Abstract
In this paper, a new method for predicting wave overtopping discharges of Accropode armored breakwaters using the non-hydrostatic wave model Simulating WAves till SHore (SWASH) is presented. The apparent friction coefficient concept is proposed to allow the bottom shear stress term calculated in the momentum equation to reasonably represent the effect of comprehensive energy dissipation caused by the roughness and seepage during the wave overtopping process. A large number of wave overtopping cases are simulated with a calibrated SWASH model to determine the values of equivalent roughness coefficients so that the apparent friction coefficients can be estimated to achieve the conditions with good agreement between numerical overtopping discharges and those from the EurOtop neural network model. The relative crest freeboard and the wave steepness are found to be the two main factors affecting the equivalent roughness coefficient. A derived empirical formula for the estimation of an equivalent roughness coefficient is presented. The simulated overtopping discharges by the SWASH model using the values of the equivalent roughness coefficient estimated from the empirical formula are compared with the physical model test results. It is found that the mean error rate from the present model predictions is 0.24, which is slightly better than the mean error rate of 0.26 from the EurOtop neural network model.
Highlights
The Accropode blocks are the most commonly used armor blocks on the sloping breakwaters in practical projects because of their low engineering cost, good wave dissipation performance and strong wave resistance stability [1]
The analyses described in the previous sections show that the equivalent roughness coefficient of the Accropode armor needs to be calibrated by numerical simulation based on the q of the physical model, which is generally not convenient for practical applications
A new method with the determination of the defined apparent friction coefficient for bottom shear stress calculation is developed in combination with the numerical simulations of the non-hydrostatic Simulating WAves till SHore (SWASH) wave model for wave overtopping on breakwaters with an armor layer of Accropode
Summary
The Accropode blocks are the most commonly used armor blocks on the sloping breakwaters in practical projects because of their low engineering cost, good wave dissipation performance and strong wave resistance stability [1]. To design an Accropode armored breakwater, the overtopping discharge needs to be estimated reasonably well because it is an important index to determine the top elevation of the breakwater [2,3]. There are many ways to estimate the overtopping discharge, such as the traditional physical model tests [4] and empirical formulas [5,6,7]. Water 2020, 12, 386 simulation has become one of the most effective methods to estimate the wave overtopping rate due to the rapid development of computer technology and computational methods. Numerical models, including the nonlinear shallow-water equation and Boussinesq equation-based models, have limitations in describing the phenomena of wave overtopping because the dynamic pressure process was not considered [8,9,10,11].
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