Study on ambient noise generated from breaking waves simulated by a wave maker in a tank

2002 ◽  
Vol 112 (5) ◽  
pp. 2363-2363
Author(s):  
Ruey‐Chang Wei ◽  
Hsiang‐Chih Chan
Keyword(s):  
Ambient Noise ◽  
Breaking Waves ◽  
Wave Maker

scholarly journals Suppression of Wind Ripples and Microwave Backscattering Due to Turbulence Generated by Breaking Surface Waves

2020 ◽  
Vol 12 (21) ◽  
pp. 3618
Author(s):  
Stanislav Ermakov ◽  
Vladimir Dobrokhotov ◽  
Irina Sergievskaya ◽  
Ivan Kapustin
Keyword(s):  
Remote Sensing ◽  
Surface Waves ◽  
Wave Breaking ◽  
Wave Train ◽  
Wind Waves ◽  
Breaking Waves ◽  
Doppler Spectrum ◽  
Strong Wave ◽  
Wave Maker ◽  
Radar Backscattering

The role of wave breaking in microwave backscattering from the sea surface is a problem of great importance for the development of theories and methods on ocean remote sensing, in particular for oil spill remote sensing. Recently it has been shown that microwave radar return is determined by both Bragg and non-Bragg (non-polarized) scattering mechanisms and some evidence has been given that the latter is associated with wave breaking, in particular, with strong breaking such as spilling or plunging. However, our understanding of mechanisms of the action of strong wave breaking on small-scale wind waves (ripples) and thus on the radar return is still insufficient. In this paper an effect of suppression of radar backscattering after strong wave breaking has been revealed experimentally and has been attributed to the wind ripple suppression due to turbulence generated by strong wave breaking. The experiments were carried out in a wind wave tank where a frequency modulated wave train of intense meter-decimeter-scale surface waves was generated by a mechanical wave maker. The wave train was compressed according to the gravity wave dispersion relation (“dispersive focusing”) into a short-wave packet at a given distance from the wave maker. Strong wave breaking with wave crest overturning (spilling) occurred for one or two highest waves in the packet. Short decimeter-centimeter-scale wind waves were generated at gentle winds, simultaneously with the long breaking waves. A Ka-band scatterometer was used to study microwave backscattering from the surface waves in the tank. The scatterometer looking at the area of wave breaking was mounted over the tank at a height of about 1 m above the mean water level, the incidence angle of the microwave radiation was about 50 degrees. It has been obtained that the radar return in the presence of short wind waves is characterized by the radar Doppler spectrum with a peak roughly centered in the vicinity of Bragg wave frequencies. The radar return was strongly enhanced in a wide frequency range of the radar Doppler spectrum when a packet of long breaking waves arrived at the area irradiated by the radar. After the passage of breaking waves, the radar return strongly dropped and then slowly recovered to the initial level. Measurements of velocities in the upper water layer have confirmed that the attenuation of radar backscattering after wave breaking is due to suppression of short wind waves by turbulence generated in the breaking zone. A physical analysis of the effect has been presented.

Simulations for Design and Reconstruction of Breaking Waves in a Wavetank

2015 ◽  
Author(s):  
R. Kurnia ◽  
T. van den Munckhof ◽  
C. P. Poot ◽  
P. Naaijen ◽  
R. H. M. Huijsmans ◽  
...  
Keyword(s):  
Eddy Viscosity ◽  
Flexible Structures ◽  
Breaking Waves ◽  
Boussinesq Model ◽  
Simulation Code ◽  
Efficient Simulation ◽  
Oil Platforms ◽  
Numerical Design ◽  
Breaking Mechanism ◽  
Wave Maker

To determine forces on fixed and flexible structures such as wind mills and oil platforms, experiments in wave tanks are useful to investigate the impacts in various types of environmental waves. In this paper we show that the use of an efficient simulation code can optimize the experiments by designing the influx such that waves will break at a predefined position of the structure. The consecutive actual measurements agree well with the numerical design of the experiments. Using the measured elevation close by the wave maker as input, the software recovers the experimental data in great detail, even for rather short (up to L/D=1) and very steep breaking waves with steepness parameter (ak) till 0.4. The experiments were carried out in the TUD-wavetank and the simulation is done by HaWaSSI-AB, a spatial-spectral implementation of a Hamiltonian Boussinesq model with an eddy-viscosity breaking mechanism that is initiated by a kinematic breaking condition.

