Study On LTI Ray Tracing In Concrete Computerized Tomography

During the construction and use of the mass concrete structures, some faults will form in the structure because of the effect of both outside and inside conditions. These faults have a grave effect on the bearing capability and endurance of the concrete structures. Using ultrasonic nondestructive testing method to test the concrete's quality and diagnose its healthy has the significant sense in assessing its safety, stability and administering diseases.Firstly, ultrasonic detection techlology and computerized tomography technology are introduced in the dissertation. Secondly, inversion algorithms and bend ray tracing are studied. An improved algebraic reconstruction technique (ART) is put forward, and linear travel time interpolation (LTI) ray tracing is used during the iterations to get the real travel paths of rays. In the first step, defective meshes are ascertained by probability and mathematical statistic method, and then defective meshes and normal meshes are provided with different initial wave velocity. In the second step, before each iteration, the projection matrix is anew computed using LTI ray tracing, and during each iteration, defective meshes and normal meshes are provided with different relaxation factors. The results of computer simulation and concrete model experiment show that the improved ART based on LTI ray tracing is effective to improve the accuracy of computation and the quality of image reconstruction.The different factors that affect image reconstruction are discussed in detail. These factors include the mode of ray tracing, inversion algorithms, test way, image disposal and the size of meshes. Experiments indicate that using high-precision inversion algorithms and LTI ray tracing is effective to improve the quality of image reconstruction, double side test is more accurate than singal side test, image diposal after image reconstruction is effective to reduce dummy image, and using appropriate size of meshes is helpful to improve the quality of image reconstruction.At last, the computerized tomography software developed with matlab 6.0 is introduced. The software realizes BPT,ART,SIRT,LSQR based on beeline ray tracing and improved ART based on LTI ray tracing. The inversion results can export in different forms, such as 2-dimension table, 3-dimension wave velocity figure, contour line figure and gray chromatogram. In order to reduce dummy image and improve resolution of image reconstruction, boundary median filter and clustering analysis are used. The software hasfriendly interface and is easy to operate.