Turbine data: Hub

Radius

The radius of the hub. It specifies the offset of the blade root, from the turbine's origin, along the pre-coned blade direction.

Mass and moments of inertia

The mass and the mass moments of inertia of the hub about the centre of mass. The axial moment of inertia is about the main shaft. The transverse moment of inertia is about any axis through the centre of mass and perpendicular to the main shaft.

Centre of mass

The offset of the centre of mass, relative to the turbine frame, along the main rotor shaft. This value is positive in the turbine $z$-axis direction.

Main shaft stiffness and damping

The linear rotational stiffness and damping of the main shaft. If the stiffness is infinity, a rigid connection is made between the hub and the gearbox's main shaft output. In this case, the damping value is unused. If the stiffness is finite, a degree of freedom is introduced and the hub can rotate, about the main shaft axis, relative to the gearbox's main shaft output.

Initial rotor state

The turbine's initial rotor angle and angular velocity, in the direction of the rotation sense, used in statics. The initial rotor angle is defined as the angle between the blade 1 root $z$-axis, projected onto the turbine $xy$-plane, and the turbine $x$-axis. The initial rotor angular velocity is the speed of the main shaft. If non-zero, then in statics the turbine is no longer in a true static equilibrium. Instead, the blade degrees of freedom and the aerodynamic load are evaluated in the non-inertial hub frame, rotating with the initial rotor angular velocity. In this way, the equilibrium can be thought of as being quasi-dynamic, fully capturing the steady-state aerodynamic and inertial loading associated with the rotation. This allows for the full system to find an equilibrium in statics that accounts for the rotating turbine loads, which leads to a smooth transition between statics and dynamics.