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Dennis B Trizna - One of the best experts on this subject based on the ideXlab platform.
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errors in bathymetric retrievals using linear dispersion in 3 d fft analysis of marine radar ocean Wave imagery
IEEE Transactions on Geoscience and Remote Sensing, 2001Co-Authors: Dennis B TriznaAbstract:The phenomenon of ocean Wave-Shoaling, and the associated reduction of ocean Wave phase speed with decreased water depth, provides useful information for inferring water depth D (bathymetry) in coastal environments. One strategy for relating D to phase speed C and Wave-vector K of long Wavelength ocean Waves involves using the one-dimensional (1-D) linear (gravity Wave) dispersion relationship C/sup 2/=g*tanh(KD)/K. In principle, this approach has limitations because the approach is based on a WKB approximation, so it cannot be applied when D varies appreciably over the Wavelength of a Shoaling Wave. Also, the approach is restricted to Waves that have small Wave height. The author uses a set of marine radar image sequences and applies this linear approximation, using a 3-D FFT analysis of 88 sets of image sequences spaced half an hour apart. The author inverts the dispersion relation to solve for D. Depths between 3.6 and 5.8 m were tested, for root mean square (RMS) Wave heights offshore between 8 and 3 m. The author shows that for low to moderate Wave heights, the approach does generally retrieve the correct depth in water depths of 5 m and greater for moderate Wave RMS heights. However, an increase in the RMS Wave height from 1 m to 3.5 m produced a much poorer depth estimate, proving the need for an application of a nonlinear Wave model to the problem. The errors also increase with shallower depths as expected, as the error dependence on depth and Wave height is determined.
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errors in bathymetric retrievals using linear dispersion in 3 d fft analysis of marine radar ocean Wave imagery
International Geoscience and Remote Sensing Symposium, 2001Co-Authors: Dennis B TriznaAbstract:The phenomenon of ocean Wave-Shoaling, and the associated reduction of ocean Wave phase speed with decreased water depth, provides useful information for inferring water depth D (bathymetry) in coastal environments. One strategy for relating D to phase speed C and Wave-vector K of long Wave length ocean Waves involves using the one-dimensional (1-D) linear (gravity Wave) dispersion relationship C 2 = g * tanh(KD)/K. In principle, this approach has limitations because the approach is based on a WKB approximation, so it cannot be applied when D varies appreciably over the Wavelength of a Shoaling Wave. Also, the approach is restricted to Waves that have small Wave height. In the present paper, we use a set of marine radar image sequences and apply this linear approximation, using a three-dimensional (3-D) FFT analysis of 88 sets of image sequences spaced half an hour apart. We invert the dispersion relation to solve for D. Depths between 3.6 and 5.8 m were tested, for root mean square (RMS) Wave heights offshore between 8 and 3 m. We show that for low to moderate Wave heights, the approach does generally retrieve the correct depth in water depths of 5 m and greater for moderate Wave RMS heights. However, an increase in the RMS Wave height from 1 m to 3.5 m produced a much poorer depth estimate, proving the need for an application of a nonlinear Wave model to the problem. The errors also increase with shallower depths as expected, as the error dependence on depth and Wave height is determined.
Fabrice Veron - One of the best experts on this subject based on the ideXlab platform.
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wind effects on Shoaling Wave shape
Journal of Physical Oceanography, 2005Co-Authors: Falk Feddersen, Fabrice VeronAbstract:Near the shore, cross-shore winds strongly affect the location of the break point and the breaking-Wave height. From casual observation from the beach, wind direction (onshore or offshore) and speed also appear to affect Wave shape (i.e., skewness and asymmetry), although as of yet this effect has not been quantified near the shore. The effect of wind on Shoaling Wave shape is investigated with laboratory experiments using monochromatic Waves and onshore-directed wind. Wind increases the Shoaling Wave energy at discrete multiples of the primary frequency and has a significant effect on the Wave shape at both a deeper and shallower Shoaling locations. At the shallower location, the ratio of Wave energy at 2 times the primary frequency to the primary frequency is also a function of wind speed, indicating interaction between the wind and the nonlinear Wave Shoaling process. Nearshore Wave models do not account for these wind effects. Incorrect predictions of third-order velocity moments (Wave shape), believed to control Wave-driven sediment transport, would result in incorrect beach morphological evolution predictions.
Falk Feddersen - One of the best experts on this subject based on the ideXlab platform.
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wind effects on Shoaling Wave shape
Journal of Physical Oceanography, 2005Co-Authors: Falk Feddersen, Fabrice VeronAbstract:Near the shore, cross-shore winds strongly affect the location of the break point and the breaking-Wave height. From casual observation from the beach, wind direction (onshore or offshore) and speed also appear to affect Wave shape (i.e., skewness and asymmetry), although as of yet this effect has not been quantified near the shore. The effect of wind on Shoaling Wave shape is investigated with laboratory experiments using monochromatic Waves and onshore-directed wind. Wind increases the Shoaling Wave energy at discrete multiples of the primary frequency and has a significant effect on the Wave shape at both a deeper and shallower Shoaling locations. At the shallower location, the ratio of Wave energy at 2 times the primary frequency to the primary frequency is also a function of wind speed, indicating interaction between the wind and the nonlinear Wave Shoaling process. Nearshore Wave models do not account for these wind effects. Incorrect predictions of third-order velocity moments (Wave shape), believed to control Wave-driven sediment transport, would result in incorrect beach morphological evolution predictions.
