نشریه صوت و ارتعاش
پیاپی 22 (پاییز و زمستان 1401)

Material cutting is one of the most widely used industrial processes, which is always accompanied by challenges. One of these challenges is the ability to cut materials with high elasticity such as rubber or soft and crispy materials such as cake. In order to increase the life of the tool and achieve a suitable and accurate cutting surface and achieve a high cutting speed, the technology of high power ultrasonic vibrations is used in the modern industries of tire and rubber production and food industries. The proper design of the ultrasonic cutting tool, guarantees the proper performance and the tool life. The design and manufacture of ultrasonic cutting horns is complicated due to the influence of various factors on the shape and dimensions of the part. In this article, the effect of the dimensional parameters of the horn design on two important output factors, namely the resonance frequency of longitudinal vibration mode and the uniformity of the vibrations of the front surface of the ultrasonic cutting horn made of titanium alloy, have been investigated and analyzed. The results have shown that by using design improvements in finite element software, it is possible to achieve a cutting horn with a frequency close to the nominal design frequency and with the highest uniformity of the vibration amplitude on the front surface of the horn.

Cylindrical shell structures are exposed to various types of defects and damages such as cracking, which may destroy their structural safety. The effects of cracks in the design of cylindrical shell structures are significant due to their impact on vibration and safety characteristics. In this article, the free vibration analysis of cracked cylindrical shell has been investigated by numerical and experimental methods. In order to investigate the actual vibration behavior, modal analysis was used in the laboratory method and commercial finite element software was used in the numerical method. In order to verify the results, by creating a crack in the laboratory model, the frequencies of the cracked cylindrical shell are measured and compared with the numerical solution. The effect of various parameters such as crack length, crack angle, crack depth, crack location, shell thickness, shell length under boundary conditions of two free ends has been investigated on vibration frequencies. To determine the influence of each parameter on the vibration frequencies, a test design has been done using RSM-CCD. The obtained results show that with a 67% increase in the ratio of crack length to diameter, the natural frequency decreases to 32.7% and also with a 50% decrease in the crack angle, the frequency decreases to 24.5%. As a result, the natural frequency created by the crack changes in a certain number of modes--condition, depending on the location of the crack.

Exposure to noise pollution in closed occupational and non-occupational places can cause disturbances in human well-being, comfort and health. The sound pressure level index (Lp) inside the building is affected by the sound power of sources outside and inside the building and the resonance caused by the reflection of the internal surfaces. The amount of sound energy inside the building caused by these real sources inside and outside the building is determined. In order to determine the effect of internal reflective surfaces as a virtual source of sound, on the amplification of energy in the closed environment and consequently the amplification of the sound pressure level, it is necessary to provide models for the prediction of the final sound pressure level. The existing calculation models show that the control intervention on the internal surfaces of the building through sound absorbing materials can theoretically reduce the ambient noise up to 30 dB and objectively up to 20 dB. So far, no valid model has been presented to separate the role of the interior surfaces of the building in the amount of sound amplification of the total of real sources. In this article, while introducing the acoustic analysis indicators inside the building, the room index (RI) is introduced to determine the role of the virtual source in the sound amplification inside the building, and an experimental model is presented to determine this index.

This article examines the effect of layer arrangement and fiber angles on the vibration behavior of cylindrical shell (FML) in GLARE and ARALL samples and on Pasternak elastic bed with different boundary conditions using 3D elasticity theory (composite/metal volume ratio is fixed in taken). The governing equations are obtained using the potential energy minimization principle. In order to ensure the accuracy and convergence of the results of this study, the numerical solution was done using the Finite Element Method (FEM). The results show that the layering has a great influence on the vibration behavior of the FML cylindrical shell. The results are in good agreement with other literature. The use of three-dimensional elasticity theory along with the analysis of different samples for the vibrations of reinforced FML shells, which is presented for the first time in this research, is one of the most important innovations of the current research, and these results can be used as a suitable criterion for analyzing and optimizing FML shells. It can be used with any number of metal and composite layers, any fiber placement angle and under any boundary conditions.

Sound reflection in different places intensifies the sound of sources. Acoustic reflection is useful in some cases and is often unavoidable. Accurate determination and control of disturbing reflections has always been one of the important positions of acoustic science. Most existing educational and office environments have a short reverberation time and cause the sound to be annoyingly loud.In this paper, the variables affecting the resonance time and its real values in the educational environments of a university site are measured and the existing computational models for estimating the resonance time are analyzed and compared. A developed experimental model is presented based on a logical method using data collected from real environments.The mean absorption coefficient of internal surfaces in Moore environments was 0.04 01 0.01 and the measured resonance time was 0.78 s 0.28 s. 9 common computational models for estimating the reflection time have unacceptable values and more than three times higher for the index. In this research, based on the development of Sabin model, a new experimental Regression model has been presented that the results of predicting its Reverberation time(RT) compared to the measured values are reliable and have a P.value = 0.001, RMSD=0.18 s and coefficient of determination equal to R2 = 0.58.

The accuracy of the large eddy simulation method near the wall depends on the non-dimensional distances y ^ +, x ^ + and z ^ + of the grid in the boundary layer. Study on these non-dimensional distances have been made in various research. But these values ​​can vary depending on the physics of the problem and the phenomena being studied. In this article, the effect of these parameters is investigated on sound estimation. For this purpose two types of grids with different setting have been used. The results obtained from both grids have been validated using experimental data in the one-third octave band . In the study of vortices, using flow lines and Q-criteria, it was observed that the use of larger non-dimensional distances on the wall surface increases the longitudinal scale and strength of vortices and as a result the strength of acoustic waves is estimated to be higher than the actual value. This issue was studied from different directions and it was observed that the differences between the two grids varies at different angles. The maximum difference between the total average sound pressure level obtained by the two meshes is about eleven decibels at an angle of 135 degrees. Considering that the two-dimensional distances used in the both grids were within the suitable ranges suggested in the previous study, it can be said that more stringent requirements for non-dimensional distances are needed to accurately predict the strength of acoustic waves.

