Masters Research - Master of Engineering (Research) / This thesis considers a number of related problems in the area of passive and semi-active vibration control of piezoelectric laminates. The thesis consists of three main parts. The first part of the thesis develops a mathematical model of a physical resonant system-piezoelectric laminated simply supported beam. It is essential to have a good understanding of the physical system so that the associated problems with passive and semi-active shunt damping can be addressed. The second part of the thesis is concerned with problems related with current passive shunt damping techniques using a single piezoelectric laminate. One of the current problems with multiple mode techniques is determining the correct resistive damping for each resonant mode. Therefore, a systematic method is presented for determining the optimal resistance elements by minimizing the H2 norm of the damped system. After the design process, shunt circuits are normally implemented using discrete resistors, capacitors and virtual inductors (Riordan Gyrators). The difficulty in constructing the shunt circuits and achieving reasonable performance has been an ongoing problem. A new approach to implementing piezoelectric shunt circuits is presented. A “synthetic impedance”, consisting of a voltage controlled current source and digital signal processor (DSP) system, is used to synthesize the terminal impedance of a required shunt network. The third part of the thesis is concerned with the semi-active vibration control of piezoelectric laminated. This part addresses a number of associated problems with the current passive shunt damping schemes. The foremost being the complexity of the shunt circuits required to dampen multiple modes. They generally act to minimize structural vibration at a specific frequency – which are rarely stationary. Therefore, a new broadband semi-active shunt technique for controlling multiple modes has been developed. The “negative capacitor” controller is proposed theoretically, and then validated experimentally. The negative capacitor is simular in nature to a passive shunt damper as it uses a single piezoelectric transducer to dampen multiple modes of a flexible structure.

In the control of the vibration structure, active vibration control is an important topic during these years. In this thesis, an active vibration control strategy is proposed to improve the vibration problem in a linear motor positioning system. The main purpose of the present research is to reduce the vibration of the positioning system. A force estimator is applied to suppress extra force produced from a linear motor positioning system. However, uncertain parameters of the system and external disturbance degrade the accuracy of the force estimator. A sliding controller has been designed to enhance the performance of the control system. The performance of the force estimator and the improvement of the control strategy have been discussed thoroughly in this research. The computer simulation and experiments both show encouraging results of the proposed control strategy. The vibration induced from a linear motor positioning system can be suppressed to the expected amplitude 0.0956 when the linear motor position completed.

Electric transmission lines suffer from many hazards, including wind-induced vibrations (WIV), which can lead to fatigue failure of the transmission conductors. Current vibration mitigation methods do not adequately address WIV because they overwhelmingly rely on narrow-band fixed absorbers. A mobile damping robot (MDR) can overcome the limitations of these fixed absorbers by actively transporting them to locations of highest amplitude on the cable; i.e., antinodes. These antinodes are where the absorbers can most efficiently remove energy from the system. While analyses have been performed for vibration absorbers on transmission line conductors, they have not been in the context of a mobile damping robot (MDR). There is a need to investigate the potential impact of the MDR on a transmission line and the resulting implications for the MDR's development. In this thesis, we explore the dynamics of a power line conductor through finite element analysis (FEA) and modal testing. We perform numerical analysis in MATLAB using equations of motion obtained via Hamilton's Principle. We discuss the design and validation of an appropriate test bench and MDR prototype. We also experimentally investigate the ability of the MDR prototype to transport a mass along a conductor to antinode locations. Experimental results indicate that the damping robot is indeed able to navigate to cable locations of highest amplitude corresponding to antinodes. We then conclude and discuss future work. The insights gained from this research lay a foundation to guide further development of the MDR. Through this work, we are better able to define the operating conditions of the MDR, which will facilitate the creation of a more robust, adaptable control framework for expanded capability. / Master of Science / Power transmission lines are important civil structures used to deliver electricity across the nation. However, these lines are subject to an array of hazards that can damage them. One such hazard is vibration due to wind, which can cause fatigue damage, leading to power line failure and outages. A popular form of vibration control is the use of a fixed vibration absorber, which has significant limitations. A mobile damping robot (MDR) can greatly improve upon the efficiency of these absorbers by transporting them to optimal locations along the power line. This thesis explores the utility and feasibility of an MDR to do so. We investigate with the help of engineering software and establish the conditions for experimentation. Our research suggests that the MDR prototype we constructed can autonomously navigate itself along the power line to optimal locations. This research will guide improvements to the MDR so that it can be more effective under real-world conditions.

