With the progress of civilization, buildings and residential constructions become taller and taller. Seismic design for buildings to resist earthquakes also attracts more attentions. The common vibration energy dissipation devices such as TMD, TLD, etc. have been popular but they have limitations such as requirement for large space to install and difficult to be installed after the building is finished. TLCD as an alternative may improve these defects. The new developed MR-TLCD system has the advantages of real-time control and is reversible. Based on the theorem of TLCD, the control equation of MR-TLCD considered the fluid viscosity. The parameters of external control magnetic force and properties of MR-fluid inside the tube needed in damping ratio calculation were measured in the experiment, where a model free vibration experiment was performed. A MR-TLCD system of which the damping ratio was designed in harmony with optimal damping ratio. The comparison was also made for the damping effect of traditional TLCD, MR-TLCD(uncontrolled), MR-TLCD(passive controlled) under dynamic loadings of various frequencies and amplitudes. The experimental results showed that MR-TLCD is more suitable in large amplitude external force. TLCD plays the best vibration mitigation effect when the external force is resonant to the structure, but MR-TLCD is better in other frequency range. It is encouraging that the application of MR-TLCD can have larger scope than TLCD. Keyword: vibration mitigation, experiment, TLCD, MR-TLCD

Passive vibration mitigation via multi-stable, mechanical means is relatively unexplored. In addition, achieving vibration suppression through avoiding resonance is at the forefront of up and coming research. This thesis investigates the application of a purely mechanical, bistable device as a passive method of vibration suppression. A purely mechanical device does not require power, multiple materials, or electrical circuits, and a passive device does not require external interaction or control. Therefore, a passive, mechanical device could be implemented with ease even in physically constrained environments with large dynamic loads, such as turbomachinery. The purely mechanical, bistable device presented herein replicates the two switches per resonance crossing evident in semi-active Resonance Frequency Detuning method. This work explores two different bistable, mass-spring models. The first is a single degree of freedom nonlinear mass spring model aiming to utilize asymmetry in the potential function to change the stiffness of the overall system. The second model is a coupled, two degree of freedom system that combines the nonlinear softening and hardening spring characteristics with the unique stiffnesses of two stable states. The performance is verified by targeting the first mode of a cantilever beam, with the device shifting the resonance away from the excitation frequency. Future research could apply these idealized models to complex, rotating structures and replicate the performance of the passive, mechanical devices in a physical geometry that could be manufactured as a part of a target structure.

A vector form intrinsic finite element method ( plane frame element ) is developed and applied to study the dynamic responses of offshore template platform under wave force. The horziontal, vertical and rotational motions at each node in the finite element model also were analyzed by the developed solution procedure of offshore structures. Besides, this paper also discussed the application of viscoelastic dampers on the offshore structures. A design for the dampers incorporated in the template structure were presented, and dynamic analyses were carried out to observe the effect of the vibration mitigation on the structures .

Los sistemas tales como edificios y veh¨ªculos est¨¢n sujetos a vibraciones que pueden causar mal funcionamiento, incomodidad o colapso. Para mitigar estas vibraciones, se suelen instalar amortiguadores. Estas estructuras se convierten en sistemas adaptr¨®nicos cuando los amortiguadores son controlables. Esta tesis se enfoca en la soluci¨®n del problema de vibraciones en edificios y veh¨ªculos usando amortiguadores magnetoreol¨®gicos (MR). Estos son unos amortiguadores controlables caracterizados por una din¨¢mica altamente no lineal. Adem¨¢s, los sistemas donde se instalan se caracterizan por la incertidumbre param¨¦trica, la limitaci¨®n de medidas y las perturbaciones desconocidas, lo que obliga al uso de t¨¦cnicas complejas de control. En esta tesis se usan Backstepping, QFT y H2/H¡Þ mixto para resolver el problema. Las leyes de control se verifican mediante simulaci¨®n y experimentaci¨®n. / Buildings and vehicle systems are subject to vibrations that may cause malfunctioning, discomfort or collapse. It is an extended practice to install damping devices in order to mitigate such vibrations. With controllable dampers, structures act as adaptronic systems. This dissertation focuses on solving the vibration mitigation problem in buildings and vehicles making use of magnetorheological (MR) dampers which are controllable devices characterized by a highly nonlinear dynamics. Additionally, the systems where they are installed, are characterized by parametric uncertainties, limited measurement availability and unknown disturbances. This implies the use of complex control techniques in order to get a reliable performance of the control system. This research makes use of Backstepping, QFT and Mixed H2/H¡Þ control techniques for achieving the proposed goal. These are verified thorugh simulations and experimentation.

