Research On Model Updating And Validation Of Bolt Jointed Structures Based On Multi Dynamic Responses

Modeling and simulation(M&S)plays an increasingly important role in many aspects of engineering practice as the requirements for structural design and manufacturing and the need to monitor the operational status of structures are constantly being proposed.It has now become another pillar method after the theoretical analysis and experimental testing methods for academic and engineering research.Although modeling and simulation analysis have gradually become popular in various engineering fields,and corresponding industry standards have been proposed and released in some fields,research on modeling and simulation analysis is far from mature.As one of the most widely used connections in engineering structures,bolt connections play a role in connecting parts and transferring loads.During the modeling and analysis phase,the simplification and equivalent processing in the modeling process,as well as the existence and transformation of uncertain factors in the whole process from design to service will lead inaccuracies and uncertainties to the analysis results.In order to maximize the role of model in engineering practice,it is a hot topic in current research to use reasonable means to improve the accuracy of modeling and simulation analysis and to reasonably evaluate the confidence of the model.In this dissertation,the typical bolted frame structure was taken as the object,and the dynamics modeling,model updating,uncertainty analysis,response prediction and quantification of margins and uncertainties(QMU)of the structure were studied based on the model validation method.According to the composition relationship,the structure was decomposed into different levels from top to bottom.Brick elements and thin layer elements were used to establish the model of part-level structures and the connection between different parts,so as to obtain the pre-updating model of each level structure.Based on the deterministic modal test results,material properties of the part-level models and those of thin-layer elements which describing the connection characteristics were updated.In order to improve the computational efficiency of the model updating,surrogate models between the modal frequencies and the model parameters were established,and the model updating of each structures were realized based on the corresponding surrogate models.The superiority of surrogate model in model updating was verified by comparing the updated results of the two types of models and computational efficiency.For the problem that the modal characteristics such as modal frequency were less sensitive to the local connection parameters and the relative inaccuracy of damping parameter identification in the modal updating process,the frequency response function was used as the objective response to update the connection parameters in the model.Model updating based on different form of objective functions and frequency points selection methods were studied.The research indicates that using the improved correlation coefficient and frequency points outside the resonance hump region to construct the objective function can gain access to the optimal results of model updating.In order to obtain a more comprehensive model,the updating stragety that combining multi frequency response functions was proposed.The superiority of the method was verified by the model updating of the jointed substructure.In addition,surrogate model of frequency response function was proposed,and the feasibility of this method in model updating was verified.For the inevitable uncertainties in the structural testing and simulation,the probabilistic method,interval method and the probability box method were used to carry out the uncertainty forward propagation in structural dynamics.Area metrics and interval coincidence criterion were used to evaluate the consistency between simulated and experimental results.The Mahalanobis distance was combined with the area metrics to enable the criterion to be used for the evaluation of multiple responses.Studies indicate that the uncertainties in the model leads to significant uncertainties in the structural responses,and the statistical characteristics of the response were determine by those of model parameters.In the framework of uncertainty,the Bayesian method was used to update the material properties in the models of part-level structures and those of thin-layer elements in the models of jointed structures.The statistical characteristics of uncertainty parameters in each model were obtained.The Markov Chain Mento Carol sampling method based on the Differential Evolution Adaptive Metropolis algorithm was adopted to calculate the posterior distribution of model parameters.Compared with the rest of the sampling methods,the method has the advantages of fast convergence speed and high solution precision.After evaluation of the updated model,it is shown that higher reproducibility and prediction accuracy can be obtained by using the proposed model updating method.In order to investigate the capability of the model to characterize the dynamics of the overall structure,the uncertainty analysis of random dynamic responses of the bolted frame structure were conducted based on the updated model parameters.For the existence of multi kinds of uncertainties which result in the system performance to be a probability box,the QMU methods applied to probability box situation were proposed.In addition,thresholds of system performance were calculated based on the inverse process of QMU confidence factors calculation.The calculated thresholds can provide reference for the standard definition of structure design and structure condition monitoring.