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Lucio Maestrello - One of the best experts on this subject based on the ideXlab platform.
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Interaction of Sound from Supersonic Jets with Nearby Structures
AIAA Journal, 1998Co-Authors: C. C. Fenno, Alvin Bayliss, Lucio MaestrelloAbstract:We numerically solve a model of sound generated in an ideally expanded two-dimensional supersonic (Mach 2) jet. Two configurations are considered: 1) a free jet and 2) an installed jet with a nearby array of flexible aircraft type Panels. In the later case the Panels vibrate in Response to loading by sound from the jet, and the full coupling between the Panels and the jet is simulated, accounting for Panel Response and radiation as well as the jet acoustics. We consider the long time behavior of the jet/Panel system and present results for the flowfield and far-field pressure and the vibration of, and radiatlon from, the Panels. The pressure within the jet changes from a nearly discrete spectrum peaked at a preferred frequency f * , which depends on properties of the jet, to a continuous spectrum as downstream distance increases. The far-field pressure is characterized by a highly directional beaming of sound with a spectral peak at f * within the Mach line and a lower-level breakup into small-scale structures away from the Mach line. We show that the location of the Panels relative to the Mach line is critical in determining Panel Response. Panels located upstream of the Mach line are subject to a low-level continuous spectrum loading and exhibit a comparable Response. In contrast, Panels located within the Mach line are subject to a high-level loading due to the intense Mach wave radiation of sound peaked at f * and exhibit a comparable Response. The Panels radiate in a simil ion to the sound in the particular, the is a strong beaming of sound waves at frequency f * from the ex ted Panels Mach-angle-from the bounding wall, indicating a significant effect of Mach wave radiation both interior spectral content in the supersonic regime.
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Interaction of Sound from Supersonic Jets with Nearby Structures
35th Aerospace Sciences Meeting and Exhibit, 1997Co-Authors: C. C. Fenno, Alvin Bayliss, Lucio MaestrelloAbstract:A model of sound generated in an ideally expanded supersonic (Mach 2) jet is solved numerically. Two configurations are considered; (i) a free jet and (ii) an installed jet with a nearby array of flexible aircraft type Panels. In the later case the Panels vibrate in Response to loading by sound from the jet and the full coupling between the Panels and the jet is considered, accounting for Panel Response and radiation. The long time behavior of the jet is considered. Results for near field and far field disturbance, the far field pressure and the vibration of and radiation from the Panels are presented. Panel Response crucially depends on the location of the Panels. Panels located upstream of the Mach cone are subject to a low level, nearly continuous spectral excitation and consequently exhibit a low level, relatively continuous spectral Response. In contrast, Panels located within the Mach cone are subject to a significant loading due to the intense Mach wave radiation of sound and exhibit a large, relatively peaked spectral Response centered around the peak frequency of sound radiation. The Panels radiate in a similar fashion to the sound in the jet, in particular exhibiting a relatively peaked spectral Response at approximately the Mach angle from the bounding wall.
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Control of Panel Response to turbulent boundary-layer and acoustic excitations
AIAA Journal, 1996Co-Authors: Lucio MaestrelloAbstract:Nonlinear Response of a Panel structure results when forced by a subsonic turbulent boundary layer and puretone sound in a wind tunnel. It is a coupled problem, where flow, structure, and sound interact. The structure exhibits a broadband Response typical of turbulent boundary-layer loading with superimposed pure tone and harmonics over the band, a process which is statistically stationary, but non-Gaussian. The mechanism is an energy transfer process : the amount of energy supplied to the harmonics is removed from the low-frequency band and the fundamental tone. The objective is to control the nonlinear wave using a time-harmonic actuator tone. Full control is almost achieved using a single controller. Two steps are taken : first, control the harmonics by feeding the energy back into the fundamental and low-frequency band, and second, control the fundamental tone to shift the energy further back into the low-frequency band. Consequently, the Response of the Panel is reduced to the broadband level of the turbulent boundary-layer excitation, a reduction in peak amplitude power level by 20 dB or more. The experiments are motivated by considerations for aircraft interior noise and structural Response.
