The Experts below are selected from a list of 546 Experts worldwide ranked by ideXlab platform
T.d. Tsiboukis - One of the best experts on this subject based on the ideXlab platform.
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Higher-order non-standard FDTD modeling of complicated EMC structures in 3-D curvilinear lattices
2003 IEEE International Symposium on Electromagnetic Compatibility 2003. EMC '03., 2003Co-Authors: N.v. Kantartzis, T.d. TsiboukisAbstract:A systematic higher-order FDTD-PML methodology for the accurate simulation of complex curvilinear 3-D EMC problems is presented in this paper. Developing an efficient covariant-Contravariant Vector classification, the novel technique introduces a parametric family of higher-order non-standard schemes for the suppression of the critical dispersion errors. The wider spatial stencils near boundary walls are treated by self-adaptive compact operators, while for the temporal variable a multi-stage leapfrog integration is utilized. Moreover, this optimal formulation leads to enhanced curvilinear PMLs that significantly annihilate outgoing waves. Numerical validation indicates the benefits of the proposed algorithm via several demanding and practical EMC applications.
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Analysis of multiport waveguide structures by a higher-order FDTD methodology based on non-orthogonal curvilinear grids
2001 IEEE MTT-S International Microwave Sympsoium Digest (Cat. No.01CH37157), 2001Co-Authors: N.v. Kantartzis, M. Gatzianas, T.i. Kosmanis, T.d. TsiboukisAbstract:A generalized methodology for the construction of nonstandard higher-order finite-difference time-domain schemes, as well as their application to complex electromagnetic problems in curvilinear non-orthogonal coordinate systems, are presented in this paper. As a consequence, a new class of low-dispersion operators is designed for the approximation of spatial and temporal derivatives. Their extension to curvilinear non-orthogonal coordinates is attained by a higher-order variation of the covariant and Contravariant Vector component theory, in which all metric terms are taken into account. Finally, the proposed method is validated by the analysis of diverse multiport microwave structures with realistic features.
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A nonorthogonal higher-order wavelet-oriented FDTD technique for 3-D waveguide structures on generalized curvilinear grids
IEEE Transactions on Magnetics, 2001Co-Authors: N.v. Kantartzis, T.i. Kosmanis, T.v. Yioultsis, T.d. TsiboukisAbstract:A generalized higher-order FDTD rendition of the covariant and Contravariant Vector component theory for the accurate modeling of complex waveguides in 3-D nonorthogonal curvilinear coordinates, is presented in this paper. The novel algorithm, which postulates conventional and nonstandard concepts, embodies a spatially-localized wavelet-Galerkin formulation in order to efficiently deal with fast field variations in the vicinity of arbitrarily-angled wedges. The proposed method is combined with a pulsed excitation and enhanced unsplit-field PMLs thus, achieving significant accuracy and suppression of all discretization errors with a simultaneous diminishment of computational resources, as indicated by various numerical results.
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Fully nonorthogonal higher-order FDTD schemes for the systematic development of 3-D PML's in general curvilinear coordinates
IEEE Transactions on Magnetics, 2000Co-Authors: N.v. Kantartzis, T.i. Kosmanis, T.d. TsiboukisAbstract:The efficient construction of reflectionless PML's in 3-D curvilinear coordinates via a new higher-order FDTD methodology, is presented in this paper. By accurately treating the div-curl problem, the technique introduces a higher-order rendition of the covariant/Contravariant Vector theory with generalized conventional and nonstandard schemes. Moreover, a mesh expansion algorithm decreases the absorbers' thickness. In the time domain, the four-stage Runge-Kutta integrator is also invoked, while the wider spatial stencils are effectively limited by self-adaptive compact operators. Numerical verification indicates that the novel PML's offer a serious suppression of dispersion errors and significant savings in the computational burden.
