Dynamics Study Of Medium And Low Speed Maglev Vehicle With Flexible Levitation Bogies

As economy developments,communication is becoming more and more closer,and the dependence and needs of transportation are also increasing.To meet such needs,urban rail transportations have profound developments these years,including metro,light rail transit,modern tram car and other forms of transportation.Medium and low speed maglev trains have their advantages,such as without wheel-rail contact,driven by linear motor,low vibration noise,strong climbing ability,short turning radius,simple and light structure,low cost of construction,environmental friendliness and etc.Hence,medium and low speed maglev trains have a very promising applicable future,as a urban public transportation.This thesis aims at a new generation of medium and low speed maglev vehicle.Vehicle structure and applied technologies were introduced,and the equivalent expressions of the levitation forces were derived.Theoretical dynamic equations of such vehicle were developed.A dynamic model of such vehicle was developed based on an equivalent modeling method.Levitation bogies of medium and low speed maglev vehicle are the main structure which supporting carbody and load.Levitation bogies are made of squeezed and casted of aluminum alloy for lightweight instead of conventional steel.Carried loads would cause deformation of levitation bogies which might have influences on vehicle dynamics.This thesis gave full considerations of the flexibility of levitation bogies.A rigid-flexible coupling model of the medium and low speed maglev vehicle was developed with the finite element software ANSYS and the dynamic software SIMPACK,considering the levitation bogies as flexible bodies.Comparisons were made between simulation results from models with and without considering the levitation bogie flexibility,including levitation bogie dynamic performances,vehicle dynamics on tangent track conditions and curve conditions.Analyses results include:1)The first two-order natural frequencies of the levitation bogie were relatively low and close to each other,which have significant influences on levitation bogie vibrations.The displacement and accelerations of flexible levitation bogie at the mass center were slightly larger than those under rigid levitation bogie condition.The maximum vertical deformation of the longitudinal beam of levitation bogie was close to 3mm for the loaded vehicle condition at the speed of 160km/h,which was consistent with the finite element analysis results.2)For tangent track conditions,the calculated electromagnet forces from the model with and without considering the flexibility of levitation bogies have subtle differences,which indicated that the flexibility of levitation bogies had limited influences on levitation system.For low speed conditions,the maximum vertical carbody accelerations and vehicle ride comfort indices would be reduced after considering the flexibility of levitation bogies,high-frequency vibrations of levitation bogies would be excited with increased speed,which would cause the maximum vertical carbody accelerations and vehicle ride comfort indices from the rigid-flexible coupling model exceeding those from the rigid model.In general,both the maximum vertical carbody accelerations and vehicle ride comfort indices were within the level of “Excellent”.3)For curve conditions,the lateral displacement of airsprings,the lateral displacement and force of electromagnet,the lateral displacement and the roll angle of a carbody would increase slightly after considering the flexibility of levitation bogies,due to the considered elastic deformation of the levitation bogie.4)For curves with medium radius curve and large radius curve,the track line would show torsions caused by the gradual elevation of the outer rail on transition curves.The vertical force of the electromagnet(or levitated force)would have remarkable fluctuations,and the peak value of such fluctuations of the rigid-body model was larger than that of the rigid-flexible coupling model,which indicated that the flexibility of levitation bogies offered certain stiffness and allowed the left and right levitation modules relatively twisted to adapt the curve line.Without considering the flexibility of levitation bogies,the relative torsion between the left and right levitation modules would be limited,and a larger peak of the levitation force occurred.Comparison results indicate that it is necessary for rigid-body models to give more considerations of the motion decoupling effects caused by the levitation bogie flexibility.5)For smooth curve conditions,the lateral electromagnet displacement,the lateral displacement between the carbody and the intermediate levitation bogie were less than those under sharp curve conditions.Hence,a maglev vehicle would show better levitation stability and curving performance under smoother curve conditions.For curves with large radius,a maglev vehicle needs higher speed for curve negotiations,hence the vehicle dynamic system would show more dramatic responses under larger speed excitations than those under sharp curve conditions,including lateral airspring displacement and roll angle of a carbody.It is suggested to apply lateral stops for airpsprings to prevent deteriorations under the larger speed excitations.