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Dissertations / Theses on the topic 'Mechanical Vibration'
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Trimble, A. Zachary. "Downhole vibration sensing by vibration energy harvesting." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39891.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 117).
This thesis outlines the design of a prototype electromagnetic induction vibration energy harvesting device for use in a downhole environment. First order models of the necessary components for a generic vibration energy harvester are presented and used to predict the most sensitive parameters for the design of energy harvesting systems. A subset of the design tools created in MATLAB and Excel for vibration energy harvester design and first order optimization is introduced and used to aid in the design of an energy harvester specific to the downhole environment. The manufacture of a prototype design is documented and recommendations for future manufacturing processes are given. The prototype is then tested against the models. Based on the results, final conclusions and recommendations for future refinements are made, and other applications are suggested.
by A. Zachary Trimble.
S.M.
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Donarski, Robert J. "Bone fracture measurement using mechanical vibration." Thesis, University of Kent, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256998.
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LIMA, ROBERTA DE QUEIROZ. "RAMDOM VIBRATION ANALYSIS OF MECHANICAL SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19543@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORA parte inicial da dissertação apresenta uma discussão sobre o método de Monte Carlo e sobre geradores de realizações de variáveis aleatórias e vetores aleatórios. São analisados geradores baseados em: congruência linear, Método da Transformada Inversa e algoritmo de Metrópolis-Hastings (método de Monte Carlo com Cadeia de Markov MCMC). Posteriormente, são apresentadas técnicas para a análise de vibrações estocásticas em sistemas mecânicos com grau de liberdade, múltiplos graus de liberdade e contínuos. As propriedades dos sistemas são consideradas determinísticas e as forças são caracterizadas por processos estocásticos. Ao longo das seções do trabalho, é mostrado como características da resposta do sistema em deslocamento (média, autocorrelação e densidade espectral) podem ser obtidas a partir das informações sobre o forçamento. A transformada de Fourier, a função densidade eséctral e a função de transferência são importantes ferramentas utilizadas no estudo. No caso de sistemas com múltiplos graus de liberdade, análise é feita por dois métodos: Resposta ao Impulso e Modos Normais. Nos sistemas contínuos, análise é feita através do Método de Monte Carlo. Para isso, foi desenvolvido um exemplo de um sistema mecânico contínuo submetido a dois carregamentos caracterizados por processos estocásticos. Nesse exemplo, o MCMC foi utilizado para gerar amostras dos forçamentos. Em cada realização, o sistema foi discretizado através do Método dos Elementos Finitos e uma aproximação para solução do problema foi obtida utilizando o Método de Galerkin. Nessa parte da dissertação são apresentados a formulação fraca de equação de movimento da viga e o modelo reduzido. Ao longo de todo o trabalho são mostrados exemplos e resultados obtidos através de rotinas desenvolvidas em MATLAB.
The initial of work presents a discussion about the Monte Carlo Method and about the generation of samples of random variables and ran dom vectors. Generators based on linear congruential, on the Inverse Trans form Method and, on Metropolis-Hastings algorithm (Markov Chain Monte Carlo Method MCMC) are analyzed. Later,techniques for vibrations ana lysis of single-degree of freedom, multi-degree of freedom and continuous stochastic mechanical systems are presented. The system properties are con sidered dertministic and, the forces are characterized by random process. Throughout the work sections, it is show how the system´s displacement response (mean, autocorrrelation and spectral density) can be characterized from the force informations. The Fourier transform, the spectral density function and transfer function are powerful tools used in the study. In the case of multi-degree of freedom systems, the analysis is done by two methods: Impukse Response and Normal modes. For continuous systems, it is made by Monte Carlo method. An example of one continuous mechanical system with two random loads were developed. In this example, MCMC is used to generate samples of the forces. For each realization, the problem is discretized by the Finite Element Method and one approximation of the solution is obtained by the Galerkin Method. In this part of the work, the weak formulation of the motion equation of the vibrating beam and the reduced model are presented. Throughout the work many rountines in MATLAB were developed.
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Petri, Patrick Andreas 1979. "Vibration-induced rotation." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/36110.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.This thesis presents, explores, and documents the validation of a mechanical mechanism dubbed Vibration-Induced Rotation, or VIR. The tendency of threaded fasteners to move under the influence of vibrations is well known, but never before has the root cause been identified and investigated in search of beneficial consequences. The sense of rotation, speed, and force with which a threaded body moves in an appropriately vibrated medium is a function of the excitation. The principal kinematic and dynamic relationships governing VIR have been developed and experimentally affirmed. There is evidence for more complex modes of motion, but pure VIR remains the dominant response under a wide variety of conditions. Simplicity, robustness, and uniqueness suggest a multitude of possible applications, particularly in the areas of product assembly and fastener insertion. This thesis should provide a cornerstone in a new and promising field of application-oriented research.
by Patrick Andreas Petri.
S.B.
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Nauclér, Peter. "Modeling and control of vibration in mechanical structures /." Uppsala : Univ. : Dept. of Information Technology, Univ, 2005. http://www.it.uu.se/research/publications/lic/2005-005/.
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Kitazaki, Satoshi. "Modelling mechanical responses to human whole-body vibration." Thesis, University of Southampton, 1994. https://eprints.soton.ac.uk/173255/.
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Nauclér, Peter. "Modeling and control of vibration in mechanical structures." Licentiate thesis, Uppsala universitet, Avdelningen för systemteknik, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-85824.
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All mechanical systems exhibit vibrational response when exposed to external disturbances. In many engineering applications vibrations are undesirable and may even have harmful effects. Therefore, control of mechanical vibration is an important topic and extensive research has been going on in the field over the years. In active control of vibration, the ability to actuate the system in a controlled manner is incorporated into the structure. Sensors are used to measure the vibrations and secondary inputs to the system are used to actuate the flexible body in order to obtain some desired structural response. In this thesis, feedback and feedforward control of active structures are addressed. The thesis is divided into four parts. The first part contains a general introduction to the subject of active vibration control and also provides an outline of the thesis. The second part of the thesis treats modeling and feedback control of a beam system with strain sensors and piezoelectric actuators. Physical modeling and system identification techniques are utilized in order to obtain a low order parametric model that is suitable for controller design. The third part introduces the concept of a mechanical wave diode, which is based on feedforward control. A controller is derived on the basis of equations that describe elastic waves in bars. The obtained controller is shown to have poor noise properties and is therefore modified and further analyzed. The final part of the thesis treats the same type of wave diode system as part three, but with more general feedforward filters. Especially, a controller based on Wiener filter theory is derived and shown to drastically improve the performance of the mechanical wave diode.
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Niknam, Alborz. "VIBRATION INSTABILITY IN FRICTIONALLY DRIVEN ELASTIC MECHANICAL SYSTEM." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1579.
