Flow noise calculations for extended hydrophones in fluid- and solid-filled towed arrays

Knight, A.

doi:10.1121/1.415891

Cited by 25 publications

(7 citation statements)

References 8 publications

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“…v * is the friction velocity and is typically of the order of 0.03U-0.04U. [124] For a rigid cylinder, rather than a flat plate, Knight [125] gives an empirical spectrum as…”

Section: Source Of Flow Noisementioning

confidence: 99%

Investigation of ocean acoustics using autonomous instrumentation to quantify the water-sediment boundary properties

Carey

Holmes

2006

The Journal of the Acoustical Society of America

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Several noise criteria methods commonly used in architectural acoustics have been quantitatively related to noise perception and task performance under a variety of ventilation systems-induced background noise conditions. Noise criteria, balanced noise criteria, room criteria, room criteria mark II, and A-weighted equivalent sound pressure level were examined. The first phase of the project included noise conditions controlled to be non-time-varying and nontonal, with neutral, rumbly, roaring, or hissy characteristics. An intermediate study examined exposure time length and types of performance tasks used. The final phase included noise conditions containing various levels of discrete tones from 120 to 595 Hz. Under each noise, subjects completed performance tasks and perception questionnaires. Results indicate task performance was significantly affected by perception of noise, but this relationship was not fully demonstrated by the criteria systems analyzed. The five criteria were generally well suited in describing subjective loudness perception, but some discrepancies in criteria spectral quality ratings and subjective perception existed. Finally, perception of annoyance changed based on the frequency and prominence of tones in noise, but these changes were not reflected in the criteria level or spectral quality ratings. Modifications to the existing criteria are recommended.

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“…v * is the friction velocity and is typically of the order of 0.03U-0.04U. [124] For a rigid cylinder, rather than a flat plate, Knight [125] gives an empirical spectrum as…”

Section: Source Of Flow Noisementioning

confidence: 99%

Investigation of ocean acoustics using autonomous instrumentation to quantify the water-sediment boundary properties

Carey

Holmes

2006

The Journal of the Acoustical Society of America

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“…The sensors on towed arrays are usually mounted along the axis of the cylinder, and measure averaged pressure in some form rather than point pressure, through a transfer function representing the transfer of the surface pressure fluctuations to the axis. The form of the transfer function will depend on the construction of the array and the configuration of the sensors, and will not be considered here (see Knight 1996 for a theoretical study of this effect). The work presented here is concerned mainly with behaviour quantities relevant to the performance of towed arrays.…”

Section: Introductionmentioning

confidence: 99%

Flow along a long thin cylinder

Tutty

2008

J. Fluid Mech.

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Two different approaches have been used to calculate turbulent flow along a long thin cylinder where the flow is aligned with the cylinder. A boundary-layer code is used to predict the mean flow for very long cylinders (length to radius ratio of up to O(10 6 )), with the effects of the turbulence estimated through a turbulence model. Detailed comparison with experimental results shows that the mean properties of the flow are predicted within experimental accuracy. The boundary-layer model predicts that, sufficiently far downstream, the surface shear stress will be (almost) constant. This is consistent with experimental results from long cylinders in the form of sonar arrays. A periodic Navier-Stokes problem is formulated, and solutions generated for Reynolds number from 300 to 5 × 10 4 . The results are in agreement with those from the boundary-layer model and experiments. Strongly turbulent flow occurs only near the surface of the cylinder, with relatively weak turbulence over most of the boundary layer. For a thick boundary layer with the boundary-layer thickness much larger than the cylinder radius, the mean flow is effectively constant near the surface, in both temporal and spatial frameworks, while the outer flow continues to develop in time or space. Calculations of the circumferentially averaged surface pressure spectrum show that, in physical terms, as the radius of the cylinder decreases, the surface noise from the turbulence increases, with the maximum noise at a Reynolds number of O(10 3 ). An increase in noise with a decrease in radius (Reynolds number) is consistent with experimental results.

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“…Each acoustic 'super-element' in ARL DTLA consisted of 6 numbers of 8 mm long 2.3 mm diameter piezo-ceramic hydrophones connected in series to achieve better sensitivity and also to increase the effective aperture of the transducer to improve TBL noise filtering. The flow noise filtering arising due to the finite dimension and distribution of multiple sensors in the acoustic element are accounted for through a procedure similar to the ones detailed in references [7], [8], [3]. Assuming uniform sensitivity along the length of the sensor, the wavenumber response characteristics of an acoustic element made of N sensors of length l connected series in can be expressed as…”

Section: Empirical Estimates Of Flow Noisementioning

confidence: 99%

Estimated flow noise levels due to a thin line digital towed array

Unnikrishnan

Pallayil

Kuselan

2011

OCEANS 2011 IEEE - Spain

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Flow noise levels for a digital thin line towed array for normal operating speeds of an AUV were estimated using empirical models and towing experiments. The wavenumber filtering associated with the finite size and distribution of hydrophones in acoustic element of DTLA was applied to the empirical models of turbulent wall pressure spectra to estimate the expected flow noise levels. The empirical results were then compared with the noise spectra measured during towing experiments conducted in a quiet lake. The results showed rapid loss of flow noise energy with increase in frequency arising due to the very nature of turbulent noise spectra and flow noise averaging introduced by the finite size of the hydrophone.

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Flow noise calculations for extended hydrophones in fluid- and solid-filled towed arrays

Cited by 25 publications

References 8 publications

Investigation of ocean acoustics using autonomous instrumentation to quantify the water-sediment boundary properties

Investigation of ocean acoustics using autonomous instrumentation to quantify the water-sediment boundary properties

Flow along a long thin cylinder

Estimated flow noise levels due to a thin line digital towed array

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