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1
Kumar, Ashok. "Active structural-acoustic control of interior noise in vibro-acoustic cavities." Thesis, IIT Delhi, 2016. http://localhost:8080/iit/handle/2074/7036.
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Rafique, Sajid. "Piezoelectric vibration energy harvesting and its application to vibration control." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/piezoelectric-vibration-energy-harvesting-and-its-application-to-vibration-control(d9edcedf-054e-4921-9ba3-5e015b9bbd8f).html.
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Vibration-based energy harvesting using piezoelectric materials have been investigated by several research groups with the aim of harvesting maximum energy and providing power to low-powered wireless electronic systems for their entire operational life. The electromechanical coupling effect introduced by the piezoelectric vibration energy harvesting (PVEH) mechanism presents modelling challenges. For this reason, there has been a continuous effort to develop different modelling techniques to describe the PVEH mechanism and its effects on the dynamics of the system. The overall aims of this thesis are twofold: (1) a thorough theoretical and experimental analysis of a PVEH beam or assembly of beams; (2) an in-depth analytical and experimental investigation of the novel concept of a dual function piezoelectric vibration energy harvester beam/tuned vibration absorber (PVEH/TVA) or 'electromechanical TVA' and its potential application to vibration control. The salient novel contributions of this thesis can be summarised as follows: (i) An in-depth experimental validation of a PVEH beam model based on the analytical modal analysis method (AMAM), with the investigations conducted over a wider frequency range than previously tested. (ii) The precise identification of the electrical loads that harvest maximum power and that induce maximum electrical damping. (iii) A thorough investigation of the influence of mechanical damping on PVEH beams. (iv) A procedure for the exact modelling of PVEH beams, and assemblies of such beams, using the dynamic stiffness matrix (DSM) method. (v) A procedure to enhance the power output from a PVEH beam through the application of a tip rotational restraint and the use of segmented electrodes. (vi) The theoretical basis for the novel concept of a dual function PVEH beam/TVA, and its realisation and experimental validation for a prototype device. A thorough experimental validation of a cantilever piezoelectric bimorph energy harvester without a tip mass is presented under random excitation. The study provided a deep insight into the effect of PVEH on the dynamics of the system for variations in electrical load. An alternative modelling technique to AMAM, based on the DSM, is introduced for PVEH beams. Unlike AMAM, the DSM is exact, since it is based on the exact solution to the bending wave equation. It also readily lends itself to the modelling of beams with different boundary conditions or assemblies of beams of different crosssections. AMAM is shown to converge to DSM if a sufficiency of modes is used. Finally, an in-depth theoretical and experimental investigation of a prototype PVEHbeam/TVA device is presented. This device comprises a pair of bimorphs shunted by R-L-C circuitry and can be used as a tuned mass damper (TMD) to attenuate a vibration mode of a generic structure. The optimal damping required by this TMD is generated by the PVEH effect of the bimorphs. Such a device combines the advantages of conventional mechanical and electrical TVAs, overcoming their relative disadvantages. The results demonstrate that the ideal degree of attenuation can be achieved by the proposed device through appropriate tuning of the circuitry, thereby presenting the prospect of a novel class of 'electromechanical' tuned vibration absorbers.
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Gu, Zhiqiang. "Application of control methods to structural vibration control." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499865.
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Jayasuriya, A. M. M. "Finite element modeling of blast vibrations and study of vibration control criteria." Ohio : Ohio University, 1989. http://www.ohiolink.edu/etd/view.cgi?ohiou1182438393.
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Heilmann, John. "A dual reaction-mass dynamic vibration absorber for active vibration control." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-09182008-063315/.
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Alexander, BXS. "ROTOR POSITION AND VIBRATION CONTROL FOR AEROSPACE FLYWHEEL ENERGY STORAGE DEVICES AND OTHER VIBRATION BASED DEVICES." Cleveland State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1218818393.
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Hirunyapruk, Chompoonoot. "Vibration control using an adaptive tuned magneto-rheological fluid vibration absorber." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/65677/.
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An adaptive tuned vibration absorber (ATVA) can be used to suppress unwanted vibrations. If the excitation frequency is time harmonic but the frequency changes with time, it is desirable to retune the ATVA so that the natural frequency of the ATVA always coincides with the excitation frequency. One way of achieving this is to adjust the stiffness of the ATVA. The key challenge is to change the stiffness in real-time. Tunable fluids such as Magneto-Rheological (MR) fluids, whose properties can be controlled by a magnetic field, may be used to address this challenge. The subject of this thesis is an ATVA exploiting the changeable properties of MR fluids in the pre-yield state. The ATVA is designed as a three-layer beam with elastic face plates and MR fluuid in the core. Electromagnets are attached to the top and the bottom layers to generate a magnetic field. By varying the current supplied to the electromagnets, the shear stiffness of the MR fluid and hence the stiffness of the ATVA can be varied. The vibration characteristics of the ATVA as a function of the magnetic field strength are predicted by a finite element model together with an empirical model for the shear modulus of the MR fluid and a model for the magnetic field applied to the fluid. An MR fluid-filled ATVA was manufactured and tested to validate the predictions. This ATVA design allows the natural frequency to be changed by 40.6%. The self-tuning of the MR fluid-filled ATVA can be achieved by integrating an adaptive-passive controller with the ATVA so that its stiffness can be continuously adjusted in real-time. The control aims to drive the cosine of phase angle between the velocities of the host structure and the ATVA to zero. Various control algorithms, i.e. non-linear proportional, derivative, and proportional-plus-derivative controls, are investigated. Computer simulations and experimental results demonstrate that the MR fluid-filled ATVA is able to retune itself in the order of 0.2 seconds. The ATVA can also maintain the tuned condition within a reasonably wide frequency range between 110 and 146 Hz in the face of changes in the forcing frequency. The MR fluid-filled ATVA has the potential to substantially reduce vibration of a host structure. The proportional-plus-derivative control was found to be the best control approach for the ATVA.
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Red, Wing Rodney D. "Adaptive tuned vibration absorber." Thesis, This resource online, 1997. http://scholar.lib.vt.edu/theses/available/etd-08252008-162250/.
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Wändell, Johan. "Multistage gearboxes : vibration based quality control." Licentiate thesis, KTH, Aeronautical and Vehicle Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3987.
