This paper describes a sound source modeling technique of a gas engine for a co-generation system. Identification of the vibration distribution using inverse-acoustic analysis was used as the modeling technique. First, the accuracy of identification by inverse-acoustic analysis was discussed. And the sound source model was constructed by using inverse-acoustic analysis. However, because the constructed sound source model is complex shape and the calculation man-hour in the analysis is large, there is a limit in the environment that predicts noise. Then, the sound source model was simplified. And we verified the shape of the sound source model influence the accuracy of the predicted sound pressure and the calculation time for the prediction. In addition, we also describe applications of the constructed sound source model and set up a wall between the measured position and the sound source to examine the effectiveness of a sound source modeling technique of simplified sound source model. The effectiveness of the proposed modeling method was able to be confirmed by comparing this result with the actual measurement value.

Heavy vehicles are regarded as one category for the normal estimation of the A-weighted equivalent continuous sound pressure level (L_Aeq) of road traffic noise. Although it is suspected that the accuracy of the calculation of L_Aeq is affected by differences in the percentages of heavy trailers with many axles, the quantitative effect is still unknown. Through this study, we learned that the A-weighted sound power level (L_WA) of trailers exceeds that of other heavy vehicles by 2.5 dB on the basis of measurements carried out on highways, and we clarified the effect of the number of trailers on the accuracy of the estimation of L_Aeq. We have also provided the conditions under which considering the effect of the trailer ratio is preferable when estimating traffic noise.