Combining shock and vibration isolation into a single isolation system package is explored through the use of an air spring in parallel with a controlled magnetorheological fluid damper. The benefits of combining shock and vibration isolation into a single package is discussed. Modeling and control issues are investigated and test and simulation results are discussed. It is shown that this hybrid isolation system provides significantly increased performance over current state-of-the-art passive systems. Also explored is the feasibility of scavenging and storing ambient shipboard vibration energy for use in powering the isolation system. To date the literature has not adequately explored the direct design of a combined shock and vibration isolation system. As shock and vibration isolation are typically conflicting goals, the traditional approach has been to design separate shock and vibration isolation systems and operate them in parallel. This approach invariably leads to compromises in terms of the performance of both systems. Additionally, while considerable research has been performed on magnetorheological fluids and devices based on these fluids, there has been little research performed on the use of these fluids in devices that are subjected to high velocities such as the velocity seen by a ship exposed to underwater near-miss explosive events. Also missing from the literature is any research involving the scavenging and storage of ambient shipboard vibration energy. While the focus of this work is on the use of this scavenged energy to power the subject isolation system, many other uses for this energy can be envisioned. Experimental and analytical results from this research clearly show the advantages of this hybrid isolation system. Drop tests show that inputs as great as 167 g's were reduced to 3.42 g's above mount at 1.11 inches of deflection using a Velocity Feedback controller suggested by the author. When contrasted with typical test results with similar inputs, the subject isolation system achieved reductions in above mount accelerations of 300% and reductions in mount deflections of 200% over current state-of-the-art passive shipboard isolation systems. Furthermore, simulations using a validated model of the isolation system suggest that this performance improvement can be achieved in multi-degree-of-freedom isolation systems as well. It was shown that above mount accelerations in the vertical and athwartship directions could be effectively limited to a predefined value, while achieving the absolute minimum mount defections, using an Acceleration Limiting Bang-Bang controller suggested by the author. Further experimentation suggests that the subject isolation system could be entirely self-powered from scavenged ambient shipboard vibration energy. An experiment using an energy scavenging and storage system consisting of a Piezoelectric Stack Generator and a bank of ultracapacitors showed that enough energy could be harvested to power the isolation system though several shock events. / Ph. D.

As a racecar negotiates a track, it is subjected to many inputs at both high and low frequencies. These inputs come from the track surface, the motion of the body, and from aerodynamic disturbances. The damper's ability to control these inputs leads to improved grip at the tires, which increases overall handling of the vehicle. Since dampers have always been assumed to be primarily velocity dependent, little work has gone into exploring damper's frequency dependent nature. Therefore, this study evaluates the effect input frequency has on the damper's output force. Utilizing experimental testing, with a state of the art damper dynamometer, and computer simulation with a parametric damper model developed for this study, several inputs and key parameters are tested, and the damper's frequency dependent nature starts to emerge. Constant peak velocity sinusoidal and sinusoidal sweep inputs are used for the experimental testing. The results show that as the input frequency is increased, the damper's output force lissajou transitions from the characteristic shape of a damper's lissajou to a shape characteristic of a spring's lissajou. This change in the lissajou is linked to hysteretic effects, which includes the gas spring effect. Damper parameters that are suspected to contribute to the hysteretic effects are explored with computer simulation and additional experimental testing. The results from this show that fluid preparation, fluid type, initial gas pressure, and friction have a predictable effect on the damper's output force. / Master of Science

The purpose of this research is to establish the effectiveness of tuned-mass-dampers (TMD) using semi-active magneto-rheological (MR) dampers to mitigate annoying floor vibrations. Annoying floor vibration is becoming more common in today's building structures since building materials have become stronger and lighter; the advent of computers has resulted in "paperless" offices; and the use of floors for rhythmic activities, such as aerobics and concerts, is more common. Analytical and experimental studies were conducted to provide an understanding of the effects of incorporating the semi-active-TMD as a remedy to annoying floor vibration. A pendulum tuned mass damper (PTMD) in which the tuning parameters could independently be varied was used. Closed form solutions for the response of the floor using passive dampers were developed. In addition, a numerical integration technique was used to solve the equations of motion where semi-active dampers are utilized. The optimum design parameters of PTMDs using passive and semi-active dampers were found using an optimization routine. Performances of the PTMD in reducing the floor vibration level at the optimum and when subjected to off-tuning of design parameters using passive and semi-active dampers were compared. To validate the results obtained in the analytical investigation, an experimental study was conducted using an 8 ft x 30 ft laboratory floor and a commercial PTMD. Comparative studies of the effectiveness of the PTMD in reducing floor vibrations using semi-active and passive dampers were conducted. / Master of Science

