This paper deals with dynamics of moving flexible bodies. The formulations proposed so far usually use Cartesian coordinates for the position of a body, Euler angles or Euler parameters for the orientations, and deformation modal coordinates for the elastic degrees of freedom. The equations of motion with these coordinates are complicated because of coupling terms between rigid-body motion and elastic vibration. In this paper, we propose a new formulation which uses rigid-body modes and a local observer frame to express large amplitude rigid-body motion and uses elastic modes to express small amplitude elastic vibration. The new formulation simplifies the coupling terms and gives the uniform description of equation in each modal coordinate, thus enables to accommodate the gross motion dynamics and the small amplitude elastodynamics effectively.
