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*PWNAC

Data format:

One line with six parameters

NO DIR IREF R C GAM

Status :

Optional

Purpose :

To define a in frequency domain the forces due to wind on the center of forces of a wind turbine

Restriction :

The node defining the center of force must have been previously defined

Details :

Parameter Description
NO node number
DIR direction of the rotor (perpendicular to the blade plane) in the general frame of reference or in a specific frame if IREF is not 0
IREF frame number ( defined thru BCREFGLO or BCREFLOC)
R blade radius
C constant derived from experimental results
GAM filter parameter

Based on Tarp-Johansen and Fransen model the equivalent force has three main components:

  1. A static component Ps=uU10/2,

  2. A dynamic excitation force Fd,

  3. A dynamic damping force: -uv.

With

  • U10 : the wind average velocity

  • u Damping coefficient: u =rho.CtU10A

  • v is the rotor velocity.

  • rho is the density of air

  • A is the blade area (based on blade radius R)

  • Ct is the thrust coefficient.

The Thrust coefficient can be approximated by c/U10 which simplifies the damping coefficient to rcA. An approximation for c is 5m/s.

Finally the dynamic excitation spectrum can be approximated by:

\[ S_p = \frac{v^2 S(\omega)}{(1 + \frac{\gamma R \omega}{U_{10}})^2} \]

The main assumption is that the force spectrum is a filter of the wind spectrum S(w).