Session: 06-16-02 Wave Mechanics, Modeling and Wave Effects II

Paper Number: 79462

79462 - A Semianalytical Framework for the Prediction of Weakly Nonlinear Broadband Surface Waves With Large Directional Spreading 

Surface waves are ubiquitous in the open ocean and coastal water regions. Their effects on the reliability and safety of offshore structures have been widely recognized. In order to quantify and estimate these effects and thereby, lower the risk of structure failures, a good design and model is needed, which considerably relies on the accurate and fast predictions of
realistic wave-induced sea states. This work deals with weakly nonlinear broadband waves with large directional spreading which are essential to the loading on offshore structures. Specifically, a semianalytical framework is proposed, based on potential flow theory and a perturbation expansion (Li & Li, 2021). The framework proposes to solve for the second-order superharmonic and subharmonic bound waves separately by the decomposition of wave harmonics, a pseudospectral method for the nonlinear terms evaluated on a still water surface, and a time integration method. The framework is validated through comparisons with the results based on Dalzell (1999). The numerical implementation of the framework and Dalzell (1999) require the computational operations at O(N log(N)) and O(N^2), respectively, with N the number of linear wave components chosen for computations. In contrast to the high order spectral method (HOS) (see, e.g., Dommermuth & Yue, 1987; West, et al., 1987), the framework expresses the superharmonic contents in an envelope form, which allows for a much coarse grid and larger time step for achieving the same accuracy as the HOS and hence, a much improved computational efficiency. The framework would embrace a great potential in the predictions of wave-induced quadratic forces on offshore structures.

Presenting Author: Yan Li Norwegian University of Science and Technology

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