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

异常浪是指海面上突然出现的异常浪，浪高或浪形异常。异常巨浪对海洋结构物和船舶的破坏性影响已经导致许多人的生命损失，巨大的经济损失，甚至石油泄漏造成的环境污染。本研究旨在了解异常波的产生及其影响。对拖曳舱弹性船模进行了模型试验。介绍了色散聚焦波和Benjamin-Feir不稳定波的产生机理及其在实验室波槽中的产生方法。采用考虑船底涌现、船身几何形状和水动力冲击等非线性因素的非线性时域耐波性程序，模拟弹性船模的垂直运动和结构响应。规则波中模型试验的频域结果与水弹性程序的预测结果吻合得很好。在色散聚焦波中，实验和预测的运动和结构响应在时域上进行了比较。数值预测对最大垂直弯矩的预测效果较好，但对碰撞分量的估计略高，对船体结构的撞击动力响应估计不足。基本上，目前的水弹性规范可以用来预测极端波浪荷载，尽管改进是必要的。在此基础上，利用小波变换技术将色散聚焦波和不稳定波中的模型试验结果分解为遇波频率分量和高频分量。系统地考察了异形波各参数对这些分量的影响，以及两种假想异形波中船模表现出的行为差异等。最后，结合钢的塑性特性和应变率效应，采用显式动力有限元程序计算了当前异常波浪作用下实船纵向强度的安全裕度。结果表明，在28m巨浪的冲击下，结构的纵向强度可以保证结构的完整性。提出了基于梁单元模型的船体纵向强度评估流程图，以便在初步设计时快速校核船体在异常波浪作用下的纵向强度。此外，还研究了撞击时间的影响。研究发现，船体在动载荷作用下比静载荷作用下能承受更大的载荷。最后，从能量的角度出发，讨论并提出了一种基于能量吸收能力的偶然极限状态评价方法。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