published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (December 12, 2006) Includes bibliographical references.

Shear wave attenuation measurements were made using ceramic bimorph transducers to excite transverse vibrations in a cylindrical column of unconsolidated sediment. Three different water-saturated sediments were used in an attempt to determine the effects of grain shape and sorting on the frequency dependence of attenuation. The mean grain size of the sediments was held constant while the grain shape and size distributions were varied. The sediment assemblages used in the attenuation measurements included a moderately-sorted angular quartz sand, a well-sorted angular quartz sand, and well-sorted spherical glass beads. The moderately-sorted sand showed the greatest attenuation over the measurement frequency range of 1 to 20 kHz. The well-sorted sand and the glass beads showed generally lower attenuation with the beads being the least lossy propagation medium. All three sediments showed evidence of viscous attenuation due to fluid-to-grain relative motion. This mechanism leads to a non-linear relationship between attenuation and frequency. Sediment physical properties were measured for use as inputs to a theoretical attenuation model based on the Biot theory of propagation of waves in porous media. The model allowed attenuation versus frequency predictions to be made for each of the three sediment assemblages. The resultant comparisons between the measured and predicted attenuations demonstrated the importance of using measured model inputs obtained under controlled laboratory conditions when theoretical model capabilities are being evaluated. The model comparison shed significant light on the ability of this particular model to predict shear wave attenuation in non-ideal sediments. / Graduation date: 1984

Thesis (M.S.)--University of Notre Dame, 2004. / Thesis directed by Eric J. Jumper for the Department of Aerospace and Mechanical Engineering. "April 2004." Includes bibliographical references (leaves 66-68).

Thesis (M.S.)--Ohio State University, 1987. / Includes bibliographical references (leaves 92-95). Available online via OhioLINK's ETD Center

Recent developments in cone penetration testing have resulted in the addition of both pore pressure measurements and seismometers. The seismometers allow shear wave velocity testing to be performed at designated intervals. Both of these additions were researched to improve their application and interpretation. The significant factors effecting the pore pressure generated during cone penetration tests are discussed. The importance of various factors is especially dependent upon permeability, strength, and stiffness. For all sands tested, pore pressures lower than static were recorded behind the tip and higher than static were recorded on the face of the cone. It is believed that the large compressive stresses on the cone face result in positive pore pressures. As the cone tip passes a soil element unloading and continued shearing generate pore pressures lower than static in all sands. The sign of this pore pressure (higher or lower than static) was therefore considered primarily a function of the test equipment. Pore pressure response and the rate of dissipation of excess pore pressures were found useful in distinguishing fine granular soils and explaining soil stratigraphy. In cohesive soils the details of pore pressure measurement were found to be important only in stiff soils. Pore pressures at all measurement locations were found to increase with soil strength in soft to firm clays but may be negative of static in very stiff clays. Pore pressures behind the cone tip were often negative of static in stiff clays. Measurement techniques were refined to improve the accuracy of downhole shear wave velocity measurements. Comparisons of downhole and crosshole measurements were made at three well documented sites validating the technique. At several sites it was found useful to consider the Gmax values determined from shear wave velocity and density to distinguish soil type. Gmax to cone resistance ratios were shown to vary systematically with cone resistance values in sands. A wide range in Gmax to cone resistance was observed in clays. The dependence of both cone penetration resistance and Gmax to increased stress level or overburden stress is discussed. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Thesis (Ph. D.)--California Institute of Technology, 1977. UM #77-24,050. / Advisor names found in the Acknowledgments pages of the thesis. Title from home page (viewed 03/09/2010). Includes bibliographical references.

No description available.

To date, most shear velocity heterogeneity models in the lower mantle have been derived using long period data. Comparatively little use has been made of the vast ISC database of shear wave arrival times, which covers the years 1964 to 1991. The aim of this study is to use this database to construct global models of shear wave heterogeneity in the lower mantle and compare it with existing P models using similar period data in order to evaluate the hypothesis that P and S heterogeneity are proportional. In order to reproduce the resolution operator inherent in these existing models, the same parameterization has been employed; lateral dependence is in terms of spherical harmonics up to degree and order 6, and radial dependence in terms of a quartic polynomial. The inversion uses data from over 4500 events selected according to criteria which minimize the bias introduced by uneven source receiver coverage. Despite having approximately one sixth of the amount of data the model correlates well with a P wave model computed using data from the same events, and this in turn is almost identical to models computed by other authors using similar inversion methods. Assuming proportionality of P and S heterogeneity, a joint inversion of the P and S data has been performed. The resultant model correlates extremely well with the P model of this study, and similar variance reductions are obtained for both the P and S datasets as were found in the original inversions. Several model parameterizations have been used to try to investigate the dependence of the model expansion on the results. Consequently, taking into account results from synthetic experiments and from experiments into trade-offs with other inversion parameters, the average ratio of relative S to P heterogeneity ^{d ln v_s}andfrasl;_{d ln v_p} throughout the lower mantle is constrained to be in the interval (1.8,2.1) with emphasis on higher values within these bounds. This value is in agreement with other studies using similar period data, and the upper bound is close to the optimum value of 2.27 obtained by Li et al., 1991 from normal mode data, suggesting that the ratio is at least only weakly dependent on frequency. In addition evidence is presented that the ratio is increasing with depth although attempts to extract specific gradients have failed because of the very poor distribution of S rays in the deepest mantle.