiros capazes de serem lidos por softwares comerciais de simulação numérica estrutural. Usando esta aplicação para a conversão dos dados, foram realizadas simulações e comparadas com os respetivos modelos físicos. Verificou-se que é possível replicar o comportamento do molde em modelos digitais. No entanto, os modelos digitais dos moldes de injeção estudados tenderam a apresentar resultados conservadores quando comparados com os modelos físicos. Por fim, foi desenvolvida uma aplicação capaz de usar dados calculados a partir de softwares comerciais de cálculo numérico estrutural para a determinação da resistência dos moldes à fadiga. Aqui foi tido em conta o modelo para geração das curvas de fadiga dos materiais validado. Os modelos de cálculo à fadiga na aplicação baseiam-se na regra de Palmgren – Miner para a determinação dos ciclos até à nucleação da fissura. O cálculo das tensões alternadas foi realizado a partir de dois métodos, o critério da tensão de corte octaédrica e o método de Sines. Para testar a aplicação foram escolhidos cinco moldes que apresentaram falhas por fadiga. Em seguida, foi aplicada a metodologia proposta neste trabalho para a determinação da resistência dos mesmos à fadiga. A partir da aplicação desta metodologia e das ferramentas desenvolvidas para o seu emprego, foi possível verificar que esta é capaz de prever as zonas onde ocorreram as falhas, bem como outras com probabilidade de nucleação de fissuras. Portanto, no decorrer deste trabalho foi possível criar uma metodologia e ferramentas de apoio para o cálculo de moldes à fadiga. Assim, projetistas de moldes podem ter uma boa perspetiva da resistência à fadiga de moldes de injeção ainda em projeto, tendo por base métodos científicos.The objective of this work is to create a methodology to analyze the fatigue resistance of thermoplastic injection molds. A methodology capable of satisfying the current market that demands a decrease in the delivery time and costs of injection molds, without compromising their reliability. To develop this methodology, digital models were used. With these models it is possible to execute several iterations without the costs of a physical model. Besides the lower cost of digital models, it is also possible to understand the behavior of each mold during the design phase. With the increasing complexity of injected components, the study of fatigue resistance tends to be more and more important. In this work, care will be presented in the preparation of the digital models, in order to obtain reliable results. In the development of this methodology, two numerical simulation software’s were used to generate the digital models. One of them is dedicated to the rheological study of thermoplastic parts and the other to the structural behavior of injection molds. The execution of numerical simulations requires a good characterization of the materials used. In the case of thermoplastics, manufacturers have a large database with the information needed for numerical simulations. However, for structural simulations, manufacturers tend to provide only monotonic curve data, which do not provide any information about fatigue behavior. Therefore, in this work, empirical models that fit the steels used in injection molds were studied, from which it is possible to generate the S-N and e-N curves. In order to evaluate which empirical model would best fit this area, experimental tests were performed with specimens made in EN 1.2311. From these tests, the most conservative empirical model was chosen. Based on the chosen empirical model, an application capable of generating the S-N and e-N curves from the information provided by the steel mill was developed. Besides the characterization of the materials, it is also important that the loading conditions of the numerical structural model are as close as possible to what will occur in the physical model. Since the loads of this numerical model can be predicted from the rheological numerical model, the creation of a bridge between these two numerical models is essential. Therefore, in this work was built an application capable of converting the data generated by the commercial software Moldflow into files capable of being read by commercial structural numerical simulation software. Using this application for data conversion, simulations were performed and compared with the respective physical models. It was found that it is possible to replicate the mold behavior in digital models. However, the digital models of the injection molds studied tended to present conservative results when compared to the physical models. Finally, an application capable of using data calculated from commercial numerical structural calculation software was developed for determining the fatigue resistance of molds. Here the validated model for generating the fatigue curves of the materials was taken into account. The fatigue calculation models in the application are based on the Palmgren - Miner rule for the determination of the cycles until crack nucleation. The alternating stresses calculation was performed from two methods, the octahedral shear stress criterion and the Sines method. To test the application, five molds that presented fatigue failures were chosen. Then, the methodology proposed in this work was applied to determine their fatigue resistance. From the application of this methodology and the tools developed for its use, it was possible to verify that it is able to predict the areas where the failures occurred, as well as others with a probability of crack nucleation. Therefore, during this work it was possible to create a methodology and support tools for the calculation of fatigue molds. Thus, mold designers can have a good perspective of the fatigue resistance of injection molds still in project, based on scientific methods

