Thematische Bibliographien / Spectral element modelling

Inhaltsverzeichnis

  1. Zeitschriftenartikel
  2. Dissertationen
  3. Buchteile
  4. Konferenzberichte

Auswahl der wissenschaftlichen Literatur zum Thema „Spectral element modelling“

Autor: Grafiati
Veröffentlicht am 25. Mai 2024

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Zeitschriftenartikel zum Thema "Spectral element modelling"

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Seriani, G. „3-D spectral element-by-element wave modelling on Cray T3E“. Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy 24, Nr. 3 (Januar 1999): 241–45. http://dx.doi.org/10.1016/s1464-1895(99)00025-3.

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Griffith, M. D., K. Hourigan und M. C. Thompson. „Modelling blockage effects using a spectral element method“. ANZIAM Journal 46 (21.04.2005): 167. http://dx.doi.org/10.21914/anziamj.v46i0.954.

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Fiborek, Piotr, Paweł H. Malinowski, Paweł Kudela, Tomasz Wandowski und Wiesław M. Ostachowicz. „Time-domain spectral element method for modelling of the electromechanical impedance of disbonded composites“. Journal of Intelligent Material Systems and Structures 29, Nr. 16 (27.02.2018): 3214–21. http://dx.doi.org/10.1177/1045389x18758193.

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The research focuses on the electromechanical impedance method. The electromechanical impedance method can be treated as non-destructive testing or structural health monitoring approach. It is important to have a reliable tool that allows verifying the integrity of the investigated objects. The electromechanical impedance method was applied here to assess the carbon fibre–reinforced polymer samples. The single and adhesively bonded samples were investigated. In the reported research, the electromechanical impedance spectra up to 5 MHz were considered. The investigation comprised of modelling using spectral element method and experimental measurements. Numerical and experimental spectra were analysed. Differences in spectra caused by differences in considered samples were observed.
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Grabowska, Joanna, und Marek Krawczuk. „Identification of Discontinuities in Composite Rods and Beams Based on Lamb Wave Propagation“. Key Engineering Materials 293-294 (September 2005): 517–24. http://dx.doi.org/10.4028/www.scientific.net/kem.293-294.517.

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The article presents a method of damage identification in composite rods and beams based on the analysis of changes in Lamb wave propagation. For modelling of the problem the spectral element method is used. Spectral elements of rod and beam suitable for modelling the composites are employed. In the presented paper the following discontinuities are analysed: the fatigue open and not propagating crack, changes in the cross-section area, material discontinuities, various fibres volume and angle. The influence of discontinuities on the Lamb wave propagation processes is analysed.
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Kudela, Pawel, und Wiesław M. Ostachowicz. „Wave Propagation Modelling in Composite Plates“. Applied Mechanics and Materials 9 (Oktober 2007): 89–104. http://dx.doi.org/10.4028/www.scientific.net/amm.9.89.

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The paper presents results of numerical simulation for transverse elastic waves corresponding to A0 mode of Lamb waves propagating in a composite plate. This problem is solved by using the Spectral Finite Element Method. Spectral plate elements with 36 nodes defined at Gauss-Lobatto-Legendre points are used. As a consequence of selecting Lagrange polynomials discrete orthogonality guaranteed leading to a diagonal mass matrix. This results in a crucial reduction of numerical operations required for a chosen time integration scheme. Numerical calculations have been carried out for various orientations of reinforcing fibres within the plate as well as for various fibre volumes fractions. The paper shows that the velocities of transverse elastic waves in composite materials are functions of the fibre orientation and the fibre volume fraction.
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Schulte, Rolf T., Ke Jia Xing und Claus Peter Fritzen. „Spectral Element Modelling of Wave Propagation and Impedance Based SHM Systems“. Key Engineering Materials 413-414 (Juni 2009): 683–90. http://dx.doi.org/10.4028/www.scientific.net/kem.413-414.683.

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In recent years many SHM approaches based on elastic waves that are generated and sensed by surface-bonded piezoelectric patches have been developed. Some of those utilize wave propagation phenomena; others use changes in the electromechanical impedance to detect structural damage. The capability of most approaches strongly depends on adequate choice of SHM system parameters like excitation signals and actuator/sensor types and positions. For this reason there is a growing interest in efficient and accurate simulation tools to shorten time and cost of the necessary tedious pretests. To detect small damage generally high frequency excitation signals have to be used. Because of this a very dense finite element mesh is required for an accurate simulation. As a consequence a conventional finite element simulation becomes computationally inefficient. A new approach that seems to be more promising is the time domain spectral element method. This contribution presents the theoretical background and some results of numerical calculations of the propagation of waves. The simulation is performed using the spectral element method (SEM), which leads to a diagonal mass matrix. Besides a significant saving of memory this leads to a crucial reduction of complexity of the time integration algorithm for the wave propagation calculation. A new approach to simulate the E/M impedance using time domain spectral elements is shown. An example demonstrates a good correlation of simulation and measurement data, so that the proposed simulation methodology seems to be a promising tool to make impedance based SHM systems more efficient, especially regarding the necessary parameter studies.
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von Winckel, G., S. Krishna und E. A. Coutsias. „Spectral element modeling of semiconductor heterostructures“. Mathematical and Computer Modelling 43, Nr. 5-6 (März 2006): 582–91. http://dx.doi.org/10.1016/j.mcm.2005.05.028.

