A robust algorithm for computational floating body dynamics

TL;DR

The paper introduces FloatStepper, a non-iterative, stable algorithm for simulating the interaction of floating bodies with fluids, effectively addressing added mass instability in CFD simulations.

Contribution

It presents a novel coupling method that decomposes forces into added mass and other components, implemented as an open source extension for OpenFOAM.

Findings

Demonstrates excellent stability even with massless bodies

Validated with multiple benchmark cases showing high accuracy

Highlights areas for further improvement in mesh motion methods

Abstract

We present a non-iterative algorithm, FloatStepper, for coupling the motion of a rigid body and an incompressible fluid in computational fluid dynamics (CFD) simulations. The purpose of the algorithm is to remove the so-called added mass instability problem, which may arise when a light floating body interacts with a heavy fluid. The idea underlying the presented coupling method is to precede every computational time step by a series of prescribed probe body motions in which the fluid response is determined, thus revealing the decomposition of the net force and torque into two components: 1) An added mass contribution proportional to the instantaneous body acceleration, and 2) all other forces and torques. The algorithm is implemented and released as an open source extension module to the widely used CFD toolbox, OpenFOAM, as an alternative to the existing body motion solvers. The accuracy of the algorithm is investigated with several single-phase and two-phase flow benchmark cases. The benchmarks demonstrate excellent stability properties, allowing simulations even with massless bodies. They also highlight aspects of the implementation, such as the mesh motion method, where more work is needed to further enhance the flexibility and predictive capabilities of the code.