An application of binary state latch device with proper real-time control algorithm for energy redistribution application is introduced in this thesis. Unlike traditional tuned vibration absorber, the latch device can be viewed as variable semi-active dampers such as magnetorheological (MR) and piezoelectric friction dampers. The distinct difference between other semi-active dampers and our latch device is that other semi-active dampers can provide continuous resistance according to the amount of input current, however, the binary latch device can only provide two different values of resistance - either the maximum or no resistance at all. This property brings the latch possibly having higher maximum and minimum ratio of resistance than MR dampers. As for the operating structure, the mechanism of latch element is nearly the same as the piezoelectric friction dampers which the resistance force is provided according to the normal force acting on two rough plates. Nonetheless, because of the characteristic of the binary states output of the latch element, this make it very different from the ordinary variable dampers. Since it is either being turned on or turned off, a novel control law is required for shifting energy. Also, because of the simplicity of the binary states output, it is very accessible to implement the controller on Field Programmable Gate Array (FPGA). With this accessibility, it is promising to apply plenty of latch elements in the same time for large scale application, such as multi-agent networks. In this thesis, an energy-based analytic solution is proposed to illustrate the universal latch-off condition. And a latch-on condition under ideal situations is discussed. At the end, a control law under nonideal condition is being suggested for real-time periodically excited system. We found that energy redistribution is achievable by using the proper control law under fairly broad conditions. / Master of Science

<p> A brief comparison between the ROM models is made in this study.</p>

No description available.

Vibration in metal cutting is a common problem in the manufacturing industry, especially when long and slender tool holders or boring bars are involved in the manufacturing process. Vibration has a detrimental effect on machining. In particular the surface finish is likely to suffer, but tool life is also most likely to be reduced. Tool vibration also results in loud noise that may disturb the working environment. The first part of this thesis describes the development of a robust and manually adjustable analog controller capable of actively controlling boring bar vibrations related to internal turning. This controller is compared with an adaptive digital feedback filtered-x LMS controller and it displays similar performance with a vibration attenuation of up to 50 dB. A thorough experimental investigation of the influence of the clamping properties on the dynamic properties of clamped boring bars is also carried out in second part of the thesis. In relation to this, it is demonstrated that the number of clamping screws, the clamping screw diameter size, the screw tightening torque and the order the screws are tightened, have a significant influence on a clamped boring bar’s eigenfrequencies as well as on its mode shape orientation in the cutting speed - cutting depth plane. Also, an initial investigation of nonlinear dynamic properties of clamped boring bars was carried out. Furthermore, vibration in milling has also been studied in relation to millingtool holders with a long overhang. A basic investigation concerning the spatial dynamic properties of the tool holders of milling machines, both when not cutting and during cutting, has been carried out. Also, active control of milling tool holder vibration has been investigated and a first prototype of an active milling tool holder was implemented and tested. The challenge of transferring electrical power while maintaining good signal quality to and from a rotating object is addressed and a solution to this is proposed. Finally, vibration is also a problem for the hydroelectric power industry. In Sweden, hydroelectric power plants stand for approximately half of Sweden’s electrical power production and are also considered to be a so-called green source of energy. When renovating water turbines in small-scale hydroelectric power plants and modifying them to optimize efficiency, it is not uncommon that disturbing vibrations occur in the power plant. These vibrations have a negative influence on the production capacity and will wear various components quickly. Occasionally, these vibrations may cause severe damage to the power plant. To identify this vibration problem, experimental modal analysis and operating deflection shape analysis were utilized. To reduce the vibration problem, active control using inertial mass actuators was investigated. Preliminary results indicate a significant attenuation of the vibrations.

The objective of this research is to develop a wearable device that could harvest waste mechanical energy of the human hand movement and utilize this energy to suppress wrist tremors. Piezoelectric material is used to measure the hand movement signals, and the signal of wrist tremor is filtered to be utilized to suppress the tremor. In order to conduct the experiment of energy harvesting and tremor suppression, an experimental rig was fabricated. Two types of piezoelectric materials, PVDF (polyvinylidene fluoride) films and MFC (macro fiber composite) films, are used to harvest mechanical energy and used as actuators to suppress hand tremors. However, due to some shortages of the materials, these two types of materials are not used as actuators to suppress the wrist tremors. Thus, we use Matlab Simulink to simulate the tremor suppression with AVC (active vibration control) algorithm.

