Research On Structural Finite Element Model Updating Method And Its Application In Damage Identification

Model updating is a technical method used to construct high-quality finite element models,which is often used in aerospace and civil engineering.In view of the fact that the finite element model established according to the design drawings may be quite different from the actual structure,model updating method can modify and verify the finite element model according to the measured data,so as to improve the reliability of the numerical analysis and performance evaluation based on the model.In addition,the model updating method is also an effective means for structural health monitoring and damage identification.The updating methods proposed in this thesis are mainly tested through the application of damage identification.Although in the past few decades,model updating method has been widely studied and applied,there are still many problems that need to be solved urgently when model updating is carried out for complex engineering structures.For example:the problem of failure to converge to the optimal solution due to too many updating parameters,the calculation efficiency problem of updating large-scale structures,and the insufficient development and utilization of some specific responses.Therefore,several new model updating methods are proposed in this paper,which aims to improve the accuracy and efficiency of model updating and increase the types of dynamic response that can be used.The main work includes the following aspects:(1)Based on the construction principle of the Kriging model and its efficient global algorithm for solving optimization problems,the traditional response surface method is improved,and a new model updating strategy based on the surrogate model of the objective function is proposed.The modelling of large and complex structures often requires the help of finite element software while the model’s stiffness,mass matrix,and specific connection and boundary conditions are difficult to be extracted.Therefore,the main way to modify them is to use response surface method,that is to use evolutionary algorithms to solve optimization problems and then to build surrogate models to improve computational efficiency.At present,the 2 main difficulties faced by this response surface-based model updating method are that the method is difficult to be applied to cases where the response changes drastically,and the number of parameters and responses used for updating is limited.In this thesis,a Kriging model based finite element model updating strategy is proposed which can broaden the response types that can be used in response surface methods,avoid the computational burden of constructing a response surface for each response separately,and increase the number of parameters and responses that can be used for updating.Based on this strategy,the model updating based on the surrogate model of the frequency response function is successfully implemented,and the significant improvement of the calculation rate by the introduction of the Kriging model to build the surrogate model was compared.(2)The specific steps of model updating using modal strain energy sensitivity are explored.Stress concentration usually occurs in the damaged part of structure,so the sensitivity of modal strain energy to damage is often higher than traditional vibration test data(frequency,mode shape and frequency response function).The application of this response in the field of damage identification is mainly reflected in the damage index method.This thesis combines it with the model updating method,and proposes a model updating method based on the sensitivity of modal strain energy.Specifically,it includes the derivation of the calculation formula of the modal strain energy sensitivity matrix,the introduction of a specific penalty function in the objective function to control the variation range of the updating parameters,and the effective data processing of the measured modal data to obtain the available experimental data.The proposed method has successfully passed the experimental verification of damage identification of the beam structure with cracks.(3)Modelling,updating and damage identification of seam welded structures are studied.Seam welding is one of the common ways to connect components to assembled structures.However,there are few studies on its modelling and how to correctly reflect the structural dynamic characteristics of the welding part.This thesis studies the specific way of using the specially designed CSEAM element in Nastran to construct the seam welded joint for connecting the plate structure,and demonstrates how to obtain an accurate theoretical model through effective model updating.In addition,combining the updating strategy and modal strain energy mentioned above,this thesis proposes a damage identification method for weld gaps,and designs a set of T-plate structure numerical simulations and experiments to verify this method.Due to the complexity of modelling,the model updating of this structure is a typical optimization problem that must use the surrogate model based model updating method to reduce the computational cost.The related theoretical analysis and experimental verification can prove that the method proposed in this thesis has excellent performance in the accuracy,robustness and computational efficiency of the initial updating and damage identification of the structure.