Study On Operational Modal Shape Estimation Of Time-varying Structural Dynamic Systems

With continuously developing of engineering structures,the dynamic characteristics of time-varying structures is becoming one of the focuses.Modal parameter estimation for timevarying structural dynamic systems have gradually become a hot topic in the field of structural dynamics of aerospace vehicle.Furthermore,mode shapes of time-varying structural dynamic systems have important significance for the structural design,vibration control,damage detection and health monitoring.According to the requirements of mode shape estimation for engineering time-varying structures,this paper proposes a parameterized time-dependent partial fraction model to describe time-varying structures.Based on that parameterized model and expanding the least squares frequency domain method(LSFD)in the frequency domain into the joint time-frequency-domain,a least squares time-frequencydomain(LSTFD)operational mode shape estimator for linear time-varying structures is proposed.Moreover,the time domain method based on functional series time-dependent autoregressive moving average(FS-VTARMA)model is studied and modified to estimate mode shapes of the time-varying structural dynamic systems.Based on the experimental data,the proposed least squares time-frequency-domain operational mode shapes estimator and the FS-VTARMA-based method are analyzed and validated.The research results can provide theoretical basis and technical supports for modal shape estimation for time-varying engineering structures.This paper studies on mode shape estimation method of time-varying structural dynamic systems in joint time-frequency domain.In order to solve the potentially existing problems,the following works are mainly carried out:(1)The research progress and the classic methods of modal parameters estimation of time-varying structures are introduced to supply the primary support for the further research on the theory and methods of time-varying structural mode shape estimation.(2)The basic theory and research methods involved in mode shapes estimation of time-varying structures are summarized,which supply the basis and assumptions for mode shape estimation of time-varying structural dynamic systems.(3)Based on the parameterized mode shape estimation method of time-invariant structures in the frequency domain,a parameterized partial fraction structural dynamic model is established.A least squares time-frequency-domain(LSTFD)method for time-varying structures is proposed based on the time-invariant least squares frequency domain(LSFD)method.(4)A time-varying structural modal shape estimation method is proposed based on solving eigenvalues and eigenvectors of time-dependent auto-regression coefficients of the functional series time-dependent autoregressive moving average(FS-VTARMA).(5)Based on a cantilever beam-like time-varying structure with a movable mass,a series of “configuration-frozen” reference experiments and a continuous-time structural dynamic experiment for the time-varying structure are carried out.The method presented in this thesis is validated by these experiments,and compared with the classical time-domain method.