High-Frequency Vibro-Acoustic Response Analysis Of Heated Panels In Supersonic Airflow Based On Energy Finite Element Method

The service environment of supersonic aircraft is severe and complex.The skin panels of supersonic aircraft are subjected to aerodynamic load,thermal load due to aerodynamic heating,aerodynamic noise from turbulent boundary layer and jet noise from engine.The acoustic load on panels of supersonic aircraft is extremely heavy even in the high-frequency range,and thus it can lead to high-frequency vibration response of the panels.In addition,the requirements of high speed,high mobility,and light weight promote large scale thin-walled structures are widely adopted in supersonic aircraft design,which makes the high-frequency vibration of panels more serious.Therefore,it is of important academic research value and engineering application background to efficiently and accurately predict the high-frequency vibro-acoustic response of heated panels in supersonic airflow under acoustic load,thermal load and aerodynamic load simultaneously.Energy Finite Element Method(EFEM)is a new method for predicting high-frequency vibration response.However,the current EFEM cannot be applied to structures under multi-field complex loads.In the present work,a two-dimensional panel under acoustic load,thermal load and aerodynamic load simultaneously is studied.Based on the fundamental principles of EFEM,an energy finite element model of the heated panel in supersonic airflow is established,considering the effects of thermal load,aerodynamic load and the in-plane force due to aerothermoelasticity on the elastic waves in the panel.A novel EFEM for predicting high-frequency vibro-acoustic response of heated panels in supersonic airflow is proposed,and the high-frequency vibro-acoustic response characteristics are studied.The main research work and conclusions in this thesis are as follows:(1)The energy balance equation,the energy transmission equation and the energy loss equation of a two-dimensional panel in vacuum are derived based on the equation of motion.Then the energy density governing equation and the corresponding energy finite element equation are established,and the fundamental principles of EFEM are expounded.In addition,the validation,applicability,limitations and error sources of EFEM are studied by numerical simulations,and the physical essence of the solutions of EFEM is explored,and thus the understanding of EFEM is enhanced.(2)Thermal load and geometric nonlinearity due to aerothermoelastic response can cause in-plane force in panels.In order to investigate the effects of in-plane force on the high-frequency vibration response characteristics of panels,a two-dimensional panel with in-plane force is studied.The wavenumbers and group velocities of the elastic waves in the panel are calculated,and the mechanical impedance of the panel with in-plane force is derived to evaluated the input power from the excitation force to the panel.The energy finite element model of the panel with in-plane force is established by considering the energy density and energy intensity due to in-plane force.The correctness of the presented energy finite element model is verified by numerical simulations.What’s more,it is found that when the in-plane compressive force is lower than the critical buckling load of the panel,the in-plane compressive force has not significant effects on the high-frequency vibration response of the panel,while the large in-plane tensile force can change the input power and group velocities of the panel,and then affect the energy density and energy intensity of the panel.(3)A two-dimensional panel in supersonic airflow is studied.The effects of aerodynamic load on the wavenumbers and group velocities of elastic waves in the panel are considered.The additional damping due to supersonic airflow is introduced.The input power is calculated by deriving the mechanic impedance of the panel in supersonic airflow.And then the energy finite element model of the panel in supersonic airflow is established.Numerical simulations show the validity of the proposed energy finite element model.The results also indicate that supersonic airflow nearly has no effects on input power,equivalent masses and group velocities of the panel,but can change the equivalent damping of the panel significantly and cause difference between the damping of left-traveling and right-traveling waves,and thus affect the high-frequency vibration response of the panel.(4)A heated two-dimensional panel in supersonic airflow is studied.Based on the properties of the static or low-frequency aerothermoelastic response and the high-frequency forced vibration response,the nonlinear vibration equation of the panel is linearized so as to obtain the linearized high-frequency forced vibration equation of the heated panel in supersonic airflow.And then the energy finite element model of the heated panel in supersonic airflow is established by taking the effects of the in-plane force and aerodynamic load into account.Numerical simulations indicate that the proposed energy flow model is effective for high-frequency vibration analysis of heated panels in supersonic airflow under states of steady flat panel,thermal buckling,periodic limit cycle oscillation and chaotic motion.(5)A two-dimensional panel under acoustic load,thermal load and aerodynamic load simultaneously is studied.Considering the effects of aerothermoelasticity,the frequency response function method and mechanical impedance method suitable for the heated panel in supersonic airflow are established to calculated the input power from the band-limited high-frequency acoustic load to the panel.And then the high-frequency vibro-acoustic response of the panel is obtained by utilizing the energy finite element model of the heated panel in supersonic airflow.Numerical simulations show that the presented energy finite element method can be appropriate for the high-frequency vibro-acoustic response analysis of heated panels in supersonic airflow under acoustic load with various spatial distribution and frequency domain distribution.In summary,an effective energy finite element method for high-frequency vibro-acoustic response analysis of heated panels in supersonic airflow is established in this thesis,which provides a new approach to predict high-frequency vibration response of structures under multi-field complex loads including acoustic load,thermal load and aerodynamic load.