A CFD Investigation of SailingYacht Forebodies in Head Seas
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Naval architecture and ocean engineering (MPNAV), MSc
Publicerad
2015
Författare
Kostalas, Konstantinos
Pluto, Adam
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The objective of this thesis is to investigate the hydrodynamic performance of a modern 41 feet sailing yacht by comparing the performance values acquired from simulations for different forebody geometry designs on the yacht. The particulars such as length, beam, displacement and prismatic coefficient are kept as similar as possible for all hulls. The resistance of the different designs are tested in flat water and in tests with waves. The set up for the waves is made with data taken from Svenska Björn; which is a caisson lighthouse in the Baltic Sea. The wave lengths tested in this study includes lengths of 12.5m, 25m and 34.5m and the yachts are run in straight head sea. The encounter frequency for the 25m wave matches the natural pitch frequency of the yachts. To evaluate realistic upwind condition, for cruising and racing, tests with a heel angle of 20o are additionally performed. All hulls are tested at Froude number 0.35 in the conditions described in the previous paragraph. This investigation is made with the aid of CFD using Unsteady Reynolds Averaged Navier-Stokes (U-RANS) equations integrated in the solvers provided in Star CCM+ software. Also, Volume of Fluids method for surface capturing is used. At the start of the study a verification of the software is made with the use of Least Square Root method. Then, a validation of the CFD results from the software is done by a comparison with data from towing tank tests from Delft Systematic Yachts Hull Series hull. In total three hulls are tested with a systematic forebody geometry variation of shape. The main result of this study is a better understanding of how the forebody design of a sailing yacht affects the performance. The study is done at high Froude number, where the gain from having a sharp and pointed entry angle and then diving into the water is larger than having volumes in the lower part of the bow. Having a tumblehome design that prevents the yacht from diving into waves gives calmer motions but higher resistance. However it is important to conclude that the drag, pitch and heave for all yachts are close and a definite winner hull is difficult to name because some of the three yachts are better than the other in certain conditions. Nevertheless, the best design overall is the hull with sharp entry angle and flare.
Beskrivning
Ämne/nyckelord
Transport , Farkostteknik , Transport , Vehicle Engineering