LGEP 2014 ID = 1529International audienceA semi-implicit approach is proposed for computing the current density in superconductors characterized by nonlinear vectorial power law. A nodal discontinuous Galerkin method is adopted for the spatial discretization of the nonlinear system satisfied by the components of the electric field. Explicit developments are used to construct boundary conditions to avoid the modeling of a volume around the superconducting sample. A modified Newton iterative method is introduced for solving the discrete system. Numerical examples on a 2-D superconducting plate and a 3-D superconducting cube are computed. Distributions of a component of the current density are presented and differences in the diffusive process are highlighted. The penetration time and losses are compared with those obtained with an A-V formulation solved by a finite-volume method
Complete penetration magnetic field B P is a feature of a superconducting sample submitted to an applied magnetic field. It is very important to know this for applications such as an electrical motor or levitation. The electric E-J characteristics of a high-temperature superconductor (HTS) bulk is generally described by a power law. The main purpose of this paper is to investigate the influence of the n-value and the applied magnetic field rise rate V b on the B P of a cylindrical HTS pellet. The numerical results presented come from the resolution of a nonlinear diffusion problem with commercial software. In this paper, cylindrical HTS pellets are submitted to an axial applied magnetic field. With the help of these simulations, a linear relationship between B P , V b , and the n-value has been found. A comparison between measurements and simulations is done for the magnetization of cylindrical bulk superconducting samples. This comparison allows to determine the critical current density J C and n-value of the power law E(J ) = E C (J/J C )n. The experiment is based on the direct measurement of the local magnetic field in the gap between two bulk HTS pellets. The field penetration measurements have been carried out on HTS pellets at 77 K by applying increasing magnetic fields with a quasi-constant sweep rate for the axial direction of the applied magnetic field. Two values of complete penetration magnetic field B P have been measured at two different rise rates V b . The n-value of the real HTS pellet has been deduced.
In electromagnetic compatibility, scattering problems are defined in an infinite spatial domain, while numerical techniques such as finite element methods require a computational domain that is bounded. The perfectly matched layer (PML) is widely used to simulate the truncation of the computational domain. However, its performance depends critically on an absorption function. This function is generally tuned by using case-dependent optimization procedures. In this paper, we will present some efficient functions that overcome any tuning. They will be compared using a realistic scattering benchmark solved with the Discontinuous Galerkin method.
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