Numerical simulation of lowering operations from the coupling between the Composite-Rigid-Body Algorithm and the weak-scatterer approach

Abstract A consistent frame for the numerical simulation of lowering operations is investigated in this paper from a new wave-structure coupling. The mechanical modeling is based on the Composite-Rigid-Body Algorithm, which is able to simulate the nonlinear dynamics of multibody systems. The hydrodynamic model is based on the weak-scatterer approach, which allows the computation of unsteady hydrodynamic loads without being limited by the classical hypotheses of the linear potential flow theory. The coupling of these two models leads to the numerical simulation of articulated multibody systems with large relative motions in waves. The coupling equation is derived in this paper. This new numerical modeling is compared to the classical linear potential flow theory in the case of a lowering operation with a payload in the water. The impact of the lowering velocity is studied. Results show that this new model matches the classical approach for small lowering velocities but as soon as nonlinearities arise, differences between the two models appear.