# Connection between tower and nacelle

Hi,

Is it possible to model connection between tower and nacelle (base plate) connection shown in the figure attached herewith. I understand that its revolute joint with rotation about yaw axis. Suppose, wind turbine is locked in a particular position (i.e no yaw is allowed or required),I would like to model yaw bearing as spring-damper shown in the figure attached and conduct parametric study by varying both stiffness and damper. Is it possible to conduct such a study in FAST? If yes, please provide some hints. Thanks.

Regards,
Kumara

Dear Kumara,

The ElastoDyn module of FAST v8 assumes a revolute joint between the tower and nacelle. This joint can include a revolute spring-damper. I’m not sure i understand your figure, but are you proposing a translational joint with a spring damper? If so, this is not possible to model in FAST without modification of the source code, unless you can assume the tower is rigid, in which case you could use the platform degree(s) of freedom to model translation of the nacelle.

Best regards,

Dear Jason,

I’m assuming inner race of yaw-bearing is rigidly attached to the Nacelle and outer-race is rigidly attached to the tower nearly top (ref Fig 01). Strictly speaking, the inner race will have motion relative to the outer race (i.e in xy-plane) due to elasticity of the bearings. It might be very small. Do you agree till this point? The forces are transferred from nacelle to the tower through this bearing, right? I want to model the bearing elements as spring-damper (shown in fig 2) and study the force transmitted to the tower (tower top displacements) for a range of spring constant and damping coefficients. Is it possible to conduct this study using FASTV8 without changing source code?
Also, can you please suggest which variable in ElastoDyn specifies torsional stiffness and torsional damping? I could only see “YawDOF”, which i think only models the rotation between nacelle and tower as a kinematic joint. Kindly let me know if my question is still not clear.

Regards,
Kumara

Dear Kumara,

You cannot model the elasticity of the yaw bearings in FAST v8 without modification of the source code.

The rotational spring-damper of the yaw bearing is set in ServoDyn, not ElastoDyn. The variables are YawSpr and YawDamp in the ServoDyn input file. The neutral yaw position for the yaw spring is set via YawNeut.

Best regards,

Ok, Thanks Jason.