Efficient Spectral-Element Methods For Acoustic Scattering And Related Problems

He, Ying Ph.D., Purdue University, December 2013. Efficient Spectral-Element Methods for Acoustic Scattering and Related Problems. Major Professor: Jie Shen . This dissertation focuses on the development of high-order numerical methods for acoustic and electromagnetic scattering problems, and nonlinear fluid-structure interaction problems. For the scattering problems, two cases are considered: 1) the scattering from a doubly layered periodic structure; and 2) the scattering from doubly layered, unbounded rough surface. For both cases, we first apply the transformed field expansion (TFE) method to reduce the two-dimensional Helmholtz equation with complex scattering surface into a successive sequence of the transmission problems with a plane interface. Then, we use Fourier-Spectral method in the periodic structure problem and Hermite-Spectral method in the unbounded rough surface problem to reduce the two-dimensional problems into a sequence of one-dimensional problems, which can then be efficiently solved by a Legendre-Galerkin method. In order for TFE method to work well, the scattering surface has to be a sufficiently small and smooth deformation of a plane surface. To deal with scattering problems from a non-smooth surface, we also develop a high-order spectral-element method which is more robust than the TFE method, but is computationally more expensive. We also consider the non-linear fluid-structure interaction problem, and develop a class of monolithic pressure-correction schemes, based on the standard pressurecorrection and rotational pressure-correction schemes. The main advantage of these schemes is that they only require solving a pressure Poisson equation and a linear coupled elliptic equation at each time step. Hence, they are computationally very efficient. Furthermore, we prove that the proposed schemes are unconditionally stable.