Numerical study of wave transformation using the free surface reconstruction method

Abstract

The study of irregular wave field is complex due to its random hydrodynamic characteristics. Many experimental studies have been performed in the past to study irregular waves. However, numerical investigations are less time consuming and expensive as compared to the experimental studies. For a good validation of the numerical model, it is essential to reproduce the laboratory waves numerically. The reconstruction of the numerical irregular free surface elevation is necessary because the paddle signal for the wave-maker in experiments is unknown in most of the cases. It is quite challenging to reconstruct the time history of free surface elevation of irregular waves because of the random wave phases and wave periods. In the present work, a numerical investigation is performed using the open-source computational fluid dynamics (CFD) model REEF3D to test and validate the reconstruction of free surface profiles for irregular wave propagation. Two-dimensional irregular waves are generated by super-positioning of the regular wave components. In the current reconstruction approach, the free surface is reconstructed by representing the irregular free surface elevation as a summation of its Fourier components. First, the free surface reconstruction method is tested for irregular waves in a two-dimensional wave tank with constant water depth. The reconstructed free surface elevations shows a good match with the theoretical wave profiles. Further, the method is used to reconstruct the wave transformation over an impermeable fully submerged bar where the complex phenomena such as shoaling and wave breaking occur. The reconstructed numerical free surface elevations along the wave tank are compared with the experimental free surface elevations. The complex phenomena such as shoaling and breaking are represented with reasonable accuracy in the numerical model.