Parametrical studies of a new numerical model for controlled ship motions in extreme astern seas |
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Authors: | Zafer Ayaz Dracos Vassalos Osman Turan |
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Institution: | (1) Department of Naval Architecture and Marine Engineering, Universities of Glasgow and Strathclyde, Henry Dyer Building, 100 Montrose Street, Glasgow G4, OLZ, UK |
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Abstract: | Parametrical studies based on numerical simulations were carried out for very steep regular waves to assess possible improvements
in the state-of-the art numerical modelling of the control and capsizing behaviour of ships in following and quartering seas.
A nonlinear 6-DOF numerical model has been developed with the inclusion of frequency-dependent terms, the so called memory
effects, and a flexible axis system that allows straightforward combination of seakeeping and manoeuvring models while accounting
for extreme motions. The previously undertaken validation analyses using extensive model test data provided qualitatively
good agreement, whereas the comparison with numerical models without coupling of the vertical motions and frequency-dependent
hydrodynamic terms embodied in radiation forces identified improvements in the accuracy. However, to broaden the assessment
of the numerical model, further parametrical numerical analyses were carried out using two ships, which had previously been
tested in the validation analyses, for various operational and environmental conditions. These parameters were changed in
accordance with the recommendations from international organisations and experience from model tests to realise and avoid
dangerous conditions that often result in capsizing, such as broaching associated with surf riding and low-cycle resonance.
As a result of the parametric analysis, we discuss the sensitivity of the improvements in the numerical model for various
critical operational and design parameters and its possible use to provide a link between the ship's behavior and these parameters. |
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Keywords: | Capsizing Astern seas Numerical predictions Controllability Parametric resonance Broaching Surf riding Memory effect |
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