Research On Inverse Pseudo Excitation Method For Random Dynamic Loading Identification And Its Application

The external dynamic load information of structure plays an important role in structure overall design,strength check and environmental prediction.In practical engineering,limited by shape design,sensor installation arrangement and external environment,external dynamic load information of the structure cannot be measured directly by force sensors.But vibration responses of structure in some positions can normally be measured directly,and modal information of structure can also be obtained by finite element simulation or modal test.Therefore,it is an effective way to identify external dynamic load information by vibration response and structural modal information.At present,researches on load identification in time domain,such as period and impact loads,have become mature and perfect.But there are still some problems that have not yet been solved well in random dynamic loading identification in frequency domain.The research progress of dynamic loading identification methods and engineering applications is summarized.Starting with the original methods of random dynamic loading identification,unsolved problems in existing random dynamic loading identification methods are pointed out.Such as,compared with the real load power spectrum,identified random dynamic load power spectrum fluctuates largely near some natural frequencies of structure.Reasons for these problems are analyzed and summarized.Addressing these issues,it is determined that the main research contents of this paper include study of improved random dynamic loading identification method,numerical simulation verification or experimental verification,and equivalent identification of aerocraft fluctuating pressure.The following research achievements are got:In original inverse pseudo excitation method for random dynamic loading identification,there is a problem that frequency response function matrices near natural frequencies of the structure are ill-posed.In order to solve this problem,the mathematical weighted average technique is introduced to improve and optimize the original identification method.With the help of weighted average technique,the role of ill-conditioned frequency response function matrix components in the process of random load identification can be effectively weakened.So as to reduce their influence on identification accuracy of random dynamic load in order to improve identification accuracy.The multi-input and multi-output random vibration verification tests of cantilever beam structure and thermal protection and insulation load-bearing composite plate structure are carried out respectively.At the same time,the applicability of the improved method is extended while two different structures are verified.In engineering and test,the measurement process of structural model information and needed response information for load identification is bound to be affected by experimental operation,experimental surrounding environment noise and vibration sensor measurement accuracy,which leads to the measured information containing certain measurement errors.In this paper,on the basis of inverse excitation pseudo method for random dynamic loading identification,the error terms of model measurement and response measurement are introduced at the same time,the error sources of random dynamic loading identification results are deduced,factors that affect identification accuracy are summarized and analyzed.Afterwards,ways and methods to improve identification accuracy are proposed.Finally,to achieve the objective of improving the accuracy of random load identification,condition number of frequency response function matrix is reduced and its performance is improved by introducing diagonal coefficient matrix.The feasibility and effectiveness of the improved method are verified by numerical simulation and experiment of cantilever beam structure and multi-input and multi-output random vibration test of thermal protection and insulation load-bearing composite plate structure.The low frequency band of fluctuating pressure in transonic section is close to the low order modes of aerocraft structure,which will cause the vibration of inner precision instruments and fatigue failure of the structure.The fluctuating pressure information in transonic phase cannot be measured directly in practical engineering.In this paper,equivalent identification problem of fluctuating pressure on shoulder in transonic phase of aerocraft is deduced and explored.Firstly,fluctuating pressure distribution on shoulder in transonic phase of aerocraft is simplified,and fluctuating pressure equivalent identification scheme is proposed.Then the proposed scheme is applied to equivalent identification of fluctuating pressure on shoulder of a cone-cylindrical aerocraft in transonic phase.The identification results of fluctuating pressure are forward verified by the measured flight telemetry acceleration response.