Global Journal of Researches in Engineering, I: Numerical Methods, Volume 23 Issue 1

c) Effect of Viscous Characteristic Length on the Reflected Waves The impact of varying the viscous characteristic length on the 1st and 2nd reflected waves at high frequency is shown in Figure 5. With an excitation frequency of 50 kHz, a +20% change in results in a - 1.07% decrease in the amplitude of the first reflected wave and a 42.76% increase in the amplitude of the second reflected signal. Furthermore, as the frequency increases, the sensitivity of the viscous characteristic length decreases for the 1st reflected wave and increases for the 2nd reflected wave. Therefore, we can conclude that the viscous characteristic length has a relatively small influence on the 1st reflected wave at high frequency but a high sensitivity on the 2nd reflected wave. Figure 5: The sensitivity of the viscous characteristic length on the 1st and 2nd reflected waves at a frequency of 50 kHz d) Effect of Thermal Characteristic Length ' on the 1st and 2nd Reflected Waves The sensitivity of the thermal characteristic length Λ ' on the two reflected waves at low ultrasonic frequency is shown in Figure 5 for a variation from +20% to -20% of its initial value. From Figure 6, we can see that for a frequency of 50 kHz, there is very little influence of the thermal characteristic length on the 1st reflected signal. An increase of +20% in Λ ' results in a 0.17% increase in the modulus of the 1st reflected signal, while a variation of -20% results in a -0.26% decrease in the amplitude of the 1st reflected signal. However, the second reflected wave is more sensitive than the first. For a variation of +20% of Λ ', the amplitude of the 2nd reflected wave increases by 3.29%. Moreover, according to Table 1, we observe that the sensitivity of the thermal characteristic length slightly decreases with frequency for the first reflection, while it increases for the second reflected wave. Global Journal of Researches in Engineering Volume XxXIII Issue I Version I 38 Year 2023 © 2023 Global Journals ( ) I Investigating the Effects of Physical Parameters on First and Second Reflected Waves in Air-Saturated Porous Media under Low-Frequency Ultrasound Excitation