نشریه صوت و ارتعاش
پیاپی 23 (بهار و تابستان 1402)

This paper develops an intelligent attitude control and vibration suppression system for flexible spacecraft performing a single-axis maneuver with external disturbances and parameter uncertainties. Fully coupled nonlinear equations of motion are discretized by Hamilton's principle and the finite element method. The attitude control structure utilizes a fuzzy algorithm to control the attitude and vibration of the panel simultaneously. This algorithm uses a vibration criterion for flexible parts, attitude errors and time inputs. In order to evaluate the performance of such an approach, super twisting-non-singular terminal sliding mode (SNTSMC) and strain rate feedback (SRF) were used simultaneously. The proposed SNTSMC/SRF algorithm takes advantage of each as part of a hybrid algorithm that leads to increased targeting accuracy, faster convergence rate, reduced chattering, reduced residual vibrations, and reduced rigid-flexible bodies interactions. The Lyapunov theory demonstrates the system's overall stability. Simulation results as a comparative study demonstrate the effectiveness of both approaches in reducing control-structure interactions during large-angle maneuvers.

Fault Diagnosis of gearboxes using vibrations is one of the most common methods in industry, which is performed by measuring and analyzing the transverse or torsional signals. The purpose of this research is to analyze the torsional vibration signals in time and frequency domain in comparison with the transverse vibration signals at different speeds, and then to determine the advantage of the torsional vibration signals for detecting the crack defect of the gearbox. To this end, the time-varying mesh stiffness of the gear pair has been extracted using the potential energy method for healthy and defective teeth. Then, the dynamic equations of the system are derived by the lumped parameter method and the transverse and torsional vibration signals of the gearbox are obtained. In the following, the vibration signals at different speeds has been analyzed in the time and frequency domain. The results show that the amplitude of frequency components, including mesh frequency and side bands, in the transverse vibration signal, is highly dependent on the working speed of the gearbox. However, by speed change, the torsional vibration signal, the vibration amplitudes at the mentioned components have little changes. This issue becomes important in the fault diagnosis process. Therefore, by using the torsional vibration signal, it is possible to survey the defect growth at different speeds (specially low speeds) of the system better than the transverse vibration signal.

The purpose of this article is to estimate the position of sound sources. The proposed method uses two acoustic vector sensors in such a way that the intersection of the rays of each acoustic vector sensor (AVS) obtained from their azimuth angle shows the position of a source. Since in practice the sound sources are non-point, then the estimation of the position using this method indicates the area where there is a possibility of the presence of the sound source. In this article, the effect of different parameters on the estimation error of the sound source position is investigated. One of the most important parameters is the rotation angle of the sound source. The obtained results show how the position estimation error changes under what conditions and parameters. This helps to provide the best conditions for estimating the position of the sound source with the least error. The error in position estimation depends on the size of the sound source, the distance of the source to the AVS, the distance of the two sensors from each other, and the angle of the source to the sensors. The proposed method is used in identifying sound sources, especially in military industries and estimating the position of moving sound sources such as road vehicles.

In this paper, the flow field is investigated by solving the fluid dynamics and acoustics of the launch vehicle for a specific sample model with Fluent software. The model used in this research has been studied acoustically in one of the essays previously in the laboratory. The components that constitute the launch vehicle affect the level of noise exerted to the rocket as it rises. In the present study, an attempt is made to numerically examine the contribution of a component of the main launch structure, namely the launch pad, to the acoustics and the flow field around the known launch vehicle whose experimental information is available on a jet output current deflector. For this purpose, in order to ensure the numerical solution, the flow field of the fluid exiting the projectile jet was investigated in terms of pressure and flow velocity parameters as well as Mach number, which was in accordance with the experimental conditions presented in the experimental work. Then the acoustic power values were obtained as a contour on the current field symmetry plane by software. The size of the acoustic pressure level at the location of the sensors identified in the experimental work was determined in the present study and calculated according to the results of acoustic information. Comparison of acoustic results from numerical solution at near field sensors showed very close agreement in less than 3.3%. the difference is close to 8.9%, which is more than the near field results.

