In this article, the sound attenuation behavior of sandwich panels with cellular core is studied. The core consists of a repeating unit-cell with an auxetic structure and offers a high stiffness and strength-to-weight ratio due to its stretch-dominant architecture. The properties of these structures are strongly dependent on their geometric configuration. The 2D analysis was performed using finite element (FE) method to determine these truss-like structures' normal incidence sound transmission loss (STL) response in 1-1000 Hz. Some geometric parameters like structures height and aspect ratio are varied in an acceptable range with the constraint of constant total mass and fixed length of the structure to study the effect of these parameters on the STL of the structure and is helpful to find the structure with optimum STL. At the same time, effective mechanical properties of the core were calculated. These structures show increased STL compared to previously studied structures like honeycomb structures and the area under STL curve in 1-1000 Hz improved about 32%. This study's results show this truss-like structure's high potential in sound insulation applications in the 1-1000 Hz frequency range. The general relation of the mechanical properties and auxeticity with the STL of the structures was assessed.

This paper proposes a Fuzzy-FxLMS algorithm for improving sound quality (SQ) across varying speeds in hybrid electric powertrains. The algorithm integrates a frequency-domain FxLMS framework with a fuzzy system, forming the core of the Active Sound Profiling (ASP) system. ASP utilizes this combined approach to modulate the amplitude and relative phase of primary noise, achieving SQ improvement. First, primary noise signals are acquired from the hybrid electric powertrain at specific speeds. A sensitivity analysis identifies key design frequencies impacting SQ attributes like Loudness, Sharpness, Roughness, and Tonality. For these frequencies, a multi-objective optimization determines the optimal amplitude and relative phase of the design frequencies. For speeds between the optimized ones, the fuzzy system directly obtains the desired amplitude and relative phase, ensuring low computational cost and control over sound characteristics. This Fuzzy-FxLMS approach, implemented in the frequency domain, achieves SQ optimization across varying speeds. Results demonstrate improvements in Loudness and Roughness, even for speeds between those with optimized profiles. This work paves the way for enhanced sound perception in non-stationary noises, including coast-up/down scenarios in hybrid electric vehicles, while maintaining low computational cost.

Acoustic metamaterials incorporating membrane resonators strategically positioned along the path of acoustic waves have exhibited remarkable capabilities for enhancing sound attenuation in the low-frequency range. This paper presents an analytical model to investigate the sound transmission loss (STL) characteristics of an acoustic metamaterial composed of a plate structure integrated with shunted piezoelectric patches. By combining effective medium (EM) theory with circuit-based impedance modeling, the proposed method provides a rapid and accurate estimation of STL across various configurations without relying on extensive finite element (FE) method or experimental setups. The model offers design flexibility, allowing the STL to be tuned within a desired frequency range by changing the resistance and inductance of the shunt circuit. This provides a low-cost and scalable alternative to purely numerical approaches. The model is validated against FEM simulations, showing strong agreement and highlighting its potential for early stage design and optimization of sound insulation piezo-plate metamaterials.

This paper presents a comprehensive examination of finite element modeling (FEM) approaches for seismocardiography (SCG), a non-invasive method for assessing cardiac function through chest surface vibrations. The paper provides a comparative analysis of existing FEM approaches, exploring the strengths and challenges of various modeling choices in the literature. Additionally, we introduce a sample framework for developing FEM models of SCG, detailing key methodologies from governing equations and meshing techniques to boundary conditions and material property selection. This framework serves as a guide for researchers aiming to create accurate models of SCG signal propagation and offers insights into capturing complex cardiac mechanics and their transmission to the chest surface. By consolidating the current methodologies, this paper aims to establish a reference point for advancing FEM-based SCG modeling, ultimately improving our understanding of SCG waveforms and enhancing their reliability and applicability in cardiovascular health assessment.

The low frequency sound transmission loss (STL) behavior of cellular truss-like auxetic structures is investigated. For this purpose, cellular truss-like auxetic structures are used as the core of sandwich panels and the two-dimensional in-plane STL of the sandwich structures are calculated using validated FE simulations. Significant superiority of the STL behavior in terms of high bandwidth at low frequency domain (1-1000 Hz) is observed compared with other cellular materials. The results of parametric studies demonstrate strong effects of geometric parameters on the STL of the structure and could allow for fine-tuning of the acoustic properties.

