Papers by Yasser Eldeberky
Coastal Engineering, 1998
Fetch limited finite depth wind waves are subjected to a bispectral analysis to determine the ext... more Fetch limited finite depth wind waves are subjected to a bispectral analysis to determine the extent of triad nonlinear coupling. Very long yet stationary time series are utilized, enabling the determination of bicoherence values with significantly smaller confidence limits than have been achieved previously. The bispectral analysis indicates a significant degree of phase coherence between the spectral peak frequency and higher frequencies. It is concluded that this phase coherence is as a result of non-resonant or bound triad interactions with the spectral peak frequency. Previous studies of triad coupling have generally been confined to relatively shallow Ž water. Values of the relative depth, k d k is the wavenumber of the spectral peak, d is water p p. depth for these previous studies have ranged between 0.14 and 1.13. The present data set extends available data to values of k d between 1.39 and 2.35. The existence of triad coupling at these p water depths indicates that models which are to be used to predict waves in the transitional water depths found on many continental shelves may need to include the effects of such interactions. Previously, it has been assumed that triad interactions were generally only significant in the shoaling region. q 1998 Elsevier Science B.V.
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Journal of Geophysical Research, 1996
The nonlinear transformation of wave spectra in shallow water is considered, in particular, the r... more The nonlinear transformation of wave spectra in shallow water is considered, in particular, the role of wave breaking and the energy transfer among spectral components due to triad interactions. Energy dissipation due to wave breaking is formulated in a spectral form, both for energy-density models and complex-amplitude models. The spectral breaking function distributes the total rate of random-wave energy dissipation in proportion to the local spectral level, based on experimental results obtained for single-peaked spectra that breaking does not appear to alter the spectral shape significantly. The spectral breaking term is incorporated in a set of coupled evolution equations for complex Fourier amplitudes, based on ideal-fluid Boussinesq equations for wave motion. The model is used to predict the surface elevations from given complex Fourier amplitudes obtained from measured time records in laboratory experiments at the upwave boundary. The model is also used, together with the assumption of random, independent initial phases, to calculate the evolution of the energy spectrum of random waves. The results show encouraging agreement with observed surface elevations as well as spectra.
Wave hindcast is widely used to assess the wave conditions in both offshore and nearshore regions... more Wave hindcast is widely used to assess the wave conditions in both offshore and nearshore regions. A third generation ocean wind-wave model is implemented to hindcast the wave climate in the eastern Mediterranean Sea offshore Egypt coastline. The effects of the spatial grid resolution, the model physics, and input wind fields are examined using results of wave hindcast. Model results of wave hindcast during two selected storms are compared against wave observations offshore the Egyptian and Italian coasts as well as remotely sensed wave height data recorded by TOPEX satellite in the eastern Mediterranean Sea. Sensitivity computations are performed to confirm that a spatial grid with 0.5° resolution is adequate for assessment of wave conditions in the open sea (deep water). In intermediate water near the coast, a spatial grid with 0.25° resolution is required to take into account the local bathymetry and coastal details. The model-data comparisons recommend the use of Tolman and Chalikov (1996) parameterizations, for the wave input and dissipation terms, and the NCEP wind fields for wave hindcast in the eastern Mediterranean Sea.
Coastal Engineering 1998, 1999
This paper presents a new and more accurate set of deterministic evolution equations for three-wa... more This paper presents a new and more accurate set of deterministic evolution equations for three-wave interactions involving fully dispersive, weakly nonlinear, irregular, unidirectional waves. The equations are derived directly from the Laplace equation with leading order nonlinearity in the surface boundary conditions. It is demonstrated that previous fully dispersive formulations from the literature have used an inconsistent linear relation between the velocity potential and the surface elevation. As a consequence these formulations are accurate only in shallow water, while nonlinear transfer of energy is significantly underestimated for larger wave numbers. In the present work we correct this inconsistency. In addition to the improved deterministic formulation, we present improved stochastic evolution equations in terms of the energy spectrum and the bispectrum for unidirectional waves.
Coastal Engineering 1996, 1997
Coastal Engineering 1994, 1995
... by Y. Eldeberky 1 , S. Abo-Hadima 2 , A. Metwally 3 and A. Rabie 4 ABSTRACT The wave conditio... more ... by Y. Eldeberky 1 , S. Abo-Hadima 2 , A. Metwally 3 and A. Rabie 4 ABSTRACT The wave conditions in the Western Mediterranean Sea are hindcast using a third generation spectral wind-wave model. ... 4% Figure 5: Wind Rose at the Offshore Site ...
