Experiments are performed at industrial scales over the Ahmed geometry, i.e. at a Reynolds number of Re = 2.5 × 10 6 based on the height of the body. The shape of the squareback geometry is first optimised to make an initial substantial drag reduction. The separated flow at the trailing edge is orientated by introducing chamfers at the top and bottom edges. A parametric study based on both chamfered angles leads to an optimized Ahmed geometry having a drag 5.8% lower than the reference squareback model. It is evidenced that this optimized geometry produces 4 intense longitudinal vortices that still contribute significantly to the drag. The effect of a sideslip yaw angle is studied. As expected, it is found that the drag increases with an increase in the yaw angle, but surprisingly the drag remains constant for yaw angles within the interval ±0.5 • for which the side force displays very large fluctuations. This plateau is explained by recent observation of the bi-stable properties of the squareback Ahmed body (Grandemange, Gohlke & Cadot, Physical Review E 86, 2012). The suppression of the bi-stable behavior using a passive control technique is associated with an additional drag reduction of 1.6%.

Wave drift loads play a key role in station-keeping analysis of floating offshore structures. However, conventional radiation/diffraction tools have some limitations especially when the structure has sharp edges, requiring more extended validation. In this paper, a series of CFD computations are performed on a 2D simplified shape representing a rectangular-pontoon, with or without a horizontal damping plate. In the present study, the structure is considered to be fixed (radiation effects are not included). For validation, the results of CFD are compared with the results of experiments. The model tests are performed at the wave canal with an equivalent configuration. The drift forces are derived from the reflected and transmitted waves thanks to far field formulation. The incident, reflected and transmitted waves are separated by using a multi “sensors” method. The dissipation of wave energy is also investigated. The analysis is performed on two different model configurations: with and without the presence of a bottom damping plate. The effect of the damping plate on the wave energy dissipation and drift forces are discussed. The results obtained allows for a better understanding and will allow the study on more complex configurations.