Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 199-210). Available also in a digital version from Dissertation Abstracts.

Experimental nonlinear dynamics is an important area of study in the modern engineering field, with engineering applications in structural dynamics, structural control, and structural health monitoring. As a result, the discipline has experienced a great influx of research efforts to develop a versatile and reliable experimental methodology. A technical challenge in many experimental studies is the procurement of a device that exhibits the desired nonlinear behavior. As a result, many researchers have longed for a versatile, but accurate, testing methodology that has complete freedom to simulate a wide range of nonlinearities and stochastic behaviors. The objective of this study is to develop a reconfigurable test setup as a tool to be used in a wide range of nonlinear dynamic studies. The main components include a moving mass whose restoring force can accurately be controlled and reprogrammed (with software) based upon measured displacement and velocity readings at each time step. The device offers control over nonlinear characteristics and the equation of dynamic motion. The advantage of having such an experimental setup is the ability to simulate various types of nonlinearities with the same test setup. As a result, the data collected can be used to help validate nonlinear modeling, system identification, and stochastic analysis studies. A physical test apparatus was developed, and various mechanical, electrical, and programming calibrations were performed for reliable experimental studies. To display potential uses for the reconfigurable approach, examples are presented where the device has been used to create physical data for use in change detection and deterioration studies. In addition, a demonstration is presented of the device’s ability to physically simulate a large-scale orifice viscous damper, commonly used in vibration mitigation in bridges and buildings. For a large-scale viscous damper, physical testing is required to ensure structural design properties. However, due to the large scale of the dampers, expensive dynamic loading tests can be carried out at a very iii limited number of facilities. Using the reconfigurable test setup, the dynamic signature of the large-scale viscous damper can accurately be simulated with pre-collected data. The development of a system capable of emulating the restoring force of a nonlinear device with software is a novel approach and requires further calibration for increased reliability and accuracy. A discussion regarding the challenges faced when developing the methodology is presented and possible solutions are recommended. The methodology introduced by this apparatus is very promising. The device is a valuable experimental tool for researchers and designers, allowing for physical data collection, modeling, analysis, and validation of a wide class of nonlinear phenomena that commonly occur in a wide variety of engineering applications.

There has been lots of interest in designing more fuel efficient aircraft using concepts such as boundary layer ingestion (BLI) that cause large amounts of pressure and swirl distortion that enter the jet engines. To enable ground testing the performance of these engines in different distortion patterns, the StreamVane and ScreenVane systems have been developed. A StreamVane consists of a complex vane pack that is custom designed for each distortion profile and the ScreenVane combines the StreamVane with a pressure distortion screen for testing engines under both pressure and swirl distortions. The complexity and uniqueness of these devices make predicting their structural integrity and propensity to flutter a challenge, necessitating the need for studying flutter in these complex vane packs. In order to study flutter of these complex vane packs, a methodology was created to obtain trailing edge displacements and frequencies from high speed video of a StreamVane and was used on a quad swirl StreamVane and a Simplified model. Unsteady CFD with periodic mesh deformation based off of its modal analysis was used to validate if it can predict the flutter velocity as well as understanding what the unsteady aerodynamic response to flutter is. A parameter study was then conducted along with oilflow visualization to better understand the potential causes of flutter and the impact of different design parameters. A harmonic response analysis was conducted on each of these designs and a correlation between the amplitude from the harmonic response and the flutter Mach number was obtained that can be used to predict when a StreamVane will flutter. A new series of StreamVanes were designed and based off of computational analysis, two were selected for manufacture. They both successfully avoided fluttering in flutter tests and were found to accurately replicate the goal swirl profile when measured with a 5 hole probe. These results provide a basis for understanding and predicting flutter in StreamVanes. / Master of Science / There has been lots of interest in designing more fuel efficient aircraft using concepts such as boundary layer ingestion (BLI) that cause large amounts of pressure and swirl distortion that enter the jet engines. To enable ground testing the performance of these engines in different distortion patterns, the StreamVane and ScreenVane systems have been developed. A StreamVane consists of a complex vane pack that is custom designed for each distortion profile and the ScreenVane combines the StreamVane with a pressure distortion screen for testing engines under both pressure and swirl distortions. The complexity and uniqueness of these devices make predicting their structural integrity and propensity to flutter a challenge, necessitating the need for studying flutter in these complex vane packs. Flutter is when a structure experiences excess vibration when exposed to unsteady aerodynamic loads. In order to study flutter of these complex vane packs, a methodology was created to obtain trailing edge displacements and frequencies from high speed video of a StreamVane and was used on a quad swirl StreamVane and a Simplified model. Unsteady computation fluid dynamics (CFD) with periodic mesh deformation was used to validate if it can predict the flutter velocity as well as understanding what the unsteady aerodynamic response to flutter is. A parameter study was then conducted along with oilflow visualization to better understand the potential causes of flutter and the impact of different design parameters. A harmonic response analysis, which consists of a dynamic structural analysis with sinusoidal loading applied, was conducted on each of these designs. A correlation between the amplitude from the harmonic response and the flutter Mach number was obtained that can be used to predict when a StreamVane will flutter. A new series of StreamVanes were then designed and based off of computational analyses, two were selected for manufacture. They both successfully avoided fluttering in flutter tests and were found to accurately replicate the goal swirl profile when measured with a 5 hole probe downstream of the StreamVane. These results provide a basis for understanding and predicting flutter in StreamVanes and other complex vane packs.

Results of experimental tests are presented for twelve 'Sleeved Column' specimens. All the specimens had an outer sleeve and an inner core, both of rectangular cross section. Outer sleeve was 23 in. long and the inner core was 23.5 in., with axial load applied only to the core. There was a gap between the sleeve and the core for all specimens except for one which had zero gap. The parameters considered for the study were core thickness and gap. It was concluded from the study that the sleeved column system carries substantially more load than the conventional Euler's column. The stiffness of the core and the gap between the sleeve and the core affects the load carrying capacity of sleeved column system significantly. For the same core size, specimens with least gap carried more load when compared to other specimens with larger gaps.

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / Acquiring shock and vibration data from flight vehicles through rf telemetry links has numerous associated challenges. Yet, these measurements are important to establish environmental specifications to provide a basis for system or component design and testing. The principal limitation in acquiring these measurements is the frequency bandwidth available for data transmission. This limited bandwidth is often responsible for invalid data being accepted as valid. This work provides a brief review of time and frequency division multiplexing to identify the potential error contributors to shock and vibration measurements. Its focus is on the design of acceleration measurement systems to eliminate these errors and optimize individual measurement channel performance.

This work is centered on the modeling, experimental identification, and dynamic interaction of inherently present and intentionally designed nonlinearities of piezoelectric structures focusing on applications to vibration energy harvesting. The following topics are explored in this theoretical and experimental research: (1) frequency bandwidth enhancement using a simple, intentionally designed, geometrically nonlinear M-shaped oscillator for low-intensity base accelerations; (2) multi-term harmonic balance analysis of this structure for primary and secondary resonance behaviors when coupled with piezoelectrics and an electrical load; (3) inherent electroelastic material softening and dissipative nonlinearities for various piezoelectric materials with a dynamical systems approach; and (4) development of a complete approximate analytical multiphysics electroelastic modeling framework accounting for material, dissipative, and strong circuit nonlinearities. The ramifications of this research extend beyond energy harvesting, since inherent nonlinearities of piezoelectric materials are pronounced in various applications including sensing, actuation, and vibration control, which can also benefit from bandwidth enhancement from designed nonlinearities.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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