Chen Xuanyu - One of the best experts on this subject based on the ideXlab platform.
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IMPACTS OF Shoaling OCEAN SURFACE WaveS ON WIND STRESS AND STORM SURGE
DigitalCommons@URI, 2020Co-Authors: Chen XuanyuAbstract:Ocean surface Waves have been known to affect the wind stress, or air-sea momentum flux, in the open ocean under tropical cyclones. As a tropical cyclone (TC) makes landfall, the surface Waves shoal as they enter the shallower coastal waters (\u3c 30~50 m). The impacts of these Shoaling surface Waves on the wind stress have not yet been thoroughly investigated, but they have been postulated to be important for storm surge prediction. In this study, the WaveWATCH III (WW3) model is used to simulate the depth modifications on the surface Wave fields and the wind stress. Two Wave-spectrum based wind stress estimation modules in the WW3 model are used to quantify the impact of Wave Shoaling on wind stress and drag coefficient under steady uniform wind and tropical cyclone conditions. The consequence of using the Shoaling Wave modified wind stress for modeling storm surge is investigated using the Advanced Circulation (ADCIRC) model. For the Shoaling Wave simulations, an accurate Wave field generated by tropical cyclones in the open ocean needs to be established first. The sensitivity of tropical cyclone Wave simulations in the open ocean to different spatial resolutions (1/3 °, 1/6 °, 1/12 ° and 1/24 °) is evaluated using two Wave models, WW3 and Simulating Waves Nearshore. Results from both models show that the coarsest resolution (1/3 °) introduces significant errors in both the significant Wave height (Hs) and the mean Wavelength. Moreover, results reveal that sensitivity to spatial resolution strongly depends on storm characteristics. Waves simulated under the small and fast moving TC show the largest sensitivity to the coarse spatial resolutions. With the 1/3 ° resolution, maximum Hs can be underestimated by as much as 6% in WW3 and 16% in SWAN compared to those with the 1/24 ° resolution. The impacts of Shoaling ocean surface Waves on the wind stress and drag coefficient (Cd) in coastal waters are investigated with the WW3 under steady, uniform onshore wind and tropical cyclones. Our results show that under uniform onshore winds, as water depth decreases, the drag coefficient increases gradually to a peak value and then rapidly reduces compared to the deep-water value. The maximum Cd occurs roughly where depth-induced Wave breaking starts. The magnitude of Cd enhancement is more significant on a steeper slope and can reach 40%, which is mainly due to the steepening of Waves and reduction of the Wave phase speed during the Shoaling. Our results suggest significantly larger variability of Cd at a given wind speed in finite depth waters than in deep water, which is also found during idealized landfalling TCs. Specifically, Cd is enhanced in the right TC quadrants (due to Shoaling fetch-dependent Waves) and in the left TC quadrants (due to Shoaling opposing-wind swells) compared to its deep-water value. However, Cd is reduced in the front/rear quadrants due to weaker wind seas. The misalignment between wind stress and wind speed directions is also enhanced in shallow water. In general, the Shoaling Wave effects on the wind stress and Cd are much stronger on steeper bottom slopes and in faster-moving storms. At last, the Shoaling Wave modified wind stress is applied to a two-dimensional steady-state model and the ADCIRC model to investigate its impacts on storm surge. In the steady onshore wind conditions, the Shoaling Wave modified (or sea-state dependent (SSD)) wind stress can increase the sea surface elevation by as much as 15% on a steep bottom slope compared to the result using the bulk wind stress as a function of wind speed. In TC conditions, the maximum impact of the SSD wind stress occurs to the left of the storm track near the radius of maximum wind around the time of TC landfall. The set-down of the sea level is significantly enhanced due to increased offshore wind stress. However, the SSD wind stress impact on the peak surge to the right of the storm track is negligible. Hence, our analysis suggests that the SSD wind stress has the biggest impact in uniform onshore wind conditions (such as under large, slow moving extratropical cyclones) than in TC conditions. Our results also suggest that the water level prediction at the shoreline is sensitive to the wind stress in the surf zone, which is not resolved explicitly in our model
Tanimoto Katsutoshi - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of breaking Waves using a two phase flow model
Applied Mathematical Modelling, 2004Co-Authors: Phung Dang Hieu, Tanimoto KatsutoshiAbstract:Abstract In this paper, a numerical two-phase flow model for incompressible viscous fluid is presented for the simulation of Wave propagation in shallow water, including the processes of Wave Shoaling, Wave breaking, Wave reflection and air movement. The model consists of the continuity equation, the Navier–Stokes equations, the fractional VOF function equation, and the equations of density and viscosity. The turbulent eddy viscosity is evaluated by using the Smagorinsky's sub-grid scale model. The VOF method with an advection algorithm following [Int. J. Numer Meth. Fluids 35 (2001) 151] is employed for tracking the free surface. To solve the time evolution of the governing equations, the SMAC method and iteration technique are used. The convective terms in the momentum equation are approximated using a high accuracy CIP scheme proposed in [Comput. Phys. Commun. 66 (1991) 219]. A numerical test with dam break problem was conducted and compared with experimental data to verify the validity and stability of the model. The model was then applied to simulate the Wave breaking on a sloping bottom and the numerical results were compared with experimental data. The results demonstrated that the present model is capable of simulating Wave deformation in shallow water, as well as Wave breaking problem.