Passive vibration mitigation via multi-stable, mechanical means is relatively unexplored. In addition, achieving vibration suppression through avoiding resonance is at the forefront of up and coming research. This thesis investigates the application of a purely mechanical, bistable device as a passive method of vibration suppression. A purely mechanical device does not require power, multiple materials, or electrical circuits, and a passive device does not require external interaction or control. Therefore, a passive, mechanical device could be implemented with ease even in physically constrained environments with large dynamic loads, such as turbomachinery. The purely mechanical, bistable device presented herein replicates the two switches per resonance crossing evident in semi-active Resonance Frequency Detuning method. This work explores two different bistable, mass-spring models. The first is a single degree of freedom nonlinear mass spring model aiming to utilize asymmetry in the potential function to change the stiffness of the overall system. The second model is a coupled, two degree of freedom system that combines the nonlinear softening and hardening spring characteristics with the unique stiffnesses of two stable states. The performance is verified by targeting the first mode of a cantilever beam, with the device shifting the resonance away from the excitation frequency. Future research could apply these idealized models to complex, rotating structures and replicate the performance of the passive, mechanical devices in a physical geometry that could be manufactured as a part of a target structure.

Active control constitutes the state of the art in vibration management in rotating machines. However, existing designs are impractical and costly, and hence not yet widely applied. The goal of the research reported here was to develop a design which would allow the implementation of active technology in a wider range of rotating machine applications. Thus, this study focuses on a novel active rotor topology, consisting of a hollow rotor with internally mounted sensors and actuators. This layout provides greater freedom to select the sensor and actuator positions along the rotor, and naturally protects the devices from harsh working environments. The research was structured according to four themes. Firstly, the concept feasibility was explored by constructing a fully functioning prototype. MEMS accelerometers and mass balancer actuators were mounted in an assembled rotor, together with a microcontroller and radio unit to enable wireless transmission of data. Secondly, the behaviour of MEMS accelerometers in a rotating frame of reference was studied. An output model was derived and applied to the study of whirl orbits and transient vibration. Further, techniques were developed to extract mean displacement and angular velocity information from the sensor signals. An analysis of potential sources of measurement error was conducted, and methods for their mitigation devised. The third theme focused on developing active vibration control techniques suitable for use with active rotors. The core of this work is the development and successful implementation of a non a priori method, Algorithmic Direct Search Control. This technique enables vibration to be minimised without knowledge of the system characteristics, by applying a direct search optimisation technique as a control law. Finally, the combination of active rotors and Active Magnetic Bearings was considered to tackle the problem of sensor/actuator non-collocation. The challenge of levitating a rotor on AMBs using only internal accelerometers was approached via integration-based displacement information extraction, to exploit existing PID controllers. This method proved unfeasible in practice, but valuable lessons were derived from the study. The key finding of this work is that active rotor technology is versatile, cost-effective, powerful and feasible. As such, it offers great potential as a route to achieving a more practical and generalised implementation of active control technology in rotating machinery.

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.

