20 research outputs found

    PROCEEDINGS 5th PLATE Conference

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    The 5th international PLATE conference (Product Lifetimes and the Environment) addressed product lifetimes in the context of sustainability. The PLATE conference, which has been running since 2015, has successfully been able to establish a solid network of researchers around its core theme. The topic has come to the forefront of current (political, scientific & societal) debates due to its interconnectedness with a number of recent prominent movements, such as the circular economy, eco-design and collaborative consumption. For the 2023 edition of the conference, we encouraged researchers to propose how to extend, widen or critically re-construct thematic sessions for the PLATE conference, and the paper call was constructed based on these proposals. In this 5th PLATE conference, we had 171 paper presentations and 238 participants from 14 different countries. Beside of paper sessions we organized workshops and REPAIR exhibitions

    Advanced interface modelling for 2D shell & 3D continuum problems

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    This work is motivated by the need for an efficient yet accurate approach for static and dynamic contact analysis of large-scale structures which can a) capture the optimum con- tact position with a moderate number of contact elements, and b) enable across-partition adaptive contact analysis within a parallel processing environment. In addressing these two issues, a novel adaptive node-to-surface contact approach is proposed to discretise the contact boundaries and to trace the evolution of contact locations. Contact search is a demanding process that can become quite complicated for certain types of problem. In this work, an efficient and robust contact search method is proposed, which can a) locally track the master facet of a given slave node despite the appearance of highly non-smooth contact surface, including surfaces with concave/convex regions or with distinct boundaries as well as reversible normals, and b) globally reallocate the master-slave contact pairs based on the penetration state without an expensive global search, providing an effective adaptive contact approach. A dual-interface-based domain decomposition method emphasising across-partition con- tact coupling is proposed. A pair of fully decomposed node-to-surface contact element are proposed to discretise the across-partition contact boundaries. The assumption of small incremental displacements is adopted, which a) avoids the excessive coupling between the decomposed master and slave, b) reduces significantly the communication overhead, and c) facilitates a flexible across-partition adaptive analysis. This strategy is found to provide good results for a sufficiently small time- or load-step, and it also facilitates mix-dimensional contact simulation. Another interest in current thesis is the inaccuracy in non-smooth plates modelled us- ing 2D displacement-based shell elements. In this work the dominant factor causing the inaccuracy is recognised as the incompatible tangential rotations on the two sides of the in- tersection. A 3-noded coupling element is introduced to impose a continuous constraint to couple the incompatible rotations. The significance of the discontinuity in the shell-based folded structure and the effectiveness of the coupling element is demonstrated through numerical studies comparing shell-based models to high fidelity solid-based models.Open Acces

    High-performance computing for impact-induced fracture analysis exploiting octree mesh patterns

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    The impact-induced fracture analysis has a wide range of engineering and defence applications, including aerospace, manufacturing and construction. An accurate simulation of impact events often requires modelling large-scale complex geometries along with dynamic stress waves and damage propagation. To perform such simulations in a timely manner, a highly efficient and scalable computational framework is necessary. This thesis aims to develop a high-performance computational framework for analysing large-scale structural problems pertaining to impact-induced fracture events. A hierarchical grid-based mesh containing octree cells is utilised for discretising the problem domain. The scaled boundary finite element method (SBFEM) is employed, which can efficiently handle the octree cells by eliminating the hanging node issues. The octree-mesh is used in balanced form with a limited number of octree cell patterns. The master element matrices of each pattern are pre-computed while the storage of the individual element matrices is avoided leading to a significant reduction in memory requirements, especially for large-scale models. Further, the advantages of octree cells are leveraged by automatic mesh generation and local refinement process, which enables efficient pre-processing of models with complex geometries. To handle the matrix operations associated with large-scale simulation, a pattern-by-pattern (PBP) approach is proposed. In this technique, the octree-patterns are exploited to recast a majority of the computational work into pattern-level dense matrix operations. This avoids global matrix assembly, allows better cache utilisation, and aids the associated memory-bandwidth limited computations, resulting in significant performance gains in matrix operations. The PBP approach also supports large-scale parallelism. In this work, the parallel computation is carried out using the mesh-partitioning strategy and implemented using the message passing technique. It is shown that the developed solvers can simulate large-scale and complex structural problems, e.g. delamination/fracture in sandwich panels with approximately a billion unknowns (or DOFs). A massive scaling can be achieved with more than ten thousand cores in a distributed computing environment, which reduces the computation time from months (on a single core) to a few minutes

