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University of Illinois – Urbana-Champaign

1. Wang, Rui. Incorporation of feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits.

Degree: PhD, 1200, 2010, University of Illinois – Urbana-Champaign

In this dissertation, accurate and efficient numerical algorithms are developed to incorporate the feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits. First, simulation of an antenna system requires accurate modeling of interactions between the radiating elements and the associated feeding network. In this work, a feed network is represented in terms of its scattering matrix in a rational function form in the frequency domain that enables its interfacing with the time-domain finite element modeling of the antenna elements through a fast recursive time-convolution algorithm. The exchange of information between the antenna elements and the feed network occurs through the incident and reflected modal voltages/currents at properly defined port interfaces. The proposed numerical scheme allows a full utilization of the advanced antenna simulation techniques, and significantly extends the current antenna modeling capability to the system level. Second, a hybrid field-circuit solver that combines the capabilities of the time-domain finite element method and a lumped circuit analysis is developed for accurate and efficient characterization of complicated microwave circuits that include both distributive and lumped-circuit components. The distributive portion of the device is modeled by the time-domain finite element method to generate a finite element subsystem, while the lumped circuits are analyzed by a SPICE-like circuit solver to generate a circuit subsystem. A global system for both the finite-element and circuit unknowns is established by combining the two subsystems through coupling matrices to model their interactions. For simulations of even more complicated mixed-scale circuit systems that contain pre-characterized blocks of discrete circuit elements, the hybrid field-circuit analysis implemented a systematic and efficient algorithm to incorporate multiport lumped networks in terms of frequency-dependent admittance matrices. Other advanced features in the hybrid field-circuit solver include application of the tree-cotree splitting algorithm and introduction of a flexible time-stepping scheme. Various numerical examples are presented to validate the implementation and demonstrate the accuracy, efficiency, and applications of the proposed numerical algorithms. Advisors/Committee Members: Jin, Jianming (advisor), Jin, Jianming (Committee Chair), Cangellaris, Andreas C. (committee member), Feng, Milton (committee member), Schutt-Ain??, Jos?? E. (committee member).

Subjects/Keywords: Time-domain finite element method; antenna arrays; domain decomposition; feed-network modeling; vector-fitting technique; hybrid solver; linear/nonlinear circuit simulation; transient analysis; admittance matrices; multiport lumped networks; recursive convolution; full-wave analysis; time marching; tree-cotree splitting; multi-rate simulation; time-stepping scheme

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Wang, R. (2010). Incorporation of feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/16536

Chicago Manual of Style (16th Edition):

Wang, Rui. “Incorporation of feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits.” 2010. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed December 14, 2019. http://hdl.handle.net/2142/16536.

MLA Handbook (7th Edition):

Wang, Rui. “Incorporation of feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits.” 2010. Web. 14 Dec 2019.

Vancouver:

Wang R. Incorporation of feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2010. [cited 2019 Dec 14]. Available from: http://hdl.handle.net/2142/16536.

Council of Science Editors:

Wang R. Incorporation of feed-network and circuit modeling into the time-domain finite element analysis of antenna arrays and microwave circuits. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2010. Available from: http://hdl.handle.net/2142/16536

2. Ventimiglia, Florent. Schémas numérique d'ordre élevé en temps et en espace pour l'équation des ondes du premier ordre. Application à la Reverse Time Migration. : High Order time and space schemes for the first order wave equation. Application to the Reverse Time Migration.

