Abstract: This paper presents a robust method to calculate numerically the hydraulic performance of different breakwater types. For this purpose, a characteristic friction diagram was obtained to evaluate the wave transformation inside the porous medium. The friction diagram is based on a linear coefficient that does not vary within the porous medium volume and it is stationary in the wave cycle. It was calibrated by minimizing the error in the hydraulic performance (reflection and transmission coefficients and wave phase) between experimental measurements and numerical calculations (IH-2VOF numerical model). Tests were done with irregular waves, normal wave incidence and non-overtoppable conditions. Results show that the friction coefficient depends on the breakwater type and geometry, mainly on the relative diameter of the granular material, Dk, where D is the diameter and k is the wave number. It is expected that this method reduces costs and saves time in the breakwater pre-design stage. The present study is innovative compared to other existing works because it addresses two relevant issues for breakwater design: (1) it not only provides the optimal values of the moduli of the reflection and transmission coefficients and wave energy dissipation rate, but also the phase values, given that the phase of the reflection coefficient is a key factor in defining the wave regime in front of, inside, and leeward to the breakwater; (2) it uses only one friction coefficient to calculate friction forces with a minimum error.

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