Study On Acoustic Simulation, Design And Performance Optimization Of Noise Barrier

Traffic noise is becoming serious with the rapid increase of roads and vehicles. Improving the performance of noise barrier is more and more important. Reducing effect of noise barrier with T-shaped, Y-shaped top structure and multi-triangle structure was studied by noise simulating program—RAYNOISE. The applied range of the T-shaped and Y-shaped top structure was confirmed. The performance of three structures covering sound absorbent material was studied. The performance of new sound insulating material—hollow plastic-aluminum board and new sound adsorbing material—foam aluminum, was studied in laboratory. The noise barrier with T-shaped top structure and multi-triangle structure was designed and built at JingQin highway according to the simulating results.The simulating results showed that the multi-triangle structure is more effective, compared with simple erective noise barrier. The insertion loss is 14.5dB behind the noise barrier at 2m high and 30m far, and the additional insertion loss is 4.3dB higher than that of the erective noise barrier. The half multi-triangle and multi-triangle structures have the same effect on the noise reduction, which can guide the design of barrier's structure.Simulating results showed that insertion loss of Y-shaped structure has good reducing effect at higher area of the shadow area. The insertion loss is 3.4dB at the receiving point 20 height and 50m far behind the noise barrier, which is 3.2dB higher than the erective noise barrier. So it is suitable for higher receiving point. T-shaped structure has a good reducing noise effect at the area lower than 2m behind the noise barrier. The insertion loss is between 1.7 and 2.4dB higher than that of the erective noise barrier. So it is suitable for low area behind the noise barrier. Simulating results showed that sound absorbent material covered on the multi-triangle structure, T-shaped and Y-shaped top structure is no effective to improving the performance of noise barrier.Simulating results on combination of multi-triangle structure and T-shaped top structure showed that the sound reduction is obvious at area lower than 2m behind the barrier. The additional insertion loss is 2.4dB and 4.6dB to the multi-triangle and the T-shaped top structure, respectively. The reason maybe is the T-shaped structure reduced the diffraction of the noise over the top edge.Sound insulation performance of the plastic-aluminum hallow board was measured in sound insulation chamber. It is showed that the material has good sound insulating performance at low frequency. The sound insulation is over 25dB at low frequency. The sound absorbing performance of the sound absorbing material—aluminum foam was measured by standing wave tube, it is showed that the absorbing frequency peak moved to low frequency with the depth of the cavity increasing. The absorbing frequency peak moved to 500Hz when the depth of the cavity is 125mm, and the absorbing frequency brand become wider. The two new materials are suitable for noise barrier.According to the simulating results and the noise environment, the gradual changing cavity T-shaped top structure was designed and built at highway. The cavity depth of the structure changed gradually from 70mm to 140mm. The structure has wide frequency range and low frequency absorbing characteristic, can be useful to absorb the diffracting sound over the top structure. A 380m length and 3m height noise barrier with T-shaped top structure and multi-triangle structure was designed and built at Jing-Qin highway. The insertion loss measured in field was 10.4dB, 20m behind the barrier, has the same effect with the reported 4m height noise barrier. The results showed that the insertion loss measured in the sound field is lower than the simulating results. The reason maybe is the difference of the real sound source and the simulating sound source, the background noise, the leak of noise.