question about applying loads to rigid bodies

[Harada]

Hello,

I apologize as this is probably stated in one of the manuals, but I'm having trouble finding it.
I want to apply loads to rigid bodies.
I found two ways.
Loads > Body Load
Constrains > Prescribed rigid force
Is there a difference in those?

Best regards,
Takumi Harada

[maas]

Hi Takumi,

The "prescribed rigid force" applies a force to the center of mass of the rigid body or a torque about the COM. The body load applies a force per unit volume to every point in the body. The main difference is that a body load can be applied to both rigid bodies and deformable bodies. The "prescribed rigid force" is only for rigid bodies.
For rigid bodies, in principle, it's always possible (I think) for a given body load to calculate the equivalent net force and moment. So, with that in mind, you could use either one for rigid bodies.
However, one thing to keep in mind is that in FEBio you often don't need specific geometry to describe the rigid body. In the absence of such geometry you can only use prescribed rigid forces. If you want to use a body load, you have to make sure that the rigid body has a volume mesh associated with it.

Cheers,

Steve