Multiple Approaches to Numerical Modeling of Container Ship Squat in Confined Water
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 146, Issue 4
Abstract
Various unsteady Reynolds-averaged Navier–Stokes (URANS) modeling techniques to predict container ship squat in confined water are investigated and compared in this study to assess the suitability of each modeling technique. Five methods are compared, among which three are quasi-statical estimations of squat from computational fluid dynamics (CFD)-computed hydrodynamic forces and moment (QS), and two are based on directly computed squat utilizing dynamic overset meshing (OV) technique. In addition, the effect of self-propulsion on the squat is investigated by comparing different methods of propulsion, i.e., the hull is either towed (T) or self-propelled by means of body-force propulsion virtual disc (VD) model or a fully discretized propeller (DP). The investigation shows that the QS methods tend to be superior in terms of computation efficiency, range of applicability, and trim prediction accuracy. It is also shown that the effect of self-propulsion is significant and should be accounted for to provide accurate results, especially at relatively high speeds. Moreover, virtual disc modeling is more computationally economical while also providing a degree of accuracy similar to that of a discretized propeller. Thus, the most suitable method is the quasi-static method with virtual disc self-propulsion (QS-VD). However, for very shallow cases where h/T < 1.14, the towed quasi-static squat model (QS-T) is recommended due to better accuracy.
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Acknowledgments
The authors acknowledge the funding and resources provided by NCMEH Australian Maritime College, University of Tasmania and the Tasmanian Partnership for Advanced Computing for the HPC for performing the computations.
Notation
The following symbols are used in this paper:
- AE
- propeller expanded area (m2);
- AO
- propeller disc area (m2);
- B
- ship beam (m);
- CB
- block coefficient;
- C0.7
- propeller chord length at 0.7 radius (m);
- DP
- propeller diameter (m);
- Frh
- Froude depth number [Frh = U/(gh)1/2];
- g
- gravitational constant (m/s2);
- h
- water depth (m);
- LPP
- length between perpendiculars of ship (m);
- P0.7
- propeller blade pitch at 0.7 radius (m);
- T
- ship draft (m);
- U
- ship speed (m/s);
- Δ
- displacement (t);
- λ
- scale;
- ρ
- fluid density (kg/m3); and
- ∇
- volumetric displacement of ship (m3).
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Published In
Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 146 • Issue 4 • July 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Jul 10, 2019
Accepted: Jan 9, 2020
Published online: Apr 22, 2020
Published in print: Jul 1, 2020
Discussion open until: Sep 22, 2020
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