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<p>In this thesis, vibration based techniques for detection of localised surface damages in multistage gearboxes are presented and evaluated.</p><p>A modern vehicle gearbox is a complex system and the number of potential errors is large. For instance, surface damages can be caused by rough handling during assembly. Large savings can be made in the production industry by assuring the quality of products such as gearboxes. An automated quality test as a final step in the production line is one way to achieve this.</p><p>A brief review of available methods for vibration based condition monitoring of gearboxes is given in the opening summary. In the appended papers, a selection of these methods is used to design signal processing procedures for detection of localised surface damages in gearboxes. The procedures include the Synchronous signal averaging technique (SSAT), residual calculation, filtering with a prediction error filter (PEF) based on an AR-model and the use of crest factor and kurtosis as state features. The procedures are fully automatic and require no manual input during calibration or testing. This makes them easy to adapt to new test objects.</p><p>A numerical model, generating simulated gearbox vibration signals, is used to systematically evaluate the proposed procedures. The model originates from an existing model which is extended to include contributions from several gear stages as well as measurement noise. This enables simulation of difficulties likely to arise in quality testing such as varying background noise and modulation due to test rig misalignment. Without the numerical model, the evaluation would require extensive measure-ments. The numerical model is experimentally validated by comparing the simulated vibration signals to signals measured of a real gearbox.</p><p>In the experimental part of the study, vibration data is collected with accelerometers while the gearbox is running in an industrial test rig. In addition to the healthy condition, conditions including three different surface damage sizes are also considered.</p><p>The numerical and the experimental analysis show that the presented procedures are able to detect localised surface damages at an early stage. Previous studies of similar procedures have focused on gear crack detection and overall condition monitoring. The procedures can handle varying back-ground noise and reasonable modulation changes due to misalignment.</p><p>The results show that the choice of sensor position and operating conditions during measure-ments has a significant impact on the efficiency of the fault detection procedures. A localised surface damage excites resonances in the transfer path between the gear mesh and the accelerometer. These resonances amplify the defect signal. The results indicate that it is favourable to choose a speed at which the resonant defect signals are well separated from the gear meshing harmonics in the order domain. This knowledge is of great importance when it comes to quality testing. When a quality test procedure is being developed, it is often possible to choose the operating conditions and sensor positions. It can in fact be more important to choose proper operating conditions than to apply an optimal signal processing procedure.</p>
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Ulker, Fatma Demet. "Active Vibration Control Of Smart Structures." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1098409/index.pdf.
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The purpose of this thesis was to design controllers by using H1 and ¹<br>control strategies
in order to suppress the free and forced vibrations of smart structures. The smart structures
analyzed in this study were the smart beam and the smart ¯<br>n. They were aluminum passive
structures with surface bonded PZT (Lead-Zirconate-Titanate) patches. The structures were
considered in clamped-free con¯<br>guration.
The ¯<br>rst part of this study focused on the identi¯<br>cation of nominal system models of the
smart structures from the experimental data. For the experimentally identi¯<br>ed models the
robust controllers were designed by using H1 and ¹<br>-synthesis strategies. In the second part,
the controller implementation was carried out for the suppression of free and forced vibrations
of the smart structures.
Within the framework of this study, a Smart Structures Laboratory was established in the
Aerospace Engineering Department of METU. The controller implementations were carried out
by considering two di®<br>erent experimental set-ups. In the ¯<br>rst set-up the controller designs were based on the strain measurements. In the second approach, the displacement measurements,
which were acquired through laser displacement sensor, were considered in the controller design.
The ¯<br>rst two °<br>exural modes of the smart beam were successfully controlled by using
H1 method. The vibrations of the ¯<br>rst two °<br>exural and ¯<br>rst torsional modes of the smart
¯<br>n were suppressed through the ¹<br>-synthesis. Satisfactory attenuation levels were achieved for
both strain measurement and displacement measurement applications.
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Wändell, Johan. "Multistage gearboxes : vibration based quality control /." Stockholm : Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3987.
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Chang, Min-Yung. "Active vibration control of composite structures." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-09162005-115021/.
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Li, Xiao Dong. "Active vibration control of vehicle suspension." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=67007.
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Structure-borne noise generated by tire contact on road irregularities is a very important factor in interior vehicle noise. This kind of low-frequency noise can seriously affect the driver's concentration and passenger comfort. In order to reduce this vibration-induced noise, an active vibration control of the vehicle suspension is proposed, as opposed to acoustic noise control. Since modeling uncertainties are inevitable in characterizing the dynamics of the vibration transmission path, robust feedback controllers are considered. In this thesis, an H-infinity robust controller and a mu-synthesis robust controller are designed to reduce the vibrations using actuators acting directly on the suspension. First, closed-loop simulation results are obtained on a quarter-car suspension at the Université de Sherbrooke, showing a significant reduction in vibration. Second, simulation of the controllers is also conducted on a real car. Closed-loop test results are presented and the effectiveness of the robust feedback controllers is discussed.<br>Le bruit de vibration structurelle produit par le contact des pneus du véhicule sur la surface de la route est un facteur important du bruit à l'intérieur du véhicule. Ce type de bruit à basse fréquence peut affecter sérieusement la concentration du conducteur et le confort des passagers. De manière à réduire ce bruit de vibration, un contrôle actif de vibration dans la suspension du véhicule est proposé, en contraste avec la réduction active de bruit acoustique. Puisqu'il est inévitable d'avoir des incertitudes dans le modèle de la dynamique de transmission de la vibration, des contrôleurs rétroactifs robustes sont considérés. Dans cette thèse, un contrôleur robuste H-infini et un contrôleur à synthèse mu sont conçus pour réduire la vibration en utilisant des actionneurs agissant directement sur la suspension. En premier lieu, des résultats de simulation obtenus sur une suspension d'une seule roue à l'Université de Sherbrooke démontrent une réduction significative de la vibration. Puis, une simulation des contrôleurs est effectuée sur le modèle de la voiture. Les résultats des tests en boucle fermée sont présentés et l'efficacité des contrôleurs rétroactifs robustes est discutée.
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Owen, R. G. "Vibration control of magnetic suspension devices." Thesis, Bangor University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380257.
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Houlston, Paul Robert. "Active vibration control of rotating machines." Thesis, University of Nottingham, 2007. http://eprints.nottingham.ac.uk/10275/.
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Second order matrix equations arise in the description of real dynamical systems. Traditional modal control approaches utilise the eigenvectors of the undamped system to diagonalise the system matrices. Any remaining off-diagonal terms in the modal damping matrix are discarded. A regrettable automatic consequence of this action is the destruction of any notion of the skew-symmetry in the damping. The methods presented in this thesis use the `Lancaster Augmented Matrices' (LAMs) allowing state space representations of the second order systems. `Structure preserving transformations' (SPTs) are used to manipulate the system matrices whilst preserving the structure within the LAMs. Utilisation of the SPTs permits the diagonalisation of the system mass, damping and stiffness matrices for non-classically damped systems. Thus a modal control method is presented in this thesis which exploits this diagonalisation. The method introduces independent modal control in which a separate modal controller is designed in modal space for each individual mode or pair of modes. The modal displacements and velocities for the diagonalised systems are extracted from the physical quantities using first order SPT-based filters. Similarly the first order filters are used to translate the modal force into the physical domain. Derivation of the SPT-filters is presented together with a method by which one exploits the non-uniqueness of the diagonalising filters such that initially unstable filters are stabilised. In the context of active control of rotating machines, standard optimal controller methods enable a trade-off to be made between (weighted) mean-square vibrations and (weighted) mean-square control forces, or in the case of a machines controlled using magnetic bearings the currents injected into the magnetic bearings. One shortcoming of such controllers for magnetic bearings is that no concern is devoted to the voltages required. In practice, the voltage available imposes a strict limitation on the maximum possible rate of change of control force (force slew rate). This thesis presents a method which removes the aforementioned existing shortcomings of traditional optimal control. Case studies of realistic rotor systems are presented to illustrate the modal control and control force rate penalisation methods. The system damping matrices of the case studies contain skew-symmetric components due to gyroscopic forces typical of rotating machines. The SPT-based modal control method is used to decouple the non-classically damped equations of motion into n single degree of freedom systems. Optimal modal controllers are designed independently in the modal space such that the modal state, modal forces and modal force rates are weighted as required. The SPT-based modal control method is shown to yield superior results to the conventional notion of independent modal space control according to reasonable assessment.