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An enhanced higher-order FDTD technique for the construction of efficient reflectionless PMLs in 3-D generalized curvilinear coordinate systems
IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC URSI National Radio Science Meeting (Cat. N, 1999Co-Authors: N.v. Kantartzis, J.s. Juntunen, T.d. TsiboukisAbstract:A systematic implementation of reflectionless split and unsplit-field PMLs in 3-D nonorthogonal curvilinear coordinates via a novel higher-order FDTD methodology, is presented. The technique, which introduces both conventional and nonstandard schemes, incorporates a higher-order rendition of the covariant and Contravariant Vector component theory. Enhanced attenuation performance and levels of accuracy are achieved by means of new conductivity profiles and efficient ABCs terminating the PML, region. Moreover, a progressively expanding curvilinear discretization algorithm leads to a significant reduction of the absorbers' necessary thickness. In the temporal variable, the four-stage Runge-Kutta integrator is invoked, whereas the wider spatial increments near absorbing walls are effectively limited through the use of properly modified compact operators. Numerical verification demonstrates that the proposed higher order curvilinearly structured PMLs offer a considerable decrease in dispersion errors and can be imposed very close to the scatterer, thus attaining notable savings in computational resources.
N.v. Kantartzis - One of the best experts on this subject based on the ideXlab platform.
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Higher-order non-standard FDTD modeling of complicated EMC structures in 3-D curvilinear lattices
2003 IEEE International Symposium on Electromagnetic Compatibility 2003. EMC '03., 2003Co-Authors: N.v. Kantartzis, T.d. TsiboukisAbstract:A systematic higher-order FDTD-PML methodology for the accurate simulation of complex curvilinear 3-D EMC problems is presented in this paper. Developing an efficient covariant-Contravariant Vector classification, the novel technique introduces a parametric family of higher-order non-standard schemes for the suppression of the critical dispersion errors. The wider spatial stencils near boundary walls are treated by self-adaptive compact operators, while for the temporal variable a multi-stage leapfrog integration is utilized. Moreover, this optimal formulation leads to enhanced curvilinear PMLs that significantly annihilate outgoing waves. Numerical validation indicates the benefits of the proposed algorithm via several demanding and practical EMC applications.
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Analysis of multiport waveguide structures by a higher-order FDTD methodology based on non-orthogonal curvilinear grids
2001 IEEE MTT-S International Microwave Sympsoium Digest (Cat. No.01CH37157), 2001Co-Authors: N.v. Kantartzis, M. Gatzianas, T.i. Kosmanis, T.d. TsiboukisAbstract:A generalized methodology for the construction of nonstandard higher-order finite-difference time-domain schemes, as well as their application to complex electromagnetic problems in curvilinear non-orthogonal coordinate systems, are presented in this paper. As a consequence, a new class of low-dispersion operators is designed for the approximation of spatial and temporal derivatives. Their extension to curvilinear non-orthogonal coordinates is attained by a higher-order variation of the covariant and Contravariant Vector component theory, in which all metric terms are taken into account. Finally, the proposed method is validated by the analysis of diverse multiport microwave structures with realistic features.
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A nonorthogonal higher-order wavelet-oriented FDTD technique for 3-D waveguide structures on generalized curvilinear grids
IEEE Transactions on Magnetics, 2001Co-Authors: N.v. Kantartzis, T.i. Kosmanis, T.v. Yioultsis, T.d. TsiboukisAbstract:A generalized higher-order FDTD rendition of the covariant and Contravariant Vector component theory for the accurate modeling of complex waveguides in 3-D nonorthogonal curvilinear coordinates, is presented in this paper. The novel algorithm, which postulates conventional and nonstandard concepts, embodies a spatially-localized wavelet-Galerkin formulation in order to efficiently deal with fast field variations in the vicinity of arbitrarily-angled wedges. The proposed method is combined with a pulsed excitation and enhanced unsplit-field PMLs thus, achieving significant accuracy and suppression of all discretization errors with a simultaneous diminishment of computational resources, as indicated by various numerical results.
