Structural vibration control (SVC) of large scale structures using the magnetorheological (MR) dampers are studied. Some key issues, i.e. model reduction, suppression of spillover instability, optimal placement of actuators and sensors, modeling of the MR dampers and their applications in SVC system for large scale structures, are addressed in this work. A new model reduction method minimizing the error of a modal-truncation based reduced order model (ROM) is developed. The proposed method is implemented by using a Genetic Algorithm (GA), and can be efficiently used to find a ROM for a large scale structure. The obtained ROM has a finite H2 norm and therefore can be used for H2 controller design. The mechanism of the spillover instability is studied, and a methodology to suppress the spillover instability in a SVC system is proposed. The suggested method uses pointwise actuators and sensors to construct a controller lying in an orthogonal space spanned by the several selected residual modes, such that the spillover instability caused by these residual modes can be successfully suppressed. A GA based numerical scheme used to find the optimal locations for the sensors and actuators of a SVC system is developed. The spatial H2 norm is used as the optimization index. Because the spatial H2 norm is a comprehensive index in evaluating the dynamics of a distributed system, a SVC system using the sensors and actuators located on the obtained optimal locations is able to achieve a better performance defined on a distributed domain. An improved model of MR dampers is suggested such that the model can maintain the desired hysteresis behavior when noisy data are used. For the simulation purpose, a numerical iteration technique is developed to solve the nonlinear differential equations aroused from a passive control of a structure using the MR dampers. The proposed method can be used to simulate the response of a large scale structural system with the MR dampers. The methods developed in this work are finally verified using an industrial roof structure. A passive and semi-active SVC systems are designed to attenuate the wind-induced structural vibration inside a critical area on the roof. The performances of the both SVC systems are analyzed and compared. Simulation results show that the SVC systems using the MR dampers have great potentials in reducing the structural vibration of the roof structure.

Response characteristics and tactile coding capacities of single neurons of the dorsal column nuclei (DCN), and the dorsal horn, in particular, neurons of the spinocervical tract (SCT), were investigated in anaesthetized cats. Purely dynamically-sensitive tactile neurons of the DCN could be divided into two classes, one associated with hair follicle afferent (HFA) input, the other with Pacinian corpuscle (PC) input. The HFA-related class was most sensitive to low-frequency (&lt50 Hz) vibration, had phaselocked responses to vibration frequencies up to ~75 Hz and had a graded response output as a function of vibrotactile intensity changes. PC-related neurons had broader vibrotactile sensitivity, extending to ~300 Hz with tightest phaselocking between 50 and 200 Hz. The SCT neurons in the lumbar dorsal horn had tactile receptive fields on the hairy skin of the hindlimb and a very limited capacity to signal, in a graded way, the intensity parameter of the vibrotactile stimulus. Furthermore, because of their inability to respond on a cycle-by-cycle pattern at vibration frequencies above 5-10 Hz, these neurons were unable to provide any useful signal of vibration frequency beyond ~5-10 Hz, in contrast to DCN neurons. In the parallel human psychophysical study, the capacity for vibrotactile frequency detection and discrimination was examined in five subjects in glabrous and hairy skin. The vibrotactile detection threshold values obtained at four standard frequencies of 20, 50, 100 and 200 Hz were markedly higher on the hairy skin than on the glabrous skin. The discrimination task was examined by means of a two-alternative, forced-choice psychophysical procedure. Measures of the discriminable frequency increment (?????) and the Weber Fraction (????? / ??), revealed similar capacities for frequency discrimination at the two different skin sites at the standard frequencies of 20, 100 and 200 Hz, but an equivocal difference at 50 Hz. Cutaneous local anaesthesia in the dorsal forearm produced a marked impairment in vibrotactile detection and discrimination at the low frequencies of 20 and 50 Hz but little effect at higher frequencies, confirming that vibrotactile detection and discrimination in hairy skin depend upon superficial receptors at low vibrotactile frequencies, but depend on deep, probably Pacinian corpuscle receptors for high frequencies.

The subject of free vibration analysis of thin cylindrical shells is one that extends well back into the last century. In general, the computational methods can be classified as analytical methods and numerical methods. Based on the Flugge thin shell theory, this thesis presents exact solutions for vibration of closed and open cylindrical shells. The state-space technique is adopted to derive the homogenous differential equations for a shell segment and the domain decomposition method is employed to impose the equilibrium and compatability requirements along the interfaces of the shell segments. Extensive analytical and numerical results have been obtained in this thesis for vibration of open/closed cylindrical shells with different boundary conditions, step-wise thickness variations, and multiple intermediate ring supports. The results can serve as useful benchmark values for researchers and engineers to validate their numerical method for shell analysis. / Doctor of Philosophy (PhD)

