JOURNAL OF VIBRATION AND SOUND
Year:2020 | Volume:9 | Issue:17|Papers Count:10

In this paper, a piezoelectric beam is designed to receive sound energy in a real environment. The electrical energy received from this beam can be stored in a battery or used directly by electrical circuits. The use of two simulations of copper and piezoelectric beams, including polyvinylidine fluoride, in which the length of the piezoelectric layer is shorter and located at the optimal point of the copper beam, are used in this simulation. The 100 dB speaker sound power is applied in a 1 cubic meter room considering the presence of air in the environment to the pole in the middle of the room. By making the beam 7. 8 cm long, the first bending frequency of the beam reaches close to 100 Hz. By stimulating the beam at this bending frequency, the noise effect reaches its maximum value and eventually leads to the production of a voltage of about 70 mV.

Today, due to limited access to some places or unfavorable weather conditions, power transmission from the power plant and storage in the battery is very expensive. This has led researchers to find a way to solve this problem, so the use of environmental energy such as noise, motion (or displacement), light, wind, etc. has opened a new chapter for engineers. In this paper, a piezoelectric plate is designed and simulated by modeling a human eardrum. This plate is one of the components of the acoustic-electric converter, which is able to collect the noise of crowded and busy environments and convert them into electrical energy. By recording and analyzing audio signals from two highly polluted locations in MATLAB software, the two frequencies at which the highest sound weight occurred were considered as the intensification frequency. Then, using the software of the COMSOL and the obtained data, the natural frequency of the first mode shape of the converter geometry is equal to the frequency of the amplified sound. The most optimal diameter of the piezoelectric plate was 8 cm and the energy was equal to 10. 5 microwatts per second and the voltage changes were 12 volts. In order to store and use the obtained voltage, a circuit is provided for this purpose.

Along with the expansion of industries and the creation of unwanted sounds, acoustic phenomena and sound control has been the subject of many researches and so far different materials have been used to control it. In this work, samples of polyester yarns were produced by Rachel knitting machine equipped with two needle bars and six guide bars. The two sides of the all samples were similar with a texture of a simple knit on one side and a perforated knit structure on the other side. thickness of samples between the two sides due to various knit structures of samples was considered as the main difference between the samples. Acoustic absorption coefficient of the samples was measured by using impedance tube method in different frequencies by arranging the samples in one and three layers. It was found that the sound absorption coefficient of samples increases by increasing the thickness of samples.

In recent years, with the growing of fractional calculus, applications of fractional calculus in engineering sciences have been emerged. One of the applications that attracted many researchers in recent years is modelling of viscoelastic materials by using the fractional calculus. In this paper, an Euler-Bernoulli micro beam that has been modeled by fractional Kelvin-Voigt, is investigated. The beam is modeled based on linear strains, Modified Couple Stress theory (MCST) and Kelvin-Voigt fractional viscoelastic model. By the using of Hamilton principle partial fractional differential equations are derived. Equations of motions are solved by the using of Finite Element Method and Finite Difference Method. Time domain is discretized based on Finite Difference Method and space domain is discretized by utilizing the Finite Element Method. Simulations show that, fractional derivative has large effect on amplitude and response of free and forced vibration of beam and can increase or decrease the damping of the beam. Moreover, effects of beam length and viscoelastic parameter have been shown. Results of this paper can be used for improving viscoelastic model of materials.

The static and vibration studies of a tower of a surface float is investigated in this paper. Designing a ship's telecommunication tower is one of the most important issues in designing the ship from the structural point of view to install the required types of antennas and radars. Therefore, in the analysis, the telecommunication tower and the deck of the ship are modeled. After examining the static state and calculating deformations and stresses, according to the ship's movements, the resulting forces are added to the analysis and the effects on the stresses and displacements are obtained. It should be noted that in this analysis, accelerations as gravitational force, rotational accelerations as rotational volume forces, and also radar weight as a concentrated force are applied to the structure. Next, frequency analysis is performed and different structural modes are extracted. The results show that in the design process, in addition to considering the parameters of tower design (such as boundary conditions, operating load, places of members), their location of using should also be considered. The use of towers on the deck of the vessels significantly reduced the safety factor. Also, it can be observed various phenomena such as fatigue in the limbs, especially the connection place to the deck, which can have very destructive effects in the long run and reduce the life of the structure. Therefore, in designing the towers of floating structures, more safety factors should be considered and special attention should be paid to the movements of the vessel.

