In this paper, an enhanced vibrational energy harvesting system for freight wagons is developed by the concept of Auxetic resonators. The novel idea of using Auxetic structures is employed to increase the rate of power conversion by simply changing the structure of the beam without any need to change the geometry of the piezoelectric element or its material. The harvesting system is a resonating cantilever beam, and a piezoelectric element is attached on the beginning section of the beam modeled in Finite Element. Two auxetic patterns are proposed on the beam, exactly under the piezoelectric element. The vibrational input is simulated by modeling the motion of a freight wagon on the railway track using the Universal Mechanism software under different track irregularities and train speeds. The harvesting system is mounted on the axle-box where the vibration intensity received from track irregularity has the highest level. Different track irregularities and train speeds are considered in a parametric study to investigate the performance of the harvesting device. The results show that the application of the Auxetic I and Auxetic II structures enhances the output power by approximately 2 times and 4 times, respectively, compared to the plain beam. Experimental validation further confirmed the numerical results, showing up to 3.5 times improvement in harvested power. These findings demonstrate the potential of auxetic structures for efficient energy harvesting in railway vehicle applications.

In this study, lightweight membrane-type acoustic metamaterial with flexible and hierarchical structures are proposed to enhance the low-frequency sound insulation performance. Numerical and experimental analyses are conducted on the five models with identical mass in two classes with varying geometries. The sound transmission loss and modal characteristics of the membrane-type acoustic metamaterials are analyzed using the FEM. This analysis provides insight into their acoustic and dynamic behavior in the low-frequency range. The finite element simulation results are validated through reverberant-anechoic testing using a 3D-printed prototypes of the model I and Model II. Modal analysis demonstrated the influences of different geometries on the sound insulation performance. The models with complex geometry (including: Model I, Model II, and Model V) resulted in higher eigenfrequencies in high-order modes, which was caused by their rigidity. In contrast, uniformly spaced eigenfrequencies were observed in some other models including Model III, which exhibited more fluctuations in sound transmission loss across the low-frequency range. Peaks in sound transmission loss mainly occurred around the eigenfrequencies. The first resonance region corresponds to the first eigenmode, resulting in a sharp drop in the sound transmission loss curve. Furthermore, the first peak and the majority of high sound transmission loss values occurred in the anti-resonance regions. Model II presented high sound transmission loss performance in the range of 140-350 Hz, whereas Model I achieved better performance in the range of 350-1500 Hz. Superior performance in Class 2 was achieved by Model V in the ranges of 100-200 Hz and 350-700 Hz. Overall, MAM samples showed an enhancement of 14-22 dBA in sound transmission loss compared to conventional materials, such as rockwool and polyethylene acoustic foam. Statistical calculations show a relatively small difference between the numerical simulation and experimental test. This work demonstrates that lightweight membrane-type acoustic metamaterials can achieve high sound transmission loss in low-frequency ranges without any need to increase the wall mass, through optimized geometrical design.

This study numerically investigates how an auxetic re-entrant honeycomb (ARH) core improves the piezoelectric vibration energy harvesting capabilities of a finite doubly-curved sandwich shell (DcSS). First, using the modified first-order shear deformation theory (MFSDT) and Hamilton's principle, alongside the assumptions of the modified Sander shell theory for a moderately-thick shell, the coupled electro-mechanical equations governing the system are derived. These equations are then solved utilizing the Galerkin method. The amounts of specific output powers and voltage are extracted, considering various geometric parameters of the ARH, electrical circuit resistance, and types of sandwich structure, including a sandwich plate and a DcSS. These results are further validated through a numerical study in COMSOL finite element software, in addition to previous authoritative references. The analysis indicates that when comparing the DcSS with the ARH core to one with an isotropic core under the same conditions, the voltage extracted from the structure increases by 1.92 times and 1.31 times at the first and second resonant frequencies, respectively. The power extracted from the structure also shows significant increases of 3.73 times and 1.72 times for the same resonant frequencies. The DcSS with ARH core shows lower natural frequencies, desirable for energy harvesting systems.

