Investigation on Devices for Preventing Parametric Rolling

首先，为了理解参数横摇，将平均技术应用于解耦的横摇数学模型，然后识别参数横摇的阈值及其分叉结构。通过两条集装箱船的系留模型试验，对数学模型中涉及的恢复变差项进行了检验。结果表明，传统的Froude-Krylov分量本身是不够的，兴波和升力分量是不可缺少的。其次，对后巴拿马型集装箱船模型在规则波、长峰不规则波和短峰不规则波中进行了自由航行试验。在此记录了头浪和首浪中振幅约为20 °的参数横摇，并识别了操作和环境方面的影响。第三，对于在无前进速度的头浪中遭受振幅为21 °的参数横摇的拖网渔船，6自由度模型的数值分析表明，恢复变化作为弗劳德-Krylov分量很小，自然横摇与纵摇周期之间的关系很重要。最后，基于上述知识，提出了两种抗参数横摇装置：一种是用于减小回复变化的中舷体，另一种是用于增加横摇阻尼的减摇水舱。将这些装置安装在集装箱船模型上，进行了自航试验。结果表明，占船宽11.7%的舷侧横摇能减小25%的参数横摇幅度，占排水量3.2%的减摇水舱能完全消除参数横摇。此外，数值研究表明，通过改变俯仰陀螺半径可以减小拖网渔船的参数横摇。

Firstly, to understand parametric rolling, an averaging technique was applied to an uncoupled mathematical model of roll and then threshold of parametric rolling and its bifurcation structures were identified. The restoring variation term, which is involved in the mathematical model, was examined with captive model tests for two container ships. As a result, it was shown that a conventional Froude-Krylov component on its own is not sufficient and the wave-making and hydrodynamic lift components are indispensable.Secondly, free-running experiments with a post-Panamax container ship model were conducted in regular, long-crested irregular and short-crested irregular waves. Here parametric rolling with the amplitude of about 20 degrees in head and bow seas was recorded and the effects of operational and environmental aspects were identified.Thirdly, for the trawler that suffered parametric rolling with the amplitude of 21 degrees in head seas without forward speed, the numerical analysis with a 6 degrees-of-freedom model demonstrated that the restoring variation as the Froude-Krylov component is negligibly small and the relationship between natural roll and pitch period is crucial.Finally, based on the obtained knowledge mentioned above, two types of anti-parametric rolling devices were proposed : one is midship sponsons for reducing the restoring variation and the other is an anti-rolling tank for increasing roll damping. These devices were installed in the container ship model and then a free-running experiment was carried out. The results demonstrate that sponsons that is 11.7% of the ship breadth in wide reduce 25% of parametric roll amplitude and the anti-roll tank of that weight is 3.2% of the ship displacement completely exclude parametric rolling. In addition, the numerical study indicated parametric roll of the trawler can be reduced by changing the pitch gyro radius.