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Panel Response to jet noise under near sonic conditions
The Journal of the Acoustical Society of America, 1995Co-Authors: Charles C. Fenno, Alvin Bayliss, Lucio MaestrelloAbstract:The problem of the Response of an array of flexible aircraft‐type Panels excited by noise from a jet under near sonic conditions from a converging nozzle is numerically studied. The problem is computed by solving the Euler equations for the unsteady field in the jet, fully coupled to equations describing the Panel motion. Computations of the far‐field sound, Panel Response, and Panel radiation are presented. The effect of nozzle geometry on the radiated sound and jet instabilities is studied. In addition, the relationship between Panel location, relative to the jet exit, and Panel Response is determined. The computation simulates the development of large amplitude, slowly propagating instability waves in the jet which act as additional sources of sound. Thus the computation allows for direct computation of the natural sources of jet noise, as well as the propagation of the resulting jet noise. The results demonstrate large disturbances in the vicinity of the converging nozzle which act as additional sources of sound. The Panel Response is concentrated in progressively lower frequencies as distance from the jet exit increases.
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On the interaction of sound from a jet with a nearby structure
The Journal of the Acoustical Society of America, 1994Co-Authors: Jennifer L. Mcgreevy, Alvin Bayliss, Lucio MaestrelloAbstract:The excitation of a flexible beam by acoustic disturbances generated by a spreading subsonic jet and the resulting interaction and acoustic radiation is investigated numerically. The formulation consists of solving the nonlinear Euler equations coupled to a nonlinear equation governing the vibration of the Panel due to acoustic loading. The incident sound waves result from both disturbances due to the initial source as well as disturbances generated by instability waves in the jet. Under appropriate conditions, instability waves can also be generated upstream of the nozzle exit and may contribute additional sound. Results are obtained for the Panel Response as well as the transmitted and reflected acoustic field from the flexible Panel.
Hesham Hamed Ibrahim - One of the best experts on this subject based on the ideXlab platform.
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Thermo-acoustic random Response of temperature-dependent functionally graded material Panels
Computational Mechanics, 2010Co-Authors: Hesham Hamed Ibrahim, Mohammad TawfikAbstract:A nonlinear finite element model is provided for the nonlinear random Response of functionally graded material Panels subject to combined thermal and random acoustic loads. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The governing equations are derived using the first-order shear-deformable plate theory with von Karman geometric nonlinearity and the principle of virtual work. The thermal load is assumed to be steady state constant temperature distribution, and the acoustic excitation is considered to be a stationary white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The governing equations are transformed to modal coordinates to reduce the computational efforts. Newton–Raphson iteration method is employed to obtain the dynamic Response at each time step of the Newmark implicit scheme for numerical integration. Finally, numerical results are provided to study the effects of volume fraction exponent, temperature rise, and the sound pressure level on the Panel Response.
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supersonic flutter of functionally graded Panels subject to acoustic and thermal loads
Journal of Aircraft, 2009Co-Authors: Hesham Hamed Ibrahim, Hong Hee Yoo, Kwansoo LeeAbstract:of the volume fractions of the constituents. The governing equations are derived using the classical plate theory with von Karman geometric nonlinearity and the principle of virtual work. The first-order piston theory is adopted to model aerodynamic pressures induced by supersonic airflows. The thermal load is assumed to be steady-state constant temperature distribution, and the acoustic excitation is considered to be a stationary white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The governing equations are transformed to modal coordinates to reduce the computational efforts. The Newton–Raphson iteration method is employed to obtain the dynamic Response at each time step of the Newmark scheme for numerical integration. Finally, numerical results are provided to study the effects of the volume fraction exponent, aerodynamic pressure, temperature rise, and the random acoustic load on the Panel Response.
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Aerothermoacoustic Response of Shape Memory Alloy Hybrid Composite Panels
Journal of Aircraft, 2009Co-Authors: Hesham Hamed Ibrahim, Mohammad Tawfik, Hazem M Negm, Hong Hee YooAbstract:theacousticexcitationisconsideredtobeawhite-Gaussianrandompressurewithzeromeananduniformmagnitude over the Panel surface. Nonlinear temperature-dependence of material properties is considered in the formulation. The dynamic nonlinear equations of motion are transformed to modal coordinates to reduce the computational efforts. The Newton–Raphson iteration method is employed to obtain the dynamic Response at each time step of the Newmark numerical integration scheme. Finally, the nonlinear Response of a shape memory alloy hybrid composite Panel is presented, illustrating the effect of shape memory alloy fiber embeddings, aerodynamic pressure, sound pressure level, and temperature rise on the Panel Response.