    2023-2024 Boise State University Undergraduate Catalog

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    This catalog is primarily for and directed at students. However, it serves many audiences, such as high school counselors, academic advisors, and the public. In this catalog you will find an overview of Boise State University and information on admission, registration, grades, tuition and fees, financial aid, housing, student services, and other important policies and procedures. However, most of this catalog is devoted to describing the various programs and courses offered at Boise State

    Exploring the Weber dependency of jet fragmentation: a Direct Numerical Simulation investigation

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    Jet fragmentation is investigated through a Direct Numerical Simulation campaign using Basilisk (Popinet & collaborators 2013). The simulations span over one order of magnitude of gaseous Weber numbers (13 to 165), i.e. over the second wind-induced and atomization regimes, and the jets develop over distances up to 28 nozzle diameters. The study focuses on the size and velocity distributions of droplets, as well as their joint distribution. Two models derived from different theoretical backgrounds, the statistical description of the turbulence intermittency (Novikov & Dommermuth 1997) and the empirical description of the ligament-mediated fragmentation (Villermaux et al. 2004), are compared for describing the droplet size distribution close to the nozzle. The characteristics of the size-velocity joint distribution are explained using the vortex ring theory (Saffman 1992) which highlights two sources of fragmentation. Finally, the joint histogram of the particulate Reynolds and Ohnesorge numbers is analysed and a normalisation is suggested. It reveals that the delimitations of the droplet phase space, once properly normalised, are self-similar and independent of the gaseous Weber number, both numerically and experimentally.Comment: 39 pages, 22 figure

    Local-in-time structure-preserving finite-element schemes for the Euler-Poisson equations

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    We discuss structure-preserving numerical discretizations for repulsive and attractive Euler-Poisson equations that find applications in fluid-plasma and self-gravitation modeling, respectively. The scheme is fully discrete and structure preserving in the sense that it maintains a discrete energy law, as well as hyperbolic invariant domain properties, such as positivity of the density and a minimum principle of the specific entropy. A detailed discussion of algorithmic details is given, as well as proofs of the claimed properties. We present computational experiments corroborating our analytical findings and demonstrating the computational capabilities of the scheme

    Modified Theories of Gravity and Cosmological Applications

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    This reprint focuses on recent aspects of gravitational theory and cosmology. It contains subjects of particular interest for modified gravity theories and applications to cosmology, special attention is given to Einstein–Gauss–Bonnet, f(R)-gravity, anisotropic inflation, extra dimension theories of gravity, black holes, dark energy, Palatini gravity, anisotropic spacetime, Einstein–Finsler gravity, off-diagonal cosmological solutions, Hawking-temperature and scalar-tensor-vector theories

    Numerical modelling of subglacial ribs, drumlins, herringbones, and mega-scale glacial lineations reveals their developmental trajectories and transitions

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    Initially a matter of intellectual curiosity, but now important for understanding ice-sheet dynamics, the formation of subglacial bedforms has been a subject of scientific enquiry for over a century. Here, we use a numerical model of the coupled flow of ice, water, and subglacial sediment to explore the formation of subglacial ribs (i.e., ribbed moraine), drumlins and mega-scale glacial lineations (MSGLs). The model produces instabilities at the ice–bed interface, which result in landforms resembling subglacial ribs and drumlins. We find that a behavioural trajectory is present. Initially subglacial ribs form, which can either develop into fields of organized drumlins, or herringbone-type structures misaligned with ice flow. We present potential examples of these misaligned bedforms in deglaciated landscapes, the presence of which means caution should be taken when interpreting cross-cutting bedforms to reconstruct ice flow directions. Under unvarying ice flow parameters, MSGLs failed to appear in our experiments. However, drumlin fields can elongate into MSGLs in our model if low ice–bed coupling conditions are imposed. The conditions under which drumlins elongate into MSGLs are analogous to those found beneath contemporary ice streams, providing the first mechanism, rather than just an association, for linking MSGLs with ice stream flow. We conclude that the instability theory, as realized in this numerical model, is sufficient to explain the fundamental mechanics and process-interactions that lead to the initiation of subglacial bedforms, the development of the distinctive types of bedform patterns, and their evolutionary trajectories. We therefore suggest that the first part of the longstanding ‘drumlin problem’ – how and why they come into existence – is now solved. However, much remains to be discovered regarding the exact sedimentary and hydrological processes involved

