Offshore wind power generation is a promising technology in renewable energy applications due to its high reserves of wind energy in sea areas. To improve the energy transformation efficiency, the blade length of the offshore wind turbines has become larger and larger, and it has made rain erosion be one of the most frequent failures during the turbine operation. As the natural rainfall is stochastic in spatial and time domains, it is difficult to depict the damage evolution process caused by rain impact exactly. Therefore, regular and continuous droplet impact simulation and experiments present an alternative methodology for this issue. With the composite structure of the blade and deformability of the liquid droplet in consideration, a fluid solid interaction model will be established to investigate the impact response and subsequent damage evolution. In which, the Smooth Particle Hydrodynamics (SPH) model is utilized to depict the constitutive relationship within the droplet, and Finite Element Method (FEM) is used to construct the Representative Volume Element (RVE) model of the blade leading edge. The impact process is simulated first to obtain the impact pressure distribution at the contact center and velocity field in the droplet. Furthermore, the stress wave propagation in the blade multilayer structure can be analyzed. Owing to the multiaxial fatigue feature of the continuous droplet impact, the continuum damage mechanics is integrated with the fatigue criterion and the Jump-in-Cycle procedure is used to simulate the high-cycle fatigue process. The damage factor distribution on the blade coating surface and its influence on mechanical properties are analyzed. Thereafter, the droplet impact fatigue life can be accumulated based on Miner’s linear rules. The theoretical achievements are validated by experimental data provided by Rain Erosion Testing (RET), which shows a good agreement between each other. As a result, V-N curves and D-N curves, i.e. quantitative relationship between droplet falling conditions and impact fatigue life, are established. The achievements in this study can provide an effective tool for rain erosion mechanism analysis and life prediction in industrial applications.

中文翻译：

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复合材料叶片在连续液滴冲击下的损伤演化模拟和寿命预测


海上风力发电因其在海域的高风能储量而成为可再生能源应用中一项很有前途的技术。为了提高能源改造效率，海上风电机组的叶片长度越来越大，这使得雨水侵蚀成为电机组运行中最常见的故障之一。由于自然降雨在空间和时间域上是随机的，因此很难准确描述雨水影响造成的损害演变过程。因此，定期和连续的液滴冲击模拟和实验为此问题提供了一种替代方法。考虑到叶片的复合结构和液滴的变形能力，将建立流固相互作用模型，以研究冲击响应和后续损伤演变。其中，光滑粒子流体动力学 （SPH） 模型用于描述液滴内的本构关系，有限元法 （FEM） 用于构建叶片前缘的代表性体积元 （RVE） 模型。首先模拟冲击过程，以获得液滴中接触中心和速度场处的冲击压力分布。此外，还可以分析叶片多层结构中的应力波传播。由于连续液滴冲击的多轴疲劳特性，连续损伤力学与疲劳准则相结合，并使用 Jump-in-Cycle 程序来模拟高周疲劳过程。分析了叶片涂层表面的损伤因子分布及其对机械性能的影响。此后，液滴冲击疲劳寿命可以根据 Miner 线性规则累积。 雨水侵蚀测试 （RET） 提供的实验数据验证了理论成果，表明彼此之间具有良好的一致性。结果，建立了 V-N 曲线和 D-N 曲线，即液滴下落条件与冲击疲劳寿命之间的定量关系。本研究成果可为工业应用中的雨水侵蚀机理分析和寿命预测提供有效工具。