scholarly journals TRACING COASTAL SEDIMENT MOVEMENT BY NATURALLY RADIOACTIVE MINERALS

2011 ◽  
Vol 1 (8) ◽  
pp. 19
Author(s):  
A.M. Kamel ◽  
J.W. Johnson
Keyword(s):  
Breaking Waves ◽  
Breaking Point ◽  
Primary Factor ◽  
Coastal Sediment ◽  
Littoral Drift ◽  
Longshore Drift ◽  
Littoral Current ◽  
Radioactive Minerals ◽  
Set Up ◽  
The Waves

The process by which sediments are moved along the shore is known as littoral drift and it includes beach drifting and longshore drift (Johnson, 1919). Coarse material is moved along a foreshore in zig-zag paths under the influence of swash and backwash of the waves. The process of longshore drift is due to longshore currents set up within the breaker zone by breaking waves approaching the shoreline at an angle. Although the waves tend to become parallel to the coast as a result of refraction, they usually break at a slight angle to the shore with the result that a littoral current is induced and is effective in moving a mass of water (and the sediment placed in suspension by the breaking waves) slowly along the coast. It is this current combined with the agitating action of the breaking waves, that is the primary factor in causing movement of sand along a coastline. It is believed that the largest percentage of the littoral transport occurs shoreward of the breaking point of the waves .

PHYSICAL INTERPRETATION OF WAVE BREAKING CRITERIA

2017 ◽  
Author(s):  
Sergey Kuznetsov ◽  
Sergey Kuznetsov ◽  
Yana Saprykina ◽  
Yana Saprykina ◽  
Boris Divinskiy ◽  
...  
Keyword(s):  
Nonlinear Wave ◽  
Wave Breaking ◽  
Second Harmonic ◽  
Vertical Axis ◽  
Breaking Waves ◽  
Wave Transformation ◽  
Spectral Structure ◽  
Similarity Parameter ◽  
Nonlinear Harmonics ◽  
The Waves

On the base of experimental data it was revealed that type of wave breaking depends on wave asymmetry against the vertical axis at wave breaking point. The asymmetry of waves is defined by spectral structure of waves: by the ratio between amplitudes of first and second nonlinear harmonics and by phase shift between them. The relative position of nonlinear harmonics is defined by a stage of nonlinear wave transformation and the direction of energy transfer between the first and second harmonics. The value of amplitude of the second nonlinear harmonic in comparing with first harmonic is significantly more in waves, breaking by spilling type, than in waves breaking by plunging type. The waves, breaking by plunging type, have the crest of second harmonic shifted forward to one of the first harmonic, so the waves have "saw-tooth" shape asymmetrical to vertical axis. In the waves, breaking by spilling type, the crests of harmonic coincides and these waves are symmetric against the vertical axis. It was found that limit height of breaking waves in empirical criteria depends on type of wave breaking, spectral peak period and a relation between wave energy of main and second nonlinear wave harmonics. It also depends on surf similarity parameter defining conditions of nonlinear wave transformations above inclined bottom.

scholarly journals Modification of Airflow Structure Due to Wave Breaking on a Submerged Topography

2021 ◽  
Author(s):  
Petter Vollestad ◽  
Atle Jensen
Keyword(s):  
Wind Wave ◽  
Separated Flow ◽  
Flow Region ◽  
Breaking Waves ◽  
Leeward Side ◽  
Geometrical Properties ◽  
Image Velocimetry ◽  
Wind Profiles ◽  
The Waves ◽  
Sheltered Area

AbstractExperimental results from a combined wind–wave tank are presented. Wind profiles and resulting wind–wave spectra are described, and an investigation of the airflow above breaking waves is presented. Monochromatic waves created by the wave maker are directed towards a submerged topography. This causes the waves to break at a predictable location, facilitating particle-image-velocimetry measurements of the airflow above steep breaking and non-breaking waves. We analyze how the breaking state modifies the airflow structure, and in particular the extent of the sheltered area on the leeward side of the waves. Results illustrate that while the geometrical properties of the waves greatly influence the airflow structure on the leeward side of the waves, the state of breaking (i.e., whether the waves are currently in a state of active breaking) is not observed to have a clear effect on the extent of the separated flow region, or on the velocity distribution within the sheltered region.

scholarly journals PHYSICAL REQUIREMENTS FOR A TAKEOFF IN SURFING

2017 ◽  
pp. 30
Author(s):  
Akihiko Kimura ◽  
Taro Kakinuma
Keyword(s):  
Wave Front ◽  
Time Variation ◽  
Wave Breaking ◽  
Horizontal Component ◽  
Breaking Point ◽  
Front Face ◽  
The Waves

