Extraneous Frequencies Generated in Air Carrying Intense Sound Waves*

Thuras, A. L.; Jenkins, R. T.; O'Neil, H. T.

doi:10.1002/j.1538-7305.1935.tb00688.x

Cited by 8 publications

(2 citation statements)

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“…Excess attenuation at high amplitudes arises from increased flow resistance as well as energy shifted into higher, odd harmonics. Amplitude saturation occurs at high amplitudes when excess attenuation balances increased amplitude, as documented in air by Thuras et al 32 and in porous materials by Kuntz. 1 The collection of parameters KA 10 /Q 1 corresponds to the Gol'dberg number À in the familiar solution to Burgers' equation.…”

Section: Propagation Within the Materialsmentioning

confidence: 83%

Nonlinear effects on tonal sound in lined ducts

Nelson

2016

International Journal of Aeroacoustics

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Porous sound absorbers are a familiar and supposedly well-understood feature of the noise control palette. As in many other aspects of engineering, however, aerospace applications require a degree of mastery well beyond the common place: sound absorbers must be designed to be effective at high noise levels within strict mass and volume constraints. In the process of fine-tuning sound absorbers for jet aircraft, it was discovered that high incident sound pressure levels cause the performance of lined ducts to diverge from small-signal predictions. The underlying physics was not fully understood prior to the early 1980s, at which point NASA-sponsored research disclosed and quantified the primary mechanism. Further research by others continues building on that foundation down to the present. This paper gives a brief overview of the topic, summarizes one of the research efforts, and adapts its findings for lined duct applications.

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Section: Propagation Within the Materialsmentioning

confidence: 83%

Nonlinear effects on tonal sound in lined ducts

Nelson

2016

International Journal of Aeroacoustics

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“…The need to investigate this aspect is that several disciplines are interesting in this aspect, disciplines as medicine, engineering, etc. The first fluid that was investigated was air [ 16 ]. After that, some investigators studied nonlinearity in other fluids.…”

Section: Introductionmentioning

confidence: 99%

Experimental Configuration to Determine the Nonlinear Parameter β in PMMA and CFRP with the Finite Amplitude Method

Callejas

Rus

2019

Sensors

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Parameters to measure nonlinearity in polymethylmethacrylate (PMMA) and carbon fiber reinforced polymer (CFRP) materials have been determined with nonlinear ultrasound (NLUS). The nonlinear parameter β has been determined using the variation of the Finite Amplitude Method (FAM) with harmonic generation. Using this as a reference, the first contribution of this work consists of deducting the experimental configuration necessary to measure this nonlinear parameter in a correct and feasible way. Excitation level, frequency of the wave generated, number of cycles analysed and the distances transducer-specimen and specimen-hydrophone have been determined in both materials. The second contribution is a semi-analytical model that allows to obtain the nonlinear parameter in materials by removing water contribution and considering geometric and viscous attenuation, using the data obtained in an immersion tank. Finally, an application of this model has been carried out in PMMA in order to determinate the nonlinear parameter in this material. From the results, we confirm that the configuration determined in this paper to obtain the parameter β decreases the noise in the measurements.

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Analytical effective thermal conductivity model for colloidal porous composites and nanocomposites based on novolac/graphene oxide aerogels

Nazari

Allahbakhsh

Bahramian

2022

Intl J of Energy Research

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The performance of porous composite materials in thermal energy storage and management applications can be engineered by controlling the relationship between the heat transfer mechanism and the structure of these materials. Analytical thermal conductivity models are essential tools to study and manage such structure/heat transfer relations in porous composite materials. This study develops an analytical thermal conductivity model for porous composites with colloidal matrix morphologies. The model developed here is a modified series-parallel model that considers important structural parameters such as the system's porosity, the colloidal size of the matrix, and the filler's aspect ratio. Moreover, essential effects in the structure of porous composites, including the gas-solid coupling effect and contact length of particles, are also included in the model developed here. In addition, this model can be used in a wide range of porosity and can predict the thermal conductivity of porous composites with appropriate accuracy by changing temperature, pressure, specific surface area, porosity, and other textural properties. Novolac/graphene oxide nanocomposite aerogels with different contents of graphene oxide (GO) nanosheets in the structure were prepared and used to study the validity of the data calculated using the developed model. Our results confirmed that

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Extraneous Frequencies Generated in Air Carrying Intense Sound Waves*

Cited by 8 publications

References 0 publications

Nonlinear effects on tonal sound in lined ducts

Nonlinear effects on tonal sound in lined ducts

Experimental Configuration to Determine the Nonlinear Parameter β in PMMA and CFRP with the Finite Amplitude Method

Analytical effective thermal conductivity model for colloidal porous composites and nanocomposites based on novolac/graphene oxide aerogels

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