Since their invention in the early 1900s, Tuned Vibration Absorbers (TVAs) have shown to be effective in suppressing vibrations of machines and structures. A vibration absorber is a vibratory subsystem attached to a primary system. It normally consists of a mass, a spring, and a damper. Mounted to the primary system, a TVA counteracts the motions of the primary system, "absorbing" the primary structure's vibrations. A conventional passive TVA, however, is only effective when it is tuned properly, hence, the name "tuned" vibration absorber. In many practical applications, inevitable off-tuning (or mistuning) of a TVA occurs because of the system's operating conditions or parameter changes over time. For example, the mass in a building floor could change by moving furnishings, people gathering, etc., which can "off-tune" TVAs. When TVAs are off-tuned, their effectiveness is sharply reduced. Moreover, the off-tuned TVAs can excessively amplify the vibration levels of the primary structures; therefore, not only rendering the TVA useless but also possibly causing damage to the structures. Off-tuning is one of the major problems of conventional passive TVAs. This study proposes a novel semiactive TVA, which strives to combine the best features of passive and active TVA systems. The semiactive TVA in this study includes a Magneto-Rheological (MR) damper that is used as a controllable damping element, for providing the real-time adjustability that is needed for improving the TVA performance. This study is conducted in two phases. The first phase provides a numerical investigation on a two-degree-of-freedom (2-DOF) numerical model in which the primary structure is coupled with a TVA. The numerical investigation considers four semiactive control methods for the MR TVAs, in addition to an equivalent passive TVA. These numerical models are optimally tuned using numerical optimization techniques to compare each TVA system. These tuned systems then serve as the basis for numerical parametric studies for further evaluation of their dynamic performance. The parametric study covers the effects of damping, as well as system parameter variations (off-tuning). The results indicates that semiactive TVAs are more effective in reducing the maximum vibrations of the primary structure and are more robust when subjected to off-tuning. Additionally, the numerical study identifies the "On-off Displacement-Based Groundhook control (on-off DBG)" as the most suitable control method for the semiactive TVA among control methods considered in this study. For the second phase of this study, an experimental study is performed on a test setup, which represents a 2-DOF structure model coupled with an MR TVA. Using this setup, a series of tests are conducted in the same manner as the numerical study to evaluate the performance of the semiactive TVA. The primary purposes of the experiment are to further evaluate the most promising semiactive control methods and to serve as a "proof-of-concept" of the effectiveness of this MR TVA for floor vibration applications. The results indicate that the semiactive TVA with displacement-based groundhook control outperforms the equivalent passive TVA in reducing the maximum vibrations of the primary structure. This confirms the numerical result that identifies on-off DBG control method as the "best" control method for the MR TVA among four semiactive control schemes considered. The experimental robustness study is also conducted, focusing on the dynamic performance of both the passive and the semiactive TVAs when the mass of the primary system changes (mass off-tuning). The mass of the primary system varied from -23 % to +23 % of its nominal value by adding and removing external masses. The experimental results show that the semiactive TVA is more robust to changes in the primary mass than the passive TVA. These results justify the benefits of the use of semiactive MR TVAs in structures, such as building floor systems. The off-tuning analysis further suggests that, in practice, semiactive TVAs should be tuned slightly less than their optimum in order to compensate for any added masses to the structure. Additionally, the lessons learned from the experimental study have paved the way for implementing the semiactive MR TVA on a test floor, which is currently in progress under a separate study. / Ph. D.

