Passive control techniques to minimize structural vibrations are limited with respect to the amount of attenuation obtained especially in the low-frequency region but do not require adding any power. Active control methods are effective for reducing structural vibrations, especially at low frequencies, but may require significant control effort. Thus, passive and active control methods have complementary frequency ranges of application. This research consists of combining active and passive control techniques to simultaneously attenuate extensional and flexural power flows in infinite thin beams and determine the advantages and disadvantages of such a combination. An analytical model is developed for an infinite beam with a passive insert of high damping placed at some distance from a point force excitation (passive approach). The passive control of vibrations results in a reduction of both extensional and flexural power flows downstream of the passive material discontinuity. The simultaneous active control of extensional and flexural waves, using two co-located independent piezoceramic actuators bonded to the surface of the beam, is theoretically studied. The active control model shows that the use of two independent piezoceramic actuators allows complete cancellation of the total power flow (sum of the extensional and flexural power flows) downstream of the actuators. The combination of passive and active control methods for three different configurations (actuators located upstream of, downstream of, and on the passive insert) is investigated and complete control of the total power flow is again achieved. The results demonstrate that in the case of the actuators bonded to the passive material discontinuity, the active/passive combination has great potential for reducing the control effort required for the active controller. Finally, an approximation of the influence of heavy fluid flanking paths on the optimal active/passive system is developed by simulation of these flanking paths using axial and torsional springs. This last study shows that both axial and torsional springs will result in modification of the control effort required by the actuators if their respective stiffness is greater than the equivalent stiffness of the section in parallel with the springs. / Master of Science

No / This paper presents an investigation into the impact of data dependencies in real-time high performance sequential and parallel processing. An adaptive active vibration control algorithm is considered to demonstrate the impact of data dependencies in real-time computing. The algorithm is analysed in detail to explore the inherent data dependencies. To minimize the impact of data dependencies, an investigation into reducing memory access in sequential computing is provided. The impact of data dependencies with various interconnections is also explored and demonstrated in real-time parallel processing through a set of experiments.

Yes / This paper presents an investigation into the impact of algorithm design for real-time active control systems. An active vibration control (AVC) algorithm for flexible beam systems is employed to demonstrate the critical design impact for real-time control applications. The AVC algorithm is analyzed, designed in various forms and implemented to explore the impact. Finally, a comparative real-time computing performance of the algorithms is presented and discussed to demonstrate the merits of different design mechanisms through a set of experiments.

