Assessment of the Dynamic Stability of Tugs in Escort Using CFD

Master thesis (2023)

Authors

D.W.J. van der Made Mechanical Engineering

Contributors

T.J.C. van Terwisga Ship Hydromechanics and Structures - Mechanical, Maritime and Materials Engineering (supervisor 1)
Faculty
Mechanical Engineering
Copyright: © 2023 Daan van der Made
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Published Date

03-02-2023

Language

English

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Faculty

Mechanical Engineering

Abstract

In this thesis, the influence of a combined drift angle, heeling angle and forward speed on the stability of a tug is researched. This is done to gain insight in the stability of tugs during escorting, where they operate at high drift angles, heeling angles and forward speed. The Damen RSD 2513 tug was simulated in steady CFD simulation using the software FINE/Marine. The simulations were performed for 0, 15, 30 and 45 degrees drift angle, 0 to 10 degrees heeling angle for every 2 degrees of heel, and at 8 knots forward speed. Curves of the righting moment and heeling moment were created with the results of these simulations. These curves were analysed to see the effect of the drift angle, heeling angle and forward speed. Furthermore, a comparison was made between the restoring moment of the RSD 2513 calculated by SARC PIAS.

The following conclusions were drawn from the righting moment:
1. Without a drift angle, forward speed doesn’t influence the righting moment significantly. This results a minimal difference between the restoring and the righting moment of the tug.
2. Introducing a drift angle will result in a decrease of the righting moment.
3. Even with a drift angle, increasing the heeling angle will result in an increasing righting moment. In fact, the heeling angle and drift angle can be assumed to have independent effects on the righting moment.

Furthermore, two conclusions were drawn from the heeling moment:
1. The heeling moment increases when a drift angle is introduced.
2. Increasing the heeling angle will result in a slight increase in the heeling moment.

There are however concerns about the result’s numerical uncertainties and convergence. Firstly, the error estimation in the verification exercise is unreliable and therefore has a large safety factor leading to high uncertainties. Secondly, issues with convergence were experienced for higher drift angles. This was caused by large separation areas with high turbulent kinetic energy. Because of these two things, the results have limited reliability and the conclusions should be viewed with scepticism.