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nonlinear flutter of shape memory alloy hybrid composite Panels subject to thermal and random acoustic loads
한국소음진동공학회 국제학술발표논문집, 2008Co-Authors: Hesham Hamed Ibrahim, Mohammad Tawfik, Hazem M Negm, Hong Hee YooAbstract:Nonlinear flutter of a traditional composite plate impregnated with pre-strained shape memory alloy fibers and subjected to combined thermal, aerodynamic and random acoustic loads are investigated. The nonlinear governing equations are obtained using the first-order shear-deformable plate theory, von Karman strain-displacement relations and the principle of virtual work. To account for the temperature dependence of material properties, the thermal strain is stated as an integral quantity of thermal expansion coefficient with respect to temperature. The thermal load is assumed to be steady state constant temperature distribution, and the acoustic excitation is considered to be a white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The dynamic nonlinear equations of motion are transformed to modal coordinates to reduce the computational efforts. Finally, the nonlinear Response of a shape memory alloy hybrid composite plate Panel are presented, illustrating the effect of shape memory alloy fiber embeddings, sound pressure level, dynamic pressure and temperature rise on the Panel Response.
Mohammad Tawfik - One of the best experts on this subject based on the ideXlab platform.
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Thermo-acoustic random Response of temperature-dependent functionally graded material Panels
Computational Mechanics, 2010Co-Authors: Hesham Hamed Ibrahim, Mohammad TawfikAbstract:A nonlinear finite element model is provided for the nonlinear random Response of functionally graded material Panels subject to combined thermal and random acoustic loads. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The governing equations are derived using the first-order shear-deformable plate theory with von Karman geometric nonlinearity and the principle of virtual work. The thermal load is assumed to be steady state constant temperature distribution, and the acoustic excitation is considered to be a stationary white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The governing equations are transformed to modal coordinates to reduce the computational efforts. Newton–Raphson iteration method is employed to obtain the dynamic Response at each time step of the Newmark implicit scheme for numerical integration. Finally, numerical results are provided to study the effects of volume fraction exponent, temperature rise, and the sound pressure level on the Panel Response.
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Aerothermoacoustic Response of Shape Memory Alloy Hybrid Composite Panels
Journal of Aircraft, 2009Co-Authors: Hesham Hamed Ibrahim, Mohammad Tawfik, Hazem M Negm, Hong Hee YooAbstract:theacousticexcitationisconsideredtobeawhite-Gaussianrandompressurewithzeromeananduniformmagnitude over the Panel surface. Nonlinear temperature-dependence of material properties is considered in the formulation. The dynamic nonlinear equations of motion are transformed to modal coordinates to reduce the computational efforts. The Newton–Raphson iteration method is employed to obtain the dynamic Response at each time step of the Newmark numerical integration scheme. Finally, the nonlinear Response of a shape memory alloy hybrid composite Panel is presented, illustrating the effect of shape memory alloy fiber embeddings, aerodynamic pressure, sound pressure level, and temperature rise on the Panel Response.
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nonlinear flutter of shape memory alloy hybrid composite Panels subject to thermal and random acoustic loads
한국소음진동공학회 국제학술발표논문집, 2008Co-Authors: Hesham Hamed Ibrahim, Mohammad Tawfik, Hazem M Negm, Hong Hee YooAbstract:Nonlinear flutter of a traditional composite plate impregnated with pre-strained shape memory alloy fibers and subjected to combined thermal, aerodynamic and random acoustic loads are investigated. The nonlinear governing equations are obtained using the first-order shear-deformable plate theory, von Karman strain-displacement relations and the principle of virtual work. To account for the temperature dependence of material properties, the thermal strain is stated as an integral quantity of thermal expansion coefficient with respect to temperature. The thermal load is assumed to be steady state constant temperature distribution, and the acoustic excitation is considered to be a white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The dynamic nonlinear equations of motion are transformed to modal coordinates to reduce the computational efforts. Finally, the nonlinear Response of a shape memory alloy hybrid composite plate Panel are presented, illustrating the effect of shape memory alloy fiber embeddings, sound pressure level, dynamic pressure and temperature rise on the Panel Response.
Cédric Maury - One of the best experts on this subject based on the ideXlab platform.
