水流激励下转轮叶片的振动与裂纹耦合机理及安全评估方法研究

The vibration and cracks of runner blades not only seriously affect their normal work, but also directly affect the stable operation of hydraulic turbine-generator unit. Therefore, it is a great urgent task to deeply study the vibration characteristics of runner blades and the mechanism of fatigue crack formation and propagation of runner blades in order to ensure that the hydropower station can work well. So the purpose of this project is to study the vibration-crack interaction mechanism and safety assessment method of runner blades exerted by the hydraulic excitation. Firstly, based on the fluid-structure interaction relation and crack characteristics of runner blades under the hydraulic excitation, the nonlinear fluid-structure interaction dynamic equations of runner blades are established by the finite element methods, which can reflect the characteristics of fluid, structure, crack and dynamics of runner blades. Secondly, based on the nonlinear vibration theories and the fracture mechanics, the vibration characteristics of runner blades and the dynamic characteristics of cracks of runner blades are studied, when the runner blades are subjected to the hydraulic excitation. Thirdly, based on the dynamic equations of runner blades, the intrinsic relations among the dynamic characteristics of runner blades and the hydraulic parameters, structural parameters and cracked parameters are discovered. Fourthly, the vibration-crack interaction mechanism of runner blades is obtained by analyzing the nonlinear fluid-structure interaction vibration and the dynamic characteristics of cracks of runner blades. Finally, according to the theory of safety system engineering, the safety assessment method of runner blades is determined based on the vibration-crack interaction relation of runner blades. The above studies can provide actual theories for the designing, manufacturing, running and controlling of runner blades.

转轮叶片的振动与裂纹问题不仅严重影响到其自身的正常工作，更直接关系到水轮发电机组的安全稳定运行，因而积极开展有关水轮发电机组转轮叶片的振动特性及其疲劳裂纹形成与扩展机理等问题广泛而深入的研究，对确保水电站安全高效运作是十分迫切的任务。本项目在分析水流激励下转轮叶片流固耦合关系以及转轮叶片疲劳裂纹特征的基础上，应用有限单元法建立能全面反映转轮叶片水力、机械、裂纹故障和动力学状态的非线性流固耦合动力学方程，根据非线性振动理论和断裂力学理论研究转轮叶片在水流激励下的振动规律及其疲劳裂纹动态变化规律，探明转轮叶片的振动行为与水力参数、结构参数、裂纹故障参数之间的内在关系，揭示水流激励下转轮叶片的振动与裂纹之间的耦合机理，进而根据安全系统工程理论确定转轮叶片的安全评估方法，从而为转轮叶片的设计、制造、运行及控制等提供更多和更加接近客观实际的理论依据。

水轮机转轮叶片的振动与裂纹问题不仅严重影响到其自身的正常工作，更直接关系到水轮发电机组的安全稳定运行，因而积极开展有关水轮发电机组转轮叶片的振动特性及其疲劳裂纹形成与扩展机理等问题广泛而深入的研究，对确保水电站安全高效运作是十分迫切的任务。本项目以水轮机转轮叶片为研究对象研究其振动疲劳问题。首先，根据水轮机转轮叶片准三元反设计的特点，应用有限单元法构建动静干涉作用下和尾水管涡作用下的转轮叶片动水压力分布规律数学模型，探明转轮叶片动水压力分布规律；然后，考虑疲劳裂纹对转轮叶片刚度的影响以及水流激励对转轮叶片的作用，应用有限单元位移法建立含裂纹的转轮叶片动力学方程，继而应用Pairs疲劳裂纹扩展曲线模型构建转轮叶片的振动疲劳耦合模型，并通过实例进行验证；第三，在所建转轮叶片振动疲劳耦合模型的基础上，应用非线性振动理论和断裂力学理论研究转轮叶片在水流激励下的振动规律和疲劳裂纹动态变化规律，探明转轮叶片的振动行为与水力参数、结构参数、裂纹故障参数之间的内在关系，揭示转轮叶片非线性流固耦合振动与疲劳裂纹之间的耦合机理；第四，考虑呼吸裂纹表面接触力对振动疲劳特性的影响，从微细宏观角度分析转轮叶片疲劳损伤的物理过程，探明转轮叶片振动疲劳过程中的微观断裂机理；第五，在所建转轮叶片振动疲劳耦合模型基础上，分析水流激励下转轮叶片的疲劳裂纹扩展规律，探究疲劳裂纹对转轮叶片极限强度的影响，揭示振动疲劳影响下转轮叶片极限强度的动态变化规律；第六，根据转轮叶片在不同工况条件下水流激励所具有的不同特性，考虑转轮叶片流固耦合振动与疲劳裂纹之间的耦合效应，构建基于振动疲劳特性的转轮叶片可靠性安全评估模型，确定基于振动疲劳特性的转轮叶片可靠性安全评估方法。本项目的研究成果为水轮机转轮叶片的振动疲劳特性分析、运行控制、安全评估以及疲劳可靠性设计等提供更多和更加接近客观实际的理论依据。