Towards an Approach to 6 DOF Inertial Kinematics

:The interest of computer-aided investigations of structure motions in maritime applications has become more relevant during the last years. The present work deals with the 6DOF (six degrees of freedom) motion-simulation of a free floating vessel in a seaway. A comparison between the calculation of forces and moments in the body-fixed system using the Kirchhoff-Motion-Equations and the calculation within the inertial coordinate system is shown. For this purpose, the relevant equations are defined in the inertial reference frame. Special attention applies to the matrices of mass and moment of inertia. Due to hydrodynamic effects in maritime applications and the transformation from a moving body-fixed reference frame, these matrices are time varying in the inertial reference frame. Finally, a comparison of the registered ship motions in the body-fixed and the inertial reference frame is presented.