Research On Matching Optimization Of Dynamic Characteristics Of Aviation Accessory Gearbox

As the kinetic energy conversion device of the aero engine,the accessory gearbox and its internal gear transmission system are in charge of driving the aircraft’s starting,fuel,lubricating oil system and other main accessories to keep the operation of engine normally,so its performance has impact on the working condition of aero-engines directly.With the standard of aircraft engine performance growing and the continuous increase of airborne accessories,the speed and input power of accessory gearbox are also rising.But the huge vibration and shock generated by the gear meshing at high speed,and the pursuit of thin-walled structure of gearbox,will put forward higher requirements for the design and development of accessory gearbox.Therefore,studying the dynamic characteristics of gearbox and the matching of the dynamic characteristics is of vital significance to the safety of the aero-engine accessory gearbox.In this paper,for a certain type of aviation accessory gearbox,the transient performance and modal performance of the box was studied by using finite element method,and the topology optimization of the gearbox was completed;at the same time,the multi-objective size optimization model was established based on the modal performance and transient performance of the accessory gearbox through the integration of Isight optimization platform,to study the influence of wall thickness and the size of the ribs on the dynamic characteristics of the gearbox.Firstly,the transient dynamic analysis of the overall model of the accessory gearbox is carried out based on FEM,and the influence of the load on the stress and deformation of the gearbox,and the displacement of bearing sets was studied;and a set of gears with relatively large displacement was selected and analyzed by comparing the meshing state of the gear in the ideal state and the actual displacement position;the results showed that the deformation of the gearbox and bearing set would cause unfavorable effects,such as unbalance loading and disengagement of gears.Subsequently,the constrained modal analysis of accessory gearbox were calculated,and the first 10th natural frequencies and mode shapes of the gearbox were analyzed and evaluated;meanwhile,the meshing frequencies of the transmission system in the transient analysis was extracted,the results showed that the meshing frequency range of the transmission system was slightly lower than the 2^nd frequency of the accessory gearbox,so there was still a risk of resonance.Secondly,establishing the mathematical model of topology optimization of the accessory gearbox using the variable density method,and defining the corresponding optimization parameters according to the transient dynamic analysis and modal analysis results of the accessory gearbox;The objective function was set to maximize the overall stiffness of the accessory gearbox,and the constraints such as volume fraction and stress were applied at the same time to complete the topology optimization design of the box According to the trend of materials distribution in the topology optimization results,a preliminary optimization plan for the accessory gearbox was formed.Finally,the parametric model of the accessory gearbox was established by using the mesh deformation technology---the Morph function in ANSA.After that,for the low modal frequencies of the accessory casing,the wall thickness of sub-boxes was chosen for the design variables to implement the modal multi-objective optimization based on modal frequencies（direct optimization method）.Integrating the mesh deformation tool ANSA,the solver DYAN and other modules through Isight multi-objective optimization platform;setting the comprehensive modal coefficient F and the overall mass to minimized in the objective functions,and taking frequency value of each order as the constraint.Finally the NSGA-II algorithm was applied to the calculation of this multi-objective optimization model.The results showed that the first 10 modal frequencies of the optimized model had been improved to varying degrees（10Hz～120Hz）,and the mass reduced 0.41kg;The 2^nd order frequency（467.1Hz）was increased by 28.5Hz on the basis of the original model,effectively avoiding the meshing frequency（411Hz）of transmission system as well as reducing the risk of resonance.Finally,Aiming at the problem of mismatch of dynamic characteristics such as stress and deformation of the accessory gearbox,the size of the ribs were selected as design variables to carry out the transient multi-objective optimization design of the accessory gearbox.The sensitivity analysis of each variable of the gearbox was performed to choose the variables with more impact on the target responses;the indirect optimization method was adopted to do the design of experiment（DOE）,in order to fit Kriging approximate model of the target responses;the mass,comprehensive stress coefficient X and comprehensive displacement coefficient Y were set to minimized,finally the NSGA-II algorithm was used to iteratively optimize the model.The results showed that the mass reduction（0.025kg）of the accessory gearbox was achieved,and the stress concentration on the gearbox was significantly alleviated,as well as the displacement of the center point of each bearing sets declined to varying degrees.In addition,the results showed that the contact force range of gears on shaft 2-3after the optimization was smaller than that before the optimization,and there was no gear disengagement phenomenon;the unbalanced gear engagement phenomenon has been improved to a certain extent,and the stress contour on the contact surface was more symmetrical after optimization.