<p dir="ltr">Vibration is ubiquitous in the modern world, making it a topic that cannot be avoided during design, manufacture, and maintenance. Systems, such as civil structures and suspension of cars, are normally designed to stay in the attenuation zone to avoid harsh vibrations. Designing and manufacturing systems with the desired natural frequency distribution is easy. However, it is much harder to maintain the frequency response since materials keep aging as time goes by. To counter the effect of aging and attenuate vibrations, this thesis designed a meta-material that is capable of reprogramming its natural frequency distribution by inserting various masses at different locations. This ability to specifically adjust the system's natural frequency distribution is what we define as "Digital Inertia Programming".</p><p dir="ltr">The model consists of 12 identical unit cells, with each unit cell comprising two types of springs. By determining whether to insert a mass into the unit cell at various locations, the model achieves its programmability to adjust its natural frequency distribution. A "Binary Representation" is used to label the patterns of mass inserted in the model. Each unit cell is represented by a binary bit and a total of 12 bits are used to indicate the presence of mass in each unit cell. In the thesis, we mainly discuss bilaterally symmetrical patterns to avoid unwanted twisting. For the 12 unit cells, we can obtain a total of 128 bilaterally symmetrical patterns, resulting in 896 independent natural frequencies for the model. The number of patterns and independent natural frequencies will increase exponentially with the increase of the number of unit cells in the model.</p><p dir="ltr">An ideal one-dimensional analytical metamaterial model is developed. Lagrange's method is used to determine the system's mass matrix and stiffness matrix directly from the kinetic energy and potential energy equations. The natural frequencies and mode shapes are then calculated from the eigenvalue equation. Based on free response analysis and sensitivity analysis, the model successfully showed great programmability on frequency distribution by varying the insert patterns, as well as changing the value of the variables in the model, such as the weight of the inserts, the weight of the top mass, the stiffness of the unit cell wall spring and the stiffness of the connecting spring. When continuously varying the parameter, the model's natural frequency distribution also changes continuously, giving a possibility to adjust the natural frequency distribution by carefully adjusting the weight of the mass inserted at each location. Lastly, a forced-response analysis is performed, and the amplitude of the model's frequency response is plotted. This provides a straightforward view of the changes in the band gaps and the overall stiffness of the model by altering the patterns with two inserts.</p><p dir="ltr">A two-dimensional model is developed based on the one-dimensional model. The model retains the same 12 unit cells setup as the one-dimensional model. Aiming to ensure stability, the rectangular-shaped unit cell is now configured as a combination of two triangles. Taylor expansion and small angle approximation are used to eliminate nonlinear terms and triangular function terms in the stiffness matrix respectively. The model again shows its programmability by adjusting the variables of the model. Since the results of asymmetrical patterns are bounded by the results of symmetrical patterns, including the asymmetrical patterns increases the model's precision. However, the symmetrical patterns already provide a good representation of the model. The rotational motion is added to the inserts in the model, which further increases the model's complexity. In the model, the mode shapes are characterized by the rotational motion of inserts and the horizontal motion of inserts, which correspond to a zero strain mode of the model. A linear regression model is trained based on 100 bilaterally symmetrical patterns to predict the second lowest natural frequencies of the two-dimensional model for both symmetrical and asymmetrical patterns. The success in the linear regression model indicates the potential for applying machine learning algorithms to the design of meta-materials in the future.</p>

This work examines a novel concept and design of simultaneous energy harvesting and vibration control on the same host structure. The motivating application is a multifunctional composite sandwich wing spar for a small Unmanned Aerial Vehicle (UAV) with the goal of providing self-contained gust alleviation. The basic idea is that the wing itself is able to harvest energy from the ambient vibrations along with available sunlight during normal flight. If the wing experiences any strong wind gust, it will sense the increased vibration levels and provide vibration control to maintain its stability. This work holds promise for improving performance of small UAVs in wind gusts. The proposed multifunctional wing spar integrates a flexible solar cell array, flexible piezoelectric wafers, a thin film battery and an electronic module into a composite sandwich structure. The basic design factors are discussed for a beam-like multifunctional wing spar with load-bearing energy harvesting, strain sensing and self-controlling functions. Three-point bending tests are performed on the composite sandwich structure for bending strength analysis and bending stiffness prediction under a given safety factor. Additional design factors such as the configuration, location and actuation type of each piezoelectric transducer are investigated for optimal power generation. The equivalent electromechanical representations of a multifunctional wing spar is derived theoretically, simulated numerically and validated experimentally. Special attention is given to the development of a reduced energy control (REC) law, aiming to minimize the actuation energy and the dissipated heat. The REC law integrates a nonlinear switching algorithm with a positive strain feedback controller, and is represented by a positive feedback operation amplifier (op-amp) and a voltage buffer op-amp for each mode. Experimental results exhibit that the use of nonlinear REC law requires 67.3 % less power than a conventional nonlinear controller to have the same settling time under free vibrations. Nonlinearity in the electromechanical coupling coefficient of the piezoelectric transducer is also observed, arising from the piezoelectric hysteresis in the constitutive equations coupling the strain field and the electric field. If a constant and voltage-independent electromechanical coupling coefficient is assumed, this nonlinearity results in considerable discrepancies between experimental measurements and simulation results. The voltage-dependent coupling coefficient function is identified experimentally, and a real time adaptive control algorithm is developed to account for the nonlinear coupling behavior, allowing for more accurate numerical simulations. Experimental validations build upon recent advances in harvester, sensor and actuator technology that have resulted in thin, light-weight multilayered composite sandwich wing spars. These multifunctional wing spars are designed and validated to able to alleviate wind gust of small UAVs using the harvested energy. Experimental results are presented for cantilever wing spars with micro-fiber composite transducers controlled by reduced energy controllers with a focus on two vibration modes. A reduction of 11dB and 7dB is obtained for the first and the second mode using the harvested ambient energy. This work demonstrates the use of reduced energy control laws for solving gust alleviation problems in small UAVs, provides the experimental verification details, and focuses on applications to autonomous light-weight aerospace systems. / Ph. D.