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Numerous mechanical systems contain surfaces in partial or full sliding contact, and therefore, prone to friction-induced vibration instability. These include systems containing mechanical switches, brakes, clutches, gears, rolling contact bearings, journal bearings, robot end-effector grasp and motion, oil drills, etc. The prominent dynamic features of a mechanical system, subject to friction-induced vibration, can be captured by an appropriate equivalent mass-on-belt model. It is the goal of this research to provide a comprehensive study of friction-induced vibrations in mechanical systems by using their equivalent mass-on-belt models. Friction-induced vibration is manifested through three mechanisms termed Stribeck effect, mode-coupling and sprag-slip. Mechanical systems prone to vibrations by one or more of the three mechanisms of instability are considered and studied in detail. The mechanical systems fall into one of two groups. A system in the first group is the pseudo-rigid-body mass-on-belt representation of a compliant bistable linkage mechanism characterized by substantial geometric nonlinearity and nonlinear elasticity. A system in the second group is a mass-on-belt model that accounts for mass-belt contact stiffness. Such a system is excited primarily through mode coupling. In the first group of mechanical systems super and subcritical pitchfork bifurcation as well as Hopf bifurcation are observed. The normal force and spring pre-compression are bifurcation parameters leading to the subcritical pitchfork bifurcation and the belt velocity corresponds to the Hopf bifurcation. It is found that for a low damping and negligible spring nonlinearity, one equilibrium point dominates the steady-state response. Otherwise, the phase plane is split into two separate planes associated with the corresponding fixed point. The boundary is dictated by structural damping and spring nonlinearity. It is shown that the destabilizing mechanism in the bistable mechanisms is the Stribeck effect of friction. The dominant mode of instability for the second group of mechanical system is mode coupling instability. In this group intermittent loss of contact between the mass and the moving belt within a periodic cycle is allowed. Addition of a vibration absorber consisting of a second mass suspended from the first mass by a spring provides effective passive control of friction-induced instability due to mode-coupling. The research concludes with the study of a two mass system in which both masses are in contact with a belt and the friction force is characterized by the three regimes of lubricated contact that include boundary lubrication, mixed boundary and hydrodynamic lubrication and full hydrodynamic lubrication as sliding speed is increased. It is shown that such systems can experience periodic, quasi-periodic and chaotic vibration response.
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Baker, R. T. "Vibration in electromagnetically heated steel." Thesis, Aston University, 1995. http://publications.aston.ac.uk/15272/.
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When a ferromagnetic steel billet was heated by induction a large increase in the amplitude of longitudinal vibration frequently occurred as a result of resonance. This happened when a natural frequency of the bar coincided with twice the heating frequency or multiples thereof. The temperature at which resonance occurred depended on a number of factors including billet length and heating power. Resonance was most often observed when the surface temperature of the billet reached the Curie point. It is well established that magnetostrictive vibrations occur in a ferromagnetic material subjected to an alternating electromagnetic field, but existing data suggests that linear magnetostriction decreases towards the Curie point. Linear magnetostriction was measured in a sample of mild steel up to 800oC using a high temperature strain gauge. The magnetostriction constant 100 was calculated assuming an average grain orientation in mild steel. The data was found to be comparable to that published for single crystals of iron. It was discovered that linear magnetostriction was responsible for resonance below 600oC but not for temperatures near the Curie point. Other possible causes of resonance such as forces produced by the interaction between eddy currents and the alternating electromagnetic field, the alpha to gamma phase transformation and the existence of a thin ferromagnetic layer were investigated. None were found to account for resonance in bars of mild steel heated by induction. Experimental work relating to the induction heating of steel is compared to previous work on the subject of electromagnetic generation of ultrasound where a similar increase of the amplitude of longitudinal waves in steel is reported at the Curie point. It is concluded that the two phenomena are related as they show strong similarities.
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McCarthy, Daniel Joseph. "Vibration-based diagnostics of reciprocating machinery." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/10823.
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Lee, Evan J. (Evan Joseph). "Airfoil Vortex Induced Vibration suppression devices." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39874.
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Thesis (S.M. in Naval Architecture and Marine Engineering; and, S.M. in Ocean Systems Management)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2007."May 2007."
Includes bibliographical references (p. 51).
Vortex Induced Vibrations (VIV) is a major concern of the offshore oil industry. This problem leads to fatigue failure in the marine risers and causes costly replacement of the risers. Appendages such as helical strakes have proven that VIV can be eliminated but at the cost of increased drag. Increased drag reduces the time that the riser can operate. This thesis looks at adding airfoils to cylinders to both eliminate VIV as well as reducing drag. Two sets of tests were performed at the MIT Towing Tank to determine the effectiveness of these airfoils. The first tests utilized a flexible to model a riser. The second set of tests used a rigid cylinder to better understand the dynamics of the system. The airfoils were able to achieve both goals when the airfoils are aligned with the flow. Future work needs to be completed to study the airfoils when they are not aligned with the flow.
by Evan J. Lee.
S.M.in Naval Architecture and Marine Engineering; and, S.M.in Ocean Systems Management
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Lavallée, Jean G. 1960. "The effect of vibration mount aging on machinery raft displacement and vibration isolation performance." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88351.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000.Includes bibliographical references (p. 76).
by Jean G. Lavallée.
S.M.
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Thomas, Rohan J. "Prediction of aircraft fuselage vibration." Thesis, The University of North Dakota, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1594387.
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Modern unmanned aerial vehicles (UAV) are made of lightweight structures, owing to the demand for longer ranges and heavier payloads. These lightweight aircraft are more susceptible to vibrations caused by atmospheric turbulence transmitted to the fuselage from the wings. These vibrations, which can cause damage to the payload or on board avionics present a serious problem, since air turbulence is expected to increase over the next few decades, due to climate change.
The objective of this thesis is to predict the vibration of an aircraft fuselage by establishing a relationship between wing and fuselage vibration. A combination of ANSYS® and MATLAB® modeling are used to simulate aircraft vibrations. First, the displacement of a lumped mass aircraft model to step and sinusoidal forces acting on the wings are compared to displacements calculated using modal superposition equations. Next, a state space representation of this system is found using system identification techniques, which uses wing displacement as input, and provides fuselage displacement as output. This state space model is compared to a derived state space model for validation. Finally, a three dimensional aircraft with distributed displacement sensors on its wings is modeled. A state space representation is established using the wing displacement output from the sensors as its input and the motion and rotation of the fuselage along the X, Y and Z axes as the output.
It is seen that the displacement results of the lumped mass system match with those calculated using modal superposition equations. The state space model can also accurately predict the fuselage vibration of the lumped mass system, when provided with wing displacement as input. More importantly, results have shown that the distributed vibration sensors on the three dimensional plane model are able to measure the wing displacements. Using the output from these distributed sensors, the motion and rotation of the fuselage about all three axes can be effectively predicted.
