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A self·excited system with weak nonlinearities and multifrequency parametric excitation is investigated in this study. The method of multiple scales is used to analyze the system under four different resonances relating parametric excitation frequencies with the natural frequencies. In the first case, the parametric excitation frequency is approximately equal to twice the natural frequency, λ≃2ω. In the second case, the parametric excitation frequency is approximately equal to the natural frequency, λ≃ω. The third case treats a system with two parametric excitation frequencies under the condition λ₁±λ₂≃2ω. In the last case, a two-degree-of-freedom system with natural frequencies ω, and ω, is considered and the resonance λ₁+ λ₂≃ω_r- ω_q , is analyzed. Different parameters (the 1' load amplitudes, a detuning parameter, and a system stiffness parameter) are varied in each case and the responses obtained are presented in plots. The stability of the solutions is affected by all the parameters mentioned, especially the load amplitudes and the detuning parameter. / Master of Science

An investigation of the effect of the coupling value and the structural perturbation parameter is conducted on coupled systems. The analysis of a coupled pendulums system results in the analytical expression of the natural frequencies of the system. The response of the system for harmonic excitation and random input is developed. Two single Euler-Bemouilli beams coupled by a torsional spring constitute the multi degree of freedom extension of the study. Special care is given to show the variation of the natural frequencies \with the two parameters and modal overlapping is shown. The study of the response to harmonic excitation makes the localization phenomenon apparent. For the special case where one of the beam is excited by a rain-on-the roof load, the estimates of the amplitude for each beam and the power flow between the beams are analytically expressed. The power flow is proved to be concentrated around the natural frequencies, stronger for a tuned system and sensitive to the number of modes, especially v:hen modal overlapping occurs. A Monte Carlo simulation considering the perturbation parameter as a Gaussian random variable points out that the mean value of the power decreases rapidly with higher frequency. The power flow is also calculated using the theory of the Statistical Energy Analysis. / Master of Science

Interest in large flexible space structures has grown considerably over the last decade. These distributed parameter systems exhibit vibration characteristics such as low, closely spaced natural frequencies and light damping, which, when coupled with the stringent pointing accuracy and vibration control requirements imposed on these systems, bring about interesting control problems. Addressing these problems has called for the use of active vibration control. Up to now, two of the most popular means for active vibration control of large space structures have been proof mass and reaction wheel actuators. These actuators are inertial-type actuators in that they operate by applying forces or moments to masses whose reaction forces, imposed on the structure, act to dampen the vibrations of the structure. A new class of actuators, variable geometry trusses (VGT's), has been recently introduced. These actuators are actually built into the structure, and they operate by varying their link lengths to apply forces to the structure or to change the shape of the structure itself. This study compared the effectiveness of four actuators in controlling the planar vibrations of a cantilevered truss-beam. The actuators chosen for the study were a proof mass actuator, a reaction wheel actuator, and two VGT's, the planar truss actuator, and the planar truss proof mass actuator (a combination VGT/inertial type actuator). Numerical simulations of each beam/actuator system were performed in response to initial condition inputs. A full-state, LQR optimal feedback control law was used with each system. These simulations provided information such as time response of the closed-loop system, damping provided to the beam, and power required by each actuator. This information can be used to determine the "best" actuator for a given purpose. The results of these simulations show that the VGT's are preferable in terms of damping added to the beam. The proof mass actuator is more efficient as far as power required to do the control, however, the efficiencies for all actuators are very similar. / Master of Science

The primary objective of this Investigation was to determine the heat transfer rate and characteristics of three vibrated wires In a parallel flow. A simple experimental apparatus was constructed with which to pursue the investigation, and various results were obtained. Three wires of different diameters were individually tested in two configurations. One configuration consisted of electrically heated stationary wires which transferred heat to air flowing at various velocities and parallel to the wires. This was investigated to compare the results with previously reported investigations of small cylinders in parallel flow. The second configuration consisted of vibrating wires at various air velocities In parallel flow and at various frequencies and amplitudes. The results show that for the stationary wires the heat transfer characteristics are In accord In principle with the results of similar investigations. The results obtained when the wires were vibrated show that vibration in forced convection Increased heat transfer rate up to a certain value of flow Reynolds number after which the effect of vibration on heat transfer was negligible. The effect of amplitude and frequency on the Improvement of heat transfer rate was greater at a particular range of values of frequency and amplitude. As both frequency and amplitude were Increased above this range, the rate of Improvement In heat transfer was not as great. / Master of Science