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Kirby, Robert M., und Spencer J. Sherwin. „Stabilisation of spectral/hp element methods through spectral vanishing viscosity: Application to fluid mechanics modelling“. Computer Methods in Applied Mechanics and Engineering 195, Nr. 23-24 (April 2006): 3128–44. http://dx.doi.org/10.1016/j.cma.2004.09.019.

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9

Żak, A., und M. Krawczuk. „Assessment of rod behaviour theories used in spectral finite element modelling“. Journal of Sound and Vibration 329, Nr. 11 (Mai 2010): 2099–113. http://dx.doi.org/10.1016/j.jsv.2009.12.019.

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10

Eskilsson, C., und S. J. Sherwin. „Discontinuous Galerkin Spectral/hp Element Modelling of Dispersive Shallow Water Systems“. Journal of Scientific Computing 22-23, Nr. 1-3 (Juni 2005): 269–88. http://dx.doi.org/10.1007/s10915-004-4140-x.

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Dissertationen zum Thema "Spectral element modelling"

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Adam, Alexandros. „Finite element, adaptive spectral wave modelling“. Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/45307.

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The ability to predict the wave climate has a great impact on a wide range of sectors, including coastal and offshore engineering, marine renewable energy and shipping. The state of the art in wave prediction is called spectral wave modelling and is based on a phase-averaged, spectral description of the sea-surface elevation. The governing equation, called the action balance equation, is five-dimensional and describes the generation, propagation and evolution of action density in geographic space, spectral space and time. Due to the multidimensional nature of the equation the feasible resolutions are restricted by the computational costs. The aim of this work is to propose schemes which can increase the range of possible resolutions in spectral wave modelling, with the use of adaptivity in space and angle. Thus, this work focuses on the development of an unstructured, adaptive finite element spectral wave model (Fluidity-SW). A sub-grid scale model for the spatial discretisation is used, which retains the stability of discontinuous systems, with continuous degrees of freedom. Then, a new framework for angular adaptivity is developed, with results in dynamic angular and spatial anisotropy of the angular mesh. Finally a spatially h−adaptive scheme is implemented, which can dynamically treat the spatial gradients of the solution fields. The resulting framework is thoroughly verified and validated in a wide range of test cases and realistic scenarios, against analytical solutions, wave measurements and the results obtained with the widely used SWAN model. Thus, the overall ability of the code to simulate surface gravity wind-waves in fixed and adaptive spatial and angular meshes is demonstrated.
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Schulte, Rolf T. [Verfasser]. „Modellierung und Simulation von wellenbasierten Structural-Health-Monitoring-Systemen mit der Spektral-Elemente-Methode. Modelling and simulation of wave-based structural health monitoring-systems using the spectral element method / Rolf T. Schulte“. Siegen : Universitätsbibliothek Siegen, 2011. http://d-nb.info/1010297430/34.

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Conceição, Sanderson Manoel da. „Estudo de modelos espectrais de vigas para controle ativo de vibrações e monitoramento da integridade estrutural“. Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/154934.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A ideia central deste trabalho é utilizar o método dos Elementos Espectrais (SEM, do inglês Spectral Element Method) para aplicações de controle ativo de vibrações e monitoramento da integridade estrutural (SHM, do inglês Structural Health Monitoring). Diversos trabalhos têm abordado estes tópicos de forma independente. No entanto, para aplicações reais de engenharia, utilizar os mesmos atuadores, sensores e sistemas de aquisição de dados para controle e monitoramento pode reduzir investimentos e simplificar processos. Por esta motivação, este trabalho apresenta um estudo de modelos espectrais para estruturas do tipo viga considerando aplicações de controle de vibrações e monitoramento da integridade estrutural. Na modelagem são considerados os modelos de vigas de Euler-Bernoulli e Timoshenko, além de transdutores piezelétricos acoplados. A técnica de controle clássico PID (Proporcional, Integral, Derivativo) é explorada e uma nova modelagem é proposta para se considerar técnicas modernas de controle por realimentação de estados na formulação espectral. Em particular, discute-se o controlador LQR (do inglês, Linear Quadratic Regulator), no entanto, a metodologia permite se considerar outras técnicas de controle por realimentação baseada na representação no espaço de estados. Também, especificamente para monitoramento estrutural, no presente trabalho de tese apresenta-se uma discussão sobre índices de detecção de danos. Índices de detecção calculados a partir de sinais experimentais têm sido amplamente utilizados em trabalhos da literatura de SHM. No entanto, pouco tem sido esclarecido sobre seus comportamentos em função das características estruturais e dos danos. Neste sentido, o presente trabalho apresenta uma discussão do comportamento de índices baseados na norma H2, norma H∞ e no CCDM (Correlation coefficient deviation metric), para duas faixas de frequência, em função da severidade do dano e quantidade de amortecimento no sistema. Os resultados obtidos indicam que a formulação por Elementos Espectrais é adequada para viabilizar os projetos simultâneos de um controlador de vibrações e um sistema de monitoramento estrutural utilizando os mesmos equipamentos e simplificando análises ao se utilizar um único modelo dinâmico do sistema.
The main idea of this thesis is to use the Spectral Element Method (SEM), in applications of Active Vibration Control (AVC) and Structural Health Monitoring (SHM). These two topics have been approached in several works, but in an independent way. However, for real engineering applications, to use the same actuators, sensors and data acquisition systems to active control and structural monitoring can reduce the costs and simplify processes. For this reason, this thesis presents a study of spectral models for beam-like structures considering applications of vibration control and structural health monitoring. The Euler-Bernoulli and Timoshenko beam theories are used in the spectral modelling and the piezelectric transducers bonded in the structures are also considered. A classical control technique, PID (Proportional, Integral, Derivative) is explored and a new modelling approach to consider modern control methods of state feedback is proposed in spectral formulation. In particular, the Linear Quadratic Regulator (LQR) is discussed, however, this methodology allows for any other state feedback control techniques based in state space representation. Also, specifically for structural monitoring, is presented a discussion about damage detection indices. Detection indices computed from experimental data have been widely used in SHM studies. However, little has been clarified about their behaviours due to structural characteristics and damages. In this context, this work presents a discussion of the behaviour of indices based in the H2 norm, H∞ norm and CCDM (Correlation coefficient deviation metric), for two frequency ranges, depending on the severity of damage and amount of damping in the system. The obtained results indicate that the spectral element formulation is suited to enable the simultaneous design of a vibration controller and a structural monitoring system using the same data acquisition systems and simplifying analysis when using just one dynamic model of the system.
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Naeem, Qazi Sulaiman. „Finite element modelling and response spectrum snalysis of Rubble-Stone Masonry Buildings“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23767/.

