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Limitations in Scaling Towing Tests for Simple Pontoon Shapes

[+] Author Affiliations
Jan Willem Krijger, Dimitris Chalkias

GustoMSC, Schiedam, Netherlands

Paper No. OMAE2017-61465, pp. V001T01A043; 6 pages
doi:10.1115/OMAE2017-61465
From:
  • ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 1: Offshore Technology
  • Trondheim, Norway, June 25–30, 2017
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-5763-2
  • Copyright © 2017 by ASME

abstract

For merchant vessels full scale resistance is determined by extrapolating the towing tank tests using Hughes’ method. For blunt and simple shapes this approach might not be valid due to significant Reynolds dependency.

In this paper a study is presented on two semi-submersible pontoon shapes and one drillship. The resistance for these hulls was calculated using URANSE simulations. Four different scales: 1:1, 1:10, 1:20 and 1:40 were investigated for all the different hull shapes. The goal of the study was to determine a form factor to use when scaling towing test results to full scale. However due to the simple shapes of the pontoons it was found that there was a significant Reynolds dependency at all the different scales. This Reynolds dependency had much more influence on the full scale resistance than a form factor. For the drillship no significant Reynolds dependency was found and applying ITTC 1978 method [1] with a form factor improved the accuracy of the resistance prediction compared to using the Froude method which is not using a form factor.

The simple pontoon shapes used were based on a combination of boxes, cylinders and spheres. The cylindrical and spherical shapes have a Reynolds regime where a drag crisis occurs. For all the shapes the drag crisis regimes were right in the same Reynolds number range at which typical model tests would be performed. Therefore performing towing tests and making accurate full scale resistance predictions for these simple shapes is not straightforward. Applying the ITTC 1978 method does not provide the same level of accuracy as it does for merchant vessels.

The paper identifies limitations involved in scaling towing test results for typical offshore hull shapes. Further possible solutions are proposed to improve the accuracy of the resistance predictions.

Copyright © 2017 by ASME
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