This research presents the design, numerical optimization, and experimental validation of two bio-inspired membrane-type acoustic metamaterials—one based on a hexagonal honeycomb topology and the other on a spider-web configuration—for targeted low-frequency sound insulation in railway cabins. Field noise measurements from Fadak passenger trains identified two dominant interior frequency bands: a primary peak near 630 Hz and a secondary band around 1.6 kHz. The proposed meta-panels were modeled as full three-dimensional cellular arrays in COMSOL Multiphysics, with sound transmission loss (STL) computed in 1/6-octave bands and analyzed through modal decomposition. The honeycomb design, characterized by a lower first natural frequency, demonstrated enhanced attenuation at very low frequencies, whereas the spider-web structure exhibited a denser modal distribution, enabling broader suppression near 1.6 kHz. A constant volume/mass parametric analysis was followed by a single-objective Nelder–Mead optimization to maximize STL at 630 Hz by tuning two key geometric parameters. The optimized configurations achieved up to ∼10 dB improvement at the target frequency, with the honeycomb variant offering superior performance-to-mass ratio, and the spider-web variant delivering stronger attenuation peaks at the expense of increased mass. Prototypes fabricated via fused deposition modeling (FDM) using flexible thermoplastic polyurethane (TPU) and thin polyethylene membranes were tested in a coupled reverberant–anechoic setup, confirming the numerical predictions. These findings demonstrate that the integration of bio-inspired geometries with lightweight, flexible membrane structures enables precise control of low-frequency acoustic performance. The proposed designs offer a scalable and weight-efficient solution for mitigating interior noise in railway passenger environments, with potential applicability across a range of transportation and architectural contexts.

Abstract This research investigates the aerodynamic flow behavior and noise contribution of various cavity configurations designed to reduce aerodynamic noise in a simplified DSA 350 SEK pantograph model, scaled to 1/10. The cavities are classified into dual-shape and single-shape designs, with four distinct models (concave–convex, convex–concave, convex, and concave) analyzed in three sizes. A base cavity with a sloped edge at θ = 80° serves as a reference for comparison. Computational fluid dynamics (CFD) simulations are performed to evaluate flow characteristics, followed by the Ffowcs Williams and Hawkings (FW–H) aeroacoustic analogy is applied to estimate far-field sound pressure levels (SPLs). The results demonstrate that the convex-edged cavity improves aerodynamic performance by reducing the root-mean-square (RMS) drag and lift coefficients from 0.026 to 0.023 and from −0.06 to −0.038, respectively, and lowering the mean drag and lift coefficients from 0.23 to 0.18 and from −1.3 to −0.85, relative to the base cavity, thereby mitigating both steady and unsteady aerodynamic forces. Noise predictions, obtained from receivers positioned 2.5 m away in the scaled model at a train speed of 300 km/h, show reductions in noise levels from 81.9 to 77.3 dB at the top receiver and from 68.4 to 63.1 dB at the side receiver. Incorporating the pantograph into the optimal and base cavity designs reveals further aerodynamic improvements, with the optimal cavity reducing the pantograph’s aerodynamic noise by 2.7 dB(A) in total sound power. Sound pressure levels decrease by 2.3 dB(A) at the top receiver and 1.8 dB(A) at the side receiver compared to the base cavity.

This study focuses on the optimal design of an Auxetic Re-entrant Honeycomb (ARH) metamaterial structure aimed at enhancing energy harvesting (ES) performance in doubly-curved sandwich shells (DCSS). To accomplish this, the geometric parameters of the ARH are optimized using a Multi-Objective Genetic Algorithm (MOGA) and considering geometric and physical constraints. Initially, the study provides an accurate calculation for the density of the ARH layer and compares it with previous models. Then, the governing electromechanical coupled equations are derived using Modified First-Order Shear Deformation Theory (MFSDT) and Hamilton’s principle, assuming simple support boundary conditions at all four edges. Utilizing Galerkin’s principle, the frequency response function (FRF) of the specific output power is analyzed. In addition to evaluating the free vibration results against authoritative references, the finite element simulation is also used to validate both the eigenfrequencies and FRFs data derived from the analytical solution. The optimization algorithm aims to maximize the specific power output while minimizing the resonant frequency of the structure. The results from optimizing the ARH core layer demonstrate that the new designs achieve ES capabilities that are 42.96 times greater than those with an isotropic core and 6.92 times greater than those of the conventional ARH. Additionally, the optimized structures show improved stiffness metrics compared to their pre-optimization counterparts. Thus, this design successfully enhances both ES and structural behavior, particularly in terms of stiffness.

