With the hub diameter at 7.94m and the blade unchanged at 117.15m in length (arc length measurement that includes the prebend), the precise rotor diameter is 242.24m. This was due to a late design change to better accommodate the blade root chord/diameter size that did not fully propagate to all input files. There was an inconsistency in the stated hub diameter in the original report, YAML-definition, and WISDEM files (7.94m) versus the hub diameter in the OpenFAST and HAWC2 files (3.0m). That is a tough line to walk and ultimately a judgment call was made in setting the max OD for the monopile and tower to be 10m. We were trying to aim for technology level that is both reasonable and also 5+ years out. The IEA Wind 10-MW reference turbine uses a 9m diameter monopile. Is a 10m diameter too aggressive?Ĭurrent "XL monopiles" coming out of European factories are at about 8-8.5m in diameter. To use BeamDyn, set DT = 0.0005 and CompElast = 2 in the FST-file. The OpenFAST model files are configured to use ElastoDyn by default. However, we would not reduce it beyond 140m, otherwise it will approach some worst case extreme wave heights. This could have some positive effects for floating applications. We do not think there would be any major technical issues with reducing the hub height by 10m. With a rotor radius of 120m, the hub height of 150m was chosen to have a very conservative blade tip to wave clearance. The tower would likely need to be modified too as the maximum thrust and RNA mass change, but this would be more simple. If uprated, the drivetrain, generator, and bed plate would all have to be redesigned, as they were designed specifically for torque outputs of the current rotor.
We were trying to be a little forward looking with our choice of 240m and 15 MW, expecting specific power to decrease over time for offshore machines. We know the specific power is on the low side and the bigger blades lead to a heavy nacelle and require a larger substructure. Reference turbines are meant to be a starting point for improvement, redesign, and the addition of new technologies. We understand that having a single rotor design for both fixed-bottom and floating applications means it is likely suboptimal for both. We do not have plans to uprate the turbine at this time. As a conservative baseline, we expect the fatigue performance to be fair, but certainly not optimized, whether looking at the blades, tower, monopile, or other components. We also do not have plans or the resources to add that at this time. No detailed fatigue load analysis was performed in the report. Further details about Python installation requirements, when using the Python interface to OrcaFlex, can be found here. Note, as the example makes use of a Python script, Python 3 is required to view the example simulation (.sim) file. This can be achieved by downloading the demo version of OrcaFlex, available here. It is possible to view this model without having access to an OrcaFlex license. This is implemented through a Python external function which acts as a wrapper written in the "Bladed style".
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The included PDF document provides further details about the model itself, where the turbine controller is supported through a 64-bit version of NREL's ROSCO DLL. The Orcina team have created a model of the 15MW reference turbine, using OrcaFlex, which is publicly available at this link.
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