scholarly journals SHORT WAVE BREAKING EFFECTS ON LOW FREQUENCY WAVES

2011 ◽  
Vol 1 (32) ◽  
pp. 20 ◽  
Author(s):  
Christopher Daly ◽  
Dano Roelvink ◽  
Ap Van Dongeren ◽  
Jaap Van Thiel de Vries ◽  
Robert McCall
Keyword(s):  
Wave Breaking ◽  
Surf Zone ◽  
Low Frequency ◽  
Breaking Waves ◽  
Short Wave ◽  
Frequency Wave ◽  
Wave Heights ◽  
Wave Groupiness ◽  
Set Up ◽  
Low Frequency Waves

The effect of short wave breaking on low frequency waves is investigated using two breaker formulations implemented in a time-dependent numerical model (XBeach): (1) an advective-deterministic approach (ADA) and (2) the probabilistic breaker formulation of Roelvink (1993). Previous research has shown that the ADA breaker model gives different results for the cross-shore pattern of the fraction of breaking waves, which is now shown to affect not only the short wave height but also the short wave groupiness. While RMS short wave heights are comparable to measurements using both breaker models, the ADA breaker model allows higher levels of short wave groupiness into the surf zone. It is shown that this acts as an additional forcing mechanism for low frequency waves in the shoaling and nearshore zone, which, in addition to greater levels of breaking, leads to higher values of wave set-up. These findings are dependent on the complexity of the local bathymetry. For a plane slope, the differences in the low frequency wave heights and set-up predicted by both breaker models are negligible. Where arbitrary breakpoints are present in the field of wave propagation, such as nearshore bars or reefs, the ADA model predicts higher localized set-up, indicative of greater flow over such features. Differences are even more pronounced when the incident wave regime is highly energetic.

Evaluation of an Extended Operational Boussinesq-Type Wave Model for Calculating Low-Frequency Waves in Intermediate Depths

2011 ◽  
Author(s):  
Martijn P. C. de Jong ◽  
Mart Borsboom ◽  
Jan A. M. de Bont ◽  
Bas van Vossen
Keyword(s):  
Low Frequency ◽  
Wave Model ◽  
Coastal Engineering ◽  
Extended Model ◽  
Depth Range ◽  
Frequency Range ◽  
Frequency Wave ◽  
Type Wave ◽  
Wave Heights ◽  
Low Frequency Waves

The motions of (LNG) vessels moored offshore at depths ranging from about 20 to 100 m may depend significantly on the presence of (bound) low-frequency waves with periods in the order of 100 s. This is because these moored vessels show a large motion response in this frequency range and because the energy contents of low-frequency waves at these ‘intermediate’ depths is relatively large. As part of the Joint Industry Project HawaI, the operational Boussinesq-type wave model of Deltares, TRITON, was used to investigate whether this type of wave models could predict bound low-frequency waves (setdown waves) at intermediate depths. Comparison to measured and theoretical data, however, showed an underestimation of the computed levels of bound low-frequency wave heights for this depth range by a factor 2 to 4. Recently, additional tests were made with TRITON in situations for which the model has been designed: coastal engineering applications in shallow water (depths up to at most 20 m). These also showed an underestimation of the bound low-frequency wave heights, albeit smaller, up to a factor 2. In view of the importance of the energy contained in the low-frequency range for certain nearshore and shoreline processes, such as morphological processes, this underestimation is also of concern in coastal engineering. This triggered the development of a higher-order extension of the TRITON model equations (Borsboom, 2008, Wellens, 2010), with the aim to improve the accuracy of the model for long waves while still keeping computational times within acceptable (operational) limits. This paper reports on the usefulness of the extended model for the field of application considered in JIP HawaI/II: providing wave data for calculating the motions of vessels moored in intermediate depths. The results show a significant improvement of the modeling of nonlinear wave dynamics, including the prediction of bound low-frequency waves. This means that the model extension is an important step towards an operational Boussinesq-type wave model with sufficient accuracy in both the wave-frequency (sea, swell) and the low-frequency range for applications in intermediate depths.