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Coupled mode analysis of thin micro-perforated Panel absorbers
2012Co-Authors: Cédric Maury, Teresa Bravo, Cédric PinhèdeAbstract:The prediction of the isolating properties of lightweight Micro Perforated Panels (MPP) is a subject that has been intensively studied due to their important applications in a wide range of areas such as building acoustics and the aeronautic, astronautic and automotive industries. MPPs have been mostly considered as rigid structures, accounting only for inertia and neglecting any vibrating effects. However, simulation and experimental studies on thin MPPs have found that the absorbing performance can experience variations in the low frequency range from the results expected assuming a rigid structure. The work presented here is a theoretical and experimental study on the influence of Panel vibrations on the sound absorption properties of thin MPP absorbers. Measurements show that the absorption performance generates extra absorption peaks or dips that cannot be understood assuming a rigid MPP. A theoretical model is established that exactly accounts for structural-acoustic interaction between the micro-perforated Panel and the backing cavity without restriction on the absorber cross-sectional shape or on the Panel boundary conditions. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed Panel Response. The effect of micro-perforations on Panel-cavity or hole-cavity resonances is revealed through coupled mode analysis.
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Vibroacoustic properties of thin micro-perforated Panel absorbers
Journal of the Acoustical Society of America, 2012Co-Authors: Teresa Bravo, Cédric Maury, Cédric PinhèdeAbstract:This paper presents theoretical and experimental results on the influence of Panel vibrations on the sound absorption properties of thin micro-perforated Panel absorbers (MPPA). Measurements show that the absorption performance of thin MPPAs generates extra absorption peaks or dips that cannot be understood assuming a rigid MPPA. A theoretical model is established that accounts for structural-acoustic interaction between the micro-perforated Panel and the backing cavity, assuming uniform conservative boundary conditions for the Panel and separable coordinates for the cavity cross-section. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed Panel Response. It is shown analytically and experimentally that the air-frame relative velocity is a key factor that alters the input acoustic impedance of thin MPPAs. Coupled mode analysis reveals that the two first resonances of an elastic MPPA are either Panel-cavity, hole-cavity, or Panel-controlled resonances, depending on whether the effective air mass of the perforations is greater or lower than the first Panel modal mass. A critical value of the perforation ratio is found through which the MPPA resonances experience a frequency "jump" and that determines two absorption mechanisms operating out of the transitional region.
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a synthesis approach for reproducing the Response of aircraft Panels to a turbulent boundary layer excitation
Journal of the Acoustical Society of America, 2011Co-Authors: Teresa Bravo, Cédric MauryAbstract:Random wall-pressure fluctuations due to the turbulent boundary layer (TBL) are a feature of the air flow over an aircraft fuselage under cruise conditions, creating undesirable effects such as cabin noise annoyance. In order to test potential solutions to reduce the TBL-induced noise, a cost-efficient alternative to in-flight or wind-tunnel measurements involves the laboratory simulation of the Response of aircraft sidewalls to high-speed subsonic TBL excitation. Previously published work has shown that TBL simulation using a near-field array of loudspeakers is only feasible in the low frequency range due to the rapid decay of the spanwise correlation length with frequency. This paper demonstrates through theoretical criteria how the wavenumber filtering capabilities of the radiating Panel reduces the number of sources required, thus dramatically enlarging the frequency range over which the Response of the TBL-excited Panel is accurately reproduced. Experimental synthesis of the Panel Response to high-speed TBL excitation is found to be feasible over the hydrodynamic coincidence frequency range using a reduced set of near-field loudspeakers driven by optimal signals. Effective methodologies are proposed for an accurate reproduction of the TBL-induced sound power radiated by the Panel into a free-field and when coupled to a cavity.
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Turbulent boundary-layer simulation with an array of loudspeakers
AIAA Journal, 2004Co-Authors: Cédric Maury, S. J. Elliott, P. GardonioAbstract:The feasibility is discussed of simulating a random pressure field having the same spatial correlation function as a turbulent boundary-layer pressure field using an array of loudspeakers. This approach could provide a cost-effective laboratory method of measuring the boundary-layer noise transmitted through aircraft fuselage structures. Initially, a theoretical model is used to predict the vibroacoustic Response of randomly excited Panels. A method of generating a pressure field with predefined statistical properties using an array of loudspeakers is then introduced. Results are obtained in a typical test case for the simulation of boundary-layer-induced noise. It is shown how the number of loudspeakers required to achieve a reasonable approximation of the boundary-layer excitation scales with frequency. It is found that a coarse reproduction of the boundary-layer excitation, using a reduced set of loudspeakers, can still give a good approximation of the Panel vibroacoustic Response, thus suggesting that direct simulation of the Panel Response to a boundary-layer excitation using loudspeakers could be feasible.