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Long, Tammy. "Adaptive control of tuned vibration neutralisers." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243178.
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Abdul, Muthalif Asan Gani. "Active control of high-frequency vibration." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612225.
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Rastgaar, Aagaah Mohammad. "Vibration Suppression using Orthogonal Eigenstructure Control." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28492.
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A novel control method called orthogonal eigenstructure control is developed for active vibration cancellation in structures. Orthogonal eigenstructure control is a feedback control method applicable to multi-input multi-output linear systems. While the available control design methodologies offer a large and complex design space of options that can often overwhelm a designer, this control method offers a significant simplification of the design task while still allowing some experience-based design freedom. For example, eigenstructure assignment methods need definition of a desired eigenvector for the closed-loop system. The controller designer may also be required to do pole placement. Considering the fact that there are no one-to-one relationships between the elements of the closed-loop eigenvectors of a model and the states of the system, this effort could be inefficient for many practical systems. Moreover, for large-scale systems, defining or shaping the eigenstructures become a relatively difficult task. Orthogonal eigenstructure control is a state feedback-like control law that is relatively easy to design and implement to multiple-input multiple-output systems. It allows control engineers to achieve good performing designs even with little design experience, while the existing methods are highly dependent on designer experience.
Orthogonal eigenstructure control is introduced and extended to be applicable to linear systems regardless of the number and location of the actuators and sensors. Also, the concept of progressive application of the proposed control method for increasing robustness is described. Finally, the result of application of the control method for vibration cancellation of a test plate is investigated through experiments for tonal and wideband disturbances. The results show a significant reduction of vibrations using the orthogonal eigenstructure control with relative ease in finding the control gain matrix.<br>Ph. D.
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Lau, M. W. S. "Active vibration control at machinery feet." Thesis, Aston University, 2000. http://publications.aston.ac.uk/15340/.
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The unmitigated transmission of undesirable vibration can result in problems by way of causing human discomfort, machinery and equipment failure, and affecting the quality of a manufacturing process. When identifiable transmission paths are discernible, vibrations from the source can be isolated from the rest of the system and this prevents or minimises the problems. The approach proposed here for vibration isolation is active force cancellation at points close to the vibration source. It uses force feedback for multiple-input and multiple-output control at the mounting locations. This is particularly attractive for rigid mounting of machine on relative flexible base where machine alignment and motions are to be restricted. The force transfer function matrix is used as a disturbance rejection performance specification for the design of MIMO controllers. For machine soft-mounted via flexible isolators, a model for this matrix has been derived. Under certain conditions, a simple multiplicative uncertainty model is obtained that shows the amount of perturbation a flexible base has on the machine-isolator-rigid base transmissibility matrix. Such a model is very suitable for use with robust control design paradigm. A different model is derived for the machine on hard-mounts without the flexible isolators. With this model, the level of force transmitted from a machine to a final mounting structure using the measurements for the machine running on another mounting structure can be determined. The two mounting structures have dissimilar dynamic characteristics. Experiments have verified the usefulness of the expression. The model compares well with other methods in the literature. The disadvantage lies with the large amount of data that has to be collected. Active force cancellation is demonstrated on an experimental rig using an AC industrial motor hard-mounted onto a relative flexible structure. The force transfer function matrix, determined from measurements, is used to design H and Static Output Feedback controllers. Both types of controllers are stable and robust to modelling errors within the identified frequency range. They reduce the RMS of transmitted force by between 30?80% at all mounting locations for machine running at 1340 rpm. At the rated speed of 1440 rpm only the static gain controller is able to provide 30?55% reduction at all locations. The H controllers on the other hand could only give a small reduction at one mount location. This is due in part to the deficient of the model used in the design. Higher frequency dynamics has been ignored in the model. This can be resolved by the use of a higher order model that can result in a high order controller. A low order static gain controller, with some tuning, performs better. But it lacks the analytical framework for analysis and design.
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Mannchen, Thomas. "Helicopter vibration reduction using robust control." [S.l. : s.n.], 2003.
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Noormohammadi, Nima. "Hybrid control of human-induced vibration." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5769/.
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A key objective in the design of any sports stadium is to include the maximum number of spectators with minimum obstruction in the visual cone. This functional requirement often results in employing one or more cantilevered tiers, which in turn culminates in more slender grandstands often with relatively low natural frequencies and modal damping ratios. These natural frequencies may sometimes fall in the range of frequencies of human movement, which can possibly excite the structure in resonance resulting in vibration serviceability issues. One of the available techniques to reduce excessive responses is to use passive vibration control techniques such as Tuned Mass Dampers (TMD). However, the off-tuning problem is a potential drawback of this technique, whereby changes in natural frequencies caused by crowd-structure interaction may detune the TMDs. This thesis presents a study into the possibility of using Hybrid Tuned Mass Dampers (HTMDs) to augment the vibration serviceability of structures. An appropriate control algorithm is developed. It shows a comparative analysis of vibration mitigation performances that are likely to be attained by utilising the proposed HTMD. Also, an appropriate control scheme is utilised with the proposed HTMD to deal with the off-tuning issues in TMDs caused by crowd loading, and is shown to be effective. In addition, it shows a comparative experimental investigation of a passive TMD and a prototype HTMD applied on a slab strip structure. The most effective control algorithm to enhance the performance of the HTMD and also deal with the off-tuning problem is investigated. The experimental results verify the developed simulation studies and also demonstrate the effectiveness of employing a HTMD considering both structural response and cost (actuator effort).
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McHenry, Colleen Louise. "Human limb vibration and neuromuscular control." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1696.
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Mechanical loading can modulate tissue plasticity and has potential applications in rehabilitation science and regenerative medicine. To safely and effectively introduce mechanical loads to human cells, tissues, and the entire body, we need to understand the optimal loading environment to promote growth and health. The purpose of this research was 1) to validate a limb vibration and compression system; 2) to determine the effect of limb vibration on neural excitability measured by sub-threshold TMS-conditioned H-reflexes and supra-threshold TMS; 3) to determine changes in center of pressure, muscle activity, and kinematics during a postural task following limb vibration; 4) to determine the effect of vibration on accuracy and long latency responses during a weight bearing visuomotor task.
The major findings of this research are 1) the mechanical system presented in the manuscript can deliver limb vibration and compression reliably, accurate, and safely to human tissue; 2) sub-threshold cortical stimulation reduces the vibration-induced presynaptic inhibition of the H-reflex. This reduction cannot be attributed to an increase in cortical excitability during limb vibration because the MEP remains unchanged with limb vibration; 3) limb vibration altered the soleus and tibialis EMG activity during a postural control task. The vibration-induced increase in muscle activity was associated with unchanged center of pressure variability and reduced center of pressure complexity; 4) healthy individuals were able to accommodate extraneous afferent information due to the vibration interventions They maintained similar levels of accuracy of a visuomotor tracking task and unchanged long latency responses during an unexpected perturbation.
