Abstract
Extreme waves are critical for the WEC’s development. CFD toolboxes have been widely used in the simulation of extreme waves–structure interaction. However, the quality of the mesh is a sensitive issue; the WEC’s large response can lead to mesh deformation and subsequent numerical instability. In this paper, 100-year extreme waves are chosen from the environmental contour of the Humboldt Bay site in California, and their interaction with the WEC is modeled using the open-source CFD software OpenFOAM. The overset mesh technique is an advanced method recently available in OpenFOAM, able to handle great body motions. Here, the overset method is utilized and compared with the commonly used morphing method. The two methods provide equivalent results, but the latter is prone to the mesh deformation and fails to complete the simulations. Regarding the impact of extreme waves on WECs, the results further show that the combination of wave height and steepness is critical; i.e., the 100-year wave height does not necessarily result in the maximum forces, but rather steeper sea states tend to contribute in higher wave loadings. Additionally, the WEC is studied for 40% higher generator’s damping, as it is a common control strategy during the harsh environmental conditions.
Highlights
Wave energy is considered part of the future energy mix (World Bank, 2017; European Commission, 2020), but only a few wave energy converters (WECs) concepts have been operated in a sea environment
The morphing mesh method fails to provide the solution for all of the examined sea states, yet the overset mesh leads to the successful completion showing that the method is able to handle large amplitude, multi-degree of freedom (DoF) WEC motion
The WEC has been displaced in the surge direction further from its initial position having great pitch response, and this is a combination leading the cells in the morphing zone area to stretch significantly degrading the mesh quality (Fig. 9, sea states 1 and 3)
Summary
Wave energy is considered part of the future energy mix (World Bank, 2017; European Commission, 2020), but only a few WEC concepts have been operated in a sea environment. According to the Joint Research Centre Ocean Energy Database (Magagna et al, 2016), the technology readiness level for wave energy converters (WECs) ranges between 5 to 8, which means that their commercial viability is yet to be proven. A big challenge is to guarantee the survivability in the offshore extreme conditions, since the extreme loads is a key cost driver for the wave energy technology (Jenne et al, 2015; Neary et al, 2014). The standards need to be tailored for the wave energy sector since there are large uncertainties related to the prediction of wave loads on WECs. The devices are small and often with dynamical behavior, designed to be in resonance with the waves, the established knowledge from the traditional offshore industry cannot be readily translated on the WECs. Currently, there are a few technical specifications
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