Breaking Wave Impact on a Platform Column: An Introductory CFD Study

2011 ◽  
Author(s):  
Csaba Pakozdi ◽  
Timothy E. Kendon ◽  
Carl-Trygve Stansberg
Keyword(s):  
Model Test ◽  
Breaking Waves ◽  
Wave Profile ◽  
Scale Model ◽  
Computational Time ◽  
Breaking Wave ◽  
Wave Impact ◽  
Time Step ◽  
Test Setup ◽  
Wave Maker

The slamming of breaking waves on the legs of large volume offshore platforms has received increased attention over recent years. To investigate this problem, MARINTEK’s Wave Impact Loads JIP has, in one of its sub-tasks, focused towards an idealised model test setup of a rectangular cylinder in breaking waves. The model consists of a vertical column with a fragment of a horizontal deck attached. The model is fixed at a distance L ahead of the wave maker. Physical scale model test experiments of the block in regular waves and in wave groups have been carried out in Phase 1 of the JIP (2008). The objective of this study is the CFD simulation of a long crested breaking wave and its impact on the aforementioned cylinder and deck structure in order to find out the feasibility of the numerical reconstruction of such events. The commercial CFD tool Star-CCM+ V5.03.0056 (www.cd-adapco.com) is used in this study. This paper considers results from the test setup, and compares the measured wave elevation against results from the CFD code. The position of the cylinder in relation to the breaking wave front is investigated in the numerical simulation in order to analyze its effect on the slamming force. Use of an unsteady wave boundary condition, matching the exact motion history of the wave-maker with the measured free surface elevation at the wave maker gives an almost exact matching between the computed wave profile and the measured wave profile. The improvement in the numerical tool of Star-CCM+ which makes it possible to use higher order time integration scheme for VOF significantly decreases the numerical diffusion of the wave propagation. This new scheme also enables the use of a time step 10 times larger than the first order scheme which reduces the computational time. Because a large time step can be chosen it is important that the time step is small enough to capture the correct time evolution of the physical phenomena of interest. Capturing the pressure evolution at a slamming event demands very high spatial resolution. Spatially averaged slamming pressures look fairly similar to the model test observations, while further work is needed for a more detailed comparison.

MEASURING ENERGY DISSIPATION RATES IN A WAVE TANK

2005 ◽  
Vol 2005 (1) ◽  
pp. 183-186 ◽  
Author(s):  
Albert D. Venosa ◽  
Vikram J. Kaku ◽  
Michel C. Boufadel ◽  
Kenneth Lee
Keyword(s):  
Energy Dissipation ◽  
Open Water ◽  
Breaking Waves ◽  
Pilot Scale ◽  
Energy Dissipation Rate ◽  
Breaking Wave ◽  
Field Scale ◽  
Wave Tank ◽  
Dissipation Rates ◽  
Wave Maker

ABSTRACT The effectiveness of dispersants is typically evaluated at various scales ranging from the smallest (10 cm, typical of flask tests in the laboratory) to the largest (10's to 100's of meters, typical of field scale open water dispersion tests). This study aims at evaluating dispersant effectiveness at intermediate or pilot scale. The hypothesis is that the energy dissipation rate per unit mass, ɛ, plays a major role in the effectiveness of a dispersant. Therefore, it is stipulated that in fairly general conditions, conservation of ɛ between the wave tank scale and that of the field scale is sufficient to accurately evaluate the effectiveness of a dispersant to disperse oil droplets. A wave tank measuring 16 m long x 0.6 m wide x 2 m deep was constructed on the premises of the Bedford Institute of Oceanography, Halifax, Nova Scotia. Waves were generated using a flap-type wave maker. Conditions of the breaking waves were created using a dispersive focusing technique in which the wave maker is started at high frequency and then the frequency decreased to create breaking waves. Experiments defining the velocity profile and energy dissipation rates in the wave tank were conducted at 2 different induced breaking-wave energies. Energy in the wave tank was measured with an Acoustic Doppler Velocimeter (ADV) coupled to a data acquisition system. Energy in the lab flasks was measured with a Hot Wire Anemometer.

Shallow‐water ambient noise caused by breaking waves in the surf zone.

1996 ◽  
Vol 99 (4) ◽  
pp. 2453-2457
Author(s):  
Oscar B. Wilson ◽  
Marc S. Stewart ◽  
James H. Wilson ◽  
Robert H. Bourke
Keyword(s):  
Shallow Water ◽  
Ambient Noise ◽  
Surf Zone ◽  
Breaking Waves

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

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