scholarly journals LABORATORY STUDY OF SCALE EFFECTS IN TWO-DIMENSIONAL BEACH PROCESSES

2011 ◽  
Vol 1 (8) ◽  
pp. 14 ◽  
Author(s):  
Yuichi Iwagaki ◽  
Hideaki Noda
Keyword(s):  
Wave Height ◽  
Scale Effects ◽  
Breaking Waves ◽  
Two Dimensional ◽  
Sediment Size ◽  
Beach Processes ◽  
Time Period ◽  
Equilibrium Profile ◽  
Profile Changes ◽  
Constant Slope

In order to disclose the essential relationship between the beach processes and wave characteristics, two dimensional model tests are often performed for beach profile changes due to incident breaking waves normal to the beach. In applying the results of such experiments to the prototype of beaches, the scale effects of waves and sediments on the beach processes with equilibrium beach profiles should necessarily be considered. In this paper, as an approach to solve this problem in two dimensional beach studies, the effects of wave height and sediment size on the shore line movement and equilibrium beach profiles are discussed based on the results of experiments made by the authors and other experiments with smaller and larger scales by some researchers. It has been found that the ratio of wave height to sediment diameter is a very significant factor in this problem. In addition, the changes m a character of breaking waves during the time period of wave action from the beach having an initial constant slope to that with an equilibrium profile are presented.

Scars and Vortices Induced by Ship Bow and Shoulder Wave Breaking

2007 ◽  
Vol 129 (11) ◽  
pp. 1445-1459 ◽  
Author(s):  
A. Olivieri ◽  
F. Pistani ◽  
R. Wilson ◽  
E. F. Campana ◽  
F. Stern
Keyword(s):  
Wave Height ◽  
Wave Breaking ◽  
Scale Effects ◽  
Bubbly Flow ◽  
Breaking Waves ◽  
Cfd Validation ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Local Flow ◽  
Sparse Measurements

Experimental data are provided for physical understanding and computational fluid dynamics (CFD) validation for the surface combatant David–Taylor model basin Model 5415 bow and shoulder wave breaking. A photographic study was conducted using 5.72m replica and 3.05m geosim models of Model 5415 over a range of Froude numbers (Fr) to identify Fr and scale effects on wave breaking and choose the best Fr for the local flow measurements, which include near- and far-field means and rms wave elevation and mean velocity under the breaking waves. The larger model and Fr=0.35 were selected due to the large extents of quasisteady plunging bow and spilling shoulder wave breaking. A direct correlation is shown between regions of wave slope larger than 17deg and regions of large rms in wave height variation. Scars characterized by sudden changes in the mean wave height and vortices induced by wave breaking were identified. Complementary CFD solutions fill the gaps in the relatively sparse measurements enabling a more complete description of the bow and shoulder wave breaking and induced vortices and scars. The combined results have important implications regarding the modeling of the bubbly flow around surface ships, especially for bubble sources and entrainment.

Potential energy in steep and breaking waves

1994 ◽  
Vol 278 ◽  
pp. 201-228 ◽  
Author(s):  
William W. Schultz ◽  
Jin Huh ◽  
Owen M. Griffin
Keyword(s):  
Potential Energy ◽  
Wave Height ◽  
Energy Input ◽  
Breaking Waves ◽  
Smooth Transition ◽  
Stokes Wave ◽  
Two Dimensional ◽  
Spectral Algorithm ◽  
Deep Water Wave ◽  
Experimental Scatter

We find that the RMS wave height (square root of the potential energy) rather than peak-to-peak wave height is a better experimental and analytic criterion for determining when a regular, two-dimensional deep-water wave will break. A spectral algorithm for two-dimensional potential flow is developed and used to compare breaking onset criteria for energy input from (i) converging sidewalls, (ii) a submerged disturbance, and (iii) wave focusing. We also find that wave-breaking criteria (potential energy or the more classical peak-to-peak wave height) are a function of the rate of energy input. Large plunging waves occur when energy input rates are large. As energy input rates become smaller there is a smooth transition to smaller spilling waves. The various energy input methods show similar breaking trends in the limit as the energy input rate becomes small - waves break when the potential energy becomes approximately 52 % of the energy for the most energetic Stokes wave, with the formation of a singularity immediately before the crest. The effects of wave modulation and reflection are briefly discussed and shown not to affect the potential energy breaking criterion significantly. The experimental scatter of the RMS wave height is shown to be half that of wave steepness during incipient breaking in wave packets.

