Study Of Finite Element Method For Radiative Transfer In The Participatory Media And Optical Tomography Research

With the presentation of the stimulated radiation theory and the access of laser,laser is widely used in many fields and subjects,such as industrial applications,biomedicine,military detection,energy and nuclear technology.With its less aggressive,high cost performance characteristics,near infrared optical tomography,is applied in breast tumor detection,brain scans,oxygen content change detection,etc.The transmission in the internal structure of biological tissue is simulated by the incident of near infrared laser in participating media.Numerical simulation results of optical parameters can be further organization,thus get the internal structure of biological tissue.Considering irregular geometry shape in the reality,the finite element method can be applied because of its adaptability for complex geometry shape,and flexibility to the applicability for computer implementation efficiency advantages.Finite element method is widely used in structural mechanics,dynamics,and many other aspects.As a mature method with strict theoretical foundation,the application of finite element method is continuously expanding in the field of radiation heat transfer and becoming more developed.The problem of using the finite element method for the optical parameters reconstruction is still to be explored.The main topic of the paper is based on the two-dimensional radiation transmission equation.Finite element method is used to study steady state and time domain optical imaging problem.The main research content is as follows:1.Based on the two-dimensional steady state radiation transmission equation,the correctness and adaptability of Galerkin and Least Squares Finite Element to two-dimensional rules square and irregular cavity was carried out.The principle of the unit discrete thought and the weighted residual principle of integration in a unit are used.The calculation results are consistent with the reference results.It can be seen that the finite element method can deal with the irregularly shaped radiation transmission problems,and the result of the least squares finite element method is more stable and less fluctuating.2.Based on the two-dimensional time-domain radiation transmission equation,the isotropic and anisotropic scattering models are verified.For this simple two-dimensional rectangular cavity radiation transmission model,the test of grid independence,time independence is studied.3.The short pulse incident laser beam transmitting in the two-dimensional rectangular model is simulated and studied.The plastid size and the location of the output signal are studied.The method of parallel computation is applied to optimize the transmission equation of the time domain and improve the efficiency of the solution,which is portable to solve the inverse problem.By changing the width of the incident pulse and the optical parameters of the background medium,the effect of other factors on penetrating reflection is studied,which provide basic research content for solving the problem.In the study of the inverse problem,step acceleration method is used and background optical parameters are used to assume the initial value.Initial iteration step is selected to seek objective function reducing direction.By reducing the iteration step length and determine objective function reducing direction,internal parameters are calculated and corrected of the model.Finally,the internal optical parameters distribution of the model is determined.