A new concept for design of the shape ship stern
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Abstract
The paper presents an original stern shapes design which obtaining a good distribution of the ship wake able to reduce the drag. The paper begins to present the problems directly and reversely, physical mathematical shaping and the numerical implementation (including the precision of numerical approach). For this purpose, the imagining of a current tube is suggested, with increasing variable cylindrical sections, which starts from the disk in front of the propeller, extends towards the prow, very close to the cylindrical area and which includes the entire stern section of a classic hull having practiced cross corrugated sections). Certainly, the dynamics of a cavity propeller depends on the work environment system. The flow field around a propeller mounted on the ship is very different to the one that a propeller develops when tested in free water or in a section of a cavitation tunnel. A propeller with a very performance in free water may not be right for a stern shape of a hull of the given ship. For this reason, the ship wake distribution in the propeller disk plan represents a key factor for a ship design. The study tries to draw attention and briefly focuses on ships hull’s stern flows in the light of two absolutely strict original ideas (concepts) in ship hydrodynamics, belonging to the author: 1.a new stern hydrodynamic concept (NSHC), with radial crenellated-corrugated sections 2. using of an inverse piezoelectric effect [(electric current→high-frequency power generator→ piezoelectric driver made of certain ceramic material, which induces an elliptical vibratory movement (high frequency over 20 kHz), into the elastic side plates (15 mm thickness) in the streamlines direction (of the external flowing water)], able to reduce the total forward resistance. Resuming, it can be concluded that the new concept of stern shape proposed as well as the reverse mathematical problem presented above for its optimization, based on the Levenberg-Marquardt algorithm seem to be reasonable. Finally, the most important, until now, proved result, is the reducing of propeller cavitation (working in the simulated nominal wake of the hull using the new shape stern.
Keywords: vessel wake, propeller cavitation, drag, stern shape, cavitation tunnel, ultrasonic vibrator.
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References
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[3] Zhang, D.H., (1999). Body fitted coordinate systems for ship stern flow calculations, Doctoral dissertation, Department of Marine Hydrodynamics, The Chalmers University of Technology, 1999.
[4] Tănăsescu H., & Ali B. (2008). New concept, stern shape ship hulls improving for propulsion and stability performance obtaining, Grant CEEX, ICEPRONAV, 2008