In this study, the most part is acquainted with the effect of elbow pipe to the guided wave. Elbow pipes were most seen feature in work environment. It was difficult for inspection that the anti-symmetric of signal increased when it passed the elbow pipe by happening mode conversion. The study content includes the using modal solution of the finite element method to solve the dispersion curve of four different bend radius of elbow pipe, they were : 1.0 m, 0.6 m, 0.4 m and 0.2 m. Therefore, by using simulation of wave propagation and experiment to verify dispersion curve of bend pipe were accuracy. This study reveals that, the dispersion curve of elbow pipe is similar to that of straight pipe, and T(0,1) mode in the elbow pipe is most similar with it in straight pipe. Thus, the dispersion curve in elbow pipe and straight pipe were similar, but the effect of geometry of elbow pipe will make the symmetrical incident signal time delay and wave front will distortion, and then it will cause mode conversion. According to the experiment of this study, although the signal of feature behind the elbow pipe caused by mode conversion will make anti-symmetry of reflection signal increase, it still won¡¦t make shift between reflection signal location and real feature location. It is very difficult and complex for inspecting the particular geometry pipe. If we can use the modal analysis of finite element method to solve the dispersion curve of particular geometry pipe, the inspection can be improve.

Independent sets of reflection seismic and seismoelectric data were collected, processed, and interpreted with the aim of generating and studying guided waves within a fault zone. While seismic surveys have recently been utilized to investigate fault zones, past and current seismoelectric experiments have been more focused on identifying lithological interfaces and the presence of fluids within the shallow subsurface. The utilization of a fault structure to study seismoelectric conversions associated with guided waves has not hitherto been reported in the literature. The purpose of this research is to investigate the capabilities of the seismoelectric geophysical method to image fault structures, and to compare these to the capabilities of the conventional reflection seismic technique. I hypothesize that the presence of subsurface fluids will enhance seismoelectric imaging of a fault system. My results show that seismoelectric data contribute significant new for fault zone characterization and subsurface. I collected seismic and seismoelectric data sets across a fault system in the Llano Uplift of central Texas. The seismic reflection data were collected with a Geometrics Strataview seismograph equipped with 36 geophones. The seismoelectric data utilized three Geometrics Geode seismographs, with electric fields recorded by stainless steel dipole pairs instead of geophones. A sledgehammer and an accelerated weight drop provided the seismic energy sources throughout the experiment. Elementary processing techniques were applied to both data sets to enhance the signal to noise ratio. Seismic reflection studies previously have been shown capable of identifying fault zones through the characterization of guided waves. The seismoelectric phenomenon has not yet been utilized for this purpose. Identification of fault-zone trapped waves within each data set was attempted separately before the two data types were qualitatively compared as to their relative capabilities for illuminating the fault zone. The seismic data revealed dispersive energy packets, indicative of guided waves, within the fault zone and absent in the surrounding lithologies. The seismoelectric data was able to produce comparable signals in the fault zone showing guided waves.

This thesis is study about the capability of guided waves in the inspection of cracks in pipelines, and studying about the guided waves of mode conversion phenomenon caused by cracks. The generally used inspection methods in industry are all localized area inspection. It will cost expensively and spend lots of human resource and time consuming, if we want to inspect the whole area in pipelines in factory. Thus, guided waves are used to improve these shortcomings of traditional inspection methods. Guided Waves can propagate fast and long range along the pipelines without decay. With the ability that guided waves can incident at a single location then inspect the whole region of pipelines under efficiently propagating distance. In this thesis, with using laboratory equipment, 3 Toneburst Cycles, 400¡B500¡B600 kHz, and L(0,1)¡BL(0,2) incident mode set up for crack detective sensitivity experiment. By calculating the group velocity of the signals of crack, it is known that there are three separated modes L(0,1)¡BL(0,2) and F(1,2) from reflected waves by cracks. These modes are exactly mode converted by cracks. The results show that in the same crack circumferential length or crack depth, the longer length or the deeper depth cause the higher reflection coefficient. It means they are more sensitive on the inspection of cracks. Also the reflection coefficient increases with the raising cross section area loss of cracks. In two dimensional fast Fourier transform experiment (2-D FFT), with 3 Toneburst Cycles, 400¡B500¡B600 kHz, L(0,1)¡BL(0,2) incident mode, and 0.5 cm interval set up to gather 40-point signals for proceeding the experiment. It can separate signals with different group velocity which are mixing together in time domain. From results, there are three different modes L(0,1)¡BL(0,2) and F(1,2) mode separated at three-dimensional picture. Finally, using the guided waves inspection system with 3 toneburst, 90 kHz and T(0,1) incident mode set up to proceed the experiment as before. In inspecting crack sensitive experiment, the use of this system has the similar result with the use of laboratory equipment. It proves that the excellent capability of guided waves in inspection of cracks in pipelines. While in mode identification, this system can identify there is only T(0,1) and F(1,2) mode with the same group velocity exist. Then the same result is verified by 2-D FFT experiment. It shows that this system generate or receive the specific mode in detection cracks by phase construction or phase destruction of phase interference.

Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Bard K. Mansager, Keith F. Snider, Scott T. Crino. Includes bibliographical references (p. 75-76). Also available online.

Thesis (Ph. D.)--Lehigh University, 2002. / Includes vita. Includes bibliographical references (leaves 261-272).

Thesis (M.S.)--Central Connecticut State University, 2003. / Thesis advisor: Helen Abadiano. " ... in partial fulfillment of the requirements for the degree of Master of Science in Reading." Includes bibliographical references (leaves 73-85).

Thesis--School of Advanced Airpower Studies. / Title from title screen (viewed Oct. 9, 2003). "May 1992." Includes bibliographical references.

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