Research On Sound Transmission Loss Characteristics Of Train Extrusions Based On Rib Refinement Modeling

The extruded structure has the advantages of high specific strength and strong designability and is a typical representative of the lightweight design of the train body.However,the hollow design of the extrusion causes its local modes to be easily excited and resulting in poor sound insulation performance.How to consider its sound insulation performance in the lightweight design stage is an urgent problem to be solved.Due to the complexity of the extrusion,the numerical calculation method is used in most of the present research.The space harmonic expansion method is an effective analytical theoretical method to study the extrusion,which has high computational efficiency and is suitable for all frequency bands,the mechanical modelling of the ribs in extruded structure is the key to solving the analytical model,the sound insulation characteristics of the extrusions can be explored more clearly from the physical mechanism by fine modelling of the rib structure.In this thesis,a theoretical model of sound insulation of extrusion is established considering the fine modelling of rib structure,the relevant mechanism affecting the sound insulation characteristics of extrusion is explored,and the sound insulation performance of extrusion is optimized by multi-objective design.The main research work is as follows:Firstly,aiming at the deficiency of the traditional mechanical model of the ribs in extruded structure,the vertical tension spring,transverse torsion spring and longitudinal torsion spring with continuous uniform mass are used to replace the rib,and the stiffness expressions of equivalent spring and torsion spring are derived.Based on the four-end parameter analysis method,the mechanical equivalent model of the rib was modelled,and the sound insulation theoretical model of the rib was established based on the space harmonic expansion method.The convergence of the model is verified by numerical examples,and the accuracy of the model is verified by comparison with experimental and simulation results.Then,based on the above theoretical model,the influences of the type of sound source,the inclination angle of the rib and the thickness of the rib on the sound insulation characteristics of the extrusion were investigated,and the reasons for the difference in the sound insulation characteristics of the extrusion under different mechanical models of the rib were explained from the mechanism.The results show that the mechanical coupling mode between the ribs and the panels is related to the sound wave incidence angle,when the sound wave is not vertically incident,the upper panel will simultaneously have vertical translational motion and in-plane fluctuation,and the ribs will simultaneously exert vertical tensile force and torque along the direction of the in-plane component of the sound wave.The vertical tensile force of the ribs on the panels has the greatest influence on the sound insulation characteristics of the extrusion,but the torsion constraints between the ribs and the panels also provide a path for the sound wave propagation,both considering the transverse and longitudinal torsion constraints,more sound insulation valleys can be captured.The first sound insulation valley is mainly caused by the resonance of the ribs,its mechanism is similar to "plate-air-plate" resonance,the equivalent stiffness of the rib increases when its thickness increases,resulting in the increase of the resonance frequency of the rib and the stiffness of the extrusion,the frequency required for resonance becomes larger,and the sound insulation valley value shifts to high frequency,which is more significant when the inclination angle of the rib changes.Ignoring the fluctuation effect of the ribs will lead to a smaller force transfer rate,and the energy of sound waves propagating from the ribs to the lower panel will be less,resulting in a large sound insulation volume and a small number of sound insulation valleys.The first resonance frequency of the transverse and longitudinal equivalent torsion spring of the rib is much larger than that of its vertical equivalent spring,the difference in sound insulation characteristics of extrusion with or without considering the fluctuation effect of the ribs is mainly caused by the vertical fluctuation of the ribs.When the sound wave is vertically incident,the vertical component of the sound wave is the largest,and the vertical fluctuation degree of the rib is the strongest,the calculation results of sound insulation with or without considering the fluctuation effect of the ribs have the greatest difference,and the number of new sound insulation valleys is the largest after considering the fluctuation effect of the ribs.Finally,a theoretical model was established to evaluate the mechanical bearing performance of the extrusion,and the multi-objective optimization was carried out based on the sound insulation theoretical model which considers the fine modelling of the ribs.The results show that the ribs of rectangular,trapezoidal and triangular periodic element extrusion become thinner after optimization,which weakens the restraint of the ribs on the panels and improves the sound insulation performance of the extrusion in middle and high-frequency bands significantly.In addition,when optimizing the extrusion,reducing the thickness of the rib which has a smaller influence factor and increasing the inclination angle of the rib which has a larger influence factor can not only improve the sound insulation performance of the structure but also increase the stiffness and reduce the weight of the structure,to meet the requirements of multi-objective optimization design.When optimizing the thickness of the upper and lower panels of the extrusion,the total thickness of the panels on both sides can be kept unchanged,and the thickness difference between the two panels should be appropriately increased,for example,the partial mass of the original thinner side panel is allocated to the thicker side panel.