Noise reduction is very important for cavities such as long ventilation ducts, and train and airplane cabins. This paper seeks to develop, design, and implement an active noise control system to globally reduce narrowband and broadband acoustic noises inside a cylindrical cavity using the Modal FxLMS algorithm along with canceling the feedback effect of the actuator on the reference microphone. In addition, the efficiency of the proposed algorithm is compared to the conventional FxLMS algorithm for broadband noises in terms of acoustic potential energy and energy consumption of the actuators. To this end, the natural frequencies and mode shapes are derived using experimental methods and finite element simulation, and the results are compared. The modal data are used to design and implement a modal filter. The filter output is fed to the Modal FxLMS algorithm as the error signal for updating controller coefficients. Due to the presence of a reference microphone for the proposed algorithm and the effect of the control loudspeaker, it is required to remove the feedback effect. An experimental setup is developed, and an FPGA board and LabVIEW software are adopted to implement and verify the effectiveness of the proposed algorithm. The results indicate that the controller could effectively attenuate the narrowband and broadband acoustic noises globally. Furthermore, although the conventional FxLMS algorithm can suppress the noise around acoustic modes, it produces a larger control signal than the Modal FxLMS algorithm and consumes more energy.

The purpose of this study was to develop a sound quality model for real time active sound quality control systems. The model is based on an optimal analytic wavelet transform (OAWT) used along with a back propagation neural network (BPNN) in which the initial weights and thresholds are determined by particle swarm optimisation (PSO). In the model the input signal is decomposed into 24 critical bands to extract a feature matrix, based on energy, mean, and standard deviation indices of the sub signal scalogram obtained by OAWT. The feature matrix is fed into the neural network input to determine the psychoacoustic parameters used for sound quality evaluation. The results of the study show that the present model is in good agreement with psychoacoustic models of sound quality metrics and enables evaluation of the quality of sound at a lower computational cost than the existing models.

The most common injuries caused by carrying a backpack used by different strata of society are caused by the dynamic force applied to the body by the backpack. The application of vibration isolation is one of the proposed methods to reduce this force. This study has introduced a nonlinear mechanism to reduce the dynamic forces applied to the body, considering the shortcomings of common linear vibration isolators. Low dynamic stiffness and high static stiffness are the advantages of the proposed system. This feature leads to a much lower natural frequency in backpacks compared to conventional systems; thus, it will be effective at low speeds. High static stiffness prevents the initial deformation due to the backpack mass. This mechanism includes one horizontal and two oblique springs. The dynamic equations of this mechanism are extracted using the Newton method, and the analytical results are compared to those obtained from Adams software. Then, the design parameters for the proposed backpack are optimized using the transmission force objective function and the results are compared with the previous studies.

In recent years, there has been a growing interest in the application of ultrasonic cleaning techniques to textiles. However, the impact of textile properties on the cleaning performance has not been studied yet. This paper addresses this gap by systematically investigating the influence of different factors including fabric type, dirt type, and ultrasonic frequency, on the cleaning efficacy of textiles. To this end, four distinct fabric types, characterized by variations in texture, fiber material, and area density, were selected for experimentation. Additionally, two distinct dirt types, derived from chocolate milk and a carbon black-paraffin mixture, were introduced to assess their specific effects on ultrasonic cleaning. To analyze the impact of ultrasonic frequency, two transducers operating at frequencies of 19.5 Hz and 32.5 Hz were designed and fabricated. The quality of cleaning on the fabric samples, stained with the aforementioned dirt types, was evaluated using a full factorial experimental design. Measurement of washing quality was carried out employing a spectrophotometer. The findings of this investigation reveal that an increase in frequency is associated with a reduction in cleaning performance. Furthermore, the type of fabric texture directly influences the extent to which dirt stains are removed from the fabric. The choice of fiber material plays a crucial role in determining the textile's hydrophilic or hydrophobic characteristics, which, in turn, significantly impacts the bonding between textile yarn and various types of dirt. Consequently, the overall cleaning efficiency of the textile is affected by these interrelated factors.

This study aims to obtain the governing equations of free vibrations and its analytical closed-form solution for a rectangular plate with vertical patterns. These shaped plates are extensively used in several kinds of equipment in the automotive, train, and home appliance industries. Therefore, it is important for designers to have a closed-form solution for these patterned plates to study the influences of different parameters on the vibration of these plates, with a very low computational cost. Thus, designers could run optimization procedures to find the best parameters of the plate to obtain minimum vibrations. For this purpose, the governing equations of the system are extracted employing the energy method, and then the Rayleigh–Ritz method is employed for discretizing the equations and extracting the natural frequencies in a comprehensive study of different boundary conditions. Regarding the high number of obtained integrals, an analytical procedure has been applied to calculate the integrals for preventing calculation errors and minimizing computational costs. Moreover, the effect of pattern depth on the variation of natural frequencies of each mode as well as the required number of admissible functions for convergence of the method are also investigated. For the sake of validating the governing equations and the closed-form solution, an experimental modal analysis is performed on the cabinet of a washing machine. The results revealed an acceptable agreement between the numerical and experimental results, and hence, the validity of the extracted equations is confirmed.

