Investigation on Devices for Preventing Parametric Rolling

为了更好地理解参数轧制，首先将平均化技术应用于一个非耦合的轧辊数学模型，然后确定了参数轧制的阈值及其分叉结构。通过两艘集装箱船的网箱模型试验，对数学模型中包含的恢复变异项进行了检验。结果表明，常规的Froude-Krylov部件本身是不够的，兴波和水动力升力部件是必不可少的。其次，利用巴拿马型后集装箱船模型进行了规则波、长峰不规则波和短峰不规则波的自由航行试验。在此基础上，对前海无航速的拖网渔船进行了数值分析，结果表明，由于Froude-Krylov分量的影响，其恢复变化量可以忽略不计，自然横摇与纵摇周期之间的关系是至关重要的。最后，在上述认识的基础上，提出了两种减摇装置：一种是减小恢复变化量的船中横摇装置，另一种是增加横摇阻尼力的减摇水舱。将这些装置安装在集装箱船模型上，进行了自由航行试验。结果表明，宽幅为11.7%的舷台使参数横摇幅度降低了25%，该重量的减摇水舱占船舶排水量的3.2%完全排除了参数横摇。此外，数值研究表明，改变螺距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.