Abstract. In order to meet the requirements of large-blade fatigue testing, a horizontal dual-point linear exciter loading program is developed. In this paper, Lagrange's equation and FEM method are used to simulate the dual-point excitation theory model. The horizontal dual-point excitation characteristics of the blade are validated by the experimental method. The relationship among the dual-point exciting force, cycle time and bending moment during blade fatigue test in flap wise direction is studied. The advantages of horizontal dual-point excitation in blade fatigue test are analysed. Compared with vertical single-point excitation when the equal bending moment is reached, the exciting force and energy consumption required for dual-point excitation are reduced by 60.0% and 96.8%. Resonant frequency of the test system is improved by reducing the dead weight because of dual-point horizontal excitation. The entire blade fatigue test time is shortened by 7.4%. The use of horizontal dual-point excitation could save energy and shorten the entire fatigue test time.
Abstract.The reliability of large blades should be verified by means of full scale fatigue test. In order to solve the problem of lack of exciting force during fatigue test in the flap wise direction, the program that aerodynamic fairing is installed in the tip of blade to reduce the air resistance is proposed. The numerical model of blade vibration and damping ratio calculation is established. The relationship between damping ratio, exciting force and amplitude is constructed by finite element method respectively. The difference of the exciting bending moment of blade and the damping ratio before and after the installation of aerodynamic fairing is compared respectively. The results show that damping ratio decreased by 27.9%. When the vibration of the blade reaches the target bending moment, the exciting force of the equipment decreases by 45.4%. It is an effective way to reduce the exciting force.
Wind turbine blades have to withstand the rigorous test of 20-25 years of service. Fatigue testing is an accurate method used to verify blade reliability. Multi-point excitation could better fit the fatigue damage distribution, which reduces the power output of a single exciter and saves testing energy consumption. The amplitude, phase, and frequency characteristics of the fatigue test system and, moreover, the relationship between the excitation force, damping, and the amplitude variation of the blade, are analyzed by the Lagrangian equation and the finite element simulation method. The full-scale fatigue test of an equivalent full cycle life in the flapwise direction is carried out by multi-excitation. When the frequency and phase of the multi-point exciters are consistent, the maximum vibration effect can be exerted. When the phase difference of the dual exciters is 180 • , the vibration effect produced by the dual exciters can be equivalent to each other. The blade amplitude is proportional to excitation forces, while inversely proportional to the damping ratio. The bending moment deviation of the blade is controlled within 9.2%; moreover, the energy consumption is 40% lower than that of the single-point excitation. The use of multi-point excitation allows loading the blade with high precision, stable operation, and low cost, which provides the theoretical and experimental basis for the fatigue test of large wind turbine blades.Keywords: fatigue test; wind turbine blade; multi-point excitation; damage distribution; the equivalent fatigue life cycle Highlights: (1) The multi-point excitation fatigue testing method renders an equal fatigue damage distribution with a higher degree of fidelity; (2) The program fits the fatigue damage distribution by adjusting the parameters of multi-point exciters rather than tuning masses, which could reduce each exciter power and save energy; (3) The multi-point excitation has the characteristics of high loading accuracy and stable operation, which are able to meet the large blade fatigue test requirements by adding exciters.
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