Drills have many applications in industry. One of the applications of drills is in the process of converting which can be modeled as a rotor-disk overhung system. In this paper, the lateral vibration of a concrete drill is studied. For this purpose, first, the governing equations the lateral vibration of the system and its boundary conditions are derived using the Hamilton principle. The governing equations are then solved using the Assumed mode method and the first two natural frequencies of the lateral vibration of the system are calculated by the analytical method. In the following, the effect of changing the main parameters of the system, such as the rotational speed of the drill, the diameter of the drill, and the axial force on the natural frequencies is studied and the results are presented in the form of graphs. The results show that the main parameters of the system, such as axial force and rotational speed, have a significant effect on the value of the system's natural frequencies. The results can be used by design engineers to optimize such systems.

In this study, a theoretical model based on the modified nonlocal Euler-Bernoulli is presented for the detection of biologically adsorbed particles on doubly clamped carbon nanotubes as resonant nano-bio-sensors. The basis of the work of these resonant nano-bio-sensors is the accurate calculation of the change in the resonant frequency because of the change in the mass due to the surface adsorption of the viruses. In most studies, simply supported ends have been used for simplicity of calculations, while it is almost impossible to build such supports at nano-scale. For this purpose, a doubly clamped ends was used to analyze this problem and for the first time, the closed-form vibration frequency response of a doubly clamped nano-sensor was presented according to the geometric and mechanical characteristics of the nanotubes along with nonlocal, surface and rotary inertia effects. Although many researchers have ignored the effects of surface stress and rotary inertia on the vibration analysis of nano-sensors, this study found that these effects at nano-scale played a major role in changing the frequency and accuracy of resonant nano-bio-sensors. Also, based on the obtained results, six different types of viruses were examined. Based on the sensitivity analysis, the designed nano-bio-sensor was able to separate the frequency change and identify them, consequently.

In this paper, the vibrational frequency of the bridge construction structure has been studied by both experimental and simulation forms using the laser doppler vibrometer. The calculations are performed using simulation of MATLAB simulink and using of interference set-up to divide the laser beam into two reference and measurement arms. The time and frequency behavior of the received signals is calculated for vibration of the bridge structure by considering all of noises including optical noise, electrical circuit noise and test environment. Also in this paper, studies are performed during the construction of a laser Doppler vibrometer and by an interferometric set-up. The used set-up in this experiment is the same as the homodyne arrangement of the Michelson interferometer. It should be noted that in this arrangement, a differential circuit has been used to reduce noise in the electronic part of the device. Moreover, by properly processing the signals and removing all optical, electrical, and environmental noise, the frequency of the vibrating target has been investigated with high accuracy. The results of this study indicate an acceptable consistency between the results of simulation and experimental studies, which indicates the high accuracy of the device in measurements.

The interaction between student and teacher and consequently the educational performance in the classroom is significantly influenced by the student's understanding of the teacher's speech. Given the impact of the speech transmission index(STI) on the physical conditions of space along with human factors, it can be expected that creating favorable environmental conditions in these spaces to create appropriate acoustic conditions will improve quantitative measures related to speech Intelligibility and thus improve the performance of the spaces. In previous studies, researchers often focused on background noise level as an external factor or the use of soundproofing materials in walls or interior surfaces and the effect of changes in the length and width of spaces in the same volume that have equal computational reverberation time have been Less paid. Therefore, the effectiveness of speech intelligibility of listeners with the same conditions and position relative to the sound source in spaces with different lengths and widths but with the same area and volume, is the purpose of this article. Here, an attempt has been made with a descriptive-analytical approach through simulation with ODEON software to produce the necessary data for statistical tests and especially correlation test in order to investigate the effectiveness of STI values in fixed receiver points in spaces of different lengths and widths. According to the findings of the statistical tests, increasing the length as well as increasing the distance between the receiver and the lateral surfaces, in spaces with the same area and volume, reduced the values of the STI.

Strong ground motions which recorded near an active fault, have specific physical characteristics. Moreover, the time history of strong a near-fault record evidently contains a large distinct pulse as well as high amplitude spikes in the form acceleration, velocity and displacement wave-like features. The strong near-fault ground motions have potential to release a great deal of energy and create powerful impact motion along with large period pulses in the velocity time history. In order to have a comprehensive understanding and conceptualization on the nature of strong near-fault ground motions caused by high-energy earthquakes, it is possible to develop analytical closed-form pulses and artificial wavelike motions to develop the computational viewpoints related to seismic response of structures. In this study, the simulation and modeling of pulses displayed in the velocity time history of near-fault earthquake records are considered and evaluated analytically. The developed mathematical formulation has been completed based on the application of several compound trigonometric statements. It should be noted that the prepared mathematical formulation has the ability to fit the geometric shape and physical nature of velocity and acceleration pulses. The computational process of the proposed closed-shape formulation has been accomplished in such a way, not only to fit the distinct pulses in both of acceleration and velocity time histories, but also to be applicable in dynamic response analyses. In this regard, the range of kinetic energy flux variations obtained corresponding to both of the recorded ground motions and the fitted artificial motion model, have been calculated and compared.