1,720,983 research outputs found
Cost surface plots of the effective material properties
No full textThis dataset contains a video file that shows the cost surface plots of the effective material properties against the real and imaginary parts of the single monopole and single dipole control source strength at each frequency over the the presented bandwidth. This data has been collected using Matlab, where the Matlab script calculates the effective material properties from a range of the real and imaginary parts of the control source strength.
This dataset contains:
A video file that shows the cost surface plots of each effective material property against the real and imaginary parts of the corresponding control source strength.
Cost surface plots of the effective material properties against the real and imaginary parts of the single monopole and single dipole control source strength at each frequency over the the presented bandwidth.</span
Active acoustic metamaterials for high performance noise control
No full textAcoustic metamaterials have been shown to have the ability to achieve high levels of low frequency noise attenuation through the use of engineered structures, which consist of arrays of subwavelength unit cells. These metamaterials exhibit effective material properties that are not available in naturally occurring media. The bandwidth over which these metamaterials can achieve negative effective material properties is generally relatively-narrow due to the use of resonant unit cells. Although the bandwidth of negativity has been extended by integrating active control technologies into metamaterials, the performance of these hybrid systems is still limited by the use of the resonant inclusions. Thus, this thesis presents an investigation into how conventional active control systems influence the effective material properties and whether active acoustic sources can be optimally-driven to directly control the effective material properties and also realise nonreciprocal behaviour. An effective material property optimisation procedure is proposed and it is shown that the optimised single monopole and single dipole control sources achieve broadband negative effective bulk modulus and density respectively, and by combining the two optimised acoustic sources, broadband double negativity is also achieved. Nonreciprocal acoustic devices, which are based on the design of acoustic metamaterials, have shown the ability to achieve nonreciprocal sound transmission. Although existing nonreciprocal acoustic devices can achieve broadband nonreciprocal sound transmission in a one dimensional space, it has not yet been shown that nonreciprocal sound absorption can also be achieved by nonreciprocal acoustic devices in one or two dimensional spaces. Therefore, this thesis also presents an investigation into how feedforward wave-based active control systems can be used to achieve broadband nonreciprocal sound transmission and absorption in both one and two dimensional environments. This active nonreciprocal control strategies are demonstrated through both simulations and experiments in one and two dimensional spaces and demonstrate an effective and adaptable means of realising nonreciprocal control
Remote sensing for wave-based nonreciprocal active control
No full textReciprocity is an acoustic property that describes the symmetry of sound transmission between two points. However, this property is undesirable in certain applications, and this has led to significant interest in the development of nonreciprocal acoustic devices that achieve one-way sound transmission. These devices typically achieve nonreciprocal sound transmission by introducing nonlinearities or directional biasing. Previously proposed nonreciprocal acoustic devices generally have limitations; for example, they may not be fully tuneable, they can introduce signal distortions such as additional harmonics, or they can only exhibit nonreciprocal behaviour over a narrow bandwidth. To overcome these challenges, previous work has demonstrated how a wave-based active control system can be used to drive an array of acoustic sources to achieve reversible and broadband non-reciprocal behaviour. However these wave-based active control systems use external far-field pressure sensors to achieve broadband nonreciprocal behaviour and, thus, these active control systems are not self-sufficient. This paper therefore presents an experimental investigation into how remote sensing techniques can be incorporated into the previously proposed wave-based active control systems to create more self-contained nonreciprocal acoustic devices that still achieve broadband nonreciprocal behaviour in a one-dimensional acoustic system
Control of vibration using surface mounted acoustic black holes
No full textAcoustic Black Holes (ABHs) are tapered features that can either be surface mounted or embedded into structures to provide effective broadband structural damping. Generally, structures with embedded ABHs require material to be removed from the structure to create the required geometric features. However, for thin plates, it is not straightforward to embed ABHs, since the removal of the material in this case will significantly impact the strength of the structure. Therefore, this paper presents an numerical model based investigation into how surface mounted ABHs can be used to control the vibration of a thin beam over a broad frequency range. The numerical investigation compares the performance of the proposed surface mounted ABHs with a beam treated using conventional passive measures via evaluation of the total kinetic energy of the primary structure. The results presented in this paper show that the surface mounted ABHs achieve greater total kinetic energy attenuation compared to the conventionally treated beam over the presented bandwidth due to the ABH effect. The proposed surface mounted ABHs could be used as an effective broadband vibration control solution for thin structures, where it is not straightforward to design effective embedded ABHs
Analysis and optimisation of an active noise control system as a potential acoustic metamaterial building block