    Non degenerate anisotropic green's function for 3D magneto-electro-elasticity and bem shape sensitivity framework for 3D contact in anisotropic elasticity

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    The first part of the thesis presents a new expression for the magneto electro elastic (MEE) fundamental solution which is explicit in terms of the Stroh’s eigenvalues, remains welldefined for repeated Stroh’s eigenvalues and is exact. We then define a fast and robust numerical scheme to evaluate the function and its derivatives based on a double Fourier series representation. These newly developed expressions allow to compute the Fourier coefficients for any material symmetry or anisotropy, and is done only once for a given material. One evaluates the Green’s function and its derivatives through simple trigonometric formulas. Several results are presented for elastic, piezoelectric/piezomagnetic and magneto-eletro-elastic materials. The second part of the thesis provides a BEM-based formulation for shape sensitivity analysis of anisotropic elastic media, also including contact conditions, and based on the newly presented Green’s functions. The parameter sensitivity is evaluated using the complex step (CS) method: An approach similar to finite differentiation (FD), with the advantage of being step-size independent, therefore an extremely robust method. A convergence study on shape sensitivity is provided, proving the efficiency of the CS-BEM approach. We solve Hertz and non-Hertzian type contact problems as well as an application example of a dovetail joint found in gas turbines. We analyzed several parmeter sensitivities to shape variation, such as contact pressure, shear stress, as well as Von Mises stress, for both isotropic and anisotropic materials. The results showed good agreement with analytical solutions, as well as other works from the literature. In comparison with FD, which did not converged for an example case, the CS method showed excellent stability and precision for a broad range of step sizes.A primeira parte da tese apresenta uma nova expressão para a solução fundamental Magneto-Eletro-Elástica explícita em termos de autovalores de Stroh, bem definida para autovalores repetidos, e exata. Em seguida, uma série de Fourier dupla é utilizada como uma forma rápida e robusta para avaliar a solução fundamental e as suas derivadas. As expressões recém-desenvolvidas permitem calcular os coeficientes de Fourier para qualquer simetria ou anisotropia de material, o que é feito apenas uma vez para um dado material. Diversos resultados são apresentados para materiais elásticos, piezoelétricos e magneto-eletro-elásticos. A segunda parte desta tese apresenta uma formulação completa para análise de sensibilidade em estruturas elasticas anisotrópicas baseada nestas funções de Green recém apresentadas, incluindo condições de contato. A sensibilidade à parâmetros é avaliada utilizando o método do incremento complexo, método extremamente robusto, similar a diferenciação finita (FD), mas independente do tamanho do incremento. Problemas de contato de Hertz e não Hertzianos foram resolvidos, assim como um estudo de aplicação de uma palheta de turbinas a gás. Foi avaliada a sensibilidade à variação de forma das tensões de contato, tensões cisalhantes máximas e também nas tensões equivalentes de Von Mises, em diferentes materiais anisotrópicos. Os resultados mostraram boa correlação com soluções analíticas assim como em outros trabalhos da literatura. Quando comparado com FD, que não obteve convergência em um dos exemplos, o método CS demonstrou excelente estabilidade e precisão para uma larga faixa de tamanhos de incremento

