Analysis For Dynamic Response And Reliability Of The Random Structures Under Thermal-structural-acoustic Coupling

Aerospace vehicles are in a complex space environment during their operation,and the bad working conditions lead to structural vibration,which affects the normal operation of spacecraft.In particular,structural parameters such as the modulus of elasticity change with the change of ambient temperature,which further leads to the change of structural vibration characteristics and responses.Therefore,it has practical engineering background and important theoretical significance to analyze the dynamic response and reliability of the structure in the multiple-field environment.In this work,thin-walled circular tube,a common structural unit in spacecraft,is chosen as the object to be studied.Considering the coupling vibration of thermal-structure caused by the change of temperature under the continuous hot current irradiated by the sun,the air inside the structure is driven to vibrate together,which results in the interaction between air and structure.Thus,the phenomenon of thermal-structure-acoustic coupling appearing in the thin-walled tube is formed at last.When considering the randomness of structural parameters,the stochastic dynamic response of structure and its dynamic reliability are addressed in detail.The main content of this dissertation is as follows:(1)Based on the related literatures at home and abroad,the research theory and methods as well as the existing problems at present about the structural dynamic response under the conditions of thermal-structural coupling and structure-fluid coupling are firstly reviewed and summarized.The basic theoretical knowledge of thermodynamics,fluid mechanics,structural dynamics and finite element is introduced,which lays a theoretical foundation for the subsequent research.(2)In the third chapter,the dynamic finite element model of deterministic structure under the thermal-structural-acoustics coupling is first constructed.The specific process is:firstly,the temperature field is divided into the mean temperature field and perturbed temperature field,and the corresponding finite element equation of heat conduction is established respectively.Secondly,the acoustic field induced by thermal vibration is discretized and the finite element equation of acoustic field is established,and the dynamic equations of the structure under thermal-structure-acoustic coupling is then derived.Thirdly,the three-field coupling dynamic equation is solved,and the temperature field,structural dynamic response and sound field in time domain are alternately and iteratively calculated,whereby the temperature field is solved with Newton-iteration and timedifference,and the dynamic responses and the acoustic field of the structure are computed with Newmark integral method and Runge-Kutta method respectively.Furthermore,considering the randomness of the temperature field and the structure parameter,the numerical characteristics dynamic responses are derived based on the dynamic response analysis process of the deterministic structure under three-field coupling.Specifically speaking,when taking the physical parameters and geometrical parameters as well as initial heat flow of the structure as random variables with normal distribution,the random model of the structural temperature field is proposed based on the moment method of random variables,and the stochastic model of the structural dynamics is then constructed with random factor method and the algebra synthesis method.Moreover,the means and mean variances of the structure displacement and stress responses are also derived.Finally,a numerical example is used to verify the feasibility and effectiveness of the proposed method by comparing the results of method proposed with those of Monte-carlo method.The stochastic effects of different parameters on structural stochastic responses are investigated.The variations of dynamic responses of random structure with time are analyzed as well.The results show that the structure will flutter under the thermal-structure-acoustics coupling,and the dynamic response amplitude of the structure will increase with time.The influences of elastic modulus and mass density on the dispersion of structure response are obvious,and the variation coefficients of random parameters are proportional to the dispersion of structural response.(3)Based on the third chapter,the fatigue failure of thin-walled circular tube structure under three-field coupling is evaluated under alternating mean temperature field and alternating disturbance temperature field.At first,the fatigue stress generated by the alternating mean temperature and sound pressure is transformed into the constant random load,and the fatigue stress generated by the alternating perturbation temperature field and sound pressure is transformed into the variable amplitude random load.Based on the fatigue cumulative damage theory and residual strength model,the two stochastic loads are unified and the limit state equation of the structure is derived by using the stress-strength interference theory,further,the dynamic reliability index of the structure is derived.The dynamic reliabilities of the structure under different cyclic times are then computed and analyzed by an example.The results show that the fatigue reliability of structure under thermal-structural-acoustic coupling has the characteristics of "sudden death",and the coefficient of structural strength degradation and the variability of parameters have a certain impact on the dynamic reliability of the structure.The greater the variationcoefficient of random parameter is,the smaller the reliability of structure is.