Analysis Of Very Low Ferequency Wave Propagation Based On Two-Dimenasional FDTD Algorithm

The Very Low Frequency(VLF)radio waves with frequencis of 3 kHz to 30 kHz(wavelengths of 100 km to 10 km)are widely used for ultra-long-range navigation doe to their long wavelength,low propagation,loss,and far/deep propagation distance.Time,communications,and communications to the submarine.However,due to the complex changes in the ionosphere,geomagnetic field,solar zenith angle,ground electrical characteri stices,and other factors,the VLF electromagnetic wares propagating along the "ground-ionosphere"waveguitde saructure exhibit exceptionally complex spatial,temporal,and random variations.Features.Studying VLF propagation models and methods and analyzing the characteristics of VLF transmission have become one of the key issues in this field.In this paper,with the support of the Sub-topic of the Equipment Concept Study and the 13th Five-Year Equipment Foundation for Advanced Research(No.61405180202),the VLF propagation modeling method and characteristics for VLF propagation in the "geo-ionosphere"waveguide are developed.Analytical research.The content of the paper is as follows:1,Using the Finite-Differentce Time-Domain(FDTD)method of two-dimensional spherical coordinates,through the derivation and anatysis of its iterative equations,boundary conditions,and numerical dispersion characteristics a two-dimensional "ground-ionosphere" is constructed."The very low frequetcy wave propagation model in the waveguide,the correctnes of the model was verified by simuylaion experiments.2.For the problem of slow ealculation speed when global FDTD method is used for global subdivision,based on the CUD A parallel architecture,a two-dimensional spherical coordinate parallel FDTD method is proposed to increase the calculation speed by tens of times,and this method is used.the VLF propagation characteristics in a slowly varying non-uniform waveguide are simulated.3.For the problem of excessive memory occupation in the FDTD method of two-dimensional spherical coordinates in a non-uniformly undulating waveguide,the local high-resolution non-uniform FDTD algorithm is used to ensure the accuracy while effectively reducing the computer memory consumption and shortening the calculation time..At the same time,this method was used to simulate the propagation characteristics of VLF waves that propagated across the diurnal transition zone,mixed land-sea propagation routes,and mutated irregular routes.This paper adopts FDTD method,inhomogeneous FDTD method and CUDA parallel architecture to implement fast and high-precision predictive analysis of VLF wave propagation over ultra-long-distance complex propagation paths,and to realize VLF wave propagation on a large scale and to consider smaller-scale environmental changes.The resulting VLF wave characteristics change provides an effective solution to further provide a theoretical basis for the VLF navigation time service system.