How to access internal modal degrees of freedom for a reduced order felxible solid in simscape multibody ?

For my current project, I need to be able to have access during the simulation to the internal values of the modal coordinate of the eigen modes of my reduced order flexible solid during the simulation :

I have my matrix with being the stiffness at the interface frames (size of 6n with n the number of interface nodes and the diagonal part of the being the square of the angular eigenfrequencies of the internal modal degrees of freedom.

In the same manner I have a matrix wit the reduced mass of the interface frames and the I matrix being the identity matrix since the eigenmodes are mass-normalized.

I can easily access the translations and rotations of the interface frames as those frames are defined within the simscape multibody environment, however I would like to know if there is a way to access the value of the internal degrees of freedom of my flexible body during the simulation.

I have thought about adding more interface frames to my Craig-Bampton reduction in order to increase the number of output frames in simscape multibody. But it seems that by doing so I have artificially stiffened my finite element model and also added a lot of non-zero extradiagonal terms into my matrices and which seems to defeat the very purpose of reduced-order modelling and is very inefficient in terms of computational time.

My question would be then to know if there is a way to access those values from the "reduced order flexible body" block in Simscape Multibody or if I should instead rely on another method to model flexible bodies such as described in this paper this technical paper.

Thanks in advance for your time

Philippe

Answer 1

[Yannick]

Hi Philippe,

Unfortunately, as you note, the Reduced Order Flexible Solid block does not currently provide any direct outputs such as interface frame translations and rotations or modal degrees of freedom. Some indirect measurements are available, as you noted as well, but not for the internal DOFs.

I have recorded your request in our database so we can consider adding this capability in a future release.

Thank you very much for providing details on your use case and requirements.

Best regards,

Yannick