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Issa, Jimmy. "Vibration suppression through stiffness variation and modal disparity." Diss., Connect to online resource - MSU authorized users, 2008.
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Thesis (Ph.D.)--Michigan State University. Dept. of Mechanical Engineering, 2008.Title from PDF t.p. (viewed on July 7, 2009) Includes bibliographical references (p. 114-117). Also issued in print.
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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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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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Gonsalves, Diane Helen. "Chaos concepts in mechanical systems with clearances." Thesis, University of Aberdeen, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387216.
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This thesis considers the use of chaos concepts in investigating the dynamics of two discontinuously nonlinear mechanical systems having two degrees of freedom. The nonlinearity considered is in the form of a discontinuous stiffness effect, and can cause the systems to exhibit chaotic motion. The first system is a rotor system with a bearing clearance effect. The second is a nonlinear vibration absorber, comprising a conventional linear absorber and a linear snubber stiffness, which the auxiliary mass intermittently contacts. Numerical integration is used in solving the equations of motion for each system. Equivalent physical rigs are tested. Both the theoretical and experimental results are analysed using chaos techniques such as phase plane portraits, Poincaré maps, frequency spectra and bifurcation diagrams. Comparison made between the differently acquired results shows that fairly good correlation is obtained in both systems, for realistic values of damping. Periodic, quasiperiodic and chaotic responses are exhibited by both systems, for different combinations of system parameters, with the responses of the systems being extremely sensitive to changes in these parameters. Investigations of the rotor system concluded that quasi-periodic responses are only possible if there is some form of cross-coupling present. An effective discontinuously nonlinear absorber is developed, theoretically. A reduction in the amplitude of the second resonance peak of the linear absorber is achieved. This enables the primary system to be operated over a wider frequency range without reaching the large amplitudes to the second resonance. The non-linear absorber also has the effect of attenuating the response from the auxiliary mass. Fatigue analysis is carried out to investigate the effect of chaotic motions on mechanical components. The analysis reveals the subharmonic motions are more damaging than chaotic motions, which are in turn more damaging than simple fundamental responses.
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Xu, Bo. "Vibration and stability analysis of toroidal shells." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/MQ45257.pdf.
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Krull, Alexander G. (Alexander Gerhard). "Experimental testing of LIGO vibration isolation system." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40439.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaf 29).
The LIGO (Laser Interferometer Gravitational-wave Observatory) project is designed to detect gravitational waves using precision interferometry. The detection from astrophysical sources has the potential to test Einstein's Theory of General Relativity, and additionally open a new window into the universe and its origin. The Initial LIGO detectors are currently operating at a strain sensitivity of 10-21 Hz, or equivalently 1018 m/ [square root of] Hz, at 100 Hz. In order to attain improved sensitivity required for guaranteed detection of astrophysical sources, e.g. coalescing neutron star binaries and black holes, pulsars, and supernovae collapses, improvements of the strain sensitivity must be achieved. Next generation detectors such as Advanced LIGO are under development, which aims to improve the sensitivity by more than a factor of 10 at all frequencies, compared to initial LIGO. This improvement in sensitivity will be achieved in part by improved seismic isolation one component of which is an active vibration isolation platform. Currently, research and development is being conducted at MIT on a prototype of this vibration isolation system. The work described in this thesis focuses on the Internal Seismic Isolation (ISI) system under development for Advanced LIGO.
(cont.) This system consists of a three-stage in-vacuum seismic isolation system which is supported by an external hydraulic actuation stage known as the Hydraulic External Pre-Isolation (HEPI) stages of the active vibration control system. HEPI uses forces generated by hydraulic pressure to cancel low frequency seismic noise, primarily due to forces from ground vibration. The ISI is an actively controlled platform, in which each stage is supported by three maraging steel blade springs. The vibration is sensed in six degrees of freedom and reduced by applying forces through a control feedback loop. In order for the feedback loop to function properly, it is important to know and be able to predict the position of the ISI stages to within a few thousandths of an inch. Since the load being applied to the spring blades is known, the compliance of each spring along with various shim thicknesses will determine the final position of the stages. Although compliance is a material and geometric property, and should remain constant from spring to spring, due to imperfections of the fabrication process and variation in the material properties, small variations in the long and short spring compliance value were detected using a Spring Tester.
(cont.) The blades were designed based on their resonant frequencies and the load which they would be supporting - more specifically, their geometry (length, width, and thickness) were defined such that the load each supported brought them to a 1/3 of their failure stress. For my undergraduate thesis, I determined the compliance of multiple long and short springs was determined using a specially designed apparatus - the "Spring Tester." Ideally, three blade springs of identical compliance should be used to eliminate system imbalance, but to variation during fabrication may be difficult to achieve Using the Spring Tester the mean values for each set of long and short spring linear compliance data were found to be 0.729 +.008 mils/lb and 0.670 ±.027 mils/lb, respectively, while the means for the long and short angular compliance data were 0.078 + .001 mrad/lb and 0.089 ±.003 mrad/lb, respectively.
by Alexander G. Krull.
S.B.
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Fitch, Eric E. "Durability analysis method for nonstationary random vibration." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/40004.
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Singer, Neil C. "Residual vibration reduction in computer controlled machines." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14435.
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Yang, Heng S. M. Massachusetts Institute of Technology. "Ultrasound shear wave elastography imaging with external mechanical vibration." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113749.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 105-107).
Ultrasound shear wave elastography (SWE) imaging is gaining wide acceptance in clinical practice as both a non-invasive and quantitative diagnostic modality. Most commercial SWE systems generate shear waves using acoustic radiation force (ARF), which requires complex hardware and is therefore only available on high-end and premium systems. External mechanical vibration (EMV) is an alternative to induce shear waves without expensive electronics, which potentially enables low-cost systems to provide SWE for point of care and low resource settings. In this thesis, an EMV concept of sinusoidally and synchronically vibrating two ball-shaped end-effectors to induce shear waves for real time SWE imaging was simulated, prototyped and tested. Finite element method (FEM) simulation and analysis shows the sinusoidal vibration generates shear waves that are constructive across the center plane of the two balls. By tracking the local displacement profiles at different depths of the center plane, shear wave speeds can be accurately estimated for different tissue stiffness. A mechatronic device using a voice coil actuator (VCA) to realize the EMV concept was prototyped. The mechanical vibrator was mounted on a commercial ultrasound probe and the vibration was synchronized with commercial ultrasound platform to induce shear waves as replacement of ARF. The generated shear waves were imaged by commercial ultrasonic systems to calculate shear wave speed and estimate tissue elasticity. Experimental data on liver phantoms under various vibration schemes demonstrated the capability of using this EMV device to conduct real-time SWE imaging that is comparable to ARF based systems.
by Heng Yang.
S.M.
