Adaptive Mesh-free Shooting And Bouncing Ray Technique For Complicated Targets And Its Applications

The high frequency asymptotical method(HFAM)is one of the most practical electromagnetic modeling algorithms in the military applications.Xpatch~?developed in the United States is the topmost HFAM software.This thesis is aimed to realize an HFAM algorithm based on the parametrically geometric model,which is an important part of the software“National Electromagnetic Scattering Code(NESC2.0)”of China.In this thesis,we systemically study the parametrically geometric modeling method,the adapted ray-surface-intersection test algorithm and curvature self-adaptive tube splitting algorithm for geometric models,and finally propose a Kd-Tree accelerated high-frequency algorithm for parametrically geometric models,which is mesh free and suitable for multi-bounce ray tracing.The proposed techniques have been applied in modeling the radar scattering characteristics of complicated targets,the model corrections for undetermined models,and the hexahedral discretization algorithm for the finite-difference time-domain(FDTD)method,which have become the important parts of NESC2.0.The proposed methodology opens a new way to analyze the radar scattering characteristics of complicated targets.The main contributions and innovations in this thesis are summarized as follows:1)An adaptive high-frequency method is proposed and realized for geometric model ofcomplicated target,which is mesh free,suitable for multi-bounce ray tracing,and can smartlycontrol the tube density according to the surface curvature.2)An adaptive ray-tracing framework is established for geometric model,which can automaticallychoose the best ray-surface-intersection scheme for different kinds of surfaces to improve bothaccuracy and efficiency in determining intersections.The proposed method has been applied inthe hexahedral discretization for FDTD,which can directly use parametrically geometric modelsto improve the accuracy and efficiency.3)A concise and efficient origin-mirrored geometric-optics algorithm is proposed,in which themulti-bounce effects can be presented by just one-bounce effect.4)An efficient reverse-engineering technique is proposed for geometric modeling.Compared withthe commercial software Geomagic~?,the proposed technique is able to make the optimizedgeometric descriptions based on component modeling,and hence makes use of fewer surfaces toconstruct the model.This technique is more suitable for the proposed high-frequency method.5)Based on the parametrically geometric modeling and the fast high-frequency algorithm,amodel-correction method is proposed for undetermined targets based on the V-like iterationprocedure.Using this approach,a general mode-correction methodology is established,whichincludes the intelligence collection,structure and medium parameter estimation,electromagnetic simulation,and model design and fabrication.This methodology provides asystemic solution for the evaluation and design of modern weapons.