No abstract

A method based on the wave field synthesis is proposed to estimate the insertion loss of a noise barrier under the complex diffracted sound field due to the characteristics of the noise source and the transmitted sound through the barrier. This method is equivalent to evaluating the acoustical performance of the noise barrier in a reproduced sound field. There are two advantages of the proposed method. First, by storing the radiated sound of various noise sources as a database in advance, the insertion loss for them can be obtained. Second, the impulse responses from multipoint can be measured by changing one loudspeaker position sequentially, so it does not necessarily require many loudspeakers. In order to validate this method, numerical simulation was performed for a diffracted sound field consisting of a point source and a rigid barrier. Moreover, the insertion loss of simple noise barriers for one loudspeaker was estimated under the primary and synthesized sound field conditions experimentally. As a practical example, the insertion loss of the same noise barriers for a moving automobile was also estimated. The results show that the estimation error is within a few decibels in the frequency band where spatial aliasing does not occur.

This research offers a new composite-revamping method for railway bridges by assuming composite remodelling process of existing steel bridges having no specific fissure damages or serious corrosions and effectively making use of relatively new materials to it. Effects of noise reduction and improved stiffness were further confirmed through Impact tests (vibration and noise measurement tests) in order to prove the efficacy of the composite remodelling. By the tests, it can be confirmed that the composite structuring work tended to reduce the vibration level by around 10 to 35 dB and the AP value by about 30 dB. In addition, the stiffness increases from the bridges of only steel members. The remainder life of the structure is extended by this effect. These effects are confirmed by the experiments for railway bridges.