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Fully nonorthogonal higher-order FDTD schemes for the systematic development of 3-D PML's in general curvilinear coordinates
IEEE Transactions on Magnetics, 2000Co-Authors: N.v. Kantartzis, T.i. Kosmanis, T.d. TsiboukisAbstract:The efficient construction of reflectionless PML's in 3-D curvilinear coordinates via a new higher-order FDTD methodology, is presented in this paper. By accurately treating the div-curl problem, the technique introduces a higher-order rendition of the covariant/Contravariant Vector theory with generalized conventional and nonstandard schemes. Moreover, a mesh expansion algorithm decreases the absorbers' thickness. In the time domain, the four-stage Runge-Kutta integrator is also invoked, while the wider spatial stencils are effectively limited by self-adaptive compact operators. Numerical verification indicates that the novel PML's offer a serious suppression of dispersion errors and significant savings in the computational burden.
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An enhanced higher-order FDTD technique for the construction of efficient reflectionless PMLs in 3-D generalized curvilinear coordinate systems
IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC URSI National Radio Science Meeting (Cat. N, 1999Co-Authors: N.v. Kantartzis, J.s. Juntunen, T.d. TsiboukisAbstract:A systematic implementation of reflectionless split and unsplit-field PMLs in 3-D nonorthogonal curvilinear coordinates via a novel higher-order FDTD methodology, is presented. The technique, which introduces both conventional and nonstandard schemes, incorporates a higher-order rendition of the covariant and Contravariant Vector component theory. Enhanced attenuation performance and levels of accuracy are achieved by means of new conductivity profiles and efficient ABCs terminating the PML, region. Moreover, a progressively expanding curvilinear discretization algorithm leads to a significant reduction of the absorbers' necessary thickness. In the temporal variable, the four-stage Runge-Kutta integrator is invoked, whereas the wider spatial increments near absorbing walls are effectively limited through the use of properly modified compact operators. Numerical verification demonstrates that the proposed higher order curvilinearly structured PMLs offer a considerable decrease in dispersion errors and can be imposed very close to the scatterer, thus attaining notable savings in computational resources.
T.i. Kosmanis - One of the best experts on this subject based on the ideXlab platform.
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Analysis of multiport waveguide structures by a higher-order FDTD methodology based on non-orthogonal curvilinear grids
2001 IEEE MTT-S International Microwave Sympsoium Digest (Cat. No.01CH37157), 2001Co-Authors: N.v. Kantartzis, M. Gatzianas, T.i. Kosmanis, T.d. TsiboukisAbstract:A generalized methodology for the construction of nonstandard higher-order finite-difference time-domain schemes, as well as their application to complex electromagnetic problems in curvilinear non-orthogonal coordinate systems, are presented in this paper. As a consequence, a new class of low-dispersion operators is designed for the approximation of spatial and temporal derivatives. Their extension to curvilinear non-orthogonal coordinates is attained by a higher-order variation of the covariant and Contravariant Vector component theory, in which all metric terms are taken into account. Finally, the proposed method is validated by the analysis of diverse multiport microwave structures with realistic features.
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A nonorthogonal higher-order wavelet-oriented FDTD technique for 3-D waveguide structures on generalized curvilinear grids
IEEE Transactions on Magnetics, 2001Co-Authors: N.v. Kantartzis, T.i. Kosmanis, T.v. Yioultsis, T.d. TsiboukisAbstract:A generalized higher-order FDTD rendition of the covariant and Contravariant Vector component theory for the accurate modeling of complex waveguides in 3-D nonorthogonal curvilinear coordinates, is presented in this paper. The novel algorithm, which postulates conventional and nonstandard concepts, embodies a spatially-localized wavelet-Galerkin formulation in order to efficiently deal with fast field variations in the vicinity of arbitrarily-angled wedges. The proposed method is combined with a pulsed excitation and enhanced unsplit-field PMLs thus, achieving significant accuracy and suppression of all discretization errors with a simultaneous diminishment of computational resources, as indicated by various numerical results.
