Predicting The Dynamic Response Of Thin-walled Structures Under Thermo-mechanical And Vibration Loads

During the operation of a hypersonic vehicle,it must endure a highly complex dynamic environment that includes thermo-mechanical,noise,and vibration.Thermal loads alter material properties and generate thermal stress within the structure.Thin-walled structures are susceptible to large deformations under mechanical loads.Changes in material mechanical properties,thermal stress,and geometric nonlinearity caused by large deflection deformation alter the stiffness characteristics of the structure,thereby affecting the mechanical response of the aircraft structure.Accurate dynamic response prediction is essential for safety assessment of thin-walled structures under mechanical,thermal,and vibrational environments.Predicting structural dynamic response under these conditions has significant theoretical significance and application value for aircraft structural design.This article focuses on predicting the dynamic response of thin-walled structures under thermo-mechanical,and vibrational loads,covering five research areas:Firstly,a semi-analytical method for dynamic characteristics of thin-walled structures under high pressure and noise loads is proposed.This method takes into account the large deformation caused by pressure load as the initial deformation term.To solve the variable coefficient differential structural dynamic equation considering the initial deformation,a segmented solving method based on local homogenization theory is used.The influence of load,elastic modulus,and other parameters on the dynamic characteristics of the structure considering initial deformation is investigated.The research indicates that when the deflection is small,the modal frequency increases with increasing deflection,and the modal shape does not change significantly.Assumed mode methods can be utilized to analyze this type of problem.In cases where the deflection is substantial,the modal frequency increases alongside deflection,and this deflection also affects the modal shape,necessitating the consideration the changes in structural mode shape in structural dynamic response analysis.Compared with the traditional assumed mode method,this method considers the effect of the variable coefficient term in the dynamic equation and provides a semianalytical solution for the modal frequency and modal shape considering the effect of initial deformation.Secondly,the effect of thermal influence on the dynamic characteristics of the structure is investigated.The semi-analytical method and finite element method for dynamic characteristics of thin-walled structures are established to solve uniform and non-uniform thermal loads problem,respectively.For uniform thermal load conditions,a semi-analytical method that considers the effects of thermal loads and the large deformation caused by aerodynamic on the dynamic characteristics is established.For non-uniform thermal load conditions,the dynamic characteristic analysis and thermal buckling analysis of composite plate under static-thermal combined action are investigated by finite element method.The additional stiffness matrix caused by thermal and pressure loads are introduced into the structural dynamic equation.The study shows that uniform stress mainly affects the structural modal frequency,with minimal impact on the mode shape.The non-uniform stress affects both the structural modal frequency and the mode shape.And the change of the mode shape is also affected by the load and boundary conditions.Due to the non-uniformity of the local additional stiffness increment,the modal shape and buckling mode shape of the plate undergo significant changes.Thirdly,this research investigates the predictive approach for dynamic response of thinwalled structures under noise loads,based on the analysis of dynamic characteristics considering the effects of thermal loads and the large deformation caused by aerodynamic.The orthogonality of modal functions was verified,and then the dynamic response analysis was conducted using modal superposition method.Furthermore,the effects of single aerodynamic load,single thermal load and aerodynamic-thermal combined load on the dynamic response are analyzed.The results show that the influence proportion of the two factors depends on the size of the load and the structural characteristics.With the influence due to structural stiffness changes,the modal frequency offset leads to the shift of the peak frequency of dynamic response.The change in structural modal shape affects the modal participation factor in dynamic response,resulting in a significant change in the root-mean-square value of local acceleration response.The impact of combined load on structural acceleration response is greater than the linear superposition of single load impacts.Under the combined loads,the structure is in a new vibration equilibrium state.The vibration mode of the structure may disappear or jump,which can impact the dynamic response of the structure.Fourthly,a predictive approach for dynamic response of complex thin-walled structures considering the effects of thermal loads and the large deformation caused by aerodynamic was developed.The modal tests were carried out on the stitched sandwich panel structure under room and high temperature conditions to obtain the modal test data of the structure.Then,the finite element model of the structure under room and high temperature was modified based on the experimental data.The modified finite element model was used to conduct the dynamic response analysis under complex force,thermal and vibration loads.The results show that the modal participation factor of the centrosymmetric mode shape in the dynamic response is significantly larger than that of other order modes,and the acceleration response of the structure is mainly dominated by the long-edge bending mode.The peak frequency of the structure shifts to a lower frequency due to the influence of thermal load,and there is a slight decrease in the response of the peak point.Considering the geometric nonlinearity caused by aerodynamic,the peak frequency increases,and the value of the peak point increases slightly.Due to the difference between the restraint conditions in the experiment and the ideal fixed support constraint,the slight deformation at the boundary position can reduce axial thermal stress in the structure and the impact of thermal effect on the modal characteristics.Finally,a coupling experimental system for structure under force,thermal,and vibration loads was constructed based on the modal test system.The stitched sandwich panel was taken as the research object.And the tests including vibration,force-vibration,thermal-vibration and forcethermal-vibration were carried out to study the influence of thermal effect and the large deformation caused by aerodynamic on the response.The results show that when the shape of the modal vibration mode is centrally symmetrical,the corresponding modal contribution factor is larger than that of other order modes.The acceleration response of the structure is mainly dominated by the long-edge bending mode.The experimental result is consistent with the simulation results.There exists a small difference between experiment and the ideal symmetrical structure,which leads to the influence of asymmetric load on the test.The small deformation also amplifies the response of the structural asymmetric mode and increases the error between the experimental and simulation results.When the boundary constraints are affected by thermal stress and deformation,the asymmetric mode of the structure is suppressed,resulting in a reduction in error between test and simulation results.The findings validate the accuracy of the simulation analysis method for structural dynamic response under force,thermal and vibration loads.