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In underwater robotics, we model the inertia of the surrounding fluid using an added mass matrix. The added mass matrix has different masses in different directions, and also contains nonzero off-diagonals:

M_A =
[
m11 m12 m13 m14 m15 m16
m21 m22 m23 m24 m25 m26
m31 m32 m33 m34 m35 m36
m41 m42 m43 m44 m45 m46
m51 m52 m53 m54 m55 m56
m61 m62 m63 m64 m65 m66
]

Unfortunately, DRAKE's SpatialInertia only supports a scalar-valued mass, and calculates the mass matrix based on the gyration matrix, the scalar mass, and the center of mass.

What is the best practice to integrate the added mass matrix into a MultiBodyPlant?

In Can a SpatialInertia object be constructed from a 6x6 matrix? I read about the ArticulatedBodyInertia class. However, I can't find any documentation on how to use the ArticulatedBodyInertia as a replacement for the SpatialInertia.

Thank you in advance for your help!

Tom Slawik
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  • FYI -- we have an issue tracking this request here: https://github.com/RobotLocomotion/drake/issues/19440 . I'll see if others respond with shorter term work-arounds. – Russ Tedrake Jul 07 '23 at 15:45

1 Answers1

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I believe this is duplicate of Can SpatialInertia be bypassed when simulating a MultiBodyPlant in Drake?, where I provided some guidance on how to do this. Particulars might be different depending on your application.

Hopefully you find the answer there useful.

Alejandro
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