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GASTALDI, CHIARA. "Vibration control and mitigation in turbomachinery." Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2677053.
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The thesis project is directly concerned with safety and reliability as it addresses the problem of High Cycle Fatigue (HCF) failure of turbine blades. Turbine blades can be found in engines used to power aircrafts and electrical generators. Statistics suggest that on average 2.5 HCF events occur on each new design engine. These failures happen suddenly, as resonant vibrations cause cracks which usually propagate very rapidly. Since it is often impossible to avoid the presence and growth of such resonant vibrations, designers frequently incorporate dry friction devices into turbine designs. Typical examples of
friction dampers are shrouds, snubbers and underplatform dampers. Despite the continuous effort found in the literature in terms of modeling and optimization strategies, the lack of knowledge on the damping mechanism and on the parameters used to characterize it cause problems at all levels of the life cycle of bladed disks. The design process is uncertain, and therefore lengthy and costly because the knowledge of the dynamic behavior of the system has to be substituted with extensive experimental verifications. Furthermore, the imperfect knowledge of the real life expectancy of components prevents scheduling opportune periodic maintenance leading to potential safety hazard and logistical problems associated with unreliability.
The focus of the dissertation is on under-platform dampers and their effect on bladed disks. All numerical models of friction-damped bladed arrays require information of contact parameters. The main goal is to face part of this knowledge limitation through a purposely developed experimental-numerical method. Direct measurements on dampers are used to estimate contact parameters to be used as input to a state-of-the-art numerical model. The numerical model, validated against independent experimental evidence, is proven to be predictive, thus paving the way to the creation of a reliable design and optimization tool.
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Cook, Nathan Lindquist. "Investigation of vibration control of hypotrochoidally driven machninery." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17391.
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Nguyen, Phillip Huu. "An exploration of parametric excitation as a tool for vibration control." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17509.
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Koo, Jeong-Hoi. "Using Magneto-Rheological Dampers in Semiactive Tuned Vibration Absorbers to Control Structural Vibrations." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/29023.
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Since their invention in the early 1900s, Tuned Vibration Absorbers (TVAs) have shown to be effective in suppressing vibrations of machines and structures. A vibration absorber is a vibratory subsystem attached to a primary system. It normally consists of a mass, a spring, and a damper. Mounted to the primary system, a TVA counteracts the motions of the primary system, "absorbing" the primary structure's vibrations. A conventional passive TVA, however, is only effective when it is tuned properly, hence, the name "tuned" vibration absorber. In many practical applications, inevitable off-tuning (or mistuning) of a TVA occurs because of the system's operating conditions or parameter changes over time. For example, the mass in a building floor could change by moving furnishings, people gathering, etc., which can "off-tune" TVAs. When TVAs are off-tuned, their effectiveness is sharply reduced. Moreover, the off-tuned TVAs can excessively amplify the vibration levels of the primary structures; therefore, not only rendering the TVA useless but also possibly causing damage to the structures. Off-tuning is one of the major problems of conventional passive TVAs.
This study proposes a novel semiactive TVA, which strives to combine the best features of passive and active TVA systems. The semiactive TVA in this study includes a Magneto-Rheological (MR) damper that is used as a controllable damping element, for providing the real-time adjustability that is needed for improving the TVA performance.
This study is conducted in two phases. The first phase provides a numerical investigation on a two-degree-of-freedom (2-DOF) numerical model in which the primary structure is coupled with a TVA. The numerical investigation considers four semiactive control methods for the MR TVAs, in addition to an equivalent passive TVA. These numerical models are optimally tuned using numerical optimization techniques to compare each TVA system. These tuned systems then serve as the basis for numerical parametric studies for further evaluation of their dynamic performance. The parametric study covers the effects of damping, as well as system parameter variations (off-tuning). The results indicates that semiactive TVAs are more effective in reducing the maximum vibrations of the primary structure and are more robust when subjected to off-tuning. Additionally, the numerical study identifies the "On-off Displacement-Based Groundhook control (on-off DBG)" as the most suitable control method for the semiactive TVA among control methods considered in this study.
For the second phase of this study, an experimental study is performed on a test setup, which represents a 2-DOF structure model coupled with an MR TVA. Using this setup, a series of tests are conducted in the same manner as the numerical study to evaluate the performance of the semiactive TVA. The primary purposes of the experiment are to further evaluate the most promising semiactive control methods and to serve as a "proof-of-concept" of the effectiveness of this MR TVA for floor vibration applications. The results indicate that the semiactive TVA with displacement-based groundhook control outperforms the equivalent passive TVA in reducing the maximum vibrations of the primary structure. This confirms the numerical result that identifies on-off DBG control method as the "best" control method for the MR TVA among four semiactive control schemes considered. The experimental robustness study is also conducted, focusing on the dynamic performance of both the passive and the semiactive TVAs when the mass of the primary system changes (mass off-tuning). The mass of the primary system varied from -23 % to +23 % of its nominal value by adding and removing external masses. The experimental results show that the semiactive TVA is more robust to changes in the primary mass than the passive TVA.
These results justify the benefits of the use of semiactive MR TVAs in structures, such as building floor systems. The off-tuning analysis further suggests that, in practice, semiactive TVAs should be tuned slightly less than their optimum in order to compensate for any added masses to the structure. Additionally, the lessons learned from the experimental study have paved the way for implementing the semiactive MR TVA on a test floor, which is currently in progress under a separate study.<br>Ph. D.
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McKinnell, Robert James. "Active isolation of vibration." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306465.
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Boffa, John. "Model Reduction of Large Structural Systems for Active Vibration Control." University of Technology, Sydney. Faculty of Engineering, 2006. http://hdl.handle.net/2100/338.
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This thesis studies the applicability of the Dynamic model reduction method that is used for direct plant order reduction in the active vibration control of large and flexible structures. A comparison of the performances between the reduced models produced by the Dynamic model reduction method and those obtained by other common model reduction methods such as the Guyan method, and the Mode-displacement method have been carried out. By using a full analytical model of a twenty storey building as the reference, each three degrees of freedom model was compared by computer simulation. The open-loop frequency response simulation, open-loop earthquake simulation, and the closed-loop earthquake simulation were all used to initially evaluate the reduced models. The accuracy of the frequency responses was assessed with sinusoidal applied forces, and for the closed-loop dynamic analysis, an active mass damper at the top storey and a recorded earthquake excitation was used. When compared with the simulation results of the Guyan method, the Dynamic method has many advantages, especially in terms of its accuracy at the high frequency range. The Mode-displacement method produces reduced models that are good for dynamic analysis of open-loop systems, but it was found to be inconvenient for use in active control. Finally, the Dynamic model reduction method and Guyan method were compared using experimental test results. A 2.5m tall building model with 20 floors was used as the plant, with a linear motor installed at the top storey for the purposes of active-damping. Although the results of simulations would suggest that both models perform sufficiently, experimental testing proved that only the Dynamic model performs adequately for this specific application of active control. The problem associated with most model reduction methods, such as the Guyan, is that they are based on full-order models that were derived from the linear elastic theory. The versatility of the Dynamic model reduction method is such that it provides the option of obtaining system parameters directly from experiment, not just from theory. The experimental procedure ensures that the Dynamic model reduction method forms an accurate description of the real system dynamics. The applicability of this method for obtaining low-order plant models was demonstrated through real-time active control testing of the model structure, while it was subject to a sinusoidal excitation. The tests have shown that the Dynamic model reduction method can be used as an alternative approach for the model reduction of structural systems for the purpose of active vibration control.
