Coordinate System Used for Joint Forces and Moments in Altair Inspire

Huyen

Hi all,

In Altair Inspire, when I define a joint, I don't need to create a local coordinate system for that joint. So does that mean the joint uses the global coordinate system?

Also, the output values Fx, Fy, Fz and Mx, My, Mz in Inspire — which coordinate system are these calculated in?

Best regards,

SouravDas0306

Hi Huyen,

when you define a joint you are not required to manually create a local coordinate system. However, this does not mean the joint uses the global coordinate system. Instead, Inspire automatically generates an internal joint reference frame based on the geometry you select while creating the joint. For example, if a revolute joint is defined using cylindrical faces, the software typically aligns one axis of the joint coordinate system with the cylinder axis and constructs the other two perpendicular axes automatically. Therefore, even though the user does not explicitly define a coordinate system, the joint still operates in its own auto-generated local coordinate system, which may or may not align with the global coordinate system depending on the orientation of the selected geometry.

Similarly, the output reaction components Fx, Fy, Fz and Mx, My, Mz reported in Inspire are calculated in the joint’s local coordinate system, not the global one. The force components Fx, Fy, Fz represent the reaction forces along the joint’s local X, Y, and Z axes, while Mx, My, Mz represent the reaction moments about those same axes. As a result, interpreting these values correctly requires understanding the orientation of the joint axes, since the physical meaning of each component depends on how the automatically generated joint frame is oriented in the model.

Regards,

Sourav