Low-cost and highly effective noise reduction has recently become one of the substantial challenges for industrial manufacturers.This paper presents the design and construction of a cost-effective system for attenuating single-frequency annoying noise generated from industrial products and machines.To achieve this goal, narrowband active noise control using Filtered-x Least Mean Square (FxLMS) method has been used with the help of a two-factor digital adaptive filter, called the adaptive notch filter.Therefore, a duct structure has been designed, and experimental tests have been performed.To reduce implementation costs, the Arduino Uno board, which has an AVR microcontroller (ATmega328P), has been used as the controller.About 15dB noise attenuation at 400Hz and 750Hz frequencies and about 30dB noise attenuation at 650Hz and 950Hz frequencies have been achieved.Then, active noise control for two separate and simultaneous frequencies was performed, which had somewhat effective results, and in one of these frequencies, noise attenuation of about 18dB was observed.

The design of sound-absorbing wedges as the main elements used in anechoic rooms is of great importance. There are general standards for the design of an anechoic room and sound-absorbing wedges. The absorption coefficients of the wedges can be obtained in two ways, a numerical technique such as the finite element method and an experimental test either in the impedance tube or in the reverberation chamber. In this paper, the absorption coefficient of a wedge covered by a perforated plate is obtained by simulating the 3D wedge in an impedance tube using COMSOL Multiphysics. To verify the finite element model, the perforated plate wedge is fabricated and tested in a real impedance tube based on ASTM C384. A comprehensive study is carried out on the effect of geometrical parameters on the sound absorption coefficient. These parameters include geometrical properties of the perforated plate such as hole diameter, hole percentage, plate thickness, and geometrical properties of the wedge, such as hub thickness, air gap thickness, wedge cross-section, and wedge width. Moreover, side wedges (semi wedges), the gap at sides of the wedges and lack of absorptive material in the wedge tip under the perforated panel are investigated. Finally, the effect of the arrangement of the wedges on the sound absorption coefficient is also studied. (C) 2020 Elsevier Ltd. All rights reserved.

This approach employs a robust controller on the basis of sliding mode control to propose a novel strategy nominated as self-adjusting boundary layer in order to prevent occurrence of chattering phenomenon. Since the boundary layers and the controller parameters are adjusted just for the special conditions, it is possible that the system losses its desirable performance and leads to this event. In order to better understand the applied procedure, in addition to classification of the paper in two sections, a closed loop block diagram for a system equipped with sliding mode controller is configured, in detail. Therefore, in the first step, on the basis of considering sliding mode control technique, a robust controller is designed in order to control the radiated noise from an intelligent cylinder. In fact, this procedure is employed to extend the offered new strategy. To cover this issue, a series of formulations are developed. Accordingly, the vibration equations of the construction subjected to piezoelectric patches are derived and discretized according to Rayleigh-Ritz procedure. Additionally, by the aid of using the effective control signal for each mode and extracting uncertainties of the system, the robust control signals for uncertainties in sensor and actuator are determined. The results prove that the considered methodology either suppresses the noise transmitted or keeps the system consistency. Moreover, it establishes a compromise between error and chattering that preserves the stability and admissible performance of the system in a wide range of disturbances and uncertainties. As another consequence, this study also develops a new approach to show the effect of using controller on the acoustic pressures at various coordinates taking account self-adjusting boundary layer.

In this study, a robust controller against the uncertainties in piezoelectric patches including sensor and actuator is designed based on sliding mode method to control the radiated sound from cylindrical shells. Accordingly, in order to extract and discretize the dynamic equations of a smart cylinder equipped with piezoelectric patches, the Hamilton’s principle and the Rayleigh-Ritz method are, respectively, used . The radiated sound is estimated by the Kirchhoff-Helmholtz integral and the acoustic structural sensing method. Furthermore, an innovative approach is proposed on sliding mode control to model system uncertainties and design robust control signals against these disturbances. Using effective control signals for each mode is the applied methodology for establishing independent sliding surfaces. In fact, it is attempted to relate between actuator matrix determinant and system control ability in generating the efficient control signals and error reduction due to actuators uncertainties. By the aid of this relation, optimization of the actuators position according to the genetic algorithm is implemented. The obtained results show that by optimizing the actuators position not only the appropriate performance of the system in controlling the radiated sound from the structure is enhanced but also the essential control voltage for each actuator is significantly decreased.

In this paper, a modified sound quality evaluation (SQE) model is developed based on combination of an optimized artificial neural network (ANN) and the wavelet packet transform (WPT). The presented SQE model is a signal processing technique, which can be implemented in current microphones for predicting the sound quality. The proposed method extracts objective psychoacoustic metrics including loudness, sharpness, roughness, and tonality from sound samples, by using a special selection of multi-level nodes of the WPT combined with a trained ANN. The model is optimized using the particle swarm optimization (PSO) and the back propagation (BP) algorithms. The obtained results reveal that the proposed model shows the lowest mean square error and the highest correlation with human perception while it has the lowest computational cost compared to those of the other models and software.

