Dear @Baoxuan.Wang,
See my post dated Jan 28, 2011 in the following forum topic: NREL 5MW Rotor Geometry.
Best regards,
Dear @Jason.Jonkman
Thank you~
sincerely
Dear @Jason.Jonkman
In my understanding,
PitchAxis = Fraction of chord from leading edge to pitch axis;
and the local blade span outputs from ElastoDyn (SpniMLzb1, SpniFLxb1, SpniFLyb1, SpniFLzb1; i=1-17) lie along the pitch axis ;
that is to say: the local blade span outputs from ElastoDyn for structure analysis nodes (1-17) lie on the range from 0.253chord to 0.375chord, at the blade span from 1.809m to 59.691m, right?
But in your post dated Jan 28, 2011 in the following forum topic: NREL 5MW Rotor Geometry, I find the given values of PitchAxis are from 0.5chord to 0.375chord.
…
Dear @Baoxuan.Wang,
The local span outputs at the pitch axis for the NREL 5-MW baseline wind turbine blade lie between 0.5chord and 0.375chord.
In the ElastoDyn blade input file, there is only a single input PitchAxis, and AeroRef is not entered. Instead, AeroRef is defaulted to 0.25 internally within ElastoDyn, thus: AeroCent = 0.5 - PitchAxis. So the PitchAxis input to ElastoDyn should be interpreted a bit differently than the PitchAxis column explained in NREL 5MW Rotor Geometry.
But please note that the PitchAxis input to ElastoDyn is only used by the older AeroDyn v14, which will soon be depracated. When that happens, the PitchAxis input will be removed from ElastoDyn altogether as it will not longer be needed. When AeroDyn v15 is used, the aerodynamic center is specified relative to the pitch axis via AeroDyn v15 inputs BlCrvAC and BlSwpAC.
I hope that helps.
Best regards,
Dear @Jason.Jonkman
Thank you for your reply.
As for the local blade span outputs from ElastoDyn (SpniMLzb1, SpniFLxb1, SpniFLyb1, SpniFLzb1; i=1-17) lie along the pitch axis, I seem to find their span-position are located at the distributed blade aerodynamic Node as follows:
rather than
I am not sure.
Best regards,
Dear @Baoxuan.Wang,
NBlInpSt in ElastoDyn is the number of blade input stations for specifying the distributed mass and stiffness sectional data. Internally within ElastoDyn, these data are interpolated to the blade structural analysis nodes. When AeroDyn v14 is enabled, the blade structural analysis nodes in ElastoDyn and the blade aerodynamic analysis nodes in AeroDyn v14 are aligned and defined by the distributed blade aerodynamic data table in AeroDyn v14 (need not be evenly distributed). When AeroDyn v15 is enabled, the blade structural analysis nodes in ElastoDyn and the blade aerodynamic analysis nodes in AeroDyn v15 are independent, with the structural analysis nodes dictated by ElastoDyn input BldNodes (evenly distributed) and the aerodynamic analysis nodes dictated by AeroDyn v15 input NumBlNds and the distributed blade aerodynamic data table (need not be evenly distributed).
Best regards,
Dear @Jason.Jonkman
Thank you for your time and constant assistence, this is very helpful. 
By the way, about the structural damping, If I want to get the consistency between the FAST results and the three-dimensional finite element model results, should the modal damping be taken as 0?
Best regards,
Dear @Baoxuan.Wang,
Can you clarify what loads you are transferring from FAST/OpenFAST and how you are applying them to your 3D blade FEM model?
Best regards,