The force transmissibility of a floating slab track
The force transmissibility of a track isolation system is the ratio of the force transmitted to the track bed over the force applied at the railheads. This paper focuses on the force transmissibility of a double-tie or ‘mini-slab’ floating slab track installation. The power spectral densities of the forces transferred to ground due to ‘white noise’ force sources at the rail heads are calculated. Analytical models and the Finite Element (FE) method are used to analyse a floating slab track supported on a rigid foundation. The effect of rail fastener stiffness is discussed. The influence of the flexibility of the floating slabs and the effects of a non-rigid foundation on the force transmissibility is investigated within the framework of the FE method.
USING INSERTION GAINS TO EVALUATE RAILWAY VIBRATION ISOLATION SYSTEMS
The insertion gain describes, all other parameters remaining equal, the vibro-acoustic performance of a particular railway system measured relative to a reference trackform. The insertion gain of a track-system is dependent on the physical dynamic parameters of both the train and trackform (including the sub-base), and is therefore highly system dependent. Measured and predicted insertion gains of various railway isolation systems can be used to evaluate the expected reduction (or increase) in wayside groundborne noise and vibration that the isolation system will provide. However, accurately measuring actual insertion gains achieved on site is notoriously difficult, since it is generally impractical to separate the many system or location-dependent effects from the results. Using inappropriate insertion gains based on measurements of ‘similar’ systems can result in significant inaccuracies in the predicted vibration and groundborne noise levels. For the designer, this can result in unnecessary overor under-design of the vibration mitigation requirements. Several methods of dynamic analysis are reviewed which allow the prediction of track system insertion gains. This allows more accurate prediction of overall groundborne noise and vibration and therefore better comparison of the benefits of various track isolation systems.
Nuclear spin-lattice relaxation in transition metal compounds with local tetragonal symmetry.
We report on the various contributions to the total spin-lattice relaxation rate in metallic materials with local tetragonal symmetry. The analytical formulae are given in the tight-binding approximation. The calculations show the relation between various partial electron densities of states and corresponding contributions to the relaxation rates. The presented formulae can be used to compare theoretically calculated electron band structure parameters with those obtained from NMR spin-lattice relaxation time measurements.