The 3D printing technology allows the production of parts with complex geometry quickly. However, the printed parts have poor mechanical properties due to the nature of their layers and the presence of defects such as cavities and poor adhesion between the layers. This paper investigates the use of ultrasonic vibrations to improve the mechanical properties of acrylonitrile-butadiene-styrene printed components. Samples were fabricated with standard geometry of tensile test using a desktop 3D FDM printer. Process parameters are layer thickness and infill. Also, the time of ultrasonic imposing was selected as a variable parameter. The thickness of the print layers are 0.15, 0.2, and 0.30 mm, and the infill is 60, 80, and 100%. The design of the experiment was performed by the response level method. Then the uniaxial tensile test was performed on the samples, and the data were analyzed by analysis of variance (ANOVA). The results showed that the application of ultrasonic vibrations significantly improves the tensile strength of printed parts, which is greater in lower thickness. Also, with increasing the infill, the effect of ultrasonic vibrations increases, which can be due to better bonding of the print layers due to ultrasonic vibrations and reducing the number of pores in the low infill values. Therefore, it is found that by applying ultrasonic vibrations to the 3D printed samples, their mechanical properties were improved and could be used in performance evaluation.

One of the common methods of producing two-dimensional layers is the use of exfoliation in the liquid phase by the physical method of using an ultrasonic probe. In this research, graphene layers were produced using an ultrasonic probe in different liquid medium. In order to obtain the optimal conditions for the production of two-dimensional graphene from graphite powder by shelling in the liquid phase under ultrasound radiation, the simulation of the distribution of ultrasonic pressure in the solution and the calculation of the pressure difference were performed using COMSOL software. This simulation was done for an ultrasonic probe with a working frequency of 20 kHz for a probe with a diameter of 22 mm in order to calculate the difference in sound pressure inside the solution with changes in the immersion depth of the probe. Then, the condition that shows the greatest pressure difference was studied in the experimental work to investigate the effects of immersion depth under ultrasound radiation in producing the amount and thickness of graphene layers. As expected from the simulation results, the experimental results showed that the amount of graphene production increases with the increase of the acoustic pressure difference in the solution. The results obtained with UV-visibl, FESEM, TEM and Raman spectrum show that with the solution obtained from the combination of water-ethanol, the density of graphene layers with thickness less is more possible. In addition, the immersion depth of the probe plays a significant role in producing the amount and number of graphene layers.

Vibrations can have favorable or undesirable effects on systems. The discomfort of the vehicles as a result of moving on rough roads is an example of the adverse effects of vibrations. A variety of dampers are used to prevent these damages. MR is one of the advanced technologies in the field of suspension systems. There is a lot of research today to increase the damping force, reduce construction costs, and design and simulate a damper with ease of construction, which indicates the necessity of a progressive research. In this paper, after the theoretical reviews the equations governing the mechanical model (by the Bingham plastic model), the electromagnetic field (by the Maxwell and Amp law) and the flow field (by the Naviers-Stokes equation) Until a double-rod Damper, which is an exquisite example of these dampers, is designed and simulated through the Camsol software through a multiphysics coupling (fluid-solid-magnet) interaction and then analyze the results. Also, the sample designed, unlike previous examples of these dampers, does not require a gas compensatory chamber. The information obtained from the simulation results showed that due to the requirements of a light car aid that requires a damping force of more than 1000 Nm, the damper is a suitable semi -active device and can produce the minimum amount of the required in the required intense force. Transportation and other areas, such as the suspension of light cars, should be used and improve the comfort and increase the quality of the vehicle.

This article is a review of traditional and modern methods of speech recognition. Speech recognition has a history of several decades and started with methods based on signal processing and dynamic time warping. Statistical methods were noticed and welcomed in the 1980s and the methods based on the hidden Markov models were known as the leading methods. Since the 2000s, statistical methods gradually gave way to models based on neural networks, and with the use of deep neural networks, resulted in higher performances compared to the hidden Markov models. Models based on deep neural networks also were transformed and improved immensely. In the next step, models based on transformers and pre-trained models were proposed and achieved higher accuracies. In this article, after an overview of the methods based on the hidden Markov models, the methods based on deep neural networks and their various structures are discussed, and finally, the methods based on pre-trained models are explained and the latest methods of this kind are surveyed. Finally, the results obtained from the reviewed methods are presented and compared based on the word error rate measure.

With the passage of time and as a result of the growth of societies and the complexity of industry and technology, the human need for energy sources and the use of renewable energies such as wind has been increasing day by day. Therefore, the development of wind turbines is one of the ways to achieve this goal. A wind turbine without vortex blades is an energy generator that is like a column and is placed in the path of air flow and begins to oscillate using the vibrations created by van Karman vortices. And it produces electricity by changing the magnetic field in the alternator. In this study, we intend to design this turbine model in modeling software by considering analytical relationships. Then we analyze the model by numerical solution in Ansys software in different frequency ratios and optimize the parameters such as the diameter and height of the mast, which have a direct impact on the efficiency of the system.