Last but not the least, 3-D results show that aerosol parameters interestingly have significant effect on the cut-off frequencies of the duct. On the other hand, the 3-D solution has been analyzed for higher order duct modes and impedance wall conditions, emphasizing on the discrepancies between 1-D cases. The dependency of dispersion on the mean flow and the concentration level is not similar for all frequencies. Furthermore the effect of mean flow has relatively different behavior on attenuation with respect to concentration level and flow direction. Results of 1-D solutions have shown that the effect of finite mass loading on attenuation is not linearly proportional. The codes have been validated with the corresponding analytical results, while existing analytical solutions are extended to cover the cases of mean flow and 3-D (axisymmetric) cases. Perfectly Matched Layers (PML) equations are adopted for inlet and outlet boundaries. The developed codes in 1-D and 3-D (axisymmetric) forms are based on finite difference method in frequency domain. In this study, a coupled phase approach is chosen due to its superiority for aerosol acoustics among others. There exist several analytical approaches in literature for treatment of basic aerosol problems with certain limitations however in order to solve rather complex cases, these limitations must be handled and worked out. The aim of this thesis is to develop a numerical approach which can solve the sound propagation problem in air-filled circular duct containing water droplets (regarded as an aerosol) in order to obtain acoustic absorption and dispersion characteristics of the system. These sound files can also be found at the web page (Ref. 46 for the sound file of the data in (a), and for the equivalent sound file when fog is added to air. The inset clearly displays the rising notes that can be heard as the rising bubbles effectively shorten the length of the “organ pipe” above them. The insert overlying the upper right corner of this plot shows, with the same dB greyscale, a high-resolution detail of the low-frequency ( < 2 kHz) section of this plot for $ 5 seconds after the bubbles are first injected. The chirps are clearly visible until t $ 7 s, but after that are increasingly attenuated as more bubbles are injected into the pipe, such that after around t 1⁄4 13 s only the bubble noise is detectable.
(c) A time-frequency spectrogram of the data in (a). Bubble injection began at time t $ 7 s and the valve was closed over the 3 s from $ 35 to 38 s.
#DEMONSTAR SOUND EFFECTS FULL#
(a), (b) The hydrophone signal from the water column, (a) being the full spectrum data and (b) being the signal after filtering by the 10 kHz high pass signal.
0 kommentar(er)