    Non-equilibrium wall-bounded turbulence and associated noise generation

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    Abstract : The present study investigates the response of turbulence in a non-equilibrium flows such as transient periodic channel flows and spatially developing boundary layers subjected to pressure gradients. Such a fundamental study is important to understand noise generation in complex wall-bounded turbulent flows. First, to understand the flow dynamics in transient accelerating flows, direct numerical simulations (DNS) of periodic channel flows responding to an impulse acceleration are carried out. The turbulent flow undergoes reverse transition toward a quasi-laminar state, followed by a retransition phase to the new equilibrium state. To reduced simulation cost, the minimal-span methodology is applied and evaluated for simulations of transient flows. Detailed comparisons with a full-span case show that the small-span test case captures the essential dynamics during the transition process despite small, quantitative differences attributed to a slower streak transient growth. A small span is used to characterize accelerating channels with riblets. Results indicate that riblets delay the transition to high Reynolds number state, as it reduces streak meandering. Next, to study non-equilibrium boundary layer flows in the presence of convex wall curvature, DNS simulations over an airfoil (suction side) and a flat plate are compared. Both cases are characterized by matching adverse pressure gradient (APG) along the streamwise direction. For the airfoil boundary layer, existing DNS data obtained by \cite{wu2019effects} of flow around a controlled-diffusion (CD) airfoil is used. For the flat-plate boundary layer, a DNS simulation is carried out, with prescribed pressure gradient distribution that matches that of the airfoil flows in the APG region. Comparison between the two cases shows how the wall curvature affects turbulence in an APG boundary layer, important in industrial applications such as fan flows. Overall, the comparison shows that the boundary layer developments are very similar. This indicates that a flat-plate boundary layer can serve as a low-cost surrogate of an airfoil boundary layer in numerical studies of important features of an airfoil flow. The difference between the two cases represents the effect of a mild convex wall curvature. Specifically, in the region of weak APG, the curvature effect dominates that of the pressure gradient and yields a lower friction coefficient. In high-APG regions (near the trailing edge of the airfoil) the effects of wall curvature and APG appear to interact. Lastly, various existing analytical models are evaluated on their predictions of wall pressure fluctuations, which are essential for noise prediction in non-equilibrium boundary layer turbulent flows that develop on fan blades. Limitations of the existing models are evaluated; new parameters that do not involve the ill-defined wall friction in a boundary layer under strong adverse pressure gradients are proposed. The primary role of the mean velocity logarithmic layer in affecting the overlap range of the wall pressure spectrum is also demonstrated. A new wall pressure spectrum model is proposed and tested in a wide range of boundary layer flows under different Reynolds numbers and zero, adverse and favorable pressure gradients. The test database includes existing experimental data and various DNS flat-plate simulations. The new wall pressure spectrum model is the first generalized model designed for boundary layer flows with a wide range of pressure gradients and Reynolds numbers.Ce mémoire étudie la réponse de la turbulence dans des écoulements hors équilibre, tels que les écoulements transitoires dans un canal périodique et les couches limites se développant spatiallement soumises à des gradients de pression. Une telle étude fondamentale est importante pour comprendre la génération du bruit dans des écoulements complexes turbulents. Premièrement, pour comprendre la dynamique d’écoulements transitoires soumis à une accélération, des simulations directes d’écoulements instationnaires dans un canal périodique soumis à une accélération impulsionnelle ont été réalisées. L’écoulement turbulent subit une transition inversée vers un état quasi-laminaire, suivi par une nouvelle phase de transition vers un nouvel équilibre. Pour réduire le coût de calcul, la méthode de l’envergure minimale du domaine de calcul est appliquée et validée pour de telles simulations instationnaires. Des comparaisons détaillées avec un cas d’envergure complète montrent que la simulation avec une envergure minimale capture l’essentiel de la dynamique de l’écoulement durant la phase