Modal Parameter Identification Of Mechanical Systems Based On HHT Method

Based on the "Research on Vibration Modal Analysis of Rotating Machinery Based on Empirical Mode Decomposition Method" (National Nature Science Fund Project, No:50675194), and the "Research on the Condition Monitoring and Fault Diagnosis Techniques and its Application System of Supercritical and Ultra-supercritical Steam Turbines and Pressure Generating Untis" (High Technology Research and Development Program of China, No:2008AA04Z410), aiming at modal analysis of mechanical systems, introduced Hilbert-Huang transform (HHT) method into modal parameter identification. Taking simply supported beam as the research object, applied finite element analysis, experimental modal analysis with HHT method to identify the modal parameters, and then proposed a new method based on ICA-HHT which can identify the modal parameters more effectively. The details were as follows:In chapter one:Introduced the background and significance about modal analysis, discussed the research situation and existing problems of modal parameter identification method. And then introduced HHT method into modal analysis for mechanical systems.In chapter two:Expounded the basic theory and development process of the HHT method. Studied the vibration characteristic of the one-degree-of-freedom systems and multi-degree-of-freedom systems, applied the HHT method to process simulated vibration signal of those systems and the result verified the validity of the HHT method in extracting vibration mode components of the mechanical systemsIn chapter three:Analysised the vibration characteristics of a kind of typical mechanical vibration system—simply supported beam theoretically. Performed modal analysis, harmonic analysis and transient dynamic analysis by ANSYS, proceeded the transient responses obtained by transient dynamic analysis with empirical mode decomposition (EMD) and ensemble empirical mode decomposition (EEMD) method, and then used Hilbert transform (HT) to indentify the modal parameters from intrinsic mode functions (IMF).In chapter four:The IMF obtained by EMD method might have mode mixing problem and it might lead to relatively large identification error. Aimed at these shortcomings, proposed a new method based on EEMD-ICA-HT to improve the recognition performance. Finally appiled ICA-HT method to process several transient response signals from different nodes and it turned out to be have good identification result.In chapter five:Conducted impulsive excitation experiments on the typical mechanical vibration system—simply supported beam using impulse hummer, developed a modal parameter identification system with HHT method. Then got the transient response, used the method proposed in this thesis to identify the modal parameters, and acquired good recognition performance.In chapter six:Summarized the research results and problems existing problems in this thesis, and then pointed out the future research direction.