Discrepancy in ChInertiaCosseratAdvanced with CG Offsets

[Matt Tuman]

Hi Project Chrono Team,

I’ve been comparing mass properties of a Chrono IGA beam to a similar beam model in Nastran and noticed a small discrepancy. The beam elements include CG offsets, so I used ChInertiaCosseratAdvanced. The issue appears to stem from the inertia terms in the element mass matrix.

As shown in the screenshot below (lines 1110–1114), it looks like the inertia contributions due to the CG offset are not included:

Once I manually added the parallel axis theorem terms, the mass properties from Chrono matched those from Nastran. For instance, I updated the inertia about the x-axis as follows:

M(3, 3) = this->Jyy + this->Jzz + this->mu*(std::pow(this->cm_z, 2) + std::pow(this->cm_y, 2));

This is likely a niche case, but I wanted to bring it to your attention in case it's helpful.

Best,

Matt