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Funnell, M. E. (Marc Edwin). "Helicopter tail boom vibration analysis and suppression." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52873.
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Thesis (MScEng)--University of Stellenbosch, 2002.ENGLISH ABSTRACT: An experimental investigation was conducted usmg a cantilever beam to illustrate an understanding of vibration techniques and phenomena. The [Tee and forced vibration of the cantilever beam was investigated using various modelling strategies. Theoretical models such as the Lumped parameter, Myklestad, Distributed Parameter and Finite Element Methods were analysed and compared with experimental measurements. Excellent agreement of the natural frequencies, mode shapes and the harmonic transfer functions were found. To investigate tail boom vibration, a Finite Element Model of a simplified helicopter tail boom design was tested against experimentally measured data. The results correlated accurately and the model was used to evaluate the effectiveness of a vibration suppression system designed for the tail boom. The vibration suppression system was designed using two, parallel dynamic absorbers to reduce tail boom vibrations at its two dominant frequencies. For the purposes of this thesis, the dynamic absorbers were tuned to reduce the resonant peaks at the dominant excitation frequencies of the excitation force in-line with the thrust of the tail rotor only. This excitation force was estimated using a simplified tail rotor dynamic model, which when compared with actual vibration data was assumed to predict the basic frequency trends of the force, reliably. Incorporating the designed components into an accurate Lumped Parameter model of a cantilever beam structure and simulating the response of the structure at the dominant excitation frequencies of the calculated excitation force, tested the vibration suppression system. The results of this investigation proved the effectiveness of the design procedure and optimisation process of the design parameters. A similarly designed suppression system was incorporated into the Finite Element tail boom model and from the analytical results obtained it was shown to cause a fair reduction in the vibration response at the two dominant frequencies of the excitation force. Finally, two possible applications were suggested from the research presented in this thesis. The first application was the simplified configuration of a vibration monitoring system for the tail boom. The second application was the possible development of a system using the response of vibration suppression absorbers to predict the magnitudes of the excitation forces on the tail boom.
AFRIKAANSE OPSOMMING: 'n Experimentele ondersoek is ondemeem deur gebruik te maak van 'n ingeklemde balk om vibrasie tegnieke te illustreer. Die vrye en geforseerde vibrasie van die ingeklemde balk is ondersoek deur verskillende model tegnieke te gebruik. Teoretiese modelle soos die Lumped parameter, Myklestad, Distributed Parameter en Eindige Element Metodes was geanaliseer en vergelyk met die eksperimentele waardes. Uitstekende ooreenstemmings was gevind tussen die natuurlike frekwensies, die eievektore en die harmoniese oordragsfunk:sie. Om stert vibrasie te ondersoek, was'n eindige element model van 'n helikopter stert getoets teenoor die eksperimentele data. Die resultate het akuraat gekorreleer en dus was die model gebruik om die effektiwiteit van 'n vibrasie supressie sisteem te evalueer. Die vibrasie supressie sisteem was ontwerp deur gebruik te maak van twee parallele dinamiese absorbeerders om die helikopter stert se eerste twee dominante vibrasie frekwensies te minimeer. Vir die doel van hierdie tesis was die dinamiese absorbeerders ingestel om net die resonante pieke van die opgewende krag wat in lyn is met die drykrag van die stert rotor te minimeer Hierdie opgewende krag was, deur gebruik te maak van 'n basiese stert rotor dinamiese model, aanvaar om die basiese frekwensie tendense van die krag te voorspel. Die supressie sisteem wat ontwerp was, was getoets op die lumped parameter balk en het veroorsaak dat die voorspelde opgewende krag by al twee van sy dominante . frekwensies baie geminirneer was. Die effektiwiteit van die sisteem was dus bewys en die sisteem was gebruik om die respons van die eindige element model van die stert te verbeter. Die resultate het 'n aanvaarbare reduksie in die respons by die twee dominante frekwensies van die opgewende krag, gewys. Laastens, deur gebruik te maak van die resultate in hierdie tesis. was twee moontlikhede voorgestel. Die eerste een was die konfigurasie van 'n vibrasie moniterings sisteem vir die helikopter stert. Die tweede mmontlikheid was die moontlike ontwikkeling van 'n sisteem wat die grootte van die opgewende krag by die stert rotor kon voorspel, deur gebruik te maak van die vibrasie suppressie absorbeerders.
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Triplett, Angela L. "Vibration-Based Energy Harvesting." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1226614650.
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Lim, Geok H. "Vibration analysis of a printed circuit board." Thesis, Aston University, 2000. http://publications.aston.ac.uk/15341/.
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The reliability of the printed circuit board assembly under dynamic environments, such as those found onboard airplanes, ships and land vehicles is receiving more attention. This research analyses the dynamic characteristics of the printed circuit board (PCB) supported by edge retainers and plug-in connectors. By modelling the wedge retainer and connector as providing simply supported boundary condition with appropriate rotational spring stiffnesses along their respective edges with the aid of finite element codes, accurate natural frequencies for the board against experimental natural frequencies are obtained. For a PCB supported by two opposite wedge retainers and a plug-in connector and with its remaining edge free of any restraint, it is found that these real supports behave somewhere between the simply supported and clamped boundary conditions and provide a percentage fixity of 39.5% more than the classical simply supported case. By using an eigensensitivity method, the rotational stiffnesses representing the boundary supports of the PCB can be updated effectively and is capable of representing the dynamics of the PCB accurately. The result shows that the percentage error in the fundamental frequency of the PCB finite element model is substantially reduced from 22.3% to 1.3%. The procedure demonstrated the effectiveness of using only the vibration test frequencies as reference data when the mode shapes of the original untuned model are almost identical to the referenced modes/experimental data. When using only modal frequencies in model improvement, the analysis is very much simplified. Furthermore, the time taken to obtain the experimental data will be substantially reduced as the experimental mode shapes are not required.In addition, this thesis advocates a relatively simple method in determining the support locations for maximising the fundamental frequency of vibrating structures. The technique is simple and does not require any optimisation or sequential search algorithm in the analysis. The key to the procedure is to position the necessary supports at positions so as to eliminate the lower modes from the original configuration. This is accomplished by introducing point supports along the nodal lines of the highest possible mode from the original configuration, so that all the other lower modes are eliminated by the introduction of the new or extra supports to the structure. It also proposes inspecting the average driving point residues along the nodal lines of vibrating plates to find the optimal locations of the supports. Numerical examples are provided to demonstrate its validity. By applying to the PCB supported on its three sides by two wedge retainers and a connector, it is found that a single point constraint that would yield maximum fundamental frequency is located at the mid-point of the nodal line, namely, node 39. This point support has the effect of increasing the structure's fundamental frequency from 68.4 Hz to 146.9 Hz, or 115% higher.
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Li, Nong. "Vibration of laminated orthotropic composite plates and shells." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6946.
