Research On Signal Processing And Modal Parameters Identification Of Time-varying Under Ambient Excitation

The maintenance of Aircraft has a very important role in the aviation safety, and the continuing airworthiness of aircraft management and the link which is closely related in all aspects of the aircraft used also has the influence to aviation safety. In continuing airworthiness, how to monitor the aircraft and to realize its fast fault diagnosis is the issue which the world various Airline and the research institute concerned and modal parameters based on structural changes is the hot research in this area. This paper does research on modal identification of the time-varying systems on the aircraft under Ambient Excitation.When the aircraft structural damage or engine fail, the system modal parameters will change .The paper mainly study how to use the vibration response of time-varying to process an analysis, and reflecting aircraft structures modal parameter of the health status. This provides an important guarantee for the safety of aircraft.This paper aims at modal parameter identification of time-varying structures. The main work is as follow:(1) In signal processing, the first, Empirical Mode Decomposition (EMD) is introduced, including the theory of dissociation ,screening stop criterion and this method advantage and disadvantage. The second, the wavelet transformation is proposed and introduced the promotion algorithm, called second generation of wavelet transformation;.(2) The Hilbert and the ant colony algorithm schemes on empirical mode decomposition (EMD) are proposed to identify modal parameter of time-varying structures; (3) The Hilbert and the ant colony algorithm schemes on second generation of wavelet transformation are studied to identify modal parameter of time-varying structures.In order to verify the validity of the proposed method, the applications of the proposed method are illustrated using three degree of freedom systems with changing stiffness characteristics. Numerical simulation results demonstrate that the methods based on EMD and ant colony algorithm schemes based on second generation of wavelet transformation yield accurate results, but the Hilbert on second generation of wavelet transformation yield poor results.A simple-supported beam system with moving mass is built with ADAMS software, and the results obtained of the many kinds of plan were compared and analyzed. The studies indicated that the methods presented in this paper are able to effectively carry on the modal identification under ambient excitation.