The failure of rolling element bearings is one of the foremost causes of breakdown in rotary machinery. So far, a variety of vibration-based techniques have been developed to monitor the condition of bearings; however, the role of vibration behavior is rarely considered in the proposed techniques. This thesis presents an analytical study of a healthy rotor-bearing system to gain an understanding of the different categories of bearing vibration. In this study, a two degree-of-freedom model is employed, where the contacts between the rolling elements and races are considered to be nonlinear springs. The analytical investigations confirm that the nature of the inner ring oscillation depends on the internal clearance. A fault-free bearing with a small backlash exhibits periodic behavior; however, bearings categorized as having normal clearance oscillate chaotically. The results from the numerical simulations agree with those from the experiments confirming bearing’s chaotic response at various rotational speeds. Bearing faults generate periodic impacts which affect the chaotic behavior. This effect manifests itself in the phase plane, Poincare map, and chaotic quantifiers such as the Lyapunov exponent, correlation dimension, and information entropy. These quantifiers serve as useful indices for detecting bearing defects. To compare the sensitivity and robustness of chaotic indices with those of well-accepted fault detection techniques, a comprehensive investigation is conducted. The test results demonstrate that the Correlation Dimension (CD), Normalized Information Entropy (NIE), and a proposed time-frequency index, the Maximum Approximate Coefficient of Wavelet transform (MACW), are the most reliable fault indicators. A neuro-fuzzy diagnosis system is then developed, where the strength of the aforementioned indices are integrated to provide a more robust assessment of a bearing’s health condition. Moreover, a prognosis scheme, based on the Adaptive Neuro Fuzzy Inference System (ANFIS), in combination with a set of logical rules, is proposed for estimating the next state of a bearing’s condition. Experimental results confirm the viability of forecasting health condition under different speeds and loads.

The failure of rolling element bearings is one of the foremost causes of breakdown in rotary machinery. So far, a variety of vibration-based techniques have been developed to monitor the condition of bearings; however, the role of vibration behavior is rarely considered in the proposed techniques. This thesis presents an analytical study of a healthy rotor-bearing system to gain an understanding of the different categories of bearing vibration. In this study, a two degree-of-freedom model is employed, where the contacts between the rolling elements and races are considered to be nonlinear springs. The analytical investigations confirm that the nature of the inner ring oscillation depends on the internal clearance. A fault-free bearing with a small backlash exhibits periodic behavior; however, bearings categorized as having normal clearance oscillate chaotically. The results from the numerical simulations agree with those from the experiments confirming bearing’s chaotic response at various rotational speeds. Bearing faults generate periodic impacts which affect the chaotic behavior. This effect manifests itself in the phase plane, Poincare map, and chaotic quantifiers such as the Lyapunov exponent, correlation dimension, and information entropy. These quantifiers serve as useful indices for detecting bearing defects. To compare the sensitivity and robustness of chaotic indices with those of well-accepted fault detection techniques, a comprehensive investigation is conducted. The test results demonstrate that the Correlation Dimension (CD), Normalized Information Entropy (NIE), and a proposed time-frequency index, the Maximum Approximate Coefficient of Wavelet transform (MACW), are the most reliable fault indicators. A neuro-fuzzy diagnosis system is then developed, where the strength of the aforementioned indices are integrated to provide a more robust assessment of a bearing’s health condition. Moreover, a prognosis scheme, based on the Adaptive Neuro Fuzzy Inference System (ANFIS), in combination with a set of logical rules, is proposed for estimating the next state of a bearing’s condition. Experimental results confirm the viability of forecasting health condition under different speeds and loads.

Increased demand for smaller electronics is driving the electronic packaging industry to develop smaller, more efficient component level packages. Surface mounted components, such as flip chips, ball grid arrays (BGAs), and chip-scale packages (CSPs), are being developed for use in high-volume production. All of these technologies use solder bumps to attach the active silicon to the substrate, and traditional nondestructive methods such as machine vision, acoustic microscopy or x-ray inspection cannot easily find solder bump defects. Therefore, a system, consisting of an Nd:YAG laser that delivers pulses of infrared energy to the surface of the chip, a laser interferometer to record surface vibrations, and a high-speed data acquisition system to record the signals, was developed. The pulsed laser generates ultrasound on the chips surface, exciting the whole chip into a vibration motion, and the interferometer measures the vibration displacement of the chips surface at several points. Changes in the quality of the device or its attachment to the board produce changes in the free vibration response. Characterization of the differences between good devices and devices with defects, both in time domain and frequency domain, is performed using signal analysis. The system has inspected flip chips and chip scale packages for missing and misaligned solder balls, but to characterize the resolution of the system for open solder joints, a study of the vibration modes excited by the laser source in a flip chip was performed on specimens with intentionally created defects. Experimental measurements of excited modes were compared with a modal analysis model created in ANSYS, and defects were detected as small changes in the mode shape on the surface of the chips. Current inspection methods have also been inadequate for inspecting multi-layer ceramic capacitors (MLCCs). Flex cracks, caused by manufacturing processes, often cause the capacitors to fail in-service. Samples that have been cracked intentionally were compared with reference samples to determine the feasibility of using this technique to monitor the condition of MLCCs on an assembly line. Currently, there is no on-line inspection method for controlling this problem, but this technique was able to differentiate between good and damaged capacitors.

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