1,720,972 research outputs found
An adaptive electrodynamic metamaterial for the absorption of structural vibration
No full textThis paper presents an adaptive shunted electrodynamic metamaterial, for broadband robust vibration control. The study considers a unit cell of 12 miniature, low-cost proof-mass actuators for the control of vibration in a three degree-of-freedom structure subject to parametric uncertainty. In order to modify their dynamic responses, each actuator is connected to a shunt circuit consisting of a parallel resistor and a switched in/out inductor and capacitor. Provided the impedance of the actuator is cancelled out using a negative impedance, the shunt circuit is capable of tuning the resonance of the actuator up or down in frequency. An adaptive tuning approach is proposed, whereby the shunted actuator resonance frequencies are periodically switched to the centre frequencies of the highest magnitude bins of a real-time frequency analysis of the velocity measured on the structure. This approach is compared to a blind swept tuning method and a fixed-shunt tuning in terms of the robustness to parametric uncertainty, and in practical terms for realisation using analogue or digital shunt impedances
Metamaterials for robust vibration control.
No full textAs structures become thinner and lighter to conserve materials, they become more compliant and prone to vibration. These structures may also not be able to support a traditional vibration control system with concentrated control forces. Elastic metamaterials (EMMs) consist of distributed resonators, small compared to the wavelength of vibration, and offer a potential solution. Such metamaterials also offer an opportunity to control vibration in the presence of uncertainty, by distributing the resonator tuning frequencies. This thesis investigates the use of EMMs for robust vibration control.In the first instance, different optimisation algorithms are investigated for the tuning of an EMM for the robust control of vibration. A particle swarm optimisation (PSO) is shown to achieve similar performance compared to both a more complex genetic algorithm (GA) and a hybrid genetic algorithm (HGA). To be able to realise an EMM with variously tuned resonators, a concept resonator is proposed, which utilises multi-material 3D inkjet printing. The dynamic response of the novel resonator design is characterised experimentally, and an EMM utilising the resonator is optimised using a PSO. The optimised EMM is validated experimentally, and it is shown that in the presence of structural uncertainty, the robustly optimised EMM outperforms a design optimised based on a nominal structure alone. A semi-active approach to EMM design is also investigated, where an impedance connected across the terminals of an electrodynamic transducer, known as shunting, is used to tune the resonance frequency and damping. An electrodynamic metamaterial (EDMM) is proposed, consisting of shunted mass-produced electrodynamic proof-mass transducers. Series resistive and inductive (RL) shunt impedances are optimised for the absorption of vibration in the presence of both structural uncertainties and realistic uncertainties in the actuators. The simulation study demonstrates the limitations of the design due to the potential for instability and the wide range of uncertainty in the transducer's electrical parameters. An adaptive tuning algorithm is also proposed, in which an array of shunted actuators are tuned to the frequencies corresponding to the highest magnitude components of a real-time frequency analysis of the structural dynamics. Using a parallel resistive-inductive-capacitative (RLC) shunt, this approach is shown to achieve greater robustness to structural uncertainties compared to a fixed tuning and a swept tuning approach, where the resonance frequency is continuously swept between bounds. <br/
Designing a tuned-shunt electrodynamic metamaterial in the presence of uncertainties
No full textResonant structural vibrations are a common source of disruptive noise, and suppressing these vibrations is often the most direct way to reduce the noise levels. Elastic metamaterials (EMMs) consist of distributed resonant substructures, at a scale which is small compared to the wavelength of vibration. This allows these materials to be used in applications where space is limited, and more traditional vibration suppression techniques would be impractical. Tuned resonators can be designed through selection of geometry or material properties, but an alternative approach, which requires significantly less prototyping, is through the use of shunted electrodynamic inertial actuators. In this paper, a novel electrodynamic metamaterial (EDMM) is proposed consisting of an array of mass-produced inertial actuators, each connected to a tuned shunt impedance. It is considered impractical to measure the dynamic and electrical parameters of a large number of actuators, and so the effect of uncertainties in the actuators is investigated on both the performance and the stability of the EDMM.</p
Integration of active control with a compound acoustic black hole
