scholarly journals COMPUTATION OF LONGSHORE CURRENTS

1974 ◽  
Vol 1 (14) ◽  
pp. 40 ◽  
Author(s):  
Ivar G. Jonsson ◽  
Ove Skovgaard ◽  
Torben S. Jacobsen
Keyword(s):  
Surf Zone ◽  
Numerical Algorithms ◽  
Field Measurements ◽  
Breaking Waves ◽  
Bottom Friction ◽  
Rip Currents ◽  
Longshore Current ◽  
Lateral Mixing ◽  
Set Up ◽  
The Given

The steady state profile of the longshore current induced by regular, obliquely incident, breaking waves, over a bottom with arbitrary parallel bottom contours, is predicted. A momentum approach is adopted. The wave parameters must be given at a depth outside the surf zone, where the current velocity is very small. The variation of the bottom roughness along the given bottom profile must be prescribed in advance. Depth refraction is included also in the calculation of wave set-down and set-up. Current refraction and rip-currents are excluded. The model includes two new expressions, one for the calculation of the turbulent lateral mixing, and one for the turbulent bottom friction. The term for the bottom friction is non-linear. Rapid convergent numerical algorithms are described for the solution of the governing equations. The predicted current profiles are compared with laboratory experiments and field measurements. For a plane sloping bottom, the influence of different eddy viscosities and constant values of bottom roughness is examined.

scholarly journals Rip currents in the non-tidal surf zone with sandbars: numerical analysis versus field measurements

Oceanologia ◽  
2020 ◽  
Vol 62 (3) ◽  
pp. 291-308
Author(s):  
Aleksandra Dudkowska ◽  
Aleksandra Boruń ◽  
Jakub Malicki ◽  
Jan Schönhofer ◽  
Gabriela Gic-Grusza
Keyword(s):  
Numerical Analysis ◽  
Surf Zone ◽  
Field Measurements ◽  
Rip Currents

scholarly journals FIELD MEASUREMENTS AND MODELLING OF NEARSHORE CURRENTS AT A HIGH-ENERGY GEOLOGICALLY-CONSTRAINED BEACH

2020 ◽  
pp. 18
Author(s):  
Arthur Mouragues ◽  
Philippe Bonneton ◽  
Bruno Castelle ◽  
Vincent Marieu
Keyword(s):  
Surf Zone ◽  
Low Frequency ◽  
Field Measurements ◽  
High Energy ◽  
Oblique Wave ◽  
Wave Forcing ◽  
Circulation Patterns ◽  
Wave Conditions ◽  
Nearshore Currents ◽  
Set Up

We present field measurements of nearshore currents at a high-energy mesotidal beach with the presence of a 500-m headland and a submerged reef. Small changes in wave forcing and tide elevation were found to largely impact circulation patterns. In particular, under 4-m oblique wave conditions, our measurements indicate the presence of an intense low-frequency fluctuating deflection rip flowing against the headland and extending well beyond the surf zone. An XBeach model is further set up to hindcast such flow patterns.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EiqnjBIkWJE

scholarly journals TIME DOMAIN COMPARISONS OF MEASURED AND SPECTRALLY SIMULATED BREAKING WAVES

2017 ◽  
pp. 12
Author(s):  
Mustafa Kemal Ozalp ◽  
Serdar Beji
Keyword(s):  
Time Domain ◽  
Surf Zone ◽  
Field Measurements ◽  
Wave Model ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Dissipative Effects ◽  
Spectral Components ◽  
Breaking Mechanism ◽  
Acceptable Agreement

For realistic wave simulations in the nearshore zone besides nonlinear interactions, the dissipative effects of wave breaking must also be taken into account. This paper presents the applications of a spectral nonlinear wave model with a dissipative breaking mechanism introduced by Beji and Nadaoka (1997). Results obtained for spectral components are converted to the time series and compared with Beji and Battjes' (1993) laboratory measurements and the field measurements of Nakamura and Katoh (1992) in the surf zone. While the model predicts the spilling-type breaking of irregular waves in acceptable agreement with the measurements in time domain, the agreement is unsatisfactory for plunging-type breakers.

