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The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude–Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.

The effect of the mooring loads on floator motions can be significant for small water plane are floaters like CALM buoys. Not only does the mooring system contribute to the static restoring force components, but the dynamic behaviour of the mooring lines also affects the inertia and damping of the moored CALM buoy. The results from model tests with a moored CALM buoy were compared with the results from two series of time-domain computer simulations. First, fully dynamic coupled simulations were carried out, in which the interaction between the floater motions and the dynamic mooring line loads was modelled for all 6 modes of motion. Second, quasi-static simulations were carried out, in which only the (non-linear) static restoring force characteristics of the mooring system were taken into account. The comparison of results from the simulations and the model tests clearly indicates that the fully dynamic coupled simulations show a much better correspondence with the model test results than the quasi-static simulations. It is concluded that for the simulation of the behavior of a moored CALM buoy in waves a fully dynamic coupled mooring analysis is essential.

About 70% of the earth’s surface area is covered with water. Due to the sea level rise and increasing population in coastal areas we need to use our oceans more for energy production, food production, working and living. In the present paper we discuss the results of a model test for a floating mega island in large waves up to 15.5 m significant wave height. The objective of this study is to investigate the motion response and loads on the island. These results may then be used to support further innovation of these islands. The proposed island comprises 87 large floating triangles that are connected to one another. Together they form a flexible floating island of 1.5 by 2 km in cross-section at scale 1:250. The results are presented for the motion response of the island as well as the forces between the islands triangular modules and the mooring loads. These were measured using forces transducers and motion sensors. The present work is part of a conceptual test carried out at MARIN. The island modules are interconnected with springs and fenders. This method is much similar to what is used in side by side offshore operations in the oil and gas industry. Due to the flexibility in the connections the island will follow the waves in high seas. The forward two rows of the island will move in phase with the sea and therefore the amount of green water is much smaller than for a rigid island.

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