Dear Jason,
1: I conducted a dynamic analysis of a 5MW fixed bottom wind turbine.I encountered an issue where I calculated free decay cases considering only an initial out-of-plane deflection (OoPDefl) of 1 m and an initial in-plane deflection (IPDefl) of 1 m. I observed that the baseline of the fluctuations in the out-of-plane blade-tip displacement deviates from zero, unlike the in-plane blade-tip displacement. Could you explain the potential causes of this phenomenon?
2: the wave elevation (ζ) is represented as H/2
cos(kx-(2pi/T)
t),The x-coordinate and y-coordinate of the output point are both 0,Therefore, the output elevation should be H/2cos(-(2*pi/T)*t),However, the output of OpenFast has a phase difference from this expression,I don’t if I should change something else or if I am ignoring something that I should have considered.
I would be appreciated it if you could reply. Thank you 
Best regards,
Dear @Yingxin.Lv,
I’m not sure I understand your question. What you do mean when you refer to the “baseline of the fluctuations”?
Best regards,
Dear @Jason.Jonkman,
Thank you for your response, and I apologize for any confusion in my earlier explanation.
In-plane (IP): Symmetric oscillations around zero .
Out-of-plane (OoP): Asymmetric oscillations ( +1.05 m to -0.16 m), yielding a non-zero mean displacement.
Could you advise on the potential causes of this asymmetry? Your expert insights would be greatly appreciated.
Best regards,
Dear @Yingxin.Lv,
You haven’t said if the rotor is spinning, if aerodynamic loads are enabled, or if gravity loads are applied, but I am guessing one or more of these is the source of the mean out-of-plane displacement.
Regarding the regular wave elevation, the SeaState module of OpenFAST will assign a random phase (when WaveMod = 1), unless you’ve directly specified the phase, e.g., (WaveMod = 1P0 for zero phase).
Best regards,