scholarly journals LONGSHORE TRANSPORT OF SAND

1968 ◽  
Vol 1 (11) ◽  
pp. 18 ◽  
Author(s):  
Douglas L. Inman ◽  
Paul D. Komar ◽  
Anthony J. Bowen
Keyword(s):  
Energy Flux ◽  
Surf Zone ◽  
Field Measurements ◽  
Breaking Waves ◽  
Transport Rate ◽  
Wave Power ◽  
Longshore Transport ◽  
Wave Conditions

Simultaneous field measurements of the energy flux of breaking waves and the resulting longshore transport of sand in the surf zone have been made along three beaches and for a variety of wave conditions. The measurements indicate that the longshore transport rate of sand is directly proportional to the longshore component of wave power.

scholarly journals NUMERICAL MODELLING OF NEARSHORE CIRCULATION

1980 ◽  
Vol 1 (17) ◽  
pp. 160 ◽  
Author(s):  
Bruce A. Ebersole ◽  
Robert A. Dalrymple
Keyword(s):  
Numerical Model ◽  
Finite Difference ◽  
Numerical Models ◽  
Bottom Topography ◽  
Rip Currents ◽  
Time Dependency ◽  
Longshore Current ◽  
Governing Equations ◽  
Nearshore Circulation ◽  
Lateral Mixing

Waves impinging on beaches induce mean flows, such as longshore and rip currents. This nearshore circulation is of fundamental importance in the study of the transport of nearshore contaminants as well as littoral materials. Analytic models of this nearshore flow {see, e.g. 4, 9, 11, 12) have been constrained to be linear (in the governing equations) and simplistic in the bottom topography. Only recently have numerical models been developed to examine more complex situations. Steady state, finite difference models (1, 14), as well as a finite element model (10), have been proposed. The numerical model, developed by Birkemeier and Dalrymple (1), allowed for time dependency. Yet, in all of these cases, the governing equations have not included the nonlinear convective accelerations or lateral mixing terms. In this study, a nonlinear numerical model is presented based on a leapfrog finite difference scheme, which includes time dependency and eddy viscosity terms. Results are shown for a planar beach showing a comparison with the analytical longshore current models (with and without lateral mixing) of Longuet-Higgins (11, 12). The longshore current over a prismatic beach profile including an offshore bar is presented next, showing the effects of the bar on the velocity profile. The circulation set-up by a rip channel inset into a plane beach is then computed. A comparison is made to the linear model of Birkemeier and Dalrymple. Finally the model is applied to the case of synchronous intersecting wave trains (4). An interesting result occurs when the waves are of different amplitudes, which could provide an explanation of the formation of finger bars on a beach.

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.

scholarly journals Longshore current profiles and lateral mixing across the surf zone of a barred nearshore

1986 ◽  
Vol 10 (2) ◽  
pp. 149-168 ◽  
Author(s):  
Brian Greenwood ◽  
Douglas J. Sherman
Keyword(s):  
Surf Zone ◽  
Longshore Current ◽  
Lateral Mixing

scholarly journals MODIFICATION OF WAVE SPECTRA ON THE CONTINENTAL SHELF AND IN THE SURF ZONE

2011 ◽  
Vol 1 (8) ◽  
pp. 2 ◽  
Author(s):  
Charles L. Bretschneider
Keyword(s):  
Continental Shelf ◽  
Shallow Water ◽  
Surf Zone ◽  
Wind Waves ◽  
Wave Spectrum ◽  
Breaking Waves ◽  
Bottom Friction ◽  
Breaking Wave ◽  
Predominant Period ◽  
Significant Period

