FEM simulations of acoustic wave propagation in the vicinity of the railroad structure

Abstract

Noise is one of the major environmental concerns nowadays. The problem is especially significant around large urban agglomerations where high levels of noise can have a negative impact on physical or psychological well-being of citizens while a long-term exposure can be harmful to health. Residential areas are protected by the introduction of maximum allowable sound pressure levels according to appropriate norms. There are also similar regulations concerning natural areas under environmental protection. Different measures used in order to reduce levels of noise should be applied primarily to the source of the sound. This is the task mainly for the manufacturers of all kinds of machines as well as means of transport. However, noise levels can be also controlled by the introduction of appropriately designed or chosen elements or materials in civil engineering structures. The noise levels emitted by the rail traffic depend on the number, kind and speed of trains, night and day traffic organization as well as on the type of the railroad structure and its location (e.g. on an embankment, on a bridge or flyover). Railway noise mainly develops between wheels and rails and depends on the roughness of both these elements, rolling speed and dynamic characteristics of the railroad. The paper presents the mathematical formulation of a coupled acoustic-structure problem. Solving the problem with finite element method gives the possibility to predict sound pressure levels in the vicinity of a railway structure. A numerical model of a certain type of a railroad structure was built in order to simulate the acoustic wave propagation caused by a wheel-rail interaction. The harmonic analysis was carried out using the Abaqus software. The acoustic pressureobtained based on the harmonic analysis was evaluated in certain points of the acoustic medium for various excitation frequencies. The final results were presented in the form of one-third octave bands. In the article, a possible methodology for estimating noise levels from railway structures based on a numerical analysis was shown. In the future works, the numerical model will be validated by field test data and applied to evaluate different types of technological solutions (silencers) used to reduce railway noise levels. This paper is part of the project “Innovative solutions for the protection of people and building against noise from rail traffic”. The project is co-financed by the European Union from the European Regional Development Fund within the framework of the Smart Growth Operational Programme and by PKP PLK S.A. within the framework of a joint venture BRIK. Keywords: Finite Element Method; Acoustics; Railway Noise