Abstract
The experimental wave paddle signal is unknown to the numerical modellers in many cases. This makes it quite challenging to numerically reproduce the time history of free surface elevation for irregular waves. In the present work, a numerical investigation is performed using a computational fluid dynamics (CFD) based model to validate and investigate a non-iterative free surface reconstruction technique for irregular waves. In the current approach, the free surface is reconstructed by spectrally composing the irregular wave train as a summation of the harmonic components coupled with the Dirichlet inlet boundary condition. The verification is performed by comparing the numerically reconstructed free surface elevation with theoretical input waves. The applicability of the present approach to generate irregular waves by reconstructing the free surface is investigated for different coastal and marine engineering problems. A numerical analysis is performed to validate the free surface reconstruction approach to generate breaking irregular waves over a submerged bar. The wave amplitudes, wave frequencies and wave phases are modelled with good accuracy in the time-domain during the higher-order energy transfers and complex processes like wave shoaling, wave breaking and wave decomposition. The present approach to generate irregular waves is also employed to model steep irregular waves in deep water. The free surface reconstruction method is able to simulate the irregular free surface profiles in deep water with low root mean square errors and high correlation coefficients. Furthermore, the irregular wave forces on a monopile are investigated in the time-domain. The amplitudes and phases of the force signal under irregular waves generated by using the current technique are modelled accurately in the time-domain. The proposed approach to numerically reproduce the free surface elevation in the time-domain provides promising and accurate results for all the benchmark cases.
Highlights
The real sea state is highly random and stochastic in nature
The numerical simulations are performed for the verification of the free surface reconstruction method for irregular waves
A two-dimensional numerical wave tank (NWT) with a flat bed is employed for carrying out the simulations
Summary
The real sea state is highly random and stochastic in nature. The most common external force responsible for generating the ocean surface waves is wind. The frequency range associated with wind is quite wide which causes a broad range of wavelengths, amplitudes, phases and periods in the ocean surface. This makes the study of the real sea state quite complex. The auto- and cross-correlation functions are determined from the measured wave records [1] These functions can be further used to perform the harmonic analysis of the time-series data. The numerical models require experimental wavemaker input for reproducing the irregular wave signals in the time-domain. The phase and amplitude information of each individual wave component is required in order to reproduce the experimental free surface elevation time-series in the numerical models. Some researchers have made notable efforts in the past to investigate the free surface elevation in the time-domain using the stream functions, the wavelet approach and Fast Fourier Transform (FFT) technique [6,7,8]
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