نشریه صوت و ارتعاش
پیاپی 19 (بهار و تابستان 1400)

Today, hepatocellular carcinoma is one of the most common and dangerous types of liver cancer. In most treating methods of liver cancer such as using microwaves, radio frequency radiation, etc., the electrode enters the patient's body, so these methods are ineffective in the case of metastatic cancer. High-intensity focused ultrasound (HIFU) therapy is an appropriate non-invasive treatment method which no external elements enter the patient's body and can be used frequently. However, the success of the treatment depends on treatment parameters such as exposure time. Therefore, in this paper HIFU heat therapy is simulated for the treatment of hepatocellular carcinoma as a non-invasive method. For this purpose, Model-JC HIFU System, tissue and tumor, and water are included in the simulations. The tumor is considered as a symmetrical sphere with a radius of 0.4 cm. Then Helmholtz and bioheat equations are solved by finite element method (FEM) with considering the boundary and initial conditions. The frequency and power of ultrasonic waves are 1 MHz and 150 W, respectively. Investigation of the temperature distribution and fraction of necrotic tissue declare that the exposure time of HIFU is an important parameter. If the treatment is performed in 100 seconds with this HIFU system, the oval area with large diameter and small diameter of 21.1 and 9.95 mm is completely destroyed. Also, complete tumor destruction is available in HIFU exposure time of 72 seconds. Furthermore, the results also show that this method is suitable for deep and oval tumors.

In this paper, vibrational analysis of a composite rotor blade of a Helicopter, which is required by industrial application, is carried out using Lumped Masses method to investigate probability of occurrences of resonance phenomenon. First of all, out of plane and in-plane equations of motion of rotor blade were obtained, and vibration equations of blade and boundary condition at center of rotation and root blade with and without hinges were derived. Effect of different parameter on blade natural frequency was investigated. To obtain mode shapes of blade, the Myklestad method was used, and using computer code in Matlab software and after its validation, the spoke diagram of blade vibration was represented. The results show the resonance phenomenon will not occurs at first and second modes of vibration of helicopter working condition. As the rotor speed increases, the frequencies in the out-of-plane direction increase faster than the in-plane frequencies. Also increase of rotating velocity (rpm) leads to increase of centrifugal force, thus it increases the related force for evaluation of stiffness distribution along blade. Furthermore, the maximum variation of displacement is transmitted to blade tip and the same behavior for increase of stiffness distribution appeared.

Advanced technologies and complex systems in different industrial areas such as electronics, aerospace, medicine, optics, and so on require producing parts with high surface quality and low roughness. To this end, different non-conventional methodologies such as electro discharge machining, electro chemical machining, laser beam machining, and so forth are proposed for machining and polishing parts that each one has pros and cons. Applying advanced abrasive ceramic grits for polishing is one of the prevalent techniques that has attracted researcher and manufacturer’s attention to produce high precision workpieces. Beside minimum thermal and chemical side effects of abrasive powders on the workpieces, this technique can be applied with various types of energy such as hydraulics, pneumatics, magnetics, and etc. Abrasive polishing uses vibration energy to generate kinetic energy in the powders in order to polish the surface of the parts. even though this method was applied for many years,,, There are some unkown aspects of this process. The focus of this work is on the mathematical modeling and numerical simulations which is done recently by some of researchers in this field.

By reducing the shear force in machining processes, benefits such as tool life and improved machined surface quality can be achieved. In recent decades, one of the most effective ways to reduce shear force is to apply ultrasonic vibrations to tools or workpieces in the machining process. In this paper, a 3D simulation of the milling process using ultrasonic vibrations on Ti-6Al-4V titanium alloy with 5 frequencies and 6 vibrational amplitudes has been performed using ABAQUS software. The simulation results show that the maximum shear force does not change with increasing frequency from 18 to 20 kHz. In this paper, different modes of milling process to achieve the minimum shear force according to the frequency and vibration amplitude parameters have been investigated and by comparing the results, it has been observed that the minimum shear force is obtained between different simulation modes for frequency 18 kHz and vibration amplitude 25 micron.

In the maintenance system in the industry, there are different strategies that are tried in each industry.Implement a specific strategy as the top strategy.Attempt to implement a specific strategy in product maintenance and repair system is a closed view and it is necessary to suit the situation of each industry, the desired strategies select and implement.For example, a predictive repair strategy should be combined with an operational preventive strategy to pave the way for organizational maintenance goals. In some cases it is even necessary for some equipment resorted to work strategy until failure.This paper describes a case study of the achievements of simultaneous implementation of condition monitoring techniques including vibrations and acoustic emissions. The effect of water pollution on bearing life is also investigated has taken. In the following, while examining the observed failure, to find the root causes of the failure and provide targeted solutions Similar failures have been prevented.

The sled system is the main alternative for evaluation of the performance of ejection seat of high-speed aircraft and fighter jets instead of in-flight testing. This system consists of various components, of which the connection of rails and slipper is one of the most important parts. Using an air-gap between the rail and the slipper allows the sled to track the rail with high speed easier, but may lead to deflection and even overturning of the sled system. Researchers in countries owning this technology have investigated and analyzed the forces transmission between the rails and slipper, and showed that the gouging phenomenon, which causes separation of part of the rails or slipper in the form of tear, can cause intensive vibrations transmission to the sled body. The results of research in this field show that the vibrating environment of the sled test is a linear function of velocity, and surface defects can lead to the gouging phenomenon. Also, the most collision of rails with slipper occurs at the upper part of the rail track and using wire rope dampers inside the propulsion segment, and foam in the inner container of the sled reduces the intensity of vibrations transmitting to the sled.