Experimental Research on Flow Induced Oscillations in Moonpool Encountered Through Waves

2007 ◽  
Author(s):  
Zhuang Kang ◽  
Xiongliang Yao ◽  
Sadiq Salman
Keyword(s):  
Wave Height ◽  
Experimental Research ◽  
Flow Condition ◽  
Frequency Ratio ◽  
Pressure Sensors ◽  
Breaking Waves ◽  
Green Water ◽  
Wave Condition ◽  
Time Period ◽  
Calm Water

Model experiments in this paper explains the response of the moonpool encountered through waves at different wave heights, time periods and attack angles, which reflect close to real situation at sea for ships equipped with moonpool. EMD method is used to have a meaningful data collected through hydrophone, pressure sensors, acceleration sensor and wave height meter. Results show that fluid natural oscillating frequency remains constant at 0.7 Hz in calm water with forward model speed condition (Fr = 0.26∼1.3), while by increasing the time period, wave height or both; it fluctuates between 0.6 Hz∼0.9 Hz. The fluid inside the moonpool faces internal sloshing, resulting in transverse breaking waves that are added to the vertical motions. Sloshing motion in the moonpool couples with the piston mode due to which results of calm water with forward speed, and combined waves and flow condition are quite different. Square shaped moonpool at different attack angles and circular shaped moonpool are also discussed for fluctuating pressure level (dB) at increasing time period and wave height. Moreover, Oscillation pressure results at only-wave condition and wave and flow condition together are represented by using frequency ratio between ‘oscillation pressure frequency’ and ‘sloshing natural frequency’ with varying ‘KC’ number. KC varies from 4.16 to 5.67 at 1-sec time period having frequency ratio f/fo of 1. Once time period increases to 2-sec, KC becomes around 22.69 at same frequency ratio. Dynamic magnification due to waves and flow combined situation may cause slamming on diving bells or ROV that are launched, green water over the edge of the moonpool which can be dangerous for the crew, or can increase drastically the resistance of the vessel in transit conditions therefore, this experimental research gives very important factors and results for designing moonpool; we believe that this paper has a significant contribution in the permanent literature.

scholarly journals TWO-DIMENSIONAL EMPIRICAL EIGENFUNCTION MODEL FOR THE ANALYSIS AND PREDICTION OF BEACH PROFILE CHANGES

1986 ◽  
Vol 1 (20) ◽  
pp. 87 ◽  
Author(s):  
T.W. Hsu ◽  
S.R. Liaw ◽  
S.K. Wang ◽  
S.H. Ou
Keyword(s):  
Breaking Waves ◽  
Relative Importance ◽  
Two Dimensional ◽  
Coastal Structures ◽  
Beach Profile ◽  
Radiation Stress ◽  
Profile Data ◽  
Profile Changes ◽  
D Model ◽  
Profile Change

A two-dimensional empirical eigenfunction model is proposed for the analysis and the prediction of beach profile change due to longshore and cross-shore sediment transports. Beach profile data from Redhill coast, Taiwan, measured every two months at 150 meters interval along the detached breakwaters are analyzed and the relative importance from two directions is investigated. Furthermore, by employing the method of Markov process and linear regression, a prediction model is formulated which takes into account the effect of breaking waves, bottom sediment and radiation stress of waves. This 2-D model is shown to be effective in the analysis and the prediction of beach changes near the coastal structures.

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.