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Fully nonorthogonal higher-order FDTD schemes for the systematic development of 3-D PML's in general curvilinear coordinates
IEEE Transactions on Magnetics, 2000Co-Authors: N.v. Kantartzis, T.i. Kosmanis, T.d. TsiboukisAbstract:The efficient construction of reflectionless PML's in 3-D curvilinear coordinates via a new higher-order FDTD methodology, is presented in this paper. By accurately treating the div-curl problem, the technique introduces a higher-order rendition of the covariant/Contravariant Vector theory with generalized conventional and nonstandard schemes. Moreover, a mesh expansion algorithm decreases the absorbers' thickness. In the time domain, the four-stage Runge-Kutta integrator is also invoked, while the wider spatial stencils are effectively limited by self-adaptive compact operators. Numerical verification indicates that the novel PML's offer a serious suppression of dispersion errors and significant savings in the computational burden.
Darrin M. York - One of the best experts on this subject based on the ideXlab platform.
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Exact Relation between Potential of Mean Force and Free-Energy Profile
2016Co-Authors: Kin Yiu Wong, Darrin M. YorkAbstract:We apply concepts of covariant and Contravariant Vector space in differential geometry and general relativity to derive new, general, exact relations between potential of mean force and free-energy profile. These relations are immensely practical in free-energy simulations because a full Jacobian transformation (which is usually unknown) is not required; rather, only knowledge of the (constraint) coordinate of interest is needed. We reveal that in addition to the Jacobian determinant, the Jacobian scale factor and Leibnizian contributions must also be considered, as well as a Fixman term with correct mass dependence. Our newly derived relations are verified with new nontrivial benchmark numerical examples for which exact results can be computed and compared with relations available in the literature that turn out to exhibit significant deviations from the exact values
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Exact Relation between Potential of Mean Force and Free-Energy Profile
Journal of Chemical Theory and Computation, 2012Co-Authors: Kin Yiu Wong, Darrin M. YorkAbstract:We apply concepts of covariant and Contravariant Vector space in differential geometry and general relativity to derive new, general, exact relations between potential of mean force and free-energy profile. These relations are immensely practical in free-energy simulations because a full Jacobian transformation (which is usually unknown) is not required; rather, only knowledge of the (constraint) coordinate of interest is needed. We reveal that in addition to the Jacobian determinant, the Jacobian scale factor and Leibnizian contributions must also be considered, as well as a Fixman term with correct mass dependence. Our newly derived relations are verified with new nontrivial benchmark numerical examples for which exact results can be computed and compared with relations available in the literature that turn out to exhibit significant deviations from the exact values.
Sawa Manoff - One of the best experts on this subject based on the ideXlab platform.
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On the Existence of a Gyroscope in Spaces with Affine Connections and Metrics
General Relativity and Gravitation, 2003Co-Authors: Sawa Manoff, B. DimitrovAbstract:Conditions for the existence of a gyroscope in spaces with affine connections and metrics are found. They appear as special types of Fermi-Walker transports for Vector fields, lying in a subspace, orthogonal to the velocity Vector field (a non-null Contravariant Vector field) of an observer.
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Spaces with Contravariant and covariant affine connections and metrics
arXiv: General Relativity and Quantum Cosmology, 2000Co-Authors: Sawa ManoffAbstract:The theory of spaces with different (not only by sign) Contravariant and covariant affine connections and metrics [}$(\bar{L}_n,g)$\QTR{it}{-spaces] is worked out within the framework of the tensor analysis over differentiable manifolds and in a volume necessary for the further considerations of the kinematics of Vector fields and the Lagrangian theory of tensor fields over}$(\bar{L}_n,g)$\QTR{it}{-spaces. The possibility of introducing affine connections (whose components differ not only by sign) for Contravariant and covariant tensor fields over differentiable manifolds with finite dimensions is discussed. The action of the deviation operator, having an important role for deviation equations in gravitational physics, is considered for the case of Contravariant and covariant Vector fields over differentiable manifolds with different affine connections A deviation identity for Contravariant Vector fields is obtained. The notions covariant, Contravariant, covariant projective, and Contravariant projective metrics are introduced in (}$\bar{L}_n,g$\{)-spaces. The action of the covariant and the Lie differential operators on the different type of metrics is found. The notions of symmetric covariant and Contravariant (Riemannian) connections are determined and presented by means of the covariant and Contravariant metrics and the corresponding torsion tensors. The different types of relative tensor fields (tensor densities) as well as the invariant differential operators acting on them are considered. The invariant volume element and its properties under the action of different differential operators are investigated.