Degree: Docteur es, Mathématiques appliquées, 2014, Pau

L’imagerie du sous-sol par équations d’onde est une application de l’ingénierie pétrolière qui mobilise des ressources de calcul très importantes. On dispose aujourd’hui de calculateurs puissants qui rendent accessible l’imagerie de régions complexes mais des progrès sont encore nécessaires pour réduire les coûts de calcul et améliorer la qualité des simulations. Les méthodes utilisées aujourd’hui ne permettent toujours pas d’imager correctement des régions très hétérogènes 3D parce qu’elles sont trop coûteuses et /ou pas assez précises. Les méthodes d’éléments finis sont reconnues pour leur efficacité à produire des simulations de qualité dans des milieux hétérogènes. Dans cette thèse, on a fait le choix d’utiliser une méthode de Galerkine discontinue (DG) d’ordre élevé à flux centrés pour résoudre l’équation des ondes acoustiques et on développe un schéma d’ordre élevé pour l’intégration en temps qui peut se coupler avec la technique de discrétisation en espace, sans générer des coûts de calcul plus élevés qu’avec le schéma d’ordre deux Leap-Frog qui est le plus couramment employé. Le nouveau schéma est comparé au schéma d’ordre élevé ADER qui s’avère plus coûteux car il requiert un plus grand nombre d’opérations pour un niveau de précision fixé. De plus, le schéma ADER utilise plus de mémoire, ce qui joue aussi en faveur du nouveau schéma car la production d’images du sous-sol consomme beaucoup de mémoire et justifie de développer des méthodes numériques qui utilisent la mémoire au minimum. On analyse également la précision des deux schémas intégrés dans un code industriel et appliqués à des cas test réalistes. On met en évidence des phénomènes de pollution numériques liés à la mise en oeuvre d'une source ponctuelle dans le schéma DG et on montre qu'on peut éliminer ces ondes parasites en introduisant un terme de pénalisation non dissipatif dans la formulation DG. On finit cette thèse en discutant les difficultés engendrées par l'utilisation de schémas numériques dans un contexte industriel, et en particulier l'effet des calculs en simple précision.

Oil engineering uses a wide variety of technologies including imaging wave equation which involves very large computing resources. Very powerful computers are now available that make imaging of complex areas possible, but further progress is needed both to reduce the computational cost and improve the simulation accuracy. The current methods still do not allow to image properly heterogeneous 3D regions because they are too expensive and / or not accurate enough. Finite element methods turn out to be efficient for producing good simulations in heterogeneous media. In this thesis, we thus chose to use a high order Discontinuous Galerkin (DG) method based upon centered fluxes to solve the acoustic wave equation and developed a high-order scheme for time integration which can be coupled with the space discretization technique, without generating higher computational cost than the second-order Leap Frog scheme which is the most widely used . The new scheme is compared to…

Advisors/Committee Members: Barucq, Hélène (thesis director).

Subjects/Keywords: Ordre élevé; Galerkine discontinu; Pas de temps local; Schémas numériques; Propagateurs en temps; Reverse Time Migration; Equation des ondes; Formulation du premier ordre; Ondes acoustiques; Ondes élastiques; Dispersion numérique; Analyse numérique; Schéma Nabla; Schéma ADER; High Order methods; Discontinuous Galerkin; Local time stepping; Numerical schemes; Time propagators; Reverse Time Migration,; Wave Equation; First order formulation; Acoustic waves; Elastic waves; Numerical dispersion analysis; Numerical analysis; Nabla scheme,; ADER scheme.

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Ventimiglia, F. (2014). Schémas numérique d'ordre élevé en temps et en espace pour l'équation des ondes du premier ordre. Application à la Reverse Time Migration. : High Order time and space schemes for the first order wave equation. Application to the Reverse Time Migration. (Doctoral Dissertation). Pau. Retrieved from http://www.theses.fr/2014PAUU3009

Chicago Manual of Style (16th Edition):

Ventimiglia, Florent. “Schémas numérique d'ordre élevé en temps et en espace pour l'équation des ondes du premier ordre. Application à la Reverse Time Migration. : High Order time and space schemes for the first order wave equation. Application to the Reverse Time Migration.” 2014. Doctoral Dissertation, Pau. Accessed December 14, 2019. http://www.theses.fr/2014PAUU3009.

MLA Handbook (7th Edition):

Ventimiglia, Florent. “Schémas numérique d'ordre élevé en temps et en espace pour l'équation des ondes du premier ordre. Application à la Reverse Time Migration. : High Order time and space schemes for the first order wave equation. Application to the Reverse Time Migration.” 2014. Web. 14 Dec 2019.

Vancouver:

Ventimiglia F. Schémas numérique d'ordre élevé en temps et en espace pour l'équation des ondes du premier ordre. Application à la Reverse Time Migration. : High Order time and space schemes for the first order wave equation. Application to the Reverse Time Migration. [Internet] [Doctoral dissertation]. Pau; 2014. [cited 2019 Dec 14]. Available from: http://www.theses.fr/2014PAUU3009.

