A modification of the ITTC57 correlation line for shallow water

A modification of the ITTC57 correlation line for shallow water

Zeng, Q. (TU Delft Ship Design, Production and Operations)
Thill, C.H. (TU Delft Ship Hydromechanics and Structures)
Hekkenberg, R.G. (TU Delft Ship Design, Production and Operations)
Rotteveel, E. (TU Delft Ship Design, Production and Operations)

2018

The ITTC57 correlation line, which is derived based on the assumption that the water in which ships advance is infinite deep and wide. However, for ships sailing in the waterway with limited water depth, the frictional resistance will be influenced leading to a decreasing accuracy of the prediction with this correlation line. In this study, a modification of the ITTC57 correlation line is proposed to correct the effects in very shallow water specifically for the flat area of the bottom of the ship. Under some assumptions, this area can be simplified to a 2D flat plate with a parallel wall close to it to study how the shallow water conditions of two interacting boundary conditions are affecting the flat plate friction coefficient. Computational fluid dynamics (CFD) calculations are applied to investigate how a friction line specifically in shallow water deviates from the conventional lines. Such deviations may severely affect the extrapolation of a ship model’s resistance to full scale and, therefore, the accuracy of ship’s performance prediction. Cases at ten Reynolds numbers from 10⁵ to 10⁹ are simulated on the 2D flat plate. Seven different distances between the flat plate and the parallel wall were chosen to generate various shallow water conditions, and consequently, a database including frictional resistance coefficients, Reynolds numbers and the distance between those two walls is built. Results indicate that thinner boundary layers are observed in shallow water conditions, and the scale effects which has a significant impact on resistance extrapolation are also observed. Furthermore, the assumption of the zero pressure gradients (ZPG) which is commonly used in deep water is no longer valid in extremely shallow ones. Finally, a modification for the ITTC57 correlations line considering shallow water effects is proposed, which is willing to improve the prediction of the frictional resistance of those ships with a large area of flat bottom and sail in shallow water.

Boundary layer
CFD
Friction line
Shallow water
Zero pressure gradient

http://resolver.tudelft.nl/uuid:b93142d9-4ed5-4015-982f-f79142d0530b

https://doi.org/10.1007/s00773-018-0578-7

0948-4280

Journal of Marine Science and Technology, 24 (2019) (2), 642-657

Institutional Repository

journal article

© 2018 Q. Zeng, C.H. Thill, R.G. Hekkenberg, E. Rotteveel