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A history and study of violin acoustics
(1984) Oakes, Stanley Joe; Nelson, Robert G.; Jones, Robert J.; Wheeler, Lawrence
Violins from the Cremonese masters (Nicolo Amati, Antonio Stradivari, and Guiseppi Guarneri) are regarded as the most nearly perfect instruments known to string players. In efforts to duplicate the exquisite acoustical qualities of these instruments, scientists and musicians have advanced technological research from primarily three areas of investigation-varnishes/chemical analysis, the wood, and construction/acoustics. This thesis traces important historical and scientific research in the areas which contemporary violin makers and scientists feel are more important. These include the varnishes, chemical treatment, and acoustics. From this research it can be concluded that scientists have made definite progress in studying the very complex properties of the violin. Through technical innovations associated with increasingly sensitive measuring equipment, modern violin makers should be able to make consistently good instruments to replace and rival those of the great Italian masters.
A comparison of multi-fold seismic data with CDP gathers recorded along the strike versus the dip of a two-dimensional overthrust model
(1984) Pascual, Ruben Valenzuela; McDonald, John A.; Gardner, Gerald H. F.; Sheriff, Robert E.; Wiggins, James W.
Using the multiple pulse technique of generating signals in the seismic tank, two 48 fold CDP lines were recorded over a two-dimensional overthrust model. The first seismic line was obtained with the CDP gathers recorded along the strike of the structure at each of the CDP positions along the profile line parallel to the dip direction of the structure while the second line was based on conventional data acquisition method in which shot gathers (hence CDP gathers after sorting) are collected along the dip of the structure. A comparison between these two acquisition methods indicates that the 48 fold line with the CDP gathers recorded along the strike of the structure is better than that with the CDP gathers collected along its dip. The former has stacking velocities which differ from the theoretical RMS velocities by less than 1 % suggesting that it practically "sees" all the interfaces along the strike as horizontal, its velocity spectra are easier to interpret, and the changes in the stacking velocities closely follow the major changes in the velocity between the different propagating media. In contrast, the latter method has stacking velocities greater than or less than the theoretical RMS velocities by as much as 14 % depending on the travel paths of the signals, interpretation of the velocity spectra tend to be involved, and the measured stacking velocities do not follow the major changes in the velocity of the different media. As anticipated, a better stacked section was obtained fron the multi-fold data with the CDP gathers recorded along the strike of the structure than along its dip. The F-K migration results for both sets of data further show the advantage in collecting multi-fold line along the strike of the structure. Synthetic data generated from ray tracing were used in identifying and comparing the various events in several CDP gathers and in the seismic sections obtained in this study.
A method to evaluate the consequences of member failure in jacket-type offshore platform structures
(1983) Nelson, James K., Jr.; Graff, William J.; Hsu, Thomas T. C.; Han, Kye J.; Poage, Scott T.; Tucker, Charles T.
An evaluation of the consequences in a structural system caused by the failure of a component within the system is a necessary part of reliability based design. Presented in this dissertation is a method to determine the consequences of member failure in offshore jacket-type platform structures. The method presented herein utilizes the same computer model of the structure that is used for the initial analysis of the structure. In this dissertation, failure is defined as the complete loss of a member's resistance to load. Such failures can occur as the result of fatigue, poor construction, excessive load, or mechanical damage caused by dropping heavy equipment or ship collisions. To evaluate the consequences of a member failing, the behavior of the remaining members in the structure was determined. This was accomplished by mathematically removing a single member from the structure and computing the change in the behavior, i.e. the change in stresses, of the other members. This member then was replaced and another member was removed; the process was repeated for all members in the jacket structure. Each member can be classified quantitatively according to the change in the stresses in the other members in the platform and also the serviceability of the platform. A typical steel template or jacket-type offshore platform is composed of many members. If a complete analysis is required each time a member is removed, the cost of design will become exorbitant. A computationally efficient procedure to remove members from the structure has been developed and is presented in this dissertation. The new algorithm is based upon the initial strain concept of structural reanalysis. Advantage was taken of the fact that the degrees-of-freedom to be modified during reanalysis for the removal of a single member are very well defined; they are the degrees-of-freedom associated with the member being removed. Using this new algorithm, the computer time required for reanalysis is less than would be required if a new analysis of the platform were to be performed. For the jacket structures studied, the time required for reanalysis was approximately one-third of the time required for the original analysis. The structures were all three-dimensional rigid frames with six degrees- of-freedom at each joint. Example problems are included in the dissertation that demonstrate the application and the computational efficiency of the new algorithm. Presented in the dissertation also is a proposed classification system for members in jacket-type offshore platforms. The classification system is quantitative and considers both the stress changes in the components of the platform and also the serviceability of the platform. Each time a member is removed, the stresses in the remaining members are computed. These stresses are compared to the stresses in the members in the original, intact structure. The original structure was assumed to be designed in the elastic range of the material. This assumption is consistent with the American Petroleum Institute design specifications. The serviceability of the platform is measured by the rotation of a reference plane defined by the analyst. Typically, the reference plane would be taken to be the sea-deck level of the platform. Four member categories have been proposed: Non- Redundant Members, Primary Structural Members I, Primary Structural Members II, and Redundant Members. Failure of a Non-Redundant Member causes a collapse of the platform or necessitates shutdown of the platform due to a loss of serviceability. Failure of a Primary Structural Member I causes the stresses in other members of the platform to become inelastic but the structure does not collapse. Members in the second category of primary structural members cause a significant change in the behavior of the platform when they fail but the stresses in the other members remain in the elastic range of the material. A Redundant Member is one which does not cause significant change in the behavior of the platform when it fails. Through the study of a typical jacket structure configuration, the applicability of this member classification system was demonstrated. The results of this study are presented in this dissertation.
