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University of Illinois – Urbana-Champaign

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

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

URL: http://hdl.handle.net/2142/93014

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; ElectromagneticÂ â€“ 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 (6^{th} 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 (16^{th} Edition):

Yan, Su. “Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems.” 2016. Doctoral Dissertation, University of Illinois – Urbana-Champaign. Accessed December 08, 2019. http://hdl.handle.net/2142/93014.

MLA Handbook (7^{th} Edition):

Yan, Su. “Computational modeling and simulation of nonlinear electromagnetic and multiphysics problems.” 2016. Web. 08 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 08]. 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