Dissertations / Theses: 'KKR Green's function method'

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Thieß, Alexander R. [Verfasser]. "Development and application of a massively parallel KKR Green function method for large scale systems / Alexander Reinhold Thieß." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1020255145/34.

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Zahn, Peter. "Screened Korringa-Kohn-Rostoker-Methode für Vielfachschichten." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1119864864984-42479.

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Im Rahmen der vorliegenden Arbeit wird eine Tight-Binding-Formulierung der Korringa-Kohn-Rostoker-Greenschen-Funktionsmethode vorgestellt. Dabei werden mittels eines geeignet gewählten Referenzsystems abgeschirmte Strukturkonstanten konstruiert. Es werden die Vorteile und Grenzen dieser Transformation des Formalismus diskutiert. Es wird gezeigt, daß der numerische Aufwand zur erechnung der Elektronenstruktur von Systemen mit langgestreckter Elementarzelle linear mit der Systemgröße wächst. Damit ist eine Behandlung von Systemen mit 500 und mehr Atomen pro Elementarzelle möglich. Anhand von umfangreichen Testrechnungen kann demonstriert werden, daß das neue Verfahren bezüglich seiner Genauigkeit mit dem traditionellen KKR-Verfahren vergleichbar ist. Es werden Anwendungen zur Berechnung der Elektronenstruktur sowie zur Zwischenlagenaustauschkopplung von Co/Cu(100)-Vielfachschichten vorgestellt
A newly developed ab initio tight-binding-formulation of the Korringa-Kohn-Rostoker-Green's function method for layered systems is presented. Screened structure constants are calculated by means of a repulsive reference system. Advantages and limits of this transformation of the formalism are discussed in detail. The numerical effort for self consistent electronic structure calculations of systems with a large prolonged supercell scales linearly with the system size. Systems with up to 500 atoms per unit cell can be treated easily. The accuracy of the new method is of the same order as the traditional KKR method. Applications to electronic structure calculations and magnetic interlayer exchange coupling in Co/Cu(100) multilayers are presented

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Zahn, Peter. "Screened Korringa-Kohn-Rostoker-Methode für Vielfachschichten." Doctoral thesis, Technische Universität Dresden, 1998. https://tud.qucosa.de/id/qucosa%3A24521.

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Im Rahmen der vorliegenden Arbeit wird eine Tight-Binding-Formulierung der Korringa-Kohn-Rostoker-Greenschen-Funktionsmethode vorgestellt. Dabei werden mittels eines geeignet gewählten Referenzsystems abgeschirmte Strukturkonstanten konstruiert. Es werden die Vorteile und Grenzen dieser Transformation des Formalismus diskutiert. Es wird gezeigt, daß der numerische Aufwand zur erechnung der Elektronenstruktur von Systemen mit langgestreckter Elementarzelle linear mit der Systemgröße wächst. Damit ist eine Behandlung von Systemen mit 500 und mehr Atomen pro Elementarzelle möglich. Anhand von umfangreichen Testrechnungen kann demonstriert werden, daß das neue Verfahren bezüglich seiner Genauigkeit mit dem traditionellen KKR-Verfahren vergleichbar ist. Es werden Anwendungen zur Berechnung der Elektronenstruktur sowie zur Zwischenlagenaustauschkopplung von Co/Cu(100)-Vielfachschichten vorgestellt.
A newly developed ab initio tight-binding-formulation of the Korringa-Kohn-Rostoker-Green's function method for layered systems is presented. Screened structure constants are calculated by means of a repulsive reference system. Advantages and limits of this transformation of the formalism are discussed in detail. The numerical effort for self consistent electronic structure calculations of systems with a large prolonged supercell scales linearly with the system size. Systems with up to 500 atoms per unit cell can be treated easily. The accuracy of the new method is of the same order as the traditional KKR method. Applications to electronic structure calculations and magnetic interlayer exchange coupling in Co/Cu(100) multilayers are presented.

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Yeo, Stephen K. N. "Generalised periodic Green's function analysis of microstrip dipole arrays /." Title page, contents and abstract only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phy46.pdf.

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da, Costa Filho Carlos Alberto. "Elastodynamic Green's function retrieval : theory and applications in exploration geophysics." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28760.

