Flange flange_b is forced to move relative to the support connector with a predefined motion according to the input signals:
u[1]: position of flange u[2]: velocity of flange u[3]: acceleration of flange
The user has to guarantee that the input signals are consistent to each other, i.e., that u[2] is the derivative of u[1] and that u[3] is the derivative of u. There are, however, also applications where by purpose these conditions do not hold. For example, if only the position dependent terms of a mechanical system shall be calculated, one may provide position = position(t) and set the velocity and the acceleration to zero.
The input signals can be provided from one of the signal generator blocks of the block library Modelica.Blocks.Sources.