Research On Modeling And Fast Algorithm For Electromagnetic Scattering By Complex Moving Objects

The electromagnetic scattering modeling and calculation of complex moving targets have important values in military and civilian applications.One of the main research objects in the field of traditional computational electromagnetics(CEM)is the electromagnetic(EM)scattering of stationary or single object.From the perspective of practical application,this paper specifically studies and analyzes several types of complex EM scattering problems by moving objects.First,an overall review is given to the method of moments and the multi-level fast multi-pole algorithm(MLFMA).Then a brief introduction is presented to the iterative solution method of matrix equations and the singular integral processing method.These provide a firm foundation for subsequent work demonstration.Aiming at the problem of EM scattering from multiple moving objects,the limitations of the traditional MLFMA on this problem are first explained in detail.In order to improve the calculation efficiency of EM scattering of multiple moving objects,a fast algorithm for multiple moving objects is proposed.The new algorithm is based on a dynamic octree structure,which can accurately and efficiently calculate the couplings between moving sub-objects by transferring between the highest levels of the sub-object octrees.Numerical examples show that the new algorithm has significant advantage in calculating efficiency for analysis of scattering from multiple moving objects.Aiming at the EM scattering by a cluster of moving objects which consists of dozens or hundreds of moving sub-objects,in order to improve the calculation efficiency,a dual octree structure is proposed.The dual octree structure consists of a main octree structure and multiple sub-octree structures that move with the sub-objects.The EM coupling between two distant objects is calculated by aggregation transfer and disaggregation on the main octrees.The dual octree structure can reduce the computational complexity of EM coupling of multiple moving objects.The numerical results prove that the fast algorithm based on the dual octree structure can efficiently and accurately calculate the EM scattering by a cluster of multiple moving objects.Aiming at the problem of EM scattering by moving objects in complex backgrounds in practical engineering,two difficulties in the rapid calculation of EM scattering by a moving object in complex backgrounds are analysed.The first difficulty is that the sizes of the complex background and the moving target are very different,which results in the octree structure at different layers cannot achieve the coupling between the object and the complex background through the transfer between the highest layers.The second difficulty is that the size of the complex background is generally very large,and the side length of the corresponding highest-level grouping cube is also very large.The distance between the object and the complex background is easily smaller than this side length,which makes the addition law unusable.To overcome these two difficulties,a level adaptive octree structure is proposed.Numerical examples show that the fast algorithm based on level adaptive octree structure can accurately and efficiently calculate the coupling between a complex background and moving objects.Aiming at the EM scattering by moving object on the water surface,this paper uses the Kelvin wake method to establish the wake of a moving ship.Considering the wind background of the sea surface,Monte Carlo method and Pierson-Moskowitz(PM)spectrum are used to generate a wind-drvien wave surface model.Firstly,the influence of ships on the EM scattering by wind-driven sea surface is calculated and analyzed.Secondly,the EM scattering by the composite object consisting of ships,wakes and winddriven wave are calculated.For EM scattering by the surface wake due to an underwater moving object,the computational fluid dynamics(CFD)method is used to establish the wake model.By analyzing the geometric characteristics of the wake model,it is verified that the wake model is credible.The small-slope approximation(SSA)method is adopted to calculate the EM scattering by the composite surfaces made of wind waves and the wake due to an underwater object moving at different speeds,different depths,and different directions.By comparing and analyzing the results of EM scattering in different situations,it is found that EM scattering exhibit some different characteristics in different states of underwater moving object.These conclusions may provide some reference and basis for the EM detection method of underwater moving objects.