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The ability to synthesize recordings from surface data as if they had come from subsurface sources has allowed geophysicists to estimate subsurface properties. Either in the form of classical seismic migration which creates structural maps of the subsurface, to the more recent seismic interferometry which turns seismic sources into receivers and vice-versa, this ability has provided a rich trove of methods with which to probe the Earth's interior. While powerful, both of these techniques suffer from well-known issues. Standard migration requires data without multiply-scattered waves (multiples). Seismic interferometry, on the other hand, can be applied to full recorded data (containing multiples and other wave types), but requires sources (receivers) to be physically placed at the location from (to) one wishes to estimate responses. The Marchenko method, developed recently for the seismic setting, circumvents both of these restrictions: it creates responses from virtual subsurface sources as if measured at the surface. It requires only single-sided surface data, and a smooth estimate of the subsurface velocities. Initially developed for acoustic media, this thesis contributes the first elastic formulation of the Marchenko method, providing a more suitable setting for applications for the solid Earth. In another development, this thesis shows how the obtained virtual recordings may be used for migration. With these two contributions, this thesis shows that for elastic surface seismic data, the main drawbacks of migration and interferometry can be overcome using the Marchenko method: multiples do not harm migrated images, and sources (receivers) need not be physically placed in the medium for their responses to be accessible. In addition to the above methods, generating images devoid of multiple-related artifacts can be achieved in several other different ways. Two approaches to this are the use of a post-imaging filter, and attenuation of internal multiples in the data itself. This thesis contributes one new method using each of these approaches. First, a form of Marchenko imaging is known to create spurious reflectors, as also occurs in standard reverse-time migration (RTM). However, these artifacts usually appear at different locations in RTM and this form of Marchenko imaging. Using this insight, this thesis presents a way to combine pairs of seismic images in such a way that their differences (e.g. artifacts) are attenuated, while similarities (e.g. true reflectors) are preserved. Applying this to RTM and Marchenko-derived images markedly improves image quality. Second, this thesis presents a method to estimate multiples in the data. Multiples can either be migrated on their own to aid in interpretation, or be adaptatively removed from the data to improve image quality. However, because of the nature of adaptive subtraction, this second method may harm primary energy. To avoid this problem, this thesis develops a final method to directly image using only primary energy in the recorded data using only a small number of virtual points. This method bypasses the need for multiple removal and the estimation of subsurface responses at every depth location. In addition, primaries from particular reflectors may be particularly selected such that they can be imaged individually. Overall this thesis provides several new ways to use surface seismic data in such a way that multiples do not hamper the end product of seismic data processing: the seismic image. It demonstrates this use on synthetic and real data, proving their effectiveness.

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Fooladi, Samaneh, and Samaneh Fooladi. "Numerical Implementation of Elastodynamic Green's Function for Anisotropic Media." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/623144.

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Displacement Green's function is the building block for some semi-analytical methods like Boundary Element Method (BEM), Distributed Point Source Method (DPCM), etc. In this thesis, the displacement Green`s function in anisotropic media due to a time harmonic point force is studied. Unlike the isotropic media, the Green's function in anisotropic media does not have a closed form solution. The dynamic Green's function for an anisotropic medium can be written as a summation of singular and non-singular or regular parts. The singular part, being similar to the result of static Green's function, is in the form of an integral over an oblique circular path in 3D. This integral can be evaluated either by a numerical integration technique or can be converted to a summation of algebraic terms via the calculus of residue. The other part, which is the regular part, is in the form of an integral over the surface of a unit sphere. This integral needs to be evaluated numerically and its evaluation is considerably more time consuming than the singular part. Obtaining dynamic Green's function and its spatial derivatives involves calculation of these two types of integrals. The spatial derivatives of Green's function are important in calculating quantities like stress and stain tensors. The contribution of this thesis can be divided into two parts. In the first part, different integration techniques including Gauss Quadrature, Simpson's, Chebyshev, and Lebedev integration techniques are tried out and compared for evaluation of dynamic Green’s function. In addition the solution from the residue theorem is included for the singular part. The accuracy and performance of numerical implementation is studied in detail via different numerical examples. Convergence plots are used to analyze the numerical error for both Green's function and its derivatives. The second part of contribution of this thesis relates to the mathematical derivations. As mentioned above, the regular part of dynamic Green's function, being an integral over the surface of a unit sphere, is responsible for the majority of computational time. From symmetry properties, this integration domain can be reduced to a hemisphere, but no more simplification seems to be possible for a general anisotropic medium. In this thesis, the integration domain for regular part is further reduced to a quarter of a sphere for the particular case of transversely isotropic material. This reduction proposed for the first time in this thesis nearly halves the number of integration points for the evaluation of regular part of dynamic Green's function. It significantly reduces the computational time.