The objective of this thesis is to describe the design, construction, implementation and performance of a prototype adaptive pendulum tuned mass damper (APTMD). Furthermore the thesis aims at demonstrating the performance improvements obtained when the tuned mass damper (TMD) parameters are optimized. The study considers the effect of adjusting the APTMD tuned frequency and damping ratio on a two storey test structure subjected to broadband and narrowband excitation. An analytical model of the APTMD for a single-degree-of-freedom (SDOF) structure is used to demonstrate the performance improvements when the APTMD parameters are optimized. The optimized model considers the effects of adjusting the frequency ratio, damping ratio, and mass ratio of the combined system to reduce the maximum deflection when the structure is subjected to a harmonic excitation force. The analytical model is used to simulate the optimal performance of the APTMD system. The experimental APTMD is capable of identifying the structural vibration modes in real time and tuning to the desired mode. The structural vibration modes are identified by calculating the windowed power spectral density of the structure’s acceleration, followed by peak-picking algorithm to identify the modal frequencies. Tuning is performed by moving the pivot location of the pendulum arm via a tuning frame along a set of rails. The design also allows for changes in the external dampening force. An adjustable damper is attached to the pendulum mass to allow for control of the APTMD damping ratio. A prototype of the APTMD is built and tested in a modal testing setup. The test structure is a two-storey model of a building structure. The structure is excited using a shaker fixed to the lower storey of the structure. The performance of the APTMD under broadband and narrowband excitation is examined for various tuning and damping parameters. The performance of the APTMD system under optimally tuned and detuned conditions is investigated. The results of the experimental studies demonstrate the importance of optimizing the TMD tuned frequency and damping ratio to reduce structural vibrations. Since the APTMD is designed to autonomously update both parameters, it is an effective tool in mitigating structural vibrations where user interaction is either difficult or expensive. Further study on the performance of a prototype APTMD applied to a large scale structure is required before implementation on full-scale structures.

This thesis explores next generation passive and semi-active tuned mass damper (PTMD and SATMD) building systems for reducing the seismic response of tall structures and mitigating damage. The proposed structural configuration separates the upper storey(s) of a structure to act as the 'tuned' mass, either passively or semi-actively. In the view point of traditional TMD system theory, this alternative approach avoids adding excessive redundant mass that is rarely used. In particular, it is proposed to replace the passive spring damper system with a semi-active resetable device based system (SATMD). This semi-active approach uses feedback control to alter or manipulate the reaction forces, effectively re-tuning the system depending on the structural response. In this trade-off parametric study, the efficacy of spreading stiffness between resetable devices and rubber bearings is illustrated. Spectral analysis of simplified 2-DOF model explores the efficacy of these modified structural control systems and the general validity of the optimal derived parameters is demonstrated. The end result of the spectral analysis is an optimally-based initial design approach that fits into accepted design methods. Realistic suites of earthquake ground motion records, representing seismic excitations of specific return period probability, are utilised, with lognormal statistical analysis used to represent the response distribution. This probabilistic approach avoids bias toward any particular type of ground motion or frequency content. Statistical analysis of the performance over these suites thus better indicates the true overall efficacy of the PTMD and SATMD building systems considered. Several cases of the segregated multi-storey TMD building structures utilising passive devices (PTMD) and semi-active resetable devices (SATMD) are described and analysed. The SATMD building systems show significant promise for applications of structural control, particularly for cases where extra storeys might be added during retrofit, redevelopment or upgrade. The SATMD approach offers advantages over PTMD building systems in the consistent response reductions seen over a broad range of structural natural frequencies. Using an array of performance metrics the overall structural performance is examined without the typically narrow focus found in other studies. Performance comparisons are based on statistically calculated storey/structural hysteretic energy and storey/structural damage demands, as well as conventional structural response performance indices. Overall, this research presents a methodology for designing SATMD building systems, highlighting the adaptable structural configuration and the performance obtained. Thus, there is good potential for SATMD building systems, especially in retrofit where lack of space constrains some future urban development to expand upward. Finally, the approach presented offers an insight into how rethinking typical solutions with new technology can offer dramatic improvements that might not otherwise be expected or obtainable.