A device was developed to directly measure skin friction on an external test plate in transonic flight conditions. The tests would take place on the FTF-II flight test plate mounted underneath a NASA F-15 aircraft flying at altitudes ranging from 15,000 to 45,000 ft. at Mach numbers ranging from 0.70 to 0.99. These conditions lead to predicted shear levels ranging from 0.3 to 1.5 psf. The gage consisted of a floating element cantilevered beam configuration that was mounted into the surface of the test plate in a manner non-intrusive to the flow it was measuring. Strain gages mounted at the base of the beam measured the small strains that were generated from the shear forces of the flow. A non-nulling configuration was designed such that the deflection of the floating head due to the shear force from the flow was negligible. Due to the large vibration levels of up to 8 grms that the gage would experience during transonic flight, a vibration damping mechanism needed to be implemented. Viscous damping had been used in previous attempts to passively dampen the vibrations of skin friction gages in other applications, yet viscous damping proved to be an undesirable solution due to its leakage problems and maintenance issues. Three methods of damping the gage without a fluid filled damper were tested. Each gage was built of aluminum in order to maintain constant material properties with the test plate. The first prototype used a small internal gap and damping properties of air to reduce the vibration levels. This damping method proved to be too weak. The second prototype utilized eddy current damping from permanent magnets to dampen the motion of the gage. This mechanism provided better damping then the first prototype, yet greater damping was desired. The third method utilized eddy current damping from an electromagnet to dampen the motion of the gage. The eddy current damper achieved a much larger reduction in the vibration characteristics of the gage than the previous designs. In addition, the gage was capable of operating at various levels of damping. A maximum peak amplitude reduction of 33 % was calculated, which was less than theoretical predictions. The damping results from the electromagnetic gage provided an adequate level of damping for wind tunnel tests, yet increased levels of damping need to be pursued to improve the skin friction measurement capabilities of these gages in environments with extremely high levels of vibration. The damping provided by the electromagnet decreased the deflections of the head during 8 grms and 2 grms random noise vibrations bench tests. This allowed for a greater survivability of the gage. In addition, the reduction of the peak amplitude provided output with vibration induced noise levels ranging from 24 % to 5.9 % of the desired output of the gage. The gage was tested in a supersonic wind tunnel at shear levels of tw=3.9 to 5.3 psf. The shear levels encountered during wind tunnel verification tests were slightly larger than the shear levels encountered on the F-15 flight test plate during the flight tests, but the wind tunnel shear levels were considered adequate for verification purposes. The experimentally determined shear level results compared well with theoretical calculations / Master of Science

Esta dissertação propõe uma solução padronizada de aplicação de Tuned-Mass Damper (TMD) para controle de vibrações em lajes baseada na análise das características de carregamentos associados à utilização humana e nas características estruturais mais comuns à engenharia contemporânea. De modo a simplificar sua aplicação técnica, a sintonização é proposta por meio da escolha de componentes pré-determinados para a montagem do TMD e pela distribuição e posicionamento dos mecanismos. A eficácia do sistema é então verificada em um estudo de caso, usando um modelo de elementos finitos de uma laje, antes e depois da aplicação dos mecanismos. / This thesis proposes a standardized solution for the application of Tuned-Mass Dampers to the control of floor vibrations based on the characteristics of the acting loads associated to human usage and the characteristics of the most common structures of the contemporary engineering practice. In order to simplify its usage by the technical community, the tuning is proposed through the selection of pre-determined components for the assembly of the TMD and the choice of disposition and spacing of the mechanisms. The system efficacy is then verified in a computational case study, by means of a finite-element model of a floor, before and after the application of the mechanisms.

Capturing what is going on and what may happen related to vehicle handling behaviour in cases of desired or non-desired actions and interventions has a crucial importance. Strategies implemented to improve vehicle stability or algorithms and control modules designed to compensate the non-desired effects on handling behavior may appear to be inadequate as the vehicle goes through uncountable experiences. The importance of understanding and introducing the possible sources of undesired effects which may be encountered throughout driving action cannot be underemphasized. One of the possibilities that may lead the driver face with unexpected results concerning vehicle&rsquo / s handling is suspension damper failure, which has not yet been dealt with adequately in the literature. The fast developing technology and consequently the expanding utilization of chassis electronics and electronic vehicle components make the investigation of damper failure phenomenon essential since reliability decreases by the continuously increasing introduction of electronic means. In this study, possible failure types of dampers including electrical failure are taken into account, their effects on vehicle stability under critical driving conditions are examined. Shortcomings and comments are made on criticality of failed damper and its failure point. This work as a result, constitutes a particular contribution to the literature in that it brings up a concrete knowledge to the stated research area.

No description available.

Esta dissertação propõe uma solução padronizada de aplicação de Tuned-Mass Damper (TMD) para controle de vibrações em lajes baseada na análise das características de carregamentos associados à utilização humana e nas características estruturais mais comuns à engenharia contemporânea. De modo a simplificar sua aplicação técnica, a sintonização é proposta por meio da escolha de componentes pré-determinados para a montagem do TMD e pela distribuição e posicionamento dos mecanismos. A eficácia do sistema é então verificada em um estudo de caso, usando um modelo de elementos finitos de uma laje, antes e depois da aplicação dos mecanismos. / This thesis proposes a standardized solution for the application of Tuned-Mass Dampers to the control of floor vibrations based on the characteristics of the acting loads associated to human usage and the characteristics of the most common structures of the contemporary engineering practice. In order to simplify its usage by the technical community, the tuning is proposed through the selection of pre-determined components for the assembly of the TMD and the choice of disposition and spacing of the mechanisms. The system efficacy is then verified in a computational case study, by means of a finite-element model of a floor, before and after the application of the mechanisms.

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.

Vehicle Suspension is an important sub-system in an automobile as it is directly related to the subjective qualities of ride comfort that the passengers perceive. A vehicle suspension works by insulating the driver and the passengers from the irregularities of the road. Moreover, a suspension is required to ensure the tires properly contact the surface for adequate traction. This study aims to analyze whether a damper that is made out of two individual dampers joined together can be used to provide better ride comfort and better road handling with appropriate control strategies and if this damper can work more effectively than a single semi-active damper / Master of Science / A car's suspension is crucial for a smooth ride and passenger comfort, as it absorbs bumps and keeps your tires in contact with the road. This research looks at a new type of shock absorber made of two connected parts to see if it improves ride comfort and handling compared to the traditional single shock absorber. We'll explore how this new design, along with smart control methods, might make driver and passenger comfort better.