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Chen, Shuguang, and 陈曙光. "Nonequilibrium Green's function-hierarchical equation of motion method for time-dependent quantum transport." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206344.

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The nonequilibrium Green’s function-hierarchical equation of motion (NEGFHEOM) method has been developed to simulate the time-dependent electron transport process. The real-time evolution of the reduced single-electron density matrix is solved through the Liouville-von-Neumann equation. The method is very efficient compared to conventional NEGF formulas which need to discretize the simulation time. The hierarchical equation of motion (HEOM) is closed at the second-tier in the time-dependent noninteracting Kohn-Sham framework. When combined with the wide band limit (WBL) approximation, the HEOM terminate at the first-tier. The resulting NEGF-HEOM-WBL method is particularly suitable for simulating the long time transient dynamics for large systems. The method developed is first applied to calculate the transient current through an array of as many as 1000 quantum dots. Upon switching on the bias voltage, the current increases linearly with respect to time before reaching its steady state value. And the time required for the current to reach its steady state value is exactly the time for a conducting electron to travel through the array at Fermi velocity. These phenomena can be understood by simple analysis on the energetics of the quantum dots or by classical electron gas model. Then the method is employed to investigate several simple molecular circuits, in which the para-linkage or meta-linkage benzene acts as the transmitting molecular entity. The simulation results shows that it takes a certain amount of time before the quantum interference manifests itself, and that the transmission through the meta case is hundreds of times smaller than that through the para case. To investigate the quantum interference process in molecular electronics, the concept of Büttiker probe is introduced. The Büttiker probe is an electrode that, when attached to electronic devices, causes the coherence passing through disappear. Simulation results show that the Büttiker probe can enhance the transmission of the meta benzene system through destroying the constructive interference. By turning the probe on and off, it can be observed that large strong correlations are indeed built up as electrons are transported through benzenoid structures - when the decoherence is turned off, the current rises, and when the decoherence is turned back on, the current falls. Finally, TDDFT(B)-NEGF-HEOM-WBL method is implemented to solve realistic systems in the formalism of time-dependent density functional theory (tightbinding). Ab initio calculations are carried out to simulate the time-dependent electron transport through a CNT-based device. The simulation results show that when the input bias voltage is in low frequency, both the conventional adiabatic approximation method and the NEGF-HEOM-WBL methods are good enough. However, when high frequency dynamic responses are need to be captured, the NEGF-HEOM-WBL method is more suitable.
published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy

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Yasuda, Koji, and Daisuke Yamaki. "The extension of the fragment molecular orbital method with the many-particle Green's function." American Institute of Physics, 2006. http://hdl.handle.net/2237/8739.

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Ma, Weili. "Discrete Green's function formulation of the finite difference time domain method and its application." Thesis, Queen Mary, University of London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408009.

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Delaney, J. A. Christopher. "Local density of states for one dimensional aperiodic binary sequences using local green's function method." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq21087.pdf.

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Watrous, Mitchell James. "Finite temperature densities via the Green's-function method with application to electron screening in plasmas /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9705.

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Fooladi, Samaneh, and Tribikram Kundu. "Application of distributed point source method (DPSM) to wave propagation in anisotropic media." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/625391.

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Distributed Point Source Method (DPSM) was developed by Placko and Kundu 1, as a technique for modeling electromagnetic and elastic wave propagation problems. DPSM has been used for modeling ultrasonic, electrostatic and electromagnetic fields scattered by defects and anomalies in a structure. The modeling of such scattered field helps to extract valuable information about the location and type of defects. Therefore, DPSM can be used as an effective tool for Non-Destructive Testing (NDT). Anisotropy adds to the complexity of the problem, both mathematically and computationally. Computation of the Green's function which is used as the fundamental solution in DPSM is considerably more challenging for anisotropic media, and it cannot be reduced to a closed-form solution as is done for isotropic materials. The purpose of this study is to investigate and implement DPSM for an anisotropic medium. While the mathematical formulation and the numerical algorithm will be considered for general anisotropic media, more emphasis will be placed on transversely isotropic materials in the numerical example presented in this paper. The unidirectional fiber-reinforced composites which are widely used in today's industry are good examples of transversely isotropic materials. Development of an effective and accurate NDT method based on these modeling results can be of paramount importance for in-service monitoring of damage in composite structures.

