An Innovative numerical modeling approach for train noise sources simulation

The recent growth in the railway sector has involved a fast increment in technologies and requirements. The first trains were slow, noisy and polluting, the modern ones are more comfortable and the electrical engine can guarantee a safe-life for nature. The recent improvement in technology has been pulled by the more strictly requirements imposed by the law and by the customers, especially in terms of safety and comfort criteria. One of the more hard-to-satisfy criteria is the acoustical one. The European Union has recently approved a new technical regulation that must be satisfied for trains: the value of allowable SPL inside the cabin is fixed to 65 dB. This requirements is than generally lowered by the customer requirements that imposes a "technical minimum requirement" more strictly than legislative one. Before the train is available for experimental tests just a numerical approach can be used to forecast the acoustic performance of the system. Many numerical approaches are available in this sense, as those based on Fem, BEM, SEA or Ray Tracing formulations; the availability of new computers and technologies has increased the computational capabilities and increased the accuracy of these tools . In any case, all these approaches can be used only to predict the distribution of noise field (in terms of SPL for example) and/or to identify the relative spectral characteristics; they cannot exactly replicate the subjective response to noise exposure. To reproduce this sensation of sound or noise, during this work, an hybrid approach based upon "standard" numerical technique and novel mathematical approaches have been used . Two train noise sources have been chosen (wheel and engine) and mathematical models have be developed to calculate the SPL vs time relationship. The model, implemented in a Simulink® environment, has been used for a real-time simulation of the source noise emission and relative interaction with the physical environment . The computed noise can be heard using a speaker system.