Active control of structural sound radiation using a spatial control method with multiple structural sensors

This paper introduces a method to control structural sound radiation using multiple structural sensors. Tonal radiation from a vibrating arbitrary structure is considered in this paper. Based on the estimation of the vibration profile of a noise radiating structure, spatial signals that represents radiated pressure field can be generated. These spatial signals can also be spatially weighted to control radiated noise at some far-field regions more than at others. Numerical studies on a simply-supported plate were performed which demonstrate the ability of the proposed method to control sound radiation that is spatially weighted over certain regions in the far-field.Dunant Halim and Ben S. Cazzolat

Acoustic absorption behaviour of a tall carbon nanotube forest

Previous investigations have shown that a 3-mm-high carbon nanotube (CNT) forest has an acoustic absorption coefficient of about 5-10% within the frequency range 125 Hz-4 kHz, which is above that of conventional acoustic materials on a per-mass basis. It was hypothesised that a CNT array of greater height, lower density, and with a non-uniform arrangement of the nanotubes could enhance the amount of acoustic absorption. In order to investigate this hypothesis, an impedance tube test was conducted to measure the acoustic absorption coefficient of a relatively tall 6-mm CNT forest. The results indicate that a greater length and lower density of CNTs may improve the absorption performance of CNT-based acoustic absorbers. Analyses of the results showed anomalies in the measured acoustic absorption coefficient compared with previous investigations. Theoretical analyses were performed based on classical models of acoustic absorption to explain the anomalies. This study describes the factors that may affect the acoustic absorption behaviour of nanomaterials.M. Ayub, A. C. Zander, C. Q. Howard, B. S. Cazzolato, D. M. Huang, N. T. Alvarez, and V. N. Shano

Molecular dynamics simulations of sound wave propagation in a gas and thermo-acoustic effects on a carbon nanotube

Published: 19 January 2016Molecular dynamics (MD) simulations have been performed to study sound wave propagation in a simple monatomic gas (argon) and the thermo-acoustic effects on a single walled carbon nanotube (CNT). The objective of this study was to understand the acoustic behavior of CNTs in the presence of acoustic waves propagating in gaseous media. A plane sound wave was generated within a rectangular domain by oscillating a solid wall comprising Lennard-Jones (LJ) atoms with the same intermolecular potential as the gas molecules. A CNT was aligned parallel to the direction of the flow at the wall at the opposite end of the domain. Interatomic interactions in the CNT were modeled using the REBO potential. The behavior of the sound wave propagation in argon gas without the CNT was validated by comparison with a previous study. The simulation results show that the thermo-acoustic behavior of CNTs can be simulated accurately using MD and that large-scale MD can be performed in the ultrasonic frequency range. This investigation will contribute to an improved understanding of the acoustic absorption mechanism of these nanoscopic fibers.Md Ayub, Anthony C. Zander, Carl Q. Howard, David M. Huang, Benjamin S. Cazzolat

Graphene oxide-based lamella network for enhanced sound absorption

Published online October 23, 2017Noise is an environmental pollutant with recognized impacts on the psychological and physiological health of humans. Many porous materials are often limited by low sound absorption over a broad frequency range, delicacy, excessive weight and thickness, poor moisture insulation, high temperature instability, and lack of readiness for high volume commercialization. Herein, an efficient and robust lamella-structure is reported as an acoustic absorber based on self-assembled interconnected graphene oxide (GO) sheets supported by a grill-shaped melamine skeleton. The fabricated lamella structure exhibits ≈60.3% enhancement over a broad absorption band between 128 and 4000 Hz (≈100% at lower frequencies) compared to the melamine foam. The enhanced acoustic absorption is identified to be structure dependent regardless of the density. The sound dissipation in the open-celled structure is due to the viscous and thermal losses, whereas it is predominantly tortuosity in wave propagation and enhanced surface area for the GO-based lamella. In addition to the enhanced acoustic absorption and mechanical robustness, the lamella provides superior structural functionality over many conventional sound absorbers including, moisture/mist insulation and fire retardancy. The fabrication of this new sound absorber is inexpensive, scalable and can be adapted for extensive applications in commercial, residential, and industrial building structures.Md Julker Nine, Md Ayub, Anthony C. Zander, Diana N. H. Tran, Benjamin S. Cazzolato and Dusan Losi