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Finite element modelling is an efficient tool for the performance assessment of masonry structures. In particular, it facilitates the accurate prediction of the seismic response of a structure to earthquakes using dynamic analysis procedures. Numerical models using response spectrum analysis based on modal analysis allow to predict realistic failure modes observed after preceding seismic events with reasonable computational effort, a characteristic which is suitable for engineering practice. This thesis deals with modelling as a finite element model and analyse using response spectrum analysis of masonry buildings and the subsequent discussion of the obtained results. SAP2000 software is used for developing the numerical models, which are then analysed on the basis of design acceleration response spectra obtained according to the different building codes for different regions. Different structural demands under static and dynamic loading are obtained from the models and compared with theoretical results made with various mathematical models.
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El, khoury Christine. „Seismic ambient noise amplitude anomalies induced by an anticline structure : application to the context of gas reservoirs“. Electronic Thesis or Diss., Université Paris sciences et lettres, 2022. http://www.theses.fr/2022UPSLM100.

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Des anomalies spectrales dans le bruit sismique ambiant, définies comme de fortes amplifications spectrales de la composante verticale pour des fréquences de 1 à 5 Hz, sont couramment observées au droit de réservoirs de gaz. Si elles sont bien comprises, ces anomalies pourraient avoir un potentiel pour l'exploration ou la surveillance des réservoirs de fluides. La nature de ces anomalies s'explique principalement par la structure géologique plutôt que par le réservoir lui-même, pour une modélisation purement élastique. L'analyse sur des jeux de données réels de bruit ambiant montre que les ondes de surface, principalement le mode fondamental, sont les principaux contributeurs à l'anomalie. Ce travail explore comment les ondes de Rayleigh interagissent avec une structure anticlinale, un piège géologique typique pour un réservoir d'hydrocarbures. L'analyse de la signature spectrale d'une structure anticlinale est effectuée pour différentes configurations de source, pour finalement fournir une relation reliant les paramètres géométriques et élastiques de l'anticlinal à l'anomalie induite pour le cas du mode fondamental des ondes de Rayleigh
Spectral anomalies in the seismic ambient noise, defined as strong spectral amplification of the vertical component at frequencies of 1 to 5 Hertz, are commonly observed above gas reservoirs. If properly understood, these anomalies could have a potential for fluid reservoir exploration or monitoring. The nature of these anomalies was mainly explained by the geological structure more than the fluid reservoir itself, for purely elastic waves. Analysis on real datasets of ambient noise measurements shows that surface waves, mainly fundamental mode, are the main contributors to the anomaly. This work further explores how Rayleigh waves interact with an anticline structure, a typical geological trap for a hydrocarbon reservoir. Analysis of the spectral signature of an anticline structure is performed for different source configurations, to finally provide a relationship linking the anticline geometrical and elastic parameters to the induced anomaly for the case of the fundamental mode Rayleigh waves
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Touil, Hatem. „Modélisation spectrale de la turbulence inhomogène anistrope“. Ecully, Ecole centrale de Lyon, 2002. http://www.theses.fr/2002ECDL0020.

