Helicopter Vibration Load Identification Using Inverse Pseudo Excitation Method

A helicopter works in a complex flow environment with many kinds of couplings fromaerodynamic, inertia, structure and geometrical. As a result that determination of helicopter vibrationload is a difficult task in the research field of helicopter. The helicopter vibration loads are importantparameters in design, producing and test, directly related to design and test of helicopter structure andeach component. From that, it is very necessary to develop the helicopter vibration load identificationmethod for helicopter design, manufacturing, monitoring and maintenance.In order to identify the helicopter vibration load, this paper offers load identification methods infrequency domain, including frequency response function inverse method, modal coordinatetransformation method and inverse pseudo-excitation method. And using Gaussian eliminationmethod by the characteristics of multiple input output system to estimate the frequency responsefunction is a better way to measure noise suppression and improve identification accuracies.The inverse pseudo-excitation method is applied to random and periodic loads identification withsome simulations and experiments. It proves that this method is accurate and feasible. The analysisresults show that this method has a higher accuracy in the periodic load identification. And therandom load identification error is less than5%, but some beating has been found near the naturalfrequency of vibration (especially in the low frequency area). This error comes from morbid matrix inthe inverse problem solving process. Weighted average method and singular value decompositiontechnique will markedly reduce the effect to the identification results by the matrix. And choosingsome suitable combination point will also raise the identification accuracy. Finally, use the inversepseudo-excitation method to identify the helicopter vibration load. The results show that the frequencycomponents of hub load include the fundamental and the second order passage frequency from themain rotor, and frequency components of the tail rotor load not only include the fundamental and thesecond order passage frequency but also contain the frequency of tail rotor speed.Inverse pseudo-excitation method can greatly reduce computation and obtain higheridentification accuracy. But this requires good frequency response function matrixes which aredetermined by the accuracies of simulation models and experimental data.