## ActuatorDiskFromPower:

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Compute actuator disk area and power coefficient.
Uses actuator disk theory.
This provides a limit on how much power a wind turbine can produce.
"a" is defined from the relationship v3 = v0*(1 - 2*a) where v0 is the
wind speed in front of the machine and v3 is the wind speed at the end
of the wake. Note that v3 = 0 is NOT the optimum value. The optimum
value is with a = 1/3 so cP = 16/27. This can never be achieved in
practice due to aerodynamic losses.

Type ActuatorDiskFromPower for a demo.

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Form:
[A, cP] = ActuatorDiskFromPower( rho, p, eff, v0, a )
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Inputs
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rho  		        (1,1)  Atmospheric density (kg/m^3)
p                   (1,:)  Power (W)
eff                 (1,1)  Efficiency
v0                  (1,:)  Wind velocity (m/s)
a                   (1,1)  See above

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Outputs
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```Common: Graphics/Plot2D