This paper discusses the problem pertaining to the modification of the wave spectrum over the continental shelf. Modification factors include bottom friction, percolation, refraction, breaking waves, ocean currents, and regeneration of wind waves in shallow water, among other factors. A formulation of the problem is presented but no general solution is made, primarily because of lack of basic data. Several special solutions are presented based on reasonable assumptions. The case for a steep continental shelf with parallel bottom contours and wave crests parallel to the coast and for which bottom friction is neglected has been investigated. For this case it is found that the predominant period shifts toward longer periods. The implication is, for example, that the significant periods observed along the U. S. Pacific coast are longer than those which would be observed several miles westward over deep water. The case for a gentle continental shelf with parallel bottom contour and wave crests parallel to the coast and for which bottom friction is important has also been investigated. For this case it is found that the predominant period shifts toward shorter periods as the water depth decreases. The implication is, for example, that the significant periods observed in the shallow water over the continental shelf are shorter than those which would be observed beyond the continental slope. In very shallow water, because shoaling becomes important, a secondary peak appears at higher periods. The joint distribution of wave heights and wave periods is required in order to determine the most probable maximum breaking wave, which can be of lesser height than the most probable maximum non-breaking wave. In very shallow water the most probable maximum breaking wave which first occurs would be governed by the breaking depth criteria, whereas in deepwater wave steepness can also be a governing factor. It can be expected that in very shallow water the period of the most probable maximum breaking wave should be longer than the significant period; and for deeper water the period of the most probable maximum breaking wave can be less than the significant period.

Nearshore mixing and dispersion

1994 ◽  
Vol 445 (1925) ◽  
pp. 561-576 ◽  
Keyword(s):  
Surf Zone ◽  
Three Dimensional ◽  
Dispersion Effect ◽  
Longshore Current ◽  
Turbulent Length Scale ◽  
Interaction Terms ◽  
Longshore Currents ◽  
Order Of Magnitude ◽  
Lateral Mixing ◽  
The One

Longshore currents have in the past been analysed assuming that the lateral mixing could be attributed to turbulent processes. It is found, however, that the mixing that can be justified by assuming an eddy viscosity v t = l√k where l is the turbulent length scale, k the turbulent kinetic energy, combined with reasonable estimates for l and k is at least an order of magnitude smaller than required to explain the measured cross-shore variations of longshore currents. In this paper, it is shown that the nonlinear interaction terms between cross-and longshore currents represent a dispersive mechanism that has an effect similar to the required mixing. The mechanism is a generalization of the one-dimensional dispersion effect in a pipe discovered by Taylor (1954) and the three-dimensional dispersion in ocean currents on the continental shelf found by Fischer (1978). Numerical results are given for the dispersion effect, for the ensuing cross-shore variation of the longshore current and for the vertical profiles of the longshore currents inside as well as outside the surf zone. It is found that the dispersion effect is at least an order of magnitude larger than the turbulent mixing and that the characteristics of the results are in agreement with the sparse experimental data material available.

Longshore motion due to an obliquely incident wave group

1983 ◽  
Vol 137 ◽  
pp. 273-284 ◽  
Author(s):  
S. C. Ryrie
Keyword(s):  
Wave Equations ◽  
Surf Zone ◽  
Breaking Waves ◽  
Wave Group ◽  
Edge Waves ◽  
Obliquely Incident ◽  
Long Wave ◽  
Circulation Cell ◽  
A Cell ◽  
Set Up

We consider longshore motion generated within the surf zone by obliquely incident breaking waves, and seek to describe the effect on such motion of variations, caused by wave grouping, in the incident longshore momentum flux. The effects of associated variations in set-up are not considered.We use the linear long-wave equations to describe the motion resulting from the longshore momentum contained in a wave group. This consists of a succession of edge waves which disperse along the beach, and, for the example considered, an eventual steady circulation cell at the position of the wave group. We suggest that such a cell is always likely to be formed if the wave group is sufficiently localized, and that higher-modenumber edge waves are more likely to be excited.We find timescales for the dispersal of the edge waves, and for the decay, due to bottom friction, of the circulation cell: we suggest that the latter may more generally be used, as a timescale for the effect of friction on longshore motion.

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