No full textAcoustic Black Holes (ABHs) achieve high levels of vibration control with low or negative weight requirements depending on the designed configuration. ABHs are generally realised by introducing a reducing thickness profile into a structure, which reduces the flexural wave speed, decreases the wavelength of vibration and, therefore, enhances the functional performance of damping treatment applied to the ABH. The control bandwidth of ABHs is limited by the taper length and various measures to increase the low frequency performance have been explored, including the integration of active control. Another practical limiting factor for ABHs is their susceptibility to damage due to the potential for high strain in the taper. Various design modifications have been proposed to improve the ABH strength whilst maintaining control performance, including the compound ABH. This paper will investigate the integration of active control into a compound ABH, proposing possible design configurations and exploring the potential performance
A robust optimised shunted electrodynamic metamaterial for multi-mode vibration control
No full textThis paper presents a design approach for a shunted electrodynamic metamaterial (EDMM) for broadband robust vibration control. A unit cell of 12 inertial electrodynamic transducers is proposed, where the response of each transducer is tuneable via a connected resistive and inductive shunt circuit. The variations in the parameters of an off-the-shelf transducer are characterised experimentally, before the effect of this variation on the shunted response is investigated. It is shown that instability of the system is a limiting design factor. A problem is proposed whereby the resistive and inductive shunt values of an EDMM attached to a parametrically uncertain structure are to be found, and given the complexity of the design problem, a Particle Swarm Optimisation (PSO) is utilised to find a solution using an analytical model of the system. The results of the optimisation show that the effects of uncertainty in the actuators must be included, otherwise, the solution can be unstable. However, it is also shown that it is sufficient to ignore the uncertainty in the structure and optimise the EDMM considering actuator uncertainty alone, since the EDMM motion is then highly damped and, therefore, inherently robust to structural uncertainties
Metaheuristic optimisation of an elastic metamaterial for robust vibration control
No full textParametric uncertainty in a structure can reduce modelling accuracy, leading to a reduction in the efficacy of a vibration suppression system. The suppression of modal vibration with robustness to parametric uncertainty has been demonstrated using multiple tuned-vibration-absorbers (TVAs) with distributed resonance frequencies. In this paper, an Elastic Metamaterial (EMM) unit cell consisting of multiple single-degree-of-freedom resonators is defined for the absorption of vibration in a cantilever beam. A genetic algorithm (GA), hybrid genetic algorithm (HGA) and particle swarm optimisation (PSO) are compared in their ability to optimise the resonance frequencies of the unit cell to minimise the mean kinetic energy gain of the EMM, on a beam with parametric variation. Firstly, all optimisation procedures are able to produce an EMM unit cell with good robustness to parametric uncertainty. When the optimisations are run until convergence, the PSO is shown to achieve the best fitness value, but with an increase in computation time compared to the GA. The HGA achieves a better fitness value than the GA but computation time is inflated by a factor greater than 50. By also running until a time constraint is met, it is shown that the GA and PSO perform similarly for the same time-limit
Design of a resonator-based metamaterial for broadband control of transverse cable vibration
No full textA robust optimised multi-material 3D inkjet printed elastic metamaterial
No full textThis paper presents and validates a novel elastic metamaterial design, that is optimised for broadband robust vibration control of a structure in the presence of uncertainties, and realised using multi-material additive manufacturing. A novel concept resonator design that allows the resonance frequency to be flexibly tuned via both geometrical and material property modifications is presented and characterised. A unit cell consisting of 12 of these resonators is then proposed. The resonance frequencies and damping ratios of this elastic metamaterial unit cell when attached to a parametrically uncertain example structure are then optimised using a Particle Swarm Optimisation to maximise the mean attenuation in kinetic energy of a structure with parametric uncertainties, based on an analytical model of the system. The performance of the optimised metamaterial is then validated experimentally, and it is shown that the realised metamaterial design is able to achieve a mean of 3.5 dB of broadband attenuation in the presence of uncertainties in the structure. In addition, in the presence of structural uncertainties the robustly optimised design achieves 0.5 dB greater mean attenuation than a design optimised on the nominal structural response alone, and reduced variation in attenuation for different levels of uncertainty
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