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In the noise prediction on railway viaducts by numerical acoustic analysis, it is premised that the noise barriers have sufficient sound insulation performance. Considering that the sound transmission loss of the noise barrier has frequency characteristics, which are different for each noise barrier, it is desirable to take the sound insulation performance into consideration to avoid the overestimation of noise reduction effect. In this study, the sound insulation performance of the noise barrier is regarded as a sound damping component by set the different medium domain from the air domain in the analysis. The sound damping characteristics are represented by the complex wave number, which is set as the sound attenuation per unit length related with the transmission loss and the thickness of the noise barrier. As a result, it was confirmed that the sound attenuation corresponding to the transmission loss of the noise barrier can be set appropriately for the plane wave propagating model with consideration of the sound reflection caused by impedance discontinuity. In addition, FEM analyses were conducted for the railway viaduct assuming that the additional noise barrier made of the polycarbonate plate was installed. Consequently, it is concluded that the differences due to the transmission loss can be sufficiently evaluated because the distribution of sound pressure level outside the viaduct shows the influence of the transmitted sound from the additional noise barrier.

This report shows effect of sound insulation by adhesion of porous materials and film laminated panel. It deals a technique for estimating damped vibration of automotive body panels with sound-proof structures. It calculates damping properties for sound-proof structures involving elastic body, viscoelastic body and Biot type porous materials by three-dimensional finite element method. In this analysis, particle displacement vectors for internal air in the porous materials are adopted as unknowns for the discretized equations for finite element method. And displacement vectors for frame in the porous materials are also selected as the unknowns. A numerical code is developed. For numerical examples, Biot type porous materials are sandwiched between panel and film, and laminated film. Frequency response functions were calculated for panels laminated with porous material (felt) and viscoelastic body (film) and porous material (felt) using this technique, the calculation results almost agreed with the experimental results. And effect of the vibration performance by with/without adhesion is clarified. At with adhesion, the internal air and the frame in the porous material are same vibration. But at without adhesion, the internal air and the frame in the porous material are greatly different vibration. It is thought that change of sound insulation takes place by this.

The noise and vibration caused by pressure pulsation are one of detrimental problems in hydraulic systems. A Helmholtz type hydraulic silencer, which is based on the resonant phenomena of a mass-spring-damper system for its attenuate principle, is known as one of the most practical silencers in the hydraulic systems. In the previous researches, the transmission loss characteristics of the Helmholtz type hydraulic silencer were modeled by a distributed parameter model. However, in the design case that the ratio of the length and diameter L/D of the cylindrical volume is smaller, the resonance frequency of the existing model begins to deviate from the experimental results and the disparity increases with decreasing the ratio of L/D. The purpose of this research is to clarify the influence of a neck and volume geometry on the attenuation characteristics. In particular, a mathematical model that considers the flow for the radial direction of the cylindrical volume is newly proposed for the design case that L/D is smaller. The transmission loss characteristics of the Helmholtz type hydraulic silencer are investigated theoretically for both the proposed model and existing models. In addition, the experimental examination of the influence of volume geometry on the attenuation characteristics is carried out in order to verify the theoretical investigations.