The optical power of satellites such as the Hubble telescope is directly related to the size of the primary mirror. However, due to the limited capacity of the shuttle bay, progress towards the development of more powerful satellites using traditional construction methods has come to a standstill. Therefore, to allow larger satellites to be launched into space significant interest has been shown in the development of ultra large inflatable structures that can be packaged inside the shuttle bay and then deployed once in space. To facilitate the packaging of the inflated device in its launch configuration, most structures utilize a thin film membrane as the optical or antenna surface. Once the inflated structure is deployed in space, it is subject to vibrations induced mechanically by guidance systems and space debris as well as thermally induced vibrations from variable amounts of direct sunlight. For the optimal performance of the satellite, it is crucial that the vibration of the membrane be quickly suppressed. However, due to the extremely flexible nature of the membrane structure, few actuation methods exist that avoid local deformation and surface aberrations. One potential method of applying damping to the membrane structure is to use magnetic damping. Magnetic dampers function through the eddy currents that are generated in a conductive material that experiences a time varying magnetic field. However, following the generation of these currents, the internal resistance of the conductor causes them to dissipate into heat. Because a portion of the moving conductor's kinetic energy is used to generate the eddy currents, which are then dissipated, a damping effect occurs. This damping force can be described as a viscous force due to the dependence on the velocity of the conductor. While eddy currents form an effective method of applying damping, they have normally been used for magnetic braking applications. Furthermore, the dampers that have been designed for vibration suppression have typically been ineffective at suppressing structural vibration, incompatible with practical systems, and cumbersome to the structure resulting in significant mass loading and changes to the dynamic response. To alleviate these issues, three previously unrealized damping mechanisms that function through eddy currents have been developed, modeled and tested. The dampers do not contact the structure, thus, allowing them to add damping to the system without inducing the mass loading and added stiffness that are typically common with other forms of damping. The first damping concept is completely passive and functions solely due to the conductor's motion in a static magnetic field. The second damping system is semi-active and improves the passive damper by allowing the magnet's position to be actively controlled, thus, maximizing the magnet's velocity relative to the beam and enhancing the damping force. The final system is completely active using an electromagnet, through which the current can be actively modified to induce a time changing magnetic flux on the structure and a damping effect. The three innovative damping mechanisms that have resulted from this research apply control forces to the structure without contacting it, which cannot be done by any other passive vibration control system. Furthermore, the non-contact nature of these dampers makes them compatible with the flexible membranes needed to advance the performance of optical satellites. / Ph. D.

A Magnetorheological damper is a commonly used component in semi-active suspensions that achieves a high force capacity and better performance than a passive system, without the added expense and power draw of a fully active system, all while maintaining failsafe performance. To fully exploit the capabilities of an MR Damper, a high fidelity controller is required that is simple and easy to implement, yet does not compromise the accuracy or precision needed in many high-performance applications. There is a growing need for this level of operation, and this proposed work addresses these requirements by creating an empirically derived invertible model that enables the development of more accurate command signals by capturing the effect of temperature on a MR Damper's performance capabilities. Furthermore, this solution is specifically tailored for real-time application and does not require force feedback. Thus it requires low computation power and minimizes end-user cost by eliminating the need for additional high cost sensors such as load cells. A notable observation that resulted from the development of this proposed model was the difference in behavior between on and off states. Additionally a unique behavior was recognized with respect to the transition between high speed and low speed damping. For validation, the proposed model was compared against experimental data as well as an industry standard Spencer model; it produced excellent results in both cases with minimal error. / Master of Science

