The Inertia Value Transformation in Maritime Applications

Due to recent developments in computer technology, computer-aided investigations of structural movements in a maritime environment have become more relevant during the last years. With regard to mechanically coupled multibody systems in fishery and offshore operations, the analysis of such systems is in the focus of research and development. To analyse multibody systems, forces and moments of all included bodies have to be defined within the same reference frame, which requires a transformation algorithm. Showing the correctness of the transformation algorithm, it must be also applicable for six degrees of freedom (6DOF) motions of a free floating single body in seaways. Therefore, the computation of irregular waves is discussed before the traditional motion description of a floating structure by using the Kirchhoff equations. With these basics, an approach to calculate the motion equations of single bodies within the earth-fixed reference frame is presented before the method of the inertia value transformation. To compare the body-fixed and earth-fixed calculation method, a free-floating crew transfer vessel in irregular waves is simulated and the results are discussed. Finally, the inertia value transformation will be proved by the energy conservation principle on the example of a pure rotating rigid body with none digital calculations.