纵浪中纵荡和稳性丧失对参数横摇的影响研究

The effect of the surge motion and stability loss on parametric rolling in longitudinal waves

目前国际海事组织正在制定船舶第二代完整稳性衡准,衡准方案中提出了建立可靠预报参数横摇数学模型的要求。本文针对纵浪中航速变化以及稳性丧失对参数横摇的影响开展了计算研究。首先建立了纵荡-垂荡-横摇-纵摇4自由度耦合数学模型,该数学模型中利用无横倾时的垂荡、纵摇运动以及纵荡导致的速度变化来确定船-波相对位置,然后沿着船体瞬时湿表面积分得到非线性横摇复原力的变化,同时顶浪中考虑了横倾时辐射力和绕射力对横摇复原力的贡献,随浪中考虑了大幅横倾时升力对横摇复原力的贡献。最后采用ONR内倾船型研究了顶浪和随浪中纵荡和稳性丧失对1/2倍遭遇频率参数横摇和1倍遭遇频率参数横摇的影响。研究结果表明,纵浪中除了大幅参数横摇发生的临界点之外,其余工况纵荡对1/2倍遭遇频率参数横摇影响很小,随浪中较高航速时纵荡和稳性丧失对1倍遭遇频率参数横摇影响比较显著。

The guidelines for direct stability assessment of parametric rolling are currently under development at the International Maritime Organization(IMO)for the second generation intact stability criteria and a reliable mathematical model is necessary.The effect of the surge motion and stability loss on parametric rolling is studied.A surge-heave-pitch-roll coupled equation in 4 DOF is established for predicting parametric rolling in longitudinal waves.Firstly,heave and pitch motions obtained by a strip method applied to an upright hull with the speed variation due to the surge motion is used to determine the simultaneous relative position of the ship to waves in time domain.Secondly,the nonlinear Froude-Krylov roll restoring variation is calculated by integrating wave pressure up to wave surface.Thirdly,the dynamic radiation and diffraction forces in head seas and the heel-induced hydrodynamic forces for large heel angle in calm water in following seas are considered in the 4 DOF mathematical model.Finally,the ONR tumblehome vessel is utilized to study the effect of the surge motion and stability loss on parametric rolling.The results show that the effect of the surge motion on parametric rolling with half encounter frequency in longitudinal waves is generally small except the critical forward speed of large parametric rolling.The effect of the surge motion and stability loss on parametric rolling with encounter frequency at a high speed in following waves is significant.