    A parallel algorithm for deformable contact problems

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    In the field of nonlinear computational solid mechanics, contact problems deal with the deformation of separate bodies which interact when they come in touch. Usually, these problems are formulated as constrained minimization problems which may be solved using optimization techniques such as penalty method, Lagrange multipliers, Augmented Lagrangian method, etc. This classical approach is based on node connectivities between the contacting bodies. These connectivities are created through the construction of contact elements introduced for the discretization of the contact interface, which incorporate the contact constraints in the global weak form. These methods are well known and widely used in the resolution of contact problems in engineering and science. As parallel computing platforms are nowadays widely available, solving large engineering problems on high performance computers is a real possibility for any engineer or researcher. Due to the memory and compute power that contact problems require and consume, they are good candidates for parallel computation. Industrial and scientific realistic contact problems involve different physical domains and a large number of degrees of freedom, so algorithms designed to run efficiently in high performance computers are needed. Nevertheless, the parallelization of the numerical solution methods that arises from the classical optimization techniques and discretization approaches presents some drawbacks which must be considered. Mainly, for general contact cases where sliding occurs, the introduction of contact elements requires the update of the mesh graph in a fixed number of time steps. From the point of view of the domain decomposition method for parallel resolution of numerical problems this is a major drawback due to its computational expensiveness, since dynamic repartitioning must be done to redistribute the updated mesh graph to the different processors. On the other hand, some of the optimization techniques modify dynamically the number of degrees of freedom in the problem, by introducing Lagrange multipliers as unknowns. In this work we introduce a Dirichlet-Neumann type parallel algorithm for the numerical solution of nonlinear frictional contact problems, putting a strong focus on its computational implementation. Among its main characteristics it can be highlighted that there is no need to update the mesh graph during the simulation, as no contact elements are used. Also, no additional degrees of freedom are introduced into the system, since no Lagrange multipliers are required. In this algorithm the bodies in contact are treated separately, in a segregated way. The coupling between the contacting bodies is performed through boundary conditions transfer at the contact zone. From a computational point of view, this feature allows to use a multi-code approach. Furthermore, the algorithm can be interpreted as a black-box method as it solves each body separately even with different computational codes. In addition, the contact algorithm proposed in this thesis can also be formulated as a general fixed-point solver for the solution of interface problems. This generalization gives us the theoretical basis to extrapolate and implement numerical techniques that were already developed and widely tested in the field of fluid-structure interaction (FSI) problems, especially those related to convergence ensurance and acceleration. We describe the parallel implementation of the proposed algorithm and analyze its parallel behaviour and performance in both validation and realistic test cases executed in HPC machines using several processors.En el ámbito de la mecánica de contacto computacional, los problemas de contacto tratan con la deformación que sufren cuerpos separados cuando interactúan entre ellos. Comunmente, estos problemas son formulados como problemas de minimización con restricciones, que pueden ser resueltos utilizando técnicas de optimización como la penalización, los multiplicadores de Lagrange, el Lagrangiano Aumentado, etc. Este enfoque clásico está basado en la conectividad de nodos entre los cuerpos, que se realiza a través de la construcción de los elementos de contacto que surgen de la discretización de la interfaz. Estos elementos incorporan las restricciones de contacto en forma débil. Debido al consumo de memoria y a los requerimientos de potencia de cálculo que los problemas de contacto requieren, resultan ser muy buenos candidatos para su paralelización computacional. Sin embargo, tanto la paralelización de los métodos numéricos que surgen de las técnicas clásicas de optimización como los distintos enfoques para su discretización, presentan algunas desventajas que deben ser consideradas. Por un lado, el principal problema aparece ya que en los casos más generales de la mecánica de contacto ocurre un deslizamiento entre cuerpos. Por este motivo, la introducción de los elementos de contacto vuelve necesaria una actualización del grafo de la malla cada cierto número de pasos de tiempo. Desde el punto de vista del método de descomposición de dominios utilizado en la resolución paralela de problemas numéricos, esto es una gran desventaja debidoa su coste computacional. En estos casos, un reparticionamiento dinámico debe ser realizado para redistribuir el grafo actualizado de la malla entre los diferentes procesadores. Por otro lado, algunas técnicas de optimización modifican dinámicamente el número de grados de libertad del problema al introducir multiplicadores de Lagrange como incógnitas. En este trabajo presentamos un algoritmo paralelo del tipo Dirichlet-Neumann para la resolución numérica de problemas de contacto no lineales con fricción, poniendo un especial énfasis en su implementación computacional. Entre sus principales características se puede destacar que no hay necesidad de actualizar el grafo de la malla durante la simulación, ya que en este algoritmo no se utilizan elementos de contacto. Adicionalmente, ningún grado de libertad extra es introducido al sistema, ya que los multiplicadores de Lagrange no son requeridos. En este algoritmo los cuerpos en contacto son tratados de forma separada, de una manera segregada. El acople entre estos cuerpos es realizado a través del intercambio de condiciones de contorno en la interfaz de contacto. Desde un punto de vista computacional, esta característica permite el uso de un enfoque multi-código. Además, este algoritmo puede ser interpretado como un método del tipo black-box ya que permite resolver cada cuerpo por separado, aún utilizando distintos códigos computacionales. Adicionalmente, el algoritmo de contacto propuesto en esta tesis puede ser formulado como un esquema de resolución de punto fijo, empleado de forma general en la solución de problemas de interfaz. Esta generalización permite extrapolar técnicas numéricas ya utilizadas en los problemas de interacción fluido-estructura e implementarlas en la mecánica de contacto, en especial aquellas relacionadas con el aseguramiento y aceleración de la convergencia. En este trabajo describimos la implementación paralela del algoritmo propuesto y analizamos su comportamiento y performance paralela tanto en casos de validación como reales, ejecutados en computadores de alta performance utilizando varios procesadores.Postprint (published version

