Development and adaptation of the Composite Rigid Body Algorithm and the Weak-Scatterer approach in view of the modeling of marine operations

The simulation of marine operations, in particular of lifting or lowering operations, requires the modeling of the whole system (ship, cable and payload) along with a theory of multibody dynamics, an appropriate hydrodynamic theory and cable’s modeling. This paper presents a new approach to achieve this type of simulation based on a coupling between a multibody theory and a hydrodynamic one. The multibody theory uses a robotics formalism and a direct dynamic algorithm based on recursive techniques for kinematic trees to solve the Newton-Euler equations. The cable modeling is based on the same multibody approach. There is neither bending nor torsion effect. This model is compared to the classical lumped mass theory. Hydrodynamic loads are computed using a weakly nonlinear potential flow solver based on the weak-scatterer hypothesis. This approximation assumes the perturbation component of the fluid velocity potential is small compared to the incident one and the free surface boundary conditions are linearized with respect to the incident wave elevation. This solver is coupled with the mechanical one in order to perform the simulation. This new strategy to manage the coupling is presented in this paper.