The objective of this thesis is to describe the design, construction, implementation and performance of a prototype adaptive pendulum tuned mass damper (APTMD). Furthermore the thesis aims at demonstrating the performance improvements obtained when the tuned mass damper (TMD) parameters are optimized. The study considers the effect of adjusting the APTMD tuned frequency and damping ratio on a two storey test structure subjected to broadband and narrowband excitation. An analytical model of the APTMD for a single-degree-of-freedom (SDOF) structure is used to demonstrate the performance improvements when the APTMD parameters are optimized. The optimized model considers the effects of adjusting the frequency ratio, damping ratio, and mass ratio of the combined system to reduce the maximum deflection when the structure is subjected to a harmonic excitation force. The analytical model is used to simulate the optimal performance of the APTMD system. The experimental APTMD is capable of identifying the structural vibration modes in real time and tuning to the desired mode. The structural vibration modes are identified by calculating the windowed power spectral density of the structure’s acceleration, followed by peak-picking algorithm to identify the modal frequencies. Tuning is performed by moving the pivot location of the pendulum arm via a tuning frame along a set of rails. The design also allows for changes in the external dampening force. An adjustable damper is attached to the pendulum mass to allow for control of the APTMD damping ratio. A prototype of the APTMD is built and tested in a modal testing setup. The test structure is a two-storey model of a building structure. The structure is excited using a shaker fixed to the lower storey of the structure. The performance of the APTMD under broadband and narrowband excitation is examined for various tuning and damping parameters. The performance of the APTMD system under optimally tuned and detuned conditions is investigated. The results of the experimental studies demonstrate the importance of optimizing the TMD tuned frequency and damping ratio to reduce structural vibrations. Since the APTMD is designed to autonomously update both parameters, it is an effective tool in mitigating structural vibrations where user interaction is either difficult or expensive. Further study on the performance of a prototype APTMD applied to a large scale structure is required before implementation on full-scale structures.

Riesenhuber \& Poggio recently proposed a model of object recognitionin cortex which, beyond integrating general beliefs about the visualsystem in a quantitative framework, made testable predictions aboutvisual processing. In particular, they showed that invariant objectrepresentation could be obtained with a selective pooling mechanismover properly chosen afferents through a {\sc max} operation: Forinstance, at the complex cells level, pooling over a group of simplecells at the same preferred orientation and position in space but atslightly different spatial frequency would provide scale tolerance,while pooling over a group of simple cells at the same preferredorientation and spatial frequency but at slightly different positionin space would provide position tolerance. Indirect support for suchmechanisms in the visual system come from the ability of thearchitecture at the top level to replicate shape tuning as well asshift and size invariance properties of ``view-tuned cells'' (VTUs)found in inferotemporal cortex (IT), the highest area in the ventralvisual stream, thought to be crucial in mediating object recognitionin cortex. There is also now good physiological evidence that a {\scmax} operation is performed at various levels along the ventralstream. However, in the original paper by Riesenhuber \& Poggio,tuning and pooling parameters of model units in early and intermediateareas were only qualitatively inspired by physiological data. Inparticular, many studies have investigated the tuning properties ofsimple and complex cells in primary visual cortex, V1. We show thatunits in the early levels of HMAX can be tuned to produce realisticsimple and complex cell-like tuning, and that the earlier findings onthe invariance properties of model VTUs still hold in this morerealistic version of the model.