Auxiliary absorbers provide an effective means to attenuate the vibrations of a structural or mechanical system (the "primary structure"). The simplest auxiliary absorber, a tuned mass damper (TMD), provides reliable narrow-band attenuation but is not robust to the effects of detuning. Strongly nonlinear tuned mass dampers (NTMDs) are capable of wide-band, irreversible energy transfer known as "energy pumping" but can also exhibit high amplitude solutions which significantly amplify the response of the primary structure. Semi-active tuned mass dampers (STMDs) incorporate an actuating element in order to achieve real-time tuning adjustment capability. This thesis presents a global dynamic analysis of the response of a primary structure with an NTMD and then explores the performance of a novel absorber configuration consisting of an NTMD and STMD attached to the primary structure in series. The global dynamic analysis is conducted using a new cell mapping method developed by the author and introduced within the thesis: the parallelized multi-degrees-of-freedom cell mapping (PMDCM) method. The benefits of the additional STMD component are explored for two distinct applications: (1) restoring the performance of a linear TMD which develops a weak nonlinearity due to operation outside of the intended range or other means, and (2) acting as a safety device to eliminate or minimize convergence to the detached high-amplitude response. In the weakly nonlinear case, the STMD is shown to reduce the effects of the nonlinearity and improve attenuation capability by constraining the motion of the NTMD. In the strongly nonlinear case, the STMD effectively eliminates the complex response behavior and high amplitude solutions which were present in the original system, resulting in a single low amplitude response. Experimental tests using an adjustable-length pendulum STMD verify the numerical results.

Cette thèse est consacrée à l'étude d'amortisseurs passifs non linéaires innovants pour le contrôle de l'instabilité de flottement sur un profil d'aile à deux degrés de libertés. Lorsqu'un profil d'aile entre en flottement, il oscille de façon croissante jusqu'à se stabiliser sur un cycle limite dont l'amplitude peut être significative et détériorer sa structure. Le contrôle a ainsi deux objectifs principaux : retarder l'apparition de l'instabilité et réduire l'amplitude des cycles limites. Avant d'étudier l'influence des amortisseurs passifs, l'instabilité de flottement, et notamment le régime post-flottement, a été étudié. Une expérience de flottement sur une plaque plane a été menée et sa modélisation, prenant en compte le phénomène de décrochage dynamique, a été réalisée. Concernant le contrôle passif, le premier type d'amortisseur étudié est un amortisseur hystérétique réalisé à l'aide de ressorts en alliage à mémoire de forme. La caractéristique principale de tels amortisseurs est que leur force de rappel étant hystérétique, elle permet de dissiper une grande quantité d'énergie. L'objectif principal est ainsi de réduire l'amplitude des cycles limites provoqués par l'instabilité de flottement. Cet effet escompté a été observé et quantifié expérimentalement et numériquement à l'aide de modèles semi-empiriques. Le second type d'amortisseur utilisé est un amortisseur non linéaire de vibration accordé. Il est composé d'une petite masse connectée au profil d'aile à l'aide d'un ressort possédant une raideur linéaire et une raideur cubique. La partie linéaire de ce type d'amortisseur permet de retarder l'apparition de l'instabilité tandis que la partie non linéaire permet de réduire l'amplitude des cycles limites. L'influence de l'amortisseur non linéaire de vibration accordé a été étudiée analytiquement et numériquement. Il a été trouvé que l'apparition de l'instabilité est significativement retardée à l'aide de cet amortisseur, l'effet sur l'amplitude des cycles limites étant plus modeste. / The aim of this thesis is to study the effect of passive nonlinear absorbers on the two degrees of freedom airfoil flutter. When an airfoil is subject to flutter instability, it oscillates increasingly until stabilizing on a limit cycle, the amplitude of which can be possibly substantial and thus damage the airfoil structure. The control has two main objectives : delay the instability and decrease the limit cycle amplitude. The flutter instability, and the post-flutter regime in particular, were studied first. A flutter experiment on a flat plate airfoil was conducted and the airfoil behavior was modeled, taking into account dynamic stall. Regarding the passive control, the first absorber studied was a hysteretic damper, realized using shape memory alloys springs. The characteristic of such dampers is their hysteretic restoring force, allowing them to dissipate a large amount of energy. Their main goal was thus to decrease the limit cycle amplitude caused by the flutter instability. This expected effect was observed and quantified both experimentally and numerically, using heuristic model. The second absorber studied was a nonlinear tuned vibration absorber. This absorber consists of a light mass attached to the airfoil through a spring having both a linear and a cubic stiffness. The role of the linear part of such absorber was to repel the instability threshold, while the aim of the nonlinear part was to decrease the limit cycle amplitude. It was found, analytically and numerically, that the instability threshold is substantially shifted by this absorber, whereas the limit cycle amplitude decrease is relatively modest.

