At present, there is a lack of efficient numerical calculation methods for electromagnetic scattering from an infinite ground by a long duration source. Based on the two-dimensional frequency domain finite difference (FDFD) method, the surface impedance boundary conditions (SIBC) suitable for TM mode are derived, and an efficient FDFD-SIBC hybrid method is developed, which can be used to quickly calculate the ground electromagnetic scattering caused by long-term current source radiation. Firstly, the finite-size ground is intercepted and equivalent by using impedance boundary conditions to form a half-space calculation region. Then, according to the electric field component of a grid adjacent to the ground, combined with the ground reflection coefficient and the wave propagation phase delay factor, the FDFD formula of the electric field at the impedance boundary is derived. Finally, the FDFD method is used to construct the matrix equation between the electric field and the source of all grids in the half-space, and the complex conjugate gradient method is used to solve the equation to obtain the electric field distribution. The numerical simulation results of half-space ground electromagnetic scattering are in good agreement with the traditional FDTD method, which verifies the correctness of the FDFD-SIBC hybrid method.
In order to evaluate the performance status of the speed sensor for the key components of EMU (Electric Multiple Units), according to the main environmental factors experienced by the service life-time, the type test scheme and corresponding detection requirements of the speed sensor are formulated. Combined with the test results after each type test, the performance status of the speed sensor is checked, the main faults occurring are summarized, and the failure analysis is carried out. The speed sensor is not a full-life product (less than 30 years), so it is recommended to repair it in fifth class, and the main failure location and failure stress of the product are found out, which provides important basis for the maintenance of the repair cycle and repair system.
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