Dear Yinping Yang,
In FAST, you could, of course, modify the blade mass distribution to not only match the overall mass, but also the center of mass, moment of inertia, etc. These will all influence the resulting dynamic response, but it is difficult to state this influence in general terms.
In the Modes, BModes, and FAST codes, the tower mass is defined as a distributed mass per unit length (varying along the length), which gets integrated along the tower in order to find the overall mass. None of these codes allow one to specify separate point masses. In FAST, 20 tower elements is typically suitable. You can specify more than 20 elements, but the code will become slower.
I cannot comment on how GH Bladed defines the aerodynamic offset nor can I comment on how it calculates the blade pitching moments. In FAST, the blade (bending and pitching) moments are calculated by integrating along the blade the ( applied aerodynamic pitching moments ) + ( radial vector ) x ( applied aerodynamic forces + gravitation forces - inertia forces ). All of these forces, moments, and distances are vectors and are oriented with the blade as the blade deflects. I know that GH Bladed ingores the influence of the blade deflection on at least the aerodynamic forces. Perhaps this is one reason why the pitching moments don’t agree between your models.
Neither can I comment on why GH Bladed predicts a “beat phenomenon” in YawBrFyp. I suggest you ask GH about this.
Best regards,