مجله انجمن مهندسی صوتیات ایران
سال ششم شماره 1 (بهار و تابستان 1397)

Underwater Acoustic Tomography (AT) system transmits acoustic waves into the water. The AT systems continuously measure the physical characteristics of the flow in rivers, seas and the oceans. The AT systems are synchronized via a GPS clock connectied to the satellites. Hence, the systems transmit the acoustic waves at the same time. The systems record the arrival time of acoustic waves. After analyzing the received signals, the flow characteristics would be estimated. In the present study, design, manufacture and performance of an AT system are investigated in the Kousar Channel, Malek-Ashtar University of Technology. Two Fluvial Acoustic Tomography Systems (FATS) were deployed on both sides of the channel. The horizontal distance between two systems was 127m. The FATS simultaneously transmitted sound pulses from the 30 kHz omnidirectional transducers every 60 seconds. The results showed that the underwater sound speed and the water temperature were 1482 m/s and 20.3 ˚C, respectively. The temperature sensor measured the surface temperature in the various points of the channel and confirmed the validity of the FATS measurement with the relative error of 5%. The estimated flow velocity was zero. Due to the water stagnation.

Investigating waves propagation’s equation in the atmosphere is one of the important and widely used issues in various sciences, which has attracted many researchers. A type of propagating waves is an acoustic-gravity wave. These type of waves have a lot of stationarity properties and can be propagate to a high altitude in the atmosphere. The equation of acoustic-gravity wave propagation is a hyperbolic nonlinear hydrodynamic equation consisting of continuity, motion, and energy equations. To obtain the solution of the acoustic-gravity waves propagation equation, the related hydrodynamic equations are written in the form of a conservation equation. In the next step, the propagation of the acoustic-gravity wave is simulated in the atmosphere using a two-stage Lax-Wendroff method, which is a finite difference method with a second order accuracy in place and time.

The aim of this study is to evaluate the changes of effective stress distribution in plaque by progressing to the stenosis throat and to assess the pulsatile pulse pressure effect on effective stress of a viscoelastic finite-element model of carotid arteries having less and more than 50% stenosis. In-vivo geometries of the arteries were reconstructed using consecutive transverse ultrasound images. Pulse pressure waveform exerted on the artery walls and Kelvin viscoelastic model parameters were extracted from consecutive longitudinal ultrasound image processing. According to the results of this study, the effective stress applied to the mild stenotic plaque decreases with progression to the throat and there after increases again. However, in more than 50% stenosis, thickness of the layer between the plaque component and artery lumen determines the trend of effective stress exerted on different sites of the plaque. Moreover, results showed that regardless of extremum effective stress locations in different cross-sections, maximum differences between the extremum effective stresses of different cross-sections accure in systole whilst in the beginning and end parts of the cardiac cycle differences are not considerable. It seems that this viscoelastic model can be used for accurate evaluation of stress distribution during the atherosclerotic stenosis progress.

In this study, the acoustic properties of porous absorbents with different porosity levels have been evaluated using different mathematical models. These models use one or more parameters of materials for calculating acoustic characteristics. In all of these models, materials are considered as equivalent fluid and reactionary characteristics have not been taken into account.

Muffler is one of the main components of an automotive exhaust system, which reduces the noise of the exhaust system. In this paper, modeling and simulation of the acoustic behavior of a muffler is presented with the aid of  an engineering software. For this purpose, firstly, an analytical model is presented to evaluate the sound transmission loss in cylindrical shells based on Sander's theory. Then, catalytic converter and muffler are modeled by considering the model's major dimensions in the engineering software. The comparison of the present results with previous studies shows the accuracy of the analytical model as well as the simulation results. In addition, the contour of sound pressure inside the catalytic converter and the muffler, as well as the direction of  the exhaust gas flow inside the muffler, indicate that the sound level created by Muffler is in the safe range according to the limitations posed by the standards.

The mathematical modeling of the acoustic wave propagation in seawater is the basis for realizing goals such as, underwater communication, seabed mapping, advanced fishing, oil and gas exploration, marine meteorology, positioning and explore the unknown targets within the water. However, due to the existence of various physical phenomena in the water environment and the various conditions governing the sea environment, such as, noise, sea state, depth, substrate, temperature and salinity, various methods have been proposed for the propagation of acoustic wave, which results in a high computational complexity in the numerical solution of acoustic wave propagation. Since the high speed of computing is a key factor in most real-time applications, in this study, a parallel algorithm for the implementation of computerized underwater acoustic wave propagation is presented, using the Gaussian Beamtracing method. In order to compare the performance of the proposed parallel algorithm with respect to the serial mode, the results are reported in figure and table for several different scenarios. The simulation results indicate a much higher rate of parallel algorithm than the serial mode despite its very precise accuracy.

Ultrasonic horn with transfer of acoustic wave into an aqueous solution results in unique properties. When, transfer of sound wave into a liquid results in liquid movement in the direction of wave propagation which gradually loses its energy due to the viscous friction. This wave motion induces a flow which is known as acoustic streaming or micro-streaming. In this article, a simple innovative system is designed and built to measure the power generated by micro-streaming. By measuring and analyzing the physical relations, the micro-streaming power obtained for various amplitudes was between 0.5 to 2.61 watts and the maximum displacement of the tip acquired was between 8 to 25 micro-meter for this ultrasonic horn.