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A WAVENUMBER APPROACH TO MODELLING THE Response OF A RANDOMLY EXCITED Panel, PART I: GENERAL THEORY
Journal of Sound and Vibration, 2002Co-Authors: Cédric Maury, Paolo Gardonio, Stephen J. ElliottAbstract:Part I of this paper presents a self-contained analytical framework for determining the vibro-acoustic Response of a plate to a large class of random excitations. The wavenumber approach is used, which provides an insight into the physical properties of the Panel Response and enables us to evaluate efficiently the validity of several simplifying assumptions. This formulation is used in Part II for predicting the statistical Response of an aircraft Panel excited by a turbulent boundary layer. In this paper, we first provide a general statement of the problem and describe how the spectral densities of the Panel Response can be obtained from an analysis of the system Response to a harmonic deterministic excitation and a statistical model for the forcing field. The harmonic Response of the system is then expanded as a series of the eigenmodes of the fluid-loaded Panel and these fluid-loaded eigenmodes are approximated by a perturbation method. Then, we evaluate the conditions under which this series simplifies into a classical modal formulation in terms of the in vacuo eigenmodes. To illustrate the use of a wavenumber approach, we consider three examples, namely, the vibro-acoustic Response of a Panel excited by an incidence diffuse acoustic field, by a fully developed turbulent flow and by a pressure field which is spatially uncorrelated from one point to another. Convergence properties of the modal formulations are also examined.
Hong Hee Yoo - One of the best experts on this subject based on the ideXlab platform.
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supersonic flutter of functionally graded Panels subject to acoustic and thermal loads
Journal of Aircraft, 2009Co-Authors: Hesham Hamed Ibrahim, Hong Hee Yoo, Kwansoo LeeAbstract:of the volume fractions of the constituents. The governing equations are derived using the classical plate theory with von Karman geometric nonlinearity and the principle of virtual work. The first-order piston theory is adopted to model aerodynamic pressures induced by supersonic airflows. The thermal load is assumed to be steady-state constant temperature distribution, and the acoustic excitation is considered to be a stationary white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The governing equations are transformed to modal coordinates to reduce the computational efforts. The Newton–Raphson iteration method is employed to obtain the dynamic Response at each time step of the Newmark scheme for numerical integration. Finally, numerical results are provided to study the effects of the volume fraction exponent, aerodynamic pressure, temperature rise, and the random acoustic load on the Panel Response.
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Aerothermoacoustic Response of Shape Memory Alloy Hybrid Composite Panels
Journal of Aircraft, 2009Co-Authors: Hesham Hamed Ibrahim, Mohammad Tawfik, Hazem M Negm, Hong Hee YooAbstract:theacousticexcitationisconsideredtobeawhite-Gaussianrandompressurewithzeromeananduniformmagnitude over the Panel surface. Nonlinear temperature-dependence of material properties is considered in the formulation. The dynamic nonlinear equations of motion are transformed to modal coordinates to reduce the computational efforts. The Newton–Raphson iteration method is employed to obtain the dynamic Response at each time step of the Newmark numerical integration scheme. Finally, the nonlinear Response of a shape memory alloy hybrid composite Panel is presented, illustrating the effect of shape memory alloy fiber embeddings, aerodynamic pressure, sound pressure level, and temperature rise on the Panel Response.
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nonlinear flutter of shape memory alloy hybrid composite Panels subject to thermal and random acoustic loads
한국소음진동공학회 국제학술발표논문집, 2008Co-Authors: Hesham Hamed Ibrahim, Mohammad Tawfik, Hazem M Negm, Hong Hee YooAbstract:Nonlinear flutter of a traditional composite plate impregnated with pre-strained shape memory alloy fibers and subjected to combined thermal, aerodynamic and random acoustic loads are investigated. The nonlinear governing equations are obtained using the first-order shear-deformable plate theory, von Karman strain-displacement relations and the principle of virtual work. To account for the temperature dependence of material properties, the thermal strain is stated as an integral quantity of thermal expansion coefficient with respect to temperature. The thermal load is assumed to be steady state constant temperature distribution, and the acoustic excitation is considered to be a white-Gaussian random pressure with zero mean and uniform magnitude over the plate surface. The dynamic nonlinear equations of motion are transformed to modal coordinates to reduce the computational efforts. Finally, the nonlinear Response of a shape memory alloy hybrid composite plate Panel are presented, illustrating the effect of shape memory alloy fiber embeddings, sound pressure level, dynamic pressure and temperature rise on the Panel Response.
