مجله انجمن مهندسی صوتیات ایران
سال چهارم شماره 2 (پاییز و زمستان 1395)

In the present article, hydro-acoustic computations of a hydrofoil has been accomplished, using Navier-Stokes and Kirchhoff as well as Fowcs-Williams-Hawkings methods and the results have been compared against each other. A Hydrofoil NACA-0012 in water has been considered at Reynolds number and hydrodynamic analysis has been conducted at seven different angles of attack, using Ansys-CFX solver. For the acoustic computation, a computer code named AcoPy has been developed which has the capability of parallel processing. Sound pressure level has been obtained for these methods at angle of attack of 10 degrees for five different surface integrals and at distances of , 0.01, 0.076, 0.25, and 1.0 of the hydrofoil chord. The computed sound pressure levels have been compared against those obtained by the Navier-Stokes equations. Finally, by comparison of the results of various surface integrals, an optimum surface integral has been determined for the Kirchhoff as well as Fowcs-Williams-Hawkings methods. On the other hand, acoustics behavior of the foil has been presented for various angles of attack. It was concluded that the FWH method, due to the consideration of nonlinear behavior of the pressure, produces better results than the Kirchhoff method.

In this paper, we have investigated the propagation of sound waves into one- and two- dimensional phononic crystals. The phonon crystals constituted of square rows consist of metal filled cylinders in epoxy and air background. The metals are of the third group of periodic table, for instance Aluminum and Nickel. Frist, we calculated the band structure by using the plane wave expansion method (PWE). Then, we determined the absorption and transmission coefficient, and Pressure distribution. The crystal sizes of the crystals are directly proportional to the wave length, therefore making it possible to create crystals which vary from macrometers to nanometers and with frequencies which vary from Hz to THz. The results of the numerical simulation for absorption and transmission coefficient and pressure distribution for five metals are presented.

In last two decades, a considerable enhacement in developing and using of nondestructive techniques in the field of agriculture yields quality-metering is achived. Ultrasonic test, as a nondestructive test method, is being developed in agriculture yields quality-metering. Among native fruits, tomato, for many reasons have a special place, but main studies about damages to its texture have not been conducted. For this reasons, tomato was selected for this study. In this study, Ultrasonic Quali-Meter System (UQS) is utilized to investigate the texture and other sougth properties of tomatos by sending and receiving the ultrasound waves through the tomatos. UQS by sending and receiving non-continuous signals determines ultrasonic indexes such as velocity of waves passing through tomatos, attenuation coefficient and so on. In this study, 360 ripe early tomato (first tomato) samples of Khuzestan province were made available and prepared for the tests. The tomatoes are divided into four groups of 90 units each. Out of these groups, the fourth group was selected as the instance group, on which loading it is not performed. The other three groups were exposed to traumatic loading by free drop test method at three energy levels of 0.8, 1 and 1.2 J.. Every day, out of each group, 9 samples were randomly selected and surveyed for the ultrasonic, biochemical, mechanical and physical indices. Results showed that tomato damage level and storage time have meaningful effect on ultrasonic wave velocity and stiffness. Hence, use of the ultrasonic method provides the possibility of determination and estimation of some parameters related to tomato ripening in supplying lines such as separating operation and fruit grading.

In this paper, a two stage synthetic aperture sequential beamforming (SASB) is presented to abtain better lateral resolution besides more range independent lateral resolution and contrast enhancement compared to dynamic receive focusing (DRF) method. Proposed two stage beamforming includes two sequential beamformers. First, a set of B-mode image lines using a single focal point in both transmit and receive are stored. The second stage uses the focused image lines from the first stage as input data, so a high resolution image will be obtained. Obtained results show for the lateral resolution (in terms of FWHM) there is improvement of almost a factor of 2.5 (dB 6) compared to DRF method. The proposed method on average improves 5 dB and 60% in contrast ratio (CR) and contrast to noise ratio (CNR) compared to DRF method, respectively. Also, the SASB image for the simulated phantom clearly shows the 2 mm diameter cyst which is not detectable in the DRF image.

Underwater vessel is one the most important naval equipments, especially from the defence point of view. Therefore, Camouflage of these vessels is a key factor in their survival. Thermal noise and hydroacoustic noise are two major noises of underwater vessels. As a result, in this paper, these noises are investigated around an underwater vessel body with three different speeds. To this end, thermohydroacoustic analyses are conducted using the Navier-stokes and heat transfer equations. In addition, Ffowcs Williams and Hawkings model are implemented to obtain sound pressure level in far field. Ansys-CFX solver is used to compute the Navier-stokes and heat transfer equations and a parallel processing code in Python named AcoPy is prepared for calculating the sound pressure level. Thermal radiation intensity and sound pressure level (SPL) characteristics are evaluated for thermal noise and hydroacoustic noise, respectively. The obtained Results have shown that change in speed does not have any significant effects on the thermal noise. Also, increase of hot wake behind the underwater vessel with enhancement of its radiation intensity is achieved by an increase in the vessel speed. On the other hand, thermohydroacoustic analysis has shown non-uniform pressure and velocity distribution at Reynolds number Re=45×106.

Pattern matching is a method that used for quality control in production lines. In this study, the pattern of ultrasonic wave propagation in rubber compounds was used. Ultrasonic test is a non-destructive test. In addition to identifying defects, non-destructive tests are used to study material characteristics such as the mechanical and structural properties. The main advantage of non-destructive tests is detecting defects and characteristics of materials without changing the test piece. In this research, this method was used to investigate passenger radial tire tread compound formulation. To investigate the radial passenger tire tread compound formulation at first 14 samples with different formulations were prepared and for each of the samples the propagation velocity of the longitudinal sound waves was measured. Another sample with a new formulation was developed and longitudinal wave velocity was measured for validation of proposed method. The validation results show that the proposed method can accurately predict longitudinal wave propagation velocity in radial passenger tire tread compounds. Thus, this method can be used for validation of compound formulation in rubber production lines.

Direction of arrival estimation of acoustic wave has been an active research area in signal processing field. Conventional methods in this area usually use the beamforming concept to provide a spatial filter and to estimate the propagation direction of wave. Low resolution, low discriminability of closely spaced sources and high sensitivity to spatial aliasing effect are the main disadvantages of this approach. In order to prevent these drawbacks, this study utilized the joint sparse representation models to estimate the direction of wideband acoustic sources. To this end, an Augmented Lagrangian-based method is proposed in the estimation of sparse coefficient matrix stage. The performance of the joint sparse model is compared with three well-known methods (Bartlett, MUSIC and Capon) in the context of direction of arrival estimation. Simulation results show that the method with sparsity constraint outperforms the three previously mentioned methods in terms of angular resolution, discriminability of closely spaced sources, robustness to spatial aliasing and detection of simultaneous acoustic sources. Furthermore, the robustness of the joint sparse method in terms of noise level was almost similar to that of MUSIC and Capon (optimum beamformer). Comparison of the proposed method and one of the most significant sparse approaches in estimation of sound direction show that, complexity (execution time) is reduced by the presented method in this paper while the good performance in terms of angular resolution, discrimination power and detection rate are also preserved.