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On the parameterization of the free-stream non-linear wave orbital motion in nearshore morphodynamic models
Abstract Nearshore morphodynamic models are computationally demanding, especially when the time scale of interest is weeks or longer. Hence, they often rely on a simple parameterization or non-linear wave theory to estimate the skewed-asymmetric shape of the near-bed, free-stream wave orbital motion, relevant to the prediction of onshore sand transport during mild wave conditions. Recently, Abreu et al. (2010) presented a simple analytical expression for this shape. Here, we present parameterizations to estimate the non-linearity parameter r and phase ϕ in this expression, such that the non-linear orbital motion can be estimated efficiently from values of the significant wave height H s, wave period T, and water depth h, standard output of nearshore morphodynamic models. The parameterizations are based on a data set of 30.000+ field observations of the orbital skewness S u and asymmetry A u, collected under non-breaking and breaking wave conditions. Consistent with earlier observations, we find that the Ursell number, which includes H s, T and h, describes the variability in S u and A u well and we use it to link H s, T and h to r and ϕ. The comparison of our findings to another large field data set suggests that wave non-linearity depends weakly on wave directional spread and that our parameterizations may underestimate S u for narrow-banded swell and (unidirectional) laboratory conditions. Furthermore, the use of the parameterizations is not advised on bed slopes steeper than in our data set (i.e., >1:30).
Highlights ► Near-bed velocity skewness and asymmetry depend on wave height, period and water depth ► We use 30.000+ field observations to parameterize velocity skewness and asymmetry. ► Parameterization can be extended to predict sand transport for mild wave conditions.
On the parameterization of the free-stream non-linear wave orbital motion in nearshore morphodynamic models
Abstract Nearshore morphodynamic models are computationally demanding, especially when the time scale of interest is weeks or longer. Hence, they often rely on a simple parameterization or non-linear wave theory to estimate the skewed-asymmetric shape of the near-bed, free-stream wave orbital motion, relevant to the prediction of onshore sand transport during mild wave conditions. Recently, Abreu et al. (2010) presented a simple analytical expression for this shape. Here, we present parameterizations to estimate the non-linearity parameter r and phase ϕ in this expression, such that the non-linear orbital motion can be estimated efficiently from values of the significant wave height H s, wave period T, and water depth h, standard output of nearshore morphodynamic models. The parameterizations are based on a data set of 30.000+ field observations of the orbital skewness S u and asymmetry A u, collected under non-breaking and breaking wave conditions. Consistent with earlier observations, we find that the Ursell number, which includes H s, T and h, describes the variability in S u and A u well and we use it to link H s, T and h to r and ϕ. The comparison of our findings to another large field data set suggests that wave non-linearity depends weakly on wave directional spread and that our parameterizations may underestimate S u for narrow-banded swell and (unidirectional) laboratory conditions. Furthermore, the use of the parameterizations is not advised on bed slopes steeper than in our data set (i.e., >1:30).
Highlights ► Near-bed velocity skewness and asymmetry depend on wave height, period and water depth ► We use 30.000+ field observations to parameterize velocity skewness and asymmetry. ► Parameterization can be extended to predict sand transport for mild wave conditions.
On the parameterization of the free-stream non-linear wave orbital motion in nearshore morphodynamic models
Ruessink, B.G. (author) / Ramaekers, G. (author) / van Rijn, L.C. (author)
Coastal Engineering ; 65 ; 56-63
2012-03-07
8 pages
Article (Journal)
Electronic Resource
English
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