The Experts below are selected from a list of 22845 Experts worldwide ranked by ideXlab platform
Xiaolin Zhong - One of the best experts on this subject based on the ideXlab platform.
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a high order cut cell method for numerical simulation of hypersonic boundary layer instability with surface roughness
Journal of Computational Physics, 2010Co-Authors: Le Duan, Xiaowen Wang, Xiaolin ZhongAbstract:Laminar-turbulent transition of hypersonic boundary layers can be affected significantly by the existence of surface roughness. Currently many important mechanisms of roughness-induced transition are not well understood. In recent years, direct numerical simulation (DNS) has been extensively applied for investigating instability and transition mechanisms of hypersonic boundary layers. Most of the past DNS studies, however, have been based on body-fitted Grids for smooth surfaces without roughness. Due to complex geometry of embedded roughness, the use of body-fitted Grids can be very difficult for flow with arbitrary surface roughness. In this paper, we present a new high-order cut-cell method to overcome the natural complexities in Grid generation around arbitrary surface of roughness. The new method combines a non-Uniform-Grid finite-difference method for discrete Grid points near the solid boundary and a shock-fitting method for the treatment of the bow shock. The non-Uniform-Grid finite-difference formulas are expressed in a general explicit form so that they can be applied to different multi-dimensional problems without any modification. The computational accuracy of new algorithms of up to O(h^4) are tested on several one- and two-dimensional elliptic equations in irregular domains. In addition, the new method is applied to the simulation of the receptivity process of a Mach 5.92 flow over a flat plate under the combined effect of an isolated surface roughness element and surface blow and suction. A good agreement is found between the unsteady flow results and those obtained by a Linear Stability Theory (LST).
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derivation of high order compact finite difference schemes for non Uniform Grid using polynomial interpolation
Journal of Computational Physics, 2005Co-Authors: Ratnesh K Shukla, Xiaolin ZhongAbstract:In this paper simple polynomial interpolation is used to derive arbitrarily high-order compact schemes for the first derivative and tridiagonal compact schemes for the second derivative (consisting of three second derivative nodes in the interior and two on the boundary) on non-Uniform Grids. Boundary and near boundary schemes of the same order as the interior are also developed using polynomial interpolation and for a general compact scheme on a non-Uniform Grid it is shown that polynomial interpolation is more efficient than the conventional method of undetermined coefficients for finding coefficients of the scheme. The high-order non-Uniform schemes along with boundary closure of up to 14th order thus obtained are shown to be stable on a non-Uniform Grid with appropriate stretching so that more Grid points are clustered near the boundary. The stability and resolution properties of the high-order non-Uniform Grid schemes are studied and the results of three numerical tests on stability and accuracy properties are also presented.
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high order non Uniform Grid schemes for numerical simulation of hypersonic boundary layer stability and transition
Journal of Computational Physics, 2003Co-Authors: Xiaolin Zhong, Mahidhar TatineniAbstract:The direct numerical simulation of receptivity, instability and transition of hypersonic boundary layers requires high-order accurate schemes because lower-order schemes do not have an adequate accuracy level to compute the large range of time and length scales in such flow fields. The main limiting factor in the application of high-order schemes to practical boundary-layer flow problems is the numerical instability of high-order boundary closure schemes on the wall. This paper presents a family of high-order non-Uniform Grid finite difference schemes with stable boundary closures for the direct numerical simulation of hypersonic boundary-layer transition. By using an appropriate Grid stretching, and clustering Grid points near the boundary, high-order schemes with stable boundary closures can be obtained. The order of the schemes ranges from first-order at the lowest, to the global spectral collocation method at the highest. The accuracy and stability of the new high-order numerical schemes is tested by numerical simulations of the linear wave equation and two-dimensional incompressible flat plate boundary layer flows. The high-order non-Uniform-Grid schemes (up to the 11th-order) are subsequently applied for the simulation of the receptivity of a hypersonic boundary layer to free stream disturbances over a blunt leading edge. The steady and unsteady results show that the new high-order schemes are stable and are able to produce high accuracy for computations of the nonlinear two-dimensional Navier-Stokes equations for the wall bounded supersonic flow.
Vladislav V Serov - One of the best experts on this subject based on the ideXlab platform.
