Next-generation equipment and procedures for combined resonant column and torsional shear testing

In this dissertation, work aimed at developing next-generation equipment and procedures for combined resonant column and torsional shear (RCTS) testing are detailed. The work in this dissertation covers three key areas of RCTS testing that need improvement to reach the next level of RCTS testing. The first area involved improvement in measurement resolution with modern control and monitoring equipment. Concurrently, original software was written to enhance the efficiency, accuracy, and repeatability of the test. The second area involved advancing concepts for evaluating and modeling nonlinear behavior of soil, which was done in part by using raw RCTS test data collected and stored from 2013-2017. The third area involved evaluating and modifying the design of the existing RCTS device to accommodate higher levels of shearing strain and provide higher loading capacity. First, when testing at small shear strains (< 0.001%) within the linear-elastic range of soils, very small excitation voltages must be used and very small voltages are recorded from the RCTS sensors. Obtaining accurate measurements in the linear-elastic range is critically important when testing at low confining pressures (in the range of 0.1 to 1 atm). In traditional RCTS data acquisition systems, very small recorded voltages are lost due to limited resolution of the control and monitoring subsystems. Concurrently, the very small recorded voltages are generally heavily contaminated by environmental background noise that invalidates the automated process for reducing raw data into engineering results. Control and monitoring equipment and software were developed that can enhance the measurement and data reduction process when making low-strain measurements. Second, testing of soil in the nonlinear shear strain range (typically greater than 0.001%) is a complex process that departs from traditional dynamic models for single-degree-of-freedom (SDOF) systems. Traditionally, RCTS results from testing in the nonlinear shear strain range involve slight adaptation of traditional SDOF models to obtain nonlinear relationships. Nonlinear dynamics model concepts were taken from literature and adapted to better understand and model nonlinear behavior of soils in RCTS testing. Furthermore, development of nonlinear models at moderate strains help to bridge the spectrum of soil testing which tends to divide into evaluating soils at small to moderate strains (< 0.2%) or at large strains (≥ 0.2%). Third, when testing soils at large shearing strains (> 0.2%), traditional RCTS systems are physically or electronically limited. At higher confining pressures (> 2 atm) where soils become quite stiff, the traditional RCTS control equipment is electronically incapable of driving enough torque output to strain soils in shear above desired levels (> 0.1%). At low confining pressures ( 0.5%). An RCTS testing device was designed that has a torque-output capacity at least three times greater than a traditional RCTS device and an allowable degree of twist that can generate shearing strains above 1%.Civil, Architectural, and Environmental Engineerin

Dynamics and Control of Smart Structures for Space Applications

Smart materials are one of the key emerging technologies for a variety of space systems ranging in their applications from instrumentation to structural design. The underlying principle of smart materials is that they are materials that can change their properties based on an input, typically a voltage or current. When these materials are incorporated into structures, they create smart structures. This work is concerned with the dynamics and control of three smart structures: a membrane structure with shape memory alloys for control of the membrane surface flatness, a flexible manipulator with a collocated piezoelectric sensor/actuator pair for active vibration control, and a piezoelectric nanopositioner for control of instrumentation. Shape memory alloys are used to control the surface flatness of a prototype membrane structure. As these actuators exhibit a hysteretic nonlinearity, they need their own controller to operate as required. The membrane structures surface flatness is then controlled by the shape memory alloys, and two techniques are developed: genetic algorithm and proportional-integral controllers. This would represent the removal of one of the main obstacles preventing the use of membrane structures in space for high precision applications, such as a C-band synthetic aperture radar antenna. Next, an adaptive positive position feedback law is developed for control of a structure with a collocated piezoelectric sensor/actuator pair, with unknown natural frequencies. This control law is then combined with the input shaping technique for slew maneuvers of a single-link flexible manipulator. As an alternative to the adaptive positive position feedback law, genetic algorithms are investigated as both system identification techniques and as a tool for optimal controller design in vibration suppression. These controllers are all verified through both simulation and experiments. The third area of investigation is on the nonlinear dynamics and control of piezoelectric actuators for nanopositioning applications. A state feedback integral plus double integral synchronization controller is designed to allow the piezoelectrics to form the basis of an ultra-precise 2-D Fabry-Perot interferometer as the gap spacing of the device could be controlled at the nanometer level. Next, an output feedback linear integral control law is examined explicitly for the piezoelectric actuators with its nonlinear behaviour modeled as an input nonlinearity to a linear system. Conditions for asymptotic stability are established and then the analysis is extended to the derivation of an output feedback integral synchronization controller that guarantees global asymptotic stability under input nonlinearities. Experiments are then performed to validate the analysis. In this work, the dynamics and control of these smart structures are addressed in the context of their three applications. The main objective of this work is to develop effective and reliable control strategies for smart structures that broaden their applicability to space systems

Numerical Analysis of a Nonlinear Mechanical-Electrical-Acoustical Model of the Cochlea

The overarching goal of my research project is to develop a computational model of the mammalian auditory system and compare the results with the experimental data. This model describes the response of the cochlea to both external acoustic and internal electrical stimulations. The cochlea is the spiral-shaped part of the inner ear where the fluid-borne vibrations are detected by the auditory sensors and then the information, in the form of neural signals, are transferred to the brain by the auditory nerves. The cochlear model will enhance our understanding of failure mechanisms in the cochlea, answering important questions as to the morphological elements of the cochlea that fail and why. A mathematical model of the cochlear response to sound over the entire spectrum will help us understand how important classes of signals are processed in the cochlea (such as speech and music) which can lead to better speech processing algorithms or cochlear implant electrical stimulation paradigms. One important question of biophysics of the cochlea is the underlying mechanism of the cochlear active process which enables sound processing over a broad range of frequencies and intensities. Two mechanisms are hypothesized as the main active processes: outer hair cell (OHC) somatic electromotility and hair bundle (HB) motility. The proposed active mechanisms are implemented into our model and their relative contribution on the cochlear nonlinear amplifier is investigated. It is shown that somatic based activity plays a fundamental role in amplification while the HB motility contribution remains elusive. Two distinct mechanisms are identified through which the HB activity affects the cochlear dynamics. The extracellular voltage is shown to undergo a phase shift at frequencies slightly below the peak, that coincides with the onset of the nonlinear amplification. It is hypothesized that this phase difference between the electrical and mechanical responses gives rise to effective power generation of the OHC somatic force. A three-dimensional model of the cochlea is utilized along with experimental data and it is shown that the electro-mechanical phase transition, generated by the tectorial membrane (TM) shear mechanics, activates the cochlear nonlinear amplifier. The cochlear computational model is also used to simulate a series of active in vitro experiments and interpret the results. It is shown that our model of the electrical, mechanical, and acoustical conditions of the experimental configuration is able to replicate the important findings of the experiments while our interpretation of the results contradicts conclusion of the experiments. It is shown that the OHC somatic electromotility, rather that HB motility, is sufficient to predict the nonlinearities observed in the experiments.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144086/1/nankali_1.pd

Improved performance of hard disk drive servomechanism using digital multirate control

Ph.DDOCTOR OF PHILOSOPH

Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems, part 2

A collection of papers presented at the Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems is given. The papers address modeling, systems identification, and control of flexible aircraft, spacecraft and robotic systems