The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument, under development for the Subaru Telescope, has currently the fastest on-sky wavefront control loop, with a pyramid wavefront sensor running at 3.5 kHz. But even at that speed, we are still limited by low-frequency vibrations. The current main limitation was found to be vibrations attributed mainly to the rotation of the telescope. Using the fast wavefront sensors, cameras and accelerometers, we managed to identify the origin of most of the vibrations degrading our performance. Low-frequency vibrations are coming from the telescope drive in azimuth and elevation, as well as the elevation encoders when the target is at transit. Other vibrations were found at higher frequency coming from the image rotator inside Subaru's adaptive optics facility AO188. Different approaches are being implemented to take care of these issues. The PID control of the image rotator has been tuned to reduce their high-frequency contribution. We are working with the telescope team to tune the motor drives and reduce the impact of the elevation encoder. A Linear Quadratic Gaussian controller (LQG, or Kalman filter) is also being implemented inside SCExAO to control these vibrations. These solutions will not only improve significantly SCExAOs performance, but will also help all the other instruments on the Subaru Telescope, especially the ones behind A0188. Ultimately, this study will also help the development of the TMT, as these two telescopes share very similar drives.

The work described in this paper aims to test whether or not it is possible to power a system on energy harvested from vibrations and use that energy to measure how much it vibrates. The goal has been to produce a prototype system that uses that technique to discover damages on drones in an early stage. The reader will get to experience everything from design to testing of the system. The reader will also get an insight in which problems occurred during the project, how they have been handled and which conclusions have been made.The system could be applied in a variety of different situations to detect damages and which could prevent the damages from leading to severe problems. / Arbetet som beskrivs i denna rapport ämnar testa huruvida det är möjligt att driva ett system med alstrad energi från vibrationer och använda den energi för att mäta hur mycket det vibrerar. Målet har varit att ta fram ett prototypsystem som använder sig av tekniken för att upptäcka skador på drönare i ett tidigt stadie. Läsaren får uppleva allt från design av system till aktiva tester och får en inblick i vilka problem som uppstått under arbetet, hur de har bearbetats och vilka slutsatser som dragits.Systemet skulle kunna appliceras i många olika situationer för att upptäcka skador och skulle kunna förhindra att skadorna leder till allvarligare problem.

Condition based monitoring is today essential for any machine manufacturer tobe able to detect and predict faults in their machine fleet. This reduces the maintenancecost and also reduces machine downtime. In this master’s thesis twoapproaches are evaluated to detect long term vibration deviations also called vibrationanomalies in Siemens gas turbines of type SGT-800. The first is a simplerule-based approach where a series of CUSUM test are applied to several signalsin order to check if the an vibration anomaly has occurred. The secondapproach uses three common machine learning anomaly detection algorithm todetects these vibration anomalies. The machine learning algorithms evaluatedare k-means clustering , Isolation Forest and One-class SVM. This master’s thesisconclude that these vibration anomalies can be detected with these ML modelsbut also with the rule-based model with different levels of success. A set of featureswas also obtained that was the most important for detection of vibrationanomalies. This thesis also presents which of these models are the best suitedanomaly detection and would be the most appropriate for Siemens to implement.

The diploma thesis deals with the issue of bearings noisiness. The bearings noisiness appears as a negative phenomenon in all the mechanical devices that generate any kind of movement. Analysis of this phenomenon enables to analyse the technical condition of the bearing and predict its defects as well. The theoretical part of the thesis is devoted to the vibration diagnostics and noisiness diagnostics, which are deeply linked. The practical part of the thesis deals with the real problem of the bearing’s noisiness in the engineering company. The main asset of this thesis is a design and successful implementation of the measures, which reduce noisiness of the selected type of the bearing.

When a bluff body is placed in flow, vortices are shed downstream of the body. For the case of a bluff body with a circular cross-section (a cylinder) attached to a spring and a damper, when the frequency of vortex shedding is close to the natural frequency of the structure, the cylinder oscillates in a direction perpendicular to the flow. This is called Vortex Induced Vibration (VIV) and is a canonical problem in fluid-structure interactions. The majority of studies on VIV of a flexibly mounted rigid cylinder are for the cases where the flow direction is perpendicular to the long axis of the structure. However, in many engineering applications, such as cable stays in bridges, mooring lines of floating offshore wind turbines and undersea pipelines, the flow direction may not be perpendicular to the structure. The hypothesis is that the VIV in inclined cylinders is similar to a normal-incidence case, if only the component of the free stream velocity normal to the cylinder axis is considered. This is called the Independence Principle (IP). The IP neglects the effect of the axial component of the flow, which is legit for small angles of inclination, but not for large angles. In this Thesis, a series of experiments have been conducted on a flexibly-mounted rigid cylinder placed inclined to the oncoming flow with various angles of inclination (0° < θ < 75°) in a subcritical Reynolds number range of 500 – 4,000 to investigate how the angle of inclination affects VIV. In these experiments, a rigid cylinder was mounted on springs, and air bearings were used to reduce the structural damping of the system. The system was placed in the test section of a recirculating water tunnel and crossflow displacements were measured. Even at high angles of inclination, large-amplitude oscillations were observed. The IP was found to be valid for angles of inclination up to 55°. While for all inclinations the onset of lock-in was observed to be at the same normalized flow velocity, for angles of inclination larger than 55°, the lock-in region (the range of dimensionless flow velocities for which the cylinder oscillates with a large amplitude) was smaller. These results show that the influence of the axial component of the flow is non-negligible for angles of inclination larger than 55°.

