Abstract
Scour may act as a threat to coastal structures stability and reduce their functionality. Thus, protection against scour can guarantee these structures’ intended performance, which can be achieved by the accurate prediction of the maximum scour depth. Since the hydrodynamics of scour is very complex, existing formulas cannot produce good predictions. Therefore, in this paper, Genetic Programming (GP) and Artificial Neural Networks (ANNs) have been used to predict the maximum scour depth at breakwaters due to non-breaking waves (Smax/Hnb). The models have been built using the relative water depth at the toe (htoe/Lnb), the Shields parameter (θ), the non-breaking wave steepness (Hnb/Lnb), and the reflection coefficient (Cr), where in the case of irregular waves, Hnb=Hrms, Tnb=Tpeak and Lnb is the wavelength associated with the peak period (Lnb=Lp). 95 experimental datasets gathered from published literature on small-scale experiments have been used to develop the GP and ANNs models. The results indicate that the developed models perform significantly better than the empirical formulas derived from the mentioned experiments. The GP model is to be preferred, because it performed marginally better than the ANNs model and also produced an accurate and physically-sound equation for the prediction of the maximum scour depth. Furthermore, the average percentage change (APC) of input parameters in the GP and ANNs models shows that the maximum scour depth dependence on the reflection coefficient is larger than that of other input parameters.
Highlights
Coastal structures such as breakwaters are constructed to protect harbors and vessels from wave attacks
Since the present paper focuses on predicting of the maximum scour depth at breakwaters due to non-breaking waves, only the non-breaking wave-induced scour depth at the trunk section of coastal structures has been discussed here
The performance of the Genetic Programming (GP) and Artificial Neural Networks (ANNs) models in the prediction of Smax/Hnb for all the datasets of interest has been evaluated in terms of statistical parameters like the Correlation Coefficient (CC), the Root Mean Square Error (RMSE), the Scatter Index (SI) and the BIAS, as given in Eqs. (11)–(14)
Summary
Coastal structures such as breakwaters are constructed to protect harbors and vessels from wave attacks. Using small-scale experiments, Oumeraci [23] studied the effect of breakwater slope on Smax and suggested that the maximum scour depth in front of a vertical breakwater is larger than that at sloped breakwaters. He indicated that the key mechanism for scour due to non-breaking waves is the action of standing waves (fully or partially), which leads to a steady streaming pattern. The modeling approach and the data at the basis of the analyses are reported in Section 3; the results and discussions are given in Section 4; the sensitivity analysis is given in Section 5 and Section 6 contains this study summary and the conclusion
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