Session: 09-02-03: Wave Energy - Design and Performance Analysis 2

Paper Number: 105016

105016 - An Efficient Three-Dimensional Cfd-Based Numerical Wave Tank for a Wave Energy Converter in Extreme Irregular Waves 

A numerical wave tank approach with coupling between fully nonlinear potential flow and computational fluid dynamics (CFD) solvers can reduce computation costs for wave load modeling. Recently this method has become attractive both for the research community and the industry working with offshore structures. In this paper, we present the modeling work of a fully nonlinear irregular wave condition propagating around a submerged differential wave energy converter (WEC) using the high fidelity CFD code, STAR-CCM+. Potential flow based numerical models are commonly used to predict motions and performance of wave energy converters. Wave kinematics can deviate from potential flow predictions for extreme wave conditions; the excitation loads on an absorber can also be increasingly influenced by viscous effects and wave breaking, not captured in engineering level models. In these extreme conditions, a Reynolds-averaged Navier-Stokes CFD model can better predict motions and loads for a WEC. Long time series with varying random seed numbers can be used to identify singular extreme wave events from a stochastic irregular sea state. This approach simulates a more realistic wave series for a given sea state than a regular wave or a focused wave. However, it is computationally infeasible to run these long time series for three-dimensional CFD simulations.  In this work, two-dimensional CFD simulations with a long domain allow the full development of an extreme nonlinear wave condition. The results are used to identify extreme events from a 50-year storm condition for the PacWave site off the coast of Oregon. A relatively short time window including this extreme event is then mapped to a three-dimensional simulation using a user defined wave methodology. User defined wave forcing zones with momentum source terms and boundary conditions are set to match the solution of the two-dimensional domain. This approach can model a fully nonlinear extreme wave in a much shorter domain, significantly reducing computation cost. Convergence studies for the different wave forcing lengths, mesh resolutions, and time steps were conducted using a monotonic regular wave. A code-to-code verification was also performed with a smaller operational wave condition using a potential flow based model.

Presenting Author: Will Wiley National Renewable Energy Laboratory

Presenting Author Biography: Will Wiley received a M.Sc. in Offshore Engineering from the Delft University of Technology and a M.Sc. of Wind Energy from the Norwegian University of Science and Technology in 2021. Before that he received a B.Sc. of Naval Architecture and Marine Engineering from Webb Institute in 2019. He is now a researcher at the National Renewable Energy Laboratory working on both high-fidelity and mid-fidelity hydrodynamic modeling for marine energy devices and floating offshore wind turbines.

Authors:

Will Wiley National Renewable Energy Laboratory
Thanh Toan Tran National Renewable Energy Laboratory
Thomas Boerner CalWave
Collin Weston CalWave
Lu Wang National Renewable Energy Laboratory