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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Vibration analysis of dry sand models

Aoki, Yoshinori January 1969 (has links)
Using the shaking table, two types of tests have been made with 8 feet long by 1-1/2 feet wide and from 1/2 foot to 1 foot high dry Wedson sand models. One of them was a response study of the horizontal model, from which the affects of boundary restraints, the frequency-response of soil layer and the dynamic properties of dry sand were studied. The measured results with regard to the effects of boundary restraints and the frequency response of soil layer agreed with predictions by the linear visco-elastic theory. The measured shear wave moduli and damping ratio also agreed, with those obtained by previous workers. The other type of tests performed was a study of slope stability using tilted models, in which the accumulative displacement of slope was induced, by a sinusoidal base motion, the critical slope angle and the stable slope angle were studied. The measured accumulative displacement agreed with the theory suggested by Goodman and Seed (1966). It has been found that there are two distinctly different characteristic angles of slope associated with dynamic stability for a slope. These are the critical slope angle and the stable slope angle. Moreover, the stable slope angle is unique for a material and a frequency of the sinusoidal base motion and independent of the initial condition of the slope. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate
22

Autonomous quasi-harmonic and forced vibration of frictional systems

Ko, Pak Lim January 1969 (has links)
The behaviour of a system subject to quasi-harmonic type frictional oscillation was investigated. The same frictional system with external excitation was also investigated both experimentally and theoretically. Various frictional material combinations including steel, polymer, rubber and fibre materials and lubricants were used to provide different forms of friction characteristics. The dynamic friction-velocity curves were obtained by recording simultaneously the acceleration force, damping force, spring force and friction force during one cycle of the quasi-harmonic oscillation. The curves were expressed as a function of sliding velocity and were represented by nth order polynomials as well as by exponential expressions. The first approximation methods by Krylov and Bogoliuboff were used to solve the nonlinear, differential equations of motion in both the autonomous and non-autonomous cases. In addition, the method of harmonic balance was also used in the non-autonomous case. In both cases, the Runge-Kutta numerical method was used to investigate the transient state of the oscillations. Theoretical results for the autonomous system indicated that the humped form friction-velocity curve was a necessary condition for the existence of quasi-harmonic oscillation. Subharmonic entrainment at the frequency of the autoperiodic oscillation or harmonic entrainment at the external excitation frequencies, depending on the magnitude of the external excitation, were also predicted from the analysis. Experimental results were obtained from a pin on disc type frictional system having a track velocity range of 0.04 in/sec to 13.5 in/sec. External excitation forces were obtained by applying the principle of out-of-balance mass. The frequency range of the external excitation is 0-90 cps. The growth and decay of the quasi-harmonic oscillation was observed. In the non-autonomous case, 'quenching' of the autoperiodic oscillation by the external excitation was recorded. In general, the experimental results substantiate the predictions of the theoretical analyses. The experimental results also showed that the vertical external excitation has the effect of reducing the maximum static friction and subsequently extinguishing stick-slip oscillation. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate
23

Model Reduction of Large Structural Systems for Active Vibration Control

Boffa, John January 2006 (has links)
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.
24

Free vibration of a beam subjected to a large static deflection

Cornil, Marie-Blanche 12 1900 (has links)
No description available.
25

Investigation of vibration control of hypotrochoidally driven machninery

Cook, Nathan Lindquist 05 1900 (has links)
No description available.
26

An exploration of parametric excitation as a tool for vibration control

Nguyen, Phillip Huu 08 1900 (has links)
No description available.
27

Model Reduction of Large Structural Systems for Active Vibration Control

Boffa, John January 2006 (has links)
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.
28

The effects of whole body vibration on the neuromuscular system /

Hong, Junggi. January 2008 (has links)
Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.
29

Dynamic models of a small ac induction motor

Martin, Derek D. January 1995 (has links)
The Power Electronics Group at Aberdeen University is working towards the provision of a complete time domain model of an electrical drive for marine applications. The model has been developed using the SABER electrical simulation software package and includes a cycloconvertor which supplies an ac induction motor which in turn drives the shaft/propeller assembly. Effects such as vibration, noise and shaft oscillations due to the cycloconvertor will be studied. This thesis reports on the development and investigation of a mathematical model of the ac induction motor which can be incorporated into the existing system model to predict vibration levels at any point on the structure of the motor. The development of the mathematical model was achieved by combining a finite element (FE) representation of the motor structure with the modal parameters of the motor extracted using modal analysis techniques. The main experimental programme on the selected motor was based on a series of parallel tests on two "identical" machines. These machines were broken apart and subjected to a modal analysis at various stages. The vibration properties of a laminated structure, similar to the core of an ac motor, were also investigated. The experimental data was then used to direct the creation of the FE models. The models were created and analysed using SDRC I-DEAS integrated software. The modal analysis results were introduced into test software, where they were "curve-fitted" to extract the modal mass, modal stiffness and modal damping parameters. The FE model, created in the finite element modelling package, was then correlated with the test model and modifications implemented until the FE and test models compared well.
30

Vibration sensors utilizing fiber fabry-perot interferometers and permanent magnets

Conkey, Andrew P. 15 May 2009 (has links)
A unique set of vibration sensors was designed that incorporate the fiber Fabry-Perot interferometer (FFPI) and permanent magnets. Feasibility of the design and its advantages over traditional sensors were verified by experiments. The new sensors consist of one that monitors the motion of a body across an air gap with the other designed to respond to the motion while in contact with the vibrating body. The FFPI is the device used to transmit the vibrational response while permanent magnets are used to transfer the vibratory motion to the FFPI. In the non-contacting sensor, a permanent magnet was used as the motive to transfer the vibratory motion to be registered at the FFPI. Although the magnet resulted in a non-linear response, the effect of the non-linearity can be removed by signal processing. The fiber optic gap sensor (FOGS) developed has a sensitivity of 250 mV/mil for a 30 mil gap to 50 mV/mil for a 65 mil gap and a dynamic range up to 820 Hz. An advantage of the FOGS over traditional eddy current based gap sensors (ECP), for measuring rotor vibration, was demonstrated with a test rotor face that had brass strips attached to it. The FOGS response was not affected by the strips whereas the response of the traditional ECP was greatly affected by the strips. This demonstrated the potential of the FOGS for measuring the motion of a coated shaft. The fiber optic vibration sensor (FOVS) had a marginal response as its construction led to spurious signals. The feasibility of it to act as a vibration sensor, however, was demonstrated. Due to problems in maintaining the proper gap between the proof mass and sensor head during assembly the natural frequency of the FOVS was around 31 Hz and not the targeted 10 Hz. The sensors presented were meant to be a first generation. However, access to additional FFPI elements was restricted limiting further development. Improvements to the sensors would be to modify the sensing head, magnet size, and the embedment of the FFPI as well as to employ tighter machining precision and assembly practices.

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