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Geng, Weihua. "Interface method and Green's function based Poisson Boltzmann equation solver and interface technique based molecular dynamics." Diss., Connect to online resource - MSU authorized users, 2008.

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Tang, Wee-Hua. "EFFICIENT INTEGRAL EQUATION METHOD FOR 2.5D MICROWAVE CIRCUITS IN LAYERED MEDIA." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_diss/345.

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An efficient integral equation method based on a method of moment (MoM) discretization of the Mixed-Potential Integral Equation (MPIE) for the analysis of 2.5D or 3D planar microwave circuits is presented. The robust Discrete Complex Image Method (DCIM) is employed to approximate the Greens functions in layered media for horizontal and vertical sources of fields, where closed-form formulations of the z-integrations are derived in the spectral domain. Meanwhile, an efficient and accurate numerical integration technique based on the Khayat-Wilton transform is used to integrate functions with 1/R singularities and near singularities. The fast iterative solver - Quadrature Sampled Pre-Corrected Fast Fourier Transform (QSPCFFT) - is associated with the MoM formulation to analyze electrically large, dense and complex microwave circuits.

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Zhang, Yan. "Analysis of Elastic and Electrical Fields in Quantum Structures by Novel Green's Functions and Related Boundary Integral Methods." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1290184113.

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Ludick, Daniel Jacobus. "Efficient numerical analysis of finite antenna arrays using domain decomposition methods." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96124.

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Thesis (PhD) -- Stellenbosch University, 2014.
ENGLISH ABSTRACT: This work considers the efficient numerical analysis of large, aperiodic finite antenna arrays. A Method of Moments (MoM) based domain decomposition technique called the Domain Green's Function Method (DGFM) is formulated to address a wide range of array problems in a memory and runtime efficient manner. The DGFM is a perturbation approach that builds on work initially conducted by Skrivervik and Mosig for disjoint arrays on multi-layered substrates, a detailed review of which will be provided in this thesis. Novel extensions considered for the DGFM are as follows: a formulation on a higher block matrix factorisation level that allows for the treatment of a wider range of applications, and is essentially independent of the elemental basis functions used for the MoM matrix formulation of the problem. As an example of this, both conventional Rao-Wilton-Glisson elements and also hierarchical higher order basis functions were used to model large array structures. Acceleration techniques have been developed for calculating the impedance matrix for large arrays including one based on using the Adaptive Cross Approximation (ACA) algorithm. Accuracy improvements that extend the initial perturbation assumption on which the method is based have also been formulated. Finally, the DGFM is applied to array geometries in complex environments, such as that in the presence of finite ground planes, by using the Numerical Green's Function (NGF) method in the hybrid NGF-DGFM formulation. In addition to the above, the DGFM is combined with the existing domain decomposition method, viz., the Characteristic Basis Function Method (CBFM), to be used for the analysis of very large arrays consisting of sub-array tiles, such as the Low-Frequency Array (LOFAR) for radio astronomy. Finally, interesting numerical applications for the DGFM are presented, in particular their usefulness for the electromagnetic analysis of large, aperiodic sparse arrays. For this part, the accuracy improvements of the DGFM are used to calculate quantities such as embedded element patterns, which is a major extension from its original formulation. The DGFM has been integrated as part of an efficient array analysis tool in the commercial computational electromagnetics software package, FEKO.
AFRIKAANSE OPSOMMING: In hierdie werkstuk word die doeltre ende analise van eindige, aperiodiese antenna samestellings behandel. Eindige gebied benaderings wat op die Moment Metode (MoM) berus, word as vetrekpunt gebruik. `n Tegniek genaamd die Gebied Green's Funksie Metode (GGFM) word voorgestel en is geskik vir die analise van `n verskeidenheid van ontkoppelde samestellings. Die e ektiewe gebruik van rekenaargeheue en looptyd is onderliggend in die implementasie daarvan. Die GGFM is 'n perturbasie metode wat op die oorspronklike werk van Skrivervik en Mosig berus. Laasgenoemde is hoofsaaklik ontwikkel vir die analise van ontkoppelde antenna samestellings op multilaag di elektrikums. `n Deeglike oorsig van voorafgaande word in die tesis verskaf. In hierdie tesis is die bogenoemde werk op `n unieke wyse uitgebrei: `n ho er blok matriks vlak formulering is ontwikkel wat dit moontlik maak vir die analise van `n verskeidenheid strukture en wat onafhanklik is van die onderliggende basis funksies. Beide lae-vlak Rao-Wilton-Glisson (RWG) basis funksies, asook ho er orde hierargiese basis funksies word gebruik vir die modellering van groot antenna samestellings. Die oorspronklike perturbasie aanname is uitgebrei deur akkuraatheidsverbeteringe vir die tegniek voor te stel. Die Aanpasbare Kruis Benaderings (AKB) tegniek is onder andere gebruik om spoed verbeteringe vir die GGFM te bewerkstellig. Die GGFM is verder uitgebrei vir die analise van antenna samestellings in `n komplekse omgewing, bv. `n antenna samestelling bo `n eindige grondplaat. Die Numeriese Green's Funksie (NGF) metode is hiervoor ingespan en die hibriede NGF-GGFM is ontwikkel. Die GGFM is verder met die Karakteristieke Basis Funksie Metode (KBFM) gekombineer. Die analise van groot skikkings wat bestaan uit sub-skikkings, soos die wat tans by die \Low- Frequency Array (LOFAR) " vir radio astronomie in Nederland gebruik word, kan hiermee gedoen word. In die werkstuk word die GGFM ook toegepas op `n reeks interessante numeriese voorbeelde, veral die toepaslike EM analise van groot aperiodiese samestellings. Die akkuraatheidsverbeteringe vir die GGFM maak die berekening van elementpatrone vir skikkings moontlik. Die GGFM is by the sagteware pakket FEKO geintegreer.

