Load calculations

Every wind turbine design process starts with calculating the design driving mechanical loads. Wind/environmental conditions and load cases are usually defined by design standards such as Germanischer Lloyd’s “Guideline for the Certification of Wind Turbines” or IEC 61400-1 Ed. 3. The turbine design and control concept is stated by the manufacturer.

The simulation model consists of 4 important components:
  •  Wind model (turbulence, gusts, direction changes etc.)
  •  Aerodynamic rotor model (usually based on the 2D Blade-Element-Momentum theory using cL, cD and cM aerofoil coefficients with 3D corrections)
  •  Dynamic structural model (usually based on a modal approach, built of a very low number of DOF, typically 28)
  •  Functional turbine model (pitch and torque controller and supervisory control)

Well-known software codes for these applications are Bladed (from Garrad Hassan), Flex5 or others. wind-direct is using Bladed, which has been thoroughly validated against measurements.

The calculations can be divided into extreme and fatigue loads: typically, thousands of short extreme load cases are run, compared to a relatively low number (less than 100) of 10 minutes fatigue runs. The results have to be “post-processed” creating certain statistics and load spectra for being useful for the structural design of the wind turbine.

load calculations