In this thesis, we examine the Linear DC Motor in a configuration such that it provides the forces necessary to damp vibrations in a large flexible structure. The design is broken down into three steps where in each step, a feedback loop is placed around the actuator and/or the structure. The first loop is a motor compensation loop which effectively decouples the motor model from the structure model by removing the effect of the velocity of the structure on the motor's performance. The second loop stabilizes the relative position response of the combined actuator/structure model. This loop also shapes the magnitude response of the system, thus determining the bandwidth of the actuator. Two designs are developed: a narrow bandwidth design and a wide bandwidth design. The third loop is the vibration suppression design loop and can be designed a number of ways. In this thesis, we develop two decentralized designs and a centralized design. The final system is simulated to check design results. The various nonlinearities of the proof mass actuator are considered and their effect on results noted. These nonlinearites, the stroke and current limits, determine the effectiveness of each vibration suppression design. The linear model is checked for robustness to parameter uncertainty. Results for the various designs are tabulated and discussed. / M.S.

M. Beniušis „Kelto „Victoria Seaways“ šilumokaičio ir aušinimo vamzdyno virpesių tyrimas“. Laivų projektavimo ir statybos magistratūros studijų programos baigiamasis darbas. Darbo vadovas dr. P. Mažeika, Klaipėdos universitetas: Klaipėda, 2014. Raktažodžiai: virpesiai, laivas, keltas, virpesių tyrimai, šilumokaitis. Baigiamojo darbo teorinėje dalyje aprašoma virpesių klasifikacija, pagrindiniai virpesių žadintojai ir analizuojami įvairūs virpesių lygio mažinimo laive, virpesių skaičiavimo būdai. Eksperimentinėje dalyje pateikiama keltų „Victoria Seaways“ ir „Athena Seaways“ aušinimo sistemos dalies virpesių matavimo metodika. Nagrinėjami reiso Klaipėda-Kylis-Klaipėda metu atliktų matavimų rezultatai, bei nustatomos tiriamos aušinimo sistemos dalies padidintų virpesių lygio priežastys. Paskutinėje darbo dalyje pateikiamos išvados ir rekomendacijos. / M. Beniušis “Vibration research of heat exchanger and cooling piping in Victoria Seaways ferry”. Final work of the master studies of ship design and building program. Academic supervisor Dr. P. Mažeika, Klaipeda University: Klaipėda, 2014. Keywords: vibrations, ship, ferry, vibration research, heat exchanger. The theoretical part of the final work describes the classification of vibration, main excitations of vibration and analyses various methods for reduction of the vibration level on board and vibration calculation. The experimental part presents the vibration measurement methodology in the cooling systems of Victoria Seaways and Athena Seaways ferries. It examines the results of measurements carried out during Klaipėda-Kiel-Klaipėda trip and identifies the reasons for the recent level of vibration in the analysed cooling system. The final part of the work contains the conclusions and recommendations.

A vibrated bed is a mobile layer of solid particles contained in a vessel that is vibrated vertically. This study investigates bed dynamics and heat transfer from a vertical surface in shallow vibrated beds in absence of aeration. In general, "shallow" means a depth-to-width ratio less than one. In this study, bed depth is 30 mm, and this ratio is about 0.2. All experiments are at 25 hertz and at vibrational amplitudes affording peak accelerations between 2 and 7 times gravity. The study uses spherical glass beads of two densities and "Master Beads," nearly spherical particles of a crude, dense alumina, in size fractions from 63 to 707 micrometers. A disc embedded in the vessel floor, vibrated at 4.5 kilohertz, gives data on bed-vessel separation, showing it to occur later than predicted by plastic, single-mass models. The delay is attributed to bed expansion, monitored by piezoelectric force gauges mounted on floor and wall of the vessel. In large-particle beds, bed-vessel collision occurs simultaneously everywhere. In small-particle beds, exhibiting an uneven top surface, collision occurs first at the side walls and moves toward the center. In small-particle beds, pressure gradients appearing during the bed's free flight drive a horizontal component of particle circulation from the vessel's side walls toward its center. An apparent viscosity of the bed, estimated crudely by pulling a rod through it, influences this component's velocity. In beds of large particles, circulation is almost entirely vertical, a layer of two or three particles moving downward at a wall, and a slow return flow moving upward elsewhere. The study confirms the downward wall motion to be driven by friction. Heat transfer closely follows trends in rate of circulation. Greater dependence upon vibrational intensity is seen in small-particle beds. Values as high as 578 W/m²-K are measured. Comparison of vertical-surface heater geometry with an earlier horizontal tube shows the former to be generally superior for surface-to-bed heat transfer. / Ph. D.