Nonlinear Mechanical Metamaterial: A Novel Approach Towards Wideband Sound and Vibration Attenuation

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dc.contributor.advisor Das, R en
dc.contributor.advisor Calius, EP en
dc.contributor.advisor Dodd, G en Banerjee, Arnab en 2018-04-11T00:47:44Z en 2018 en
dc.identifier.uri en
dc.description.abstract Metamaterials have become very popular in the field of noise and vibration suppression, cloaking, wave guide, wave shield, wave absorber owing to its frequency dependent material properties. However, due to the dependency on the linear resonance, the performance of a linear metamaterial is restricted to a narrow bandwidth, which limits its application. The main objective of this thesis is to investigate the various possibilities towards the wideband metamaterial. Resonating metamaterials can be mathematically modelled as a periodic chain of mass-in-mass structures. As a first step towards the wideband metamaterial, an aperiodic or graded variation of frequencies of each building block is investigated, instead of a periodic repetition of the mass-in-mass units. Furthermore, keeping the periodic pattern of a metamaterial intact, the possibility of bandwidth increment is evaluated by assigning nonlinearity to the resonating unit of the metamaterial. The effects of the cubic nonlinearity and discontinuity on the vibration transmission through metamaterials are investigated in this thesis. Semi-analytical and numerical solution algorithms are developed to solve the wave propagation through these various nonlinear and graded linear metamaterials and the associated dynamics are identified and validated experimentally. Implementing 3D printing technology, initially curved beams are fabricated as a representative model of the bistable metamaterial unit. Attaching this unit with an electro-dynamic shaker, it is experimentally shown that the nonlinear metamaterial can be used for wideband vibration isolation. Impacting metamaterials are tested on the impedance tube and found that it can improve the acoustical performance of the light weight partition wall for a wide range of frequencies. A properly tuned graded metamaterial can extend the attenuation bandwidth almost 40% more in the lower frequency side and by attenuating the second transmission band it can infinitely widen the higher side of the attenuation band. Computationally and experimentally it is illustrated that performance of nonlinear metamaterials depends on excitation amplitude. To achieve the desired nonlinear behaviour, higher amplitudes are required. In low excitation level, the response is close to the linear response and for medium levels it is mostly chaotic. The attenuation band increases to infinity for the high nonlinearity. Impacting metamaterial can attenuate both the transmittance peak and can widen the attenuation bandwidth simultaneously in the lower and higher frequency side. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA99265070113402091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri en
dc.rights.uri en
dc.title Nonlinear Mechanical Metamaterial: A Novel Approach Towards Wideband Sound and Vibration Attenuation en
dc.type Thesis en Mechanical Engineering en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The author en
dc.rights.accessrights en
pubs.elements-id 735869 en
pubs.record-created-at-source-date 2018-04-11 en

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