C. Esveld

Developments in High-Speed Track Design

Presently high-speed tracks are built on a large scale. Although ballasted tracks are still popular, more and more slab tracks are constructed. They have some significant advantages such as low maintenance, high availability, low structure height, and low weight. The main emphasis of this paper is on the application of non-ballasted concepts for high-speed operation. Special attention is given to slab soil interaction and optimization with respect to bearing capacity.

Use of Expanded Olystyrene (EPS) Sub-Base in Railway Track Design

The dynamic behavior such the track structure in high-speed applications has been analyzed using RAIL software (TU Delft). An optimization on material properties of EPS, slab thickness and stiffness of subsoil has been performed. The optimization criteria are minimization of the ‘dead’ weight of a track structure and the costs related to the sub-grade improvement (i.e. the vertical stiffness of the subsoil should be as low as possible) while imposing constraints on the stresses in the EPS and subsoil layers.

Identification of Dynamic Properties of a Railway Track

The paper presents a methodology for assessment of dynamic characteristics of a railway track in application to an Embedded Rail Structure. First, the dynamic responses of a track are obtained using a Hammer Excitation Test (HET) by applying a vertical impulse load to a rail and measuring resulting accelerations of a track. The measured data is then analyzed using the Frequency Response Function (FRF). The hammer test is also simulated by the finite element model (RAIL), which can be used for analysis of the dynamic behavior of a track under various loading. Both HET and RAIL are developed at Delft University of Technology (DUT). To match the simulation and measurement data a numerical optimization technique called a Multipoint Approximation based on Response Surface fitting (MARS) method has been used. The parameters of the model related to the material properties of elastic compound (polyurethane and cork mixture) wherein the rails are embedded have been varied during the identification process. The numerical model with the obtained parameters of compound can then be used for estimation of performance characteristics of the railway track. The compound parameters have been compared with the ones obtained using a single degree of freedom mass-spring system. The results of the identification problems are presented and discussed.

Optimisation of a Railway Wheel Profile

During the last decades substantial progress has been made in design of railway vehicles and running gears. Tilting trains, high speed trains, active steering wheelsets and many other sophisticated solutions have been implemented in recent years on the railways. But despite this progress, the mechanics of railway wheelset remains the same and an inappropriate combination of wheel and rail profiles can easily diminish all this technological advances. Besides, many old fashioned vehicles are still in too good condition to be replaced. They have a special need for appropriate combinations of wheel/rail profiles since such vehicles do not have high-tech devices which improving performance. The paper presents a procedure for optimal design of a wheel profile based on geometrical wheel/rail contact characteristics such as the rolling radii difference (RRD). The procedure uses an optimality criteria based on a RRD function. The criteria accounts for stability of wheelset, cost efficiency, minimum wear of wheels and rails as well as safety requirements. The shape of the wheel profile approximated by a piecewise cubic Hermite interpolating polynomial is varied during the optimisation process in order to satisfy the optimality criteria. The optimization problem described above has been solved using the MARS method (Multipoint Approximations based on Response Surface fitting). The method has been specifically developed for problems where multiple response analyses and (time consuming) simulations are involved. Finally dynamic simulations of vehicle with obtained wheel profile have been performed in ADAMS/Rail program package in order to control wheel/rail wear and safety requirements. A solution of the optimization problem is then taken as a new wheel profile. Wheels with such profile have the given contact characteristics, which results in improved wheelset dynamics and in reduction of wheel wear. The proposed optimum design procedure has been applied to improve the performance of the metro trains in Rotterdam, The Netherlands (RET), which were suffering from severe wheel wear and as a result the hunting of the vehicles. The results of the optimisation have shown that the performance of railway vehicle can be improved by improving the contact properties of the wheel and rail. Using the proposed procedure a new wheel profile has been obtained and applied to the RET metro trains. Due to the application of the optimised wheel profile the instability of the metro trains has been eliminated and the lifetime of the wheels has been increased from 15000 km to 114000 km.