Le travail de thèse s’appuie sur un recueil exhaustif des travaux effectués dans le domaine du contrôle des vibrations auxquels sont soumis les ouvrages génie civil. Une contribution innovante et originale est apportée et permet de classifier, de généraliser et d’optimiser certains critères dans le but d’assurer une conception optimale de divers dispositifs d’atténuation des vibrations, et ce, selon leur application. L’un des objectifs de la thèse a donc consisté à traiter ces critères de manière originale. Après avoir résolu le problème dit « direct » s’appuyant sur la modélisation des systèmes dotés d’un ou de plusieurs AMAs, nous nous sommes intéressés au problème dit « indirect » en envisageant divers critères d’optimisation. Ainsi, plusieurs critères d’optimisation des paramètres mécaniques de plusieurs AMAs appliqués à un système principal comportant 1 ou plusieurs degrés de liberté peuvent être utilisés. L’excitation du système principal est envisagée de deux manières, soit à sa base (en vue d’une application à la sismique), soit au niveau de la structure (en vue d’une application aux effets du vent).Des simulations numériques sont réalisées dans le but d’étudier la performance de chaque modèle optimisé en se fondant sur des approches fréquentielles et temporelles. La robustesse de chaque critère d’optimisation face aux incertitudes liées au changement des paramètres physiques de la structure principale a été examinée. Nous avons également étudié la sensibilité des critères par rapport aux incertitudes des paramètres optimisés des AMAs. La conception et l’optimisation de p AMAs placés en parallèle pour un système principal à Nddl, a constitué une nouvelle contribution originale dans le cadre de cette thèse. Dans ce contexte, lors d’une sollicitation sismique, nous estimons la contribution de chaque mode dans la structure principale et nous conservons seulement les modes de vibrations qui ont un rapport de masses modales cumulées supérieur à 90%. Le choix du critère d’optimisation s’appuie seulement sur les étages les plus sensibles aux modes conservés et permet ainsi de tenir compte des modes élevés de la structure principale. Dans le but de limiter les dommages subis par les constructions du génie civil lors de sollicitations sismiques, nous cherchons à évaluer l’efficacité des AMAs afin d’atténuer les réponses temporelles sismiques. Ainsi une étude comparative est réalisée en appliquant quatre séismes réels sur les modèles optimisés. Afin d’illustrer les résultats obtenus, des tests de caractérisation d’un AMA utilisant un amortissement par courants de Foucault et un ajustement de la rigidité, ont été menés. Ils ont permis d’obtenir une validation expérimentale du modèle et du critère d’optimisation adopté / The architectural demand and the desire to reduce costs permit the construction of light structures with innovating shapes. The great flexibility of these structures makes them increasingly sensitive to the external dynamic loads such as traffic, wind and earthquakes. Vibration control techniques allow to construct modern buildings increasingly slender, and, whether they are economic or architecturally audacious. Instead of modifying the geometrical and mechanical characteristics of a structure, vibration control consists in producing reaction forces which are opposed to the negative effects of the external excitations when they appear. This technological advance has the great advantage to not influencing planners and architects’ work and it provides them with additional creative options in both geometrical and mechanical characteristics of buildings. We restrict our focus to passive vibration control. Among available passive vibration absorber systems, Tuned Mass Dampers (TMDs) were selected for their simplicity and reliability. A TMD consists of a mass, a dashpot, and a spring, and is commonly attached to a vibrating primary system to suppress undesirable vibrations. The performance of TMDs is strongly affected by the adjustment of their parameters. The problem is the optimization of the mechanical parameters of TMD and their location in order to attenuate vibrations of the main structure. This thesis is based on understanding the dynamic characteristics of TMD. It aims to make an innovative and original contribution to classify, generalize and optimize some criteria in order to ensure an optimal design of TMDs, depending on their application. Our work consisted to treat these criteria in an original way. After solving the direct problem based on the modelling of systems with one or several TMD, we tackled the indirect problem by considering various optimization criteria. Thus, several optimization criteria of the mechanical parameters of TMDs applied to a main system (single (SDOF) or multiple degrees of freedom (MDOF)) are used. The excitation of the main system can be done in two different ways; either on the base (for seismic application) or on the structure (for wind effects).Numerical simulations based on a time and frequency approach are used to examine the performance of each optimized model. The robustness of each optimization criterion is assessed by taken into account the uncertainties related to the change of the physical parameters of the main structure. Such problems can be discussed by considering sensitivity analysis for criteria under uncertainty of the optimum TMD parameters. A new and original contribution of this thesis is the design and optimization of multiple TMDs in parallel with a MDOF main structure. In this context, during seismic loads, modes in the main structure with relatively high effective masses can be readily excited by base excitation. Afterwards, optimization criterion can be developed based on the most sensitive storeys to vibration modes which are a cumulative modal effective mass fraction exceeding 90%. To protect structures under earthquake loads, we seek to assess the effectiveness of TMDs in mitigating the response of structure under different real earthquakes. A comparative study is then achieved with four real earthquakes applied on systems with TMD optimized parameters. To illustrate the results obtained, characterization tests are conducted on a TMD with damping by eddy currents effect and adjustable stiffness. They allow the validation of the model and optimization criterion adopted

