مجله انجمن مهندسی صوتیات ایران
سال دوم شماره 1 (بهار و تابستان 1393)

Functionally Graded Materials (FGMs) are a class of composites that have continuous variation of material properties from one surface to another. So, unlike composite laminates, there is no stress concentration. FGMs offer great promise in applications where the operating conditions are severe, including spacecraft heat shields, heat exchanger tubes, plasma facings for fusion reactors and engine components. In the present study, sound transmission through FGM cylindrical thin shell is investigated. The shell is assumed to be infinitely long and subjected to harmonic plane waves. The shell is immersed in a fluid medium and an external fluid (air) passes over it with a uniform speed. An exact solution is obtained by solving the shell equations in three directions and acoustic wave equations simultaneously. The transmission losses (TLs) obtained from the numerical solution are compared with those of other authors. Comparison shows a good agreement between the results. Because the pressure and displacement terms are expressed in infinite series form, the convergence checking is performed. Numerical results are used to show the effects of structural properties and flight conditions such as Mach number, flight level and volume fraction. The results shows as volume fraction exponent increases the TL decreasesin stiffness region, but the TL increases at in frequency higher than the ring frequency (mass-controlled region).

The aim of the present study is to propose a mathematical- clinical model for the estimate of axial stresses acting on the carotid artery In order to determine the stresses, a quantitative knowledge of the mechanical properties of cardiovascular tissues, i.e. delineation of constitutive models, is indispensable. In this study, a Fourier series based mathematical model for the displacement of the carotid artery wall in the longitudinal direction was defined, providing a satisfactory representation of the axial stresses applied to the arterial wall. The proposed technique was applied on the consecutive ultrasonic images of the common carotid artery of a healthy man. The waveforms and the equations of the kinematic parameters of the longitudinal motion of the arterial wall and the axial stresses applied to it were obtained during three cardiac cycles. The high correlation between the clinical and model data (0.986) reveals the potential of this technique to provide a new method to assess arterial stresses from clinical data, and overcoming the limitations of the finite element and other simulation techniques.

A particular weakness of using a propeller propulsion system in a vessel is its relatively large acoustic noise which is emanated during its operation and is propagated into its surroundings. Various methods are available for reducing this noise and each of which can lead to the reduction of some portion of the generated propeller’s noise. One of the common methods is to increase the number of the blades and another is to utilize of a duct around the propeller. In this article, by using a computer code called “Acoustic Python,” developed for the purpose of acoustic analysis, along with the results of hydrodynamic analyses produced by ANSYS-CFX software, the effect of each of these two methods is investigated for a Series-B propeller. It is observed that, the application of a duct can indeed reduce the sound pressure level (SPL) of the noisefrom a propeller by more than 20%. On the other hand, it was also evident that increasing the number of blades from 5 to 7, causes a 5% reduction in the generated noise. Based on the obtained results and ease of installation, it is concluded that using a duct around an existing propeller is more appropriate and economical for reducing the generated acoustic noise.

Common medical ultrasound beamformers such as Delay and Sum can be interpreted as element-space methods. In element-space, the received data would be added after applying delays and appropriate weights. The main idea in beam-space beamforming is to use orthogonal beams steered in different directions instead of using spatial statistics of elements in array to distinguish between desired signal and interferences. This means a map from element-space to beam-space. The amount of computation would be reduced because of less signal dimensions, but extra computation is needed to make the map from element-space to beam-space. This additional calculation can be reduced by using FFT. In this paper, minimum variance beamformer is implemented in beam-space instead of element-space to reduce computational complexity. Results show that minimum variance in beam-space can achieve similar resolution and can decrease side lobes as element-space.

In this study, the rate of change in intensity of sound waves in different locations of an ultrasonic bath is investigated. Due to the change in resonance mode of ultrasonic bath, lack of monotony in waves’ intensity, and as a result, unrepeatability of experiment has been observed. The spherical ultrasonic reactor is proposed to minimize this problem. The spherical reactor is a100 ml round-bottomed flask, in which two ultrasonic transducers are attached on the sides of the container in front of each other. In order to study the characteristics of sound intensity in spherical reactor model, the power and influence of standing waves produced by ultrasonic irradiation with both reactor transducers are photographed using the chemical luminescence produced due to the radical hydroxide formation. In ultrasonic bath, dependant on distance from the bottom of the container, the yield of reaction differs from 0.133 to 0.407 nanomolar per Joule for 1 to 30 millimeter distances from the bottom. The yield of reaction in the center of container is considerably different from the yield of reaction in sites closer to the side walls. In the distance of 30 mm from the bottom on the right side of reactor, the yield of reaction is equal to 0.032 nM.J-1, while in the same depth in the center of the reactor, the yield is equal to 0.407 nM.J-1,which isalmost 13 times larger. In spherical reactor, the ultrasound waves obey the Bessel function and as a result of the container’s radius being the constant value of 6.3 cm, nodes and antinodes are always in the same spots. Also, by comparing the yield of reaction when both probes are radiating, with the yield of reaction when just one probe works, one can realize the formation of standing modes. Additionally, the yield of reaction for spherical reactor is about 4.625 nM.J-1, while for ultrasonic bath, the optimum magnitude is about 0.407 10 times more efficient.

Collapse of cavitation bubbles and formation of free radicals are of routine consequence of ultrasound in liquid media. Generation of reactive oxygen species has been proposed to activate the cell signaling pathway in plant cell to get ready to protectfrom stress. Among different reactive oxygen species, H2O2 has a potential to act as a secondary messenger to promote subsequent defense reactions in plants and is capable of triggering changes in the plant cell which leads to a cascade of reactions, ultimately resulting in the formation and accumulation of secondary metabolites. In the present research suspension-cultured parsley cells were treated with ultrasound at 29 kHz with the power of 455 mW/cm2, for 10, 20, and 40 min. The viability of cells, PAL activity, certain flavonoids of parsley cells i.e., apigenin and quercetin and H2O2 content of the cells were assessed. According to the results, exposure of parsley cells to ultrasound increased the amount of quercetin, apigenin and PAL activity. Induction of phenyl propanoid metabolism was accompanied by increase of H2O2 production after exposure to ultrasound. The results implied a stimulatory effects of ultrasound on secondary metabolism of parsley cells which is mediated by signaling role of hydrogen peroxide.

The vibration assisted turning has received intensive attentions due to its advantages such as reduced machining forces and surface roughness. Chattering is a type of self-excited vibrations, occurring in various machining processes. Chattering vibrations, when started, grow rapidly and destabilize the machining process. Moreover, chattering affects surface finish, reduces tool life, and even damages workpiece and machine tool. In this paper, a method is proposed to investigate chattering phenomenon in vibration turning and to predict stability boundaries. The method is in time domain and is solved by numerical methods. The effects of vibration frequency and cutting time ratio are examined. It is shown that frequency has negligible effect while cutting time ratio has the most influence.