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orthogonal fast spherical bessel transform on Uniform Grid
Computer Physics Communications, 2017Co-Authors: Vladislav V SerovAbstract:Abstract We propose an algorithm for the orthogonal fast discrete spherical Bessel transform on a Uniform Grid. Our approach is based upon the spherical Bessel transform factorization into the two subsequent orthogonal transforms, namely the fast Fourier transform and the orthogonal transform founded on the derivatives of the discrete Legendre orthogonal polynomials. The method utility is illustrated by its implementation for the problem of a two-atomic molecule in a time-dependent external field simulating the one utilized in the attosecond streaking technique.
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orthogonal fast spherical bessel transform on Uniform Grid
arXiv: Numerical Analysis, 2015Co-Authors: Vladislav V SerovAbstract:We propose an algorithm for the orthogonal fast discrete spherical Bessel transform on an Uniform Grid. Our approach is based upon the spherical Bessel transform factorization into the two subsequent orthogonal transforms, namely the fast Fourier transform and the orthogonal transform founded on the derivatives of the discrete Legendre orthogonal polynomials. The method utility is illustrated by its implementation for the numerical solution of the three-dimensional time-dependent Schrodinger equation.
Amir Boag - One of the best experts on this subject based on the ideXlab platform.
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adaptive multilevel non Uniform Grid algorithm for the accelerated analysis of composite metallic dielectric radomes
IEEE Transactions on Antennas and Propagation, 2021Co-Authors: Yair Hollander, Amir BoagAbstract:An adaptive multilevel non-Uniform Grid (MLNG) algorithm is developed for the accelerated computation of fields radiated through composite metallic-dielectric radomes as well as antenna-radome interactions. The MLNG approach is applied to the mixed potential formulation of the coupled surface and volume electric field integral equations. The radome is decomposed into a hierarchy of subdomains (SDs) by an adaptive algorithm that closely follows the radome geometry, allowing significant savings in memory and CPU time. In the MLNG algorithm, only local generalized impedance matrices of the finest level SDs are evaluated. Far-zone potentials and fields are indirectly evaluated through a multilevel aggregation involving phase and amplitude compensated interpolation on non-Uniform Grids (NGs), requiring considerably fewer calculations as compared with the classical Method of Moments (MoM). The MLNG algorithm is incorporated in a preconditioned iterative solver. Accuracy as well as memory consumption and computation times of the algorithm are studied on realistic examples. The radome effect on the antenna input impedance and electric current density distribution is demonstrated. The method is validated by comparison with a commercial MoM software and shown to exhibit a computational complexity (CC) of O(NlogN), N being the number of unknowns.
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optimizing kernel methods for poisson integrals on a Uniform Grid
Computer Physics Communications, 2017Co-Authors: Dor Gabay, Amir Boag, Amir NatanAbstract:Abstract We analyze the error and error propagation in the calculation of the Poisson integral on a Uniform Grid within Density Functional Theory (DFT) real-space calculations. We suggest and examine several schemes for near neighbors’ interaction correction for the Green’s function kernel to improve the accuracy. Finally, we demonstrate the effect of the different kernels on DFT eigenvalues and Hartree energy accuracy in systems such as C 60 and C 40 H 82 .
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a multilevel cartesian non Uniform Grid time domain algorithm
Journal of Computational Physics, 2010Co-Authors: Jun Meng, Amir Boag, Vitaliy Lomakin, E MichielssenAbstract:A multilevel Cartesian non-Uniform Grid time domain algorithm (CNGTDA) is introduced to rapidly compute transient wave fields radiated by time dependent three-dimensional source constellations. CNGTDA leverages the observation that transient wave fields generated by temporally bandlimited and spatially confined source constellations can be recovered via interpolation from appropriately delay- and amplitude-compensated field samples. This property is used in conjunction with a multilevel scheme, in which the computational domain is hierarchically decomposed into subdomains with sparse non-Uniform Grids used to obtain the fields. For both surface and volumetric source distributions, the computational cost of CNGTDA to compute the transient field at N"s observation locations from N"s collocated sources for N"t discrete time instances scales as O(N"tN"slogN"s) and O(N"tN"slog^2N"s) in the low- and high-frequency regimes, respectively. Coupled with marching-on-in-time (MOT) time domain integral equations, CNGTDA can facilitate efficient analysis of large scale time domain electromagnetic and acoustic problems.
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adaptive multilevel non Uniform Grid algorithm for fast field evaluation in multilayered media
IEEE Antennas and Propagation Society International Symposium, 2007Co-Authors: B Livshitz, V Lomakir, Amir BoagAbstract:In this work, we introduce a multilevel layered medium NG (ML-LMNG) algorithm that is a multilevel generalization of the two-level LMNG and multi-level free-space NG algorithms. The LMNG algorithm inherits most of the advantages of the free-space NG scheme and offers additional advantages as compared to other fast schemes for layered media when quasi-planar configurations are of interest.