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Yoerger, Edward J. Jr. "Vertical Acoustic Propagation in the Non-Homogeneous Layered Atmosphere for a Time-Harmonic, Compact Source." ScholarWorks@UNO, 2019. https://scholarworks.uno.edu/td/2709.

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In this work we study vertical, acoustic propagation in a non-homogeneous media for a spatially-compact, time-harmonic source. An analytical, 2-layer model is developed representing the acoustic pressure disturbance propagating in the atmosphere. The validity of the model spans the distance from the Earth's surface to 30,000 meters. This includes the troposphere (adiabatic), ozone layer (isothermal), and part of the stratosphere (isothermal). The results of the model derivation in the adiabatic region yield pressure solutions as Bessel functions of the First (J) and Second (Y) Kind of order $-\frac{7}{2}$ with an argument of $2 \Omega \tau$ (where $\Omega$ represents a dimensionless frequency and $\tau$ is a dimensionless vertical height in z (vertical coordinate)). For an added second layer (isothermal region), the pressure solution is a decaying sinusoidal, exponential function above the first layer. In particular, the vertical, acoustic propagation is examined for various configurations. These are divided into 2 basic classes. The first class consists of examining the pressure response function when the source is located on boundary interfaces, while the second class consists of situations where the source is arbitrarily located within a finite layer. In all instances, a time-harmonic, compact source is implicitly understood. However, each class requires a different method of solution. The first class conforms to a general boundary value problem, while the second requires the use of Green's functions method. In investigating problems of the first class, 3 different scenarios are examined. In the first case, we apply our model to a semi-infinite medium with a time-harmonic source ($e^{-i \omega t}$) located on the ground. In the next 2 cases, a semi-infinite medium is overlain on the previous medium at a height of z=13,000 meters. Thus, there exist two boundaries: the ground and the layer interface between the 2 media. Sources placed at these interfaces represent the 2nd and 3rd scenarios, respectively. The solutions to all 3 cases are of the form $A \frac{J_{-\frac{7}{2}}(2 \Omega \tau)}{{\tau}^{-\frac{7}{2}}} + B \frac{Y_{-\frac{7}{2}}(2 \Omega \tau)}{{\tau}^{-\frac{7}{2}}}$, where \textit{A} and \textit{B} are constants determined by the boundary conditions. For the 2nd class, we examine the application to a time-harmonic, compact source placed arbitrarily within the 1st layer. The method of Green's functions is used to obtain a particular solution for the model equations. This result is compared with a Fast Field Program (FFP) which was developed to test these solutions. The results show that the response given by the Green's function compares favorably with that of the FFP. Keywords: Linear Acoustics, Inhomogeneous Medium, Layered Atmosphere, Boundary Value Problem, Green's Function Method

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Banerjee, Sourav. "Elastic Wave Propagation in Corrugated Wave Guides." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1182%5F1%5Fm.pdf&type=application/pdf.