    Méthode locale de type mortar pour le contact dans le cas de maillages incompatibles de degré élevé

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    In this thesis, we develop a local "mortar" kind method to deal with the problem of contact with non-matching meshes in an optimal way into a finite element code of industrial level. In the first part of the thesis, we introduce the mathematical framework of the Local Average Contact method (LAC). This approach consists in satisfying the non-interpenetration condition in average on each element of a macro-mesh defined in a suitable way. We start by developing a new technique for proving the optimality of variational inequality approaches discretized by finite elements modeling Signorini problem without other hypothesis than the Sobolev regularity of the solution of the continuous problem. Then we define the LAC method and prove, using the new technical tools, the optimality of this local approach modeling the unilateral contact in the general case of non-matching meshes. Finally, we introduce the equivalent mixed formulation and prove its optimality and stability. In the second part of the thesis, we are interested in the numerical study of the LAC method. We confirm its ability to optimally treat the contact problem when considering non-matching meshes like standard "mortar" methods, while remaining easily implementable in an industrial finite element code. We show, for example, that the method successfully passes the Taylor patch test. Finally, we show its contribution in terms of robustness and at the quality of the contact pressures on an industrial study.Dans cette thèse, nous développons une méthode locale de type "mortar" pour traiter le problème de contact avec maillages incompatibles de manière optimale dans un code de calcul par éléments finis de niveau industriel. Dans la première partie de la thèse, nous introduisons le cadre mathématique de la méthode intitulée "Local Average Contact" (LAC). Cette approche consiste à imposer la condition de non-interpénétration en moyenne sur chaque élément d'un macro-maillage défini de manière idoine. Nous commençons par développer une nouvelle technique de preuve pour démontrer l'optimalité des approches de type inéquation variationnelle discrétisée par éléments finis standards pour le problème de Signorini, sans hypothèse autre que la régularité Sobolev de la solution du problème continu. Puis nous définissons la méthode LAC et démontrons, à l'aide des nouveaux outils techniques, l'optimalité de cette approche locale modélisant le contact unilatéral dans le cas général des maillages incompatibles. Pour finir, nous introduisons la formulation mixte équivalente et démontrons son optimalité et sa stabilité. Dans la seconde partie de la thèse, nous nous intéressons à l'étude numérique de la méthode LAC. Nous confirmons sa capacité à gérer numériquement le contact unilatéral avec maillages incompatibles de manière optimale à l'instar des méthodes "mortar" classiques, tout en restant facilement implémentable dans un code de calcul industriel. On montre ainsi, entre autres, que la méthode passe avec succès le patch test de Taylor. Finalement, nous montrons son apport en terme de robustesse et au niveau de la qualité des pressions de contact sur une étude de type industrielle

    Числове дослідження задач про контакт трьох пружних тіл методами декомпозиції області

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    Досліджено методи декомпозиції області для числового розв’язування задач про односторонній контакт без тертя багатьох пружних тіл скінченних розмірів. З використанням скінченноелементних апроксимацій розв’язано задачі про односторонній контакт трьох пружних тіл, обтиснених жорсткими плитами, та контакт трьох закріплених тіл, одне з яких перебуває під дією зовнішнього навантаження. Вивчено розподіли нормальних контактних та еквівалентних напружень у тілах.Исследованы методы декомпозиции области для численного решения задач об одностороннем контакте без трения многих упругих тел конечных размеров. С использованием конечноэлементных аппроксимаций решены задачи об одностороннем контакте трех упругих тел, сжатых жесткими плитами, и контакте трех закрепленных тел, на одно из которых действует внешняя нагрузка. Изучено распределение нормальных контактных и эквивалентных напряжений в телах.The domain decomposition methods for the numerical solution of frictionless unilateral multibody contact problems of elasticity are investigated. The unilateral contact problem of three elastic bodies, which are contracted by rigid plates, and the contact problem of three fixed bodies, one of which is uniformly loaded by constant external load, are solved with the use of finite element approximations. The distributions of normal contact stresses and equivalent body stresses are studied

    Towards a more efficient spectrum usage: spectrum sensing and cognitive radio techniques

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    The traditional approach of dealing with spectrum management in wireless communications has been through the definition on a license user granted exclusive exploitation rights for a specific frequency.Peer ReviewedPostprint (published version

    IMA2010 : Acta Mineralogica-Petrographica : abstract series 6.

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