Additional Virtual Mass Damage Identification Method Based On Narrow Band Frequency Responses

Dynamic-based damage identification method is one of all important methods for structural damage identification.Among them,the method of using the dynamic response to construct additional virtual mass can increase the amounts of structural test modals and improve the sensitivity of structure to damage,thus has a good prospect.However,constructing virtual mass tends to utilize the wide band frequency response.When the excitation frequency band is narrow,the natural frequency of the structure with additional virtual mass may not be within the excitation frequency band,and it may not be possible to obtain additional virtual mass values.To solve this problem,the additional virtual mass method based on narrow-band frequency response is studied.The main research contents are as follows:(1)Develop additional virtual mass methods based on narrow band frequency responses.First,this thesis introduces the principle theory of the additional virtual mass method,proposes the concept of target frequency,and explains the process of damage identification using narrow band frequency response.This method can utilize one or more points of the structure frequency responses to identify the damage,without relying on the structural entire frequency responses.Furthermore,an approximate finite element model of track and sleeper is established in this thesis to explore the damage identification method for track structures under simple harmonic excitation.The results show that the proposed method can identify the damage of the track structure well.Finally,the effectiveness of the method is verified by a truss structure experiment.(2)Design simple harmonic excitation exciter and numerical simulation of simply supported beam.First,to obtain stable and accurate narrow band excitation,according to the principle that in any direction,the projection of the inertial force generated by eccentric masses rotating at a constant speed outside the center of gravity is the simple harmonic force,the simple harmonic excitation exciter is designed.It can record excitation and response data at the same time.Moreover,based on the designed exciter,this thesis establishes a coupling model of the exciter and simply supported beam,and uses the excitation generated by the exciter to research the damage identification of the structure under simple harmonic excitation.The results show that under the simple harmonic excitation of the exciter,the damage location and degree of the simply supported beam structure can be well identified.(3)Frame structural damage identification experiment based on narrow band frequency response and Bayesian method.Due to the uncertainty of measurement information and the influence of environmental noise,this thesis proposes a narrow band frequency response damage identification method based on Bayesian theory.Using multiple sets of frame experimental data,this thesis gives the probability distribution of the frame’s damage factor.The results show that the identified damage factors are mainly distributed near the true value of the damage factors,and the damage identification results are accurate.