<p>This thesis reports on a numerical and experimental investigation of the unsteady loading of high solidity vertical axis wind turbines (VAWTs). Two-dimensional, unsteady Reynolds averaged Navier-Stokes simulations of a small scale, high solidity, H-type Darrieus vertical axis wind turbine revealed the dominant effect of dynamic stall on the power production and vibration excitation of the turbine. Operation of the turbine at low blade speed ratios resulted in complex flow-blade interaction mechanisms. These include; dynamic stall resulting in large scale vortex production, vortex impingement on the source blade, and significant flow momentum extraction.</p> <p>To validate the numerical model, a series of full-scale experimental wind tunnel tests were performed to determine the aerodynamic loading on the turbine airfoils, vibration response behaviour, and wake velocity. In order to accomplish this, a complex force measurement and wireless telemetry system was developed. During the course of this investigation, high vibration response of the turbine was observed. This resulted in conditions that made it difficult or impossible to measure the underlying aerodynamic loading. A vibration mitigation methodology was developed to remove the effect of vibration from the measured aerodynamic forces. In doing so, an accurate and complete measurement of the aerodynamic loading on the turbine blades was obtained.</p> <p>Comparison of the two-dimensional numerical model results to the experimental measurements revealed a considerable over-prediction of the turbine aerodynamic force and power coefficients, and wake velocity. From this research, it was determined that the three-dimensional flow effects due to the finite aspect ratio of the turbine and blades, as well as parasitic losses, could be accounted for through the application of inlet velocity and turbine height correction factors. In doing so, the two-dimensional numerical model results could be properly scaled to represent the three-dimensional flow behaviour of the turbine prototype. Ultimately, a validated VAWT design tool was developed.</p> / Doctor of Philosophy (PhD)

At the moment of writing, an expansion of the Swedish railway network has started, by constructions of new lines for high-speed trains. The aim is to create a high-speed connection between the most populous cities in Sweden - Stockholm, Göteborg and Malmö, and the rest of Europe. Thereby, the likelihood of faster, longer and heavier foreign trains crossing the Swedish lines is increased. However, this could be problematic since the dynamic response in railway bridges and, consequently, the risk of resonance increases with increasing train speeds. Bridges are usually designed based on contemporary conditions and future requirements are rarely considered, due to e.g. cost issues. Prospectively, the dynamic performance of existing bridges may become insufficient. Hence, the current expansion of the high-speed railway network results in an increased demand of innovative design solutions for new bridges and cost-efficient upgrading methods for existing lines. The aim of the present thesis is to propose a vibration mitigation strategy suitable for new and existing high-speed railway bridges. The main focus is a retrofit method with fluid viscous dampers installed between the bridge superstructure and the supports, which is intended to reduce the vertical bridge deck acceleration below the European design code limits. Furthermore, the intention is to investigate the efficiency of such a system, as well as to identify and analyse the parameters and uncertainties which could influence its functionality. In order to examine the applicability of the proposed retrofit, case studies, statistical screenings and sensitivity analyses are performed and analysed. Two different models, a single-degree-of-freedom system and a finite element model, are developed and compared. From the different models, it is possible to study the influence from the damper parameters, the variability of the material properties and different modelling aspects on the bridge response. After the installation of the fluid viscous dampers, it is found that the acceleration level of the bridge deck is significantly reduced, even below the design code requirements. / I skrivande stund har en utbyggnad av det svenska järnvägsnätet initierats. Målet är att skapa en höghastighetsanslutning mellan de folkrikaste städerna i Sverige - Stockholm, Göteborg och Malmö, och vidare ut i Europa. Därmed ökar sannolikheten att snabbare, längre och tyngre utländska tåg korsar de svenska järnvägslinjerna. Dock kan detta bli problematiskt i och med att järnvägsbroars dynamiska respons och, följaktligen, risken för resonans ökar med ökad tåghastighet. Broar dimensioneras ofta utifrån nuvarande förutsättningar och hänsyn tas sällan till framtida hållbarhetskrav, exempelvis p.g.a. kostnadsbesparingar. Ur ett framtidsperspektiv kan därför det dynamiska beteendet hos befintliga broar komma att bli otillräckligt. Utbyggnaden av höghastighetsnätverket ökar därmed behovet av innovativa konstruktionslösningar för nya broar och kostnadseffektiva uppgraderingsmetoder för befintliga sträckor. Syftet med föreliggande avhandling är att föreslå en metod för att minska de vibrationsnivåer som kan uppstå i både nybyggda och befintliga järnvägsbroar för höghastighetståg. Huvudfokus är en eftermonteringsmetod med viskösa dämpare, som har installerats mellan brons överbyggnad och landfästen, för att minska brobanans vertikala acceleration under gällande europeiska dimensioneringskrav. Vidare avses att undersöka effektiveteten av ett sådant system, samt att identifiera och analysera de parametrar och osäkerheter som kan påverka dess funktionalitet. Fall- och parameterstudier, samt statistiska metoder används och utvärderas för att undersöka tillämpbarheten av den föreslagna vibrationsdämpningsmetoden. Två olika modeller, ett enfrihetsgradssystem och en finit elementmodell, har skapats och jämförts. Utifrån dessa modeller kan påverkan av dämparens parametrar, variabiliteten hos materialegenskaperna och behandlingen av olika modelleringsaspekter studeras. Från resultaten är det tydligt att brobanans accelerationsnivå avsevärt reduceras efter monteringen av viskösa dämpare, till och med under dimensioneringskraven. / <p>QC 20170425</p>

No description available.