A multilevel method for large-eddy simulation of turbulent compressible flows is proposed. The method relies on the splitting of the turbulent flowfield into several frequency bands in space and time, each band being ...
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A multilevel method for large-eddy simulation of turbulent compressible flows is proposed. The method relies on the splitting of the turbulent flowfield into several frequency bands in space and time, each band being associated to a specific computational grid in physical space. This allows to take into account in a deterministic way the information contained on finer grids. A subgrid model adapted to such a decomposition-based on a generalization of the Germane's identity to multilevel decomposition-is also introduced. The approach is validated by several multilevel simulations in a subsonic plane channel flow configuration for a low and a high value of the Reynolds number, while reductions of the CPU times up to 80% are obtained. (C) 2001 Academic Press.
作者：
Aydiner, AAChew, WCSong, JMCui, TJUniv Illinois
Dept Elect & Comp Engn Ctr Computat Electromagnet & Electromagnet Lab Urbana IL 61801 USA Iowa State Univ Sci & Technol
Dept Elect & Comp Engn Ames IA 50011 USA SE Univ
Dept Radio Engn Ctr Computat Electromagnet Nanjing 210096 Peoples R China SE Univ
Dept Radio Engn State Key Lab Millimeter Waves Nanjing 210096 Peoples R China
A multilevel algorithm that efficiently Fourier transforms sparse spatial data to sparse spectral data with controllable error is presented. The algorithm termed "sparse data fast fourier transform" (SDFFT) ...
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A multilevel algorithm that efficiently Fourier transforms sparse spatial data to sparse spectral data with controllable error is presented. The algorithm termed "sparse data fast fourier transform" (SDFFT) is particularly useful for signal processing applications where only part of the k-space is to be computed-regardless of whether it is a regular region like an angular section of the Ewald sphere or it consists of completely arbitrary points scattered in the k-space. In addition, like the various nonuniform fast Fourier transforms, the O(N log N) algorithm can deal with a sparse, nonuniform spatial domain. In this paper, the parabolic reflector antenna problem is studied as an example to demonstrate its use in the computation of far-field patterns due to arbitrary aperture antennas and antenna arrays. The algorithm is also promising for various applications such as back-projection tomography, diffraction tomography, and synthetic aperture radar imaging.
A multilevel method for Large-Eddy Simulation of turbulent unsteady compressible flows is proposed. It relies on the splitting of the turbulent flowfield into several frequency bands in space and time, each band being...
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A multilevel method for Large-Eddy Simulation of turbulent unsteady compressible flows is proposed. It relies on the splitting of the turbulent flowfield into several frequency bands in space and time, each band being associated to a computational grid in physical space, allowing to take into account in a deterministic way the information contained on finer grids. A subgrid-scale model adapted to such a decomposition based on a generalization of the Germane's identity to multilevel decomposition - is also introduced. The approach is validated by a simulation in a subsonic plane channel flow configuration. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
Based on the multilevel fast multipole algorithm (MLFMA), an efficient method is proposed to accelerate the solution of the combined field integral equation in electromagnetic scattering and radiation, where the fast ...
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Based on the multilevel fast multipole algorithm (MLFMA), an efficient method is proposed to accelerate the solution of the combined field integral equation in electromagnetic scattering and radiation, where the fast far-field approximation (FAFFA) is combined with MLFMA. The translation between groups in MLFMA is expensive because spherical Hankel functions and Legendre polynomials are involved and the translator is defined on an Eward sphere with many (k) over cap directions. When two groups are in the far-field region, however, the translation can be greatly simplified by FAFFA where only a single k direction is involved in the translator. The condition for using FAFFA and the way to efficiently incorporate FAFFA with MLFMA are discussed. Complexity analysis illustrates that the computational cost in FAFFA-MLFMA can be asymptotically cut by half compared to the conventional MLFMA. Numerical results are given to verify the efficiency of the algorithm.
A novel algorithm for radar imaging is presented. The method comprises two steps. First, a decomposition of the radar data domain into subdomains and computation of pertinent low resolution images. Second, interpolati...
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A novel algorithm for radar imaging is presented. The method comprises two steps. First, a decomposition of the radar data domain into subdomains and computation of pertinent low resolution images. Second, interpolation, phase correction and aggregation of the low-resolution images into the final high resolution one. A multilevel algorithm is formulated via a recursive application of the domain decomposition and image aggregation steps. The computational cost of the proposed algorithm is comparable to that of the fast Fourier transform (FFT) based techniques while it appears to he considerably more flexible than the latter.
In this paper we describe a fast multilevel algorithm for the solution of a system of nonlinear integro-differential equations that model steady-state combined conductive-radiative heat transfer in two space dimension...
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In this paper we describe a fast multilevel algorithm for the solution of a system of nonlinear integro-differential equations that model steady-state combined conductive-radiative heat transfer in two space dimensions. This extends our previous work in one space dimension. We formulate the equations as a compact fixed point problem with the temperature as the unknown. The fixed point map requires both a Poisson solve and a transport solve for its evaluation. As a solver for both the transport problem and the full system we apply the Atkinson-Brakhage algorithm, using Newton-GMRES as the solver on the coarse mesh. We compare our solver choices with Newton-GMRES. Under modest stability and convergence assumptions on the transport solver, we prove convergence of the multilevel method for the complete system.
In this paper we describe and analyze a fast multilevel algorithm for the solution of a system of nonlinear integro-differential equations that model steady-state combined conductive-radiative heat transfer. This syst...
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In this paper we describe and analyze a fast multilevel algorithm for the solution of a system of nonlinear integro-differential equations that model steady-state combined conductive-radiative heat transfer. This system of equations for radiative intensity and temperature can be formulated as a compact fixed point problem in temperature alone with a fixed point map that requires both a solution of the linear transport equation and the linear heat equation for its evaluation. We obtain an efficient evaluation of the fixed point map by coupling a finite element diffusion solver with a fast transport solver developed by the second author. As a solver we apply a modification of the Atkinson-Brakhage method, with Newton-GMRES as the coarse mesh solver, to the full nonlinear system. We compare our discretization/solver pair with Newton-GMRES and the classical Atkinson-Brakhage algorithm.
The biconjugate gradient-fast Fourier transform (BCG-FFT) method is a very efficient and useful technique to analyze microstrip antennas and arrays. In order to increase the efficiency of the BCG-FFT method by reducin...
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The biconjugate gradient-fast Fourier transform (BCG-FFT) method is a very efficient and useful technique to analyze microstrip antennas and arrays. In order to increase the efficiency of the BCG-FFT method by reducing the number of iterations a multilevel BCG-FFT method is constructed using the idea of multigrid methods. The analysis of microstrip antennas and arrays illustrates that the multilevel BCG-FFT method has good accuracy and is much faster than the BCG-FFT method. (C) 2000 John Wiley & Sons, Inc.
We study the convergence rate of multilevel algorithms from an algebraic point of view. This requires a detailed analysis of the constant in the strengthened Cauchy–Schwarz inequality between the coarse-grid space an...
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An efficient algorithm combining multilevel fast multipole method and the discrete complex image method is presented for analyzing large-scale microstrip structures. The resulting algorithm has the memory requirement ...
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An efficient algorithm combining multilevel fast multipole method and the discrete complex image method is presented for analyzing large-scale microstrip structures. The resulting algorithm has the memory requirement and the CPU time per iteration proportional to O(N log N). where N denotes the number of unknowns. Numerical results for microstrip antennas are presented to demonstrate the efficiency and accuracy of this method.
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