Influence of Offshore Reefs on Low-Frequency Waves During Harbor Resonance

2017 ◽  
Author(s):  
Junliang Gao ◽  
Chunyan Ji ◽  
Xiaojian Ma
Keyword(s):  
Low Frequency ◽  
Resonant Mode ◽  
Short Wave ◽  
Long Waves ◽  
Boussinesq Model ◽  
Wave Groups ◽  
Frequency Wave ◽  
Wave Separation ◽  
The Given ◽  
Low Frequency Waves

In this paper, a fully nonlinear Boussinesq model is used to simulate the shoreward propagation of bichromatic wave groups over different fringing reef topographies and the subsequent low-frequency oscillations inside a harbor. Based on a low-frequency wave separation technique, the effects of the reef-face slope and the reef ridge on the bound and free long waves inside the harbor and their relative components under the condition of the lowest resonant mode are systematically investigated. For the given harbor, the given reef ridge and the range of the incident short wave amplitudes and the reef-face slopes studied in this paper, results show that the amplitude of the free long waves inside the harbor increases with the reefface slope, while the bound long waves inside the harbor is insensitive to the variation of the reef-face slope. The existence of the reef ridge can notably restrain the bound long waves inside the harbor when the incident short wave amplitudes are large, while it has little influence on the free long waves inside the harbor.

scholarly journals Two-point observations of low-frequency waves at 67P/Churyumov-Gerasimenko during the descent of PHILAE: comparison of RPCMAG and ROMAP

2016 ◽  
Vol 34 (7) ◽  
pp. 609-622 ◽  
Author(s):  
Ingo Richter ◽  
Hans-Ulrich Auster ◽  
Gerhard Berghofer ◽  
Chris Carr ◽  
Emanuele Cupido ◽  
...  
Keyword(s):  
Low Frequency ◽  
Minimum Variance ◽  
Wave Source ◽  
Frequency Wave ◽  
Final Destination ◽  
Connection Line ◽  
New Type ◽  
Current Instability ◽  
Comet 67P ◽  
Low Frequency Waves

Abstract. The European Space Agency's spacecraft ROSETTA has reached its final destination, comet 67P/Churyumov-Gerasimenko. Whilst orbiting in the close vicinity of the nucleus the ROSETTA magnetometers detected a new type of low-frequency wave possibly generated by a cross-field current instability due to freshly ionized cometary water group particles. During separation, descent and landing of the lander PHILAE on comet 67P/Churyumov-Gerasimenko, we used the unique opportunity to perform combined measurements with the magnetometers onboard ROSETTA (RPCMAG) and its lander PHILAE (ROMAP). New details about the spatial distribution of wave properties along the connection line of the ROSETTA orbiter and the lander PHILAE are revealed. An estimation of the observed amplitude, phase and wavelength distribution will be presented as well as the measured dispersion relation, characterizing the new type of low-frequency waves. The propagation direction and polarization features will be discussed using the results of a minimum variance analysis. Thoughts about the size of the wave source will complete our study.

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 LABORATORY EXPERIMENTS ON THE INFLUENCE OF WIND ON NEARSHORE WAVE BREAKING

1988 ◽  
Vol 1 (21) ◽  
pp. 46
Author(s):  
Scott L. Douglass ◽  
J. Richard Weggel
Keyword(s):  
Wind Direction ◽  
Wave Breaking ◽  
Laboratory Experiments ◽  
Surf Zone ◽  
Breaking Waves ◽  
Wave Tank ◽  
Zone Width

The influence of wind on nearshore breaking waves was investigated in a laboratory wave tank. Breaker location, geometry, and type depended upon the wind acting on the wave as it broke. Onshore winds tended to cause waves to break earlier, in deeper water, and to spill: offshore winds tended to cause waves to break later, in shallower water, and to plunge. A change in wind direction from offshore to onshore increased the surf zone width by up to 100%. Wind's effect was greatest for waves which were near the transition between breaker types in the absence of wind. For onshore winds, it was observed that microscale breaking can initiate spilling breaking by providing a perturbation on the crest of the underlying wave as it shoals.