<p dir="ltr">Energetic materials are a special class of materials which are immensely useful across applications due to their high energy density. However, energetics present unique challenges in manufacturing, processing, and handling. Sensitivity depends on microstructural features (i.e., porosity) established during manufacturing processes, external stimulation (i.e., electrostatic discharge, shock), environmental conditions (i.e. humidity), etc. Improving control of microstructure with new, safe manufacturing techniques such as powder deposition could expand the capabilities of energetic materials and improve sensitivity. Industries such as pharmaceuticals and additive manufacturing routinely use vibration to control dispensing of fine powders, but this has not been applied often to energetics. This research uses a DC vibration mini motor and Luer-lock nozzle tips to investigate controlled dispensing of sugar, soda lime, and nylon powders as energetic surrogates or potential binders. Changes in powder flow due to powder characteristics (size, shape, density), orifice sizes (0.2-1.6 mm), nozzle geometry (tapered and blunt-end), and motor voltages (1-3.4V) were quantified with high-speed image data and novel image processing scripts. Free flowing powders (> 150 µm) formed natural bridges in nozzles 2-4x larger. Finer, more cohesive powders bridged across larger orifice diameters. Vibration was applied to toggle flow by disrupting bridging. Higher vibration voltages created erratic dispensing patterns, while lower motor voltages (< 2V) yielded smaller cone angles and cyclic behavior tied to the motor frequency. A mixture of sugar and nylon was dispensed, and partial segregation was observed over time. This research demonstrated the range of vibration-controlled deposition conditions applicable to energetic materials which are currently lacking in literature.</p>

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-05-26Bitstream added on 2014-06-13T19:55:33Z : No. of bitstreams: 1 galavotti_tv_me_ilha.pdf: 4073080 bytes, checksum: 0605ef5edb68c7bc2b71f8c976c0fe09 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nos últimos anos, as indústrias têm mostrado bastante interesse no desenvolvimento de novas técnicas para o controle de vibrações. O objetivo principal é atribuir valores aceitáveis das amplitudes de vibrações nos sistemas, garantindo um bom funcionamento dos mesmos e evitando falhas que provoquem paradas abruptas, mostrando-se uma área científica muito importante e que aproxima vários campos da engenharia moderna. Atualmente essa tecnologia é crescente e grande investimento tem sido aplicado no seu desenvolvimento. Este trabalho apresenta resultados obtidos para técnicas ativas e semi-ativas de controle de vibrações, considerando que as modificações estruturais são provenientes da alteração da rigidez e amortecimento. Utiliza-se para essa análise, Amortecedores Ativos Controlados por Atuadores Piezelétricos, denominados em inglês por Piezoelectric Friction Damper (PFD). A aplicação da metodologia é realizada em máquinas rotativas modeladas pelo Método dos Elementos Finitos e em um protótipo projetado e construído em laboratório. Os resultados procuram atenuar os níveis de vibrações e demonstram a viabilidade da aplicação de PFDs em estruturas. / Nowadays industries have shown great interest in developing new techniques for vibration control. The target is getting acceptable values of the amplitudes of vibrations in systems, ensuring proper working order avoiding failures. This is a scientific area of very important and approach fields of modern engineering. Currently this technology is growing and large investments has been applied in its development. This paper presents results obtained for active and semi-active techniques vibration control, where the structural changes are from the modification of stiffness and damping. It is used for this analysis a system known by Piezoelectric Friction Damper (PFD). The methodology was applied in rotating machines modeled by finite element method and in a prototype designed and built in the laboratory. The results try to mitigate the vibration levels and demonstrate the feasibility of applying PFDs in rotating machine.