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Ce travail de thèse porte sur le développement d'un modèle pour la turbulence anisotrope et inhomogène au moyen d'une approche statistique spectrale. La variable de base de ce nouveau modèle est le spectre du tenseur de Reynolds, quantité qui dépend des variables d'espace et du temps, mais aussi du module du vecteur d'onde. Ce travail s'appuie sur les fondements théoriques posés par A. Laporta (1995) pour le développement autour de l'homogénéité des équations des corrélations en deux points et sur les travaux de S. Parpais (1996) pour la modélisation des termes les plus complexes mis à jour dans ce type de démarche. Dans cette thèse, un modèle exploitable numériquement dans des géométries complexes a été proposé. Il faut noter que ce modèle repose sur des hypothèses quasi-normales amorties pour représenter les flux d'énergie vers les petites échelles et ne nécessite donc pas, comme les modèles de turbulence usuels, l'utilisation d'une équation de transport pour la dissipation de l’énergie cinétique turbulente. Les informations spectrales fournies par le modèle ont été utilisées pour analyser finement la turbulence. Nous avons ainsi pu caractériser dans des écoulements tels que celui autour d'un profil d'aile en incidence certaines situations de déséquilibre de la turbulence. Ce déséquilibre s'exprime en particulier au niveau des spectres de l’énergie cinétique turbulente par un écart à la théorie de Kolmogorov (1941) et à une distribution d'énergie selon les nombres d'onde k proportionnelle à k-5/ 3 (dans la zone inertielle). L'analyse spectrale permet aussi de proposer des quantités en un point pertinentes pour mettre en évidence ces états de déséquilibre, ouvrant ainsi de nouvelles voies de modélisation
Spectral modelling for anisotropic and inhomogeneous turbulence This work concerns the development of a model for anisotropic and inhomogeneous turbulence by means of a spectral statistical approach. The basic unknown of this new model is the spectrum of the Reynolds stress tensor, a quantity which depends on space and time variables as well as on the wave vector module. The theoretical base of this work was provided by A. Laporta (1 995), who expanded about homogeneity the equations for the two point velocity correlations, and on the work of S. Parpais (1996) for the modelling part of the complex terms involved in this kind of approach. In this thesis, a numerical model was proposed that can be used in complex geometries. It should be noted that this model is based on quasi-normal assumptions intended to represent the energy cascade towards the small scales and therefore does not require, like usual turbulence models, the use of a transport equation for the dissipation of the turbulent kinetic energy. The spectral information provided by this new model was used to scrutinize some properties of turbulence. The model allows to characterize situations of turbulence desequilibrium in flows such as that around an airfoil with incidence. The spectral desequilibrium is characterized by comparisons with the Kolmogorov (1941) theory leading to a distribution of energy proportional to k-5/ 3, for wave numbers k in the inertial range. The spectral analysis enables to propose relevant one-point quantities to highlight these non-equilibrium states, thus opening new modelling frontiers
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Jamet, Guillaume. „Modélisation d'ondes sismo-acoustiques par la méthode des éléments spectraux : application à un séisme en Atlantique Nord“. Thesis, Brest, 2014. http://www.theses.fr/2014BRES0030/document.

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Depuis plus de deux décennies, I'enregistrement des signaux hydroacoustiques par des hydrophones dans le canal SOFAR (SOund Fixing And Ranging) a permis la détection et la localisation de nombreux séismes de faible magnitude dans I'océan. Cependant, I'interprétation de ces signaux est actuellement incomplète. La complexité de la conversion des ondes sismiques en ondes acoustiques, appelées « ondes T », au niveau du plancher océanique, et de leur propagation dans la tranche d'eau n'est pas intégralement comprise et ne permet pas d'extraire beaucoup d'informations sur les séismes à leur origine. Une simulation numérique de ces signaux est proposée pour identifier et comprendre les paramètres environnementaux et les phénomènes majeurs entrant en jeu dans la génération des ondes T. L'approche proposée est la méthode des éléments spectraux, mise en œuvre dans le code SPECFEM2D. Cette approche s'avère adaptée à cet usage car elle permet d'aborder le phénomène de la génération et la propagation des ondes T dans son ensemble en tenant compte ses principales caractéristiques : le couplage fluide/solide (propagation sismique, conversion, et propagation acoustique), les profils de vitesse d'onde dans I'eau et dans la croute, et le tenseur des moments sismiques donnant le diagramme de radiation de la source. Les signaux simulés présentent des formes, des durées, des temps d'arrivée, et des amplitudes relatives tout à fait comparables aux enregistrements réels. Les différences observées proviennent sans doute du traitement 2D du problème et d'une représentation trop simpliste des environnements et de la source sismique
For more than 2 decades, recording of hydroacoustic signals in the sopen channel (Sound Fixing And Ranging) has allowed the detection and localization of many low-magnitude earthquakes in the ocean. However the interpretation of these signals is still incomplete.The generation of acoustic waves, known as T-waves, resulting from the conversion of seismic waves into acoustic waves at the sea-bottom, and their propagation in the water column are not yet fully understood, which prevents to extract more information about the earthquakes they originate from. Here, we use numerical modelling to identify and understand the main environmental parameters and phenomena that control the generation and propagation of acoustic T-waves in the ocean. The proposed approach is a spectral element method, implemented in the code SPECFEM2D, which allows to address the problem in a comprehensive way taking into account the solid/fluid coupling (seismic propagation, conversion, acoustic propagation), velocity profiles of the waves in the crust and the ocean, and the moment tensor of the earthquake that defines the radiation pattern of the seismic source. Simulated acoustic signals present many similarities in the shape, duration, arrival times and amplitudes of the predicted T-waves with observed T-waves. Differences are likely due to the 2D representation of the problem and to the simplistic representation of the environment and of the seismic source
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Martire, Léo. „Characterisation of Infrasound in the Coupled Solid-Atmosphere System : Numerical Modelling, Terrestrial and Planetary Applications“. Thesis, Toulouse, ISAE, 2020. http://www.theses.fr/2020ESAE0028.