The conditions required for a takeoff in surfing, are discussed, with the waves simulated numerically, considering two types of wave breaking, i.e., a plunging type, and a spilling type. First, a surfer is required to obtain a sufficient value for the horizontal component of paddling speed, not to be overtaken by a wave peak. Second, when the surfer stops paddling, he needs to be floating at a location where the force on him is downward, along the wave front face. On the basis of both conditions, the time variation of the required value for the horizontal component of paddling speed, is evaluated for both the plunging-type, and spilling-type, cases. When the paddling speed is sufficient, the surfable area is larger in the former case, than in the latter, on the offshore side of the wave-breaking point.

scholarly journals Coastline changes in relation to longshore sediment transport and human impact, along the shoreline of Kato Achaia (NW Peloponnese, Greece)

2001 ◽  
Vol 2 (1) ◽  
pp. 5 ◽  
Author(s):  
S. POULOS ◽  
G. CHRONIS
Keyword(s):  
Sediment Transport ◽  
Human Activities ◽  
Dynamic Equilibrium ◽  
Littoral Drift ◽  
Coastal System ◽  
Longshore Sediment Transport ◽  
Longshore Drift ◽  
Management Plans ◽  
Natural Equilibrium ◽  
Oblique Approach

Coastal configuration depends upon the equilibrium between available sediment budget and prevailing nearshore wave and current conditions. Human activities often disturb this natural equilibrium by altering the sources of beach material and littoral drift pattern. In the coastal zone of NW Peloponnese, an essentially tideless environment, the oblique approach of wind-induced waves implies an overall longshore drift from east to west. On an annual basis, the potential longshore sediment transport rates at the different sections of the study area (Kato Achaia) is estimated to vary between 0.02 10-3 m3/s and 5 103 m3/s and to fluctuate seasonally. The construction of a port and the extraction of aggregates from the R. Peiros have changed significantly the pattern of sediment transport inducing dramatic changes on coastline configuration; thus, the part of the coastline west to the port had retreated as much as 70 m eliminating a touristic beach, while the entrance of the port was silted inhibiting navigation. Coastal engineering measures, such as modification of port-breakwaters and construction of groins have had only minimal contribution in beach recovery. Hence, coastal management plans should consider this dynamic equilibrium and protect the natural coastal system from the arbitrary human activities.

scholarly journals ENERGY LOSS AND SET-UP DUE TO BREAKING OF RANDOM WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 32 ◽  
Author(s):  
J.A. Battjes ◽  
J.P.F.M. Janssen
Keyword(s):  
Wave Height ◽  
Dissipation Rate ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Height Distribution ◽  
Random Waves ◽  
Dissipation Of Energy ◽  
Wave Height Distribution ◽  
Set Up ◽  
Local Depth

A description is given of a model developed for the prediction of the dissipation of energy in random waves breaking on a beach. The dissipation rate per breaking wave is estimated from that in a bore of corresponding height, while the probability of occurrence of breaking waves is estimated on the basis of a wave height distribution with an upper cut-off which in shallow water is determined mainly by the local depth. A comparison with measurements of wave height decay and set-up, on a plane beach and on a beach with a bar-trough profile, indicates that the model is capable of predicting qualitatively and quantitatively all the main features of the data.

Loads and Dynamic Response of a Floating Wave Energy Converter due to Regular Waves From CFD Simulations

2016 ◽  
Author(s):  
Anna Büchner ◽  
Thomas Knapp ◽  
Martin Bednarz ◽  
Philipp Sinn ◽  
Arndt Hildebrandt
Keyword(s):  
Dynamic Response ◽  
Boundary Conditions ◽  
Wave Energy ◽  
Single Point ◽  
Breaking Waves ◽  
Wave Energy Converter ◽  
Wave Loads ◽  
Regular Waves ◽  
Energy Converter ◽  
Set Up

The commercial CFD code ANSYS Fluent is used for the three-dimensional estimation of wave loads and the dynamic response of a floating single point wave energy converter of the SINN Power wave power plant due to non-breaking and unidirectional waves in coastal waters. The VoF method is used to model the free surface and wave theories to set up the boundary conditions at the inlet for regular waves. The wave induced vertical motions of the floating module are computed by a sixDoF solver. Preliminary 2D and 3D studies to set up boundary conditions, mesh densities and solver settings were performed. The numerical results were compared to analytical solutions in form of water surface elevations and wave kinematics which showed good agreement. The paper presents the dynamic response of the floating module for different load cases in terms of non-breaking waves. The resulting horizontal and vertical forces at the floating module will be presented and explained by the flow dynamics. Time and space depending velocities and pressure distributions including details on vortex separation will be given, which reveal valuable insights on the contribution of inertia and drag forces leading to the dynamic structural response of the floating devices.

