Analysis Of Vertical Dynamic Response Of Long And Big Cargo Freight Flat Car Depressed Center Underframe

Depressed center car has the advantage of wide range of freight and easy loading.Due to its large structure size and long distance of core plate,the vertical bending stiffness of depressed center underframe is lower.With the requirement of high speed,heavy load and light weight,the elastic vibration problem of depressed center underframe is increasingly prominent.In this thesis,the vertical dynamic response of depressed center underframe is analyzed in detail from the steady-state vibration characteristics and the simulation test of two directions.This thesis mainly carries on the following research work in several respects:(1)With discretizing the geometry model into a finite element model and reducing the model freedom through substructure technology,a rigid-flexible coupling model of depressed center car was established.In addition,the nonlinear factors were simplified,and the suitable wheel-rail relationship was determined.By using the numerical simulation technique,the American five-level spectrum was used as the wheel-rail incentive,and the model was preliminarily validated by comparing with experimental data.(2)The depressed center underframe was equivalent to a variable cross-section Euler beam which was dispersed into several parts such as uniform beams.Using SolidWorks quality and cross-section analysis function,linear density and vertical bending stiffness distribution of depressed center underframe were fitted.Based on the vibration theory of beams,the inherent frequencies of free vibration and the forced vibration displacement response of depressed center underframe was calculated by MATLAB programming.(3)The maximum critical response of depressed center underframe in steady state resonance was computed by using the harmonic response analysis of finite element.(4)The dynamic simulation of a rigid-flexible coupling model was carried out.Combining time domain and frequency domain analysis,the variation regularity of vertical displacement and dynamic deflection of depressed center underframe under different speeds and suspension parameters was analyzed.(5)The dynamic stress time history of depressed center underframe was obtained by transient dynamic analysis,and the numerical and frequency distribution statistics of dynamic stress were performed.The variation regularity of dynamic stress under different speeds and suspension stiffness were discussed.The calculation formulas of dynamic load coefficient were compared and verified using simulation data.The completion of the above research work can provide guidance for the design and improvement of this kind of vehicle.