Semi-active suspension systems promise to significantly reduce the necessary trade-off be-tween handling and passenger comfort present in conventional suspension systems by enabling active chassis and wheel control. Öhlins Racing AB have developed a semi-active suspension technology known as CES, Continuously controlled Electronic Suspension, based on solenoid control valves which are integrated into specially designed hydraulic dampers, and are currently developing control and estimation systems which will enable their application in advanced motorcycle suspensions. In these systems an important aspect is being able to accurately control the forces produced. Öhlins’ current system uses an open loop control strategy in which currents sent through the solenoid valves, to achieve the requested damping force under the prevailing circumstances, is calculated using experimentally derived static lookup tables. In this thesis a new closed loop control system, based on the direct measurement of the damper force, is developed and its performance is evaluated in comparison to the old one’s. Sufficient understanding of the system requires extensive modeling and therefore two different models have been developed; a simpler one used for model based control design and a more extensive, high fidelity model used for high accuracy simulations. The developed simulation model is the first of its kind that is able to capture the studied systems behavior with satisfactory accuracy, as demonstrated against real dynamometer measurements. The valves and damper behave in a highly non linear manner and the final controller design uses a combination of exact linearization, non linear state estimation, dynamical inversion and classical control theory. Simulation results indicate that the new controller reduces the root mean square force tracking error to about 63% of that of the existing controller in the evaluation scenarios used. Cascaded within the system is also closed loop current controllers. A developed model based controller is shown to reduce the rise time to less than 30% of that of the existing PID-controllers, reduce the overshoot and provide online estimates of the winding series resistance, providing the basis for future solenoid diagnosis and temperature tracking systems.

