Study On Operational Modal Analysis Method Based On Power Spectrum Density Transmissibility Function

In the field of engineering vibration,modal parameters are the key attributes of the structures,and modal analysis is necessary to obtain modal parameters.Currently,the Operational Modal Analysis(OMA)technique is widely studied and applied because it does not need to measure excitation data,thus reducing the difficulty of experiment.Typical large structures,such as wind turbine blade,have so-called harmonic input problem under operating conditions,which challenges the wide application of OMA technique.Transmissibility-based OMA(TOMA)method has been proposed in the past ten years,which can identify structure mode according to the response data of multiple load conditions,and at the same time,this method can solves the harmonic input problem,which has become a hot topic in current research.As one of the branches of TOMA method,Power Spectrum Density Transmissibility(PSDT)and PSDT-based OMA(PSDTOMA)is a new concept and method emerged in recent years.It is generally believed that PSDTOMA method inherits the advantages of TOMA method and has a remarkable feature of extracting modal parameters only based on response data of a single working condition,so it has good potential for solving the harmonic input problem of wind turbine blades.For this reason,this paper takes PSDTOMA method as the core,combined with the practical application of wind turbine blade,and systematically studied it from the aspects of basic theory,application effect and calculation method.It mainly includes the following work and conclusion:First of all,starting from the basic definition of PSDT,three expressions of PSDT were derived based on the response information,excitation and system characteristics,excitation coherence,the properties of PSDT under different excitation coherence conditions and the basic principle for extracting modal parameters by PSDTOMA method are researched,meanwhile the applicability of PSDTOMA method was further studied.And then,numerical examples and physical experiments were used to verify these conclusions;Secondly,the wind load characteristics of blades in different operating condition were obtained by means of numerical simulation,and PSDTM-SVD method was used to extract modal parameters of the blade,thus the applicability problem of PSDTOMA method was found and further analyzed.The results showed that the PSDTOMA method can be directly applied to non-rotating blade,but it still cannot solve the harmonic input problem of rotating blade,this method needs to be improved;Finally,in order to provide foundation for the research and improvement of PSDTOMA method,the pseudo Frequency Response Function matrix based on PSDT was studied and pseudo output response matrix was proposed.Meanwhile,PSDT-FSDD(FSDD of PSDT)method was proposed by combining Frequency-Spatial Domain Decomposition(FSDD)method,and five degrees of freedom system numerical example was used to compare these methods.The results showed that PSDT-FSDD method has the same precision as FSDD method.