Council of Science Editors:

Ventimiglia F. Schémas numérique d'ordre élevé en temps et en espace pour l'équation des ondes du premier ordre. Application à la Reverse Time Migration. : High Order time and space schemes for the first order wave equation. Application to the Reverse Time Migration. [Doctoral Dissertation]. Pau; 2014. Available from: http://www.theses.fr/2014PAUU3009


University of Illinois – Urbana-Champaign

3. Yan, Su. Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems.

Degree: PhD, Electrical & Computer Engr, 2016, University of Illinois – Urbana-Champaign

In this dissertation, nonlinear electromagnetic and multiphysics problems are modeled and simulated using various three-dimensional full-wave methods in the time domain. The problems under consideration fall into two categories. One is nonlinear electromagnetic problems with the nonlinearity embedded in either the permeability or the conductivity of the material's constitutive properties. The other is multiphysics problems that involve interactions between electromagnetic and other physical phenomena. A numerical solution of nonlinear magnetic problems is formulated using the three-dimensional time-domain finite element method (TDFEM) combined with the inverse Jiles-Atherton vector hysteresis model. A second-order nonlinear partial differential equation (PDE) that governs the nonlinear magnetic problem is constructed through the magnetic vector potential in the time domain, which is solved by applying the Newton-Raphson method. To solve the ordinary differential equation (ODE) representing the magnetic hysteresis accurately and efficiently, several ODE solvers are specifically designed and investigated. To improve the computational efficiency of the Newton-Raphson method, the multi-dimensional secant methods are incorporated in the nonlinear TDFEM solver. A nonuniform time-stepping scheme is also developed using the weighted residual approach to remove the requirement of a uniform time-step size during the simulation. Breakdown phenomena during high-power microwave (HPM) operation are investigated using different physical and mathematical models. During the breakdown process, the bound charges in solid dielectrics and air molecules break free and are pushed to move by the Lorentz force produced by the electromagnetic fields. The motion of free electrons produces plasma currents, which generate secondary electromagnetic fields that couple back to the externally applied fields and interact with the free electrons. When the incident field intensity is high enough, this will lead to an exponential increase of the charged particles known as breakdown. Such a process is first described by a nonlinear conductivity of the solid dielectric as a function of the electric field to model the dielectric breakdown phenomenon. The air breakdown problem encountered with HPM operation is then simulated with the plasma current modeled by a simplified plasma fluid equation. Both the dielectric and air breakdown problems are solved with the TDFEM together with a Newton's method, where the dielectric breakdown is treated as a pure nonlinear electromagnetic problem, while the air breakdown is treated as a multiphysics problem. To describe the plasma behavior more accurately, the plasma density and velocity are modeled by the equations of diffusion and motion, respectively. This results in a multiphysics and multiscale system depicted by the nonlinearly coupled full-wave Maxwell and plasma fluid equations, which are solved by a nodal discontinuous Galerkin time-domain (DGTD) method in three dimensions. The air breakdown during the HPM… Advisors/Committee Members: Jin, Jianming (advisor), Jin, Jianming (Committee Chair), Chew, Weng Cho (committee member), Kudeki, Erhan (committee member), Aluru, Narayana (committee member).

Subjects/Keywords: Nonlinear Electromagnetic Problems; Multiphysics Problems; Multiscale Problems; Time-Domain Simulation; Newton's Method; Jiles-Atherton Model; Hysteresis Model; Nonuniform Time-Stepping Scheme; Time-Domain Finite Element Method (TDFEM); Discontinuous Galerkin Time-Domain (DGTD) Method; Local Discontinuous Galerkin (LDG) Method; High-Power Microwave (HPM); Dielectric Breakdown; Air Breakdown; Electromagnetic – Plasma Interaction; Boltzmann's Equation; Nonlinear Conductivity; Plasma Fluid Model; Plasma Formation; Plasma Shielding; Hyperbolic Equation; Diffusion Equation; Divergence Cleaning Technique; Purely Hyperbolic Maxwell Equations; Damped Hyperbolic Maxwell Equations; Continuity Preserving; Dynamic h-Adaptation Algorithm; Dynamic p-Adaptation Algorithm; Adaptive Cartesian Mesh; Local Time-Stepping

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Yan, S. (2016). Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems. (Doctoral Dissertation). University of Illinois – Urbana-Champaign. Retrieved from http://hdl.handle.net/2142/93014

Chicago Manual of Style (16th Edition):

Yan, Su. “Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems.” 2016. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed December 14, 2019. http://hdl.handle.net/2142/93014.

MLA Handbook (7th Edition):

Yan, Su. “Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems.” 2016. Web. 14 Dec 2019.

Vancouver:

Yan S. Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems. [Internet] [Doctoral dissertation]. University of Illinois – Urbana-Champaign; 2016. [cited 2019 Dec 14]. Available from: http://hdl.handle.net/2142/93014.

Council of Science Editors:

Yan S. Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems. [Doctoral Dissertation]. University of Illinois – Urbana-Champaign; 2016. Available from: http://hdl.handle.net/2142/93014

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