抽水蓄能电站钢岔管月牙形几何边界周期性高应力的演化机制

The crescent geometric boundary of steel bifurcated pipe is in state of cyclical high stress in the long term and it easily leads to low-cycle fatigue cracks. It is because of cyclical hydraulic pressure in runner system of pumped storage hydroelectric power plants. This research programme will take a new look at steel bifurcated pipe in pumped storage hydroelectric power plants. Physical model test, analytical method and FEM-based numerical simulation will be performed to clarify the composition and evolution rule of local high stress at crescent geometric boundary. PID control technology will be employed, in order to overcome difficulty of manual operation and low load stability because of many inner hydraulic pressure cycles. Damage plastic model and bilinear kinematic hardening model will be respectively used to describe constitutive relation of concrete and steel when numerical simulation is performed. It is focused on two issues which are non-uniform distribution of concrete cracks and angular distortion geometric imperfection at crescent geometric boundary. To easily identify geometric parameters of angular distortion, beam model will be used to simplify pipe shell with angular distortion geometric imperfection in analytical method. The results can provide vital support for anti-fatigue design and fatigue life prediction of steel bifurcated pipe in pumped storage hydroelectric power plants. The findings have important implications for development of research into fatigue mechanics in runner system of hydropower station.

抽水蓄能电站流道系统内频繁的水压循环作用使得钢岔管月牙形几何边界局部长期处于高应力循环状态，极易造成此处萌生低周疲劳裂纹。本项目以抽水蓄能电站中的钢岔管结构为研究对象，开展物理模型试验、有限元数值模拟和理论研究，澄清钢岔管月牙形几何边界局部高应力的组成成分和演化规律。物理模型试验拟采用PID控制技术解决内压循环次数较多所带来的手动操作困难和加载稳定性低的问题；数值模拟拟采用损伤塑性模型和双线性随动强化模型分别描述混凝土和钢材的本构关系，聚焦于混凝土裂缝的非均匀分布和钢衬月牙形几何边界处的角变形几何缺陷；理论研究拟采用梁模型模拟含角变形几何缺陷的焊接管壳，克服含角变形管壳几何体型描述参数较多所带来的实际量测困难。研究成果可为抽水蓄能电站钢岔管的抗疲劳设计及疲劳寿命预测提供科学依据，以期推进水电站流道结构疲劳力学研究的发展。

抽水蓄能电站频繁的内水压力循环作用使得钢岔管月牙形几何边界长期处于高应力循环状态，极易造成低周疲劳失效。本项目首先围绕“内水压力作用下钢岔管的传力行为”这一科学问题，采用非线性有限元数值模拟技术分别建立了考虑钢岔管外部不均匀约束和均匀约束的数值模型，并借助原型监测验证了有限元预测结果的可靠性，结果表明，相比之下考虑外部不均匀约束条件的数值模拟方法在预测钢岔管月牙形几何边界传力行为方面表现更优。数值模拟成果揭示了月牙肋可以改变钢岔管内水外传的路径，月牙肋虽然并非呈现规范提倡的轴心受拉状态，但受力状态良好，钢衬外围混凝土出现较高程度的开裂损伤，但由于其仅在钢衬与围岩之间起传力作用，因此建议在埋藏式钢岔管的结构设计中无需过分关注混凝土的开裂问题。然后，采用S-N曲线方法给出了钢岔管的低周疲劳寿命，结果表明在抽水蓄能电站有效运行期内不能排除出现低周疲劳失效的风险。研究成果揭示了抽水蓄能电站钢岔管月牙形几何边界局部高应力的形成演化机制，可以为抽水蓄能电站钢岔管的抗疲劳设计提供科学依据。