This is a connector for 1-dim. rotational mechanical systems and models which represents a mechanical flange of a shaft. The following variables are defined in this connector:
phi: Absolute rotation angle of the shaft flange in [rad]. tau: Cut-torque in the shaft flange in [Nm].
There is a second connector for flanges: Flange_a. The connectors Flange_a and Flange_b are completely identical. There is only a difference in the icons, in order to easier identify a flange variable in a diagram. For a discussion on the actual direction of the cut-torque tau and of the rotation angle, see section Sign Conventions in the user's guide of Rotational.
If needed, the absolute angular velocity w and the absolute angular acceleration a of the flange can be determined by differentiation of the flange angle phi:
w = der(phi); a = der(w);