Numerical frameworks for simulations of wave energy converter systems: power performance and mooring fatigue analysis in wave energy parks

Doktorsavhandling, 2025

Wave energy has attracted public attention as an important renewable energy source for many years. Wave energy has many advantages over wind and solar energy, such as around-the-clock availability and high power density. However, further development is needed for wave energy converter (WEC) technology to reach full commercial readiness; in particular, there is an urgent need for a systematic numerical analysis of certain WEC concepts and wave farms to guide their development and design and unleash their enormous potential.

This thesis focuses on the simulation of three point-absorber WEC concepts with different working principles and the wave parks they compose. The primary aim was to develop accurate numerical models and generalised numerical frameworks for the respective WECs and wave parks and analyse their power performance and mooring fatigue damage, two key factors that need to be assessed before wave parks can be commercialised on a large scale.

This thesis contributes to WEC numerical modelling by proposing two numerical frameworks, the DNV SESAM framework and the FMI-based (Functional Mock-up Interface-based) co-simulation framework. The numerical framework refers to the computational structure for modelling WEC systems, in which several numerical methods are integrated to simulate coupled subsystems. The DNV SESAM framework can model WEC systems with some inevitable simplifications in the subsystem models in an integrated software environment. The FMI-based co-simulation framework facilitates convenient coupling between separated solvers and tools without programming and shows great potential for fast inter-team model integration in real industrial applications.

The subsystems of WECs, such as mechanical joint connections and power take-off (PTO) systems, were modelled in detail, thanks to the flexible coupling feature of the proposed FMI-based co-simulation framework. It was found that the fidelity of the subsystem models directly impacts the accuracy of the power performance and mooring fatigue damage predictions, particularly under environmental conditions (ECs) where simplified models cannot capture the nonlinearity introduced by the subsystem. This highlights the necessity of modelling the exact working principles of all subsystems to ensure accurate numerical results.

Various wave parks were modelled and simulated under different ECs. Their power performance and mooring fatigue damage were compared and analysed in detail. The results demonstrate the scope and capabilities of the proposed numerical frameworks, providing valuable insights for modelling and simulating wave parks with different WEC prototypes.