The need to attenuate noise transmitted into enclosed spaces such as aircraft cabins, automobiles and mining cabins has provided the impetus for many active noise control studies. Studies into active interior noise control began with a pressure squared cost function utilising multiple error sensors and control sources in an attempt to produce global control of the interior sound field. This work found problems with observability of the primary disturbances and a large number of error sensors and control sources were required to produce global control. Since this early work in the 1980's, many new acoustic based cost functions have been developed to improve on the performance of the pressure squared cost function. This thesis will focus on one novel acoustic cost function, virtual error sensing. Virtual error sensing is a relatively new technique which produces localised zones of attenuation at a location remote to the physical sensors. The practical advantage of this method is the people within these enclosed spaces are able to observe a reduction in sound pressure level without their movement being restricted by error sensors located close to their ears. The aim of this thesis is to further investigate the performance of forward-difference virtual error sensors in order to understand the factors that affect the accuracy of the pressure prediction at the virtual location and use this information to develop more accurate and efficient forward- difference virtual sensors. These virtual sensors use linear arrays of microphones containing two or more microphone elements and a linear or quadratic approximation is used to predict the sound at the virtual location. The prediction method determines the weights applied to each microphone signal to predict the sound pressure level at the virtual location. This study investigates susceptibility of the sensors to corruption as a result of phase and sensitivity mismatch between the microphones, as well as in the location of the elements in the error sensing array. A thorough error analysis of the forward-difference virtual microphones was performed in a one-dimensional sound field and in a plane wave sound field. The accuracy of the quadratic virtual microphone was found to be strongly affected by the presence of short wavelength extraneous noise. From this study, two novel virtual error sensing techniques were developed, namely; higher-order virtual sensors and adaptive virtual sensors. The higher-order virtual error sensors still employ the linear and quadratic prediction method but extra microphone elements are added to the array. The aim of these higher-order virtual microphones is to produce a more accurate prediction of the pressure at the virtual location by spatially filtering out any short wavelength extraneous noise that may corrupt the prediction. These virtual sensors were tested in a realtime control scenario in both a one-dimensional reactive sound field and in a free field. This work found that the higher-order virtual microphones can improve the prediction accuracy of the original virtual sensors but are still prone to problems of phase, sensitivity and position errors. Finally, the adaptive LMS virtual sensors were investigated in a SIMULINK simulation and tested experimentally using real-time control in a one-dimensional sound field. It was hoped that an adaptive LMS algorithm could overcome previous difficulties arising from inherent and transducer errors by adapting the weights of the signals from the sensing elements which form the array. The algorithm adapts the sensing microphone signals to produce the same signal as the microphone at the virtual location. Once this has been achieved, the sensing microphone weights are fixed and the microphone at the virtual location is removed, thus creating a virtual microphone. The SIMULINK simulation allowed the performance of the fixed weight and virtual microphones to be investigated in the presence of only phase errors, sensitivity errors and position errors and in the presence of all three combined. This work showed that the adaptive virtual sensors had the ability to compensate for the errors. The number of modes used in the simulations was varied to observe the performance of all virtual sensors in the presence of higher-order modes. The prediction accuracy of the fixed weight virtual sensors was found to be greatly affected by the presence of higher-order modes. The use of the adaptive virtual microphones to produce localised zones of quiet was examined experimentally using real-time control. The study found the real-time control performance is superior to that of the fixed weight higher-order virtual microphones and the original forward-difference virtual microphones. / Thesis (Ph.D.)--School of Mechanical Engineering, 2003.

