## Flexible Bodies

Each flexible body has three translational, four rotational, and s elastic coordinates. The number s represents the number of shape functions (modes) which are used for the description of the flexibility of the body.

The body coordinate system is attached to the body by a dynamical concept, the so-called Buckens frame, i.e., the frame follows the body such that the origin of the body coordinate system is always located at the center of mass of the body. At the beginning of the simulation the body has to be in its undeformed state. Thus, the initial values of the elastic coordinates are zero. As it is the case for a rigid body, the location of the center of mass of the undeformed body represents the initial translational degrees of freedom, while the rotation matrix defines the initial values of the rotational parameter.