In recent years, due to a need to reduce emissions, the automotive industry has focused on increasing vehicle efficiency. One of the areas being examined for potential improvement is the automatic transmission; specifically, the torque converter clutch damper. The better the performance of the damper, the more time the torque converter can be kept in the optimum locked position, thus increasing vehicle efficiency. Currently a large number of vehicle manufacturers use transmission technology sourced from external OEMs; due to a lack of available performance data or validated simulations, sometimes vehicle manufacturers are not able to fully understand the behaviour of the damper. If damper performance (or interactions with other components) cannot be fully assessed during the design development phase, key issues may become known too late in the development process. Thus a deeper understanding of the processes of experimentally characterising and simulating torque converter dampers is required. This thesis describes the development of an arc spring torque converter damper simulation, including the gathering of the experimental data required to validate the simulation. The simulation is used to draw conclusions on the impact of excitation signal form on damper behaviour, leading to new knowledge on the signals required to experimentally characterise a damper. In this thesis a methodology for (and implementation of) the characterisation of torque converter dampers is detailed. It was found that existing available technologies (e.g. fired engines, electric dynamometers) were either too inflexible or prohibitively expensive; thus a novel high frequency mechanical pulsation generator was developed. This solution was developed from a 4 cylinder motored diesel engine; the cylinders are filled with compressed air and the crankshaft driven using an electric dynamometer. Simulation and experimental data has confirmed that mean torque can be controlled using the input dynamometer, with the compressed air producing fluctuations of up to 900Nm amplitude. However, it was found that the frequency of the output pulsations varied from a fired engine; this is due to reactions between the pulsation generator and the stiffness and inertias of other components on the rig. A review of the performance of the novel pulsation generation concept against other damper excitation methods was also conducted. It was determined that fired engines and electric motors are more suitable for durability testing; the flexibility of the electric motors and the low running costs of the pulsation generator suit damper performance tests. The second phase of this project was to develop a simulation of a two-stage arc spring turbine damper. This damper consists of three inertias, separated by two spring sets; the outer spring set has 3 individual arc springs, while the inner spring set has 5 nested pairs. The principle of conservation of angular momentum is applied to each of the three inertias in order to calculate their individual accelerations. This method is also applied when calculating the acceleration and movement of the springs; the arc springs are discretised into mass and (massless) spring segments. Two features not previously seen in literature are included in the simulation; hardstops and nested springs. The physical hardstops limit the movement of the spring sets (relative movements of the inertias). In this study, the nested springs were simulated as a pair of parallel springs, rather than as a single stiffer arc spring; this is due to the friction that occurs between the springs (the inner race of the larger spring forms the housing for the inner spring). These two features highlight the need for hardware examination before simulation development; disassembling the hardware also allows the location of hardstops (and other features) to be measured rather than relying on the test data. Once a damper simulation was designed, a methodology for simulation parameterisation was required; parameterisation is the process of improving simulation performance through iterations of estimated parameters. The simulated damper was excited using sampled experimental data; to maximise parameterisation process efficiency, each time a parameter change was made, a set of key test points were selected in order to assess simulation performance change. It is not recommended that single test points be examined individually; parameter changes may improve simulation performance at one test point but have an adverse reaction at another. A clear causal relationship between simulation timestep and accuracy (as well as simulation run time) was found; a link between the number of discretised segments and simulation accuracy (and run time) was also confirmed. It was determined that 8 segments was optimal for the inner springs and 18 outer segments offered the best balance between computing power and simulation time. A variety of methods for analysing damper (and simulation) performance are presented in this thesis; it was found that for the 2.5 bar torque curve experimental data set the simulation performs excellently, with on average less than 5% error. Overall torque error is less than 10% across the tested speed range (900 to 2800rpm), with mean torque differences between simulated and tested order magnitudes of less than 5Nm. It has been determined that hysteresis loops are not an accurate predictor of real-world damper performance; while they can approximate general trends, they do not cover the normal operating condition. In the final phase of this thesis, the validated simulation has been used to investigate excitation signal, areas of poor damper performance and the link between speed and damper stiffness. By subjecting the simulation to a variety of sinusoidal input signals, it was established that if a sinusoidal signal approximates the 3 most dominant frequencies in a real signal, the damper will behave in a representative manner. Additional orders that have lower frequencies than the dominant order will have a greater impact on the attenuation behaviour of the damper; the effect of additional orders on attenuation behaviour is also linked to their magnitude (relative to the dominant order). A methodology for efficient damper mapping is proposed; the key aim is to produce a dataset that will minimise the length of the parameterisation process while capturing key damper behaviours. It was found that the magnitude of the torque oscillations used to excite the damper is linked to parameter adjustment impact, though this relationship is not linear for all parameters; an approximate level of 300Nm should be used for excitation. Parameters such as spring stiffness and plate inertias are more likely to have a substantial impact on damper performance at frequencies below 70Hz; friction tuning factors are impacted more by magnitude changes at frequencies above 150Hz. It has been demonstrated that while speed can have an effect on magnification ratio, this effect is far less significant at mean torques above the knee point and when sinusoidal input magnitude is kept at or above 300Nm. It was concluded that neither engine speed nor precise excitation magnitude must be replicated in order to predict approximate performance. During the investigation into areas of poor damper performance, it was confirmed that the trend of increasing magnification ratio with lower frequencies ( < 30Hz) seen in experimental data continued. Simulation testing above 140Hz revealed that there is not a linear relationship between increased frequency and increased magnification ratio; these areas of magnification ratio spikes are likely due to system resonances. It has been confirmed that while fluctuation magnitude does impact magnification ratio, fluctuation frequency has the most significant (dominant) impact. Finally, the effect of speed on apparent damper stiffness was investigated for both hysteresis loop testing and across a range of outer spring vibration angles; it was confirmed that increasing speed does result in non-homogeneous compression of the springs. It was established that while speed can have an effect on spring stiffness, this effect will vary significantly depending on the movement range (vibration angle) of the spring. / The largest increase in spring stiffness with speed is seen when segments of the spring become inactive (cease to move), hence why the effect of speed is more substantial at vibration angle of < 10°. The simulation was used to confirm the theories linking speed and stiffness found in the literature; higher speeds increase frictional forces, slowing damper segments, resulting in reduced movement. The findings of this thesis are relevant to damper simulation and testing engineers; by expanding knowledge of damper behavioural responses to high frequency excitation signals, as well as demonstrating an effective method for producing validated damper simulations, it is hoped that the vehicle design process will be more efficient and damper modifications more effective.