Full textAbstract:
Almost all of the analytical solution techniques presented for composite plates and shells deal with either simply supported conditions or boundary conditions with at least a pair of opposite edges simply supported. In the present study, an alternative general approach, combining superposition and state space techniques is developed for the free vibration analysis of laminated orthotropic composite plates and shells having arbitrary boundary conditions. This study concentrates on the antisymmetric angle-ply laminated plates and cross-ply laminated plates and shells. Three commonly adopted theories, i.e., classical theory, first-order shear deformation theory and third-order shear deformation theory, have been employed and compared with one another to investigate the influence of transverse shear deformation, structural aspect ratio, length-to-thickness ratio, degree of anisotropy and the number of layers on natural frequency. Convergence tests have been carried out to guarantee the accuracy of the closed-form solutions. Wherever possible, numerical results generated by the present approach are compared with those reported in the published references. Accurate non-dimensional fundamental frequencies are presented for laminated plates and shells with two adjacent edges, three edges and four edges clamped and other edges simply supported. Such analyses have not been reported in the literature previously. Also, vibration analysis of a cantilever angle-ply antisymmetric plate with a point support is conducted to demonstrate the applicability of the present technique. It has been shown that the method works extremely well and excellent agreements are found between the present results and those generated by previous researchers. It has also been shown that more complicated boundary-value problems can be solved by this technique without any difficulty.
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Alizadeh, Y. "Free vibration of partially supported plates and shells." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/10751.
Full textAbstract:
First-order transverse shear-deformation Mindlin theory has been used to predict the free vibration frequencies and modal shapes for isotropic, laminated and composite plates or shells. A finite element model based on the small deflection linear theory has been developed to obtain numerical solutions for this class of problems. The results for some of the degenerate cases are compared with other results available in the literature. These analyses involve a wide number of variables, namely; material properties, aspect ratios, support conditions and also radius to base ratio. The cracked base plates, shells and blades are idealized as partially supported models with varying support lengths. The effects of the detached base length on natural frequencies, modal shapes and nodal lines of these types of structures are investigated. Although the expected decrease in frequency with increase in the detached base length is observed almost for all modes it is seen that this behavior is very pronounced for higher modes in both plates and shells. Analysis also showed that the variation of the detached base length has a small effect on the natural frequencies of plates and shells with large aspect ratios ( b/a > 2, r/a > 2).
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Min, Byung No 1967. "Non-linear free vibration of a spinning tether." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=27243.
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Non-linear vibration of a spinning tether is studied in this thesis. The tether is thought to be a part of a spinning tethered satellite system in the station-keeping phase so that the tether has a constant nominal length and is forced to spin at a constant rate about its nominal axis. Using the extended Hamilton's principle the governing equations of motion are derived retaining non-linear terms up to the third order that originate from geometric non-linearity. They are discretized by the assumed-modes method, truncated to one-mode equations, and transformed to the phase-space form. Then the method of averaging is applied.When the tether has high nominal tension, averaging with two variables results in a closed form solution, which shows dependence of the frequency contents on the initial amplitude parameters of the system. In the case of very low nominal tension, averaging with a single variable is useful to obtain the steady state and the limit steady state solutions, both of which result in a circular whirling motion like a skip-rope. Without damping, a general transverse mode appears to be quasi-periodic but it can be periodic under certain initial conditions. Numerical investigations reveal that the material damping through the longitudinal mode derives the steady state to the limit steady state. Also, several interesting shapes are observed in phase plots.
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Chan, Alfred. "Vocal fold vibration measurements using laser Doppler vibrometry." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106574.
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The objective of this study was to measure the velocity of the superior surface of human vocal folds during phonation using laser Doppler vibrometry (LDV). A custom-made endoscopic laser beam deflection unit was designed and fabricated. An in vivo clinical experimental procedure was developed and performed at the Montreal General Hospital Voice Laboratory in order to simultaneously collect velocity data from the LDV and video from endoscopy. The velocity along the direction of the laser beam, ie. the inferior-superior direction, was captured and found to be synchronous with electroglottograph (EGG) and sound level meter data. Recorded phonation onset/offset times were found to be commensurate with reported data obtained using EGG and high-speed imaging. The vibration energy of the vocal folds was determined to be significant up to a frequency of 3 kHz. The velocity amplitude was found to be approximately 45 mm/s and was consistent between subjects. A sparse map of the vocal fold surface velocity was obtained, which showed that the velocity amplitude did not change significantly with location. Different characteristic vibration waveforms were identified and attributed to the presence of a mucosal wave over the vocal fold surface. Laser Doppler vibrometry offers potential as a diagnostic tool for the early detection of vocal disorders. It may provide online biofeedback for voice professionals, and help them to tune their laryngeal tension to obtain the desired voice output.La présente étude avait pour but de mesurer directement la vitesse des cordes vocales de la voix humaine en utilisant la vibrométrie laser (VL). Une buse endoscopique pour la re-direction du faisceau laser a été conçue et construite. Un protocole expérimental de mesures en clinique a été développé et mis en oeuvre afin d'obtenir des signaux de vitesse simultanément avec des images vidéoendoscopiques. Les mesures furent prises au laboratoire de la voix de l'Hôpital Général de Montréal. La vitesse mesurée est dans l'axe du faisceau laser, soit dans la direction inférieure-supérieure. Des signaux synchrones provenant d'un électroglottogramme (EGG) et d'un microphone furent recueillis pour fins de comparaisons et de vérifications. Les signaux provenant du VL sont parfaitement corrélés et consistants avec les signaux du EGG et microphone ainsi que les informations provenant du vidéo. L'énergie vibratoire semble être présente dans un bande de fréquence allant jusqu'à 3 kHz. La vitesse est de 45 mm/s dans les trois cas étudiés, pour toute fréquence, amplitude et position. Différents modes vibratoires avec des formes d'ondes distinctes furent identifiés, probablement dus à la propagation d'ondes sur la surface supérieure des cordes vocales. Les résultats suggèrent que l'utilisation du VL pourrait mener à des applications intéressantes pour la détection de problèmes tels que des lésions. La VL pourrait aussi sans doute fournir une rétroaction à des professionnels de la voix qui leur permettrait d'ajuster la tension et la position de leur cordes vocales afin d'obtenir le timbre ou l'intonation désirée.
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Xu, Ruize Ph D. Massachusetts Institute of Technology. "Low-frequency, low-amplitude MEMS vibration energy harvesting." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115673.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 187-195).
