EFFICIENT METHOD FOR FATIGUE TESTING MULTI-MEGAWATT COMPOSITE WIND TURBINE BLADES USING RESONANT EXCITATION

摘要

A new dynamic testing system for fatigue testing full-scale wind turbine blades has been analyzed. The new system overcomes problems associated with conventional resonance testing and forced hydraulic loading methods. Similar to conventional resonance methods, the new system generates an excitation force that coincides with the fundamental flap frequency of the blade system, but a linear hydraulic actuator replaces an eccentric rotating mass. Simultaneously, forced hydraulic loading in the lead-lag direction allows biaxial loading. Calculations show that the mean and alternating flap moments along the blade can be tuned to match a linear distribution prescribed by a single-point forced hydraulic load method by adding masses at specific spanwise locations. For the 1.5-MW blade analyzed, an excitation force of 1779-N (400 lbs) at a frequency of 0.76 Hz was required. An oversized 66.7-kN (15-kip)/0.508-m (20-in.) double-ended actuator and a 410-kg (904-lb) reciprocating mass were selected to satisfy these flap actuator requirements. The new test system uses less hydraulic fluid than conventional forced loading systems and increases the test cycle frequency. Maintaining equal test time, the previous method requires a flow rate of 1400 LPM (370 GPM) compared with 556 LPM (147 GPM) for the resonance test system. This reduces the requirements of the test apparatus and the energy needed to perform a test by a proportional amount and can potentially increase the test's accuracy.