ECEF 6DOF block - Abb output

In the ECEF 6DOF (Quaternion) block from Aerospace Blockset, there is an output labeled as "Abb - Accelerations in body-fixed axes" that is distinct from the inertial acceleration (Ab ff). The calculation for Abb appears to use the parameters of the ECEF frame to calculate the Coriolis and centrifugal terms, but I am unsure what the physical meaning of this quantity is.

I understand that if I wished to determine the acceleration of a point not at the body CG in the body-fixed frame, I would need to account for fictitious force terms (Coriolis, centrifugal, Euler) due to the moment arm between the CG and the point; however, this quantity appears to be something else. Any clarification would be appreciated.

Answer 1

[Sreeram]

Hi Thomas,

refers to the inertial acceleration of the body with respect to the ECEF frame expressed in body frame. Inertial acceleration with respect to the ECEF frame does not account for Coriolis and centrifugal accelerations, and is calculated as . For reference, on the other hand refers to the acceleration of the body with respect to the ECEF coordinate system expressed in the body frame. The relationship between the two is

So, it does not account for the Euler force.

Please refer to the supporting equations in the documentation:

https://www.mathworks.com/help/releases/R2024a/aeroblks/6dofecefquaternion.html#mw_c0f72e39-9122-477c-95ce-479884fa5839

Please note that is denoted as in the equation given in the page. However, it is clarified in the Version History section that the port name subscripts of ecef have changed to ff from MATLAB R2023b:

https://www.mathworks.com/help/releases/R2024a/aeroblks/6dofecefquaternion.html?#mw_4d5d8022-07aa-4233-990c-c179d0fb3bec

Thanks