Dear community,
I am investigating the response of IEA22MW floating wind turbine to different coherence models. Here, the field is generated using Davenport’s empirical model. One of the outputs I am interested in is the Nacelle responses, forces and moments. However, since the nacelle itself does not have displacement response nor channels of forces and moments, i chose to use the tower top outputs as suggested in Nacelle Motions
When i plotted the forces of tower top / yaw bearing (YawBrFyn), i saw that during 4000 seconds in the simulation, the forces in the yn are almost always negative.
As I understand the nacelle coordinate system, it has origin on the center of tower top and components as follows:
+xn: in the downwind direction
+yn: to the left when looking in the positive x- direction
+zn : vertical, opposite for gravitation for an undeflected wind turbine
Thus from the results, since YawBrFxn is always positive, the turbine is always pushed backward toward downwind direction (which is reasonable). But looking at the output of YawBrFyn, it seems like the turbine is always pushed to its left, thus in the -yn direction (which puzzles me.). The turbine rotor plane is perpendicular to inflow wind (undeflected yaw). And although we have coherence, the spatial correlation between points is equal in both direction (horizontally), thus I would expect to see the turbine oscillating between negative and positive yn. The displacement also confirms that the tower top is pushed to -yn direction all the time. My question is as follows: isn’t it odd to have such a result for such a long simulation ? why would the forces be only negatively directed all the time ?