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Cette thèse porte sur le couplage mécanique entre le corps solide d’une planèteet son atmosphère. Nous étudions les événements géophysiques naturels et anthropiquesgrâce aux ondes sismiques et infrasonores. Ces phénomènes sont clés pour découvrir lastructure atmosphérique de la Terre, l’intérieur de Vénus, et Mars dans son intégralité.Les formes d’ondes acoustiques et sismiques contiennent des informations importantes, à lafois sur l’événement source et sur le milieu de propagation. L’objet de ce travail est double.Premièrement, nous développons un logiciel de simulation numérique pour le systèmecouplé sol-atmosphère. Nous nous appuyons sur les équations linéarisées de Navier-Stokespour modéliser l’atmosphère, et sur la visco-élastodynamique pour modéliser le sous-sol.Nous utilisons la méthode des éléments finis spectraux discontinus, permettant la simulationcomplète des formes d’ondes. L’implémentation est validée à l’aide de deux techniques :les solutions analytiques et manufacturées. Le logiciel permet de modéliser tous les types decouplages air-sol, et prend en compte avec précision la propagation des ondes acoustiqueset sismiques. Des topographies complexes peuvent être utilisées, ainsi que des modèles atmosphériques variant latéralement. Il est donc particulièrement bien adapté à l’étude de laplupart des phénomènes géophysiques dans les atmosphères planétaires. Parmi les exemplesd’événements, nous pouvons citer les ondes sismiques, les microbaroms, les explosionssouterraines ou aériennes, ou encore les ondes de gravité. Deuxièmement, nous étudionsde nombreux cas d’application liés à la planétologie. En vue de l’exploration de l’intérieurde Vénus, nous menons des expériences terrestres dont le but est d’étudier les infrasonsinduits par les séismes, et utilisons notamment des instruments sous ballons. Nous montronsqu’il est possible de déduire les propriétés et la structure du sous-sol grâce à ces ondesinfrasonores. Ces ballons instrumentés permettent également de localiser les événements ausol. Ce sujet est crucial pour l’exploration planétaire, mais également pour la surveillancede la Terre depuis l’atmosphère. Enfin, nous démontrons que des infrasons sont présentsdans l’atmosphère de Mars, établissant pour la première fois l’existence d’infrasons sur uneautre planète. Ceci est possible grâce au sismomètre SEIS d’InSight, capable de mesurer lesinfimes mouvements du sol causés par le passage des infrasons
This thesis focuses on the mechanical coupling between a planet’s solid bodyand its atmosphere. We study natural and anthropogenic geophysical events under thescope of seismic waves and infrasound. These phenomena are keys to uncover the atmosphericstructure of Earth, the interior of Venus, and Mars as a whole. Acoustic and seismicwaveforms contain valuable information, about both the source event and the propagationmedium. Our work is two-fold. Firstly, we develop a numerical simulation software for thecoupled ground-atmosphere system. We rely on the linearised Navier-Stokes equations tomodel the atmosphere, and on visco-elastodynamics to model the sub-surface. We employa discontinuous spectral finite elements method, allowing the simulation of full waveforms.The implementation is validated using two techniques: analytical and manufactured solutions.Our software can model all types of air-ground couplings, and accurately accountsfor acoustic and seismic wave propagation. Complex topographies can be used, as well asrange-dependant atmospheric models. As a result, it is particularly well suited to studymost geophysical phenomena in planetary atmospheres. Example events include seismicwaves, microbaroms, underground and overground explosions, or gravity waves. Secondly,we study numerous application cases related to the aforementioned planetary science objectives.With the exploration of Venus’ interior in mind, we conduct terrestrial experiments tostudy seismically-induced infrasound, and involve balloon-borne instruments. We show thatit is possible to infer the properties and structure of the sub-surface from these infrasonicwaves. These instrumented balloons also render the localisation of ground events possible,which is crucial both for planetary exploration and for the airborne monitoring of the Earth.Finally, we demonstrate that the Martian atmosphere features infrasound, establishing forthe first time the existence of infrasound on another planet. This is achieved thanks toInSight’s seismometer SEIS, able to measure the faint ground motion caused by passingairwaves
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Salah, Adham M. S. „Investigation of Integrated Decoupling Methods for MIMO Antenna Systems. Design, Modelling and Implementation of MIMO Antenna Systems for Different Spectrum Applications with High Port-to-Port Isolation Using Different Decoupling Techniques“. Thesis, University of Bradford, 2019. http://hdl.handle.net/10454/18427.