System identification (SI) for constructed structural systems has received a lot of attention with the continuous development of modern technologies. This thesis proposes a new nonlinear time series model for use in system identification (SI) of smart structures. The proposed model is implemented by the integration of a wavelet transform (WT) and nonlinear autoregressive moving average (NARMA) time series model. The approach demonstrates the efficient and accurate nonlinear SI of smart structures subjected to both ambient excitation and high impact load. To demonstrate the effectiveness of the wavelet-based NARMA modeling (WNARMA), smart structures equipped with magnetorheological (MR) dampers are investigated. The simulation results show that the computation of the WNARMA model is faster than that of the NARMA model without sacrificing the modeling accuracy. In addition, the WNARMA model is robust against noise in the data since it inherently has a denoising capacity.

Magneto-rheological damper is a nonlinear system. In this case study, system has been identified using Neural Network tool. Optimization between number of neurons in the hidden layer and number of epochs has been achieved and discussed by using multilayer perceptron Neural Network.

In the field of electric machine design, a trend in many applications has been to design machines with increasing torque density. When machines fail to meet torque density requirements or are simply incapable of matching load torque, gears are commonly used. Magnetic gears have been proposed as a means of increasing torque density within electromechanical systems, while avoiding problems associated with traditional mechanical gears. While the idea behind magnetic gears goes back to early patents, their study and use in industry has been very limited to date. This study looks into variations of the gear which could lead to more industrial use. The effect of pole count upon torque ripple is investigated with finite element analysis (FEA). The analysis is extended to new magnetic layouts which borrow from permanent magnet machine design. One of the most critical components of the gear, the stator pole pieces, are also investigated for variations which aid in construction while maintaining the performance of the gear. As a means of supplementing analysis of the gear, winding function theory (WFT) is used to analyze the gear. Winding function theory has enjoyed success with induction, synchronous, and even switched reluctance machines in the past. This study is the first of its kind to apply winding function theory to a device devoid of windings altogether. It is shown that this method is capable of generating the stall torque and steady-state torque ripple waveforms which have been commonly attempted with FEA. While magnetic gears enjoy distinct advantages over mechanical gears such as inherent overload protection, they are not as torsionally stiff as their mechanical counterparts. As such, the use of damper windings for the purpose of stiffening the gear against transient oscillations is also investigated. Several competing designs are investigated for their performance, and a final design is studied which is capable of arresting transient oscillations in less than a second. In addition, a prototype has been fabricated and will be used to verify the analysis undertaken. The prototype is used to verify variations of the stator pole pieces as well as the inner rotor magnetic layout. A dynamometer has been assembled to test the performance of the prototype. A new design is also proposed for future work.

Changes in the characteristics of the structure, such as damage, have not been considered in most of the active and semi-active control methods that have been used to control and optimize the response of civil engineering structures. In this dissertation, a direct adaptive control which can deal with the existence of measurement errors and changes in structural characteristics or load conditioning is used to control the performance of structures. A Simple Adaptive Control Method (SACM) is modified to control civil structures and improve their performance. The effectiveness of the SACM is verified by several numerical examples. The SACM is used to reduce the structural response such as drift and acceleration using active and semi-active devices, and its performance is compared with that of other control methods. Also, a probabilistic indirect adaptive control method is developed and its behavior is compared to the SACM using a simple numerical example. In addition to the simplicity of the SACM implementation, the results show that SACM is very effective to reduce the response of structures with linear and non-linear behavior in comparison with other control methods.