Three-dimensional wave-envelope elements of variable order for acoustic radiation and scattering. Part II. Formulation in the time domain

FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS INSTITUTE OF SOUND AND VIBRATION RESEARCH Doctor of Philosophy SOUND RADIATION FROM PERFORATED PLATES by Azma PutraPerforated plates are quite often used as a means of engineering noise control to reduce the sound radiated by structures. However, there appears to be a lack of representative models to determine the sound radiation from a perforated plate. The aim of this thesis is to develop such a model that can be used to give quantitative guidance corresponding to the design and effectiveness of this noise control measure.Following an assessment of various models for the radiation efficiency of an unbaffled plate, Laulagnet's model is implemented. Results are calculated and compared with those for baffled plates. From this, simple empirical formulae are developed and give a very good agreement with the analytical result. Laulagnet's model is then modified to include the effect of perforation in terms of a continuously distributed surface impedance to represent the holes. This produces a model for the sound radiation from a perforated unbaffled plate. It is found that the radiation efficiency reduces as the perforation ratio increases or as the hole size reduces. An approximate formula for the effect of perforation is proposed which shows a good agreement with the analytical calculation up to half the critical frequency. This could be used for an engineering application to predict the noise reduction due to perforation.The calculation for guided-guided boundary conditions shows that the radiation efficiency of an unbaffled plate is not sensitive to the edge conditions. It is also shown that perforation changes the plate bending stiffness and mass and hence increases the plate vibration.The situation is also considered in which a perforated unbaffled plate is located close to a reflecting rigid surface. This is established by modifying the Green's function in the perforated unbaffled model to include an imaginary source to represent the reflected sound. The result shows that the presence of the rigid surface reduces the radiation efficiency at low frequencies.The limitation of the assumption of a continuous acoustic impedance is investigated using a model of discrete sources. The perforated plate is discretised into elementary sources representing the plate and also the holes. It is found that the uniform surface impedance is only valid if the hole distance is less than an acoustic wavelength for a vibrating rectangular piston and less than half an acoustic wavelength for a rectangular plate in bending vibration. Otherwise, the array of holes is no longer effective to reduce the sound radiation.Experimental validation is conducted using a reciprocity technique. A good agreement is achieved between the measured results and the theoretical calculation for both the unbaffled perforated plate and the perforated plate near a rigid surface.

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“…This can be implemented to solve an unbounded acoustical problems [45,46] as an alternative to the BEM.…”

Section: Numerical Modelsmentioning

confidence: 99%

Sound radiation from perforated plates

Putra

Thompson

2010

Journal of Sound and Vibration

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“…The structure-acoustic coupling method employed in this paper is also based on fluid-structure interaction proposed by Astley et al [17]. When the interaction is continually occurring, an additional force is exerted on the structure due to the…”

Section: The Structure-acoustic Coupling Methodsmentioning

confidence: 99%

Numerical Analysis of Thermoacoustic Characteristics of Components inside a Complex Aircraft Related to the Coupling Effect of High Temperature and Random Vibration

Bai

Zhao

Xia

et al. 2015

Journal of Low Frequency Noise, Vibration and Active Control

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Hypersonic aircraft always face bad flight environment related to the coupling effects of high temperature and random vibration. Numerical analysis of thermoacoustic characteristics of components inside such an aircraft is presented in this paper. An actual aircraft cabin composite structure including a heat resistant layer, an adiabatic layer and metal frameworks is modeled with the finite element mesh generation method. Transient heat conduction of the hypersonic flight aircraft is analyzed based on a block-iterative coupling method which can consider the atmosphere-aircraft interaction. Then the Von Karman turbulence spectrum is employed to define the random vibration environment of the present aircraft. The thermodynamic response of the system is solved by the pseudo-excitation method which can improve the computation efficiency greatly. Finally, thermoacoustic characteristic of the cavity inside the aircraft cabin is analyzed when the transient heat conduction and random vibration due to atmosphere turbulence are both included. A numerical method is proposed based on a structure-acoustic coupling method which can use acoustic equations to simulate the propagation of the acoustic wave in the flow. It can be found from the computed results that the change of the temperature influences both the thermodynamic characteristic of the aircraft cabin and thermoacoustic characteristic of the component inside the present aircraft significantly. So the coupling effects of high temperature and random vibration on thermoacoustic characteristic of a hypersonic flight aircraft cannot be neglected. The proposed numerical analysis method in this paper can be widely applied to numerical investigations of thermoacoustic systems inside hypersonic aircraft.

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“…Owing to a mapping approach, the Astley-Leis scheme provides a formulation which may be optimized with respect to condition of the system matrices, as will be seen later. In addition, the extension of this formulation to time-dependent analyses is straightforward [24]. Therefore, we restrict ourselves in this contribution to the Astley-Leis elements.…”

Section: Introductionmentioning

confidence: 99%

Improved conditioning of infinite elements for exterior acoustics

Dreyer

Estorff

2003

Numerical Meth Engineering

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SUMMARYAn optimized version of the so-called mapped wave envelope elements, also known as Astley-Leis elements, is introduced. These elements extend to inÿnity in one dimension and therefore provide an approach to the simulation of exterior acoustical problems in both frequency and time domains. Their formulation is improved signiÿcantly through the proper choice of polynomial bases in the direction of radiation. In particular, certain Jacobi polynomials are identiÿed which behave well with respect to conditioning of the system matrices. As a consequence, the size of the ÿnite element discretization may reduce considerably without any loss of accuracy. In addition, the new polynomial bases lead to superior performance of the inÿnite elements in conjunction with iterative solvers.

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Three-dimensional wave-envelope elements of variable order for acoustic radiation and scattering. Part II. Formulation in the time domain

Cited by 63 publications

References 16 publications

Sound radiation from perforated plates

Sound radiation from perforated plates

Numerical Analysis of Thermoacoustic Characteristics of Components inside a Complex Aircraft Related to the Coupling Effect of High Temperature and Random Vibration

Improved conditioning of infinite elements for exterior acoustics

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