【作者】 张丽霞；

【导师】 潘际銮；

【作者基本信息】 清华大学 ， 材料科学与工程， 2010， 博士

【摘要】 大型水轮机组运行中转轮叶片出现的裂纹问题是水轮机设计和运行部门亟待解决的关键课题之一。工程上按水轮机运行状态将叶片上的疲劳裂纹分为两类:快速疲劳裂纹和损伤累积疲劳裂纹。由于转轮叶片工作载荷和几何构型的复杂性,还没有成熟的叶片疲劳裂纹控制方法。本文以预防和预测这两类裂纹为目标,提出了基于动载面力下复杂空间曲面结构的控制疲劳裂纹发生的系统方法,为工程应用提供理论基础。为了避免卡门涡等激振力频率与叶片固有频率接近发生共振产生快速疲劳裂纹,本文以相邻两流道中心面为周围水体边界,建立了叶片在水体中固有频率的计算模型,得出了水体对叶片固有频率的降低系数具有非线性且降低的幅度主要与叶片构型和振动模态有关的结论。应用捶击法对模型水轮机叶片的模态进行实验分析,验证了模型和方法的有效合理性,为转轮叶片在几何构型设计上控制快速疲劳裂纹的发生提供了技术支持。论文深入研究了水轮机组预期寿命内基于概率统计与模型的疲劳累积损伤裂纹的预防控制理论和方法。根据水轮机组运行工况复杂多变的特点,提出了叶片载荷谱的确定和处理、根据水力载荷计算应力-时间历程进行叶片薄弱环节的选择、基于von Mises屈服准则的叶片高周疲劳等效损伤参数、叶片材料的二维疲劳强度分布、采用二维统计参量的剩余强度和疲劳累积损伤的疲劳可靠性分析模型的方法,实现了叶片疲劳损伤裂纹的预防和预测计算。在上述理论研究的基础上,分析了水轮机叶片在非定常流场压力下应力历程数值计算方法以及编制应力载荷谱的方法流程。采用雨流计数法、最优化参数估计和权系数法获得了叶片在各典型工况下合成后的疲劳应力二维概率密度函数。针对计算模型的复杂性提出了采用Monte Carlo试验模拟方法求解的有效数学模型。最后以典型转轮叶片为例,详细分析转轮叶片的疲劳裂纹控制流程,通过理论计算分析和疲劳试验验证了将二维概率Miner准则和二维应力-强度干涉模型应用到混流式转轮叶片疲劳寿命预测上具有良好的效果。应用所研究的叶片疲劳裂纹控制理论与方法,开发了混流式转轮叶片疲劳裂纹控制系统软件平台。更多还原

【Abstract】 The issue of runner blade cracking of large-sized hydropower units during the operation conditions has become one of significative tasks that should be urgently resolved for departments of design, research, manufacture and operation. Study on the cracks in the operating blade shows that there are two kinds of fatigue cracks: rapid resonance cracks and fatigue damage cracks. Due to the complexity of working loads and the geometry of runner blade, however, well accepted method is still not available to guide the cracks prevention and control design in the open area. This dissertation aimed on the prevention and control of two kinds of blade cracks so as to develop the cracks prevention and control method of complex curved surface under the dynamic pressure on the surface.In order to avoid the influence of abnormal vibration induced by Karman vortex on rapid cracks, the algorithmic equation of dynamic and fluid-structure interaction (FSI) vibration characteristic are set up in this paper, and the conclusions are that water influenced coefficients on the natural frequencies of blades are nonlinear reduced with the geometry and the mode of blades. Lastly, effectiveness of the proposed model and method was demonstrated using the experimental modal analysis on the model Francis blade by using hammer-hitting pulse excitation method and FFT analysis, which provided technology support for the geometry design of blade to prevent and control of rapid cracks.The control design method and theory is deeply researched in this paper to prevent the fatigue damage cracks in various operation conditions。According to the characteristic of the complex operation conditions of the hydropower units, five theories and methods are proposed in the fatigue reliability analysis of the blade under random stresses spectrum, the determination and processing to the pressure load spectrum, the transformation of the pressure load to the stress history to find the dangerous area on the blade, an effective damage parameter of the high cycle fatigue based on von Mises yielding criterion and the P-Sa-Sm-N fatigue surface of the blade material, the two fatigue reliability analysis model of the fatigue accumulated damage and residual strength for the 2-D statistical parameters of stress mean and amplitude. At last, the predictive and control design calculation is realized to prevent the happen of fatigue damage cracks.Based on above theories, the method of the unsteady stress of the blade in the unsteady incompressible turbulence flow calculated by numerical simulation is determined and the process of load spectrum compiling is analyzed. the distribution of dynamic stress and displacement in the blade are obtained. The fatigue stress has been counted and deals with in statistics methods, synthesized and extended with these theories and method, including the advanced rain flow counting method, optimal method of estimation to parameters in forecasting model, the weight coefficient method. And numerical simulation by Monte Carlo method is made to calculate the complex mathematic modal.At lastly, take some typical turbine blades as study cases, a theoretical framework for the evaluation and control of cracks is formed. It is proved that the 2-D probabilistic Miner’s rule and 2-D stress-strength interference model are more reliable and effective to forecast the fatigue life by theoretical calculated and fatigue experiment. Based on the research results, a software system for hydraulic turbines blade‘s cracks control is developed.更多还原