Vibro-acoustic Analysis Of Sturctures In Normal And High Temperature Environment Based On SmEdA

High-speed vehicle suffers extreme flight environments with the combination of aeroheating,noise and mechanical loads during service.The structure and equipments are more likely to vibrate in the acoustic-vibration load environment,which could result in the failure of precision instruments.The vibration of thin-walled structures are prone to crack damage,which affects structural stability and even brings potential safety hazards to aircraft during long-term service.The high temperature environment caused by aeroheating could change material properties of structure and induce thermal stresses in structures.The vibration characteristics of structure induce fatigue failure at local regions by thermal-acoustic load.In addition,the effect of noise environment on the health of astronauts should be considered for manned spacecraft.Therefore,the prediction of vibro-acoustic response for systems in thermal environment is essiential for structural design.It also has an important guiding significance for ground test.The main research work in this paper is presented as follows.Firstly,with the combination of the finite element method(FEM)and the statistical modal energy distribution analysis(SmEdA),a FEM-SmEdA approach is presented to predict the structural modal coupling loss factor and coupling loss factor.The accuracy and application scope of the proposed approach are explored.Numerical simulations on a plate/cavity coupling system are studied to verify the accuracy of the approach by comparing with the finite element method-power injection method(FEM-PIM).Then,numerical simulations on an L-shaped plate are conducted.The influence of frequency band,subsystem stiffness ratio and structural damping on the accuracy of coupling loss factor predicted by FEM-SmEdA is studied.The applicability of the FEM-SmEdA on complex structure is verified by the L-shaped stiffened plate.Results show that the coupling loss factor predicted by FEM-SmEdA agree with result of FEM-PIM.The coupling loss factor of cavity to plate is much lower than that of plate to cavity.Within the frequency band satisfying the assumption of modal energy homogenization,the accurancy of FEM-SmEdA improves with increasing L-shaped plate subsystems' stiffness ratio and structural damping.The critical stiffness ratio between subsystems,which satisfies the accuracy of coupling loss factor,decreases with increasing structural damping.When the assumptions of modal energy homogenization,stiffness ratio of subsystems and structural damping are satisfied,the FEM-SmEdA can be capable of predicting the coupling loss factor accurately and efficiently.Secondly,the FEM-SmEdA approach is adopted to predict the local response of structuralacoustic coupling system under high frequency excitation.A plate/cavity coupling system under a point force excitation is investigated to demonstrate the effectiveness and accuracy of the proposed approach.Then the approach is applied to a plate/cavity coupling system and a cabin/cavity coupling system under Turbulent Boundary Layer(TBL)excitation.The influence of analysis frequency band and stiffener on the energy distribution of cabin/cavity coupling system are investigated by the approach.The relationship between stress and energy is deduced,and local stress response of structural-acoustic coupling system under high frequency excitation is predicted.The accuracy of this approach is verified by comparing the maximum stress obtained by FEM and statistical energy analysis(SEA).Results show that the FEM-SmEdA approach is capable of predicting local energy response of structural-acoustic coupling system under high frequency excitation with sufficient accuracy and under TBL excitation.With the increase of analysis frequency band,the energy distributions of cabin and cavity become uniform.The energy distribution of stiffened cabin/cavity coupling system is more uniform than that of cabin/cavity coupling system.The suppression of stiffener to response of cavity is more obvious than structure.The stress spatial distribution predicted by FEM-SmEdA method is in good agreement with FEM.Compared with FEM results,the local stress level predicted by FEM-SmEdA method is more conservative.Meanwhile,the maximum stress predicted by FEM-SmEdA is more accurate and reasonable than that predicted by SEA.Finally,the FEM-SmEdA approach is presented to predict the local energy response of structural-acoustic coupling system under thermal environment.A plate/cavity coupling system is studied,the influence of thermal effect on the parameters in statistical modal energy distribution analysis is investigated under three cases:(1)only the material properties are affected by the thermal environment;(2)only the additional stiffness due to thermal stress is considered;(3)considering both(1)and(2).Modal energy analysis and the local energy response of structural-acoustic coupling system under thermal environment based on FEMSmEdA is studied.Results show that coupling loss factors decreases gradually with increasing temperature under three cases;When both(1)and(2)are considered,the influence of thermal stress on coupling loss factor,modal input power,modal energy of plate and cavity is dominant.The additional stiffness effect caused by thermal stress has mainly influence on the natural characteristics and structural-acoustic coupling characteristics under high temperature environment.