The nonlinear nonplanar steady-state responses of cantilever beams to direct and parametric harmonic excitations are investigated using perturbation techniques. Modal interactions between the bending-bending and bending-bending-twisting motions are studied. Using a variational formulation, we obtained the governing equations of motion and associated boundary conditions for monoclinic composite and isotropic metallic inextensional beams. The method of multiple scales is applied either to the governing system of equations and associated boundary conditions or to the Lagrangian and virtual-work term to determine the modulation equations that govern the slow dynamics of the responses. These equations are shown to exhibit symmetry properties, reflecting the conservative nature of the beams in the absence of damping. It is popular to first discretize the partial-differential equations of motion and then apply a perturbation technique to the resulting ordinary-differential equations to determine the modulation equations. Due to the presence of quadratic as well as cubic nonlinearities in the governing system for the bending-bending-twisting oscillations of beams, it is shown that this approach leads to erroneous results. Furthermore, the symmetries are lost in the resulting equations. Nontrivial fixed points of the modulation equations correspond, generally, to periodic responses of the beams, whereas limit-cycle solutions of the modulation equations correspond to aperiodic responses of the beams. A pseudo-arclength scheme is used to determine the fixed points and their stability. In some cases, they are found to undergo Hopf bifurcations, which result in limit cycles. A combination of a long-time integration, a two-point boundary-value continuation scheme, and Floquet theory is used to determine in detail branches of periodic and chaotic solutions and assess their stability. The limit cycles undergo symmetry-breaking, cyclic-fold, and period-doubling bifurcations. The chaotic attractors undergo attractor-merging and boundary crises as well as explosive bifurcations. For certain cases, it is determined that the response of a beam to a high-frequency excitation is not necessarily a high-frequency low-amplitude oscillation. In fact, low-frequency high-amplitude components that dominate the responses may be activated by resonant and nonresonant mechanisms. In such cases, the overall oscillations of the beam may be significantly large and cannot be neglected. / Ph. D.

<p> Transverse vibrations of a beam with one end fixed and the other supported on nonlinear spring have been studied. Theoretical analysis has been carried out for two different cases of springs, viz.; cubic nonlinear and bilinear types. </p> <p> Theoretical results for bilinear case have been compared with those obtained experimentally. The effect of end mass has also been considered in theoretical analysis. </p> / Thesis / Master of Engineering (MEngr)

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A time-domain model-based crack diagnostic methodology using vibration data is presented. Most of the damage detection methods proposed to date are based on modal parameters and are limited by the loss of information caused by data reduction and by the implicit assumption of linearity. The use of time domain information permits the direct inclusion of the nonlinear behavior due to crack opening-closure cycles. In addition, very little information is lost, since no signal processing or parameter identification steps are involved. The proposed method is based on a continuous model for the transverse vibrations of beams consisting of partial differential equations of motion with varying coefficients to account for the presence of damage. In order to provide accurate representation of the structure's behavior over a broader frequency range, a new continuous cracked beam model including shear effects and rotatory inertia is developed using the Hu-Washizu-Barr variational method. The resulting equations of motion are discretized by a Galerkin method using local B-splines as test functions. The crack is assumed to be either fully open or fully closed, resulting in a bilinear system. The simultaneous identification of crack location and depth is performed by minimizing the norm of the differences between the numerical and experimental time responses to multiple excitations. Impact, low frequency sinusoidal and Schroeder--phased multisine inputs are investigated as potential excitation methods. The cost function to be minimized presents several local minima that are shown to be related to the length of the response records. A genetic algorithm is used to overcome the multimodal nature of the objective function. The methodology is validated through simulated identifications of several damage scenarios. The importance of the inclusion of the nonlinear behavior is addressed, and the effects of model uncertainties and measurement noise are quantified in terms of minimum identifiable crack size. / Ph. D.