abstract: As urban populations grow, water managers are becoming increasingly concerned about water scarcity. Water managers once relied on developing new sources of water supply to manage scarcity but economically feasible sources of unclaimed water are now rare, leading to an increased interest in demand side management. Water managers in Las Vegas, Nevada have developed innovative demand side management strategies due to the cities rapid urbanization and limited water supply. Three questions are addressed. First, in the developed areas of the Las Vegas Valley Water District service areas, how did vegetation area change? To quantify changes in vegetation area, the Matched Filter Vegetation Index (MFVI) is developed from Mixture Tuned Match Filtering estimates of vegetation area calibrated against vegetation area estimates from high-resolution aerial photography. In the established city core, there was a small but significant decline in vegetation area. Second, how much of the observed decline in per capita consumption can be explained by Las Vegas land cover and physical infrastructure change that resulted from extensive new construction and new use of water conserving technology, and how much can be attributed to water conservation policy choices? A regression analysis is performed, followed by an analysis of three counter-factual scenarios to decompose reductions in household water into its constituent parts. The largest citywide drivers of change in water consumption were increased water efficiency associated with new construction and rapid population growth. In the established urban core, the most significant driver was declining vegetation area. Third, water savings generated by a conservation program that provides incentives for homeowners to convert grass into desert landscaping are estimated. In the city core, 82 gallons of water are saved in June for each square meter of landscape converted in the first year after conversion, but the savings attenuate to 33 gallons per meter converted as the landscape ages. Voluntary landscape conversion programs can generate substantial water savings. The most significant result is that the most effective way to ensure long term, sustainable reductions in water consumption in a growing city without changing water prices is to support the construction of water efficient infrastructure. / Dissertation/Thesis / Doctoral Dissertation Sustainability 2014

The master thesis deals with computational modeling of a turbocharger vibrations and and assessment of influnce of passive dynamic vibration absorber on vibrations of actuator bracket. The use of dynamic vibration absorber was summarized in the research study. The analysis were performed using finite element method in ANSYS. Several computational models of turbocharger were created with different ways of modeling bolted joints between turbocharger parts. Modal analysis of each model was performed and the results were compared. For the selected model, the response to the kinematic excitation from the internal combustion engine for two load conditions was calculated using harmonic analysis. A simple model of vibration dynamic absorber was applied to the turbocharger model with reduced degrees of freedom and its influnce on vibrations of actuator bracket was investigated. Significant decrease of the maximum acceleration amplitude was achieved in a given frequency range when absorber parameters were optimized.

In the current thesis, the Banafjäl Bridge located on the Bothnia line (Botniabanan) in northern Sweden was studied. The bridge is a 40m long composite ballasted high-speed railway bridge. A 3D FE model of the bridge was developed using a commercial FE software, Abaqus. The FE model was calibrated against the measured data of the bridge. The dynamic response of the bridge's FE model was investigated under the dynamic load of the passing HSLM-A train using modal dynamic analysis. The vertical acceleration induced by excitation of the passing train exceeded the permissible limit of 3.5 m/s2 for the speed range of 220-240 km/h. Thus, damping solutions using multiple tuned mass dampers (MTMDs) were investigated. According to the results of this study, a 4 tonnes MTMD system consist of 5 parallel TMDs attached to the mid-span of the bridge could effectively control the undesired vibration of the bridge. The suggested solution could account for the changes in the stiffness of the bridge caused by freezing and ice forming in the ballast.

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