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Multiple-Input-Multiple-Output (MIMO) antenna technology refers to an antenna with multiple radiators at both transmitter and receiver ends. It is designed to increase the data rate in wireless communication systems by achieving multiple channels occupying the same bandwidth in a multipath environment. The main drawback associated with this technology is the coupling between the radiating elements. A MIMO antenna system merely acts as an antenna array if the coupling between the radiating elements is high. For this reason, strong decoupling between the radiating elements should be achieved, in order to utilize the benefits of MIMO technology. The main objectives of this thesis are to investigate and implement several printed MIMO antenna geometries with integrated decoupling approaches for WLAN, WiMAX, and 5G applications. The characteristics of MIMO antenna performance have been reported in terms of scattering parameters, envelope correlation coefficient (ECC), total active reflection coefficient (TARC), channel capacity loss (CCL), diversity gain (DG), antenna efficiency, antenna peak gain and antenna radiation patterns. Three new 2×2 MIMO array antennas are proposed, covering dual and multiple spectrum bandwidths for WLAN (2.4/5.2/5.8 GHz) and WiMAX (3.5 GHz) applications. These designs employ a combination of DGS and neutralization line methods to reduce the coupling caused by the surface current in the ground plane and between the radiating antenna elements. The minimum achieved isolation between the MIMO antennas is found to be better than 15 dB and in some bands exceeds 30 dB. The matching impedance is improved and the correlation coefficient values achieved for all three antennas are very low. In addition, the diversity gains over all spectrum bands are very close to the ideal value (DG = 10 dB). The forth proposed MIMO antenna is a compact dual-band MIMO antenna operating at WLAN bands (2.4/5.2/5.8 GHz). The antenna structure consists of two concentric double square rings radiating elements printed symmetrically. A new method is applied which combines the defected ground structure (DGS) decoupling method with five parasitic elements to reduce the coupling between the radiating antennas in the two required bands. A metamaterial-based isolation enhancement structure is investigated in the fifth proposed MIMO antenna design. This MIMO antenna consists of two dual-band arc-shaped radiating elements working in WLAN and Sub-6 GHz 5th generation (5G) bands. The antenna placement and orientation decoupling method is applied to improve the isolation in the second band while four split-ring resonators (SRRs) are added between the radiating elements to enhance the isolation in the first band. All the designs presented in this thesis have been fabricated and measured, with the simulated and measured results agreeing well in most cases.
Higher Committee for Education Development in Iraq (HCED)
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Sinclair, Catherine Ellen. „Elastic wave modelling in anisotropic media using the spectral-element method“. Thesis, 2010. http://hdl.handle.net/2440/59434.

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Forward modelling of seismic waves is an essential tool in the determination of the underlying structure of the Earth using inversion techniques. Despite recent advances in computer power and memory resources, full 3-D elastic wave modelling continues to place a heavy burden on a typical personal computer. 2.5-D modelling reduces the computational burden while maintaining 3-D wavefield characteristics. In this thesis I present 2.5-D frequency-domain equations of motion for elastic wave modelling in anisotropic media. The reduced set of equations for vertical transversely isotropic media and tilted transversely isotropic media are presented separately. Using the spectral-element method, I develop the equations of motion into readily implemented sub-equations by identifying simple 1-D and 2-D patterns. Some aspects of my computational implementation are unique, in particular the use of a system of dynamically growing binary trees to serve as a system matrix. Using this system, the matrix is automatically stored in compressed row format. I investigate the use of both distributed memory and shared memory super-computers for 3-D modelling and compare the resource use of various matrix solvers. In this thesis I adapt recently developed Perfectly Matched Layer formulations to the 2.5-D elastic case, and find them to be adequate in most situations. I investigate the possiblity of instability in the absorbing layers. Observation of 2.5-D modelling results in the frequency wavenumber domain uncovers polelike behaviour at critical wavenumbers within the spectrum. I demonstrate how this behaviour threatens the accuracy of the inverse Fourier transformed frequency-domain solution. However for inhomogeneous media, under certain conditions the only medium that exhibits pole-like behaviour is the medium containing the source. Further study of the phenomenon shows that in homogeneous, transversely isotropic media, the critical wavenumber values are not dependent on the receiver position, but rather can be predicted using the maximum phase velocities of the media. The recommended strategy for wavenumber sampling is to use dense even spacing of values, to adequately capture the behaviour close to the critical wavenumbers. A further recommendation it to introduce slight attenuation through the use of complex velocities (or elastic constants) to eliminate any pole-like behaviour at the critical values.
Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2010
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Buchteile zum Thema "Spectral element modelling"

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Fichtner, Andreas. „Spectral-Element Methods“. In Full Seismic Waveform Modelling and Inversion, 59–81. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-15807-0_4.

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Hulshoff, S., E. Munts und J. Labrujere. „h and p Refinement with Wall Modelling in Spectral-Element LES“. In Direct and Large-Eddy Simulation VII, 201–4. Dordrecht: Springer Netherlands, 2010. http://dx.doi.org/10.1007/978-90-481-3652-0_30.

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Moxey, D., C. D. Cantwell, G. Mengaldo, D. Serson, D. Ekelschot, J. Peiró, S. J. Sherwin und R. M. Kirby. „Towards p-Adaptive Spectral/hp Element Methods for Modelling Industrial Flows“. In Lecture Notes in Computational Science and Engineering, 63–79. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-65870-4_4.

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Shone, Simon P., Brian R. Mace und Tim P. Waters. „A Combined Finite and Spectral Element Approach to Wave Scattering in a Cracked Beam: Modelling and Validation“. In Damage Assessment of Structures VI, 541–48. Stafa: Trans Tech Publications Ltd., 2005. http://dx.doi.org/10.4028/0-87849-976-8.541.

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Baer, F., Joe Tribbia und Mark Taylor. „Global and Regional Atmospheric Modeling Using Spectral Elements“. In IUTAM Symposium on Advances in Mathematical Modelling of Atmosphere and Ocean Dynamics, 81–86. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0792-4_6.

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„Ground motion modelling using the 2-D Chebyshev spectral element method“. In Numerical Analysis and Modelling in Geomechanics, 274–97. CRC Press, 2003. http://dx.doi.org/10.1201/9781482267679-17.