Subgrid models are employed to predict the effect of small eddies in the LES method, and their performance is important in calculating the Reynolds stress and transferring the kinetic energy of turbulence to the grid. In this paper, the effect of sub-grid scale models in the LES method on the calculation of aerodynamic sound is investigated. For this purpose, five different sub-grid scale models including Smagorinsky-Lilly, WMLES, WMLES S-Omega, WALE, and KET have been used. First, the statistical convergence of computational methods has been investigated by employing aerodynamic coefficients, and the WMLES S-Omega model has been discarded due to aerodynamic instability. The near-wall flow study reveals models’ differences in the prediction of separation location and length-scale of vortices, which has changed the flow pattern. Aeroacoustic results obtained for the sound pressure level in the one-third octave band are validated using experimental data for the Naca-0012 3D airfoil. Based on the obtained results, the WALE model has presented the best approximation among different models in terms of the amount and trend of sound changes in different frequencies.

The purpose of condition monitoring is to monitor the conditions of an asset in order to predict its failure. The first step in implementing condition monitoring is to establish a health indicator. To construct the health indicator, operational data such as vibrational data should be collected from the asset during its operation, followed by extracting meaningful features from the data.This study introduces an artificial intelligence model (convolutional autoencoder) for feature extraction from the vibration data, which only requires healthy status data for training. For this purpose, the vibration data of the asset is gathered online during operation in a healthy state to establish the healthy dataset. Then, the deep learning model is trained by the healthy dataset. Finally, after the failure stage is detected, the health indicator is established by measuring the differences in the vibrations of the healthy and the failure conditions. The performance of the proposed model is evaluated by vibrational data of a gearbox. The health indicator exhibits a monotonically increasing degradation trend and has good performance in terms of detecting incipient faults.

The study of pendent drop behavior as a nonlinear dynamical system has long been the focus of researchers. The vibrational behavior of the pendent drop at resonant frequencies contains useful information for investigating more complex dynamic systems. The oscillatory behavior of pendent drop at resonant frequencies contains useful information for investigating more complex dynamical systems. Dimensionless Bond and capillary numbers are important and effective parameters in the pendent drop behavior. In this work, the effect of dimensionless Bond and capillary numbers on the resonant frequency of the pendent drop is investigated. Two-dimensional multi-relaxation ‎time lattice Boltzmann method (MRT-LBM) was used to simulate the oscillations of the drop using a conservative model for high-density ratio. Using this model, the drop oscillatory characteristics were calculated for different values of Bond and capillary numbers. It was realized that increasing the Bo number from 0.11 to 1.96 causes an increase in natural frequency from 3.278E-4 to 1.88E-3 in an almost linear manner. Also, increasing the capillary number from ‎1.8E-5‎ to ‎7.3E-4‎ causes an increase in natural frequency from 3.278E-4 to 5.700E-4 in a non-linear logarithmic manner.

Today, there are many methods and equipment for estimating the speed of a moving vehicle, which many of them are expensive due to the installation conditions and requirements. One of these methods is the use of sound intensity quantity. Sound vector sensors, which are passive sensors, can obtain sound intensity values from the environment. In this article, using two sound vector sensors, the average speed of moving vehicles in circular paths is obtained. In this method, to get the speed, it is necessary to estimate the location of the source first. A sound vector sensor alone cannot determine the location of the sound source and can only estimate the direction of arrival (DoA). By using two sensors and determining the intersection of the rays of each sensor, the location of the sound source can be detected. The methods and equations governing this method are presented in this article. In the end, the numerical results are analyzed. In this article, various circular paths have been studied. The results show that the proposed method is good at estimating the location and speed of the moving vehicle at different times.

