Impact Failure Limit against Freak Wave and Development of the Collision-Avoidance System

反常波是指海面上出人意料地出现的具有异常波高或异常形状的异常波。反常海浪对海洋结构物和船舶造成的破坏性影响已经造成了许多人的生命损失，巨大的经济损失，甚至是石油泄漏造成的环境污染。本研究旨在了解反常波的产生，并研究其影响。在拖曳水池中进行了弹性船模试验。介绍了色散聚焦波和本杰明-费尔不稳定波的产生机理及其在实验室水槽中的产生方法。采用考虑了船底涌出、船型几何形状和水动力冲击等非线性因素的非线性时域适航程序，模拟了弹性船模的垂向运动和结构响应。规则波模型试验结果与…计算结果在频域上吻合较好。由水弹性规范得到更多的d。在频散聚焦波中，将实验和预测的运动和结构响应在时间域上进行了比较。数值预测的最大竖向弯矩得到了很好的预测，但相遇分量被高估了，结构的砰击动力响应似乎被低估了。目前的水弹性规范基本上可以用来预报极端波浪荷载，但仍有必要改进。在此基础上，利用小波变换技术将频散聚焦波和不稳定波的模型试验结果分解为遇波频率分量和高频分量。系统地考察了各种反常波参数对这些分量的影响，以及船模在两种假定反常波作用下的行为差异等。最后，利用显式动力有限元程序，考虑钢材的塑性和应变率效应，对实船在当前反常波浪作用下的总纵强度进行了安全裕度计算。结果表明，在28m反常波的作用下，结构的纵向强度可以保证结构的完整性。提出了以梁单元模型为基础的评估流程图，以便在初步设计时快速校核船体在反常波浪中的纵向强度。此外，还对砰击持续时间的影响进行了研究。结果表明，船体在动态意义上比在静态意义上可以承受更多的载荷。最后，从能量的角度，讨论并提出了基于能量吸收能力的事故极限状态评价方法。较少

Freak waves are abnormal waves surprisingly appearing on the sea surface with exceptional wave height or abnormal shape. The devastating effect of freak waves on offshore structures as well as ships has led to many people's life losses, great economic losses, even environmental pollution from oil leakage. This research aims to understand the generation of the freak wave and study their influences. Model test of elastic ship model in towing tank is carried out. the generation mechanisms of the dispersive focusing waves and Benjamin-Feir unstable waves as well as their generation methods in laboratory wave tank are presented. Nonlinear time domain seakeeping code accounting for the nonlinearities such as bottom emergence, hull shape geometry and hydrodynamic impact, etc is adopted to simulate the vertical motion and structural responses of the elastic ship model. The experimental results of model tests in regular waves agree very well in frequency domain with the predicted ones calculate … More d by the hydroelastic code. In dispersive focusing waves, the experimental and predicted motion and structural responses are compared in time domain. The maximum vertical bending moments are predicted very well, while the encounter components are a little overestimated and the dynamic responses of ship structure due to slamming seem to be underestimated by the numerical predictions. Basically, the current hydroelastic code can be used to predict the extreme wave loads, although the improvements are necessary. Following this, the experimental results of the model tests in dispersive focusing waves as well as unstable waves are decomposed into wave encounter frequency components and high frequency components by wavelet transform technique. The influence of various parameters of freak waves on these components, the differences of behaviors the ship model exhibited in both supposed freak waves, etc are examined systematically. Finally, the safety margin of the longitudinal strength of the real ship under the current freak waves is conducted with the explicit dynamic finite element code incorporating the plastic property and strain rate effects of steel. The results show that the structural integrity can be assured under the attack of 28m freak wave in terms of longitudinal strength. The evaluation flowchart is suggested based on the beam element model so as to provide a fast check of longitudinal strength of ship hull in freak waves during the preliminary design. Moreover, the influence of the slamming duration is also investigated. It is found that the ship hull could carry more loads in dynamic sense than it could in static sense. In the end, from the viewpoint of energy, an evaluation approach in accidental limit state based on energy absorption capacity is discussed and proposed. Less