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Project ID: G3RD-CT-2002-00810
Financiado con arreglo a: FP5-GROWTH
País: Finland

Tanker wakefield & resistance - case study report

Initially, a tanker was supposed to be computed being similar to the previous cases. However, the construction of passenger vessels is the main task of this shipyard nowadays, and the knowledge of the flow field around such vessels may improve its competitiveness. According to the wishes of the shipyard, it was decided to take a new challenge and to compute a new ship type.

Due to the huge amount of work and computations performed in WP 4, only very little time was left for the computations in WP 5. Therefore, the propeller computations with appendages were skipped. The viscous flow around the bare hull of the AKF vessel was computed at full-scale Reynolds numbers. The computations were performed as viscous-free surface and as double-hull computations. The double-hull computations were not exactly double-hull computations as the free surface is slightly deformed at the bow and at the stern. The goal was to use the FINFLO-SHIP code as it is.

Difficulties appeared in the viscous-free surface computations due to the wedgelike transom. The wave height had to be kept fixed at the transom causing no deformation of the wave pattern behind the stern, which was an obvious bug in the code. The bug was corrected by Reijo Lehtim¨aki, however, due to the lack of time the free-surface computations could not be completed on the finest grid level.

The surface piecing bulbous bow did not cause particular difficulties as in the case of the Uilenspiegel. However, the change from the medium grid to the fine grid will require a manual correction of the grid at the bow, which was not carried out here. The double-hull computations did not cause particular problems for all grid resolutions.

The computational times of are too long for engineering purposes where a solution is required within less than 24 hours. However, for scientific purposes the FINFLO-SHIP is suitable due to its accuracy as shown in WP 4. At the present, the FINFLO-SHIP code is further developed for commercial purposes, which should make it user friendly and faster. In the future, the computational time will not be an issue anymore as more processors may be used due to parallel computing and the processor speed will increase still significantly. The bottleneck will remain the manual grid generation. Only an automatic grid generation would reduce the times significantly.

However, for structured grid automatic grid generation seems to be no feasible yet. The design itself may be improved by a slight modification of the bulbous bow and the stern. Close to the free surface, the curvature of the bulbous bow should be increased below the bow wave. At the stern the curvature of the hull should be slightly reduced at x = -30 m, where a low-pressure peak is present.

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Pekka EIVOLA, (Hydrodynamics)
Tel.: +358-1-06707321
Fax: +358-1-06707700
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