| In recent years,the major military powers have made rapid developments in the research of various hypersonic vehicles as strategic equipment.The dynamic response prediction of the structure under the strong noise environment caused by aerodynamic noise and jet noise is an important research.Broadband,random,and high intensity are the main characteristics of the noise load that the hypersonic vehicle bears during flight.This severe external load condition may cause fatigue or even damage to the thin-walled structure of the vehicle.Under the combined effect of the structural vibration and internal acoustic load,the precise circuits or instruments in the cabin probably are damaged or even fail,causing irreparable major losses.The harsh load environment puts forward stringent requirements for the design of hypersonic vehicle structures.Carrying out an adaptively accurate and efficient full-band vibro-acoustic environment prediction technology can provide important reference for the vehicle structure design,parameter optimization and ground test.Most of the current methods and theories of vibro-acoustic response prediction are only applicable to a specific frequency range.It is difficult to use a single method to achieve the vibro-acoustic response prediction of the entire frequency domain,and the practical application limits of various prediction methods are not clear,and especially for hybrid modeling analysis,the coupling mechanism between different methods needs further study.In addition,in the current study,the relevant verification of the existing vibro-acoustic coupling response prediction method is not very sufficient,and it is also necessary to develop the corresponding experimental research to verify the rationality of the modeling,parameter setting and data processing.In this paper,we focus on the prediction method and related problems of the vibro-acoustic coupling response of a typical vehicle structure under the excitation of wide-band random strong noise in the full frequency domain,and conducts exploratory research on the structure vibration reduction via the bandgap design of the phononic crystal besides the traditional structural reduction method.The main research contents and achievements are as follows:(1)Aiming at the problem of vibro-acoustic coupling of complex structures caused by wide-band,high-intensity random noise excitation,the experimental model was designed and processed with reference to the hypersonic vehicle X43 A,and the corresponding reverberation noise test was designed according to the national military standard.On this basis,the study on the vibro-acoustic characteristics of the vehicle structure in the full frequency band was carried out.We analyzed the parameters and excitation characteristics of the typical vehicle structure in different frequency bands,and selected corresponding simulation methods for each frequency band.Through the test results under different intensity noise excitation,the use conditions and applicable frequency ranges of different analysis methods were given.It is also found that in the mid-to-low frequency range,the test results under different excitation intensities show a certain multiple relationship,and the response results under one working condition can be used to estimate the response under other working conditions,which can save the test or calculation cost to some extent.(2)We employ the hybrid FE-BEM method to model the typical aircraft structure,and conduct the simulation analysis of its vibro-acoustic characteristics considering the coupling effect in the range of low frequency.It’s found that the structural vibration caused by strong reverberation noise field mainly depends on the dynamic characteristics of the structure,and the noise transmitted from the external noise field to the internal enclosed cavity is mainly the structural sound generated by the vibration of the elastic wall of the structure.The researches have shown that the FE-BEM method is very effective in vibro-acoustic coupling analysis under strong noise excitation in the frequency range below 1000 Hz.This work provides support to the modification of the structural dynamic model and the improvement the numerical simulation method in the noise-induced vibration analysis.(3)In the high-frequency region,we give key parameters of statistical energy analysis(SEA)using statistical energy theory and empirical formulas.Then the reasonable subsystems are divided according to the geometrical properties of the structure and the properties of the noise excitation,and the SEA vehicle model under strong noise environment is established.Then the simulation and experimental study on the dynamic characteristics of the vehicle structure under terrible noise environment is carried out.The research results demonstrate the rationality and effectiveness of the model and the analytical theory and methods used in this paper.At last,the applicable conditions of the SEA method are given according to the calculation and analysis.(4)For the problem that the modal density and modal overlap number of structural subsystems do not meet the requirements of the SEA in the mid-band,according to the essential requirements of the wave coupling theory for long-wave and short-wave subsystems,and combining with the principle of statistical energy method,we modify the system model to meet the applicable conditions of the FE-SEA method.And use the Monte Carlo simulation of the beam-plate structure to verify the effectiveness of the hybrid FE-SEA method which is then adopted to predict the vibro-acoustic coupling response of the vehicle structure.Then the vibro-acoustic characteristics of the vehicle structure in the mid-frequency range are computed,which show that the simulation results are well coincident with the test results.Those demonstrate the accuracy of the hybrid FE-SEA method and make up for the limitation of the deterministic method and statistical energy method in solving complex vibro-acoustic problems during intermediate frequency range.(5)We explore the vibration reduction method and mechanism of the structure from the perspective of phononic crystals,in order to provide new methods and perspectives for the vibration reduction of the structure beyond the traditional vibration reduction technology.A new type of two-dimensional re-entrant hexagonal honeycomb grid structure is proposed.Through the study of its band gap invariant characteristics,it is found that the rotational resonance mode is an important reason for different topologies with the same band gap.And through the analysis of the folding beam of the unit cell wall,it is found that the natural frequency of the folding beam under the simple-supported and fixed-supported state is completely consistent with the boundary of part of the band gap.So a simple folding beam model can be used to predict the position and width of the low-order band gap of the structure itself,which simplifies the calculation process of band gap characteristics.The appearance of the same forbidden band and its predictability make the structural re-entrant honeycomb structure have obvious design advantages in the control of elastic waves,which can provide a new method for the prediction of the band gap and for vibration reduction. |
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