Wave‐number domain separation of the incident and scattered sound field in Cartesian and cylindrical coordinates

1995 ◽  
Vol 97 (4) ◽  
pp. 2293-2303 ◽  
Author(s):  
Ming‐Te Cheng ◽  
J. Adin Mann ◽  
Anna Pate
Keyword(s):  
Sound Field ◽  
Wave Number ◽  
Cylindrical Coordinates ◽  
Domain Separation

A high-precision reconstructing technique for a high-frequency acoustic field based on the angular spectrum method

2010 ◽  
Vol 225 (3) ◽  
pp. 745-753
Author(s):  
Y Shao ◽  
D Mei ◽  
Z Fan ◽  
K Yang
Keyword(s):  
High Precision ◽  
High Frequency ◽  
Sound Field ◽  
Angular Spectrum ◽  
Wave Number ◽  
Reconstruction Technique ◽  
High Frequency Sound ◽  
Frequency Sound ◽  
Spectrum Method ◽  
Angular Spectrum Method

To apply ultrasonic radiation force in precise manipulation for micro-components, a reconstruction technique for low-frequency sound field based on angular spectrum method (ASM) was adopted in the reconstruction for high-frequency sound field, and a high-precision reconstructing technique for high-frequency sound field was developed. First, the principle of reconstructing the sound field by ASM and four key factors on reconstruction precision were analysed. Second, the marginal Gibbs phenomenon and aperture replication effect were decreased by optimizing of the sampling interval and holographical aperture, and the signal-to-noise ratio (SNR) was increased by using the tapered filter to pretreat the signal data in wave number space. Then, the ill-posedness in reverse problem was eliminated by using a new kind of k-space filter to refine the transfer function. Finally, the reconstruction experiment of 1.75 MHz ultrasonic field was conducted by using the three-dimensional precise scanning system and needle-type hydrophone, and the experimental results validate the feasibility and efficiency of the method proposed in this study.

Reconstruction of Interior Sound Fields of Vibrating Shells with an Open Spherical Microphone Array

2016 ◽  
Vol 24 (04) ◽  
pp. 1650013 ◽  
Author(s):  
Minzong Li ◽  
Huancai Lu
Keyword(s):  
Cross Validation ◽  
Microphone Array ◽  
Sound Field ◽  
Reconstruction Error ◽  
Wave Number ◽  
Tikhonov Regularization Method ◽  
Sound Fields ◽  
Noise Regularization ◽  
Enclosed Space ◽  
The Impact

Spherical acoustic holography was utilized to reconstruct the interior sound field of an enclosed space with vibrating boundaries using an open spherical microphone array. The interior sound fields of vibrating shells, including a pulsating shell, a [Formula: see text]-axis oriented oscillating shell, a partially vibrating shell and a point-excited vibrating shell, were reconstructed, and numerical simulations were carried out to examine the impact of reconstruction parameters, the radius of the microphone array, the number of microphones, the distribution of microphones on the array surface, the wave number, the number of basis functions used, and the radius of the reconstruction surface on the accuracy of reconstruction. In order to minimize the error of reconstruction caused by a variety of factors and uncertainties, such as the measurement noise, regularization treatments were introduced into the process of reconstructing, to suppress the divergent trends of the reconstruction error along with the increase of the wave number and the increase of the radius of the reconstruction surface. Results showed that a Tikhonov regularization method with generalized cross validation (GCV) could yield the least error of reconstruction among the investigated regularization methods.

Parabolized Stability Equation Based Analysis of Noise From an Axisymmetric Hot Jet

Volume 1 ◽  
2004 ◽  
Author(s):  
Ray-Sing Lin ◽  
Ramons A. Reba ◽  
Satish Narayanan ◽  
Nathan S. Hariharan ◽  
Fabio P. Bertolotti
Keyword(s):  
Large Scale ◽  
Near Field ◽  
Sound Field ◽  
Wave Number ◽  
Navier Stokes ◽  
Mean Flow ◽  
Noise Sources ◽  
Stability Equation ◽  
Low Frequencies ◽  
Potential Core

Noise generated from large-scale wave-like eddies in a Mach 0.9 hot axisymmetric jet is studied. The mean jet flow is computed using a Reynolds-Averaged Navier-Stokes solver with the k-ω turbulence model. Spatial development of near-field pressure perturbations is computed using a 3D Parabolized Stability Equation (PSE) method, and the far-field noise radiated from these convective instabilities is obtained by solving the wave equation. The 3D PSE method developed here allows the effects of strong azimuthal mean-flow variations to be captured and analyzed. Results show that large-scale wave-like eddies, or instability waves, travel slightly above sonic speed for the first few jet diameters, and that the dominant noise sources are concentrated near the edge of the time-averaged potential core. Good agreement between computed results and experiment are found for relative sound pressure levels and directivity. Also, at the low frequencies considered, the sound field associated with azimuthal wave-number m = 0 shows better agreement with experimental data than with (the most amplified) m = 1.

