DOF-YAW in linearization

Wind & Water Computer-Aided Engineering Software Tools
1

Dear Jason,

1、I am trying to use the linearization module to obtain a WT model. I enable the FlapDOF1 and YawDOF in ElastoDyn, then I get eight states in my state-space model, the state ED 1st flapwise bending-mode DOF of blade 1 (internal DOF index = DOF_BF(1,1)) represents Blade 1 flapwise tip deflection, but I don’t know
what ED Nacelle yaw DOF (internal DOF index = DOF_Yaw) represents for. I set the initial yaw angle to 5 degree in the linearization, but in the .lin file, the value of DOF_Yaw is 5.819316811539E-006, it is not equal to 5 degree. So I wonder what the DOF_Yaw represents for.

2、In the linearization module, the standard input of yaw system is the yaw moment command, but if I want to use the yaw angle as the input in the linearization, what should I do? or if I can use some equations to transfer the yaw moment into the yaw angle in the linearization?

Best regards.

2

Dear Zhiheng.Liu,

Regarding (1), ED Nacelle yaw DOF (internal DOF index = DOF_Yaw) is the nacelle-yaw degree of freedom that you enabled in ElastoDyn (ED). The internal units for yaw angle are radians instead of degrees and 5 deg = 0.087 rad. Because the operating point yaw angle is different from your initial yaw angle, I would guess you are not linearizing at initialization but sometime later (likely after a steady-state solution has been reached); is that correct?

Regarding (2), as per (1), the yaw angle is a state, so the influence of the yaw angle on the state derivatives and outputs are already available in the A and C matrices of the linear state-space model.

Best regards,