Effect of random velocity fluctuations on underwater scattering

1987 ◽  
Vol 81 (3) ◽  
pp. 647-649 ◽  
Author(s):  
Mark J. Beran ◽  
Alan M. Whitman
Keyword(s):  
Velocity Fluctuations ◽  
Random Velocity

Paper 7: Sump for Tilbury Dock Extensions

1967 ◽  
Vol 182 (13) ◽  
pp. 48-53
Author(s):  
L. Fellerman
Keyword(s):  
Velocity Fluctuation ◽  
Flow Conditions ◽  
Low Velocity ◽  
Velocity Fluctuations ◽  
Random Velocity ◽  
Use Of Models

This paper describes the study, by use of models, of two sumps for the installation of impounding pumps at the Tilbury Dock extension. The first design studied indicated that there would be excessive random velocity fluctuations in the area of the impeller. Modifications reduced the fluctuations to more reasonable proportions. Problems of locating the impeller in a plane of low-velocity fluctuation led to a study of a second design of sump. The second design, with the aid of flow straightening diaphragms, produced improved flow conditions in the plane of the impellers.

Isotropic scattering coefficient of the solid earth

2019 ◽  
Vol 218 (3) ◽  
pp. 2079-2088 ◽  
Author(s):  
Haruo Sato
Keyword(s):  
Solid Earth ◽  
Upper Mantle ◽  
Scattering Coefficient ◽  
Isotropic Scattering ◽  
Spectral Envelope ◽  
The Moon ◽  
Velocity Fluctuations ◽  
Random Velocity ◽  
Scattering Coefficients ◽  
Wide Range

SUMMARY The isotropic scattering model is a simple mathematical model of the radiative transfer theory (RTT) for the propagation of the wave energy density in random media. There have been many measurements of the isotropic scattering coefficient of the heterogeneous solid earth medium, where the target region varies from the lower and upper mantle, the crust, sediments, volcanoes, mines, rock samples and also the crust and the upper mantle of the moon. Reported isotropic scattering coefficients increase according to some power of frequency with some scatter. We know that the RTT is well approximated by the diffusion equation in the multiple scattering regime, where the equipartition is established. Then, the transport scattering coefficient effectively functions as an isotropic scattering coefficient even if the scattering coefficient derived by the Born approximation for the random velocity fluctuation is anisotropic. Recent review of the power spectral density functions of random velocity fluctuations in the solid earth revealed from various kinds of measurements shows that their spectral envelope is well approximated by the inverse cube of wavenumber for a wide range of wavenumbers (Sato, 2019). The transport scattering coefficient derived from the spectral envelope linearly increases with frequency, which well explains the observed isotropic scattering coefficients for a wide range of frequencies. However, some reported isotropic scattering coefficients show unusual behaviour: the isotropic scattering coefficient increases as depth decreases in the crust and the upper mantle of the earth and the moon, those beneath volcanoes are larger than those in the lithosphere, and that in a sandstone sample with a large porosity is larger than that in a gabbro sample with little porosity. Those differences may suggest possible scattering contribution of pores and cracks widely distributed in addition to the scattering by random velocity fluctuations.

Characteristics of Long-Period Flow Velocity Fluctuations around Tomakomai Harbor

1999 ◽  
Author(s):  
Hiroya Kinoshita ◽  
Hideki Hoshi ◽  
Youichi Atsumi ◽  
Shin-ichiro Sekiguchi ◽  
Toshihiko Yamashita
Keyword(s):  
Flow Velocity ◽  
Velocity Fluctuations ◽  
Long Period

Local Measurements of Radial Plasma Velocity Fluctuations in the FT-2 Tokamak Using Equatorial Enhanced Scattering

2020 ◽  
Vol 46 (8) ◽  
pp. 767-770
Author(s):  
A. D. Gurchenko ◽  
E. Z. Gusakov ◽  
A. B. Altukhov ◽  
V. A. Ivanov ◽  
A. V. Sidorov ◽  
...  
Keyword(s):  
Plasma Velocity ◽  
Velocity Fluctuations ◽  
Local Measurements

scholarly journals Three-dimensional analysis of intracycle velocity fluctuations in frontcrawl swimming

2010 ◽  
Vol 20 (1) ◽  
pp. 128-135 ◽  
Author(s):  
S. G. Psycharakis ◽  
R. Naemi ◽  
C. Connaboy ◽  
C. McCabe ◽  
R. H. Sanders
Keyword(s):  
Dimensional Analysis ◽  
Three Dimensional ◽  
Velocity Fluctuations

scholarly journals Fractal-induced 2D flexible net undulation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Michael Joon Seng Goh ◽  
Yeong Shiong Chiew ◽  
Ji Jinn Foo
Keyword(s):  
3D Reconstruction ◽  
Cross Section ◽  
Channel Cross Section ◽  
Time Varying ◽  
Blockage Ratio ◽  
Transient Time ◽  
Cross Sectional ◽  
Velocity Fluctuations ◽  
Square Grid ◽  
Multilength Scale

AbstractA net immersed in fractal-induced turbulence exhibit a transient time-varying deformation. The anisotropic, inhomogeneous square fractal grid (SFG) generated flow interacts with the flexible net to manifest as visible cross-sectional undulations. We hypothesize that the net’s response may provide a surrogate in expressing local turbulent strength. This is analysed as root-mean-squared velocity fluctuations in the net, displaying intensity patterns dependent on the grid conformation and grid-net separation. The net’s fluctuation strength is found to increase closer to the turbulator with higher thickness ratio while presenting stronger fluctuations compared to regular-square-grid (RSG) of equivalent blockage-ratio, σ. Our findings demonstrate a novel application where 3D-reconstruction of submerged nets is used to experimentally contrast the turbulence generated by RSG and multilength scale SFGs across the channel cross-section. The net’s response shows the unique turbulence developed from SFGs can induce 9 × higher average excitation to a net when compared against RSG of similar σ.

scholarly journals Decay of turbulence in a liquid metal duct flow with transverse magnetic field

2019 ◽  
Vol 867 ◽  
pp. 661-690 ◽  
Author(s):  
Oleg Zikanov ◽  
Dmitry Krasnov ◽  
Thomas Boeck ◽  
Semion Sukoriansky
Keyword(s):  
Magnetic Field ◽  
Transverse Magnetic Field ◽  
Large Scale ◽  
High Amplitude ◽  
Transverse Magnetic ◽  
Duct Flow ◽  
Velocity Fluctuations ◽  
Turbulence Decay ◽  
The Moment ◽  
Typical Length

Decay of honeycomb-generated turbulence in a duct with a static transverse magnetic field is studied via direct numerical simulations. The simulations follow the revealing experimental study of Sukoriansky et al. (Exp. Fluids, vol. 4 (1), 1986, pp. 11–16), in particular the paradoxical observation of high-amplitude velocity fluctuations, which exist in the downstream portion of the flow when the strong transverse magnetic field is imposed in the entire duct including the honeycomb exit, but not in other configurations. It is shown that the fluctuations are caused by the large-scale quasi-two-dimensional structures forming in the flow at the initial stages of the decay and surviving the magnetic suppression. Statistical turbulence properties, such as the energy decay curves, two-point correlations and typical length scales are computed. The study demonstrates that turbulence decay in the presence of a magnetic field is a complex phenomenon critically depending on the state of the flow at the moment the field is introduced.

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