de transition et ce malgré quelques petites différences attribuées à la croissance plus lente des tourbillons longitudinaux le long de la paroi (“streaks”). Une envergure réduite est ensuite appliquée à l’étude d’un écoulement accéléré dans un canal avec de micro-sillons ou “riblets”. Les résultats montrent que les riblets retardent la transition du fait qu’ils stabilisent la turbulence de proche paroi. Deuxièmement, pour étudier les couches limites hors équilibre sur une paroi convexe, des simulations directes sur l’extrados d’un profil aérodynamique et d’une plaque plane sont comparées. Les deux cas sont caractérisés par le même gradient de pression adverse dans la direction de l’écoulement. Pour la couche limite sur le profil, on utilise les données existantes de la simulation directe de Wu et al. (2019) autour du profil à diffusion controllée (CD). Pour la couche limite sur la plaque plane, une nouvelle simulation directe a été réalisée avec le même gradient de pression adverse que sur le profil. La comparaison des deux cas montre que la courbure de la paroi convexe peut modifier la turbulence dans une couche limite soumise à un gradient de pression adverse qui est important dans les applications industrielles comme les écoulements dans des ventilateurs. Cependant les modifications restent mineures et la comparaison montre que le développement des couches limite turbulentes dans les deux cas est semblable. Ceci implique que la couche limite sur une plaque plaque sur un domaine réduit peut servir de substitut à celle sur un profil aérodynamique qui requiert un domaine plus grand et des ressources de calcul plus importante. La différence observée entre les deux cas permet d’évaluer l’effet d’une paroi faiblement convexe. Spécifiquement, dans la région de faible gradient de pression adverse, les effets de courbure dominent ceux du gradient de pression et réduisent le coefficient de frottement pariétal. Dans les zones de fort gradient de pression adverse, près du bord de fuite, les effets de gradient de pression et de courbure interagissent. Finalement, la dernière étape a été d’évaluer les différents modèles analytiques de fluctuations de pression pariétale qui sont au centre des prédictions de bruit dans les couches limites turbulentes hors équilibre qui se développent sur les pales de ventilateurs. Les limites des modèles précédents sont évaluées et de nouveaux paramètres ne faisant pas intervenir le frottement pariétal mal défini dans une couche limite à fort gradient de pression adverse sont proposés. Le rôle primordial de la zone logarithmique dans la couche limite turbulente sur le gabarit spectral des spectres de pression pariétale est aussi mis en évidence. Le nou veau modèle de spectre de pression pariétale est ensuite testé sur plusieurs couches limites attachées avec des gradients de pression favorables, adverses, et des écoulements décollés à divers nombres de Reynolds basés sur l’épaisseur de quantité de mouvement. Les données proviennent de bases de données expérimentales et numériques existantes. Des simulations directes supplémentaires ont également été réalisées pour étendre les résultats numériques (notamment sur le profil CD) à des nombres de Reynolds plus élevés. Pour la première fois, un modèle est capable de reproduire les spectres de pression pariétale pour tous ces types d’écoulement

    Exploring QCD matter in extreme conditions with Machine Learning

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    In recent years, machine learning has emerged as a powerful computational tool and novel problem-solving perspective for physics, offering new avenues for studying strongly interacting QCD matter properties under extreme conditions. This review article aims to provide an overview of the current state of this intersection of fields, focusing on the application of machine learning to theoretical studies in high energy nuclear physics. It covers diverse aspects, including heavy ion collisions, lattice field theory, and neutron stars, and discuss how machine learning can be used to explore and facilitate the physics goals of understanding QCD matter. The review also provides a commonality overview from a methodology perspective, from data-driven perspective to physics-driven perspective. We conclude by discussing the challenges and future prospects of machine learning applications in high energy nuclear physics, also underscoring the importance of incorporating physics priors into the purely data-driven learning toolbox. This review highlights the critical role of machine learning as a valuable computational paradigm for advancing physics exploration in high energy nuclear physics.Comment: 146 pages,53 figure
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