Domain Decomposition strategies for modelling survivability conditions of WECs

Abstract

The increasing TRL of WECs requires that their survivability both in Ultimate Limit States (ULS) and Accidental Limit States (ALS) should be assessed. However, the definition of these conditions is not easy because they depend largely on the deployment site and on the kind of WEC. In fact, because of the use of resonance conditions for the amplification of the waves, the largest response in terms of motions and/or loads is not always triggered by the largest waves [1]. Generally, nonlinear free-surface effects and important flow-separation phenomena take place. To guarantee accuracy and preserve computational efficiency, the use of multi-methods numerical simulations can become very useful. We have already experience with Time and Spatial Domain Decompositions (DD): a potential-flow and a full Navier-Stokes solvers were coupled to investigate violent wave-body interaction and occurrence of green-water events [2] and a Harmonic Polynomial Cell Method (HPC) and OpenFOAM were coupled to model the behavior of a damaged ship section [3]. We propose to apply these kind of DD strategies to WECs and to study the local non linear and viscous effect by a Navier-Stokes solver around the WEC and couple it with a method that can accurately and efficiently describe the flow field afar. For the latter, we propose also the use of a Depth-Semi-Averaged model [4] to accurately describe the WEC motion in the deployment site