A very efficient numerical simulation method of the railway vehicle-track dynamic interaction is described. When a vehicle runs at high speed on the railway track, contact forces between a wheel and a rail vary dynamically due to the profile irregularities existing on the surface of the rail. A large variation of contact forces causes undesired deteriorations of a track and its substructures. Therefore these dynamic contact forces are of main concern of the railway engineers. However it is very difficult to measure such dynamic contact forces directly. So it is important to develop an appropriate numerical simulation model and identify structural factors having a large influence on the variation of contact forces.When a contact force is expressed by the linearized Hertzian contact spring model, the equation of motions of the system is expressed as a second-order linear time-variant differential equation which has a time-dependent stiffness coefficient. Applying a well-known Newmark direct integration method, a numerical simulation is reduced to solving iteratively a time-variant, large-scale sparse, symmetric positive-definite linear system.In this study, by defining a special vector named a contact point one, it is shown that this time-variant stiffness coefficient can be expressed simply as a product of the contact point vector and its transpose and so the Sherman-Morrison-Woodbury formula applied for updating the inverse of the coefficient matrix. As a result, the execution of numerical simulation can be carried out very efficiently. A comparison of the computational time is given. Description of railway vehicle-track dynamic interaction by contact point vectorA railway vehicle-track system is excited by contact forces generated beween a wheel and a rail. Fig.1 shows the mathematical model developed to study a railway vehicle-track dynamic interaction. A vehicle model is represented as a single car train with two bogies and four wheels. It runs on the track from left-side to right-side at high speed. In a track model the rail is discretely supported by the sleepers laid on the multi-layer ballasts. Elastic railpads are placed between the rail and the sleepers to attenuate dynamic loads. The rail is represented as an Euler beam with uniform flexural rigidity. The equation of motion of a beam is given by the 4th-order partial differential equation.In this study, according to the linearized Hertzian contact theory, a dynamic contact force , P dyn (t) is represented as being proportional to a total dynamic elastic deformation , ∆ dyn (t) of the rail and the wheel generating at the contact point aswhere k H is a coefficient of linearized Hertzian spring stiffness.As shown in Fig.2, the vehicle has four contact points. To find the dynamic contact force developed at each contact point, the elastic deformation is expressed as 2, 3, 4 (2) y w,i (t) : vertical displacement of the i -th running wheel u w,i (t) : vertical displacement of the rail, just beneath the i -th running wheel r w,i (t) : rail profile irregula...

Dynamic wheel load variation is one of the major causes of railway track deterioration and ground vibration. Lightening of vehicle unsprung-mass is more effective on reducing dynamic wheel load than that of sprung or intermediatemass. In this paper, we estimate and discuss this effect by combining the following three methods; (1) field tests and measurements with a special equipped train, (2) an experimental method with a unique test facility and real track, and (3) a computer simulation which can calculate dynamic interaction between vehicle and track.

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