Measurement of Green Water on a 3D Structure

2009 ◽  
Author(s):  
Kusalika Ariyarathne ◽  
Kuang-An Chang ◽  
Richard Mercier
Keyword(s):  
Vertical Wall ◽  
3D Structure ◽  
Maximum Velocity ◽  
Breaking Waves ◽  
Velocity Fields ◽  
The Other ◽  
Green Water ◽  
Incoming Wave ◽  
Linear Distribution ◽  
The Waves

The present study investigates the velocity fields of plunging breaking waves impinging on a three-dimensional simplified ship-shape structure in a laboratory wave tank. Green water was generated as the waves break and overtop the structure. Bubble image velocimetry (BIV) was used to measure the velocity field of green water along the centerline of the deck. Two plunging wave conditions were tested and compared: one with waves impinging on the vertical wall of the structure at the initial still water level; the other with waves impacting on the horizontal deck surface. The velocity fields are quite different for the two cases even though the incoming wave heights and the wave periods are nearly identical. It was observed that the maximum horizontal velocity is higher for the case with waves compacting on the deck. The waves also passed the deck quicker than the other case. For both cases the profiles of the green water velocity shows a non-linear distribution with the maximum velocity occurring near the front of the water.

scholarly journals KNSwing—On the Mooring Loads of a Ship-Like Wave Energy Converter

2019 ◽  
Vol 7 (2) ◽  
pp. 29
Author(s):  
Kim Nielsen ◽  
Jonas Thomsen
Keyword(s):  
Numerical Model ◽  
Wave Energy ◽  
Numerical Models ◽  
Breaking Waves ◽  
Wave Energy Converter ◽  
Experimental Results ◽  
Irregular Waves ◽  
Mooring System ◽  
Energy Converter ◽  
The Waves

The critical function of keeping a floating Wave Energy Converter in position is done by a mooring system. Several WECs have been lost due to failed moorings, indicating that extreme loads, reliability and durability are very important aspects. An understanding of the interaction between the WEC’s motion in large waves and the maximum mooring loads can be gained by investigating the system at model scale supported by numerical models. This paper describes the testing of a novel attenuator WEC design called KNSwing. It is shaped like a ship facing the waves with its bow, which results in low mooring loads and small motions in most wave conditions when the structure is longer than the waves. The concept is tested using an experimental model at scale 1:80 in regular and irregular waves, moored using rubber bands to simulate synthetic moorings. The experimental results are compared to numerical simulations done using the OrcaFlex software. The experimental results show that the WEC and the mooring system survives well, even under extreme and breaking waves. The numerical model coefficient concerning the nonlinear drag term for the surge motion is validated using decay tests. The numerical results compare well to the experiments and, thereby, the numerical model can be further used to optimize the mooring system.

scholarly journals TOWARD A SIMPLE MODEL OF THE WAVE BREAKING TRANSITION REGION IN SURF ZONES

1986 ◽  
Vol 1 (20) ◽  
pp. 72 ◽  
Author(s):  
David R. Basco ◽  
Takao Yamashita
Keyword(s):  
Simple Model ◽  
Transition Region ◽  
Surf Zone ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Zone Model ◽  
Similarity Parameter ◽  
Set Up ◽  
Linear Growth Model ◽  
Semi Empirical

Breaking waves undergo a transition from oscillatory, irrotational motion, to highly rotational (turbulent) motion with some particle translation. On plane or monotonically decreasing beach profiles, this physically takes place in such a way that the mean water level remains essentially constant within the transition region. Further shoreward a rapid set-up takes place within the inner, bore-like region. The new surf zone model of Svendsen (1984) begins at this transition point and the new wave there contains a trapped volume of water within the surface roller moving with the wave speed. This paper describes a simple model over the transition zone designed to match the Svendsen (1984) model at the end of the transition region. It uses a simple, linear growth model for the surface roller area development and semi-empirical model for the variation of the wave shape factor. Breaking wave type can vary from spilling through plunging as given by a surf similarity parameter. The model calculates the wave height decrease and width of the transition region for all breaker types on plane or monotonically depth decreasing beaches.

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