High-frequency Energy Response Analysis Of Thin-walled Structures Under Thermal And Acoustic Load

For a high-speed aircraft under service,it will encounter a complex mechanical environment composed of loads such as thermal,vibration,and acoustic load.The high-level and broadband acoustic excitation could lead to the broadband dynamic response of the system,which is an important basis for guiding the structural design of the aircraft,the formulation of ground test plans and test conditions.Due to the high-level modal density of thin-walled structures under the high-frequency excitation and the sensitivity of high-frequency response to uncertainty,the high-frequency dynamic response is normally characterized by the statistical averaged energy.Statistical energy analysis(SEA)is the most commonly used method for the high-frequency dynamic response analysis of structures.Most of the existing researches about SEA only focus on systems with deterministic SEA parameters under normal temperature environment.However,in engineering practice,the influence of the thermal environment,timevarying characteristics,and uncertain SEA parameters on the high-frequency dynamic response of systems cannot be neglected.Therefore,the research of predicting the high-frequency dynamic response of systems under thermal and acoustic load is essential for the development of high-speed aircraft.This thesis aims at solving these problems.The main contributions of this work are performed as follows.First,an algorithm is presented to predict the high-frequency dynamic response of structures under thermal and acoustic load.The SEA parameters considering thermal effects are obtained by using the energy flow model and power injection method.The high-frequency dynamic analysis for structures under thermal and acoustic load is subsequently conducted.The influence of thermal effect and temperature load on SEA parameters and energy response is investigated.For the simulation case used in this chapter,when both the effects of temperaturedependent material properties and additional stiffness due to thermal stresses are taken into account,the influence of thermal stresses on the damping loss factor,coupling loss factor,and energy response is dominant.Both the damping loss factor and coupling loss factor decrease with the increase of temperature.Secondly,to predict the dynamic behavior of systems under broadband impact loads,the transient statistical energy analysis(TSEA)and the transient local energy approach(TLEA)are adopted to quantify the transient response of systems under impulse load.The influence of coupling strength on the peak time,peak energy,and computational accuracy is investigated.Subsequently,the transient response of systems under impulse excitation and thermal load is predicted by using the SEA parameters considering thermal effects.Results indicate that the transient local energy approach achieves better performance than the transient statistical energy analysis for systems with different coupling strengths.With the increasing coupling ratio between subsystems,the rise time and peak energy of the transient energy response of subsystems decrease gradually.The increase of temperature load leads to the decrease of coupling loss factors between subsystems and subsequently results in the decrease of the peak energy of the transient energy response.Thirdly,SEA is developed to predict the transient energy response of structures with timevarying parameters.The power balance equations of systems with time-varying parameters are derived by considering time-varying SEA parameters and energy flow item caused by the timevarying damping loss factor.The influence of time-varying parameters on the transient energy response of systems is investigated.Subsequently,the transient response of systems under timevarying thermal load is predicted by using the SEA parameters considering thermal effects.Results show that the proposed SEA method for systems with time-varying parameters is capable of predicting the transient energy response of structures with time-varying parameters,accurately and efficiently.For structures subjected to impulse load in a temperature-varying environment,the energy dissipates quickly after reaching its peak in a short time.Fourthly,to quantify the uncertain energy response of SEA systems considering interval parameters in the frequency domain and the time domain,an affine interval perturbation statistical energy analysis and an interval-based transient local energy approach are proposed,respectively.The sub-interval technique is introduced in the proposed methods to improve their computational accuracy.Results indicate that the proposed methods achieve better performance than the traditional methods in the high-frequency analysis of the system with interval parameters.By employing the sub-interval technique,the computational accuracy of the proposed methods is significantly improved.The proposed methods are capable of predicting the interval energy response in the case that high levels of uncertain parameters exist in systems.Finally,to investigate the high-frequency energy response of SEA systems with fuzzy parameters,a modified perturbation statistical energy analysis is proposed by combining the level-cut strategy,perturbation method,Sherman-Morrison-Woodbury formula,and SEA.The sub-interval technique is further introduced in the proposed method to improve its accuracy.Results indicate that the proposed method has better performance than the traditional method for the high-frequency analysis of systems with fuzzy parameters.The proposed method with a suitable number of sub-intervals is capable of predicting the energy response of systems with large fuzzy parameters,accurately and efficiently.