Vibration control of the beam of the future linear collider

This paper proposes a new approach for beam stabilization of the future Compact LInear Collider (CLIC). The method attempts to increase the efficiency of traditional methods. It is composed of a hybrid adaptive filtering algorithm that uses both feedback and adaptive control. The scheme uses an estimate of the prediction error to update the adaptive filter's parameters. The strategy of this method is described considering the process environment. The method efficiency is evaluated, and it is demonstrated that it provides high damping, fast vibration suppression, good robustness and easy realization thanks to the simplicity of the computations

Cooling and sensing using whispering gallery mode resonators

This thesis reports on a detailed exploration of the optomechanical interaction between a tapered optical fibre and a silica microsphere mounted on a cantilever. The amount of light evanescently coupled from the fibre into the optical whispering gallery mode of the sphere is exquisitely sensitive to their separation allowing fast measurement of picometre displacements of both the microsphere-cantilever and the fibre. By exploiting this enhanced transduction, strong active feedback damping/cooling of the thermal motion of both the fibre and microsphere-cantilever have been demonstrated to the noise limit of the system. The cavity enhanced optical dipole force between the fibre and the sphere was used to damp multiple mechanical modes of the tapered fibre, while a piezo-stack at the clamped end of the microsphere-cantilever allowed for cooling of its centre-of-mass motion and the second mechanical eigenmode. The effect of noise within the feedback loop was shown to invert the measured mechanical mode spectrum at high feedback gain as the noise itself is fed into the resonator. A rich variety of feedback induced spring stiffening and softening of the mode is measured when time delays are introduced. Cooling of the mechanical modes of the taper, which are ubiquitous to many whispering gallery mode experiments and are considered as unwanted noise, has not been achieved previously. Simultaneous operation of both feedback schemes was demonstrated for the first time, providing stabilization of the system. By using the microsphere-cantilever as an inertial test mass, measurement of its displacement induced by acceleration can resolve micro-g accelerations at high bandwidth

Advanced Modelling of Helicopter Nonlinear Dynamics and Aerodynamics

The work presented here provides a comprehensive dynamic and aerodynamic helicopter model. The possible applications of this work are wide including, control systems applications, reference and trajectory tracking methods implementation amongst others. The model configuration corresponds to a Sikorsky helicopter; a main rotor in perpendicular combination with a tail rotor. Also, a particular model of unmanned aerial vehicle has been modelled as part of collaboration with the La Laguna University (Spain). The modelling tool is VehicleSim, a program that builds rigid body systems, solves the nonlinear equations of motion and generates the time histories of the corresponding state variables of the vehicle under study. VehicleSim is able to provide the linearised equations of motion in a Matlab file and the symbolic state-space model. This is useful when control systems are to be designed. The main rotor model accounts for flap, lag and feather motions for each blade as well as for their nonlinear dynamic coupling. The tail rotor is modelled including the flap-feather coupling via delta three angle. The main and tail rotors' angular velocities are implemented by PID controllers. Main rotor linear and nonlinear equations are derived and validated by comparison with the theory. Main rotor flap and lag degrees of freedom are validated using frequency domain approaches in the absence of external forces. Also, fuselage-main rotor interaction is studied and validated by using modal analysis and root locus methodology. Vibrations originated at the main rotor are simulated and their effects on the fuselage are examined by a Short Time Fourier transformation. The aerodynamic model uses blade element theory on the main-tail rotors. Hover, climb, descent and forward flight conditions are simulated and they allow the helicopter to follow certain trajectories. Finally, the ensuing vibrations when an external perturbation is applied to the main rotor are investigated