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Du, Yu. "Internal Resonances in Vibration Isolators and Their Control Using Passive and Hybrid Dynamic Vibration Absorbers." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/27493.
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Conventional isolation models deal with massless isolators, which tend to overestimate the isolator performance because they neglect the internal resonances (IRs) due to the inertia of the isolator. Previous researches on the IR problem is not adequate because they only discussed this problem in terms of vibration based on single degree-of-freedom (SDOF) models. These studies did not reveal the importance of the IRs, especially from the perspective of the noise radiation. This dissertation is novel compared to previous studies in the following ways: (a) a three-DOF (3DOF) model, which better represents practical vibration systems, is employed to investigate the importance of the IRs; (b) the IR problem is studied considering both vibration and noise radiation; and (c) passive and hybrid control approaches using dynamic vibration absorbers (DVAs) to suppress the IRs are investigated and their potential demonstrated.
The 3DOF analytical model consists of a rigid primary mass connected to a flexible foundation through three isolators. To include the IRs, the isolator is modeled as a continuous rod with longitudinal motion. The force transmissibility through each isolator and the radiated sound power of the foundation are two criteria used to show the effects and significance of the IRs on isolator performance. Passive and hybrid DVAs embedded in the isolator are investigated to suppress the IRs. In the passive approach, two
DVAs are implemented and their parameters are selected so that the IRs can be effectively attenuated without significantly degrading the isolator performance at some other frequencies that are also of interest. It is demonstrated that the passive DVA enhanced isolator performs much better than the conventional isolator in the high frequency range where the IRs occur. The isolator performance is further enhanced by inserting an active force pair between the two passive DVA masses, forming the hybrid control approach. The effectiveness and the practical potential of the hybrid system are demonstrated using a feedforward control algorithm. It is shown that this hybrid control approach not only is able to maintain the performance of the passive approach, but also significantly improve the isolator performance at low frequencies.<br>Ph. D.
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Pesaresi, Emanuele. "Leptokurtic signals in random control vibration testing." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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In several industrial sectors, some components are subjected to mechanical vibrations which may lead to a premature failure. To ensure that they operate properly during their service life, the utilization of qualification tests has been consolidated over the years. It is often required to carry out accelerated tests for obvious reasons as feasibility and cost: the aim is to limit the duration of tests. The Test Tailoring procedure requires an appropriate definition for vibratory test profiles to be utilized as an excitation in terms of motion generated by vibrating tables or shakers. The synthesis of such profiles requires that signals be measured in real environments and then that their most important characteristics be reproduced in a laboratory, in particular their spectral content and damage potential.The conventional procedures permit the synthesis of an accelerated test profile in terms of a Power Spectral Density, which is characterized by a Gaussian distribution of the corresponding timeseries values. Such a kind of synthesis might be unfit to represent the real environment signal taken as a reference, owing to the latter’s usual non-Gaussianity. As a consequence, reliability could be compromised since the “nature” of the real signal is not preserved. Typical examples of non-Gaussian signals coming forth in real applications are the so-called Leptokurtic signals, whose high amplitude peaks originate a strongly non Gaussian probability distribution. A parameter called kurtosis is often employed to represent the number and severity of the peaks of the signal. A common reference is made to “kurtosis control” whenever it is required that the synthesized and the measured signal have not only the same spectral content but the same kurtosis value as well. In this work some novel Mission Synthesis algorithms are proposed, which generate test profiles by controlling precisely the kurtosis value and complying with the spectral content of the reference signal.
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Rentzos, Panagiotis. "Active vibration control of civil engineering structures." Thesis, City University London, 2007. http://openaccess.city.ac.uk/8571/.
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This thesis is in the area of active vibration control of Civil Engineering structures subject to earthquake loading. Existing structural control methods and technologies including passive, active, semi-active and hybrid control are first introduced. An extensive analysis of a frame-pendulum model is developed and analysed to investigate under what conditions effective energy dissipation is achieved in Tuned Mass Damper systems and the limitation of these devices under stiffness degradation when the structure enters the inelastic region. Linear Quadratic Gaussian and H-infinity active control schemes are designed, simulated and assessed for buildings, modelled as lumped parameter systems, including base and actuator dynamics. Various aspects of the designs are extensively evaluated using multiple criteria and loading conditions and validated in large-scale benchmark problems under practical limitations and implementation constraints. A novel design method is proposed for minimising peak responses of regulated signals via a deadbeat parametrisation of all stabilising controllers in discrete-time. The method incorporates constraints on the magnitude and rate of the control signal and is solved via efficient Linear Programming methods. It is argued that this type of optimisation is more relevant for structural control, as failure occurs when maximum member displacements are exceeded. The problem of stiffness matrix estimation from experimental data is formulated as an optimisation problem and solved under various conditions (positive definiteness, tridiagonal structure) via an alternating convex projection scheme. Both static and dynamic loading is considered. The method is finally incorporated in an adaptive control scheme involving the redesign in real-time of an LQR (Linear Quadratic Regulator) active vibration controller. It is shown that the method is successful in recovering the stability and performance properties of the nominal design under conditions of significant uncertainty in the stiffness parameters.
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Anderson, David. "Active control of turbulence-induced helicopter vibration." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/2175/.
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Helicopter vibration signatures induced by severe atmospheric turbulence have been shown to differ considerably from nominal, still air vibration. The perturbations of the transmission frequency have significant implications for the design of passive and active vibration alleviation devices, which are generally tuned to the nominal vibration frequency. This thesis investigates the existence of the phenomena in several realistic atmospheric turbulence environments, generated using Computational Fluid Dynamic (CFD) engineering software and assimilated within a high-fidelity rotorcraft simulation, RASCAL. The RASCAL simulation is modified to calculate blade element sampling of the gust, enabling thorough, high frequency analyses of the rotor response. In a final modification, a numerical, integration-based inverse simulation algorithm, GENISA is incorporated and the augmented simulation is henceforth referred to as HISAT. Several implementation issues arise from the symbiosis, principally because of the modelling of variable rotorspeed and lead-lag motion. However, a novel technique for increasing the numerical stability margins is proposed and tested successfully. Two active vibration control schemes, higher harmonic control 'HHC' and individual blade control 'IBC', are then evaluated against a 'worst-case' sharp-edged gust field. The higher harmonic controller demonstrates a worrying lack of robustness, and actually begins to contribute to the vibration levels. Several intuitive modifications to the algorithm are proposed but only disturbance estimation is successful. A new simulation model of coupled blade motion is derived and implemented using MATLAB and is used to design a simple IBC compensator. Following bandwidth problems, a redesign is proposed using H theory which improves the controller performance. Disturbance prediction/estimation is attempted using artificial neural networks to limited success. Overall, the aims and objectives of the research are met.
