Applied Investigation Of The Modal Identification For Engineering Structures Undergoing Ambient Excitation

The modal parameter identification of large engineering structure has a important sense to applied civil engineering such as health monitoring, structure damage estimate, active control (fuzzy control), etc. It is difficult to exert artificial excitation and difficult to measure excitation signal on large engineering structures for them having huge volume, mixed material, complex bind condition, etc. So it is not easy to use traditional modal parameter identification technology with testing input and output signal on large engineering structures. Having theory reliability and engineering applied feasibility, the ambient excitation method to identify large structure modal parameter is widely used in engineering for it can identify structure modal parameter in time domain or frequency domain only requiring analysis output data with mechanics and mathematics theory.Two modal identification methods undergoing ambient excitation are investigated for the object of large structures based on modern experimental modal analysis theory and ambient vibration technology. Stochastic subspace identification is improved in modal accuracies and in calculating stability. The new stochastic subspace identification method can be used in non-stationary signal domain. Special research and analysis is focused on cross-point spectrum modal parameter identification method in the field of presenting a rounded parameter identification method in which can be used with existent testing instruments and with the FFT technology. After integrating characteristic of the two methods, the dissertation presents a theory and engineering applied mode aiming at modal parameter identification of large engineering structure. The theory reliability and engineering applied feasibility of the modal parameter identification methods presented by the paper are validated through some experiments and simulation computes of engineering structures. The basic theories of the ambient excitation modal parameter identification in time domain or frequency domain are roundly investigated, and their advantages and disadvantages are discussed. Some familiar ambient excitations of large engineering structures are investigated and a flow is presented to examine the input signal's stationary characteristics. Modal parameter identification of large structure undergoing non-stationary excitation is the next important research domain for the presupposition of excitation signal being close to reality, so it is discussed in this paper.The research results of this paper show that the modal parameter identification undergoing ambient excitation presented by the paper can identify large engineering structure modal parameters fleetly,economy and efficiently.