Abstract
Survivability assessment is the complexity compromising Wave energy development. The present study develops a hybrid model aiming to reduce computational power while maintaining accuracy for survivability assessment of a Point-Absorber (PA) Wave Energy Converter (WEC) in extreme Wave Structure Interaction (WSI). This method couples the fast inviscid linear potential flow time-domain model WaveDyn (1.2, DNV-GL, Bristol, UK) with the fully nonlinear viscous Navier–Stokes Computational Fluid Dynamics (CFD) code OpenFOAM (4.2, OpenFOAM.org, London, UK). The coupling technique enables the simulation to change between codes, depending on an indicator relating to wave steepness identified as a function of the confidence in the linear model solution. During the CFD part of the simulation, the OpenFOAM solution is returned to WaveDyn via an additional load term, thus including viscous effects. Developments ensure a satisfactory initialisation of CFD simulation to be achieved from a ‘hot-start’ time, where the wave-field is developed and the device is in motion. The coupled model successfully overcomes identified inaccuracies in the WaveDyn code due to the inviscid assumption and the high computational cost of the OpenFOAM code. Experimental data of a PA response under extreme deterministic events (NewWave) are used to assess WaveDyn’s validity limit as a function of wave steepness, in order to validate CFD code and develop the coupling. The hybrid code demonstrates the applicability of WaveDyn validity limit and shows promising results for long irregular sea-state applications.
Highlights
Wave energy is a promising sector for sustainable low-carbon energy production
In 2016, survivability assessment has been identified as the main Wave Energy Converter (WEC) concern in the five years to come by the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI)
Numerical modelling can play a key role in the assessment of extreme responses that are necessary to the understanding of WEC capacity to survive extreme conditions
Summary
Wave energy is a promising sector for sustainable low-carbon energy production. Despite the efforts made in the last decade, uncertainties in wave energy performance and cost remain. In 2016, survivability assessment has been identified as the main Wave Energy Converter (WEC) concern in the five years to come by the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI). Numerical modelling can play a key role in the assessment of extreme responses that are necessary to the understanding of WEC capacity to survive extreme conditions. WECs are subjected to complex hydrodynamics phenomena, such as slamming waves or green water effect. Numerical models that are based on the weakly simplified Navier–Stokes equations, assumed of ’high-fidelity’ (Figure 1), are necessary to model such hydrodynamics and the interaction
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