Wave Equation-Based Implicit Subdomain DGTD Method for Modeling of Electrically Small Problems

A second-order wave equation-based implicit discontinuous Galerkin time-domain (DGTD) method is proposed to efficiently model electrically small problems. The proposed method employs the second-order wave equation for electric field (or magnetic field) as the governing equation of the DG formulation, instead of the first-order Maxwell's curl equations. A modified version of the Riemann solver (upwind flux) is introduced to evaluate the numerical flux resulting from the weak form of the wave equation. Compared with previous first-order Maxwell's curl equation-based implicit DGTD methods, which typically solve all electric and magnetic field unknowns for each subdomain, the proposed method only needs to solve for the electric field unknowns plus the surface magnetic field unknowns at subdomain interfaces. This reduces the dimensions of the resultant linear system and thus allows for modeling larger problems. Furthermore, unlike element-based DGTD methods, the proposed method is subdomain-based. The computational region is divided into multiple subdomains based on the domain-decomposition method, and each subdomain may contain multiple elements. Different element types and orders of basis functions can be employed in different subdomains to exploit the geometry property of the model. A nonconformal mesh is allowed between different subdomains to increase meshing flexibility. The Newmark-beta time-integration scheme is used for implicit temporal discretization, and fast direct linear solvers, such as the lower-diagonal-upper decomposition algorithm, are employed to accelerate time integration when all the subdomains are in a sequential order. Numerical results show that the proposed method is more efficient in terms of CPU time, and also saves memory with respect to the previous implicit DGTD method when modeling electrically small problems.