Concept and design validation of floating wave energy converter arrays

The drastic change of our energy systems from fossil resources to renewable resources is one of the largest challenges of current times. To cope with the increasing electricity demands, mainly stemming from the electrification of heating and transport, further renewable energy resources, in addition to the well-established wind, solar, and hydropower energy resources, need to be investigated. Wave energy conversion could be one of these alternative resources, since it has a large potential. This potential is yet untapped, since no wave energy converter has reached commercial feasibility yet. The present thesis focuses on the early design process (concept validation and design validation) of floating wave energy converter arrays. In this stage, the system fundamentals (layout, geometry, etc.) are not yet fixed, and various optimizations are necessary to increase the technological readiness as well as its performance. These optimizations are usually conducted using time- and cost-efficient numerical modeling, particularly mid-fidelity modeling relying on potential flow assumptions. However, the validity of these simulations needs to be evaluated to reach trustworthy decisions. Data from experimental model testing can be used to increase the trust in the numerical models through validation. However, experimental modeling is time- and cost-consuming. This interdependence between mid-fidelity numerical models and experimental model testing is investigated. Particularly, the importance of mechanical coupling, hydrodynamic coupling, mooring influence, and viscous effects is investigated, as well as their incorporation in mid-fidelity models. Three journal publications build the scientific base of this thesis. The first two publications focus on the experimental and numerical modeling of a floating wave energy converter array, respectively, and lead to insights on the effects of hydrodynamic coupling, mechanical coupling, and mooring influence. The third publication focuses on viscous effects. While the employed mid-fidelity model can reproduce the mechanical coupling effects accurately, hydrodynamic coupling is neglected in the presented approach. However, the mechanical coupling has a more significant impact on the motion response of the floating wave energy converter array compared to the hydrodynamic coupling, which is deemed negligible. The mooring effects cannot be captured accurately as well. These results are used to give recommendations to wave energy converter array designers with regard to the application of numerical models and the usage of experimental model tests for the validation of the hydrodynamics of an individual point absorber, as well as the mooring design. Finally, future research directions are given, which complement open points from the scientific contributions, e.g., the incorporation of hydrodynamic interactions in floating wave energy converter array simulations with mid-fidelity models. Additionally, the importance of advanced control methods and their potential to increase the energy output of floating wave energy converter arrays is emphasized.