No description available.

Noise emission is a major drawback of the positive displacement machine. The noise source can be divided into structure borne noise source (SBNS) and fluid borne noise source (FBNS). Passive techniques such as valve plate optimization have been used for noise reduction of axial piston machines. However, passive techniques are only effective for limited operating conditions or at least need compromises in design. In this paper, active vibration control of swash plate is investigated for vibration and noise reduction over a wide range of operating conditions as an additional method to passive noise reduction techniques. A 75cc pump has been modified for implementation of active vibration control using the swash plate. One tri-axial acceleration sensor and one angle sensor are installed on the swash plate and a high speed servovalve is used for the swash plate actuation. The multi-frequency two-weight least mean square (LMS) filter synthesizes the servovalve input signal to generate a destructive interference force which minimizes the swash plate vibration. An experimental test setup has been realized using Labview field-programmable gate array (FPGA) via cRIO. Simulation and experimental studies are conducted to investigate the possibility of active vibration control.

The target of the research is to employ the autoresonant control technique in order to maintain the nonlinear oscillation mode at resonance (i.e. ultrasonic vibration at the tip of a drill bit at a constant level) during vibro-impact process. Numerical simulations and experiments have been executed. A simplified Matlab-Simulink model which simulates the ultrasonically assisted machining process consists of two parts. The first part represents an ultrasonic transducer that contains a piezoelectric transducer and a 2-step concentrator (waveguide). The second part reflects the applied load to the ultrasonic transducer due to the vibro-impact process. Parameters of the numerical models have been established based on experimental measurements and the model validity has been confirmed through experiments performed on an electromechanical ultrasonic transducer. The model of the ultrasonic transducer together with the model of the applied load was supplemented with a model of the autoresonant control system. The autoresonant control intends to provide the possibility of self-tuning and self-adaptation mechanism for an ultrasonic transducer to maintain its resonant regime of oscillations automatically by means of positive feedback. This is done through a signal to be controlled (please refer to Figure 7.2 and Figure 7.3) transformation and amplification. In order to examine the effectiveness and the efficiency of the autoresonant control system, three control strategies have been employed depending on the attributes of the signals to be controlled . Mechanical feedback control uses a displacement signal at the end of the 2nd step of the ultrasonic transducer. The other two control strategies are current feedback control and power feedback control. Current feedback control employs the electrical current flowing through the piezoceramic rings (piezoelectric transducer) as the signal to be controlled while power feedback control takes into account both the electrical current and the power of the ultrasonic transducer. Comparison of the results of the ultrasonic vibrating system excitation with different control strategies is presented. It should be noted that during numerical simulation the tool effect is not considered due to the complexity of a drill bit creates during the Ultrasonically Assisted Drilling (UAD) process. An effective autoresonant control system was developed and manufactured for machining experiments. Experiments on Ultrasonically Assisted Drilling (UAD) have been performed to validate and compare with the numerical results. Two sizes of drill bits with diameters 3mm and 6mm were applied in combination with three autoresonant control strategies. These were executed during drilling aluminium alloys with one fixed rotational speed associated with several different feed rates. Vibration levels, control efforts, feed force reduction were monitored during experiments. Holes quality and surface finish examinations supplement analysis of the autoresonant control results. In addition, another interesting research on the investigation of the universal matchbox (transformer) has been carried out. Introducing a varying air gap between two ferrite cores allows the optimization of the ultrasonic vibrating system, in terms of the vibration level, effective matchbox inductance, voltage and current level, phase difference between voltage and current, supplied active power etc (more details please refer to Appendix I).