Study On Structural Dynamics Characteristics Of Rocket Based On Simplified Modeling Of Bolted Flange Connection

Bolted flange connection structures are widely used in many industrial fields,such as in aeronautics and astronautics engineering,nuclear equipments,chemical and mechanical industries.Many of these structures often carry different kinds of loads in complex working environments.Meanwhile,the nonlinear characteristics are caused by the deformation sensitive of the joint structure subjected to one or more combined action of tension,compression,bending moment and shearing force.Therefor,the analysis of the dynamic characteristics of bolted flanged joints is very important in the design and pre-research of the equipment.To study the dynamic characteristics and vibration response characteristics of bolted flanged connection structure under external excitation,in this paper,the contact nonlinear problem of connection structure is transformed into the material nonlinear problem with different tension and compression stiffness,after that,a multi-degree-of-freedom(MDOF)simplified dynamics model is established.By comparative analysis of the coupling vibration and the dynamic characteristics under different excitation and considering the influence of specific parameters of the simplified model,the key parameters of dynamic control can be obtained.Finally,the validity of the simplified modeling method is verified by comparing the experimental data with a actual rocket body and applied to the analysis of the dynamics in spacecraft.Main works of this dissertation are:1.According to the static experiment of bolted flange connection structure and mechanical analysis results,we establish a simplified dynamics model of bolted flanged connection structure with shear pin(cone).The nonlinear characteristics of the connection structure are characterized by three-degree-of-freedom(3 DOF)mass-spring system,and the model accuracy is verified.The fully coupled vibration phenomenon in three directions is found in the nonlinear system with the assistance of mathematical analysis and numerical experiment,in which the decoupling conditions of system's degrees of freedom are given in detail.The coupled frequency between the vertical vibration and transverse vibration are analyzed to give the most appropriate design of bolted flange connection structure.2.Based on the established simplified dynamics model of bolted flanged connection structure,the transient response characteristics of the system under different excitations are analyzed.It is found that different ratios of the longitudinal vibration frequency to the bending vibration frequency lead to superharmonic response or sub-harmonic response,even the vibration with two dominant peaks.The comparing computational results indicate that the classical linear model is inadequate in the analysis results.In addition,the shear pin in the bolted flange connection structures causes a force redirection effect which can redirect a part of transversal loads to longitudinal force.Moreover,to investigate the transient response characteristics of the connection structure under impact excitation,a contour map of the transient response of the connection structure is illustrated over an angle range from 0° to 40°.3.Two nonlinear spring-mass system are established as simplified dynamic models to study influence of shear pin which subjected to the combined action of bending moment,shearing force and torsion moment in actual working status.The vibration characteristics and coupling relationship of combined action of bending and shearing and torsional loading are discussed.On this basis,the effects of cone angle and assembly clearance on the maximal axial tensile force on the bolts are investigated.Then,the dynamic characteristics of different simplified connection structure models are analyzed in finite element analysis.4.A new simplified 3DOF model with a bilinear spring is established to simulate the longitudinal elastic characteristics of the part which is connected by the bolted flange structure.Analysis of the natural frequency of the dynamic equation is completed.The characteristics of transient response of system are studied under the longitudinal excitation.The characteristics of steady-state response of system under different excitation directions are discussed.And difference between the rigid body assumption system and elastic system in the sensitivity is analyzed.5.A simplified model of nonlinear multi-connection rocket structure is proposed,and simplified dynamic model is verified byexperimental data.To study effects of local stiffness of some cabin part on the mode of vibration and mode shape slope of installation location of inertial components,a hybrid method of modelling is proposed through combining the equivalent beam structure with a three-dimensional finite element model.Effects of the stiffness of opening cabin reinforcing beam,section geometry parameter of cross beam,stiffness of fixed support and shell thickness on the mode shape slope are discussed by using modal analysis.Moreover,a simplified dynamic model with nonlinear multi-connection surface is established to analyse the variation of maximum tension of bolt spring and maximum axial force of cabin respect to the mass,stiffness of cabin and inclination angle of shear pin,based on the equivalent of structural mode shape.Finally,the simplified dynamic model with multiple nonlinear connect that is proposed in current study is verified by the test results of a rocket.