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Newton, Jeffrey Michael. "Vibration control in a machine tool barfeed." Thesis, University of Huddersfield, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254734.
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Newman, M. J. "Active vibration control using a distributed controller." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262146.
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Benassi, Luca. "Feedback control of vibration with inertial actuators." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398607.
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Ho, C. "Nonlinear vibration control : a frequency domain approach." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5157/.
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A vibration isolator, sometimes called an isolating mount, is the device situating between the vibration source and the sensitive system preventing the transmission of undesired disturbances. The performance is measured by the force or the displacement transmissibility, both functions of frequency. A good vibration isolation system has three main properties - a low resonant peak, a large isolation range and low transmissibility at non-resonant regions. Unfortunately, these characteristics cannot be achieved simultaneously by a simple linear vibration isolation system. The thesis addresses this problem for single-degree-of-freedom (sdof) vibration isolation systems by introducing nonlinear damping and stiffness devices into the system. First, theoretical studies were carried out to rigorously reveal the benefits of the proposed nonlinear vibration isolation systems over linear ones. Next, the performance of these nonlinear systems were analysed by simulations. Then, experimental studies were conducted to verify the theoretical and simulations results. Finally, a systematic approach was developed to design the parameters of the nonlinear damping and stiffness devices in order to satisfy specific vibration isolation requirements. Many vibration isolators can be modelled as a single-degree-of-freedom mass-spring-damper system. Many researchers have attempted to enhance the vibration isolation performance by designing springs with nonlinear stiffness. Others have focused on different types of damping nonlinearities. The new vibration isolation system proposed in the thesis combines both spring and damping nonlinearities in one system to exploit the advantages of both components while avoiding their undesirable effects. The theoretical properties of this proposed nonlinear vibration isolation system were analysed rigorously using the output frequency response function (OFRF) approach, a novel and unique method recently proposed at Sheeld. The stiffness nonlinearity is already a well researched area and can readily be realised in practice. Therefore, the implementation of the proposed nonlinear vibration suppression system focused on the realisation of the nonlinear damping component using commercially available magneto-rheological (MR) dampers which provide a damping force that is dependent on a control current. With feedback control, the force-velocity relationship of an MR damper can be shaped into a designed function. This implementation has been incorporated first in a vibration isolation system by simulation, then in a physical experimental rig which has a moving mass. The simulation and experimental data not only showed the successful realisation of a damping device with a particular nonlinear damping characteristic, but also confirmed the theoretical findings on the beneficial effects of nonlinear damping on a vibration isolation application. The final part of the thesis is devoted to the practical design of the proposed vibration isolation system. Given specific transmissibility requirements at certain critical frequencies, the values of the linear parameters are first designed, then the OFRF approach is applied to determine the nonlinear parameters. This pragmatic method simplifies the design of a complicated nonlinear system, which was traditionally difficult to work with, into a step-by-step guide and, therefore, has significant potential of industrial applications. The thesis has exploited the special effects of two nonlinear components on the performance of a passive sdof vibration isolation system. With the support of theoretical, simulation and experimental studies, the newly proposed configuration has shown substantial benefits to many vibration isolation problems. The simple yet effective design and implementation has significant implications for a wide range of engineering applications such as car suspension designs and building protection against earthquakes.
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Dench, M. "Structural vibration control using multiple synchronous sources." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/349006/.
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The advantages of isolating vibrating machinery from its supporting structure are that the chances of vibration induced fatigue failure of structural components are reduced, the structure becomes more inhabitable for people due to less vibration exposure and the sound radiated by the structure into the environment is reduced. This last point is especially important for machinery operating in a marine environment because low frequency sound propagates very well underwater, and the machinery induced sound radiated from a ship or submarine is a primary detection and classification mechanism for passive sonar systems. This thesis investigates the control of vibration from an elastic support structure upon which multiple vibrating systems are passively mounted. The excitations are assumed to occur at discrete frequencies with a finite number of harmonic components and the machines are all assumed to be supplied with power from the same electrical supply. Active vibration control may be achieved by adjusting the phase of the voltage supplied to one or more of the machines, so that a minimum value of a measurable cost function is obtained. Adjusting the phase of a machine with respect to a reference machine is known as synchrophasing and is a well established technique for controlling the sound in aircraft cabins and in ducts containing axial fans. However, the use of the technique for reducing the vibration of machinery mounted on elastic structures seems to have received very little attention in the literature and would appear to be a gap in the current knowledge. This thesis aims to address that gap by investigating theoretically and experimentally how synchrophasing can be implemented as an active structural vibration control technique.
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Nourzad, Delphine. "Active vibration control of doubly-curved panels." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/363620/.
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This thesis considers active control of the vibration of doubly-curved panels. Such panels are widely used in vehicles such as cars and aircraft, whose vibration is becoming more problematic as the weight of these vehicles is reduced to control their CO2 emissions. The dynamic properties of doubly-curved panels are first considered and an analytic model which includes in-plane inertia is introduced. The results of this analytical model are compared with those from numerical modelling. Of particular note is the clustering of lower-order modes as the curvature becomes more significant. The influence of these changes in dynamics is then studied by simulating the performance of a velocity feedback controller using an inertial actuator. The feasibility of implementing such an active control system on a car roof panel is then assessed. Experiments and simulations are also conducted on a panel, mounted on one side of a rigid enclosure, which is curved by pressurising the enclosure. The active control of vibration on this panel is then implemented using compensated velocity feedback control and novel inertial actuators. It is found that the performance of the feedback control initially improves as the curvature increases, since the fundamental natural frequency of the panel becomes larger compared with the actuator resonance frequency, but then the performance is significantly degraded for higher levels of curvature, since the natural frequencies of many of the panel modes cluster together. Finally, the integration of a compensator filter in the control system ensures the robustness of the system, despite changes in curvature, which makes it a good candidate for future multi-channel implementations.
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Sciulli, Dino. "Dynamics and Control for Vibration Isolation Design." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30511.
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The single-degree-of-freedom (SDOF) system is the most widely used model for vibration isolation systems. The SDOF system is a simple but worthy model because it quantifies many results of an isolation system. For instance, a SDOF model predicts that the high frequency transmissibility increases when the isolator has passive damping although this does not occur for an isolator implementing active damping. A severe limitation of this system is that it cannot be used when the base and/or equipment are flexible. System flexibility has been considered in previous literature but the flexibility has always been approximated which leads to truncation errors. The analysis used in this work is more sophisticated in that it can model the system flexibility without the use of any approximations. Therefore, the true effects of system flexibility can be analyzed analytically.