Vibration energy harvesters work effectively only when the operating conditions match with the available vibration source. Typical resonating MEMS structures cannot be used with low-frequency, low-amplitude and unpredictable nature of ambient vibrations. Bi-stable nonlinear oscillator based energy harvesters are developed for lowering the operating frequency while widening the bandwidth, and are realized at MEMS scale for the first time. This design concept does not rely on the resonance of the MEMS structure but operates with the large snapping motion of the beam at very low frequencies when proper conditions are provided to overcome the energy barrier between the two energy wells of the structure. A fully functional piezoelectric MEMS energy harvester is designed, monolithically fabricated and tested. An electromechanical lumped parameter model is developed to analyze the nonlinear dynamics and to guide the design of the multi-layer buckled beam structure. Residual stress induced buckling is achieved through the progressive control of the deposition along the fabrication steps. Static surface profile of the released device shows bi-stable buckling of 200 [mu]m which matches very well with the design. Dynamic testing demonstrates the energy harvester operates with 35% bandwidth under 70Hz at 0.5g, operating conditions that have not been met before by MEMS vibration energy harvesters.
by Ruize Xu.
Ph. D.
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Miller, Scott E. (Scott Edward). "Distributed parameter active vibration control of smart structures." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/33473.
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Miskel, James F. (James Francis). "Fatigue-based random vibration and acoustic test specification." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12069.
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Kim, Jeung Tae. "Source and path recovery from vibration response monitoring." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14806.
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Bhaskar, Atul. "Damping in mechanical vibration : new methods of analysis and estimation." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314853.
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SERRA, REYNALDO C. "Deteccao de trincas em eixos de bombas centrifugas em operacao, atraves da tecnica de analise de vibracoes." reponame:Repositório Institucional do IPEN, 1995. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9263.
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Made available in DSpace on 2014-10-09T12:25:28Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:02:56Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Herder, Erik, and Erik Jenåker. "Vibration Isolation for Electronics on an Autonomous Truck." Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-19367.
Full textAbstract:
This thesis has been conducted on the behalf of Volvo Autonomous Solutions. Volvo autonomous Solutions is a part of the Volvo Group.The purpose of this thesis was to give a suggestion on an isolation system for the automated driving-system kits in autonomous trucks. First, a literature study was made to give an overview of the problem and already known theories. The literature study gave the students a path forward shown in the book Engineering Vibration by Daniel J. Inman.Secondly, a method was brought out and executed in form of a frequency analysis, analytical solution, FEA-studies and a market analysis. Frequency analysis was created before and after adding any type of isolations system to analyse the eigenfrequencies and determine that there was little risk for resonance to occur against the driven frequency. The analytical solution as well as a FEA-study was conducted to achieve optimal value of spring stiffness, k and damping coefficient, c. Market analysis was made to search the market for suitable isolation system with similar c and k-value. Due to the limitations of the project with lack of space the isolation systems found on the market was either too tall or too stiff (k-value).Conclusions of this thesis contains results such as, little risk for resonance determine by frequency analysis. A first step in the solution process of finding a suitable isolation system.
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Negishi, Nobuhiko. "Elliptical Vibration Assisted Machining with Single Crystal Diamond Tools." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-08292003-175201/.
Full textAbstract:
Optical quality surfaces on non-ferrous materials are commonly produced with single crystal diamond tools and precision turning machines. To add ferrous and brittle materials to the list of diamond turnable materials, a process know as elliptical vibration assisted machining (EVAM) has been developed. EVAM combines a small, less than 50 µm size, oscillatory tool path to the linear motion of standard orthogonal cutting. EVAM reduces cutting forces and tool wear by reducing chip thickness and bringing the tool tip out of contact with the workpiece 75% of the time. These characteristics may increase tool life and work piece material compatibility with single crystal diamond tools. A non-resonant piezo electric stack driven tool actuator was designed and built for a large range of operating frequencies (0-5KHz) and tool path dimensional flexibility (ellipse motion up to 50 x 9 µm). The diamond tool is mounted to a kinematic linkage. Finite element analysis (FEA) was used to aid the design of a light weight, high stiffness tool holder/kinematic linkage for high frequency operation. The effects of heat generation caused by high voltage, high frequency operation of piezo stacks were simulated using FEA and finite difference programs. These simulations were used to design and develop an efficient active cooling system. Tool path geometry and its effects on sliding distance, chip geometry, and surface finish were modeled with Maple software. Calculated chip geometry was successfully used to predict cutting and thrust forces. Force predictions were compared with measured forces for 6061 aluminum. A method generated for precision contour grinding was implemented to accurately predict theoretical surface roughness for EVAM machined surfaces. EVAM machining tests with brittle workpiece materials, such as silicon carbide, produced optical quality surfaces.
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Bonsi, Adime. "Fatigue of piezoelectric beams used in vibration energy harvesting." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=92374.
Full textAbstract:
The goal of this thesis is to determine the fatigue life of piezoelectric energy harvesters. The harvester is a cantilever beam made from the piezoelectric ceramic lead zirconate titanate (PZT). Similar structures are used in micro electromechanical systems (MEMS) as actuators and energy harvesters to convert electrical energy to mechanical energy and vice versa. A platform was built to excite PZT cantilever beams in bending vibration, and a method was developed to detect the mechanical and electrical response of the beam, and correlate changes in these responses to the onset of damage.Subsequently, test protocols were developed to experimentally determine the fatigue life of PZT beams by applying total life and damage tolerance approaches to fatigue testing. Total life tests were performed on pristine beams, while damage tolerance tests were performed on beams indented to induce localized damage. Rates of crack growth were measured by interrupting the fatigue tests and imaging the cracks using scanning electron microscopy. The observation of crack arrest is a major result arising from these studies. The test platform developed in this thesis can be used to explore the effects of size on the fatigue reliability of miniaturized energy harvesters.
Le but de ce projet est de déterminer la résistance en fatigue des générateurs d'énergie piézoélectrique. Le générateur est une poutre en porte-à-faux en miniature faite d'une céramique piézoélectrique de titano-zirconate de plomb (PZT). Des structures similaires sont utilisées dans des systèmes micro-électromécaniques (MEMS) tels que les actionneurs et les générateurs d'énergie pour convertir l'énergie électrique en énergie mécanique et vice versa. Un dispositif a été construit pour soumettre des poutres en miniature au cintrage par vibration et une méthodologie a été développée pour détecter la réponse mécanique et électrique des poutres, et corréler les variations de réponses observées au début de leur bris.
Par la suite, un protocole est développé pour déterminer l'endurance des poutres en miniature PZT, en adoptant l'approche de la durée de vie totale des poutres et celle de leur tolérance au bris. Les expériences de la durée de vie totale sont effectuées sur des poutres immaculées, et les autres sont faites sur des poutres cabossées afin d'introduire un défaut local. Les fréquences de la croissance des craquelures sont mesurées à l'arrêt des expériences et capture des images des craquelures à l'aide du microscope à balayage. L'observation de l'arrêt des craquelures est le résultat majeur émanant de ces études. Le dispositif d'expérimentation utilisé peut aussi servir à explorer l'ampleur des effets des générateurs d'énergie sur la fiabilité de la fatigue.
