The acoustic surface wave above a complex impedance ground surface

Raspet, Richard; Baird, Gordon E.

doi:10.1121/1.397588

Cited by 14 publications

(3 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4 This wave does not exist at large numerical distances because Re sin p Ͻ 1. Raspet and Baird 15 have shown that Re sin p Ͻ 1 is not always true for semiinfinite porous layers described using the empirical laws of Delany and Bazley. 16 However, this condition has always been verified for semi-infinite porous layers when the causal equivalent densities and incompressibilities of the present work are used, and for the measurements described in the next section.…”

Section: Poles and Zeros Of The Reflection Coefficient For Semi-mentioning

confidence: 98%

Impedance and Brewster angle measurement for thick porous layers

Hickey

Leary

Allard

et al. 2005

The Journal of the Acoustical Society of America

View full text Add to dashboard Cite

For thin nonlocally reacting porous layers, a method derived from the work of ͓Chien and Soroka, J. Sound Vib. 43, 9-20 ͑1975͔͒ has been used to localize the pole of the reflection coefficient located at a complex angle close to / 2 and to measure the surface impedance at this angle. Measurements are performed with a small source/receiver separation. The method is used in the present work to measure the surface impedance of acoustically thick porous layers of high flow resistivity. Simulations show that the measured impedance, which is related to a complex angle close to /2 like for thin porous layers, is close to the impedance at grazing incidence. It is also shown that for semi-infinite layers the method provides a measure of the Brewster angle of the medium. Measurements of the cosine of the complex angle and of the related impedance on two granular media of high flow resistivity, Ottawa sand and glass beads, are in a reasonable agreement with predictions for frequencies above 1 kHz for a source/receiver separation of 30 cm.

show abstract

Section: Poles and Zeros Of The Reflection Coefficient For Semi-mentioning

confidence: 98%

Impedance and Brewster angle measurement for thick porous layers

Hickey

Leary

Allard

et al. 2005

The Journal of the Acoustical Society of America

View full text Add to dashboard Cite

show abstract

“…These authors used a form of the ray-tracing algorithm. Also notable are the modifications proposed by Raspet et al 257,258 , who expressed the solution as a residue series and normal mode solution for an upward and downward refracting atmosphere, respectively. This formulation is unlikely to provide any computational advantage.…”

Section: Far-field Noise Propagationmentioning

confidence: 99%

Aircraft noise prediction

Smith¹

1989

Aircraft Noise

View full text Add to dashboard Cite

This contribution addresses the state-of-the-art in the field of aircraft noise prediction, simulation and minimisation. The point of view taken in this context is that of comprehensive models that couple the various aircraft systems with the acoustic sources, the propagation and the flight trajectories. After an exhaustive review of the present predictive technologies in the relevant fields (airframe, propulsion, propagation, aircraft operations, trajectory optimisation), the paper addresses items for further research and development. Examples are shown for several airplanes, including the Airbus A319-100 (CFM engines), the Bombardier Dash8-Q400 (PW150 engines, Dowty R408 propellers) and the Boeing B737-800 (CFM engines). Predictions are done with the flight mechanics code FLIGHT. The transfer function between flight mechanics and the noise prediction is discussed in some details, along with the numerical procedures for validation and verification. Some code-to-code comparisons are shown. It is contended that the field of aircraft noise prediction has yet not reached a sufficient level of maturity. In particular, some parametric effects cannot be investigated, issues of accuracy are not currently addressed, and validation standards are still lacking.

show abstract

“…The theoretical basis for the generation of acoustic surface waves above an impedance plane has been investigated by many workers including Thomasson 2 who showed that if a surface has an impedance with an imaginary part much larger than the real part, an acoustic surface wave can be generated when the incident wave is at or near grazing incidence. Later, Raspet and Baird 3 demonstrated that such a surface wave is an independently propagating wave. Also, it was shown by Tolstoy 4,5 and Twersky 6 that acoustic surface waves can also be generated by rough surfaces.…”

Section: Introductionmentioning

confidence: 99%