Lines design 83

Wave pattern

Plots of contourlines of the wave elevation are mainly used for quality control. Reflections on the border of the computational domain and waves at the upstream border of the grid indicate that the grid was too small and the computation should be repeated with a larger grid. Typically but with no indication of numerical error, waves at the stern are higher than at the bow. This is due to larger run angles than entrance angles and the neglect of viscosity, which in reality reduces the waves at the aftbody.

Perspective view of water surface

Perspective views of the water surface, often with `hidden-lines' or shading are popular, but have no value for designing better hull forms.

Often pressure, velocity and wave elevation are combined in one plot.

CFD reports should contain, as a minimum, the following information (Bertram, 1992):

Information for form improvement

1.Pressure contour lines (preferably in colour) in all perspectives needed to show the relevant regions. Oblique views from top and bottom have been proven as suitable.

2.Wave profile at hull with information on how the profile was interpolated and the vertical scale factor.

3.Velocity contribution at forebody showing the flow directions. The ship speed should be given as a reference vector.

4.An estimate of the relative change in resistance for comparison of variants versus a basis form.

Information for quality control

1.Plots of grids, especially on the hull, to provide a reference for the accuracy of interpolated results.

2.Information on the convergence of iterative solutions.

3.Plots of wave pattern to detect implausible results at the outer boundary of the computational domain or at the ship ends.

Generally, plots of the hull should contain main reference lines (CWL, sections) to facilitate the reference to the lines plan.

2.12 References

BERTRAM, V. (1992). CFD im Schiffbau. Handbuch der Werften Vol. XXI, Hansa, p. 19 BERTRAM, V. (1994). Numerische Schiffshydrodynamik in der Praxis. IFS-Report 545, Univ.

Hamburg

BERTRAM, V. and JENSEN, G. (1994). Recent applications of computational fluid dynamics. Schiffstechnik, p. 131

DANCKWARDT, E. (1969). Ermittlung des Widerstandes von Frachtschiffen und Hecktrawlern beim Entwurf. Schiffbauforschung, p. 124

ECKERT, E. and SHARMA, S. (1970). Bugwulste¨ fur¨ langsame, vollige¨ Schiffe. Jahrbuch Schiffbautechn. Gesellschaft, p. 129

¨ , . and , . (1968). Systematische Widerstandsuntersuchungen fur¨ schnelle

HAHNEL G LABES K.-H

Frachtschiffe mit und ohne Bugwulst. Schiffbauforschung, p. 85

HOEKSTRA, M. (1975). Prediction of full scale wake characteristics. International Shipbuilding Progress, p. 204

84 Ship Design for Efficiency and Economy

HOLDEN, K. O., FAGERJORD, O. and FROSTAD, R. (1980). Early design-stage approach to reducing hull surface forces due to propeller cavitation. Trans. SNAME 88, p. 403

HOYLE, J. W., CHENG, B. H., HAYS, B., JOHNSON, B. and NEHRLING, B. (1986). A bulbous bow design methodology for high-speed ships. Trans. SNAME 94, p. 31

JENSEN, G. (1994). Moderne Schiffslinien. Handbuch der Werften Vol. XXII, p. 93

KERLEN, H. (1971). Entwurf von Bugwulsten¨ fur¨ vollige¨ Schiffe aus der Sicht der Praxis. Hansa, p. 1031

KRACHT, A. (1973). Theoretische und Experimentelle Untersuchungen fur¨ die Anwendung von Bugwulsten¨. Report 36, Forschungszentrum des Deutschen Schiffbaus, Hamburg

¨ , . (1997). Moderne hydrodynamische Entwurfsmethoden in der Werftpraxis. Jahrbuch

KRUGER S

Schiffbautechn. Gesellschaft

LAP, A. J. W. (1954). Diagrams for determining the resistance of single-screw ships. International Shipbuilding Progress, p. 179

LARSSON, L. (1994). CFD as a tool in ship design. In N. N. (1994)

MILLER, W. and SZANTYR, J. (1998), Model experiments with surface piercing propellers, Schiffstechnik 45

N. N. (1994). CFD Workshop Tokyo 1994. Ship Research Institute

POPHANKEN, E. (1939). SchiffbaukalenderÐHilfsbuch der Schiffbauindustrie. Deutsche Verlagswerke, Berlin

SCHNEEKLUTH, H. (1959). Einige Verfahren und Naherungsformeln¨ zum Gebrauch beim Linienentwurf. Schiffstechnik, p. 130

STRUNK, H. (1986). Systematische Freifahrtsversuche mit teilgetauchten Propellern unter Druckahnlichkeit¨. Report 180, Forschungszentrum des Deutschen Schiffbaus, Hamburg

TZABIRAS, G. (1997). A numerical study of additive bulb effects on the resistance and selfpropulsion of a full ship form. Schiffstechnik, p. 98

WURR, D. (1979). Heckwulst in vereinfachter Bauweise fur¨ Einschraubenschiffe. Hansa, p. 1796