ABSTRACT
The analysis of the vibratory behavior of plates and their acoustic responses is very important in many sectors of industry. The excitation can be localized, as encountered in impact problems, or moving, as generated by a passing vehicle. Even though the dynamics of these problems have been widely studied via the finite element method, most research on the elastoacoustic response has been performed either experimentally or analytically. In addition, researchers have focused on the radiation of impacted plates at their centers and have been particularly interested in the initial transient wave. In this paper, the acoustic field radiated in air by a circular plate embedded in a rigid baffle, whether due to an impact or a moving force, is studied using isogeometric analysis, which has never been applied before to this kind of problem. For this purpose, both Reissner-Mindlin theory and the Rayleigh integral equation are discretized using the Bézier extraction method. Particular attention has been given to analysis of the near field radiation of a plate subjected to a moving force.
ABSTRACT
Ultrasonic fields propagating in viscous media undergo changes in shape due to diffraction, attenuation, and dispersion. Until now, some implementations in the transmission line matrix (TLM) method has been developed to simulate either diffraction or attenuation but never both. In this work, the quadratic frequency dependence of the absorption coefficient as well as the dispersive effect of a viscous fluid are introduced in the TLM method. The idea is to decompose the emitted wave into its components at different frequencies using Fourier transform. Then, dispersion and attenuation effects are considered for each wave component separately before superposing them to get the required acoustic response. This is possible because each one of them is characterized by a constant absorption coefficient and propagates at a single speed. This TLM model has been applied to the diffracted ultrasonic field by a circular transducer radiating a short pulse in a viscous fluid. The obtained waveforms are interpreted in terms of plane and edge waves. A study of the influence of the most important parameters on the waveform of the detected ultrasonic pulses is performed. The numerical results obtained highlight the attenuation effect on the waves' shapes and the influence of the dispersion on their arrival times.
ABSTRACT
A successful evaluation of a radiated acoustic field was obtained by discretizing a circular transducer surface into only 20 Bézier elements. Accuracy of results was highly dependent on the number of Gauss points (ngp) used. This number can lead to changing the amplitude of both plane and edge waves, especially for near field points. But most changes have been detected between those waves where unexpected waves appeared. They can be of the same amplitude as the plane wave if ngp is chosen arbitrarily. To improve accuracy, the ngp must be increased gradually from the transducer centre and not only at its edge.
