Reconstruction Of Optical And Thermal Parameter Fields In Semitransparent Media Containing Heteroplasmon Under The Laser Irradiation

Semitransparent media exist in various fields such as the thermal protection materials in spacecraft,plume of rocket motor,furnace flame,and high temperature resistant components in turbine engine.Moreover,the water,glass,air,and biological tissue in our daily lives are also semitransparent media.The optical and/or thermal properties of media are the theoretical premise to radiative transfer analysis and heat transfer simulation.However,the optical and/or thermal properties of media cannot be directly measured in most cases and need to be reconstructed by optimization techniques.Optical and thermal parameter fields reconstruction of s emitransparent media is of great importance to the non-destructive testing of semitransparent materials,medical imaging of biological tissue,and combustion diagnosis of high-temperature flame.Thus,there are profound scientific significance and broad application prospects for the intensive study on simultaneous reconstruction of multi parameter fields in semitransparent media.However,in current researches concern on the reconstruction of optical parameter fields in semitransparent media,the problems such as low imaging quality and computation efficiency are still unsolved.Efficient and accurate reconstruction model is the pivotal technical challenge to be solved.Furthermore,there is few report concerns on the simultaneous reconstruction of optical and thermal parameter fields.The sensitivity coefficients of measurement signals with respect to the optical parameters are significantly different with that to the thermophysical parameters,and thereby the reconstruction errors are usually too large to be accepted.Accurate and robust computation model for the simultaneous reconstruction of optical and thermal parameter fields is urgent to be built.Based on the interaction between incident laser and semitransparent media,this paper investigates the reconstruction of optical parameters of semitransparent media irradiated by an ultrashort pulse laser,the simultaneous reconstruction of optical and thermal parameters of semitransparent media heated by a pulse laser,and the rapid simultaneous reconstruction of optical and thermal parameters of semitransparent media excitated by a modulated laser.The specific research of this thesis includes the following five aspects:For a start,the optimization methods for solving inverse radiative problems are presented,and the advantages and disadvantages of swarm intelligent optimization algorithms and gradient-based methods are summarized.Several modified krill herd(KH)and social spider optimization(SSO)algorithms are proposed and developed.Five benchmark optimization functions are employed to test the computational performance of different intelligent algorithms,and the retrieval results show that the proposed improved KH(IKH)algorithm is superior to other algorithms in terms of computation accuracy and result stability.Moreover,the characteristics of gradient-based methods are described.To accelerate the convergence velocity in the last stage of optimization process,the restart conjugate gradient method(CGM)and the sequential quadratic programming(SQP)algorithm combined with Maratos effect preventive strategy are introduced and developed.Secondly,the time-domain and frequency-domain radiative transfer models in semitransparent media irradiated by an ultrashort pulse laser are investigated.The sensitivity relations between the radiative response signals on boundaries and the optical parameters of media are analyzed.The IKH algorithm is applied to reconstruct the optical parameters of homogeneous semitransparent media,and the maximum relative error is only 0.02%.Furthermore,the CGM and SQP algorithm are employed to reconstruct the optical parameter fields in non-homogeneous semitransparent media.The computational efficiency and accuracy of different reconstruction models including the frequency-domain adjoint differentiation,the frequency-domain adjoint equation,and the time-domain adjoint equation are compared.The retrieval results show that the computation efficienc y of adjoint equation is higher than that of adjoint differentiation,and the reconstruction accuracy of time-domain model is higher than that of frequency-domain model.Thus,an efficient,accurate and robust reconstruction model based on the time-domain adjoint equation method is built.Again,the decouple solution based on radiative source term is employed to solve the coupled radiation and conduction heat transfer in semitransparent media.The IKH algorithm is developed to simultaneously reconstruct the optical and thermophysical parameters of the homogeneous medium,and the influence of measurement signals on computational results is investigated.The maximum relative error is only 2.51% when the random measurement error is increased to 5%,which demonstrates the strong robustness of the reconstruction model.The sensitivity of measurement signals on boundaries with respect to the optical and thermal parameter of media is analyzed.The retrieval results show that the optical response signals are mainly sensitive to the optical parameters of media,whereas the thermal response signals are mainly sensitive to the thermophysical parameter of media.Based on the sensitivity analysis,a multi-stage optimization strategy(MSOS)is developed,and the distributions of absorption coefficient,scattering coefficient,and thermal conductivity of semitransparent media are accurately reconstructed.Then,the lock-in thermography(LIT)technique is firstly introduced into the estimation of optical and thermal parameter fields in semitransparent media.The LIT technique is combined with the MSOS,through which a more efficient lock-in positioning reconstruction method(LIPRM)is proposed.Compared with the MSOS,the computation efficiency and accuracy of LIPRM are signifi cantly improved and the dependency on regularization is overcome.Furthermore,the distributions of absorption coefficient,scattering coefficient,and thermal conductivity in two porous ceramics are accurately recovered using the LIPRM.Finally,the experimental researches concern on the reconstruction of optical and thermal parameter fields in semitransparent media are studied.The absorption coefficient,scattering coefficient and thermal conductivity distributions in silicon carbide(Si C)ceramic containing heteroplasmon are simultaneously reconstructed,which illustrates the reliability of the present numerical model and experimental system.In addition,the effects of the size,depth,and size factor of h eterogeneous on the LIT results are analyzed.The retrieval results show that the spatial position of heterogeneous inclusion cannot be accurately identified when the size factor is less than 2.0 or the detection depth is larger than 5.0 mm.For the test samples with small size factors,a combined reconstruction model is proposed in which the position and optical and thermal properties of heterogeneous are simultaneously reconstructed,and the optical and thermal parameter distributions are accurately reconstructed.