Spatial control of far-field structural sound radiation using structural sensors for broadband applications

The focus of the paper is to control the far-field sound radiation from an arbitrary planar structure using multiple structural sensors, particularly for broadband applications. A number of structural velocity sensors are distributed over the structure for sensing the sound radiation at a particular far-field region for control purposes. Spatial control of structural sound radiation is achieved by constructing a frequency-independent spatial filter that reflects the spatially- weighted sound radiation energy. Thus, the signal produced by the spatial filter can be used as an error signal to be minimised by standard active control methods. A numerical case study on the sound radiation of a flat panel structure is performed to investigate the control performance using the developed frequency-independent spatial filter. Copyright © (2006) by the Australian Acoustical Society.Halim, D. and Cazzolato, B. S

A multiple-sensor method for control of structural vibration with spatial objectives

This paper proposes a method to control vibration of arbitrary structures with spatially weighted objectives. Multiple discrete structural sensors are distributed over a structure and a spatial interpolation method is used to obtain the estimate of vibration at any points over the structure. The method thus does not require a priori information about the dynamic model of the structure. From the vibration information provided by structural sensors, spatial signals can then be obtained, representing the spatially weighted vibration of the entire structure. A condensation procedure allows the reduction of the required number of control input channels for active control purposes. A numerical case study of a flexible plate demonstrated that the proposed method can be used for minimising spatial vibration or for achieving a desired spatial vibration profile of a structure.Dunant Halim and Ben S. Cazzolat

Beam steering of sound from flat panels using spatially-averaged objective functions

The paper proposes a beam steering method for regulating sound radiation from flat panel structures using multiple structural velocity sensors. Velocity measurements from the structural sensors are used to estimate the velocity profile of the panel, which is then used to estimate the acoustic beam pattern of radiated sound. An objective function is defined for active beam steering purposes, representing the spatially-averaged error between the reference beam pattern and the estimated beam pattern of sound radiation in the far-field. Numerical studies on a rectangular flat panel are used to demonstrate the ability of the proposed method to regulate a beam pattern of sound for steering a beam to different directions in the far-field. It is demonstrated that the proposed method can modify the beam pattern of tonal sound radiation by modifying the vibration velocity profile of the panel.Halim, D. and Cazzolato, B. S

Active broadband control of vibrating panel structures with multiple structural sensors

The aim of the research presented in this paper is to actively control broadband vibration on panel structures using multiple sensors. The broadband vibration profile of a panel structure is estimated by using spatial interpolation functions and vibration measurements from the surface mounted sensors. The control objective is then achieved by deriving 'spatial' error signals whose energy represents the spatially-weighted vibration energy over the structure. An optimal H-2 control design using this spatial control approach is discussed to demonstrate the effectiveness of the broadband spatial control on a panel. Numerical results show that the broadband vibration profile can be spatially controlled, not just by minimising the strength of each vibration mode, but also by controlling the relative strength of each mode.Halim, D. and Cazzolato, B. S

Control of the spatially-weighted vibration of an arbitrary structure using an adaptive control strategy

The aim of the work is to develop a practical active control strategy in which vibration of an arbitrary structure can be spatially-weighted for achieving a vibration reduction at the structural region of interest. Multiple sensors are used to sense the vibration of the entire arbitrary structure and a filtered-reference Least Mean Square (FX-LMS)-based adaptive control strategy is used to minimise the instantaneous error energy representing the spatially weighted vibration energy of the structure. A numerical study for spatial vibration control of a plate structure is discussed to demonstrate the control effectiveness of the adaptive spatial controller for tonal and broadband cases. Copyright © (2006) by the Australian Acoustical Society.Halim, D. and Cazzolato, B. S