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Tanaka, Yoshiyuki, Volker Klemann und Zdeněk Martinec. „An Estimate of the Effect of 3D Heterogeneous Density Distribution on Coseismic Deformation Using a Spectral Finite-Element Approach“. In International Association of Geodesy Symposia. Berlin, Heidelberg: Springer Berlin Heidelberg, 2023. http://dx.doi.org/10.1007/1345_2023_236.

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AbstractThe advancement of the Global Geodetic Observing System (GGOS) has enabled monitoring of mass transport and solid-Earth deformation processes with unprecedented accuracy. Coseismic deformation is modelled as an elastic response of the solid Earth to an internal dislocation. Self-gravitating spherical Earth models can be employed in modelling regional to global scale deformations. Recent seismic tomography and high-pressure/high-temperature experiments have revealed finer-scale lateral heterogeneities in the elasticity and density structures within the Earth, which motivates us to quantify the effects of such finer structures on coseismic deformation. To achieve this, fully numerical approaches including the Finite Element Method (FEM) have often been used. In our previous study, we presented a spectral FEM, combined with an iterative perturbation method, to consider lateral heterogeneities in the bulk and shear moduli for surface loading. The distinct feature of this approach is that the deformation of the entire sphere is modelled in the spectral domain with finite elements dependent only on the radial coordinate. By this, self-gravitation can be treated without special treatments employed when using an ordinary FEM. In this study, we extend the formulation so that it can deal with lateral heterogeneities in density in the case of coseismic deformation. We apply this approach to a longer-wavelength vertical deformation due to a large earthquake. The result shows that the deformation for a laterally heterogeneous density distribution is suppressed mainly where the density is larger, which is consistent with the fact that self-gravitation reduces longer-wavelength deformations for 1-D models. The effect on the vertical displacement is relatively small, but the effect on the gravity change could amount to the same order of magnitude of a given heterogeneity if the horizontal scale of the heterogeneity is large enough.
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Ganghoffer, Jean-François. „Mechanical Models of Cell Adhesion Incorporating Nonlinear Behavior and Stochastic Rupture of the Bonds“. In Handbook of Research on Computational and Systems Biology, 599–627. IGI Global, 2011. http://dx.doi.org/10.4018/978-1-60960-491-2.ch027.

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The rolling of a single biological cell is analysed using modelling of the local kinetics of successive attachment and detachment of bonds occurring at the interface between a single cell and the wall of an ECM (extracellular matrix). Those kinetics correspond to a succession of creations and ruptures of ligand-receptor molecular connections under the combined effects of mechanical, physical (both specific and non-specific), and chemical external interactions. A three-dimensional model of the interfacial molecular rupture and adhesion kinetic events is developed in the present contribution. From a mechanical point of view, this chapter works under the assumption that the cell-wall interface is composed of two elastic shells, namely the wall and the cell membrane, linked by rheological elements representing the molecular bonds. Both the time and space fluctuations of several parameters related to the mutual affinity of ligands and receptors are described by stochastic field theory; especially, the individual rupture limits of the bonds are modelled in Fourier space from the spectral distribution of power. The bonds are modelled as macromolecular chains undergoing a nonlinear elastic deformation according to the commonly used freely joined chains model, while the cell membrane facing the ECM wall is modelled as a linear elastic plate. The cell itself is represented by an equivalent constant rigidity. Numerical simulations predict the sequence of broken bonds, as well as the newly established connections on the ‘adhesive part’ of the interface. The interplay between adhesion and rupture entails a rolling phenomenon. In the last part of this chapter, a model of the deformation induced by the random fluctuation of the protrusion force resulting from the variation of affinity with chemiotactic sources is calculated, using stochastic finite element methods in combination with the theory of Gaussian random variables.
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Burridge, Kate, und Pam Peters. „English in Australia – Extra-territorial Influences“. In Modelling World Englishes, 202–27. Edinburgh University Press, 2020. http://dx.doi.org/10.3366/edinburgh/9781474445863.003.0010.

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This chapter discusses the extra-territorial influence of American English on Australian English, in comparison with other varieties within the spectrum of World Englishes. Its aim is to compare the different orientations to American English in Australia that can be observed using qualitative and quantitative methods, and so to illuminate the different ways in which extra- and intra-territorial influences can impact on individual varieties. Two kinds of evidence are presented: (i) attitudinal data derived from Australians commenting in the complaint tradition on elements of pronunciation and spelling; and (ii) corpus data on lexical and morphosyntactic sets where shifting preferences are attributed to American influence. While perceptions of the extent of American influence are inflated, the inventory of Americanisms used in Australia continues to grow.
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Sambhanthan, Arunasalam, und Vidyasagar Potdar. „A Study of the Parameters Impacting Sustainability in Information Technology Organizations“. In Sustainable Business, 499–512. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-5225-9615-8.ch023.

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This paper proposes the critical themes associated with the evaluation of software business sustainability. The whole dimension of software business sustainability has been theorized into twelve elements that unfold covering the whole spectrum of software business sustainability. The twelve elements of software business sustainability include aspects such as product, process, practices, policies, people, peripherals, partners, place and profit model. The paper justifies the use of these twelve elements in ensuring sustainability in software businesses, by incorporating the case of multinational software businesses as example. This study needs to be looked as an exploratory investigation into the elements of software business sustainability lending viability towards modelling the software businesses using these twelve elements.
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Konferenzberichte zum Thema "Spectral element modelling"

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Saha, Sandip, Pankaj Biswas und Sujit Nath. „A review on spectral element solver Nek5000“. In INTERNATIONAL CONFERENCE ON COMPUTATIONAL SCIENCES-MODELLING, COMPUTING AND SOFT COMPUTING (CSMCS 2020). AIP Publishing, 2021. http://dx.doi.org/10.1063/5.0045709.