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Jian, Ming. "Theoretical and experimental studies of ITH percussive drill vibration." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68030.
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During underground, long-hole drilling operations, the bending of the drill string and vibrations exert significant effects on hole deviation and penetration rates. Little research has been conducted in the area of the bending and vibrations associated with ITH (In - The - Hole) drills. This thesis deals with the modelling of the static and dynamic properties of the ITH drill system.The bending of the drill string is the result of the string becoming unstable. The critical length and feed force of the ITH drill string before being unstabilized and its characteristics after unstabilization are studied. By analyzing the static and dynamic properties of the drill string, a continuous system mathematical model has been developed. Two different boundary conditions have been discussed and applied through computer simulations.
Measurements of downhole parameters and vibrations while drilling were acquired by a high-rate telemetry and data acquisition system from field tests of a CMS CD-90B long-hole ITH drill and prototype shock absorber in an underground nickel mine. Determining the inter-relationships between the drilling parameters and the vibrations is also a principal objective of the thesis. The performance of a prototype shock absorber developed by a third party company was also evaluated. The results of the simulations and analyses of the vibration data indicate that a prototype shock absorber effectively reduces the amplitude of the vibrations. A mathematical model using a complex boundary condition has been developed which will be of use in further research relating to the development of a vibration-based control system for ITH drills. By decreasing the vibration levels acting on the drill head and rod, the instrumentation for an automated drill can be protected to ensure maximum life and proper performance during hammer operation. (Abstract shortened by UMI.)
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Verdirame, Justin Matthew 1978. "Structural vibration damping using lightweight, low-wave-speed media." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40360.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 157-162).
Incorporation of a low-density, low-wave-speed medium (LWSM) into a structure yields significant damping if the speed of wave propagation in the medium is low enough for standing waves to arise in it. In this thesis, we characterize wave propagation in low-density granular media and foams for use as structural damping treatments and develop analytical and numerical techniques for prediction of the damping attained in structures that incorporate LWSM. Structural damping by incorporation of LWSM is attractive for hollow thin-walled structures. We develop analytical approximations for the loss-factor in the structural modes of cylindrical shells and Timoshenko beams and attain predictions in good agreement with measurements. For more complicated geometries, it is often necessary to employ a finite element model to predict the dynamics of structures. But inclusion of LWSM into a finite element model significantly increases the size of the model, introduces frequency-dependent material properties, and introduces a large number of modes that are dominated by deformation of the LWSM. Hence, the eigenvalue problem becomes significantly more difficult by addition of the LWSM.
(cont.) We develop an iterative approach based on the eigensolution of a structure without LWSM and the forced response of the LWSM to obtain approximations for the complex eigensolution. Damping by inclusion of LWSM is an attractive option for reduction of the sound radiated from vehicle driveshafts, which are typically thin-walled hollow cylinders with yokes welded at each end. The bending and ovaling modes of the driveshaft between 500 and 3000 Hz are efficient radiators of sound and are excited by gear transmission error in the rear differential. Filling the driveshaft with a. lossy, low-density foam adds significant damping to these modes and thus reduces the radiated sound.
by Justin Matthew Verdirame.
Ph.D.
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Kluger, Jocelyn Maxine. "Nonlinear beam-based vibration energy harvesters and load cells." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87958.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 216-218).
This thesis studies a novel nonlinear spring mechanism that is comprised of a cantilever wrapping around a curved surface as it deflects. Static force versus displacement tests and dynamic "initial displacement" tests verified the spring theory for a large range of oscillator parameters. Various human motion energy harvester configurations that use the nonlinear spring were numerically optimized for power, robustness, and adaptivity. Based on the optimization results, both the nonlinear and linear devices studied in this thesis generate more power per volume and per mass when excited at one's hip while walking than current commercial energy harvesters. The two degree-of-freedom (2DOF) nonlinear oscillator is more adaptive to different excitation signals and resistant to power decay when parasitic damping is present than the IDOF and 2DOF linear systems. These significant advantages are caused by the 2DOF nonlinear system harvesting its optimal power at large electromagnetic damping coefficients, whereas the optimal power generation for the linear systems occurs at low electromagnetic damping coefficients. This thesis also examined what electromagnetic damping coefficients can be generated by magnet-and-coil geometries that satisfy the energy harvester constraints. The final chapter of this thesis investigates a load cell that uses the stiffening spring to maintain high resolution over a large range of forces and prevent large forces from damaging the load cell. Future work will include testing a full energy harvester prototype and exploring other applications of the nonlinear spring.
by Jocelyn Maxine Kluger.
S.M.
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Miu, Kevin Kar-Leung. "A low cost, DC-coupled active vibration isolation system." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46061.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 303-306).
In this thesis, I designed and implemented an isolation system that interfaces with traditional air mounts for improved force disturbance rejection relative to passive optical tables.Force disturbance rejection and position alignment are two major functional requirements of vibration isolation systems. With conventional passive isolation systems, a tradeoff exists between improving force disturbance rejection maintaining ground vibration isolation. Commercial active isolators address such a tradeoff through the use of inertial sensors, but the AC-coupled nature of the sensors leads to an inconvenient low frequency response. By referencing a payload stiffly to a softly suspended proof mass, both of the aforementioned functional requirements can be resolved while maintaining ground disturbance isolation performance. Philips Applied Technologies originally developed the concept, named Advanced Isolation ModuleS (AIMS).The AIMS system uses a relative displacement measurement between a payload which is to be isolated from vibrations and a proof mass as feedback. The displacement sensor allows the inertial measurement to be DC-coupled. The objective of this research is to find a relatively low-cost approach for the AIMS concept.A 1-DOF active vibration isolation system based on closed loop control utilizing the DC-coupled inertial measurement as feedback was retrofitted onto an optical table. The coil of a commercial geophone was used as the proof mass, as the geophone provides a relatively inexpensive, low frequency suspension. Error budgeting was performed on the system to estimate and improve payload acceleration noise levels. The results yielded a system bandwidth of 30 Hz and a total system acceleration la value of approximately 1 mm/s².
by Kevin Kar-Leung Miu.
S.M.
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Thekkoodan, Dilip Joy. "Interaction of cylinders In proximity under flow-induced vibration." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92126.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 57-59).
