Resumo: Os desastres naturais são um grande interesse em engenharia, pois são fenômenos de caráter dinâmico. O desastre natural estudado neste trabalho é a ocorrência de ações sísmicas sobre estruturas, mais precisamente a ação das vibrações do terremoto em estruturas civis. Amortecedores de massa sintonizados (AMS) ou Absorvedores Dinâmicos são dispositivos para controle passivo de vibrações em máquinas, prédios ou outras estruturas. Com o passar dos anos esses dispositivos foram aprimorados e tornaram-se mais versáteis. Neste contexto, apresentam-se um dispositivo considerando uma dependência cúbica do deslocamento na rigidez do elemento elástico acoplado à massa principal e conectada ao aparelho, ambos em paralelo com um amortecimento viscoso linear. O problema é modelado através de equações diferenciais ordinárias não lineares que serão linearizadas em torno de seu ponto de equilíbrio. Como forma de excitar o AMS, foi utilizada uma excitação sísmica sendo esta uma função espectral real, o espectro Tajimi- Kanai, já que em uma situação real, as propriedades do solo local produzem alteração nas propriedades dinâmicas, causando assim uma instabilidade na estrutura onde foram utilizados parâmetros para encontrar um comportamento caótico no sistema. Como forma de minimizar as vibrações causadas pela excitação sísmica foi desenvolvido um controle hibrido estrutural. A técnica de controle utilizada tem o objetivo de minimizar as vibrações e reduzir o movimento caótico do sistema a um ponto estável. Comprovou-se que a estratégia de controle híbrido adotado demonstra eficiência para este tipo de situação e pode ser utilizada como forma de auxiliar na atenuação de danos provocados às estruturas, evitando prejuízos econômicos, perdas biológicas e materiais

Constrained layer damping (CLD) for three layer beams with viscoelastic cores and aluminum or graphite/epoxy composite laminate outer layers was investigated for model comparison, sensitivity to design parameters, and evaluation of experimental loss factor estimation techniques. Model comparison for damping estimation and resonant frequency prediction was performed between finite element analysis (FEA) Ross, Kerwin, and Ungar theory (RKU), developed moment predicted loss factor, and experimental results. Investigated design parameters include; treatment application length and placement, relative thickness of core and constraining layers to base layer, core loss factor, and boundary conditions (free/free, fixed/fixed, and cantilever). Experimental damping estimation techniques evaluated include; frequency response function (FRF) based methods of component analysis, circle-fit method a curve-fit algorithm developed by Han [30] and the time domain of log decrement. Model comparison of finite elements to experimental results showed good trend prediction correlation. Only fair prediction of absolute loss factors was achieved, possibly due to the difficulty in characterization of viscoelastic properties. Design parameters analysis showed that treatment application length and placement were critical to effective added damping. In one case, for the same amount of damping material, the effective added damping of a well designed application was seven times greater than that of a poorly considered one. The effectiveness of treatment on a region appears to be strongly related to the magnitude on the moment acting on that region. Parameter analysis also showed that although a symmetric beam realizes the highest damping, in most cases near optimal damping can be obtained with constraining layer one half as thick as the base layer. Experimental methods for damping estimation showed the simple FRF component analysis to be consistent with the other methods (experimental and FEA) and the most computationally efficient. / Master of Science

Much interest in mechanically harvesting apples has been generated, but no completely successful system has yet been developed. Bruising of the fruit has been a prime drawback to current mechanical harvesting methods. One practical approach to mechanized apple harvesting is to shake the trunk or limb of the tree to remove the fruit. With this method, apple detachment appears to be more dependent on length of stroke rather than shaking frequency. Therefore, a variable stroke shaker appeared to be a reasonable approach to a controlled rate of detachment from the tree. The objective of this project was to develop a variable stroke tree shaking mechanism. The variable stroke feature was attained with the use of a hydraulic cylinder and metering valve in the boom of the shaker with the cylinder acting as a variable rate dashpot. The design was tested in the laboratory under varying conditions of effective limb mass and shaking frequency. For comparison, a constant stroke shaker was subjected to similar tests. Both shaking mechanisms were subjected to a theoretical analysis. For the constant stroke shaker, the theoretical and test displacements of the limb were in good agreement, but the theoretical and test limb varied widely. In the variable stroke shaker, the coefficient of damping of the cylinder was determined from test work and checked, using the differential equations for the system. The testing performed in this investigation was limited to the laboratory, but for these conditions an effective variable stroke mechanism was developed. / Master of Science