Current literature has not fully explored the choice of mount frequency or actuator placement for flexible systems either. It is commonly suggested that isolators should be designed with a low-frequency mount. That is, the isolator frequency should be much lower than any of the system frequencies. It is shown that these isolators tend to perform best in an overall sense; however, mount frequencies designed between system modes tend to have a coupling effect. That is, the lower frequencies have such a strong interaction between each other that when isolator damping is present, multiple system modes are attenuated. Also, when the base and equipment are flexible, isolator placement becomes a critical issue. For low-frequency mount designs, the first natural frequency can shift as much as 15.6% for various isolator placements.
For a mid-frequency mount design, the shift of the first three modes can be as high as 34.9%, 26.6% and 11.3%, respectively, for varying isolator placements.
NOTE: (03/2011) An updated copy of this ETD was added after there were patron reports of problems with the file.<br>Ph. D.
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Eure, Kenneth W. II. "Adaptive Predictive Feedback Techniques for Vibration Control." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30342.
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In this dissertation, adaptive predictive feedback control is used to suppress plate vibrations. The adaptive predictive controller consists of an on-line identification technique coupled with a control scheme. Various system identification techniques are investigated and implemented including batch least squares, projection algorithm, and recursive least squares. The control algorithms used include Generalized Predictive Control and Deadbeat Predictive Control. This dissertation combines system identification and control to regulate broadband disturbances in modally-dense structures. As it is assumed that the system to be regulated is unknown or time varying, the control schemes presented in this work have the ability to identify and regulate a plant with only an initial estimate of the system order. In addition, theoretical development and experimental results presented in this work confirm the fact that an adaptive controller operating in the presence of disturbances will automatically incorporate an internal noise model of the disturbance perturbing the plant if the system model order is chosen sufficiently large. It is also shown that the adaptive controller has the ability to track changes in the disturbance spectrum as well as track a time varying plant under certain conditions. This work presents a broadband multi-input multi-output control scheme which utilizes both the DSP processor and the PC processor in order to handle the computational demand of broadband regulation of a modally-dense plant. Also, the system identification technique and the control algorithm may be combined to produce a direct adaptive control scheme which estimates the control parameters directly from input and output data. Experimental results for various control techniques are presented using an acoustic plant, a rectangular plate with clamped boundary conditions, and a time varying plate.<br>Ph. D.
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Edalath, Sanooj Sadique. "Fuzzy Logic Seismic Vibration Control of Buildings." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1335462916.
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Vipperman, Jeffrey S. "Adaptive feedforward control of broadband structural vibration." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-12302008-063428/.
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Stetler, Aaron M. "Active vibration control for free electron lasers." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FStetler.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003.<br>Thesis advisor(s): Bruce C. Denardo, Thomas J. Hofler. Includes bibliographical references (p. 81). Also available online.
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Young, Andrew J. "Active control of vibration in stiffened structures." Title page, contents and abstract only, 1995. http://hdl.handle.net/2440/37722.
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Active control of vibration in structures has been investigated by an increasing number of researchers in recent years. There has been a great deal of theoretical work and some experiment examining the use of point forces for vibration control, and more recently, the use of thin piezoelectric crystals laminated to the surfaces of structures. However, control by point forces is impractical, requiring large reaction masses, and the forces generated by laminated piezoelectric crystals are not sufficient to control vibration in large and heavy structures. The control of flexural vibrations in stiffened structures using piezoceramic stack actuators placed between stiffener flanges and the structure is examined theoretically and experimentally in this thesis. Used in this way, piezoceramic actuators are capable of developing much higher forces than laminated piezoelectric crystals, and no reaction mass is required. This thesis aims to show the feasibility of active vibration control using piezoceramic actuators and angle stiffeners in a variety of fundamental structures. The work is divided into three parts. In the first, the simple case of a single actuator used to control vibration in a beam is examined. In the second, vibration in stiffened plates is controlled using multiple actuators, and in the third, the control of vibration in a ring-stiffened cylinder is investigated. In each section, the classical equations of motion are used to develop theoretical models describing the vibration of the structures with and without active vibration control. The effects of the angle stiffener(s) are included in the analysis. The models are used to establish the quantitative effects of variation in frequency, the location of control source(s) and the location of the error sensor(s) on the achievable attenuation and the control forces required for optimal control. Comparison is also made between the results for the cases with multiple control sources driven by the same signal and with multiple independently driven control sources. Both finite and semi-finite structures are examined to enable comparison between the results for travelling waves and standing waves in each of the three structure types. This thesis attempts to provide physical explanations for all the observed variations in achievable attenuation and control force(s) with varied frequency, control source location and error sensor location. The analysis of the simpler cases aids in interpreting the results for the more complicated cases. Experimental results are given to demonstrate the accuracy of the theoretical models in each section. Trials are performed on a stiffened beam with a single control source and a single error sensor, a stiffened plate with three control sources and a line of error sensors and a ring-stiffened cylinder with six control sources and a ring of error sensors. The experimental results are compared with theory for each structure for the two cases with and without active vibration control.<br>Thesis (Ph.D.)--Mechanical Engineering, 1995.
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MURUGAN, JAYA MAHESH. "Vibration monitoring and control of industrial structures." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2858351.
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Reynolds, George Alexander. "REDUCTION OF VIBRATION BY OSCILLATING BOUNDARIES AND ITS APPLICATION IN ROTORDYNAMICS." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1470319955.
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Bao, Bin. "Distributed, broadband vibration control devices using nonlinear approaches." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI086/document.
