| The air-inlet acoustical panel is installed at the leading edge of the engine inlet near the fan blade.It is a typical vibration isolation device in aircraft structural parts.Under the condition of high intensity and periodic vibration,the air-inlet acoustical panel often cracks and delaminates.Once the above situation occurs,it will threaten the safety of crew members and passengers seriously.Therefore,it is of great significance for engineering practice to study the vibration of the air-inlet acoustical panel and optimize the structure to reduce the probability of failure.In this paper,the mechanical equivalent analysis of hexagonal honeycomb sandwich structure of a certain type of inlet acoustical panel is carried out based on sandwich equivalence theory,and the mechanical equivalent model of the acoustical panel is derived.Then the finite element numerical simulation software ANSYS was used to calculate the dynamic performance of the equivalent model of the air-inlet acoustical panel.Finally,the structure parameters of the acoustical panel board are optimized.The main contents are as follows:（1）The equivalent model of honeycomb sandwich curved plate structure of the air-inlet acoustical panel is derived.Based on sandwich board theory,the equivalent model of Gibson honeycomb sandwich board was extended and studied,and the equivalent model of honeycomb sandwich board related to curvature was deduced.The finite element software was used to verify the equivalent model derived in this paper,and the measured accuracy of the equivalent model was 11.5%.（2）The vibration characteristics of the air-inlet acoustical panel and the influence of structural parameters on the vibration characteristics are calculated.Using the equivalent honeycomb sandwich curved board model derived from the equivalent treatment of the sound canceller board,the numerical simulation software ANSYS was used to carry out the modal calculation of the equivalent model of the sound canceller board.The natural frequencies of the first five orders of the sound canceller board were respectively 229.8Hz,298.7Hz,311.3Hz,390.4Hz and 432.8Hz,and the first four orders were local modes,The fifth order is the overall mode.The influences of core thickness,panel thickness,back thickness and core specification on vibration characteristics of air-inlet acoustical panel were calculated respectively.It was found that the core thickness had the greatest influence on vibration performance of acoustical panel,followed by the back thickness,while the panel thickness and core specification had little influence on vibration performance of acoustical panel.（3）The vibration response analysis of the air-inlet acoustical panel is carried out.Based on the analysis of the vibration characteristics of the air-inlet acoustical panel,the response of the air-inlet acoustical panel under different engine working conditions,inlet pressure and unstable atmospheric disturbance is calculated.The maximum equivalent stress of the acoustical panel is 843.1Pa,558.2Pa and 786.2Pa respectively under the vibration load of take-off,cruise and air slow.The vibration of the air-inlet acoustical panel is more severe during take-off and landing.When the inlet flow is 403kg·s-1,the negative pressure range of the air-inlet panel is 3.3MPa to 4.9MPa.Under the negative pressure of 4.9MPa,the first five natural frequencies of the free mode air-inlet acoustical panel are increased by 14.1%on average compared with those of the free mode acoustical panel.The Gaussian Dryden model is used to simulate the unstable state of atmospheric turbulence.The maximum deformation of the acoustical panel plate under atmospheric disturbance is11.5mm and the maximum stress is 7145.2Pa.（4）The structural parameters of the inlet acoustical panel were optimized.On the basis of dynamic analysis of acoustical panel,parametric modeling and optimization calculation were carried out for panel thickness,honeycomb core thickness and backboard thickness of acoustical panel board.The size combination of acoustical panel with smaller amplitude was obtained:The inner diameter of the panel was 2900.0mm,and the outer diameter of the panel was equal to the inner diameter of the core layer,which was 2901.8mm.The outer diameter of the core layer and the inner diameter of the back plate are equal to 2984.0mm,and the outer diameter of the back plate is 2985.2mm,that is,the thickness of the panel is 0.9mm,the thickness of the core layer is41.1mm,and the thickness of the back plate is 0.6mm,which provides reference for the practical engineering application. |
