| It is well known that any complex mechanical system can be viewed as a combination of many different subsystems.Due to the difference in the material,structure and dimension of the subsystems,the dynamic characteristics of the system are different.So the vibration of the whole system structure shows the complex mixed vibration characteristics of the long-wave deformation caused by the low-density sub-structure and the short-wave deformation caused by the high-density sub-structure in a quite wide frequency range.Therefore,the complex co-existing vibration of low-frequency and high-frequency vibration in the system vibration is defined as the "mid-frequency vibration".And in this band,the conventional finite element method,boundary element method and statistical energy analysis are to a certain extent lost its accuracy and validity of calculation.Therefore,the mid-frequency vibration of complex system has been one of the major research topics in academic circles.It is inevitable that errors of subsystems of the complex system will generate in the process of manufacturing,assembling and measuring,and it is precisely because of the existence of these small errors that the uncertainty of the system is caused.However,with the increase of frequency,the dynamic characteristics of the system become more sensitive to the change of parameters,and the influence of uncertainty on the overall dynamic characteristics of the system is also increasing.In addition,many uncertain factors are coupled together,which may lead to a large deviation in the response of the real acoustic-acoustic coupling system,and even the phenomenon of inversion occurs.At present,the modeling of uncertainty is mainly confined to the non-parametric uncertainties of the system,while the impact of model uncertainty on the system response and quantitative research is less.In addition,the research of uncertain numerical analysis and optimization methods is mainly focused on the field of uncertain structures,and its research in the field of acoustic-solid coupling system is still in its infancy.Supported by Science and Technology Support Project of Jiangsu Province(BE2014133),Prospective Joint Research Project of Jiangsu Province(BY2014127-001)and Open Foundation of Key Laboratory of Underwater Acoustic Signal Processing of Southeast University(UASP1301),the paper made the further study in mid-frequency vibro-acoustic and uncertainties of the cavity.The study has important theoretical and practical value for the vibro-acoustic design and noise control.The main contents and innovations of this paper are as follows.(1)The theory of hybrid FE-SEA method was introduced in detail,and the hypothesis of mixed FE-SEA method was explained.A hybrid FE-SEA model of a typical mid-frequency frame-plate system was established.Uncertainties of structural dynamic characteristics and boundary conditions of the frame-plate structure were brought in to study its influence on the calculation results of hybrid model.And some meaningful conclusions were obtained.(2)Aiming at the problem that the internal loss factor and the coupling loss factor of the cavity structure with different boundary conditions were not easy to be acquired,a new method was proposed to determine the internal loss factor and the coupling loss factor between the subsystems by experimental measurement.The method of obtaining the rectangular cavity dissipation factor with different boundary conditions was studied.The method can directly calculate the internal loss factor and the coupling loss factor simultaneously by measuring the total dissipation factor of the substructure and the energy ratio between the subsystems.(3)The DAF-SIF prediction model of sound transmission loss of the perforated plate structure was established based on the hybrid FE-SEA theory.The sound transmission characteristics of the perforated structure were studied and compared with the analytical results.The influence of uncertainties on the sound insulation performance of the perforated structure was studied.The acoustic transmission characteristics of the structure under different boundary conditions,different perforation rates and sealing conditions were analyzed.(4)A modeling method based on stochastic matrix theory was proposed.The modeling principle and process of nonparametric uncertain model were introduced in detail.The influence of nonparametric uncertainties on the]ow and middle frequency response of vibro-acoustic coupling system was studied.Uncertainties of the mass matrix,the damping matrix and the stiffness matrix in the system were described by introducing a random matrix based on the finite element method.Based on the confidence interval analysis method,the numerical analysis of the general vibro-acoustic coupling system was studied under the condition of uncertainty of the structural stiffness.The research work in this paper will provide an effective method for the analysis and optimization of the uncertain acoustic-solid system,which has important theoretical and practical value.(5)Based on the hybrid FE-SEA method,a hybrid model of the construction machinery cab was established,and the mid-frequency noise in the cab was predicted and analyzed,and the accuracy of the model was validated by experiments.In view of the uncertainties of the parameters of the internal loss factor and the coupling loss factor in the cab model(the windshield itself is a sandwich structure and there is a viscoelastic medium connection with the surrounding structure;the welding connection between the plate structure and the cab frame),the internal loss factor and the coupling loss factor of the glass subsystem were calculated by the virtual experiment method with the relevant calculation theory presented in Chapter 3.The vibration excitation and air acoustic excitation of the model were obtained by experimental measurement.The semi-infinite field model of the cab was established,and the contribution of the plate structure to cab sound pressure was analyzed and quantified. |
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