| 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.
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