Distributed Dynamic Load Identification Technology Of Thin-walled Structures

External load information is the key issue for the design and condition monitoring of engineering structures.Due to the limitation of measurement technology and the external environment,it is difficult to directly measure the dynamic load on structures in many circumstances.Load identification technology based on measured structural response is a very important tool for obtaining external excitation.Traditional dynamic load identification methods generally treat the external load as equivalent concentrated excitations.However,numerous kinds of dynamic load in engineering practice,such as the aerodynamic load on aircraft structures,the wave impact on offshore platforms,and the wind load on high-rise buildings,etc.,have the distributed and stochastic characteristics.Existing distributed dynamic load identification methods are only suitable for obtaining the distributed dynamic load on regular surfaces and they have poor accuracy and computational efficiency when identifying the special correlated distributed stochastic dynamic load.In this paper,new distributed dynamic load identification technologies on thin-walled structures are investigated to solve the above problems.Research work includes:First,aiming to solve the problem that existing methods cannot identify the distributed dynamic load on complex structural surfaces,a distributed dynamic load identification method based on subregion interpolation is proposed.By dividing the load application area into multiple subregions,the spatial function of the dynamic load is fitted by two-dimensional interpolation functions in each subregion.By using the modified system Green’s function,a transfer relationship between the coefficients of interpolation functions and structural responses is established,then the distributed dynamic load identification problem can be transformed into the problem of identifying coefficients of basis functions.Numerical simulations on a cantilever plate and a planar structure with complex geometry are conducted to validate the proposed method,and influences of measuring points,noise level,and sampling frequency are also discussed.Finally,the experimental verification on a three-dimensional plate structure is also conducted to show the effectiveness of the proposed method.Results show that the proposed method has better adaptability on the types of load distribution and structural configurations than the existed methods,and the identification algorithm has a certain degree of resistance to noise.Secondly,aiming at solving the problem that existing methods have poor accuracy and computational efficiency when identifying the special correlated distributed stochastic dynamic load,a novel method to identify the cross power spectral density function in the distance space is proposed for spatial correlated distributed stochastic dynamic load identification.The two-dimensional Legendre polynomials are adopted to represent the power spectral density function of the correlated distributed stochastic dynamic load,then the relationship between the coefficients of the orthogonal polynomial and the auto power spectral density function of the structural responses is established in the frequency domain.Via the identification of the coefficients of the orthogonal polynomial from the auto power spectral density function of the structural responses,the distributed random dynamic load is reconstructed.Numerical simulations on a simply supported plate are conducted to validate the proposed method,and influences of measuring points,noise level,correlation length of the load are also discussed.Results show that the load identification algorithm has a certain anti-noise ability,and the accuracy is related to the correlation length of the load.Furthermore,through the identification of the turbulent boundary layer excitation on a simply supported plate and the gust load on the three-dimensional wing structure,the effectiveness of the proposed method for complex loads and complex structure cases is verified.Finally,a non-stationary stochastic dynamic load identification method considering spatial correlation is proposed.The distributed random dynamic load is regarded as a multi-dimensional non-stationary random process,by representing the special distribution function of the stochastic dynamic load using the linear superposition of the two-dimensional Legendre polynomials,the random load identification problem is transformed into the deterministic load identification problem with the implementation of K-L expansion on the random process and the orthogonal properties held by the random variables.The relationship between the polynomial coefficients and the K-L components from the covariance kernel of structural responses can be constructed,hence the distributed random dynamic load can be reconstructed from the identified polynomial coefficients.Numerical simulations on a simply supported plate are conducted to validate the proposed method,and influences of measuring noise,truncation order in the K-L expansion of the response,correlation length of the load are also discussed.By identifying the non-stationary gust load on a three-dimensional wing structure,the feasibility of the proposed algorithm of identifying the non-stationary distributed dynamic load identification on curved thin-walled structures can be verified.