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Conformal derivative and conformal transports over spaces with an affine connection and metrics
arXiv: General Relativity and Quantum Cosmology, 2000Co-Authors: Sawa ManoffAbstract:Transports preserving the angle between two Contravariant Vector fields but changing their lengths proportional to their own lengths are introduced as `conformal' transports and investigated over spaces with one affine connection and metric. They are more general than the Fermi-Walker transports. In an analogous way as in the case of Fermi-Walker transports a conformal covariant differential operator and its conformal derivative are defined and considered over spaces with one affine connection and metric. Different special types of conformal transports are determined inducing also Fermi-Walker transports for orthogonal Vector fields as special cases. Conditions under which the length of a non-null Contravariant Vector field could swing as a homogeneous harmonic oscillator are established. The results obtained regardless of any concrete field (gravitational) theory could have direct applications in such types of theories. PACS numbers: 04.90.+e; 04.50.+h; this http URL; 02.40.Vh
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Spaces with Contravariant and covariant affine connections and metrics
Physics of Particles and Nuclei, 1999Co-Authors: Sawa ManoffAbstract:The theory of spaces with Contravariant and covariant affine connections, whose components differ not only in sign, and metrics [(L n ,g) spaces] is worked out within the framework of tensoranalysis over differentiable manifolds and in a volume necessary for further consideration of the kinematics of Vector fields and the Lagrangiantheory of tensor fields over (L n ,g) spaces. The possibility of introducing affine connections for Contravariant and covariant tensor fields, whose components differ not only in sign, over differentiable manifolds with finite dimensions is discussed. The action of the deviation operator, having an important role for deviation equations in gravitational physics, is considered for the case of Contravariant and covariant Vector fields over differentiable manifolds with different affine connections (called L n spaces). A deviation identity for Contravariant Vector fields is obtained. The notions of covariant, Contravariant, covariant projective, and Contravariant projective metric are introduced in (L n ,g) spaces. The action of the covariant and the Lie differential operator on the different types of metric is found. The concepts of symmetric covariant and Contravariant (Riemannian) connection are defined and presented by means of the covariant and Contravariant metric and the corresponding torsion tensors. The different types of relative tensor fields (tensor densities) as well as the invariant differential operators acting on them are considered. The invariant volume element and its properties under the action of different differential operators are investigated.
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Projections and covariant divergency of energy-momentun tensors
arXiv: General Relativity and Quantum Cosmology, 1999Co-Authors: Sawa Manoff, Rumyan LazovAbstract:The invariant projections of the energy-momentum tensors of Lagrangian densities for tensor fields over differentiable manifolds with Contravariant and covariant affine connections and metrics [$(\bar{L}_n,g)$-spaces] are found by the use of an non-null (non-isotropic) Contravariant Vector field and its corresponding projective metrics. The notions of rest mass density, momentum density, energy current density and stress tensor are introduced as generalizations of these notions from the relativistic continuum media mechanics. The energy-momentum tensors are represented by means of the introduced notions and the corresponding identities are found. The notion of covariant differential operator along a Contravariant tensor field is introduced. On its basis, as a special case, the notion of Contravariant metric differential operator is proposed. The properties of the operators are considered. By the use of these operators the notion of covariant divergency of a mixed tensor field is determined. The covariant divergency of tensor fields of second rank of the types 1 and 2 is found. Invariant representations of the covariant divergency of the energy-momentum tensor are obtained by means of the projective metrics of a Contravariant non-isotropic (non-null) Vector field and the corresponding rest mass density, momentum density, and energy flux density. An invariant representation of the first Noether identity is found as well as relations between the covariant divergencies of the different energy-momentum tensors and their structures determining covariant local conserved quantities.