1,720,988 research outputs found
Optimisation of dynamic vibration absorbers to minimise kinetic energy and maximise internal power dissipation
No full textThe tuning of a dynamic vibration absorber is considered such that either the kinetic energy of the host structure is minimised or the power dissipation within the absorber is maximised. If the host structure is approximated as a lightly damped, single degree of freedom, system, simple expressions are obtained for the optimal ratio of the absorber natural frequency to the host natural frequency and optimal damping ratio of the absorber. These optimal values are shown to be the same whether the kinetic energy of the host structure is minimised or if the power dissipation of the absorber is maximise
Feedback control unit with an inerter proof-mass electrodynamic actuator
No full textIn this study the use of an inerter is considered for active vibration control of a structure excited by white noise. The structure is modelled as a single degree of freedom system and the control system consists of a vibration absorber with a mass suspended on a spring, a damper and an inerter. The absorber is equipped with a reactive force transducer in parallel with the passive suspension which is driven with a signal proportional to the velocity of the structure under control measured by an ideal collocated sensor. The effect of the inerter on the control stability and performance of the control system is investigated. It is shown that the effect of the inerter is to reduce the natural frequency of the inertial actuator, improving the stability of the feedback loop and thus its performance. The optimisation of the physical and control parameters of the control system such as the internal damping of the actuator, its natural frequency, its inertance and the feedback gain are considered such that either the kinetic energy of the host structure is minimised or the power dissipated by the control system is maximised
Semi–active multimodal vibration absorber
No full textThis paper presents three types of semi-active vibration absorbers, which are designed to control the response and sound radiation of a thin plate at low audio frequencies. Semi-active control systems are used to tune the absorbers to the resonance frequencies of the first three flexural natural modes of the plate where they are mounted. The first configuration consists of three axial tune mass dampers, which are properly adjusted and distributed on the plate so that each of them controls one of the first three flexural modes of the plate. The second configuration consists of a single axial switching tune mass damper that can switch to different states characterised by discrete values of the suspension stiffness and mechanical damping. At each state the parameters are set to control one of the first three flexural modes of the plate. Finally the third configuration consists of a single three-axis tune mass damper whose mass oscillates axially and rotates around two cross axis. This device is also located and tuned to control the first three flexural modes of the plate. The simulation study shows that the three axial tune mass dampers reduce the flexural kinetic energy of the plate by about 17 dB around the first three resonance frequencies and about 8 dB around the fourth and fifth resonance frequencies. Thus large control effects are produced in the low frequency range between 30 and 150 Hz. The single axial switching tune mass damper produces about 14 dB reductions around the first three resonances and 3 dB and 7 dB around the fourth and fifth resonances respectively. Finally the single three-axis tune mass damper generates about 21 dB reductions around the first three resonance frequencies and about 9 dB reductions around the fourth resonance frequency. Thus the proposed single axial and single three-axis tune mass dampers produce comparatively similar results as the three axial tune mass dampers with the same total mass. In particular it is shown that the best location for the single three-axis tune mass damper should be chosen either in the centre or inner centre of the polygon defined by the border of the plate. The control performance of the single three-axis tune mass damper has also been compared with that produced by an active velocity feedback loop using an inertial electromagnetic actuator with equivalent proof mass. The simulation study shows that the activesystem outperforms the single three-axis tune mass damper only around the first resonance frequency, where it produces 7 dB larger reduction of the flexural kinetic energy. However this result is obtained with large feedback control gains and at the expenses of low frequency control spillover. When a smaller and more realistic control gain is implemented, the control effects become comparable to that of a single three-axis tune mass damper
Self-tuning vibration absorbers
No full textThis thesis presents a theoretical and experimental study of self-tuning vibration control. Feedback design is often based on the assumption of time-invariance, which means that the controller has constant coefficients. Self-tuning control takes into account process changes in the response of the system under control by incorporating an adjusting mechanism which monitors the system, compares its status with the required one and adjusts the coefficients of the controller. In this thesis a self-tuning process is analysed for active and semi-active control of broadband vibration based on the maximisation of the power absorbed by the controller. The absorbed power can be locally estimated without using extra sensors to monitor the global response of the system under control. This is particularly advantageous in applications where many actuators are required, in which case each actuator and the collocated sensor can be treated as an independent self-tuneable unit. A theoretical analysis of vibration control using this approach is presented for lumped parameter systems and also for distributed systems, such as beam and panels. Different tuning strategies are compared in terms of the reduction of the global response of the system under control. An algorithm is then discussed that tunes the feedback gains of independent control units to maximise their individual absorbed powers. Experimental studies are then presented of a selftuning control system with two decentralised control units using velocity error signals and electromagnetic reactive actuators installed on an aluminium panel. In the second part of the thesis the analysis is extended to the use of inertial actuators. In this case the implementation of the self-tuning control based on the maximisation of the power absorbed is investigated using simulations of velocity feedback control and shunted inertial actuators
Multiple Sweeping Tuneable Vibration Absorbers for broad band vibration control
No full textThis paper presents a simulation study concerning the control of flexural vibration in a lightly damped thin plate, which is equipped with three sweeping TuneableVibration Absorbers and is excited by a rain on the roof broad frequency band stationary disturbance. The sweeping Tuneable Vibration Absorbers are semi-active mass-spring-dashpot systems whose stiffness and damping properties can be varied uniformly within given ranges. They are operated in such a way as their characteristic natural frequencies are continuously varied to control the observed flexural modes that resonate within given frequency bands. More specifically, in this study the three sweeping Tuneable Vibration Absorbers are operated asynchronously, each within one of three sequential frequency bands comprised between 20-120, 120-220, 220-320 Hz. The flexural vibration control effects produced by the three sweeping Tuneable Vibration Absorbers are compared to those produced by three classical Tuneable Vibration Absorbers, each set to control a flexural mode of the plate resonating in one of these three frequency bands. The study shows that the proposed sweeping Tuneable Vibration Absorbers outperform the classical Tuneable Vibration Absorbers and produce about 6, 5, 4 dB reduction of the panel flexural response in the three frequency bands of operation. Also, the study indicates that the sweeping Tuneable VibrationAbsorbers are robust to variations in the plate flexural response. For instance they still produce about 5.1, 5.3, 4.6 dB reductions of the panel flexural response in the three frequency bands of operation when the panel is tensioned such that the flexural natural frequencies are shifted up from about 40%, for the first resonance, to 7%, for the tenth resonanc
Vibration energy harvesting from an array of flexible stalks exposed to airflow: A theoretical study
No full textThis paper investigates the vibration energy harvesting of a system formed by an array of identical artificial flexible stalks connected by equal axial springs. The stalks are excited in bending by the propagating eddies produced by a mixing layer airflow at the top end of the canopy. The energy harvesting is localised in one pivotal stalk, which is equipped with a harvester. The paper first contrasts the spectra of the energy harvested by this system and by a classical system, formed by an equal array of mechanically uncoupled beams, which are all equipped with harvesters. Since the proposed system forms a periodic structure, this analysis considers variations of the stiffness of the harvesting stalk and of the connecting springs, which may lead to natural frequencies veering and mode localisation effects. Finally, the paper presents a parametric study that highlights how the bending stiffness of the harvesting stalk, the axial stiffness of the connecting springs and the energy absorption coefficient of the harvester influence the energy extraction. The study shows that, particularly in presence of strongly correlated drag force excitations produced on the stalks by the airflow, the energy harvested with the proposed system with a single harvester is comparable to that of a more complex and more expensive system formed by a whole array of harvesters
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