Acoustical Physics最新文献

The problem of diffraction of ultrasonic waves by a sharp-angled rigid cone is studied. In the framework of the parabolic equation method, an analytical solution of the problem with an arbitrarily located point source is constructed. Namely, the problem is reduced to the Volterra boundary integral equation, which can be solved using the Fourier transform. An experimental measurement of the diffracted field is performed. The experiment is based on the M-sequence method adapted for narrowband sound sources. The experimental and theoretical results are compared.

A SAW resonator based on langasite (LGS) substrate with (0°, 138.5°, 116.6°) cut was designed and fabricated. Simulation and experimental results demonstrate that the resonator has two resonance modes, one Rayleigh wave and the other leaky surface acoustic wave (LSAW). The temperature dependent resonance frequencies of both Rayleigh wave and LSAW had been studied. The results show that the turnover temperature of LSAW mode is below absolute zero, namely, the resonance frequency of LSAW changes monotonically in rather wide temperature range, such as from cryogenic to ultrahigh temperatures. Real-time temperature measurement shows that the temperature sensor based on the LSAW mode can effectively monitor the environment temperature, as the thermocouple does. Our work suggests that the LSAW temperature sensor has great application potential in aerospace field for wide temperature range sensing.

A numerical model for investigating the aerodynamic sound generated by the interaction between flow and bluff body is developed, and then applied to the computation of near-field noise induced by the turbulent airflow passing through a generic side mirror. The flow field is simulated by employing the viscous vortex method. Then the sound sources within the computational domain are extracted from the simulated results with a vortex sound equation. The sound waves, sum of radiated sound and scattered sound, are determined using a time-domain boundary element method combined with the convolution quadrature method for improving the stability of the time marching algorithm. Further, the fast multipole method is adopted to enhance the computational efficiency. The computed pressure coefficients and surface pressure fluctuations match the measurements and simulations very well, and the obtained spectra of near-field aerodynamic sound are also close to the measured results. The comparisons of computed results of two additional cases with the previous studies demonstrate convincingly that the proposed model can effectively predict the flow-induced near-field noise.

Cracks are one of the most common damages to thin plates. Therefore, rapid and accurate detection of cracks is of great significance in the nondestructive testing of thin plates. Most existing nondestructive testing technologies focus on crack localization rather than the quantification of the crack length and orientation. Therefore, this paper proposes a damage index, considering the wave attenuation during propagation, to quantify the crack length and orientation. Lamb waves are transmitted and received by a circular sensor array. Based on the abnormal reflection of the A0 mode of Lamb waves, the reflections at cracks are extracted by the Hilbert transform. The influence of the crack length and orientation are studied parametrically, and the relations between the proposed damage index and crack length and angle are given based on regression analysis.

In this study, phonon crystal structures embedded in acoustic black holes are discussed. The low-frequency band gap is widened by exploiting the low-frequency, broadband and multimode properties of the acoustic black hole. The energy band properties of the acoustic crystal structure embedded in an acoustic black hole are calculated by means of a finite element method. The mechanism of band gap generation is investigated. The vibration transfer characteristics of finite period structures are analyzed. The influence of the structural parameters of the acoustic black hole is analyzed. The results show that the acoustic crystal structure embedded in an acoustic black hole has multiple band gaps in the 500 Hz band and the band gap coverage is increased to 45.18%. The starting bandgap is 16.10% lower than before embedding in the acoustic black hole and the width of the first bandgap expands to 173.03% of that before embedding in the acoustic black hole. The onset and termination frequencies of the first band gap are mainly determined by the vibrational modes of the scatterer and the acoustic black hole structure. The vibrational transfer of the finite period structure is analyzed and shows good damping characteristics in the bandgap interval. Finally, vibration experiments verify the vibration damping effect of the proposed coupled acoustic black hole phononic crystal, and the relevant findings of this paper can be used in the vibration damping design of plate structures, enriching the experience of research related to acoustic black holes.