Published online by Cambridge University Press: 05 July 2014
In this penultimate chapter, the preceding discussion of the finite element method is extended to three dimensions. We start by extending the eigenanalysis of the preceding chapter to three dimensions, using Whitney elements. Although a 3D FEM code is non-trivial to implement, simple problems can nonetheless be addressed, and the eigenanalysis of a PEC cavity is used to illustrate the development of a 3D FEM code. Higher-order vector elements have already been introduced in the preceding chapter for two-dimensional analysis; in this chapter, a more detailed theoretical treatment will be presented for the more general three-dimensional case, and an LT/QN element is applied to the cavity eigenanalysis problem. Following this, the stationary functional formulation for deterministic (driven) problems will be outlined. In this and the preceding chapter, eigenvalue problems have been used to illustrate the FEM; in this chapter, a deterministic three-dimensional problem will also be discussed, namely the analysis of waveguide obstacles. Finite element analysis is ideal for this problem, and good results have been obtained by a number of workers. Results for two waveguide problems computed using FEM codes incorporating higher-order elements will be shown. The chapter concludes with a discussion on the use of absorbing boundary conditions for open-region problems, and a first-order ABC is presented. Treatment of a more sophisticated scheme is deferred to the final chapter.
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