Distribution of Wave Impact Forces From Breaking and Non-Breaking Waves

2009 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu ◽  
Edward S. Ammeen
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
Breaking Waves ◽  
Qualitative Assessment ◽  
Total Force ◽  
Impact Loads ◽  
Wave Impact ◽  
Data Set ◽  
Wave Characteristics ◽  
Wide Range

Impact loads from waves on vessels and coastal structures are highly complex and may involve wave breaking, making these changes difficult to estimate numerically or empirically. Results from previous experiments have shown a wide range of forces and pressures measured from breaking and non-breaking waves, with no clear trend between wave characteristics and the localized forces and pressures that they generate. In 2008, a canonical breaking wave impact data set was obtained at the Naval Surface Warfare Center, Carderock Division, by measuring the distribution of impact pressures of incident non-breaking and breaking waves on one face of a cube. The effects of wave height, wavelength, face orientation, face angle, and submergence depth were investigated. A limited number of runs were made at low forward speeds, ranging from about 0.5 to 2 knots (0.26 to 1.03 m/s). The measurement cube was outfitted with a removable instrumented plate measuring 1 ft2 (0.09 m2), and the wave heights tested ranged from 8–14 inches (20.3 to 35.6 cm). The instrumented plate had 9 slam panels of varying sizes made from polyvinyl chloride (PVC) and 11 pressure gages; this data was collected at 5 kHz to capture the dynamic response of the gages and panels and fully resolve the shapes of the impacts. A Kistler gage was used to measure the total force averaged over the cube face. A bottom mounted acoustic Doppler current profiler (ADCP) was used to obtain measurements of velocity through the water column to provide incoming velocity boundary conditions. A Light Detecting and Ranging (LiDAR) system was also used above the basin to obtain a surface mapping of the free surface over a distance of approximately 15 feet (4.6 m). Additional point measurements of the free surface were made using acoustic distance sensors. Standard and high-speed video cameras were used to capture a qualitative assessment of the impacts. Impact loads on the plate tend to increase with wave height, as well as with plate inclination toward incoming waves. Further trends of the pressures and forces with wave characteristics, cube orientation, draft and face angle are investigated and presented in this paper, and are also compared with previous test results.

scholarly journals UNDERWATER MOUND FOR THE PROTECTION OF DURBAN'S BEACHES

1970 ◽  
Vol 1 (12) ◽  
pp. 62 ◽  
Author(s):  
J.A. Zwaborn ◽  
G.A.W. Fromme ◽  
J.B. FitzPatrick
Keyword(s):  
Settling Velocity ◽  
Scale Effects ◽  
Similarity Criterion ◽  
Test Results ◽  
Beach Profile ◽  
Reasonable Degree ◽  
Model Predictions ◽  
Profile Changes ◽  
High Degree ◽  
Movable Bed

The construction of an underwater mound of sand for the protection and improvement of Durban's beaches has been recommended on the basis of intensive investigations These investigations included prototype measurements of beach changes as related to recorded sea conditions, basic scaling tests in which these beach changes were reproduced to scale in movable bed models and tests of the proposed underwater mound in models, using different scales in order to eliminate possible scale effects The test results showed that, provided the shear-settling velocity similarity criterion is satisfied, beach changes can be reproduced in a movable bed model to a reasonable degree of accuracy Optimum dimensions for the cross section of the mound were determined on the basis of the criterion for erosive and non-erosive wave conditions which was derived from the prototype beach profile changes and confirmed by model tests The resulting dimensions are a mound of sand about 4 5 km long, about 1 200 m offshore, reaching to 7 3 m below LWOST, with side slopes of 1 in 25 and a crest width of 61 m 3 3 Of the total quantity required (8 000 000 m ) some 2 500 000 m of sand, available from harbour dredging works in Durban Bay, had been dumped by May, 1970 Model predictions on mound stability and beach improvements were confirmed to a high degree of accuracy by the full scale events.

