A combined power flow and infinite element approach to the simulation of medium-frequency noise radiated from bridges and rails

In elevated urban rail transit systems, it can be difficult to distinguish between rail and bridge noise in the medium-frequency range (200 Hz-1 kHz). The former has been well investigated using line source models or two-dimensional boundary element models, whereas the latter has usually been simulated with either statistical energy analysis-based methods, which achieve only a rough accuracy, or with three-dimensional boundary element methods, which have low efficiency. This study combines the power flow and infinite element approaches to form a new method for simulating rail and bridge noise that makes a trade-off between accuracy and efficiency. The power flow method is first applied to obtain the spatially averaged vibration of the track-bridge system due to wheel-rail interaction in the frequency domain. An analytical model of the infinite Timoshenko beam is used to represent the rail, and the finite element method is adopted to model the bridge structure. A two-dimensional acoustical model comprising finite and infinite elements is then used to calculate the noise field that considers the boundary effects of the rails, bridge, and car bodies with constant sections. The proposed combined method is validated by the comparison with existing vehicle-track-bridge dynamic interaction analysis method in the time domain and acoustical computation method via three-dimensional boundary element model. The proposed approach is then used to compute the vibration and noise from an urban rail transit U-shaped bridge with field measurements. The measured rail vibrations are utilized to estimate the nominal wheel-rail roughness input to the numerical vibration model. The simulated noise in the frequency region where rail noise dominated agreed well with the measured one. However, the bridge noise was underestimated above 400 Hz due to the uncertainties and simplifications within the vibrational and acoustical models. Even so, the total noise is primarily dominated by bridge noise in the field underneath the bridge. Both rail noise and bridge noise should be considered in environmental noise evaluation for the lower floors of buildings. (C) 2015 Elsevier Ltd. All rights reserved.