Strongly coupled partitioned six degree-of-freedom rigid body motion solver with Aitken's dynamic under-relaxation

• Default coupled motion solver in OpenFOAM® improved with Adams-Bashforth-Moulten implicit motion solver.
• Extension of coupled motion solver with Aitken's dynamic under-relaxation to curb artificial added-mass instabilities.
• Improvements in convergence behaviour.
• Up to 80% reduction of simulation times achieved with dynamic under-relaxation for cases requiring more under-relaxations.

An implicit method of solving the six degree-of-freedom rigid body motion equations based on the second order Adams-Bashforth-Moulten method was utilised as an improvement over the leapfrog scheme by making modifications to the rigid body motion solver libraries directly. The implementation will depend on predictor-corrector steps still residing within the hybrid Pressure Implicit with Splitting of Operators - Semi-Implicit Method for Pressure Linked Equations (PIMPLE) outer corrector loops to ensure strong coupling between fluid and motion. Aitken's under-relaxation is also introduced in this study to optimise the convergence rate and stability of the coupled solver. The resulting coupled solver ran on a free floating object tutorial test case when converged matches the original solver. It further allows a varying 70%–80% reduction in simulation times compared using a fixed under-relaxation to achieve the required stability.