随机海浪下船舶横摇运动响应极值预报研究

Extreme value analysis of the roll motions under random seas

  • 摘要: 【目的】针对瘫船稳性和参数横摇两种稳性失效模式,通过对横摇运动响应极值分布进行预报,对船舶在波浪中的稳性和安全性进行评估。【方法】分别建立瘫船状态和参数横摇状态下船舶横摇运动方程,结合线性滤波器技术,采用龙格库塔法计算得到随机海浪下船舶横摇运动响应时历。将船舶横摇运动响应的绝对值定义为随机过程X(t),运用平均条件超越率法(average conditional exceedance rate, ACER)对X(t)的时历数据进行分析,对其极值分布进行预报。【结果】研究表明,ACER法能够有效地预报瘫船状态和参数横摇状态下船舶横摇运动响应的极值分布,随机过程X(t)在临界水平处(如浸水角)的超越概率可作为评估船舶倾覆的重要指标。【结论】采用ACER方法预报船舶横摇运动响应极值,能够为波浪中的船舶稳性评估提供重要参考。

     

    Abstract: In this work, two stability failure models, i.e., the dead ship condition and parametric roll are selected in order to study and evaluate ship stability as well as safety at seas. Specifically, equations are established to describe the roll motions under the dead ship condition and the parametric roll condition, respectively. Subsequently, equations of the roll motion are coupled with the linear filter, and the roll responses are obtained by solving the coupled equations via the Runge Kutta method. The stochastic process X(t) is defined as the absolute value of the roll response, and the average conditional exceedance rate (ACER) method is employed to predict the extreme value distribution of X(t). It is observed that the ACER method can provide satisfactory predictions of the extreme value distributions for the roll response under the dead ship condition and the parametric roll condition. The exceedance probability for the stochastic process X(t) at the critical level (e.g. the flooding angle), can be applied as an effective index to evaluate ship capsizing at seas. Extreme value analysis of the roll motion by application of the ACER method could be an important reference to evaluated ship stability at seas.

     

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