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L’amélioration du confort des usagers ainsi que l’augmentation du niveau de sécurité des structures requièrent le développement de techniques permettant de limiter efficacement les vibrations. Dans cette optique, les travaux exposés ici proposent le développement et l’analyse de méthodes de contrôle vibratoire pour des structures de faibles dimensions et utilisant peu d’énergie. Afin de satisfaire à ces deux critères, il est ici proposé d’utiliser des éléments piézoélectriques électriquement interfacés de manière non-linéaire et périodiquement distribués sur la structure-cible à contrôler. Ainsi, l’approche proposée permet de bénéficier à la fois des avantages des techniques de contrôle non-linéaires appliquées aux matériaux intelligents de type piézoélectrique, offrant des performances remarquables tout en étant peu consommatrices d’énergie, avec ceux des structures périodiques exhibant des bandes fréquentielles interdites présentant de fortes atténuations de la propagation d’onde. Plus particulièrement, ce mémoire s’intéresse à différentes architectures d’interconnexion des interfaces électriques non-linéaires permettant un bon compromis entre la bande fréquentielle contrôlée et les performances en termes d’atténuation des vibrations. Ainsi, trois architectures principales sont proposées, allant de structures totalement périodiques, tant au niveau mécanique qu’électrique (interconnexions), à des structures présentant un certain degré d’apériodicité sur le plan électrique (entrelacement), impactant ainsi la propagation de l’onde acoustique en élargissant la bande de contrôle, pour enfin proposer une architecture hybride entre interconnexion et entrelacement conduisant à des systèmes large bande performants<br>For ameliorating vibration reduction systems in engineering applications, miscellaneous vibration control methods, including vibration damping systems, have been developed in recent years. As one of intelligent vibration damping systems, nonlinear electronic damping system using smart materials (e.g., piezoelectric materials), is more likely to achieve multimodal vibration control. With the development of meta-structures (a structure based upon metamaterial concepts), electronic vibration damping shunts, such as linear resonant damping or negative capacitance shunts, have been introduced and integrated abundantly in the electromechanical meta-structure design for wave attenuation and vibration reduction control. Herein, semi-passive Synchronized Switch Damping on the Inductor (SSDI) technique (which belongs to nonlinear electronic damping techniques), is combined with smart meta-structure (also called smart periodic structure) concept for broadband wave attenuation and vibration reduction control, especially for low frequency applications. More precisely, smart periodic structure with nonlinear SSDI electrical networks is investigated from the following four aspects, including three new techniques for limiting vibrations: First, in order to dispose of a tool allowing the evaluation of the proposed approaches, previous finite element (FE) modeling methods for piezoelectric beam structures are summarized and a new voltage-based FE modeling method, based on Timoshenko beam theory, is proposed for investigating smart beam structure with complex interconnected electrical networks; then, the first developed technique lies in smart periodic structure with nonlinear SSDI interconnected electrical networks, which involves wave propagation interaction between continuous mechanical and continuous nonlinear electrical media; the second proposed topology lies in smart periodic structures with nonlinear SSDI interleaved / Tri-interleaved electrical networks involving wave propagation interaction between the continuous mechanical medium and the discrete nonlinear electrical medium. Due to unique electrical interleaved configuration and nonlinear SSDI electrical features, electrical irregularities are induced and simultaneously mechanical irregularities are also generated within an investigated periodic cell; the last architecture consists in smart periodic structures with SSDI multilevel interleaved-interconnected electrical networks, involving wave propagation interaction between the continuous mechanical medium and the multilevel continuous nonlinear electrical medium. Compared with the SSDI interconnected case, more resonant-type band gaps in the primitive pass bands of purely mechanical periodic structures can be induced, and the number of such band-gaps are closely related to the interconnection / interleaved level. Finally, the main works and perspectives of the thesis are summarized in the last chapter
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Rodrigues, Cunha Leandro. "Robust bandgaps for vibration control in periodic structures." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD060.
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Dans cette thèse, une méthodologie simple pour trouver des bandes interdites robustes est présentée. Quatre cellules unitaires différentes sont utilisées comme exemples numériques pour des modèles infinis et finis. Les deux premiers sont liés aux zones d'atténuation créées pour les ondes longitudinales en utilisant des cellules unitaires de masse et ressort et de barres. La méthode Matrice de Transfert est utilisée pour modéliser la cellule unitaire. Avec cette méthode, il est possible d'obtenir les réponses en fréquence, en utilisant une méthode spectrale, et des constantes de dispersion, en résolvant un problème a valeur propre. Les paramètres physiques et géométriques les plus influents sont déterminés en effectuant une analyse de sensibilité aux dérivées partielles et aux différences finies à travers un modèle infini. Dans ce cas, pour le deuxième exemple, la section de la demi-cellule est considérée comme une variable stochastique, représentée par une fonction densité de probabilité pour une analyse probabiliste. Le troisième exemple concerne les bandes interdites pour les ondes de flexion utilisant des cellules unitaires de poutres. Dans ce cas, la méthode habituelle de Matrice de Transfert ne peut pas être utilisée pour obtenir une réponse de structures finies en basse fréquence en raison de la présence de matrices mal conditionnées. Par conséquent, une méthode récursive est utilisée pour éviter la multiplication de matrices. Une analyse expérimentale est également réalisée pour ce cas, mais considérant que la longueur de la moitié des cellules unitaire comme incertaine. Le dernier exemple est un treillis périodique considérée avec et sans propriétés intelligentes. La cellule unitaire de cette structure en treillis peut avoir des membres passifs et actifs. À cause de la complexité de ce type de cellule, la méthode des éléments finis est utilisée. Cependant, ce type de structure ne présente pas de ruptures d'impédance suffisamment fortes pour ouvrir des bandes interdites même avec la présence de sous-structures répétitives. En vertu de cela, huit scénarios sont étudiés en considérant l'introduction de masse concentrée dans les articulations et les actionneurs piézoélectriques dans les circuits shunt résonants qui sont considérés comme stochastiques pour des cas spécifiques. À la fin, les résonances internes sont analysées à l'aide d'un modèle plus précis. Pour chaque modèle de structure, une simulation de Monte Carlo avec Latin Hypercube est effectuée, les distinctions entre les zones d'atténuation incertaines correspondantes pour les modèles finis et infinis sont exposées et la relation avec les modes localisés est clarifiée. Ces résultats suggèrent que les modèles finis ont une bande interdite plus large que les modèles infinis en considérant les incertitudes. En d'autres termes, les incertitudes entre les cellules voisines se compensent et les structures finies sont naturellement plus robustes. Enfin, l'effet de l'augmentation du niveau d'incertitude, en faisant varier un coefficient stochastique, est analysé et le concept de bande interdite robuste est présenté<br>In this thesis, a simple methodology to find robust bandgaps is presented. Four different periodic structures are used as numerical examples for infinite and finite models. The first two are related to attenuation zones created for longitudinal waves using spring-mass and stepped rod unit cells. The Transfer Matrix method is used to model the unit cell. With this method, it is possible to obtain the frequency responses, using a spectral method, and dispersion constants, solving an eigenvalue prob-lem. The most influential physical and geometrical parameters are determined by performing partial derivative and finite difference sensitivity analysis through an infinite model. Therein, for the second example, the cross-section area of half-cell is considered as a stochastic variable represented by a probability density function with specific deviation properties for a probabilistic analysis. The third example concerns the bandgaps for flexural waves using stepped beams unit cells. For this case, the classical Transfer Matrix method cannot be used to obtain finite structures response in low frequency because of the presence of ill-conditioned matrices. Therefore, a recursive method termed Translation Matrix, which avoid matrix multiplication, is used and the corresponding probabilistic analysis is per-formed using the half-cell thickness as a random variable. An experimental analysis is also performed for this case, but considering half-cell length as uncertain. The last example is a periodic truss that is considered with and without smart components. The unit cell of this lattice structure can present pas-sive and active members. As long as the type of unit cell is more complex, the finite element method is used. However, this kind of structure does not have impedance mismatches strong enough to open bandgaps although the presence of repetitive substructures. In virtue of this, eight scenarios are inves-tigated considering the introduction of concentrated mass on joints and piezoelectric actuators in reso-nant shunt circuit which are considered as stochastic for specific cases. For each structure model, a Monte Carlo Simulation with Latin Hypercube sampling is carried out, the distinctions between the corresponding uncertain attenuation zones for finite and infinite models are exposed and the relation with localized modes is clarified. These results lead to conclude that the finite models present a larger stop zone considering stochastic parameters than infinite models. In other words, the uncertainties be-tween neighbors’ cells compensate each other and the finite structures is naturally more robust. Final-ly, the effect of increasing the uncertainty level, by varying a stochastic coefficient, is analyzed and the concept of robust band gap is presented
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Liu, Wei. "Vibration control of large scale flexible structures using magnetorheological dampers." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-031005-105004/.
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Dayou, Jedol. "Global control of flexural vibration of a one dimensional structure using tuneable vibration neutralisers." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310842.
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