| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 91 === Abstract
Tomography is an inner image technique which generates a cross sectional picture of an object by utilizing the object’s response to the nondestructive, probing energy of an external source. Seismic tomography makes use of sources that generate seismic waves which base on the theory of wave transmission. Nowadays the theories and techniques of tomography have been well developed and applied to a number of fields such as Geophysics and Medicine. However, this technique is not well applied in civil engineering. In this thesis, reviews of some basic theories and methods of seismic tomography were conducted first. Then, the series expansion method of tomography was selected to develop the nondestructive evaluation technique for structure components.
In general, the tomography analysis contains two different procedures. The first one is the forward modeling for a given subsurface model. The second is the inversion for updating the subsurface model. At the early development stage of the tomography technology, a straight ray path was adopted. In the seismic tomography, however, it became clear that curved ray paths should be considered. Therefore, the linear traveltime interpolation (LTI) method, which can be applied to curved ray paths is selected to combine with SIRT inversion technique to develop a computational tomography (CT) scheme for concrete structure.
In order to gain more clear image of large inhomogeneous object, BB gun is used to generate seismic wave, and a piezo-electric material is used as the trigger device for signal acquisition. An image processing technique is proposed to improve the vague images and make those pictures more clear. Experimental results show that computed images can help engineers to identify sizes and position of voids, reinforcement size inside a structure component quite well.
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