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High power and loads variations using the IEA 15MW wind turbine with monopile foundation
Hello,
I am trying to run a simple simulation with the IEA 15MW wind turbine on a monopile foundation. I have downloaded the model from QBlade site and have not made modifications. I have set the wind speed to 10.58 m/s (uniform) and have added a regular linear wave with Hs = 7m and Tp = 12 m. Then I run the simulation. I send here attached the results: the aggregated power output varies between 16 and 12 MW, which was the first thing that surprised me. Furthermore, hydrodynamic forces, mostly in the y direction, seem to increase and increase during the simulation. This was the most extreme case I tested: with Hs = 7m and Tp = 6s (which should be close to the wind turbine natural frequency) I obtained smaller power (between 14.6 and 15.2 MW) and loads variations and no diverging behavior.
What could be the cause of this behavior? I also attach here the project file in case it is useful, although as I was saying I have not modified the example project.
Thank you very much!
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Hi Arianna,
I had a look at the model of the 15MW monopile and found that the p-y- stiffness values, used in the substructure, were not correctly integrated along the pile length. This led to the soil stiffness being modeled approximately five times softer than it should be, resulting in quite large lateral monopile, tower and nacelle motions which even caused the pitch actuators to respond to this movement.
Regarding the buildup of drag in the y-direction: The value you are plotting represents the total drag in the y-direction for the entire submerged monopile. Due to the small oscillations in the crosswind or crosswave direction, the drag in the y-direction is 1-2 orders of magnitude smaller than the drag in the x-direction. The observed growth in the signal is likely caused by the building up of the oscillation of the entire wind turbine as it continues to approach its limit cycle, driven by the interaction between the controller, structural dynamics, and wave forces.
You will find a fixed version (v1.2) of the IEA 15MW Monopile model in the downloads section, for which I have updated the p-y force values.
BR,
David