No full textActive Noise Control (ANC) systems have been employed in a variety of applications to provide high performance noise control at low frequencies, within a lightweight and compact package. Recently, acoustic metamaterials (AMM) have been proposed and demonstrated as an alternative approach to achieving high levels of noise control. AMM are engineered structures that consist of an array of subwavelength unit cells, which exhibit behaviour not seen in conventional materials. For example, passive resonators have been designed to achieve negative effective material properties and manipulate wave propagation. These AMMs, however, typically have narrow band gaps, where wave propagation is suppressed. When acting as an AMM, ANC systems have been shown to improve performance, tuneability and adaptability, but physical insights have generally been limited. Therefore, this paper investigates the effects of traditional ANC on the effective material properties and shows physical insight through an analysis of the wave propagation within a one-dimensional duct system. The active unit cell has then been optimised to directly minimise the effective material properties and a corresponding physical analysis has been presented
Practical realisation of an active acoustic metamaterial building block
No full textAcoustic metamaterials (AMMs) have been demonstrated as an alternative approach to achieving high levels of noise control using an array of subwavelength unit cells, exhibiting behaviour not seen in conventional materials. Specifically, active AMMs offer the potential for greater levels of broadband wave manipulation, tunability and adaptability. However, determining the optimal control source strengths that achieve broadband negative effective material properties is not straightforward. This study presents a practical method of designing an active system that directly minimises the effective material properties. The optimal control source strengths required for both single monopole and single dipole control sources to minimise the effective bulk modulus and the effective density respectively have been calculated via an optimisation procedure. The ability of the proposed active AMM building blocks to achieve broadband negative effective material properties is tested experientially through offline simulations using measured frequency responses. Interestingly, the optimised single monopole and optimised single dipole control sources achieve broadband negative effective bulk modulus and density respectively. However, when combining the two optimised control sources, the active control system only achieves bands of double negativity and, thus, only exhibits bands of negative refractive index
Wave-based active control for nonreciprocal sound transmission and absorption
No full textRecent interest has arisen in the realisation of nonreciprocal acoustic devices that achieve unidirectional sound transmission. In other words, these devices allow perfect transmission from waves travelling in one direction, whilst blocking waves travelling in the opposite direction. These devices have thus been described as the acoustic analogue of an electrical diode and could be useful in many applications. There are a variety of passive and active devices that have been designed based on the concept of acoustic metamaterials to achieve unidirectional transmission by introducing non-linearities or breaking spatial and temporal symmetries. This paper will investigate how unidirectional transmission can be achieved using active control within a one-dimensional duct. The proposed active control system has the capability to manipulate either the positive or negative travelling waves within the duct in order to achieve zero transmission in one direction, whilst allowing perfect transmission in the opposite direction. The advantage of this system is not only its capability to achieve nonreciprocal sound transmission, but it is also fully adaptable
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
Practical realisation of an active acoustic metamaterial building block
No full textAcoustic metamaterials (AMMs) have been demonstrated as an alternative approach to achieving high levels of noise control using an array of subwavelength unit cells, exhibiting behaviour not seen in conventional materials. Specifically, active AMMs offer the potential for greater levels of broadband wave manipulation, tunability and adaptability. However, determining the control source strengths that achieve broadband negative effective material properties is not straightforward. This study presents a practical method of designing an active system that directly minimises the effective material properties. The source strengths required for both single monopole and dipole control sources to minimise the effective bulk modulus and the effective density respectively have been calculated via an optimisation procedure in the frequency domain. A finite impulse response (FIR) filter has then been designed in each case to match the optimised frequency responses and enable real-time implementation. The performance of the designed FIR filters has been tested by implementation using the two different control sources in a one-dimensional duct and the ability of the proposed active AMM building blocks to achieve broadband negative effective material properties is tested. Interestingly, by combining the two optimised control sources, double negativity can be achieved, offering the potential for negative refraction
Wave-based active control for nonreciprocal acoustics using a planar array of secondary sources
No full textThere has been significant interest in the design of nonreciprocal acoustic devices that allow acoustic waves to be perfectly transmitted in one direction, whilst the acoustic waves propagating in the opposite direction are blocked or reflected. Previously proposed nonreciprocal acoustic devices have broken the symmetry of transmission by introducing nonlinearities or resonant cavities. However, these nonreciprocal acoustic devices typically have limitations, such as signal distortions and the bandwidth over which nonreciprocal behaviour can be achieved is narrow. This paper will investigate how active control can be used to minimise the transmitted and reflected waves independently to achieve nonreciprocal sound transmission and absorption using a planar array of secondary sources in a two-dimensional environment. The advantage of the proposed active control system is that it is fully adaptable, which means that the directivity of nonreciprocal behaviour can also be reversed. The performance of the proposed wave-based active control system is investigated for a range of angles of incidence and its performance limitations are explored
- …
