Date of last article update: 15 March 2023
Seismic accelerations are applied in the global coordinate system. The X,Y origin for these accelerations is on the centreline of the turbine (effectively the same as the origin in the Tower screen). The Z-origin is determined as follows:
All Bladed versions up to and including 4.13:
- For tower type “Tubular Axisymmetric” the Z-origin is placed at the foundation station at the bottom of the monopile.
- For tower type “Multi-member” the Z-origin is at the ground level for an onshore turbine, or the Mean Water Level (MWL) for an offshore turbine.
Bladed 4.14 onwards:
- The Z-origin is at the ground level for an onshore turbine, or the seabed/mudline for an offshore turbine.
An important point to note is that you cannot change this point of application. Even if you set a non-zero value for the "Z-axis origin above MWL" in the Tower screen, the seismic origin will still be as specified above.
If only translational accelerations are involved, the position of the origin does not matter with regards to the point of application. However, if there are rotational components and it is required to apply seismic accelerations at any other point, then the full 6DoF set of accelerations will need to be transformed to reflect the shift in the rotation axes.