بررسی شرایط لازم برای انتشار موج تخت در موج‌برهای آکوستیکی در محیط هوا و آب

In acoustics, measuring the acoustic properties of materials—such as the sound absorption or reflection coefficient—is of great importance. The impedance tube, as a standardized method for measuring the acoustic properties of materials, consists of a cylindrical waveguide, a sound source, and several sensors. For accurate measurement and calculation of acoustic quantities in this apparatus, it is necessary that the acoustic wave generated by the sound source propagate as a plane wave inside the waveguide.
In the standards, the dimensions of the waveguide components—including the tube diameter, the locations of the sensors, and the position of the sample—are designed in such a way that plane wave propagation is ensured. However, due to the absence of a standard for impedance tubes in water environments, and because the acoustic impedance of water is closer to that of the waveguide wall material (usually aluminum or steel) than in air, it is necessary to investigate the conditions for plane wave propagation inside a water-filled waveguide.
In this paper, numerical simulations of wave propagation inside a water-filled impedance tube and the mode shapes of the tube are performed using the finite element method (FEM). First, a model for the acoustic waveguide is developed in COMSOL Multiphysics, and a criterion for evaluating the planarity of the wave is defined. Then, two impedance tube models in air and three in water are simulated, and the plane wave propagation in each is analyzed. The modes in which the wave deviates from planarity are identified, and their mode shapes are presented.
Finally, a waveguide with optimized dimensions and a wider frequency range compared to previous studies is proposed. Additionally, plane wave propagation in the proposed waveguide is examined under three different conditions.