A free mass in mass impact based unit cell for vibration control in railway tracks: Analytical modelling, parametric optimization, and field experimentation

This study presents a novel vibration control device for railway tracks based on a nonlinear free mass-in-mass impact mechanism. The device comprises an outer mass rigidly fixed to the railway sleepers, enclosing an inner mass within a hollow cavity. Under external excitation from a passing train, the inner mass moves freely and impacts the cavity boundaries, generating impact forces that dissipate energy and attenuate vibrations. The effectiveness of the proposed device is evaluated through comprehensive analytical and experimental investigations. A linear complementarity problem (LCP)-based solver is developed to model the nonlinear impact dynamics, and an on-field experimental study validates its practical performance. In addition, a detailed parametric investigation is conducted to examine the influence of key design parameters, including mass ratio, inner gap, and stiffness, on vibration mitigation. The results reveal amplitude-dependent activation characteristics and identify optimal parameter ranges that enhance impact-induced energy dissipation. These findings provide practical design guidelines for the optimization and cost-effective implementation of the proposed device in railway track systems.