Objectif
Detailed studies have been undertaken in the course of EUROECRAN, demonstrating the possibilities and the limits of the numerical codes used. Actually, it can be safely stated that the numerical simulations guided the project in the correct optimisation direction. These codes have been extensively used for the calculations of possible solutions, as well as for specific parametric studies led to better understand the acoustic phenomena and the influencing parameters.
An existing reduced road traffic scale modelling facility - hardware and software - has been upgraded and adapted to railway noise investigations. For the acoustical scale model of a high speed train, the scaling of different boundary conditions for grassland, ballastbed and sound absorbing barriers has been demonstrated. Generic models have been used for the train, for the grassland and for sound absorbing faces of barriers and, even if the scale used was small (1/32), it was possible to look for special shape and give trends in the evaluation of solutions. Here again, the tool has demonstrated to be useful for the study of trends, when comparing different types of barriers.
A new measurement method was proposed and developed, based upon measurement made with a microphone array, in order to remove the diffraction from the vertical edges of the barrier.
The method, called "reduced length method", enables a cheaper, more efficient way for the assessment of the performance of noise barriers, on real barriers which are only 30 metres long (instead of 300 metres for full scale tests).
It is especially suited for the evaluation of different noise barrier designs which have the diffraction edge at the same position. In this case the precision of the results is around 1 dB(A). For direct comparisons of insertion loss of barriers with the different diffraction edge at different positions, care must be taken to the good description of the noise sources.
Nevertheless, the reduced length method has already shown to be a reliable tool allowing the comparison between barriers.
In terms of barriers and solutions, several conclusions can be drawn, in terms of general items concerning the acoustic efficiency of the barriers, like for example :
- General features like barrier height and distance to the track determine the barrier efficiency.
- There is no magic effect that can be expected from devices placed on top of the barrier. The important factor determining the efficiency is in fact the diffraction point. Top of barrier devices with equal diffraction edge and absorptive properties are almost equal in efficiency.
- Absorption on top of barriers can add to the efficiency when in the order of 1 meter wide.
- Non absorptive top-of-barrier designs are not efficient and not cost effective.
- Helmholtz resonators and interference devices on top of barriers are not effective.
- Reflections between train and barrier must be absolutely minimised (by barrier tilt or barrier absorption, depending of the distance between barrier and sources).
- Tilt (/ or \) and the addition of absorption have almost the same efficiency, for barriers placed at more than 5 metres from the centre of the track.
Finally, as for the cost reduction, it has been shown within EUROECRAN that the potential for cost reduction is very high. It is possible to reduce these cost, compared with a reference absorbent barrier that would be 2 metres high, by different means :
- From 20 to 40% cost reduction for the same efficiency, through implementation of acoustical effectiveness (barrier closer to the track). This is especially true for low speed trains, where rolling noise is predominant.
- Up to 30% by optimising the sound absorption performances (materials having optimised absorption or using proper air gaps).
- 35 to 50% reduction in the costs of the panels, by using panels used for other purposes and produced at a large scale (mass production).
- A gain of 4% of the costs can be reached by reducing the weight, using other materials.
- An extra gain of 1.5% of the costs can be reached by using thin steel plates, damped with low cost consumable (low cost materials).
However, some of these results have to be considered carefully since the very last results obtained show that the quality of the absorption could play an important role in the efficiency of barriers, when placed close to the track.
The noise generated by railway traffic is a source of nuissance which has to be reduced in the interest of safeguarding the environment. Nonetheless, with legislation now advocating greater severity, this reduction now takes on a more strategic nature for the development of European railway networks, their capacity to create new infrastructures and to increase both their performance and traffic, especially with respect to very high-speed traffic and combined transport. The primary objective of the research programme is to develop methodologies as well as design and evaluation tools for railway noise barriers made for this type of infrastructure, as they cannot be designed using the same criteria as roadway noise barriers. Theoretical modelling will be analysed and adapted to take into account the influence of certain parameters such as shape, materials, location of barriers, and the like. Experimental methods of characterisation for barrier efficiency will call for prototypes that are shorter and on a smaller scale, and will be developed and validated. Achievement of such an objective will serve to stimulate innovation and speed up the industrialisation process for more efficient solutions and to reduce development costs. This will also help to promote European harmony. The second objective is to optimise railway noise barriers designed for European network lines reserved for very high-speed passenger transport and combined transport, in other words, to improve efficiency while reducing production costs. The tools and methods developed within the framework of the programme will be used to study a certain number of new concepts. Those that are deemed more feasible will be materialised in the form of prototypes then tested by methods developed in the programme. Finally, the two most interesting concepts will be constructed to true scale and tested in real world conditions so as to validate all new tools and methods, as well as the technological progress emerging from the programme.
The programme results will immediately make it possible to pursue the technical and economic aspects of the optimisation effort within an industrial sphere geared for competition. These results will be published, allowing the setting of European standards, and will be circulated to all involved parties(railways companies and European committees etc...)for the benefit of all.
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CORDIS classe les projets avec EuroSciVoc, une taxonomie multilingue des domaines scientifiques, grâce à un processus semi-automatique basé sur des techniques TLN. Voir: Le vocabulaire scientifique européen.
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75379 PARIS CEDEX 08
France
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