External Mean Flow Effects on Sound Transmission Through Acoustic Absorptive Sandwich Structure

AbstractThe paper addresses the construction of a non spurious mixed spectral finite element (FE) method to problems in the field of computational aeroacoustics. Based on a computational scheme for the conservation equations of linear acoustics, the extension towards convected wave propagation is investigated. In aeroacoustic applications, the mean flow effects can have a significant impact on the generated sound field even for smaller Mach numbers. For those convective terms, the initial spectral FE discretization leads to non-physical, spurious solutions. Therefore, a regularization procedure is proposed and qualitatively investigated by means of discrete eigenvalues analysis of the discrete operator in space. A study of convergence and an application of the proposed scheme to simulate the flow induced sound generation in the process of human phonation underlines stability and validity.

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Eddy-Driven Recirculations from a Localized Transient Forcing

Journal of Physical Oceanography ◽

10.1175/jpo-d-11-060.1 ◽

2012 ◽

Vol 42 (3) ◽

pp. 430-447 ◽

Cited By ~ 22

Author(s):

Stephanie Waterman ◽

Steven R. Jayne

Keyword(s):

Group Velocity ◽

Rossby Wave ◽

Wave Spectrum ◽

Mean Flow ◽

Weakly Nonlinear ◽

Recirculation Gyres ◽

Flow Interactions ◽

Flow Effects ◽

Wave Limit ◽

Many Sources

Abstract The generation of time-mean recirculation gyres from the nonlinear rectification of an oscillatory, spatially localized vorticity forcing is examined analytically and numerically. Insights into the rectification mechanism are presented and the influence of the variations of forcing parameters, stratification, and mean background flow are explored. This exploration shows that the efficiency of the rectification depends on the properties of the energy radiation from the forcing, which in turn depends on the waves that participate in the rectification process. The particular waves are selected by the relation of the forcing parameters to the available free Rossby wave spectrum. An enhanced response is achieved if the parameters are such to select meridionally propagating waves, and a resonant response results if the forcing selects the Rossby wave with zero zonal group velocity and maximum meridional group velocity, which is optimal for producing rectified flows. Although formulated in a weakly nonlinear wave limit, simulations in a more realistic turbulent system suggest that this understanding of the mechanism remains useful in a strongly nonlinear regime with consideration of mean flow effects and wave–mean flow interaction now needing to be taken into account. The problem presented here is idealized but has general application in the understanding of eddy–eddy and eddy–mean flow interactions as the contrasting limit to that of spatially broad (basinwide) forcing and is relevant given that many sources of oceanic eddies are localized in space.

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Low-Frequency Broadband Sound Transmission Loss of Infinite Orthogonally Rib-Stiffened Sandwich Structure with Periodic Subwavelength Arrays of Shunted Piezoelectric Patches

Shock and Vibration ◽

10.1155/2017/2791351 ◽

2017 ◽

Vol 2017 ◽

pp. 1-17 ◽

Cited By ~ 1

Author(s):

Zhifu Zhang ◽

Weiguang Zheng ◽

Qibai Huang

Keyword(s):

Sandwich Structure ◽

Transmission Loss ◽

Virtual Work ◽

Low Frequency ◽

Sound Transmission ◽

Sound Insulation ◽

Convergence Criterion ◽

Sound Transmission Loss ◽

Space Harmonic ◽

Broadband Sound

This paper studies low-frequency sound transmission loss (STL) of an infinite orthogonally rib-stiffened sandwich structure flexibly connected with periodic subwavelength arrays of finite shunted piezoelectric patches. A complete theoretical model is proposed by three steps. First, the panels and piezoelectric patches on both sides are equivalent to two homogeneous facesheets by effective medium method. Second, we take into account all inertia terms of the rib-stiffeners to establish the governing equations by space harmonic method, separating the amplitude coefficients of the equivalent facesheets through virtual work principle. Third, the expression of STL is reduced. Based on the two prerequisites of subwavelength assumption and convergence criterion, the accuracy and validity of the model are verified by finite element simulations, cited experiments, and theoretical values. In the end, parameters affecting the STL performance of the structure are studied. All of these results show that the sandwich structure can improve the low-frequency STL effectively and broaden the sound insulation bandwidth.

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