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>

<p dir="ltr">This motorsport thesis explores the complete electrification of an IndyCar by simulations. Initial research was conducted on stock IndyCar specifications, and concurrently, a sequential approach was developed for MATLAB-based simulations to generate comprehensive results. The study aims to integrate extensive insights gained from courses such as Vehicle Dynamics, Aerodynamics, Data Acquisition, and Electric Powertrains, alongside practical experience from racing internships. The goal is to comprehend the impact of this conversion on engineering parameters. The analysis specifically emphasizes the engineering aspects, with a particular focus on the longitudinal dynamics of the vehicle through quarter-mile simulations.</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.

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).

A study on shape memory alloy materials as vibration dampers is reported. An important component is the strain rate-dependent and temperature-dependent constitutive behavior of shape memory alloy, which can significantly change its energy dissipation capacity under cyclic loading. The constitutive model used accounts for the thermo-mechanical strain rate-dependent behavior and phase transformation. With increasing structural flexibility, the hysteretic loop size of shape memory alloy dampers increases due to increasing strain rates, thus further decreasing the response of the structure to cyclic excitation. The structure examined is a beam, and its behavior with shape memory alloy dampers is compared to the same beam with conventional dampers. Parametric studies reveal the superior performance of the shape memory alloy over the conventional dampers even at the resonance frequency of the beam-damper system. An important behavior of the shape memory alloy dampers is discovered, in that they absorb energy from the fundamental and higher vibration modes. In contrast, the conventional dampers transfer energy to higher modes. For the same beam control, the stiffness requirement for the shape memory alloy dampers is significantly less than that of the conventional dampers. Response quantities of interest show improved performance of the shape memory alloy over the conventional dampers under varying excitation intensity, frequency, temperature, and strain rate.

<p>The presence of vibration is an important problem in many engineering applications. Various passive techniques have traditionally been used in order to reduce waves and vibrations, and their harmful effects. Passive techniques are, however, difficult to apply in the low frequency region. In addition, the use of passive techniques often involve adding mass to the system, which is undesirable in many applications.</p><p>As an alternative, active techniques can be used to manipulate system dynamics and to control the propagation of waves and vibrations. This thesis deals with modeling, estimation and active control of systems that have resonant dynamics. The systems are exposed to stochastic disturbances. Some of them excite the system and generate vibrational responses and other corrupt measured signals. </p><p>Feedback control of a beam with attached piezoelectrical elements is studied. A detailed modeling approach is described and system identification techniques are employed for model order reduction. Disturbance attenuation of a non-measured variable shows to be difficult. This issue is further analyzed and the problems are shown to depend on fundamental design limitations.</p><p>Feedforward control of traveling waves is also considered. A device with properties analogous to those of an electrical diode is introduced. An `ideal´ feedforward controller based on the mechanical properties of the system is derived. It has, however, poor noise rejection properties and it therefore needs to be modified. A number of feedforward controllers that treat the measurement noise in a statistically sound way are derived.</p><p>Separation of overlapping traveling waves is another topic under investigation. This operation also is sensitive to measurement noise. The problem is thoroughly analyzed and Kalman filtering techniques are employed to derive wave estimators with high statistical performance. </p><p>Finally, a nonlinear regression problem with close connections to unbalance estimation of rotating machinery is treated. Different estimation techniques are derived and analyzed with respect to their statistical accuracy. The estimators are evaluated using the example of separator balancing. </p>