| Nowadays more and more attention has been paid on the high-speed train interior noise,especially when the safety and high speed of trains have satisfied people’s requirements.In order to improve the NVH performance of the trains,it is necessary to predict the interior noise precisely during the manufacturing period.At present,statistical energy analysis(SEA)method has been widely used in the modelling of the high-speed train interior noise,but the key problem of this method is to determine the SEA parameters accurately such as the modal density,the internal loss factor and the coupling loss factor.The extruded aluminum is widely used in high-speed trains,which is also the most important subsystem in SEA prediction model.In this thesis,the SEA parameters of extruded aluminum used in high-speed trains have been extensively studied based on the theory,numerical analysis and experiments.The detailed studies are as follows:(1)The simulation model of the extruded aluminum used in high-speed trains is established based on finite element method.The modal parameters are obtained by modal analysis.Results are verified based on the results of the laser experiment.In order to find a proper simulation model,three different finite models of the extruded aluminum are considered: the solid element model,the shell element model and the solid-shell element hybrid model.Modal frequencies and modal shapes are compared with experimental results.The results show that compared with the experimental results,the error of the solid model is the smallest,but its computational efficiency is low because of the large number of elements.The error of shell model is larger than that of solid model,but the element number of shell model is several times smaller than that of solid model.The solid-shell hybrid model of element has less error compared with the experimental results and its computational efficiency is also higher.(2)The sensitivity analysis of SEA parameters to the subsystem energy is analyzed.Considering a coupling model of two single panel subsystems,the error of SEA parameters will introduce the energy error of subsystems.If the mode density error of subsystem 1increases by 10%,the energy of subsystem 2 will decrease by 35%.A 10% error of the internal loss of subsystem 1 will cause the energy of two subsystems decreased by 10%.The coupling loss factor from subsystem 1 to subsystem 2 increased,the energy of subsystem 1will decreased while the energy of subsystem 2 increased.The accuracy of the modal density has the greatest influence on the accuracy of SEA model.(3)In terms of the modal density of the panel,both in-plane and out-of-plane modal densities are calculated,and the influences of different boundary conditions are discussed.Results show that the in-plane mode appears at high frequency,and the out-of-plane mode density is the main contribution to the total mode density.The effect of different boundary conditions on the mode density of the panel is significant at low frequency,and the high frequency decreases gradually.In terms of the modal density of the extruded aluminum,the modal density of the extruded aluminum profile based on different finite element model is analyzed.Secondly,the influence of profile boundary conditions,chamfering and weld seam on modal density is discussed.Results show that when frequency is lower than 3150 Hz,the modal density of the free boundary condition is higher than that of the fixed boundary condition,the maximum error reaches 23%;when the frequency is higher than 3150 Hz,the influence of the boundary conditions on modal density becomes less evident.The error caused by removing the weld seam and chamfering to the modal density of the profile is large,the maximum error reaches 41%,but the results of only removing the weld seam and considering the cham and the weld seam at the same time are not different.Two DOE models(the Kriging model and RSM model)are used to fitting the modal density.It is found that the fitting results are consistent with the simulation results.Compared with the finite element simulation modeling calculation,the work efficiency is highly improved.(4)Two methods(Poly MAX and PIM)are separately used to identify the internal loss factor of the extruded aluminum profile.Results show that the internal loss factor obtained by the two methods is comparable in most frequency bands.However,the structure does not exist any one mode in the 1/3 octave frequency band of 100 Hz,250 Hz and so on,so the internal loss factor based on the Poly MAX is zero,which does not correspond to the actual physical meaning.But PIM can obtain a result even though there is no one mode in the frequency band.(5)The structure-structure and structure-cavity coupling loss factors are studied.In terms of structure-structure coupling loss factor,the ways of partitioning subsystems and the influence of boundary conditions on coupling loss factor are discussed.Results show that the coupling loss factors obtained by two different partitioning ways are obviously different,the higher the high frequency,the greater the difference;the boundary condition has a great influence on the coupling loss factor at low frequency and high frequency.In regard to the structure-cavity coupling loss factor,the coupling loss factor between a panel and an acoustic cavity and structure-cavity coupling loss factors are calculated based on the modal superposition method.Finally,the influence of boundary conditions on structure-cavity coupling loss factor is discussed.Results show that the accuracy of the coupling loss factor calculated by modal method is high,the boundary condition has a great influence at low frequency,and the coupling loss factor under the fixed support condition is generally larger than that of the free boundary condition,but the influence of the boundary condition becomes less evident as the frequency increases.All the above research methods and results can provide the systematic design,evaluation and basis for high-speed train interior noise control and SEA vehicle interior noise prediction model. |
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