WAVE-PROPAGATION WITH DIFFERENT PRESSURE SIGNALS - AN EXPERIMENTAL-STUDY ON THE LATEX TUBE

To have deeper insight into the main factors affecting wave propagatio n in real hydraulic lines, we measured the true propagation coefficien t in two latex rubber tubes via the three-point pressure method. The m easurements were performed using both sinusoidal pressure signals of d ifferent amplitudes and periodic square waves as well as aperiodic pre ssure impulses. The results obtained were then compared with those pre dicted by a classic linear model valuable for a purely elastic maximal ly tethered tube. Our measurements demonstrate that the three-point pr essure method may introduce significant errors at low frequencies (bel ow 1 Hz in the present experiments) when the distance between two cons ecutive transducers becomes much lower than the wavelength. The patter n of phase velocity in the range 2-20 Hz turns out to be about 1 0 per cent higher than the theoretical one computed using the static value of the Young modulus. This result supports the idea that the dynamic Y oung modulus of the material is slightly higher than that measured in static conditions. The experimental attenuation per wavelength is sign ificantly higher than the theoretical one over most of the frequencies examined, and settles at a constant value as frequency increases. Int roduction of wall viscoelasticity in the theoretical model can explain only a portion of the observed high frequency damping and wave attenu ation. Finally, increasing the amplitude of pressure changes significa ntly affects the measured value of the propagation coefficient, especi ally at those frequencies for which direct and reflected waves sum tog ether in a positive fashion. In these conditions we observed a moderat e increase in phase velocity and a much more evident increase in atten uation per wavelength.