This study examines the influence of a stationary cylinder that is placed in proximity to a flexibly mounted cylinder in the side-by-side arrangement. The problem is investigated with an immersed-boundary formulation of a spectral/hp element based (Nektar-SPM) fluid solver. The numerical method and its implementation is validated with benchmark test cases of the flow past an isolated cylinder in both the stationary and flexibly mounted configurations. The study examines a parametric space spanning 6 center-to-center spacing configurations in the range 1.5D-4D and 13 equispaced reduced velocities in the range 3.0-9.0. The simulations are performed in two-dimensional space and the Reynolds number is held at 100. The response characteristics of the moving cylinder are classified into regimes based on the shape of the response curve and the variation of the r.m.s. lift coefficient. It is shown that the moving cylinder influences the lift and drag force characteristics on the stationary cylinder and the frequency composition in the wake. A detailed look at the frequencies and the relative strengths of the frequencies indicates a diminishing influence of the moving cylinder on the stationary cylinder, both with increasing separation and smaller amplitudes. By examining the wake patterns and monitoring the frequencies in the wake of each cylinder, the interference level is qualified and explained to be the basis of the different families of response.
by Dilip Joy Thekkoodan.
S.M.
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Ustundag, Burak. "On the free vibration behavior of cylindrical shell structures." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67717.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 105-106).
Shell structures, especially cylindrical shells, are widely used in aerospace and naval architectural industries. Submarine hulls and aircraft bodies can be idealized as cylindrical shell structures. The study of vibrations of cylindrical shells is an important aspect in the successful applications of the cylindrical shells. The free vibration characteristics of a submarine hull have an important influence on the noise signature of the submarine. That makes the free vibration problem of the submarine hull a particular interest for the submarine community. The natural frequencies of cylindrical shells are clustered in a very narrow band and they are thus more prone to becoming involved in resonant vibrations. The determination and control of these frequencies is significant to manage the acoustic signature of the submarine. This thesis focuses on the free vibration characteristics of stiffened and unstiffened cylindrical shells. The analysis is carried out mainly in two parts. First, the unstiffened cylindrical shell is modeled and the free vibration problem is analyzed as the shell thickness decreases. Then the cylindrical shell is stiffened with ring stiffeners and the free vibration problem of the stiffened cylindrical shell is studied. The vibration modes of the unstiffened cylindrical shell are studied for four shells with different thicknesses. Initial tensile and compressive membrane stresses are applied separately to the shells to study the effect of the initial stresses on the free vibration modes. The vibration modes of the stiffened cylindrical shell are studied in two steps. First, the influence of the positions of two ring stiffeners on the fundamental frequencies is studied; second, the free vibration modes of the stiffened cylindrical shell are studied. Two cylindrical shells with different thicknesses are used and they are stiffened with different numbers of ring stiffeners, which are uniformly distributed along the longitudinal axis of the shell. The results are compared with available analytical results and finite element solutions of similar problems from the literature.
by Burak Ustundag.
S.M.
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Gomez, Nicasio. "PCV valve flutter : vibration characterization through pressure and flow." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32895.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 51).
A Positive Crankcase Ventilation, or PCV, valve is required by internal combustion engines in order to regulate the flow of blow-by gases out of the crankcase and into the intake air stream. Fluctuations in the pressure and flow of these gases lead to poor performance and can be detrimental to engine durability. This thesis addresses a specific case of PCV valve component vibration, or flutter, which in certain conditions has been severe enough to be perceived by the customer. Tests monitoring pressure and flow were performed in a variety of test setups in order to simulate every real-world scenario possible at the bench level. Data attained was analyzed in order to identify and characterize any and all patterns in pressure and flow indicative of flutter conditions. The end result of this thesis is summarized in a recommended test procedure to be followed in future cases of PCV valve flutter.
by Nicasio Gomez, III.
S.B.
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Tratch, Jorge. "Vibration transmission through machinery foundation and ship bottom structure." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15216.
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Thesis (Mech.E)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Includes bibliographical references.
by Jorge Tratch Junior.
Mech.E
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Liao, Jung-Chi 1971. "Vortex-induced vibration of slender structures in unsteady flow." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8331.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2002.Includes bibliographical references (p. 164-165).
Vortex-induced vibration (VIV) results in fatigue damage of offshore oil exploration and production structures. In recent years, the offshore industry has begun to employ curved slender structures such as steel catenary risers in deep-water offshore oil systems. The top-end vessel motion causes the slender riser to oscillate, creating an unsteady and nonuniform flow profile along the riser. The purpose of this research is to develop a VIV prediction model for slender structures under top-end periodic motions. The key approach to this problem requires identifying the dimensionless parameters important to the unsteady VIV. A set of data from a large-scale model test for highly compliant risers conducted by industry is available. The spectral analysis of the data showed a periodic pattern of the response frequencies. A constant Strouhal (St) number model was proposed such that shedding frequencies change with local inline velocities. The Keulegan-Carpenter number (KC) controls the number of vortex pairs shed per cycle. A KC threshold larger than 40 was found to have significant response for a long structure with finite length excitation region. An approximate solution to the response of an infinite beam with a finite excitation length was obtained; this solution provided an explanation for the high KC threshold. A model for an equivalent reduced damping Sg under a non-uniform, unsteady flow was proposed. This equivalent reduced damping Sg was used to establish a prediction model for the VIV under top-end periodic motions. A time domain simulation of unsteady VIV was demonstrated by using Green's functions.
(cont.) The turning point problem wave propagation was solved for a pipe resting on a linearly varying stiffness foundation. Simple rules were established for conservative estimation of TDP fatigue damage with soil interactions. Guidelines for model test experiment design were provided based on dimensional analysis and scaling rules.
by Jung-Chi Liao.
Ph.D.
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Inoue, Akira. "Quantification of parallel vibration transmission paths in discretized systens." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1167412835.
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Arunyanart, Pirapat. "Fault Identification In Drivetrain Components Using Vibration Signature Analysis." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1428351973.
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Nickerson, Mark David. "Coupled thermal and vibration numerical analysis of solder joints." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280238.
Full textAbstract:
A heat transfer subroutine has been implemented into an existing finite element code developed in theCivil Engineering and Engineering Mechanics Department at the University of Arizona by Dr. Desai and students. The code is capable of performing non linear material and dynamic analysis. The heat transfer subroutine has been implemented such that any inelastic material behavior induced by a temperature increment is captured at every time step in a loading cycle. With the addition of the heat transfer routine, both thermal sources and sinks can be modeled. For example, power generating chips and power dissipating heat sinks, respectively. This will allow a more realistic representation of electronic packages under operational conditions. A 313 ball PBGA staggered area array package was used in all the analyses performed in this dissertation. The calibration of the models was based on research performed by the JPL consortium which included members such as Raytheon, Boeing and Xilinx. The focus of this dissertation was to determine the thermal and vibration fatigue lifetimes of electronic packages using the Disturbed State Concept. To achieve this goal, numerous analyses were performed, representing different test cases. The different test cases included thermal test chamber cycling (TCT), power cycling (PCT), vibration, thermal test chamber cycling with voids in solder balls, vibration with voids in solder balls, and coupled temperature with vibration. Based on the results of these analyses, the Disturbed State Concept was found to predict the fatigue lifetimes of the 313 PBGA package with excellent accuracy, when test results were available for comparison.