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.

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

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.

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Over the past decade, offshore wind has positioned itself as one of the most promising renewable energy markets. While this field is currently dominated by fixed-bottom wind turbines located within a limited depth range, floating turbines are showing promise as a way to capture the more developed wind profiles available in deeper waters. Currently, the main challenge with floating offshore wind is that the systems experience larger ultimate loads compared to fixed bottom turbines. These larger loads are caused by the increased motion inherent with floating structures. This study looks to analyze the effects that traditional and inerter based structural control methods can have on vibration reduction of floating offshore wind turbines. Models are developed adding tuned mass dampers (TMD) and tuned inerter dampers (TID) into the three main columns of a semisubmersible platform. Results showed that for free decay tests, heave and pitch root mean square (RMS) values were reduced significantly by the addition of passive structural control. The inerter based structural control consistently outperformed traditional TMD and also allowed for similar performance with significantly reduced physical mass values. For regular wave excitation both control methods resulted in significant reductions to the heave and pitch RMS values compared to the baseline, with the TID outperforming the TMD . And for an irregular wave analysis, it was found that both control configurations were still able to provide meaningful reductions to the baseline model. / Master of Science / Over the past decade, offshore wind has positioned itself as one of the most promising renewable energy markets. While this field is currently dominated by fixed-bottom wind turbines located within a limited depth range, floating turbines are showing promise as a way to capture the more developed wind profiles available in deeper waters. Currently, the main challenge with floating offshore wind is that the systems experience larger ultimate loads compared to fixed bottom turbines. These larger loads are caused by the increased motion inherent with floating structures. This study looks to analyze the effects that traditional and enhanced motion reduction technology can have on floating offshore wind turbines. Models are developed adding the traditional and enhanced motion reduction technology into the three main columns of a semisubmersible platform. Results showed that for several different tests, the motion reduction technology has a positive effect on the turbines. For test dropping the system from a set height, the motion reduction technology allowed the system to come to rest much faster. Moreover, the enhanced technology performed better than the traditional technology. The same results were found when the system was excited by simulated waves.

No description available.

No description available.

As a result of global warming, the prevalence of renewable energy sources such as wind farms has steadily increased over the last few decades. The wind industry is experiencing a push towards the offshore market, where wind speeds are higher and steadier, and wind farms can be co-located with areas of high populations, such as along the US East Coast. However, high wind and wave loading is proving costly for offshore developments, particularly floating structures such as semi-submersibles. Vibrations in the pitch and heave directions associated with greater yaw-bearing and tower-base bending moments, respectively, reduce the lifespan of these structures. This paper compares traditional tuned-mass dampers (TMDs) and tuned-mass damper inerters (TMDIs) with a nonlinear TMDI which utilizes a mechanical motion rectifier (MMR) to translate bidirectional to unidirectional motion of the primary generator shaft. The integration of the MMR system also permits the generator to disconnect from the tuned-mass damper inerter system when the generator is already spinning at a higher rate, thus providing potential to harvest additional energy from the vibration absorber. However, results show that the optimal nonlinear tuned-mass damper inerters results in near total engagement, reducing the efficacy of the system if optimal parameters can be feasibly sourced. The technology does show promise for situations where these optimal parameters cannot be attained, such as due to high stroke lengths and extremely low stiffnesses to correspond to the low platform frequencies. The development and preliminary testing of a 1/50th scale tuned-mass damper inerter prototype will be discussed; however, the full MMR system has yet to be integrated into the prototype. / Master of Science / As a result of global warming, the prevalence of renewable energy sources such as wind farms has steadily increased over the last few decades. The wind industry is experiencing a push towards the offshore market, where wind speeds are higher and steadier, and wind farms can be co-located with areas of high populations, such as the US East Coast. However, the cost of implementing this technology has presented a major challenge in the development of these structures. This paper discusses the application of a recent technology, nonlinear tuned-mass damper inerters (TMDIs), to absorb the vibrations associated with wave excitations on floating offshore wind platforms while also allowing disengagement of a generator shaft as needed to maximize generator speed and thus maximize energy harvesting potential. Results show comparable performance between the nonlinear TMDI and its more-common common tuned-mass damper (TMD) and linear TMDI counterparts in terms of vibration reduction and power performance. The integration of nonlinearity into the system may be best suited for slightly in-optimal parameters that are selected due to feasibility of sourcing and internal size constraints. The development and preliminary testing of a 1/50th scale TMDI prototype will all be discussed; however, development of nonlinearity in the TMDI system has yet to be integrated into the prototype.