Prek M.

This paper describes the investigation of the propagation wave speed and wave attenuation in viscoelastic fluid-filled pipes. The acoustic wave number of axisymmetric waves propagating in a finite pipe is determined from pressure measurements made at three locations along the pipe. Since the measurements were made in viscoelastic pipes, the wave number is complex and encompasses both the wave speed and wave attenuation. The real part of the measured transfer function was used to determine the wave number and the phase speed is obtained with the least-squares linear regression. These values were used further to calculate the wave attenuation. For this purpose, the imaginary part of the transfer function was used. This method is based on the adjustment of both the real and imaginary parts of the wave number until the computed wave number most closely matched the measured value of transfer function. Since the relationships used to find the complex wave number are known, this method essentially finds a complex wave number such that an analytical description of the transfer function at each frequency most closely approximates the measured transfer function at the same frequency. The effectiveness of the proposed method is assessed for two types of pipe material. The fluid-borne sound signal was highly attenuated and the three-transducer method was found to be less sensitive to excessive noise. Even in these circumstances the proposed calculation method enables the determination of the acoustical properties of fluid-filled plastic pipes within a wide frequency range. The measured attenuation exhibits less fluctuation in comparison with previous published results.