BS/EN 13848-1-2019 pdf download.Railway applications – Track – Track geometry quality Part 1: Characterization of track geometry.
Fl Introduction
The dynamic behaviour of a railway vehicle and its interaction with track can be simulated with a computer software system including models for vehicle, track and wheel-rail contact. The use of measured track geometry data allows simulating the vehicle dynamics under real conditions. Important applications for the vehicles are the virtual homologation, investigation of possible designs or parameter changes. Additionally, simulations can be used for the assessment of track geometry based on vehicle responses.
This annex gives information about which data are required in order to successfully perform simulations. The required data are similar to the data used for track geometry assessment and hence can be provided by most track measurement systems. The main difference is the extended wavelength range of longitudinal level and alignment. Moreover, track layout data like curvature can be included.
F.2 Contents of track geometry data for simulation purposes
Measured track geometry data typically includes track irregularity data as well as track layout data. Both are needed in order to perform realistic simulations.
Track irregularity data of longitudinal level and alignment arc used as excitation signals for the dynamic analysis of a vehicle-track system. This requires undistorted track geometry and therefore decolouring in case of chord measurement data. The required wavelength content depends on the purpose of the simulation and on the considered speed (see F.3 for details). it differs from the Dl and D2 domains.
Track gauge and cross level shall be provided in addition to longitudinal level and alignment. It is not sufficient to compute track gauge as the difference of alignment and cross level as the difference of longitudinal level, since these have a limited wavelength range and therefore do not contain information about e.g. track gauge widening in curves.
Measured track layout data can include (horizontal) curvature, cant and vertical curvature. it can deviate from the nominal track layout, which is typically given in tabular form as a sequence of track layout elements like straight lines, transition curves, etc. In contrast, measured track layout data are sampled at the same Interval as the track irregularity data, e.g. at 25 cm. For simulations, measured track layout data are preferred over nominal layout data, because it reflects the real situation on the track, and because a potential shift along the track between two different data sources is avoided. Measured (horizontal) curvature is provided by most recording systems.
All data should be synchronized along the track
in summary, the following signals are required for simulations:
— longitudinal level of left and right rail (extended wavelength range);
— alignment of left and right rail (extended wavelength range);
F.5 Pre-processing for simulation
After the track geometry data has been provided, some pre-processing is necessary in order to make the measurement data suited for simulations.
Track measurement data typically contains both irregularity and layout data. It shall be ensured that there is no overlap and no gap of the wavelength content between the respective signals. in particular between alignment and curvature. Filtering may be used, where the cut-off wavelength depends on the line characteristics like curve radii and transition lengths.
For simulation, depending on the software, it can be necessary or may be preferred to convert the track irregularities of the individual rails (as given by most measurement systems) to irregularities at the track centre. Figure F.1 depicts both representations. The nominal track centre Co and the nominal tangent to to the top of both rails define the nominal position of the track and its rails. The actual track centre C lies on the actual tangent t to the top of both rails in the middle between the track gauge points P1 and Pr. With respect to Co. the position of C is defined by the lateral displacement y and the vertical displacement z, and t is rotated by a with respect to to. Together with the actual track gaugeg, the actual position of both rails is defined, lithe irregularities are referring to the individual rails, the left and right vertical deviations zi and zr are the vertical distances from the top of rail points TI and Tr to to. The left and right lateral deviations yl and yr plus half of the nominal track gauge go give the lateral distances from P1 and Pr to C0. The arrows in the figure indicate positive signs of the displacements and rotation.BS/EN 13848-1-2019 pdf download.