Desde o final da década de 1980 até os dias atuais a utilização de materiais inteligentes em sistemas de controle de vibrações e em problemas de conversão de energia mecânica em energia elétrica tem sido amplamente investigada. Entre os materiais inteligentes destacamos os piezelétricos, apresentando acoplamento entre os domínios elétrico e mecânico. Em casos de controle passivo de vibrações utiliza-se o efeito piezelétrico direto e a energia de vibração é dissipada em um circuito elétrico passivo. Apesar de não utilizarem uma fonte externa de energia, a faixa de frequências onde o controlador passivo tem bom desempenho é limitada em relação aos controladores ativos. Em problemas de controle ativo de vibrações o efeito piezelétrico inverso é utilizado. Neste caso, uma tensão elétrica de controle é aplicada aos piezelétricos para a atenuação de vibrações. Os sistemas híbridos de controle (ativo-passivo) associam circuitos passivos e uma fonte de tensão elétrica. Nesse caso, os efeitos piezelétricos direto e inverso são utilizados simultaneamente. Espera-se que a parte ativa do sistema híbrido necessite de menor potência elétrica de atuação (se comparado com um controlador ativo) além do sistema híbrido proporcionar melhor resposta estrutural que o sistema passivo isoladamente. Entretanto, os controladores ativos e híbridos apresentam desvantagens relacionadas com complexidades de uma lei de controle, necessidade de equipamentos externos e podem exigir elevada potência de atuação. Os controladores semi-passivos surgiram como uma alternativa aos pontos negativos dos controladores passivos, ativos e híbridos. Uma técnica semi-passiva chamada SSD (synchronized switch damping) consiste no chaveamento do material piezelétrico entre a condição de circuito aberto e a condição de curto-circuito (SSDS) ou a uma indutância (SSDI), em momentos específicos da vibração da estrutura. Em geral, a conversão eletromecânica de energia é amplificada assim como o efeito shunt damping. Dessa forma, os circuitos semi-passivos, assim como os passivos, têm sido utilizados tanto como controladores de vibração quanto em problemas de coleta piezelétrica de energia. O objetivo deste trabalho é avaliar o desempenho de controladores piezelétricos passivos, semi-passivos, ativos e híbridos na atenuação de vibrações e também em problemas aeroelásticos. O modelo piezoaeroelástico é obtido com um modelo por elementos finitos (placa de Kirchhoff) eletromecanicamente acoplado que associado a um modelo aerodinâmico não-estacionário (método de malha de dipolos) resulta um modelo piezoaeroelástico. Casos de excitação harmônica de base, entrada impulsiva e também condição de flutter são estudados. / From the late 1980s until the present date, the use of smart materials as actuators in vibration control systems and as conversers of mechanical energy into electricity has been widely investigated. Among these smart materials, the piezoelectric ones stand out, presenting a coupling between the electrical and mechanical domain. In passive vibration control, the direct piezoelectric effect is used and vibration energy is dissipated (or harvested) in a passive circuit. Although no external power source is required, the frequency bandwidth in which passive controllers have good performance is limited when compared to active controllers. In active vibration control problems, the inverse piezoelectric effect is used. In this work, a voltage source is applied on the piezoceramic patches in order to attenuate vibration. Hybrid (active-passive) vibration controllers combine passive shunt circuits with the voltage source. In this case, the direct and inverse piezoelectric effects are used simultaneously. It is expected that the active part of the hybrid system will require less energy (when compared to an active controller) and a better structural response will be obtained than the purely passive system. Nevertheless, the active and hybrid controllers present disadvantages such as complexity of a control law, require external equipment and potentially require large amounts of energy. The semi-passive controllers are a recent alternative to the drawbacks of passive, active and hybrid controllers. A semi-passive technique called SSD (synchronized switch damping) consists of using an electronic switch that the piezoelectric element is briefly switched to an electrical shunt-circuit that can be a simple short-circuit (SSDS), or a small inductance (SSDI) at specific times in the structure\'s vibration cycle (Mohammadi, 2008). In general, the electromechanical energy conversion is enhanced as well as the shunt effect damping. Therefore, the switching techniques, as well as the passive circuits, have been used both in vibration control problems and in piezoelectric energy harvesting problems. The goal of this work is to assess the performance of passive, semi-passive, active and hybrid piezoelectric controllers to attenuate vibration in aeroelastic problems. The aeroelastic model is obtained by combining an electromechanically coupled finite element model (Kirchhoff\'s plate) with an unsteady aerodynamic models (the doublet-lattice method and Roger\'s model). The case studies are carried out on an elastic wing response to a base excitation, impulse force, and the flutter condition.

This paper presents a comparison of optimization algorithms for constrained damping (CLD) patches’ layout to minimize the maximum vibration response of the odd modes, which constitutes the dominant acoustic radiation, of a simply-supported beam excited by a harmonic transverse force. An analytical model based on Euler-Bernoulli beam assumptions is derived first to relate the displacement response of the beam with bonded CLD patches and their layout. Four different nonlinear optimization methods/algorithms are then respectively used to optimize the CLD patches’ locations and lengths with aim of minimum displacement amplitude at middle of the beam. The considered methods include subproblem approximation method, the first-order method, sequential quadratic programming (SQP) and genetic algorithm (GA). The efficiency of each considered optimization method is evaluated and also compared in terms of obtained optimal beam displacement. The results show that GA is most efficient in obtaining the best optimum for this optimization problem in spite of highest computation efforts required to improve its stability. / Singapore-MIT Alliance (SMA)