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Numerical investigation & modelling of modern container ship squat


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Kok, Z ORCID: 0000-0002-4068-8343 2021 , 'Numerical investigation & modelling of modern container ship squat', PhD thesis, University of Tasmania.

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The size of container ships has increased significantly over the past decades as shipping companies merge and adopt tactics of economies of scale to meet increasing demands. Such practice has incessantly caused complications to operate larger container ships in relatively shallow approach channels and ports. This is because when ships move in water, changes in the flow around the hull causes the hull to sink vertically and trim either by the bow or stern. This hydrodynamic phenomenon is known as “ship squat”. In shallow water conditions, the squat effect is accentuated. Given that ever larger container ships are being introduced and the fact that the rate of ship size growth outpaces dredging and port expansion projects, the likelihood of grounding is increased.
Various studies have been conducted to provide empirical methods for squat prediction but most methods are based on outdated hull forms and some do not include self-propulsion effect. It is known that there are large deviations between different prediction methods and this is especially true for high speed conditions where accurate prediction of container ship squat is important. Furthermore, unlike bulk carriers, the trim direction of container ships is not well understood. There are also other unaddressed concerns regarding squat such as significance of scale effect and initial trim. The accuracy of using the typical blockage ratio to quantify the effect of lateral restriction for channels with submerged banks is also doubtful. Consequently, the reliability of readily available empirical methods for accurate rapid assessment of squat is questionable, particularly for newer and larger container ships.
Therefore, this thesis presents a systematic investigation into the hydrodynamic squat phenomenon on modern container ships when underway in shallow water conditions using Computational Fluid Dynamics (CFD) simulations. Model tests are also undertaken to validate the CFD model. The ultimate goal of this investigation is to produce a new set of improved empirical formulae suitable for more accurate prediction of container ship squat by using regression analysis on the CFD predicted results.
Firstly, various CFD modelling techniques are benchmarked against model scale experiments conducted in this study and readily available experimental results in literature. The modelling of selfpropulsion effect is also studied. Having determined the most suitable CFD modelling approach, the scale effect on squat is then investigated with account of self-propulsion effect. Upon investigating the possible influence of scale effect, systematic investigations to quantify the influence of hull principal particulars on squat are conducted. The quantified influence of principal particulars is then used to understand the trim behaviour of container ships as well as to develop a new set of regression formulae. Finally, investigations to quantify the effect of lateral restriction and initial trim effect are conducted to develop correction factors for the new empirical formulae. The final form of the formulae is tested against various cases and found to provide accurate predictions for cases that are within the recommended range. The new formulae is also shown to be consistently more accurate than existing empirical methods for the cases tested. Reasonable correlations are also observed for comparisons against actual full scale squat measurements. The empirical formulae developed is an improved tool to perform rapid assessment of container ship squat that is well suited to time domain mathematical models. Hence, all the research objectives have been addressed satisfactorily.

Item Type: Thesis - PhD
Authors/Creators:Kok, Z
Keywords: Ship squat, RANS-CFD, shallow water, regression analysis, empirical equations
DOI / ID Number: 10.25959/100.00038128
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Copyright 2021 the author

Additional Information:

Chapter 5 appears to be, in part, the equivalent of a pre-print version of an article published as: Kok, Z., Duffy, J., Chai, S., Jin, Y., Javanmardi, M., 2021. Numerical parametric study of medium sized container ship squat, Applied ocean research, 109, 102563

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