scholarly journals SIMILARITY OF EQUILIBRIUM BEACH PROFILES

1972 ◽  
Vol 1 (13) ◽  
pp. 61 ◽  
Author(s):  
M.J. Paul ◽  
J.W. Kamphuis ◽  
A. Brebner
Keyword(s):  
Long Range ◽  
Scale Effect ◽  
Research Laboratory ◽  
Scaling Laws ◽  
Coastal Engineering ◽  
Two Dimensional ◽  
Engineering Research ◽  
Mobile Bed ◽  
Beach Processes ◽  
Distorted Model

In the design of mobile bed coastal models it is inherently assumed that prototype beach processes may be modelled using lightweight sediment. At the Queen's University Coastal Engineering Research Laboratory, a long range project is currently in progress to determine scaling laws and scale effect for mobile bed coastal models. A large portion of this program is directly concerned with beach profiles and in this paper preliminary work is reported, in which a comparison is made between two dimensional laboratory beach profiles obtained from controlled "prototype", undistorted model and some distorted model tests.

scholarly journals EXPERIMENTS ON BEACH PROFILE CHANGE WITH A LARGE WAVE FLUME

1982 ◽  
Vol 1 (18) ◽  
pp. 85 ◽  
Author(s):  
Ryoichi Kajima ◽  
Takao Shimizu ◽  
Kohki Maruyama ◽  
Shozo Saito
Keyword(s):  
Simple Model ◽  
Transport Rate ◽  
Sand Transport ◽  
Two Dimensional ◽  
Beach Profile ◽  
Large Wave ◽  
Wave Flume ◽  
Grain Sizes ◽  
Profile Changes ◽  
Profile Change

Two-dimensional beach profile changes were investigated with a newly constructed prototype-scale wave flume. The flume is 205 m long, 3.4 m wide and 6 m deep. Sand of two grain sizes was used in the experiments. Analysis of the results was made through use of the parameter C, introduced by Sunamura and Horikawa (1974) to classify beaches as either erosional and accretionary. Beach profile changes obtained in the flume were similar to those in the prototype (field). Net sand transport rate distributions were classified into five types, two of which do not seem to have been observed in laboratory (smallscale) experiments. A simple model describing the five types was developed for evaluating two-dimensional beach profile changes.

A new model of shoaling and breaking waves. Part 2. Run-up and two-dimensional waves

2019 ◽  
Vol 867 ◽  
pp. 146-194 ◽  
Author(s):  
G. L. Richard ◽  
A. Duran ◽  
B. Fabrèges
Keyword(s):  
Large Scale ◽  
Turbulent Viscosity ◽  
Breaking Waves ◽  
Small Scale ◽  
Two Dimensional ◽  
Numerical Resolution ◽  
Wide Range ◽  
Scale Turbulence ◽  
Run Up ◽  
Averaged Model

We derive a two-dimensional depth-averaged model for coastal waves with both dispersive and dissipative effects. A tensor quantity called enstrophy models the subdepth large-scale turbulence, including its anisotropic character, and is a source of vorticity of the average flow. The small-scale turbulence is modelled through a turbulent-viscosity hypothesis. This fully nonlinear model has equivalent dispersive properties to the Green–Naghdi equations and is treated, both for the optimization of these properties and for the numerical resolution, with the same techniques which are used for the Green–Naghdi system. The model equations are solved with a discontinuous Galerkin discretization based on a decoupling between the hyperbolic and non-hydrostatic parts of the system. The predictions of the model are compared to experimental data in a wide range of physical conditions. Simulations were run in one-dimensional and two-dimensional cases, including run-up and run-down on beaches, non-trivial topographies, wave trains over a bar or propagation around an island or a reef. A very good agreement is reached in every cases, validating the predictive empirical laws for the parameters of the model. These comparisons confirm the efficiency of the present strategy, highlighting the enstrophy as a robust and reliable tool to describe wave breaking even in a two-dimensional context. Compared with existing depth-averaged models, this approach is numerically robust and adds more physical effects without significant increase in numerical complexity.

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