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Research report to School of Electrical and Information Engineering / An investigation was conducted into how a variable speed drive can provide a damping torque when mechanical oscillations are present. The modeling of mechanical oscillations via an analogous electrical circuit was performed. Simulation was used to demonstrate how a variable speed drive is able to damp speed oscillations using Direct Torque Control (DTC). Damping of mechanical oscillations is done by means of the variable speed drive providing a damping torque component that is in-phase with the speed deviation. The simulation showed that by applying a small torque component with the speed variation results in torque oscillations being damped by 60% after the initial disturbance. Damping is further improved by applying a torque component equal to the speed variation resulting in the oscillations being damped by 80% when compared to the initial disturbance. / MT2017

by Lai Chun Yu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 75-79). / Abstracts in English and Chinese. / LIST OF FIGURES --- p.vi / LIST OF TABLES --- p.ix / Chapter 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.1.1 --- Vibration Control of Suspension Systems --- p.1 / Chapter 1.1.2 --- Semi-active Devices --- p.3 / Chapter 1.2 --- Literature Review --- p.5 / Chapter 1.2.1 --- MR Fluid and Damper --- p.5 / Chapter 1.2.2 --- Vibration Control --- p.6 / Chapter 1.2.3 --- Robust Control --- p.8 / Chapter 1.3 --- Research Objective --- p.9 / Chapter 1.4 --- Organization of the Thesis --- p.9 / Chapter 2 --- MR DAMPER BEHAVIOR AND MODELING --- p.11 / Chapter 2.1 --- MR Damper --- p.12 / Chapter 2.2 --- Mathematical Model --- p.13 / Chapter 2.3 --- Experimental Setup --- p.15 / Chapter 2.4 --- Damper Characteristics --- p.18 / Chapter 2.5 --- Comparison Between Model with Experimental Data --- p.25 / Chapter 2.5.1 --- Graphical Study --- p.26 / Chapter 2.5.2 --- Quantitative Study --- p.26 / Chapter 2.5.3 --- Other Input Tests --- p.27 / Chapter 3 --- SEMI-ACTIVE VIBRATION CONTROL --- p.33 / Chapter 3.1 --- Dynamic Modelling of Suspension Systems --- p.33 / Chapter 3.2 --- Single-degree-of-freedom (SDOF) Passive Suspension System --- p.34 / Chapter 3.2.1 --- Viscous Damper --- p.34 / Chapter 3.2.2 --- MR Damper --- p.37 / Chapter 3.3 --- Single-degree-of-freedom (SDOF) Semi-active Suspension System --- p.41 / Chapter 3.3.1 --- Ideal Skyhook Control --- p.41 / Chapter 3.3.2 --- Semi-active Skyhook Control --- p.44 / Chapter 3.4 --- Semi-active Robust Control Development --- p.46 / Chapter 3.5 --- Sliding Mode Control --- p.47 / Chapter 3.6 --- Semi-active Damper Control --- p.51 / Chapter 3.6.1 --- On-off Control --- p.52 / Chapter 3.6.2 --- Continuous-state Control --- p.53 / Chapter 3.6.3 --- Comparison Between On-off and Continuous-state Controller --- p.54 / Chapter 4 --- SIMULATION STUDIES --- p.57 / Chapter 4.1 --- Transmissibility --- p.57 / Chapter 4.2 --- Different Base Excitations --- p.59 / Chapter 4.2.1 --- Bump Input --- p.60 / Chapter 4.2.2 --- Random Input --- p.62 / Chapter 5 --- CONCLUSION --- p.67 / Chapter 5.1 --- Summary --- p.67 / Chapter 5.2 --- Future Work --- p.68 / APPENDIX --- p.69 / Chapter A.1 --- Semi-active Control with MR Damper ´ؤ Main Program Listing --- p.69 / Chapter A.2 --- Sub-program Listing (Dynamic System) --- p.70 / Chapter A.3 --- Sub-program Listing (Sliding Mode Controller) --- p.73 / Chapter A.4 --- Sub-program Listing (MR Damper Model) --- p.73 / BIBLIOGRAPHY --- p.75

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 117-121. / by Donald T. Darling. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Bernard Dov Adelstein. / M.S.

Thesis. 1975. B.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Bibliography: leaf 39. / by Eric Hershler Bott. / B.S.