Migration of vertical seismic profiles by time-reversal extrapolation and ray tracing
(1984) Tzeng, Rong-Fung; McDonald, John A.; Gardner, Gerald H. F.; Sheriff, Robert E.; Wiggins, James W.
Vertical seismic profiles are used as a tool to help interpret surface seismic records. In a horizontally layered area, a two-way travel time shifting which horizontally aligns the upgoing events will satisfy that purpose. However, as geology becomes more complicated, an imaging or migration process is necessary since time shifts alone will not show the interfaces properly. Although the concept of migration of surface records has been widely covered, the migration of VSP records is still seldom discussed. In this research, a migration algorithm for VSP data is presented. Since the geometries of VSP records and surface offset records are similar when the earth model is rotated through 90 degree, the migration of VSP data can be approached from the migration algorithm of surface offset data. The imaging concept for surface offset records can be thought of as finding the amplitude at places where the downgoing wavefields are time coincident with upgoing wavefields; in other words, the amplitude at reflection points can be found from the upgoing wavefields at the time when the downgoing wavefields arrive. The time-reversal downward propagation algorithm was adopted to recreate the upgoing wavefields at each time step and the arrival times of downgoing wavefields were calculated by a ray tracing program. The amplitude at each defined grid point is interpolated from the recreated upgoing wavefields around the time that the downgoing wavefields arrived at. Migration results fran synthetic and physical modeling data, both surface offset data and VSP data, are used to demonstrate the effectiveness of this algorithm. Due to restrictions of physical modeling facilities, the VSP physical modeling data are not satisfactory and the migration results are not so good as synthetic results.
Recurrent species associations and species diversity of cytheracean ostracodes in the upper Austin and lower Taylor groups (Campanian, upper cretaceous) of Travis County, Texas
(1983) Ross, James E.; Maddocks, Rosalie Frances; Butler, John C.; Bryant, Edwin H.
Assemblages of cytheracean ostracodes from the Dessau, Burditt, and Sprinkle formations of the upper Austin and lower Taylor groups of Travis County, Texas, were examined in order to identify recurring species associations, the differences between them, and the paleoenvironmental factors that control their stratigraphic distribution. From Q-mode cluster analysis, six sample-groups were identified, and it was found that all of them correspond closely to observable lithofacies. Four recurrent species associations were identified from the R-mode cluster analysis and were found to correspond to four of the six sample-groups. Indices of species diversity and its components, species richness and species equitability, showed noticeable changes from one lithofacies to another with the greatest changes occurring at the Dessau-Burditt and Burditt-Sprinkle (Austin-Taylor) contacts. The stratigraphic distributions of cytheracean ostracode faunas in the upper Austin and lower Taylor appear to be controlled by the distribution of lithofacies. Some of the faunas, however, differ primarily in abundances of species, as opposed to containing different species. Appearances and disappearances of a few species, including Alatacythere cheethami, "Hazelina" austinensis, Schuleridea travisensis, Loxoconcha retidlata, and Haplocytheridea insolita, may be temporally significant. Faunas from different sample-groups that contain many of the same species can be differentiated by comparing values of species diversity and its components. Plotted trend-curves of the indices provide visual aids for this purpose. The shapes of the trend-curves in two outcrops of the upper Burditt and lower Sprinkle formations were roughly parallel to each other, but the geographic scope of this study was not broad enough to test the possibility of using trend-curves as tools for stratigraphic correlation. The major breaks in the trend-curves at the Dessau-Burditt and Burditt-Sprinkle (Austin-Taylor) disconformities indicate that trend-curves may serve to uncover previously unrecognized disconformities in future studies of other stratigraphic intervals.