Theoretical Study On Emission Spectral Tomography Algorithms And Its Application To Three-dimensional Fluid Field Reconstructions

Optical Computed Tomography (OCT) is a branch of Computed Tomography, which is a testing technique not disturbing the distribution of the fields to be reconstructed. OCT shows superiorities in testing thermophysical parameters and diagnosing plasma. Especially in physical parameters reconstruction of the three-dimensional fluid fields, OCT is almost the best technique that can't be replaced by other approaches. Emission spectral tomography (EST) is practicable and only needs simple devices, which is the combination of the emission spectral measurement with OCT and can be widely used in mechanism, metallurgy, energy sources, aeronautics, and astronautics, etc. The application of EST technique is always a difficult problem in the world. The main problems are that on the one hand, it is difficult to obtain the precise data of emission intensity of multi orientations and wavelengths, which needs a high precision, a fast mechanical scanning device, and fast response optoelectronic sensors for a testing system; on the other hand, both in parallel beam CT and fan beam CT, it is hard for EST to gain transient emission data from a lot of angels, therefore, the algorithms of EST need to be applicable to limited-view and incomplete data conditions. Firstly, focusing on reconstruction problems of EST with incomplete data, detailed studies on the traditional OCT algorithms, including transform-based and series-expansion-based algorithms, were accomplished; influences of various parameters on reconstruction precision of traditional algorithms were analyzed, which provides a theoretical foundation for improving the performance of these algorithms with incomplete data. On the basis of above studies, some new algorithms, which are applicable to the incomplete data condition, have been proposed in this dissertation, including a Changeable Relaxation-parameter Iterative Reconstruction Technique (CRIRT) algorithm, a Multi Criterion Iterative Reconstruction (MCIR) algorithm, Maximum Entropy SINC-interpolation Reconstruction Technique (MESINCRT) algorithm, and Discrete Iterative Reconstruction-Reprojection (DIRR) focusing on the fields comprising opaque objects. Furthermore, a Hopfield neural network accomplishment of multi-object-optimization based reconstruction algorithm as well as a limited-view fan-beam computed tomography algorithm reconstruction was also studied in this paper. In the experiments of EST, a multi spectral reconstruction approach for three-dimensional fluid fields has been proposed, which combines single point temperature measurement of multi wavelengths with CT reconstruction algorithms, and different testing systems have been constructed for different kinds of fluid field in the experiments. A multi spectral EST approach has been applied in the reconstruction of the temperature field of a four-peak candle flame; in the diagnosis of an argon-arc plasma, the three-dimensional distributions of temperature, electron (ion), atom densities, and ionization coefficient were reconstructed with spectrum relative-intensity method combining limited-view OCT algorithms. The experimental results are coincident with theoretical studies, therefore, the application foundation of EST has been provided in this dissertation.