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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. 相似文献
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URANS analysis of a broaching event in irregular quartering seas 总被引:1,自引:0,他引:1
Pablo M. Carrica Kwang-Jun Paik Hamid S. Hosseini Frederick Stern 《Journal of Marine Science and Technology》2008,13(4):395-407
Ship motions in a high sea state can have adverse effects on controllability, cause loss of stability, and ultimately compromise
the survivability of the ship. In a broaching event, the ship losses control, naturally turning broadside to the waves, causing
a dangerous situation and possibly capsizing. Classical approaches to study broaching rely on costly experimental programs
and/or time-domain potential or system-based simulation codes. In this paper the ability of Reynolds averaged Navier–Stokes
(RANS) to simulate a broaching event in irregular waves is demonstrated, and the extensive information available is used to
analyze the broaching process. The demonstration nature of this paper is stressed, as opposed to a validated study. Unsteady
RANS (URANS) provides a model based on first principles to capture phenomena such as coupling between sway, yaw, and roll,
roll damping, effects of complex waves on righting arm, rudders partially out of the water, etc. The computational fluid dynamics
(CFD) method uses a single-phase level-set approach to model the free surface, and dynamic overset grids to resolve large-amplitude
motions. Before evaluating irregular seas two regular wave cases are demonstrated, one causing broaching and one causing stable
surf riding. A sea state 8 is imposed following an irregular Bretschneider spectrum, and an autopilot was implemented to control
heading and speed with two different gains for the heading controller. It is concluded that the autopilot causes the ship
to be in an adverse dynamic condition at the beginning of the broaching process, and thus is partially responsible for the
occurrence of the broaching event. 相似文献
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Naoya Umeda Hirotada Hashimoto Akihiko Matsuda 《Journal of Marine Science and Technology》2003,7(3):145-155
We have attempted to develop a more consistent mathematical model for capsizing associated with surf-riding in following
and quartering waves by taking most of the second-order terms of the waves into account. The wave effects on the hull maneuvring
coefficients were estimated, together with the hydrodynamic lift due to wave fluid velocity, and the change in added mass
due to relative wave elevations. The wave effects on the hydrodynamic derivatives with respect to rudder angles were estimated
by using the Mathematical Modelling Group (MMG) model. Then captive ship model experiments were conducted, and these showed
reasonably good agreements between the experiments and the calculations for the wave effects on the hull and the rudder maneuvring
forces. It was also found that the wave effects on restoring moments are much smaller than the Froude–Krylov prediction, and
the minimum restoring arm appears on a wave downslope but not on a wave crest amidship. Thus, an experimental formula of the
lift force due to the heel angle of the ship is provided for numerical modelling. Numerical simulations were then carried
out with these second-order terms of waves, and the results were compared with the results of free-running model experiments.
An improved prediction accuracy for ship motions in following and quartering seas was demonstrated. Although the boundaries
of the ship motion modes were also obtained with both the original model and the present one, the second-order terms for waves
are not so crucial for predicting the capsizing boundaries themselves.
Received: June 20, 2002 / Accepted: October 10, 2002
Acknowledgments. This research was supported by a Grant-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science
and Technology of Japan (No. 13555270). The authors thank Prof. N. Rakhmanin of the Krylov Ship Research Institute for providing
the Russian literature, as well as Mr. H. Murata of NHK (Japan Broadcasting Corporation) for translating it into Japanese.
Address correspondence to: N. Umeda (e-mail: umeda@naoe.eng.osaka-u.ac.jp) 相似文献
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By utilizing a four-degrees-of-freedom numerical model with dense grids of control parameters and the sudden-change concept,
the qualitative aspects of the nonlinear motions of a fishing vessel complying with the International Maritime Organization's
intact stability criteria in following and quartering seas were intensively explored. As a result, capsizing due to broaching,
capsizing without broaching, broaching without capsizing, stable surf-riding, and steady periodic motion were identified.
The natures of the boundaries of these motions in the control parameter plane were investigated, and the effects of the initial
conditions and the nonlinearity of calm-water maneuvering forces are also discussed. Furthermore, comparisons with a model
experiment showed that the numerical model used here qualitatively explains capsizing phenomena, but quantitatively overestimates
the danger of capsizing.
Received: June 11, 2001 / Accepted: October 9, 2001 相似文献
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Hirotada?Hashimoto Naoya?UmedaEmail author Akihiko?Matsuda 《Journal of Marine Science and Technology》2004,9(2):80-93
In order to realize a more quantitative prediction of broaching and capsizing in following and quartering seas, existing mathematical modelling techniques should be upgraded. Therefore, it is necessary to systematically examine all factors relevant to capsizing in following and quartering seas. To this end, we first attempted to examine the prediction accuracy of wave-induced forces by comparing calculations with captive model experiments. As a result, we found that a wave-induced surge force has a certain nonlinearitiy with respect to wave steepness. The nonlinearity of sway–roll coupling with respect to sway velocity was also found, and our numerical result with these nonlinearities improves the prediction accuracy of the critical ship speed of capsizing in following and quartering seas. The importance of the wave effect on propeller thrust was also examined. We found that this effect is not negligibly small and could improve capsizing predictions in heavy following and quartering seas. Finally, we attempted to investigate the importance of nonlinear heel-induced hydrodynamic forces on numerical predictions of capsizing due to broaching. Here, we propose a new procedure for captive model experiments to obtain hydrodynamic forces with various heel angles up to 90°, and data on heel-induced hydrodynamic forces with respect to heel angle in calm water are provided. We then compare the numerical simulations with the nonlinear heel-induced hydrodynamic forces and without them. These time series comparisons show that the effect of nonlinear heel-induced hydrodynamic forces in calm water is not negligibly small for the case of ship capsizing due to broaching. 相似文献
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