The Experts below are selected from a list of 13896 Experts worldwide ranked by ideXlab platform
Gherardo Valori - One of the best experts on this subject based on the ideXlab platform.
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Computation of Relative Magnetic Helicity in Spherical Coordinates
Solar Physics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magnetohydrodynamics. While many methods for computing magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method for properly computing the relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered to be fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions and comparison with an approximate method used in the past indicates that the proposed method can be significantly more accurate, thus making our method a promising tool in helicity studies that employ Spherical geometry. Additionally, we determine and discuss the applicability range of the approximate method.
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computation of relative magnetic helicity in Spherical Coordinates
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magneto-hydrodynamics. While many methods to compute magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method to properly compute relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions, and comparison with an approximate method used in the past, indicates that the proposed methodology can be significantly more accurate, thus making our method a promising tool in helicity studies that employ the Spherical geometry. Additionally, the range of applicability of the approximate method is determined and discussed.
Kostas Moraitis - One of the best experts on this subject based on the ideXlab platform.
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Computation of Relative Magnetic Helicity in Spherical Coordinates
Solar Physics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magnetohydrodynamics. While many methods for computing magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method for properly computing the relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered to be fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions and comparison with an approximate method used in the past indicates that the proposed method can be significantly more accurate, thus making our method a promising tool in helicity studies that employ Spherical geometry. Additionally, we determine and discuss the applicability range of the approximate method.
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computation of relative magnetic helicity in Spherical Coordinates
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magneto-hydrodynamics. While many methods to compute magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method to properly compute relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions, and comparison with an approximate method used in the past, indicates that the proposed methodology can be significantly more accurate, thus making our method a promising tool in helicity studies that employ the Spherical geometry. Additionally, the range of applicability of the approximate method is determined and discussed.
Antonia Savcheva - One of the best experts on this subject based on the ideXlab platform.
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Computation of Relative Magnetic Helicity in Spherical Coordinates
Solar Physics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magnetohydrodynamics. While many methods for computing magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method for properly computing the relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered to be fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions and comparison with an approximate method used in the past indicates that the proposed method can be significantly more accurate, thus making our method a promising tool in helicity studies that employ Spherical geometry. Additionally, we determine and discuss the applicability range of the approximate method.
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computation of relative magnetic helicity in Spherical Coordinates
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magneto-hydrodynamics. While many methods to compute magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method to properly compute relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions, and comparison with an approximate method used in the past, indicates that the proposed methodology can be significantly more accurate, thus making our method a promising tool in helicity studies that employ the Spherical geometry. Additionally, the range of applicability of the approximate method is determined and discussed.
Étienne Pariat - One of the best experts on this subject based on the ideXlab platform.
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Computation of Relative Magnetic Helicity in Spherical Coordinates
Solar Physics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magnetohydrodynamics. While many methods for computing magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method for properly computing the relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered to be fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions and comparison with an approximate method used in the past indicates that the proposed method can be significantly more accurate, thus making our method a promising tool in helicity studies that employ Spherical geometry. Additionally, we determine and discuss the applicability range of the approximate method.
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computation of relative magnetic helicity in Spherical Coordinates
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Kostas Moraitis, Étienne Pariat, Antonia Savcheva, Gherardo ValoriAbstract:Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magneto-hydrodynamics. While many methods to compute magnetic helicity in Cartesian finite volumes exist, in Spherical Coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method to properly compute relative magnetic helicity in Spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions, and comparison with an approximate method used in the past, indicates that the proposed methodology can be significantly more accurate, thus making our method a promising tool in helicity studies that employ the Spherical geometry. Additionally, the range of applicability of the approximate method is determined and discussed.
Qing Huo Liu - One of the best experts on this subject based on the ideXlab platform.
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Perfectly matched layers for elastic waves in cylindrical and Spherical Coordinates
The Journal of the Acoustical Society of America, 1999Co-Authors: Qing Huo LiuAbstract:The perfectly matched layer (PML) for elastic waves in cylindrical and Spherical Coordinates is developed using an improved scheme of complex Coordinates. As is known for electromagnetic waves, Berenger’s original PML scheme does not apply to cylindrical and Spherical Coordinates. The straightforward extension of the complex Coordinates for elastic waves to cylindrical and Spherical Coordinates requires extra unknowns for time-domain solutions, wasting computer memory and computation time. The main idea of the improved scheme in this work is the use of integrated complex variables. It is shown that for three-dimensional cylindrical and Spherical Coordinates, this improved PML scheme requires no more unknowns than in Cartesian Coordinates. The number of unknowns can be further reduced through the use of symmetry in the partial differential equations. The PML scheme allows an arbitrary inhomogeneity in the medium, and is suitable for numerical solutions of wave equations by finite-difference, finite-element...
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Theory of perfectly matched layer for elastic waves and their applications in cylindrical and Spherical Coordinates
The Journal of the Acoustical Society of America, 1999Co-Authors: Qing Huo LiuAbstract:Recently, a general theory of perfectly matched layer (PML) is developed for elastic waves in anisotropic media and is applied to waves in cylindrical and Spherical Coordinates through an improved scheme of complex Coordinates [Liu, J. Acoust. Soc. Am. 105, 2075–2084 (1999)]. As is known for electromagnetic waves, Berenger’s original PML scheme does not apply to cylindrical and Spherical Coordinates. The straightforward extension of the complex Coordinates for elastic waves to cylindrical and Spherical Coordinates requires extra unknowns for time‐domain solutions, wasting computer memory and computation time. The main idea of the improved scheme in this work is the use of integrated complex variables. It is shown that for three‐dimensional cylindrical and Spherical Coordinates, this improved PML scheme requires no more unknowns than in Cartesian Coordinates. The number of unknowns can be further reduced through the use of symmetry in the partial differential equations. The PML scheme allows an arbitrary inhomogeneity in the medium, and is suitable for numerical solutions of wave equations by finite‐difference, finite‐element, and pseudospectral methods for elastic waves in inhomogeneous media with cylindrical and Spherical structures. Finite‐difference time‐domain (FDTD) results are shown to demonstrate the efficacy of the PML absorbing boundary condition.
