On the Possibility to Compute Slowly-Varying Drift in a CFD Solver

Abstract

Slowly-varying drift is a phenomenon very familiar to offshore industry, but usually not so much relevant or discussed in naval industry. The classical theoretical background consists in considering a bichromatic wave composed of two regular wave trains of pulsations ω1 and ω2 evolving in the same direction and without any forward speed. The force which varies at low frequency (ω2 – ω1) is known as the slowly-varying drift force and is important in case of moored vessels because it may excite them at their natural periods. The equivalent application in the naval industry is related to maneuvering and added resistance in waves. However, as already indicated, up to the authors’ knowledge, there has not been much work on these issues in the past. State-of-the-art potential flow tools predict well this slowly-varying drift at zero forward speed. However, with an additional forward speed or a strong current, traditional linear potential codes are outside the scope of their underlying hypothesis and cannot predict accurately the low frequency force. With the constant rise of CPU power and accuracy of CFD solvers, this problem may now be addressed in CFD. The results of foamStar, in-house OpenFOAM solver, will be shown with and without additional forward speed.