The application of Sonic Crystals (SCs) in the field of filtering and noise insulation has garnered increasing attention in recent years, but they often suffer from narrow and limited bandgaps (BGs). This study introduces a novel scatterer geometry within a square lattice with a lattice constant of 10 cm, designed to overcome the limitations of narrow BGs and limited frequency coverage. The innovative geometry is optimized using a genetic algorithm (GA) with three distinct objective functions to maximize bandgap characteristics, in terms of the summation of full BGs, bandgap coverage factor (BGCF), and fractional bandwidth (FB). In particular, a BG coverage of 370.6

Bacterial cellulose is a biodegradable and ecologically safe material that has the potential to convert mechanical vibrations into electrical energy. This review introduces green energy harvesting, a novel concept that harnesses natural processes to provide sustainable energy. A thorough overview of bacterial cellulose, covering its distinctive features, its biological origin, and its energy conversion process, is fully presented. The different materials and methods used to design and fabricate bacterial cellulose-based energy harvesters are explored. Moreover, the various applications and benefits of these devices in the context of renewable energy are examined. The current challenges and limitations of this emerging field are identified and the possible avenues for future research are suggested. The significance of adopting eco-friendly approaches in achieving a balance between human needs and environmental preservation is highlighted. By providing a comprehensive and critical assessment of bacterial cellulose as a green energy harvester, this review aims to motivate researchers, engineers, and policymakers to tap into the rhythmic potential of this natural material in building a more sustainable and resilient future.

This study presents and investigates a novel piezoelectric energy harvester. The proposed harvester comprises a cantilever beam with an embedded acoustic black hole (ABH) structure, a piezoelectric patch, and an auxetic booster between the ABH structure and the piezoelectric patch. The ABH structure reduces the energy harvesting frequency and creates a region with high energy density. Auxetic boosters enhance energy transfer from the substrate to the piezoelectric patch. The proposed harvester has been investigated numerically and experimentally. The conversion of the uniform beam to the ABH beam reduced the first natural frequency from 128 Hz to 26 Hz and increased the harvester's output power from 207 mu W to 408 mu W. The investigation found that all the examined boosters increased the output power of the ABH harvester. The simple, reentrant, anti-chiral, and chiral boosters enhanced the output power by 2, 6, 5, and 5, respectively. The superior increase in output power by auxetic boosters compared to a simple booster can be attributed to the auxetic property (negative Poisson's ratio and specific deformation mechanism) inherent to these structures. Incorporating boosters did not result in a notable alteration to the harvester's natural frequencies.

The vibrational frequencies of microparticles contain critical information about their physical state. However, direct frequency measurement remains a significant challenge, which can be addressed by designing sensors that couple particle vibrations to resonator modes in a controlled manner. Accordingly, this study first examines how dynamic interactions between foreign particles and resonator-based micro-sensors alter their vibrational response. Subsequently, a framework for designing microparticle frequency sensors is proposed, along with an algorithm to detect particle frequency using resonator data. To achieve these objectives, analytical and finite element (FE) models are developed to analyze the vibrations of a cantilever beam carrying an elastic particle. Additionally, an inverse problem-solving algorithm is introduced to simultaneously identify the particle’s mass, position, and fundamental frequency. The results reveal that when the particle’s fundamental frequency falls within the resonator’s natural frequency range, conventional mass detection methods relying on the point-mass model fail. However, this work demonstrates that a single resonator can effectively measure both mass and frequency of microparticles—provided the resonator and particle properties (mechanical and geometric) are appropriately selected. Finally, the proposed algorithm’s performance is evaluated across different particle cases, confirming its efficacy in detecting mass, position, and frequency with high accuracy.