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non Uniform Grid ng algorithm for fast capacitance extraction
Workshop on Signal Propagation on Interconnects, 2004Co-Authors: Amir Boag, B LivshitzAbstract:A novel approach for computing the capacitance matrices of arbitrary shaped three-dimensional geometries is presented. The proposed approach combines an iterative solution of the pertinent integral equations with the non-Uniform Grid (NG) algorithm for fast evaluation of potentials due to given source distributions. The NG approach is based on the observation that locally the potential produced by a finite size source can be interpolated from its samples at a small number of points of a non Uniform spherical Grid. This observation leads to a multilevel algorithm comprising interpolation and aggregation of potentials. The resulting hierarchical algorithm attains an O(N) asymptotic complexity.
Mahidhar Tatineni - One of the best experts on this subject based on the ideXlab platform.
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high order non Uniform Grid schemes for numerical simulation of hypersonic boundary layer stability and transition
Journal of Computational Physics, 2003Co-Authors: Xiaolin Zhong, Mahidhar TatineniAbstract:The direct numerical simulation of receptivity, instability and transition of hypersonic boundary layers requires high-order accurate schemes because lower-order schemes do not have an adequate accuracy level to compute the large range of time and length scales in such flow fields. The main limiting factor in the application of high-order schemes to practical boundary-layer flow problems is the numerical instability of high-order boundary closure schemes on the wall. This paper presents a family of high-order non-Uniform Grid finite difference schemes with stable boundary closures for the direct numerical simulation of hypersonic boundary-layer transition. By using an appropriate Grid stretching, and clustering Grid points near the boundary, high-order schemes with stable boundary closures can be obtained. The order of the schemes ranges from first-order at the lowest, to the global spectral collocation method at the highest. The accuracy and stability of the new high-order numerical schemes is tested by numerical simulations of the linear wave equation and two-dimensional incompressible flat plate boundary layer flows. The high-order non-Uniform-Grid schemes (up to the 11th-order) are subsequently applied for the simulation of the receptivity of a hypersonic boundary layer to free stream disturbances over a blunt leading edge. The steady and unsteady results show that the new high-order schemes are stable and are able to produce high accuracy for computations of the nonlinear two-dimensional Navier-Stokes equations for the wall bounded supersonic flow.
E Michielssen - One of the best experts on this subject based on the ideXlab platform.
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a multilevel cartesian non Uniform Grid time domain algorithm
Journal of Computational Physics, 2010Co-Authors: Jun Meng, Amir Boag, Vitaliy Lomakin, E MichielssenAbstract:A multilevel Cartesian non-Uniform Grid time domain algorithm (CNGTDA) is introduced to rapidly compute transient wave fields radiated by time dependent three-dimensional source constellations. CNGTDA leverages the observation that transient wave fields generated by temporally bandlimited and spatially confined source constellations can be recovered via interpolation from appropriately delay- and amplitude-compensated field samples. This property is used in conjunction with a multilevel scheme, in which the computational domain is hierarchically decomposed into subdomains with sparse non-Uniform Grids used to obtain the fields. For both surface and volumetric source distributions, the computational cost of CNGTDA to compute the transient field at N"s observation locations from N"s collocated sources for N"t discrete time instances scales as O(N"tN"slogN"s) and O(N"tN"slog^2N"s) in the low- and high-frequency regimes, respectively. Coupled with marching-on-in-time (MOT) time domain integral equations, CNGTDA can facilitate efficient analysis of large scale time domain electromagnetic and acoustic problems.
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non Uniform Grid time domain ngtd algorithm for fast evaluation of transient fields
International Symposium on Electromagnetic Compatibility, 2003Co-Authors: Amir Boag, Vitaliy Lomakin, E Michielssen, E HeymanAbstract:A novel algorithm to efficiently compute transient fields produced by known time dependent source constellations is proposed. The algorithm relies on domain decomposition and comprises two steps to be repeated for each subdomain. In the first step, delay and amplitude compensated fields, produced by currents residing within each subdomain are computed over a sparse set of points of a carefully designed non-Uniform spherical Grid surrounding the observation domain. During the second step, total fields in the observer domain are evaluated by interpolation, delay and amplitude restoration, and aggregation of subdomain fields.