Low-Frequency Oscillations Within the Hambantota Port During the Southwest Monsoon, 2019

2020 ◽  
Author(s):  
Zhenjun Zheng ◽  
Xiaozhou Ma ◽  
Xuezhi Huang ◽  
Yujin Dong ◽  
Guohai Dong
Keyword(s):  
Wind Waves ◽  
Low Frequency ◽  
Southwest Monsoon ◽  
Long Waves ◽  
Frequency Wave ◽  
Low Frequency Oscillations ◽  
Mild Slope Equation ◽  
Spectrum Density ◽  
Forcing Mechanisms ◽  
Low Frequency Waves

Abstract Long waves with periods greater than tens of seconds propagating into a harbor may be trapped and significantly amplified, thereby resulting in detrimental effects on port operations. The water surface elevation in the Hambantota Port, Sri Lanka, was measured to investigate the low-frequency oscillations and their forcing mechanisms. Results show that the port is protected well from short waves with periods less than 30 s; however, the protection against long waves with periods larger than 30 s is inadequate. The spectral analyses identified four dominant periods within the low-frequency wave range. Modal analysis based on the extended mild-slope equation shows that the measured spectrum density for some dominant periods is low because the measurement point is close to the corresponding modal lines. Correlation analysis shows that low-frequency oscillations inside the Hambantota Port are excited directly by the low-frequency waves contained within the incident waves. The low-frequency waves outside the Hambantota Port are generated from the higher-frequency gravity waves (swell and wind waves) due to nonlinear interactions. Empirical formula is adopted to estimate the low-frequency wave height outside the Hambantota Port.

scholarly journals Wave heights and set-up in a surf zone

1984 ◽  
Vol 8 (4) ◽  
pp. 303-329 ◽  
Author(s):  
I.A. Svendsen
Keyword(s):  
Surf Zone ◽  
Wave Heights ◽  
Set Up

Numerical Simulation of Breaking Waves in a Wave Group by SPH

2015 ◽  
Vol 776 ◽  
pp. 151-156
Author(s):  
Ni Nyoman Pujianiki
Keyword(s):  
Surf Zone ◽  
Breaking Waves ◽  
Return Flow ◽  
Wave Group ◽  
Regular Waves ◽  
Wave Groups ◽  
Smoothed Particle ◽  
Wave Heights ◽  
Smoothed Particle Hydrodynamic ◽  
Wave Break

Smoothed Particle Hydrodynamic (SPH) numerical model is used to investigate wave group effects at breaking and after breaking by comparing individual waves in a group with equivalent regular waves. Regular wave break almost at the same position and with the same wave height. Meanwhile in a wave group, the wave breaks in the variant positions and with variant wave heights. These phenomena cause the breaking point to be more scattered in a wave group rather than in regular waves. Return flow due to the breaking of wave groups appears more significant and is extended to the full depth in the surf zone rather than in regular waves. Swash oscillations of the wave group in the surf zone appear irregular. Meanwhile in regular waves, swash oscillations are almost constant.

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 Infragravity Wave Energy Partitioning in the Surf Zone in Response to Wind-Sea and Swell Forcing

2019 ◽  
Vol 7 (11) ◽  
pp. 383
Author(s):  
Stephanie Contardo ◽  
Graham Symonds ◽  
Laura Segura ◽  
Ryan Lowe ◽  
Jeff Hansen
Keyword(s):  
Surf Zone ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Sea Breeze ◽  
Peak Frequency ◽  
Short Wave ◽  
Edge Waves ◽  
Leaky Waves ◽  
Wind Speeds ◽  
Wind Sea

An alongshore array of pressure sensors and a cross-shore array of current velocity and pressure sensors were deployed on a barred beach in southwestern Australia to estimate the relative response of edge waves and leaky waves to variable incident wind wave conditions. The strong sea breeze cycle at the study site (wind speeds frequently > 10 m s−1) produced diurnal variations in the peak frequency of the incident waves, with wind sea conditions (periods 2 to 8 s) dominating during the peak of the sea breeze and swell (periods 8 to 20 s) dominating during times of low wind. We observed that edge wave modes and their frequency distribution varied with the frequency of the short-wave forcing (swell or wind-sea) and edge waves were more energetic than leaky waves for the duration of the 10-day experiment. While the total infragravity energy in the surf zone was higher during swell forcing, edge waves were more energetic during wind-sea periods. However, low-frequency (0.005–0.023 Hz) edge waves were found to be dominant in absence of wind-sea conditions, while higher-frequency (0.023–0.050 Hz) edge waves dominated when wind-sea conditions were present.

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