Session: 12-03-01 Deterministic Wave and Motion Prediction

Paper Number: 78988

78988 - Nonlinear Reconstruction and Prediction of Regular Waves 

In order run safer and more efficient offshore operations, short-term deterministic prediction of ocean waves, and induced loads on marine structures, is of crucial importance. While the usual approach relies on the linear potential flow theory to represent the ocean surface dynamics, the reliability of the linear assumption in case of severe sea state and long prediction horizon is affected by the presence of more complex nonlinear phenomena. One parameter that has been shown to be of particular importance is the appropriate modeling of the dispersion relation, modifying the waves’ propagation velocity.

It is proposed in this study to investigate the performance of the recently introduced grid-based method to reconstruct the properties of nonlinear regular waves. From a limited set of samples of true surface elevation, referred to as observations, the reconstruction method aims to retrieve the fields that describe the surface dynamics, namely the surface elevation and the corresponding velocity potential. In contrast to the usual reconstruction method that consists in the parameterization of a wave model, the originality of the grid-based method lies in the use of a predefined computational grid for the direct inversion of the wave equations. The latter are coupled to an observation operator mapping the quantities from the grid points to the locations of the observations. Nonlinear features are modeled through the use of the High-Order Spectral (HOS) method, and the obtained nonlinear fields are propagated in space and time according to the corresponding order of nonlinearity.

 

The algorithm is applied to fourth-order regular waves generated numerically by means of the HOS approach, and the observations are chosen in a way that they are randomly distributed in space and time. The influence of the order of nonlinearity of the reconstructed and predicted waves on their agreement with the true solution is investigate for different wave steepnesses. This way, the improvement of the solution pertaining to each order of nonlinearity can be characterized. The results show that the grid-based method is able to correctly reconstruct highly nonlinear regular waves, providing an accurate initial solution for the surface propagation and prediction.

Presenting Author: Nicolas Desmars Hamburg University of Technology

Authors:

Nicolas Desmars Hamburg University of Technology
Moritz Hartmann Hamburg University of Technology
Jasper Behrendt BHS Hamburg
Marco Klein Hamburg University of Technology
Norbert Hoffmann Hamburg University of Technology