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Curti, M., J. Paulides und E. Lomonova. „Magnetic modelling of a Linear Synchronous Machine with Spectral Element Method“. In 2017 IEEE International Magnetics Conference (INTERMAG). IEEE, 2017. http://dx.doi.org/10.1109/intmag.2017.8008010.

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Yin, C., X. Huang, X. Cao, X. Ren, C. Qiu, S. Sun und J. Zhu. „Airborne EM Modelling for an Anisotropic Earth Using Spectral Element Method“. In 79th EAGE Conference and Exhibition 2017. Netherlands: EAGE Publications BV, 2017. http://dx.doi.org/10.3997/2214-4609.201700500.

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Weiss*, Michael, Thomas Kalscheuer, Maya Neytcheva und Zhengyong Ren. „A Spectral-Element Approach to 3D Controlled-Source Electromagnetic forward modelling“. In GEM 2019 Xi'an: International Workshop and Gravity, Electrical & Magnetic Methods and their Applications, Chenghu, China, 19-22 April 2015. Society of Exploration Geophysicists and Chinese Geophysical Society, 2019. http://dx.doi.org/10.1190/gem2019-073.1.

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Charara, M., M. Jervis, D. Sabitov und I. Seleznev. „3D Spectral Element Modelling for Acoustically Sensing a Well from a Nearby Well“. In 75th EAGE Conference and Exhibition incorporating SPE EUROPEC 2013. Netherlands: EAGE Publications BV, 2013. http://dx.doi.org/10.3997/2214-4609.20130228.

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Koukounas, Dimitrios, Claes Eskilsson und Allan P. Engsig-Karup. „Numerical Simulations of Peregrine Breathers Using a Spectral Element Model“. In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77684.

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Breather solutions to the nonlinear Schrödinger equation have been put forward as a possible prototype for rouge waves and have been studied both experimentally and numerically. In the present study, we perform high resolution simulations of the evolution of Peregrine breathers in finite depth using a fully nonlinear potential flow spectral element model. The spectral element model can accurately handle very steep waves as illustrated by modelling solitary waves up to limiting steepness. The analytic breather solution is introduced through relaxation zones. The numerical solution obtained by the spectral element model is shown to compare in large to the analytic solution as well as to CFD simulations of a Peregrine breather in finite depth presented in literature. We present simulations of breathers over variable bathymetry and 3D simulations of a breather impinging on a mono-pile.
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Curti, M., und D. C. J. Krop. „Coupled Spectral Element Method and Harmonic Model for Magnetic Modelling of Linear Synchronous Machines“. In 2021 13th International Symposium on Linear Drives for Industry Applications (LDIA). IEEE, 2021. http://dx.doi.org/10.1109/ldia49489.2021.9505867.

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Huang, X., C. Yin, C. Farquharson, X. Cao, Y. Liu, B. Zhang und J. Cai. „3D Airborne EM Forward Modelling by the Spectral-Element Method for Deformed Hexahedral Meshes“. In 80th EAGE Conference and Exhibition 2018. Netherlands: EAGE Publications BV, 2018. http://dx.doi.org/10.3997/2214-4609.201800826.

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Paunikar, Shweta, Rohan N. Soman und Wieslaw Ostachowicz. „Numerical modelling of wave propagation in optical fibre using frequency domain spectral element method“. In Health Monitoring of Structural and Biological Systems XVI, herausgegeben von Paul Fromme und Zhongqing Su. SPIE, 2022. http://dx.doi.org/10.1117/12.2612489.

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Pitz, Diogo B., John W. Chew, Olaf Marxen und Nicholas J. Hills. „Direct Numerical Simulation of Rotating Cavity Flows Using a Spectral Element-Fourier Method“. In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56486.

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A high-order numerical method is employed to investigate flow in a rotor/stator cavity without heat transfer and buoyant flow in a rotor/rotor cavity. The numerical tool used employs a spectral element discretisation in two dimensions and a Fourier expansion in the remaining direction, which is periodic and corresponds to the azimuthal coordinate in cylindrical coordinates. The spectral element approximation uses a Galerkin method to discretise the governing equations, similarly to a finite element method, but employs high-order polynomials within each element to obtain spectral accuracy. A second-order, semi-implicit, stiffly stable algorithm is used for the time discretisation, and no subgrid modelling is included in the governing equations. Numerical results obtained for the rotor/stator cavity compare favourably with experimental results for Reynolds numbers up to Re1 = 106 in terms of velocities and Reynolds stresses. For the buoyancy-driven flow, the energy equation is coupled to the momentum equations via the Boussinesq approximation, which has been implemented in the code considering two different formulations. Numerical predictions of the Nusselt number obtained using the traditional Boussinesq approximation are considerably higher than available experimental data. Much better agreement is obtained when the extended Boussinesq approximation is employed. It is concluded that the numerical method employed has considerable potential for further investigations of rotating cavity flows.
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