The cabin of a road vehicle contains multiple noise sources, which can be airborne or structure-borne. These sources include the transmission, engine, tire and road contact noise, aerodynamics noise, and more. The noise in the cabin can significantly affect passenger comfort. Therefore, it is crucial to have an accurate vibroacoustic model for analyzing and controlling vibrations. However, creating a simulation that closely reflects reality using a finite element model is highly complex. This complexity stems from the large number of degrees of freedom in the model, which requires significant computational resources for simulation. To overcome these challenges, various model order reduction (MOR) techniques for linear or nonlinear models have been developed. MOR has two approaches: projection data-based and equivalent model energy-based. In this paper, we utilize two MOR methods to simulate a reduced coupled model. The first method is based on the Krylov subspace method, which uses projection bases to reduce the large linear model. The second method is the modal coupling method, which uses the mode shape of the model to create a reduced model. Finally, we compare the pressure and displacement of the reduced model to the model at different frequency spectra.

The selection of high-quality sperm is an essential process in assisted reproductive techniques. The increase in the success rate of these techniques using active and passive microfluidic technologies has attracted the attention of researchers. In this study, an overview of various sperm separation methods was provided. Sperm separation methods based on the most prominent sperm feature, motility, were discussed, and clinical and microfluidic-based methods were evaluated in this field. Among these methods, microfluidic-based acoustic wave methods were discussed explicitly due to their unique advantages in biological applications, such as high controllability, biocompatibility, and non-invasive characteristics. The forces exerted on a sperm cell inside a microchannel under the influence of acoustic waves and fluid were investigated, and the effects of these forces on sperm cells were examined. The research results indicate that acoustic wave actuators can be efficiently used in the design and construction of sperm separation platforms and artificial insemination.

In the existing maintenance and repair system in industries, there are different strategies that in every industry, a specific strategy is tried to be implemented as the best strategy. What is certain is that trying to implement a specific strategy in the product maintenance and repair system is a closed view and it is necessary to select and implement the desired strategies according to the situation of each industry. As an example and in particular, the predictive maintenance strategy should be operational along with the preventive strategy to make the way to achieve the organizational goals of maintenance and repairs smoother. In some cases, it is even necessary to resort to a work-until-failure strategy for some equipment. Implementing a world-class condition monitoring program should be a condition monitoring unit's first priority. This article describes three case studies of the achievements of the simultaneous application of different condition monitoring techniques in the troubleshooting of rotating equipment. Increasing the accuracy of reports of the condition monitoring unit leads to a reduction in the time and cost of repairs and increases the satisfaction and trust of the management towards the condition monitoring unit. The simultaneous use of condition monitoring techniques is the best way to avoid providing incorrect, multifaceted and misleading reports, which sometimes lead to mistrust of different units and the management of a production complex regarding the category of condition monitoring.

In this study, free vibrations of isotropic cylindrical-spherical shell panels connected to each other were investigated. Shells and panels are created by a curve around the central symmetry axis, with a rotation of 360 degrees or less. Equations were extracted using the first-order shear deformation theory, which models the effects of shear deformation and rotational inertia well. Then, assuming Donnell kinematic and Hamilton's principle, the equations of motion for the panels were extracted. The equations were discretized in both x, θ and φ, θ directions, which correspond to cylindrical and spherical sections, respectively, using the extended differential squares method. After equating the derivatives in the equations with a polynomial expansion using the method described, the differential equations were transformed into algebraic equations. In the next step, the natural frequencies of the combined cylindrical-spherical shell panels with different boundary conditions were obtained, and the accuracy of the extracted solutions was verified using Abaqus software and reputable articles. Finally, the effects of parameters such as thickness, length of the cylindrical section, and radius of the spherical section on the natural frequencies of the desired model were investigated.

Lobe compressors are one of the most important compressors used in the steel industry, and the occurrence of any failure in this equipment leads to production stoppage and imposing heavy losses on steelmaking units. Neglecting to monitor the precise condition of lobe compressors has led to the growth of the vibration range of the compressor as well as the adjacent equipment and piping, and in addition to creating misalignment between the compressor, gearbox and electric motor, it has led to the failure of bearings and the failure of precision instrument connections and branching of piping lines upstream. And it will be downstream of the compressors.In addition to the negative consequences of increasing the cost of repairs and reducing production, this issue will cause risks such as process gas leakage. In this article, the study and solution of the vibration problem of the mentioned equipment in one of the country's steelmaking complexes has been discussed.