Study On Electromagnetic Modeling Of Large Area Geographical Environment And Efficient Parabolic Equation Method

Recently, the study of radio wave propagation in complex electromagnetic environment has become a hot issue by scholars all over the world. Building the arithmetic model of complex environments and simulating and analyzing the electromagnetic distribution characteristics fast in large area complex environment can provide key numerical simulation technology and data support for practical applications, such as wireless communication, electromagnetic monitoring, electronic countermeasures, etc, which has very important military and civil value.Compared with the present radio wave propagation models, parabolic equation can not only reflect the wave refraction and diffraction effect, but also give full consideration to the influence on wave propagation by irregular terrain and non-uniform medium. Furthermore, the grid step of SSFT algorithm in propagation direction is almost not limited by wavelength. Therefore, parabolic equation is very suitable for predicting the electromagnetic cover properties in large area complex environment. Based on parabolic equation, the electromagnetic modeling method of complex geographical environment, such as forest, rough sea, etc, the efficient grid model and numerical method of parabolic equation are researched deeply, which has important significance in solving the large area wave propagation quickly and efficiently. The main works in this thesis are as follows:Firstly, the parabolic equation modeling methods of complex geographical environment are studied including forest, steep obstacles and rough sea surface. According to the physical composition of forest, the refractive model is used to improve the effective parabolic equation model and the correctness is verified by contrast with the experimental result. On this basis, the influence on radio wave propagation by the plant volume, weight water content and free water salinity of forest are discussed. To calculate the backward wave of steep obstacles, the two-way parabolic equation approach is researched, whose validity is verified by comparing with ray-tracing method. Meanwhile, the parallel method of two-way parabolic equation is proposed and its parallel performance is disused. The results show that the speed of two-way parabolic equation has been greatly increased in solving multiple reflection waves between obstacles. The Pade two-way parabolic equation is presented to deal with the reflection wave by indoor vertical metope and furniture, and is applied to computing the indoor distribution characteristics of electromagnetic waves, when two double-floor buildines exist. In addition, the parabolic equation model of rough sea surface is constructed when considering the shadow effect. The radio wave propagation characteristics are simulated, which shows that the model can reflect the influence on radio wave propagation by wave shadow effect and sea surface wind speed.Secondly, the non-uniform mesh model, multi non-uniform grid model and subgridding model of parabolic equation are presented. The value range of horizontal grid step for parabolic equation is discussed in detail and the non-uniform mesh model is constructed by dividing different grids in different areas, whose correctness and effectiveness are verified by comparing with two-ray model and uniform fine grid model. The advantage of non-uniform mesh model is further demonstrated by simulating the electromagnetic characteristics in three-dimensional complex environment. Based the non-uniform mesh model, the multi non-uniform grid model of parabolic equation and its parallel method based on OpenMP are presented by combining with coordinate transformation technology and grid interpolation technology. The electromagnetic distribution characteristics are simulated in the complex environment with four sources. The results show that parabolic equation can solve the radio wave propagation problem with multiple sources in three-dimensional space and the speed is greatly increased through the parallel method. Finally, the subgridding model of parabolic equation is put forward for the purpose of solving the radio wave propagation problems in large area complex environment existing key targets and its implementation scheme is elaborated in detail. The correctness is verified by contrast with uniform fine grid model. On this basis, the field distribution of the ship area in large scale sea is predicted and analyzed.Thirdly, to enhance the solution efficiency of parabolic equation, the efficient numerical methods are studied. The fast calculation method for the SSFT algorithm is developed based on the image theory. Compared with the existing odd and even decomposed approach, the solving speed of parabolic equation is improved effectively. Meanwhile, the ADI method of parabolic equation is studied, and the difference scheme in free space and boundary are derived. Based on OpenMP, the parallel method of ADI is put forward. It is showed that the parallel method accelerated the computation speed greatly through the analysis of speedup and parallel efficiency. In addition, the efficient numerical solution method of parabolic equation is put forward by combining the SSFT algorithm and ADI method for the purpose of efficiently solving the radio wave propagation problems in large area complex environment existing with tunnels, and the implementation scheme is given. It is showed that the efficiency of parabolic equation is improved greatly compared with the ADI method. On this basis, the electromagnetic distribution characteristics inside tunnel in large area environment are simulated and analyzed.Fourthly, to further improve the solving speed, the parallel methods of parabolic equation for the high performance simulation platform are implemented based on the "J parallel Adaptive Structured Mesh applications Infrastructure" (JASMIN) framework. The parallel computing of FD method is realized by dividing the step surface into multiple patches and assigned to different processors, and the correctness is verified by comparing with analytic solution. Meanwhile, the efficiency of parallel program is further analyzed. The example shows that the solution efficiency of finite difference parabolic equation is improved effectively. The electromagnetic characteristics of a telecom base station in urban cell with nine regular buildings are simulated. For the radio wave propagation problems in large area, the parallel method and program of SSFT algorithm are realized based on JASMIN framework, whose correctness and effectiveness are verified. Based on the parallel program, the integrative modeling of the typical comprehensive three-dimensional large-scale scene is completed, and the radio wave propagation characteristics are predicted and analyzed in typical comprehensive scene with soil, forest, atmospheric duct, etc.