機械装置騒音を対象とした音源近傍の音圧分布計測による音場推定法の研究 : 第1報, 音圧計測と同一面での粒子速度分布推定法

For the assessment of machinery noise, this paper describes a method of estimating normal particle velocity distribution from a sound pressure distribution measured at a single aperture close to the sound source based upon near acoustic holography (NAH) which is realized by discrete Fourier transform. In NAH, the distance between the surface of sound source and measurement aperture is required to be of one-tenth of a wavelength. Actualy, the distance between the machinery and measurement aperture is not short adequately for NAH because of the 3-dimensional features of a machine, so this method is investigated under the condition that sound pressure is measured about one wavelength from the sound source. The size of the measurement aperture was practically determined to be of the order of 1×1m. Through investigation of the effect of various source locations by simulation, it has been shown that the effect of evanescent waves should be taken into consideration. Experimental verification shows that this method can be applied practically in echoic situations.