A State-Switched Absorber (SSA) is a device capable of instantaneously changing its stiffness, thus it can switch between resonance frequencies, increasing its effective bandwidth as compared to classical tuned vibration absorbers for vibration control. This dissertation considers the performance of the SSA for vibration suppression of continuous systems, specifically a beam and a plate. The SSA tuning frequencies and attachment point on the continuous body were optimized using a simulated annealing algorithm. It was found that an optimized SSA outperforms and optimized TVA at controlling vibrations of both a beam and a plate. These performance gains were also observed experimentally employing magneto-rheological elastomers to achieve a stiffness change. This dissertation also considers zero strain switching criteria and the maximum work extraction switching rule used by the SSA. The zero strain switching criteria ensures the system remains stable as no energy is added or released across a switch event. The maximum work extraction switching rule is designed to maximize the power dissipated by the absorber, but also guarantees minimization of the motion of the base to which the absorber is attached.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 126-129).

The need to attenuate noise transmitted into enclosed spaces such as aircraft cabins, automobiles and mining cabins has provided the impetus for many active noise control studies. Studies into active interior noise control began with a pressure squared cost function utilising multiple error sensors and control sources in an attempt to produce global control of the interior sound field. This work found problems with observability of the primary disturbances and a large number of error sensors and control sources were required to produce global control. Since this early work in the 1980's, many new acoustic based cost functions have been developed to improve on the performance of the pressure squared cost function. This thesis will focus on one novel acoustic cost function, virtual error sensing. Virtual error sensing is a relatively new technique which produces localised zones of attenuation at a location remote to the physical sensors. The practical advantage of this method is the people within these enclosed spaces are able to observe a reduction in sound pressure level without their movement being restricted by error sensors located close to their ears. The aim of this thesis is to further investigate the performance of forward-difference virtual error sensors in order to understand the factors that affect the accuracy of the pressure prediction at the virtual location and use this information to develop more accurate and efficient forward- difference virtual sensors. These virtual sensors use linear arrays of microphones containing two or more microphone elements and a linear or quadratic approximation is used to predict the sound at the virtual location. The prediction method determines the weights applied to each microphone signal to predict the sound pressure level at the virtual location. This study investigates susceptibility of the sensors to corruption as a result of phase and sensitivity mismatch between the microphones, as well as in the location of the elements in the error sensing array. A thorough error analysis of the forward-difference virtual microphones was performed in a one-dimensional sound field and in a plane wave sound field. The accuracy of the quadratic virtual microphone was found to be strongly affected by the presence of short wavelength extraneous noise. From this study, two novel virtual error sensing techniques were developed, namely; higher-order virtual sensors and adaptive virtual sensors. The higher-order virtual error sensors still employ the linear and quadratic prediction method but extra microphone elements are added to the array. The aim of these higher-order virtual microphones is to produce a more accurate prediction of the pressure at the virtual location by spatially filtering out any short wavelength extraneous noise that may corrupt the prediction. These virtual sensors were tested in a realtime control scenario in both a one-dimensional reactive sound field and in a free field. This work found that the higher-order virtual microphones can improve the prediction accuracy of the original virtual sensors but are still prone to problems of phase, sensitivity and position errors. Finally, the adaptive LMS virtual sensors were investigated in a SIMULINK simulation and tested experimentally using real-time control in a one-dimensional sound field. It was hoped that an adaptive LMS algorithm could overcome previous difficulties arising from inherent and transducer errors by adapting the weights of the signals from the sensing elements which form the array. The algorithm adapts the sensing microphone signals to produce the same signal as the microphone at the virtual location. Once this has been achieved, the sensing microphone weights are fixed and the microphone at the virtual location is removed, thus creating a virtual microphone. The SIMULINK simulation allowed the performance of the fixed weight and virtual microphones to be investigated in the presence of only phase errors, sensitivity errors and position errors and in the presence of all three combined. This work showed that the adaptive virtual sensors had the ability to compensate for the errors. The number of modes used in the simulations was varied to observe the performance of all virtual sensors in the presence of higher-order modes. The prediction accuracy of the fixed weight virtual sensors was found to be greatly affected by the presence of higher-order modes. The use of the adaptive virtual microphones to produce localised zones of quiet was examined experimentally using real-time control. The study found the real-time control performance is superior to that of the fixed weight higher-order virtual microphones and the original forward-difference virtual microphones. / Thesis (Ph.D.)--School of Mechanical Engineering, 2003.

Thesis, PlanB (M.S.)--University of Wisconsin--Stout, 2005. / Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains ix, 77 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 75-77).

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