This paper focuses on the dynamic modeling of a cylindrical shell equipped with piezoceramic sensors and actuators, as well as the design of a broad band multi-input and multi-output linear quadratic Gaussian controller for the suppression of vibrations. The optimal locations of actuators are derived by Genetic Algorithm (GA) to effectively control the specific structural modes of the cylinder. The dynamic model is derived based on the Sanders shell theory and the energy approach for both the cylinder and the piezoelectric transducers, all of which reflect the piezoelectric effect. The natural vibration characteristics of the cylindrical shell are investigated both theoretically and experimentally. The theoretical predictions are in good agreement with the experimental results. Then, the broad band multi-input and multi-output linear quadratic Gaussian controller was designed and applied to the test article. An active vibration control experiment is carried out on the cylindrical shell and the digital control system is used to implement the proposed control algorithm. The experimental results show that vibrations of the cylindrical shell can be suppressed by the piezoceramic sensors and actuators along with the proposed controller. The optimal location of the actuators makes the proposed control system more efficient than other configurations.

This paper investigates the active structural acoustic control of sound radiated from a smart cylindrical shell. The cylinder is equipped with piezoelectric sensors and actuators to estimate and control the sound pressure that radiates from the smart shell. This estimated pressure is referred to as a virtual microphone, and it can be used in control systems instead of actual microphones to attenuate noise due to structural vibrations. To this end, the dynamic model for the smart cylinder is derived using the extended Hamilton's principle, the Sanders shell theory and the assumed mode method. The simplified Kirchhoff-Helmholtz integral estimates the farfield sound pressure radiating from the baffled cylindrical shell. A modified higher harmonic controller that can cope with a harmonic disturbance is designed and experimentally evaluated. The experimental tests were carried out on a baffled cylindrical aluminum shell in an anechoic chamber. The frequency response for the theoretical virtual microphone and the experimental actual microphone are in good agreement with each other, and the results show the effectiveness of the designed virtual microphone and controller in attenuating the radiated sound.

Structural acoustic sensing is a method of obtaining radiated sound pressure from a vibrating structure using vibration information. Structural acoustic sensing is used in active structural acoustic control for attenuating the sound radiated from a structure. In this paper, a new approach called Modal Structural Acoustic Sensing (MSAS) is proposed for estimating the pressure radiated from a vibrating cylindrical shell using piezoelectric sensors. The motion equations of a cylindrical shell in conjunction with piezoelectric patches are derived based on the Donnel-Mushtari shell theory. The locations of the piezoelectric sensors are optimized by the Genetic Algorithm based on maximizing the observability gramian matrix. The Kirchhoff-Helmholtz integral is used for estimating the sound pressure radiated from the cylindrical shell. Numerical simulations are performed to demonstrate the advantages of the proposed approach in comparison with previous methods such as discrete structural acoustic sensing and distributed modal sensors. Results show that the MSAS can increase the estimation accuracy and decrease the controller dimensionality and the number of required sensors.

A new approach is proposed in this paper based on radiation modes to control the radiated sound pressure of a smart cylindrical shell equipped with piezoelectric sensor and actuators. The radiation modes determine the specific distribution of normal velocity of the shell that independently radiates sound to the surrounding space. In this study, the first radiation mode is controlled since it is the most effective mode in terms of the radiated power. The results indicate that most of the sound power is attenuated by controlling only this mode. The extended Hamilton's principle, the Sanders shell theory and the assumed mode method are used to derive the equations of motion in a state space form that is suitable to design the controller. The radiated sound pressure is calculated using the simplified Kirchhoff Helmholtz integral along with a Kalman filter to observe the system states, and a modified higher harmonic control (MHHC) is designed to attenuate the sound power. A numerical simulation demonstrated the effectiveness of the proposed approach compared to active vibration control (AVC) in attenuating the radiated sound in the low frequency domain. (C) 2016 Elsevier Ltd. All rights reserved.

In this paper, a virtual acoustic sensor is designed and evaluated experimentally to be used instead of microphones in active noise control of vibrating cylindrical shells. Dynamic motion equations of a cylindrical shell along with the effect of bonded piezoelectric patches are derived based on the Hamilton’s principle and Rayleigh-Ritz method. The Sanders shell theory is used to relate the strains to the displacements of the cylinder. Modal structural acoustic sensing technique estimates the far-field radiated sound pressure of the cylinder. Experimental frequency response function (FRF) of the actual microphone at various locations are obtained and compared to that of the virtual one. The theoretical estimated sound pressure is in good agreement with the experimental results.