In this study, ductile cast iron (EN-GJS700-2) was evaluated to identify the initiation of cracking and failure. Uniform uniaxial tensile tests were performed on the specimens, extracted from the web of an automobile crankshaft under displacement-controlled conditions according to Iso-6892 standard. The crack initiation detection and failure were performed by the acoustic emission information entropy method. The results of this study showed that the detection of crack initiation in the method based on acoustic emission parameters is associated with uncertainties, while Shannon logarithmic cumulative entropy and Kullback-Liebler logarithmic cumulative relative entropy can be used with good accuracy to detect crack initiation and failure. Another achievement of this study is the presentation of two experimental failure criteria based on acoustic emission entropy, which makes the evaluation approach based on acoustic emission entropy for real-time monitoring purposes to be very practical. Among the two logarithmic cumulative entropies of Shannon and Kullback-Liebler relative, the results showed that Kullback-Liebler relative entropy is more suitable for detecting crack initiation.

Human activities are increasing rapidly in terrestrial and aquatic habitats. Marine and freshwater habitats are being affected by a variety of anthropogenic pollutants. Urbanization, transportation and industrialization have continuously increased ambient sound levels with different temporal and spectral patterns. As an environmental pollutant, anthropogenic sound is ubiquitous in, on and near aquatic habitats and potentially may have detrimental effects on aquatic animals at the individual and community level. Over the past few decades, public attention, activities in the field of conservation and animal welfare by non-governmental organizations (NGOs), and scientific exploration are raising awareness of the potential effects of sounds on marine mammals and fish species. Here, in a set of continuum studies, I review the impacts of experimental sound exposure on the behaviour (swimming distribution and foraging behaviour) of zebrafish and comparative sound-related behavioural responses of two fish species with different hearing abilities under laboratory conditions. However, further laboratory and field studies are needed to show the potential impacts of anthropogenic sounds on the behaviour of fishes.

Sound absorbing porous materials have a wide range of applications in various acoustic designs. In this paper, by introducing different types of acoustic porous materials, various applications of these materials in other industries are discussed. Since the designer needs to be familiar with the parameters expressing the acoustical and mechanical properties of porous materials, the main parameters of these materials are bulk density, modulus of elasticity, flow resistivity, porosity, viscosity characteristic length, etc. are introduced. Then, different methods of direct measurement of the parameters of this type of material based on the international standards are described. At the end of the article, direct and indirect methods of measuring materials are mentioned. In the second part of this paper, the mechanisms of sound absorption in porous materials, the existing experimental modeling and theory for porous materials, methods for measuring acoustic absorption coefficient, and current and future research subjects in this field are described.

In this research, a energy harvesting system was introduced in which two console beams coupled with ‎piezoelectric layers are ‎connected to a rotating rigid disk. ‎First, the system equations were written using the ‎electromechanical Lagrange equations and then solved by exact solution and resonance ‎approximation of the exact solution methods. The energy harvesting system was also simulated ‎in software. The effect of angular velocity on resistance, voltage and optimal power was ‎investigated and observed that increasing angular velocity, the optimal resistance and voltage ‎first decrease and then increase, but the optimal power first increases and then decreases. ‎Optimal minimum resistance and voltage and maximum optimal power are obtained at 44 ‎rad/s. The results showed that in this system in order to produce absolute maximum power of ‎‎0.094 W, electrical resistance of 1115 Ω is required. Power were also evaluated versus ‎electrical voltage and resistance. Moreover, comparison of the results of the three methods ‎showed very good agreement between the results of solving equations and simulation and ‎resonance approximation solution responses are simpler than exact solution ones and have ‎negligible error.‎

The classroom, as one of the most important educational environments, plays a major role in students' learning. Reverberation time is one of the most important acoustic parameters affecting the sound quality inside the environment. The inefficiency of classical formulas such as Sabin, led to the study of the use of machine learning methods as an alternative method for predicting the reverberation time of the environment. In this research, first, using the methods based on geometric acoustics and using Odeon software, the required data sets are collected at 500 and 2000 Hz frequencies. In this dataset, 4 classrooms with a rectangular space were used, along with elements such as desks, chairs, windows and doors. The convolutional neural network used to provide a machine learning based system. In this study, using a convolutional neural network for a frequency of 500 Hz with a coefficient of determination of 93% and for a frequency of 2000 Hz, a coefficient of determination of 95% was obtained.

Fresh eggs are an excellent source of nutrients and functional compounds for human health and they are in the attractive products category. Egg producers are always looking for optimal storage methods to provide safe and high-quality products with high sensory characteristics. The safety and durability of this food should be ensured through storage methods. Thermal processing is the most common method for processing of the products. However, increasing the product temperature causes destructive effects such as coagulation, as well as changes in the taste and texture of nutrients, including eggs. On the other hand, it needs high temperature to remove different bacteria such as Escherichia coli or Salmonella. Therefore, researchers should try to find a non-thermal and bactericidal processing technologies.Ultrasound is a fast, versatile, emerging, promising technology which can be replace with thermal processing. In general, ultrasound can be used in two step for egg: detection and disinfection. Assessing the freshness of eggs, which is related to the level of proteins, minerals and vitamins in them, is highly requested for the food industry. Studies show that the speed of the ultrasonic phase depends on the physical and mechanical properties of the egg and ultrasound can be used as a non-destructive and efficient tool to analyze the quality of eggs. Ultrasound is also very effective and practical technology in terms of disinfection. Studies show that ultrasound alone or in combination with other pasteurization processes can be apply for this processing.