The power spectrum and correlation of flow noise for an axisymmetric body in water

The flow noise of a sonar platform is one of the main background interferences for sonar applications. This paper focuses on the flow noise of an axisymmetric body in a complex oceanic environment. Under the condition of a constant stream velocity which comes from the axial direction, an analytical method for computing the flow noise power spectrum in the transition region of the axisymmetric body is given in detail. The flow noise power spectrum computed by the analytical method is in agreement with the numerical simulation result. Then the flow noise physical features of the axisymmetric body in different incoming stream directions and velocity states caused by the complex oceanic environment are computed and analyzed by the numerical method. The results show that as the incoming stream direction changes, the transition region will migrate and the flow noise radiation direction of the axisymmetric body will also rotate at an angle which equals the stream direction variation. The flow noise energy generated by other directional incoming streams is slightly larger than that generated by the stream coming from an axial direction. When the incoming stream velocity is time-varying, the vorticity change on the axisymmetric body surface is obviously stronger than that under a constant stream, and the generated flow noise energy is also significantly larger. In addition, it indicates that there is a significant correlation between the intensity of flow noise energy and the magnitude of flow velocity.

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Flow noise from the transition region of an axisymmetric body in water

The Journal of the Acoustical Society of America ◽

10.1121/1.4708854 ◽

2012 ◽

Vol 131 (4) ◽

pp. 3427-3427

Author(s):

Xuegang Li ◽

Kunde Yang ◽

Yuanliang Ma

Keyword(s):

Transition Region ◽

Axisymmetric Body ◽

Flow Noise

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Flow noise scaling at the stagnation point of an axisymmetric body

Journal of Sound and Vibration ◽

10.1016/0022-460x(92)90788-y ◽

1992 ◽

Vol 154 (3) ◽

pp. 568-572 ◽

Cited By ~ 5

Author(s):

G.C. Lauchle

Keyword(s):

Stagnation Point ◽

Axisymmetric Body ◽

Flow Noise

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Studies on scaling of flow noise received at the stagnation point of an axisymmetric body

Journal of Sound and Vibration ◽

10.1016/0022-460x(91)90701-k ◽

1991 ◽

Vol 146 (3) ◽

pp. 449-462 ◽

Cited By ~ 13

Author(s):

V.H. Arakeri ◽

S.G. Satyanarayana ◽

K. Mani ◽

S.D. Sharma

Keyword(s):

Stagnation Point ◽

Axisymmetric Body ◽

Flow Noise

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The on-line use of histogram data for high-speed correction and alignment of electron microscope images

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100112713 ◽

1984 ◽

Vol 42 ◽

pp. 556-557

Author(s):

William Krakow

Keyword(s):

Power Spectrum ◽

High Speed ◽

Direct Memory Access ◽

Digital Television ◽

Contrast Transfer Function ◽

The Past ◽

High Resolution Tem ◽

On Line ◽

Correction Of Astigmatism ◽

The Fourier Transform

In the past few years on-line digital television frame store devices coupled to computers have been employed to attempt to measure the microscope parameters of defocus and astigmatism. The ultimate goal of such tasks is to fully adjust the operating parameters of the microscope and obtain an optimum image for viewing in terms of its information content. The initial approach to this problem, for high resolution TEM imaging, was to obtain the power spectrum from the Fourier transform of an image, find the contrast transfer function oscillation maxima, and subsequently correct the image. This technique requires a fast computer, a direct memory access device and even an array processor to accomplish these tasks on limited size arrays in a few seconds per image. It is not clear that the power spectrum could be used for more than defocus correction since the correction of astigmatism is a formidable problem of pattern recognition.

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Log-log scale roughness spectroscopy of surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100146965 ◽

1993 ◽

Vol 51 ◽

pp. 224-225

Author(s):

P. Fraundorf ◽

B. Armbruster

Keyword(s):

Power Spectrum ◽

Autocorrelation Function ◽

Power Spectra ◽

Scanning Force Microscopy ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Scanning Force ◽

Lateral Structure ◽

Scale Roughness

Optical interferometry, confocal light microscopy, stereopair scanning electron microscopy, scanning tunneling microscopy, and scanning force microscopy, can produce topographic images of surfaces on size scales reaching from centimeters to Angstroms. Second moment (height variance) statistics of surface topography can be very helpful in quantifying “visually suggested” differences from one surface to the next. The two most common methods for displaying this information are the Fourier power spectrum and its direct space transform, the autocorrelation function or interferogram. Unfortunately, for a surface exhibiting lateral structure over several orders of magnitude in size, both the power spectrum and the autocorrelation function will find most of the information they contain pressed into the plot’s origin. This suggests that we plot power in units of LOG(frequency)≡-LOG(period), but rather than add this logarithmic constraint as another element of abstraction to the analysis of power spectra, we further recommend a shift in paradigm.

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