Evaluation of a Practical Approach for Numerical Propulsion Tests

Prediction of resistance and propulsion characteristics for a ship is among the most important steps in a ship design process. Traditionally, model tests are used for these predictions and the results are extrapolated to the full-scale ship. Model test techniques can provide reasonably accurate results, but the cost and time they require — and the unavoidable scaling issues — have lead Naval Architects to look for other alternatives. With the increasing computer power and the increasing experience with numerical simulation of fluid flow, Computational Fluid Dynamics (CFD) have become an appealing alternative to model tests. Numerical computations will always be a trade-off between computational efforts and numerical accuracy. Typically, increased accuracy requirements will cause the mesh to be very fine, and hence the computational time will increase. At a Workshop on numerical simulation of full-scale ships in Southampton in November 2016, a practical approach for predicting the propulsion characteristics of a full-scale ship was introduced by participants from Becker Marine Systems. The pragmatic CFD approach reduced the computational efforts without scarifying the level of accuracy! In the present work, the alternative practical CFD approach is evaluated in a model scale case to study its benefits and possible short-comings compared to conventional CFD simulations of the self-propulsion case.