Browsing by Author "Manyas, Alp"

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    Hybridizing physical optics with MLFMA for efficient scattering computations of three-dimensional complex targets
    (IEEE, 2009-07) Manyas, Alp; Ergül, Özgür; Gürel, Levent
    The multilevel fast multipole algorithm (MLFMA) provides accurate and efficient solutions of electromagnetic scattering problems involving large and complicated structures. On the other hand, whenever applicable, accelerations provided by approximation techniques can be useful to further improve the efficiency of solutions. In this paper, we present a hybrid technique, which combines the physical-optics (PO) method and MLFMA for efficient scattering computations of three-dimensional objects. We show that, with a careful choice of MLFMA and PO regions on the structure, the number of unknowns can be reduced and solutions can be accelerated significantly, without sacrificing the accuracy. The proposed hybrid technique is easy to implement by modifying existing MLFMA codes. ©2009 IEEE.
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    Memory-efficient multilevel physical optics algorithm for fast computation of scattering from three-dimensional complex targets
    (IEEE, 2007) Manyas, Alp; Gürel, Levent
    Multilevel physical optics (MLPO) algorithm provides a speed-up for computing the physical-optics integral over complex bodies for a range of aspect angles and frequencies. On the other hand, when computation of the RCS pattern as a function of θ, φ, and frequency is desired, the O N3 memory complexity of the algorithm may prevent the solution of electrically large problems. In this paper, we propose an improved version of the MLPO algorithm, for which the memory complexity is reduced to O N2 log N . The algorithm is based on the aggregation of only some portion of the scattering patterns at each aggregation step. This way, memory growth in each step is prevented, and a significant amount of saving is achieved.
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    Multilevel physical optics algorithm for fast solution of scattering problems involving nonuniform triangulations
    (IEEE, 2007) Gürel, Levent; Manyas, Alp
    This paper shows the computational efficiency of the multilevel physical optics (MLPO) algorithm can be further increased by employing nonuniform triangulations of the target surface so that the triangle size is not nearly uniform, but instead, is determined by the surface curvature.
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    Multilevel PO algorithm for non-uniform triangulations
    (ESA Publications, 2006) Manyas, Alp; Gürel, Levent
    Fast physical optics (FPO) algorithm provides a speedup for computing the physical optics (PO) integral over complex bodies for a range of aspect angles and frequencies. In this paper, this algorithm is further developed in order to compute the scattered field from nonuniform triangulations of complex bodies. In the original "uniform" FPO algorithm, only the radiation patterns of the smallest subdomains in the bottom level are directly computed and the radiation patterns of the larger subdomains in the upper levels are computed via interpolation and aggregation. In this modified "nonuniform" algorithm, the radiation patterns of the larger triangles, which are too large to fit in the bottom-level subdomains, are directly computed and incorporated in the appropriate aggregation levels. It is also shown that, by applying different interpolation methods, accuracy of the FPO algorithm can be improved without any computational cost.
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    PO-MLFMA hybrid technique for the solution of electromagnetic scattering problems involving complex targets
    (Institution of Engineering and Technology, 2007) Gürel, Levent; Manyas, Alp; Ergül, Özgür
    The multilevel fast multipole algorithm (MLFMA) is a powerful tool for efficient and accurate solutions of electromagnetic scattering problems involving large and complicated structures. On the other hand, it is still desirable to increase the efficiency of the solutions further by combining the MLFMA implementations with the high- frequency techniques such as the physical optics (PO). In this paper, we present our efforts in order to reduce the computational cost of the MLFMA solutions by introducing PO currents appropriately on the scatterer. Since PO is valid only on smooth and large surfaces that are illuminated strongly by the incident fields, accurate solutions require careful choices of the PO and MLFMA regions. Our hybrid technique is useful especially when multiple solutions are required for different frequencies, illuminations, and scenarios, so that the direct solutions with MLFMA become expensive. For these problems, we easily accelerate the MLFMA solutions by systematically introducing the PO currents and reducing the matrix dimensions without sacrificing the accuracy.