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19

Han, Feng. "Development of Novel Green’s Functions and Their Applications to Multiphase and Multilayered Structures." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1147874663.

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20

Zhang, Huaijian. "Boundary Integral Techniques in Three Dimensions for Deep Water Waves." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1306712208.

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21

Tautenhahn, Martin, and Ivan Veselic'. "A note on correlated and non-monotone Anderson models." Universitätsbibliothek Chemnitz, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200800063.

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22

Yu, Ke. "Multi-resolution Lattice Green's Function Method for High Reynolds Number External Flows." Thesis, 2021. https://thesis.library.caltech.edu/14253/1/Caltech_Thesis_Ke_Yu_final.pdf.

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This work expands the state-of-the-art computational fluid dynamics (CFD) methods for simulating three-dimensional, turbulent, external flows by further developing the immersed boundary (IB) Lattice Green's function (LGF) method. The original IB-LGF method applies an exact far-field boundary condition using fundamental solutions on regular Cartesian grids and allows active computational cells to be restricted to vortical flow regions in an adaptive fashion as the flow evolves. The combination of spatial adaptivity and regular Cartesian structure leads to superior efficiency, scalability, and robustness, but necessitates uniform grid spacing. However, the scale separation associated with thin boundary layers and turbulence at higher Reynolds numbers favors a more flexible distribution of elements/cells, which is achieved in this thesis by developing a multi-resolution LGF approach that permits block-wise grid refinement while maintaining the important properties of the original scheme. We further show that the multi-resolution LGF method can be fruitfully combined with the IB method to simulate external flows around complex geometries at high Reynolds numbers. This novel multi-resolution IB-LGF scheme retains good efficiency, parallel scaling as well as robustness (conservation and stability properties). DNS of bluff and streamlined bodies at Reynolds numbers O(10⁴) are conducted and the new multi-resolution scheme is shown to reduce the total number of computational cells up to 99.87%.

We also extended this method to large-eddy simulation (LES) with the stretched-vortex sub-grid-scale model. In validating the LES implementation, we considered an isolated spherical region of turbulence in free space. The initial condition is spherically windowed, isotropic homogeneous incompressible turbulence. We study the spectrum and statistics of the decaying turbulence and compare the results with decaying isotropic turbulence, including cases representing different low wavenumber behavior of the energy spectrum (i.e. k² versus k⁴). At late times the turbulent sphere expands with both mean radius and integral scale showing similar time-wise growth exponents. The low wavenumber behavior has little effect on the inertial scales, and we find that decay rates follow Saffman's predictions in both cases, at least until about 400 initial eddy turnover times. The boundary of the spherical region develops intermittency and features ejections of vortex rings. These are shown to occur at the integral scale of the initial turbulence field and are hypothesized to occur due to a local imbalance of impulse on this scale.

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23

Chen, Ku-Chen, and 陳谷塵. "A Study of Quantum Transport in Narrow-Wired Semiconductor by Using the Green's Function Method." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/29479234237483745399.

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碩士
國立清華大學
電子工程研究所
96
Green’s Function is used to calculate the conductance in narrow wires which include several types of scatters. The research subjects are narrow wires, so the transport properties of the electrons belong to quantum transport, which is totally different from classic transport. This study discusses about the narrow wires that include: (1) a single scattering center, (2) rectangular potential barrier and (3) random distributed scattering centers. Both repulsive and attractive potentials are considered in each case. The delta function potentials are used for the discrete scattering centers. First, we use the Schrodinger equation to calculate the eigenvalues and eigenfunctions of the confined transverse modes of the narrow wires. Then, we use them to calculate the Green’s function in order to calculate the transmission probability. After that, we use the Landauer formula to calculate conductance. The results display the physical phenomena of quantum transport. The stepwise increases of quantum conductance are found for these wires. For a single attractive defect in the wire, there is a dip in the conductance caused by the existence of the quasi-donor level. For the rectangular barrier in the wire, there are resonances in the conductance which are similar to those of the potential barrier and well in quantum mechanics. For the random positive defects in the wire, there appears fluctuation in the conductance. This phenomenon helps us to understand the quantum interference effects. By changing part of the defects from repulsive to negative, the conductance is modified. There are some dips in the conductance due to the quasi-donor levels. The results are consistent with the work of Bagwell and Kumar [1, 2], who use the Scattering-Matrix to calculate conductance。

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Hsu, Su-Haur, and 許書豪. "Study of the Bioheat Transfer by the Method of Green's function for the External Focused Ultrasound Hyperthermia." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/46721572317671643700.

