| Semi-flexible nozzle has become the main structural form in the wind tunnel nozzle construction in recent years due to its high flow quality and relatively low engineering cost.Given the huge external load throat block mechanism of large-size nozzle bears in operation and the limited space of diving mechanism for design and installation,how to design a driving mechanism with qualified indexes including driving force,safety,stiffness under many conditional limitations has become one of the core problems in nozzle design.This project is based on a major wind tunnel national project,conducting research regarding kinematics,optimal design,dynamics,static stiffness focusing on two throat block drive schemes of 3-RPR and 3-PRR,and establishes a scheme evaluation system to carry out design level evaluation and comparison.Firstly,based on the shortcomings of the 3-RPR scheme,a 3-PRR throat block drive scheme is proposed in this paper,and the inverse kinematics solutions of the two mechanisms are obtained by using the analytical method,the correctness of the kinematics model is verified by comparing the analytical results of MATLAB calculation with the ADAMS simulation results.Then,the forward and inverse Jacobi matrices of the two mechanisms are obtained by using the first-order effect coefficient method,and the results are verified.To optimize the driving force of the mechanism,combined with the special working condition of the nozzle,the method of extreme working condition method and the idea of “static replacing dynamic” have been respectively adopted in this paper,transforming the original dynamic optimization problem into a static optimization problem,using the method of exhaustion and iteration as well as genetic algorithm to optimize the optimization model.By comparing the two methods,the high efficiency and accuracy of genetic algorithm are verified,and ideal optimization results are obtained.Then,the dynamic analysis model of 3-RPR and 3-PRR mechanism is established by using Lagrange equation,and the dynamic model is simplified by combining data analysis,then the dynamic calculation and simulated comparison are completed.By comparing the dynamic analysis data with the static optimization results in the previous chapter,the rationality of the optimization theory is verified,and the error source of the "static replacing dynamic" method is analyzed.The static stiffness level is also one of the important characteristics of the throat block driving mechanism.In this paper,by establishing the static stiffness matrix of the two mechanisms,the change rule of the static stiffness coefficient of the mechanism is obtained.Then,the Lagrange extremum value method is used to obtain the evaluation index of the mechanism's static stiffness,and the global stiffness evaluation index of the mechanism is obtained by the full-time integration method.Then,AHP-FCE method is used to build the evaluation model of the throat block drive mechanism.In this part,AHP method is firstly used to analyze the structural composition of the throat block drive system evaluation,and the normalized weight coefficient of each index in the evaluation system is obtained.Then,FCE method is used to obtain the membership degree of each single index,and the membership matrix of index layer is formed.At last,the weighted average operator is used to fuzzy calculate the design score of the 3-RPR and 3-PRR schemes,and the fuzzy evaluation results of the two schemes are obtained.In this paper,the main mechanical characteristics of the 3-RPR and 3-PRR lump driving schemes are studied,and the main evaluation indexes of the laryngeal driving system are obtained.According to the established scheme evaluation system,different performance characteristics and scheme design of the two schemes are obtained,which provides theoretical support and application cases for the analysis of scheme characteristics and design level evaluation of the throat block driving mechanism. |
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