The estimation of geoacoustic parameters via low frequencies (50–75 Hertz) for simulated shallow water test scenarios.

2009 ◽  
Vol 125 (4) ◽  
pp. 2619-2619
Author(s):  
A. Tolstoy
Keyword(s):  
Shallow Water ◽  
Low Frequencies ◽  
Water Test ◽  
Test Scenarios

Experimental Study of Slow-Drift Ship Motions in Shallow Water Random Waves

2011 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Trygve Kristiansen
Keyword(s):  
Spectral Analysis ◽  
Shallow Water ◽  
Transfer Functions ◽  
Second Order ◽  
Ship Motions ◽  
Random Wave ◽  
Random Waves ◽  
Low Frequencies ◽  
Wave Basin ◽  
Drift Forces

Slowly varying motions and drift forces of a large moored ship in random waves at 35m water depth are investigated by an experimental wave basin study in scale 1:50. A simple horizontal mooring set-up is used. A second-order wave correction is applied to minimize “parasitic” long waves. The effect on the ship motion from the correction is clearly seen, although less in random wave spectra than in pure bi-chromatic waves. Empirical quadratic transfer functions (QTFs) of the surge drift force are found by use of cross-bi-spectral analysis, in two different spectra have been obtained. The QTF levels increase significantly with lower wave frequencies (except at the diagonal), which is special for finite and shallow water. Furthermore, the QTF levels frequencies at low frequencies increase significantly out from the QTF diagonal. Thus Newman’s approximation should preferrably not be used in these cases. Using the LF waves as a direct excitation in a “linear” ship force analysis gives random records that compare reasonably well with those from the cross-bi-spectral analysis. This confirms the idea that the drift forces in shallow water are closely correlated to the second-order potential, and thereby by the second-order LF waves.

scholarly journals Controlling the Computational Modes of the Arbitrarily Structured C Grid

2012 ◽  
Vol 140 (10) ◽  
pp. 3220-3234 ◽  
Author(s):  
Hilary Weller
Keyword(s):  
Shallow Water ◽  
Flow Direction ◽  
Water Model ◽  
Test Cases ◽  
Continuous Linear ◽  
Shallow Water Model ◽  
Advection Schemes ◽  
Water Test ◽  
Better Than ◽  
Potential Enstrophy

Abstract The arbitrarily structured C grid, Thuburn–Ringler–Skamarock–Klemp (TRiSK), is being used in the Model for Prediction Across Scales (MPAS) and is being considered by the Met Office for their next dynamical core. However, the hexagonal C grid supports a branch of spurious Rossby modes, which lead to erroneous grid-scale oscillations of potential vorticity (PV). It is shown how these modes can be harmlessly controlled by using upwind-biased interpolation schemes for PV. A number of existing advection schemes for PV are tested, including that used in MPAS, and none are found to give adequate results for all grids and all cases. Therefore a new scheme is proposed; continuous, linear-upwind stabilized transport (CLUST), a blend between centered and linear-upwind with the blend dependent on the flow direction with respect to the cell edge. A diagnostic of grid-scale oscillations is proposed that gives further discrimination between schemes than using potential enstrophy alone. Indeed, some schemes are found to destroy potential enstrophy while grid-scale oscillations grow. CLUST performs well on hexagonal-icosahedral grids and unrotated skipped latitude–longitude grids of the sphere for various shallow-water test cases. Despite the computational modes, the hexagonal icosahedral grid performs well since these modes are easy and harmless to filter. As a result, TRiSK appears to perform better than a spectral shallow-water model.

Sediment sound speed inversion at low frequencies in shallow water

2017 ◽  
Vol 142 (4) ◽  
pp. 2621-2621
Author(s):  
Zoi-Heleni Michalopoulou
Keyword(s):  
Shallow Water ◽  
Sound Speed ◽  
Low Frequencies

Track velocity control of crawler type underwater mining robot through shallow-water test

2012 ◽  
Vol 26 (10) ◽  
pp. 3291-3298 ◽  
Author(s):  
Suk-Min Yoon ◽  
Sup Hong ◽  
Sung-Jea Park ◽  
Jong-Su Choi ◽  
Hyung-Woo Kim ◽  
...  
Keyword(s):  
Shallow Water ◽  
Velocity Control ◽  
Water Test ◽  
Underwater Mining

Spectral Transform Solutions to the Shallow Water Test Set

1995 ◽  
Vol 119 (1) ◽  
pp. 164-187 ◽  
Author(s):  
Ruediger Jakob-Chien ◽  
James J. Hack ◽  
David L. Williamson
Keyword(s):  
Shallow Water ◽  
Test Set ◽  
Spectral Transform ◽  
Water Test

Weak quadratic interactions of two-dimensional waves

1971 ◽  
Vol 50 (1) ◽  
pp. 107-132 ◽  
Author(s):  
Young Yuel Kim ◽  
Thomas J. Hanratty
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Wave Train ◽  
Water Layer ◽  
Rate Of Change ◽  
Two Dimensional ◽  
Low Frequencies ◽  
Resonant Interactions ◽  
Water Layers ◽  
Phase Angles

This paper reports on weak quadratic interactions which can occur with two-dimensional waves on shallow water layers and in the capillary-gravity range on deep water layers. It supplies experimental support of theoretical predictions for resonant interactions, but, perhaps of more significance, it explores in detail interactions which occur under conditions near resonance.Waves of approximately sinusoidal form are introduced on the surface of water in a long rectangular tank. For deep water a rapid distortion in the sinusoidal wave and sometimes additional crests are observed because of energy exchange among the first, second and third harmonics at frequencies where both surface tension and gravity are important (7·5–13 c/s). An even greater exchange of energy can be observed on shallow water layers at low frequencies. For example, a wave train with seven secondary crests can be observed when the wave maker is operated at 3·04 c/s in a water layer of 0·65 cm.Measured amplitudes and phase angles of the Fourier components of the wave train are described by a system of equations using only quadratic interactions among participating harmonics. The exchange of energy among Fourier components under certain conditions is explained in terms of the rate of change of relative phase angles of the different harmonics.

Paper 10: Radial Forces in Centrifugal Pumps with Guide Vanes

1969 ◽  
Vol 184 (14) ◽  
pp. 101-107 ◽  
Author(s):  
P. Hergt ◽  
P. Krieger
Keyword(s):  
Pressure Distribution ◽  
Shallow Water ◽  
Experimental Test ◽  
Centrifugal Pumps ◽  
Test Rig ◽  
Guide Vanes ◽  
Water Test ◽  
Small Flow ◽  
Radial Forces ◽  
Load Conditions

At partial and overload conditions, radial decentralizing forces act upon the rotor of a centrifugal pump with guide vanes if the impeller is out of centre. The magnitude of these forces depends on load conditions, and the forces increase with growing eccentricity. At very small flow, these forces become non-stationary. They rotate at a considerably lower frequency than the velocity frequency and may lead to rotor vibrations. The paper discusses the effects of stationary and non-stationary radial forces, and resulting shaft deflections and vibrations, from measurements on two experimental test rigs. The paper also presents the results of research on the pressure distribution of guide vanes, carried out in air, and gives observations of flow patterns in a shallow water test rig.

Predictability of acoustic intensity in shallow water at low frequencies using parabolic approximations

1991 ◽  
Vol 89 (4B) ◽  
pp. 1896-1896 ◽  
Author(s):  
R. J. Cederberg ◽  
W. L. Seigmann ◽  
M. J. Jacobson ◽  
W. M. Carey
Keyword(s):  
Shallow Water ◽  
Acoustic Intensity ◽  
Low Frequencies
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