On the energy scattered from the interaction of turbulence with sound or shock waves

1953 ◽  
Vol 49 (3) ◽  
pp. 531-551 ◽  
Author(s):  
M. J. Lighthill
Keyword(s):  
Shock Wave ◽  
Wave Length ◽  
Acoustic Pulse ◽  
Supersonic Jet ◽  
Sound Field ◽  
Weak Shock ◽  
Wave Pattern ◽  
Wave Number ◽  
Directional Distribution ◽  
Macro Scale

ABSTRACTThe energy scattered when a sound wave passes through turbulent fluid flow is studied by means of the author's general theory of sound generated aerodynamically. The energy scattered per unit time from unit volume of turbulence is estimated (§3) aswhere I is the intensity and ∧ the wave-length of the incident sound, and is the mean square velocity and L1 the macro-scale of the turbulence in the direction of the incident sound. This formula does not assume any particular kind of turbulence, but does assume that ∧/L1 is less than about 1. For turbulence which is isotropic and homogeneous, the energy scattered, and its directional distribution, are obtained for arbitrary values of ∧/L1. It is predicted that components of the turbulence with wave-number κ will scatter sound of wave-number K at an angle 2 sin−1 (k/2k). The statistics of multiple successive scatterings is considered (§4), and it is predicted that sound of wave-length less than the micro-scale λ of the turbulence will become uniform (i.e. quite random) in its directional distribution in a distance approximately .The theory is extended (§5) to the case of an incident acoustic pulse. However, this extended theory cannot be applied directly to the case of a shock wave, for which it would predict infinite scattered energy. This is due to the perfect resonance between successive rays emitted forwards which would occur if the shock wave were propagated at the speed of sound. By taking into account (§6) the true speed of the shock wave (subsonic relative to the fluid behind it), the theory is improved to give a finite value, 0·8s tunes the kinetic energy of the turbulence traversed by a weak shock of strength s, for the total energy scattered. However, the greater part of this energy catches up with the shock wave, and probably is mostly reabsorbed by it, and only the remainder (tabulated as a function of s in Table 1) is freely scattered, behind the shock wave, as sound. The energy thus freely scattered when turbulence is convected through the stationary shock-wave pattern in a supersonic jet may form an important part of the sound field of the jet.

The two-dimensional sound field due to a pair of interacting compliant pistons

1995 ◽  
Vol 450 (1940) ◽  
pp. 513-536 ◽  
Keyword(s):  
Boundary Value Problem ◽  
Boundary Value ◽  
Sound Field ◽  
Wave Number ◽  
Two Dimensional ◽  
Fluid Loading ◽  
Time Harmonic ◽  
Loading Effects ◽  
Specific Impedance ◽  
Impedance Conditions

Compressible fluid occupies the half-space y > 0 and the plane y = 0 is acoustically hard except for two parallel compliant strips, referred to as ‘pistons’ S 0 and S 1 , on which impedance conditions apply. The pistons have respective widths 2 a 0 and 2 a 1 and their centres are separated by distance d . A two-dimensional time-harmonic sound field is induced by forcing behind the pistons or through the action of an incident wave, with coupling between the two pistons due to fluid loading effects. In the limit d ≫ max( a 0 , a 1 ) the five-part boundary-value problem is reduced to that of four separate single-piston potentials, each of which is a three-part boundary-value problem that can be solved using the modified Wiener-Hopf technique. With a 0 = a 1 and forcing that is symmetric about the midplane, there are only two potentials, ϕ p0 and ϕ c0 . The potential ϕ p0 is that of piston S 0 in isolation, and ϕ c0 accounts for the coupling between S 0 and S 1 . Details are given for the high-frequency limit ka ≫ 1, where k is the acoustic wave number, and for large real values of the specific impedance of the pistons. The method can be generalized to deal with any number of pistons, with a variety of boundary conditions.

Decay of Temporary Threshold Shift in Noise

1973 ◽  
Vol 16 (2) ◽  
pp. 267-270 ◽  
Author(s):  
John H. Mills ◽  
Seija A. Talo ◽  
Gloria S. Gordon
Keyword(s):  
Sound Field ◽  
Threshold Shift ◽  
Temporary Threshold Shift ◽  
Octave Band ◽  
Band Noise ◽  
Lower Asymptote

Groups of monaural chinchillas trained in behavioral audiometry were exposed in a diffuse sound field to an octave-band noise centered at 4.0 k Hz. The growth of temporary threshold shift (TTS) at 5.7 k Hz from zero to an asymptote (TTS ∞ ) required about 24 hours, and the growth of TTS at 5.7 k Hz from an asymptote to a higher asymptote, about 12–24 hours. TTS ∞ can be described by the equation TTS ∞ = 1.6(SPL-A) where A = 47. These results are consistent with those previously reported in this journal by Carder and Miller and Mills and Talo. Whereas the decay of TTS ∞ to zero required about three days, the decay of TTS ∞ to a lower TTS ∞ required about three to seven days. The decay of TTS ∞ in noise, therefore, appears to require slightly more time than the decay of TTS ∞ in the quiet. However, for a given level of noise, the magnitude of TTS ∞ is the same regardless of whether the TTS asymptote is approached from zero, from a lower asymptote, or from a higher asymptote.

Modified Earpieces and CROS for High Frequency Hearing Losses

1968 ◽  
Vol 11 (1) ◽  
pp. 204-218 ◽  
Author(s):  
Elizabeth Dodds ◽  
Earl Harford
Keyword(s):  
Hearing Loss ◽  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Sound Field ◽  
Intensity Level ◽  
Test Results ◽  
High Frequency Hearing Loss ◽  
Increased Sensitivity ◽  
Difficult Cases

Persons with a high frequency hearing loss are difficult cases for whom to find suitable amplification. We have experienced some success with this problem in our Hearing Clinics using a specially designed earmold with a hearing aid. Thirty-five cases with high frequency hearing losses were selected from our clinical files for analysis of test results using standard, vented, and open earpieces. A statistical analysis of test results revealed that PB scores in sound field, using an average conversational intensity level (70 dB SPL), were enhanced when utilizing any one of the three earmolds. This result was due undoubtedly to increased sensitivity provided by the hearing aid. Only the open earmold used with a CROS hearing aid resulted in a significant improvement in discrimination when compared with the group’s unaided PB score under earphones or when comparing inter-earmold scores. These findings suggest that the inclusion of the open earmold with a CROS aid in the audiologist’s armamentarium should increase his flexibility in selecting hearing aids for persons with a high frequency hearing loss.

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

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