What is the difference between Bladed 4.0 and earlier versions?
The main difference between Non-Multibody (v3.85 or earlier) and 4.0 is the structural dynamics model. The structural dynamics ‘core’ has been completely re-written using a multibody formulation. Non-Multibody made use of many approximations which were becoming gradually less accurate as turbines get larger and more flexible; the Multibody version uses a completely self-consistent and rigorous formulation of the structural dynamics, which gives more consistent and accurate results, and also makes it easy to add new degrees of freedom in future. Some of the major changes are
- Use of individual blade modes rather than rotor modes: the modes are fully three-dimensional, including coupling between flapwise and edgewise vibrations, and are valid for any pitch angle; the rotor is no longer assumed to be completely symmetrical; calculations in which the blades have different pitch angles are handled accurately, as well as situations when there is ice build-up on some blades but not all; and a full torsional degree of freedom is available.
- Use of Craig-Bampton style modes for the tower: this allows the changing coupling between rotor and tower to be handled correctly, for example as the rotor azimuth and yaw angle change.
- Blade geometry and structure can be defined more rigorously, and can now take into account such effects as any offset of the centre of mass from the chord line, offset of the shear centre from the neutral axis, differences between structural twist and aerodynamic twist, etc.
- In 3.x Bladed, the mass imbalance of the rotor only influences the first mass moment of the rotor. In Bladed 4.x the mass imbalance is added as an additional mass to the hub which influences; the first moment, moment of inertia and the total mass of the structure. Any imbalance mass added in 4.x versions should be removed from the hub mass to make sure the mass totals of the hub match with the actual turbine hub mass.