Sound propagation in the near and far-field of a broadband echolocating dolphin and a narrowband echolocating porpoise

A numerical study on multimode sound propagation in lined ducts and radiation to the far field

The Journal of the Acoustical Society of America ◽

10.1121/1.2933070 ◽

2008 ◽

Vol 123 (5) ◽

pp. 3128-3128

Author(s):

Rie Sugimoto ◽

R Jeremy Astley ◽

Claire R. McAleer ◽

Iansteel Achunche

Keyword(s):

Sound Propagation ◽

Numerical Study ◽

Far Field ◽

Lined Ducts

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Integrated “CFD - Acoustic” Computational Approach to the Simulation of Aircraft Fan Noise

Volume 2A: Turbomachinery ◽

10.1115/gt2014-26429 ◽

2014 ◽

Author(s):

Piergiorgio Ferrante ◽

Paolo di Francescantonio ◽

Pierre-Alain Hoffer ◽

Stéphane Vilmin ◽

Charles Hirsch

Keyword(s):

Unsteady Flow ◽

Sound Propagation ◽

Noise Source ◽

Acoustic Radiation ◽

Near Field ◽

Sound Field ◽

Computational Approach ◽

Far Field ◽

Fan Noise ◽

Field Noise

An innovative computational approach, integrating mesh generation, CFD simultaneous analysis of noise source and propagation, with acoustic radiation, is presented and applied to the simulation of the Advanced Noise Control Fan (ANCF) developed by NASA Glenn Research Center. The tonal noise source and the sound propagation in the nacelle duct and in the nacelle near field are simultaneously predicted, starting from the engine geometry and parameters, with a single CFD analysis based on an efficient Nonlinear Harmonic (NLH) method. The sound radiation to the far field is computed with the Green’s function approach implemented in a BEM frequency domain solver of the convective Helmholtz equation. The present method provides to a gain of close to two orders of magnitude compared to standard approaches, based on full unsteady flow simulations, followed by a near-field FEM based approach and a BEM method for the far-field noise propagation. The final comparison between the numerical results and the measurements highlights the capability of the methodology to efficiently predict the unsteady flow field and the radiated sound field.

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Possible applications of fraunhofer holography in high resolution electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108258 ◽

1978 ◽

Vol 36 (1) ◽

pp. 222-223 ◽

Cited By ~ 1

Author(s):

N. Bonnet ◽

M. Troyon ◽

P. Gallion

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Transfer Function ◽

Radiation Damage ◽

High Resolution Electron Microscopy ◽

Far Field ◽

Field Region ◽

Crystalline Materials ◽

Resolution Electron ◽

The Ideal

Two main problems in high resolution electron microscopy are first, the existence of gaps in the transfer function, and then the difficulty to find complex amplitude of the diffracted wawe from registered intensity. The solution of this second problem is in most cases only intended by the realization of several micrographs in different conditions (defocusing distance, illuminating angle, complementary objective apertures…) which can lead to severe problems of contamination or radiation damage for certain specimens.Fraunhofer holography can in principle solve both problems stated above (1,2). The microscope objective is strongly defocused (far-field region) so that the two diffracted beams do not interfere. The ideal transfer function after reconstruction is then unity and the twin image do not overlap on the reconstructed one.We show some applications of the method and results of preliminary tests.Possible application to the study of cavitiesSmall voids (or gas-filled bubbles) created by irradiation in crystalline materials can be observed near the Scherzer focus, but it is then difficult to extract other informations than the approximated size.

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