Study On Effect Of Stress Stiffening And Damage On Modal Parameters Of Wind Turbine Blade

This thesis mainly studies the influence of stress stiffening and damages on modal parameters of wind turbine blades. Specifically, the Stress Stiffening Effect of rotating blades was analyzed and then a modal experiment of rotating blades was completed, including testing damaged blades under rotating condition. The main research work is as following:(1) The mechanism of Stress Stiffening Effect of rotating blades was analyzed, and geometric stiffness matrix of Stress Stiffening Effect based on finite element theory was deduced to quantitatively study the influence of Stress Stiffening Effects on rotating blades. It was simplified that a blade to a thin plate, calculating the relationship between blade natural frequencies and rotational speeds through an ANSYS model, finally finding that the result that Stress Stiffening Effects increases the blade natural frequencies and nonlinear relationship between blade frequency with speed. Besides, four damaged rotating blade models were built for damage detection considering Stress Stiffening Effect.(2) Modal experiment of rotating blades was conducted and accelerometers and strain gauges were arranged on blades, simulating four damage conditions of rotating blades, vibration responses under different wind speeds were measured. The variation rules of blade frequencies under different wind speeds and damage extents were obtained. Finally, FFT was used to demonstrate Stress Stiffening Effects and verify damage detection results.(3) Considering various errors using frequency method in damage detection of blades, stochastic subspace identification method was used to detect blade damages. Then damage indexes of rotating blades under different damage conditions were calculated. From the variations of damage indexes, damages in rotating blades can be detected.