Browsing by Subject "Virtual manufacturing"

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Open Access
Investigation of various metamaterial structures using multilevel fast multipole algorithm
(IEEE, 2007) Ergül, Özgür; Yavuz, Çağlar; Ünal, Alper; Gürel, Levent
We consider accurate simulations of metamaterial (MM) structures consisting of split- ring-resonators (SRRs) and thin wires (TWs). We employ electric-field integral equation (EFIE) to formulate the scattering problems involving these complicated structures. Accurate modelling of MMs translates into very large computational problems, which can be solved with the aid of advanced acceleration techniques, such as the multilevel fast multipole algorithm (MLFMA). We investigate various multilayer structures of SRRs as well as composite metamaterials (CMMs) constructed by the arrangements of SRR and TW arrays. In addition, we consider various disordering scenarios, where the unit cells are not placed perfectly and they are misaligned. This way, we investigate the electromagnetic properties of MMs when the arrays are defected. In this paper, we briefly report the accurate solutions of various real-life MM problems and present power transmission properties of these important structures.
Open Access
Sequential and parallel preconditioners for large-scale integral-equation problems
(IEEE, 2007) Malas, Tahir; Ergül, Özgür; Gürel, Levent
For efficient solutions of integral-equation methods via the multilevel fast multipole algorithm (MLFMA), effective preconditioners are required. In this paper we review appropriate preconditioners that have been used for sparse systems and developed specially in the context of MLFMA. First we review the ILU-type preconditioners that are suitable for sequential implementations. We can make these preconditioners robust and efficient for integral-equation methods by making appropriate selections and by employing pivoting to suppress the instability problem. For parallel implementations, the sparse approximate inverse or the iterative solution of the near-field system enables fast convergence up to certain problem sizes. However, for very large problems, the near-field matrix itself becomes insufficient to approximate the dense system matrix and preconditioners generated from the near-field interactions cannot be effective. Therefore, we propose an approximation strategy to MLFMA to be used as an effective preconditioner. Our numerical experiments reveal that this scheme significantly outperforms other preconditioners. With the combined effort of effective preconditioners and an efficiently parallelized MLFMA, we are able to solve problems with tens of millions of unknowns in a few hours. We report the solution of integral-equation problems that are among the largest in their classes. © 2007 IEEE.