海洋平台圆柱体坠落运动轨迹及落点分析

传统的角度偏差经验值方法导致落物风险评价过程中的落点和危险区预测存在较大误差，科学化、立体化、完整化、多因素概化的落物轨迹和落点分析方法及工具缺位。为此，以海洋平台圆柱体落物为研究对象开展先导研究，在2D运动理论模型基础上，考虑3维、6度受力与运动参数，引入粘性拖曳力系数经验公式、海流运动、旋转升力和力矩项，建立了具有普适性的落物水下3D运动轨迹预测模型，并以现场实验数据校验表明模型方法可行、结果更可信；据此以Matlab 2016为程序设计平台编制了海洋平台圆柱体坠落运动预测分析工具（MREDP），分析了坠落运动落点分布规律。研究结果表明:随着初始倾斜角度的增大，落点偏移距离呈现先增后降的趋势，于62°时达到最大值，运动轨迹整体呈现螺线曲率减小、向轨迹曲线外开口侧偏移趋势；落点分布变化可分为Y轴偏移稳定主导阶段、X轴偏移实力型快速主导阶段和X轴偏移机会型主导阶段3个阶段；相对MREDP预测结果，DNVGL-RP-F107经验性角度偏差推荐结果较为保守，MREDP可为DNVGL-RP-F107提供更加准确、可信的轨迹曲线和落点取值。基于分析结果，提出了采用Monte Carlo方法表征实际工程中起始运动参数随机性和入水撞击产生的不确定性等建议。

Analysis on motion trajectory and landing points of dropped cylinder on offshore platform

The traditional empirical value method of angle deviation will cause the relatively big error in the prediction of landing points and risk zone during the risk assessment process of dropped objects, so the scientific, stereoscopic, integrated and multi factor generalized analysis methods and tools for the trajectory and landing points of dropped objects have been lacking. Therefore, the precursive research was carried out by taking the cylindrical dropped objects on the offshore platform as the research object. Based on the two dimensional (2D) motion theoretical model, considering the three dimensional and six degrees stress and motion parameters, an universal prediction model for the underwater three dimensional (3D) motion trajectory of dropped objects was established by introducing into the empirical formula of viscous drag force coefficient, ocean current motion, rotational lift force and moment terms, and the verification results of field experimental data showed that the model was feasible with the more credible results. On this basis, a prediction analysis tool for the dropped motion of cylinder on the offshore platform (MREDP) was developed by taking Matlab 2016 as the program design platform, and the distribution laws of landing points of the dropped motion were analyzed. The results showed that with the increase of the initial inclination angle, the offset distance of landing points increased first and then decreased, and reached the maximum value at 62 degree, and the motion trajectory presented the trends of decreasing spiral curvature and offsetting to the outward opening side of the trajectory curve. The change of landing points distribution could be divided into three stages, namely Y axis offset stability dominant stage, X axis offset strength type fast dominant stage and X axis offset opportunistic type dominant stage. Compared with the results of MREDP prediction, the recommended results of empirical angle deviation by DNVGL-RP-F107 were more conservative, and MREDP could provide the more accurate and credible trajectory curves and landing points values for DNVGL-RP-F107. Based on the analysis results, some suggestions were put forward, such as adopting the Monte Carlo method to represent the randomness of initial motion parameters and the uncertainty caused by the impact of water entry in the practical engineering.