In the last years MARIN has been involved in an increasing number of projects for the offshore wind industry. New techniques in model testing and numerical simulations have been developed in this field. In this paper the development of a scaled-down wind turbine operating on a floating offshore platform, similar to the well-known 5MW NREL wind turbine is discussed. To simulate the response of a floating wind turbine correctly it is important that the environmental loads due to wind, waves and current are in line with full scale. For dynamic similarity on model scale, Froude scaling laws are used successfully in the Offshore industry for the underwater loads. To be consistent with the underwater loads, the winds loads have to be scaled according to Froude as well. Previous model tests described by Robertson et al [1] showed that a geometrically-scaled turbine generated a lower thrust and power coefficient with a Froude-scaled wind velocity due to the strong Reynolds scale effects on the flow. To improve future model testing, a new scaling method for the wind turbine blades was developed originally by University of Maine, and here improved and applied. In this methodology, the objective is to obtain power and thrust coefficients which are similar to the full-scale turbine in Froude-scaled wind. This is obtained by changing the geometry of the blades in order to provide thrust equality between model and full scale, and can therefore be considered as a “performance scaling”. This method was then used to design and construct a new MARIN Stock Wind Turbine (MSWT) based on the NREL 5MW wind turbine blade, including an active blade pitch control to simulate different blade pitch control systems. MARIN’s high-quality wind setup in combination with the new model scale stock wind turbine was used for testing the GustoMSC Tri-Floater semi-submersible as presented in Figure 1, including an ECN active blade pitch control algorithm. From the model tests it was concluded that the measured thrust versus wind velocity characteristics of the new MSWT were in line with the full scale prediction and with CFD (Computational Fluid Dynamics) results.

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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Floating mega islands can provide an attractive solution for creating temporal or more permanent space in coastal areas with a high demand for real estate. Also at open sea in the vicinity of wind farms, fish farms or logistical cross points, a floating mega island could be used as a hub, eliminating costly transfers. One of the aspects which needs to be understood is the wave induced motion of such a floating mega island. A piece-wise flexible island has been model tested at MARIN. The motion behavior in mild and severe sea states has been investigated. In this paper, the motion behavior is described and explained by comparing model test results with numerical simulations. An interesting aspect in this is the relative importance of wave diffraction, wave radiation and the dissipation of energy in the construction. The wave drift loads on the island that consists of 87 interconnected triangular pontoons are calculated and analyzed.

In this paper, the flow over a marine current turbine is studied. As a test case, the benchmark turbine published in [1, 2] is selected. A bibliography review shows a variety of numerical methods applied to this specific turbine, of which a viscous-flow RANS approach seems to be the best suitable for simulations over a broad range of inflow conditions. Therefore, MARIN’s RANS solver ReFRESCO is used to study the flow over this turbine. ReFRESCO results show a good agreement with the experiments, the calculated results and associated uncertainties overlapping the model-tests results. A numerical procedure is followed to estimate these calculation uncertainties, including an estimation for the numerical, domain and geometrical uncertainties. The flow-field analysis reveals significant viscous effects. Large separation zones at the suction side of the blade are seen in the model-scale results. At model scale, the turbulence level indicates that the turbine is operating in the transitional regime between laminar and turbulent flow, leading to early flow separation. Calculations at full scale show a large scale effect. The separation zones present at model scale are significantly smaller at full scale, resulting in a higher power production and axial loading. This is explained by the fully-turbulent boundary layer.