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碩士
國立臺灣大學
機械工程學系
85
The temperature distribution induced by the focused ultrasound hyperthermia is studied theoretically with the different focused ultrasound transducers and the blood perfusion rates. The three-dimensional transient mathematical model includes both the ultrasound power depositions caused by the spherical focused transducers and the Pennes model to described the heat transfer for the blood perfusion. The tissue is treated as a semi-infinite region in the space. It is assume that the initial temperature of the tissue is 310.15 K, the surface temperature is kept at 310.15 K, and the temperature of the tissue far from the surface approaches 310.15 K. With Green's function, the temperature distribution is represent in a simple interation. Accoding to the calculated result, three different controlling mechanics of the temperature development are identified. The ultrasound power deposition plays an important role in the beginning of time. At the time near the initial time, the variation of the temperature is proportional to the ultrasound power deposition. As the time goes by, the heat conduction shows its effect in the temperature development. It explains why the position with the low ultrasound power deposition may have a growth of the temperature and why the temperature distribution finally becomes smoother. When the time is longer, the blood perfusion becomes domiant. The blood perfusion not only determines when the transient process of the temperature development stops but also affects the asymptotic value of the temperature development. If the blood perfusion is stronger, the transient process will be shorter and the asymptotic value of the temperature will be lower.

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25

Xu, Shu-Hao, and 許書豪. "Study of the Bioheat Transfer by the Method of Green's function for the External Focused Ultrasound Hyperthermia." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/06483700702120936089.

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26

Lin, Shih-Yao, and 林士堯. "A Study of Quantum Transport of Narrow Scale n+-n-n+ Devices by Using the Green's Function Method." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/08789953098718264136.

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27

Guha, Amitava 1984. "Development of a Computer Program for Three Dimensional Frequency Domain Analysis of Zero Speed First Order Wave Body Interaction." Thesis, 2012. http://hdl.handle.net/1969.1/148193.

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Abstract:

Evaluation of motion characteristics of ships and offshore structures at the early stage of design as well as during operation at the site is very important. Strip theory based programs and 3D panel method based programs are the most popular tools used in industry for vessel motion analysis. These programs use different variations of the Green’s function or Rankine sources to formulate the boundary element problem which solves the water wave radiation and diffraction problem in the frequency domain or the time domain. This study presents the development of a 3D frequency domain Green’s function method in infinite water depth for predicting hydrodynamic coefficients, wave induced forces and motions. The complete theory and its numerical implementation are discussed in detail. An in house application has been developed to verify the numerical implementation and facilitate further development of the program towards higher order methods, inclusion of forward speed effects, finite depth Green function, hydro elasticity, etc. The results were successfully compared and validated with analytical results where available and the industry standard computer program WAMIT v7.04 for simple structures such as floating hemisphere, cylinder and box barge as well as complex structures such as ship, spar and a tension leg platform.

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Wang, Cynthia Dewi. "The linear wave response of a single and a periodic line-array of floating elastic plates: a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mathematics at Massey University, Albany, New Zealand." 2004. http://hdl.handle.net/10179/1625.

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We propose an improved technique to calculate the linear response of a single and multiple plates models due to ocean waves. The single plate model is the basis for the multiple plates model which we take to be a periodic array of identical plates. For the single plate model we solve the plate displacement by the Finite Element Method (FEM) and the water potential by the Boundary Element Method (BEM). The displacement is expanded in terms of the basis functions of the FEM. The boundary integral equation representing the potential is approximated by these basis functions. The resulting integral operator involving the free-surface Green's function is solved using an elementary integration scheme. Results are presented for the single plate model. We then use the same technique to solve for the periodic array of plates problem because the single and the periodic array plates model differ only in the expression of the Green's function. For the periodic array plate model the boundary integral equation for the potential involves a periodic Green's function which can be obtained by taking an infinite sum of the free-surface Green's function for the single plate model. The solution for the periodic array plate is derived in the same way as the single plate model. From this solution we then calculate the waves scattered by this periodic array.

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Dissertations / Theses on the topic 'KKR Green's function method'

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