Coastal Engineering Journal, 2015
Wave hindcast is widely used to assess the wave conditions in both offshore and nearshore regions... more Wave hindcast is widely used to assess the wave conditions in both offshore and nearshore regions. A third generation ocean wind-wave model is implemented to hindcast the wave climate in the eastern Mediterranean Sea offshore Egypt coastline. The effects of the spatial grid resolution, the model physics, and input wind fields are examined using results of wave hindcast. Model results of wave hindcast during two selected storms are compared against wave observations offshore the Egyptian and Italian coasts as well as remotely sensed wave height data recorded by TOPEX satellite in the eastern Mediterranean Sea. Sensitivity computations are performed to confirm that a spatial grid with 0.5° resolution is adequate for assessment of wave conditions in the open sea (deep water). In intermediate water near the coast, a spatial grid with 0.25° resolution is required to take into account the local bathymetry and coastal details. The model-data comparisons recommend the use of Tolman and Chalikov (1996) parameterizations, for the wave input and dissipation terms, and the NCEP wind fields for wave hindcast in the eastern Mediterranean Sea.
International Journal of Oceans and Oceanography
The degree of nonlinear coupling in a random wavefield propagating over and beyond a bar is exami... more The degree of nonlinear coupling in a random wavefield propagating over and beyond a bar is examined using a physical wave flume as well as numerical simulations based on time-domain extended Boussinesq equations and their frequency-domain counter-part. The nonlinear phase speed is computed from the evolution of the nonlinear part of the phase function inherent in the frequency-domain model. Over the bar, the phase speeds of the higher harmonics are larger than the linear estimates due to the nonlinear couplings, resulting in virtually dispersionless propagation, while beyond the bar crest, nonlinear effects on the phase speed vanish rapidly, implying full release of bound harmonics. Quantitative measures of nonlinearity such as the skewness and asymmetry have also been determined. They have near-zero values in the deep-water region on either side of the bar and a pronounced peak over the bar. On the downwave side, the random wave field is found to be spatially homogeneous. This imp...
Ain Shams Engineering Journal, 2011
The spectral evolution of waves in shallow water is considered, in particular, wave breaking and ... more The spectral evolution of waves in shallow water is considered, in particular, wave breaking and the generation of sub-and super-harmonics. Modeling of these processes is based on a set of deterministic evolution equations for the propagation of fully dispersive nonlinear waves. Energy dissipation due to wave breaking is formulated in a spectral form and incorporated in the model. Previous laboratory measurements for wave transformation and breaking over barred and nonbarred beaches were compared against the model results. In order to obtain wave field statistics, Monte Carlo simulations are performed by assuming the wave field Gaussian at the upwave boundary. Modal amplitudes are derived from the observed density spectrum together with the assumption of random independent initial phases. The overall statistical parameters such as the significant wave height, mean wave period and skewness are determined. The overall model results show agreement with the measurements including the generation of low-frequency waves.
Coastal Engineering Journal, 2012
Nonlinear energy transfers due to triad interactions change the characteristics of the wave-field... more Nonlinear energy transfers due to triad interactions change the characteristics of the wave-field in the shoaling region. The degree of nonlinear coupling is examined using numerical simulations based on an accurate set of deterministic evolution equations for the propagation of fully dispersive weakly nonlinear waves. The model validation, using existing experimental measurements for wave transformation over a shoal, showed that it accurately predicts nonlinear energy transfer for irregular waves with large wave-numbers. The bound higher harmonics and nonlinear statistical measures, i.e. the wave skewness and asymmetry, are well simulated by the model in both the shoaling and deshoaling regions. Numerical simulation of steep waves in shallow water with the Ursell number O(1), showed that nonlinear dispersion and phase locking lead to triad interactions even on a horizontal bottom. Nonlinear energy transfers in monochromatic waves lead to rapid spatial recurrence of the primary wave amplitudes. This is in contrast to the case of irregular waves where the Fourier coefficients of the wave-field do not recur due to the presence of innumerable interactions, which are expected to cancel resulting in no spatial evolution of the wave spectrum.
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Papers by Yasser Eldeberky