In this paper, a Helmholtz shape sonic crystal is proposed for bandgap realization and sound attenuation. Using Bloch’s theory, bandgap properties of the sonic crystal are investigated for the primitive design of the unit-cell. A geometrical parametric study is implemented for the unit-cell to present its potential in creating bandgaps over the low-frequency range, and an optimization is applied to find its best design according to the low-frequency objective function. A frequency analysis and experimental tests are used to verify the calculated bandgaps from Bloch’s theory and to confirm the sound attenuation ability of the proposed design. It is shown that the present design not only creates wide bandgap frequencies in the low-frequency range but also, due to the Helmholtz shape of the unit-cell, provides significant sound attenuation.

Since it is possible for the nano-particle to have any asymmetric shape and may attach to every position of the resonator-based mass sensors, any type of mass eccentricity and subsequently coupled vibrations are possible. So, in the present work, the 3D coupled axial-torsional-flexural vibrations of the mass nano-sensors are investigated considering both in-plane and out-of-plane bending as well as axial and torsional vibrations. In addition, the integral form of the two-phase local/nonlocal strain gradient (LNSG), as the consistent type of the common nonlocal strain gradient (NSG) elasticity theory, is employed for the first time to consider the size effects in the mass nano-sensors. A quasi-3D coupled FE model is constructed with no shear-locking within the complicated environment of the integral LNSG. The impacts of the LNSG elasticity and diverse types of possible coupling in changing the vibrational behavior of the mass nano-sensor are scrutinized and their crucial role in modeling of the nano-sensors is indicated. Furthermore, molecular dynamic (MD) simulations are implemented to identify and analyze the coupled vibrations of a mass nano-sensor consisting of a fixed-free carbon nanotube. Comparison between the MD results with those of the present coupled FE model reveals that considering the coupling effects reduces the modeling error, especially in the cases in which the coupling influences intensify. The present work can help to provide more accurate models of mechanical resonance-based nanosensors to detect nanoparticles with different shapes, larger sizes, and high mass ratios, which can lead to achieving sensors with higher sensitivity.

In this research, a new polyhedral geometry for a 2D unit-cell with ultrawide frequency bandgaps is proposed. The genetic algorithm is combined with the finite element (FE) model to obtain an optimal geometry of the unitcell based on the two objective functions: (i) the largest bandgap within 0-1500 Hz and (ii) the largest bandgap summation in the range of 0-6000 Hz. Frequency analysis is conducted for the optimized geometries to illustrate the performance of the sonic crystal for the noise attenuation in bandgap frequencies. In order to validate the numerical results, an experimental test for a 3D model is designed and implemented. It is shown that a strong correlation is observed between the results from the bandgap diagram, frequency analysis, and experimental measurements. The proposed design presents a fractional bandwidth (FB) of 80.69 % and a bandgap coverage factor (BGCF) of 179.01 % in the applied frequency range, which are remarkable results in terms of bandgap indexes compared to the available literature of sonic crystals. The proposed design for unit-cell represents highly promising properties as a candidate for the noise control applications at both low and high-frequency ranges.

This paper aims at to improve the vibration behavior of the train floor panel by the use of a cellular auxetic layer. A field measurement is performed to obtain the vibrational frequency content of the body floor moving on the tangent track. Using acceleration sensors, the vibrational response is measured on the bogie (as the input excitation) and on the floor panel (as the observation response). Finite Element modeling for the floor panel is accomplished and measurement data are used for both the input excitation and the verification of the numerical results. The floor panel is a sandwich panel containing multiple layers. In this study, the conventional wooden layer of the panel is substituted with a cellular auxetic one with a re-entrant hexagonal pattern. Then, an optimization problem is defined while the topological parameters of the auxetic layer are the design variables and the dynamic performance of the panel is the objective function. The parameter of power–mass–ratio (PMR) is defined taking the effects of both weight and dynamic response amplitude into calculation. It is found that the PMR is reduced to almost 0.6 by replacing the wooden layer with an auxetic one, and after topological optimization, it is reduced to 0.35.

This paper is comprehensively reviewing various analytical models and experimental results in the fluid-induced vibration of nonlinear plates subjected to sub and supersonic airflow. Studies are classified based on their thematic correspondents. The research outcomes are then reviewed and summarized based on the methodologies and novel findings. Different theories, including those in two and three dimensions, are addressed. The impact of various parameters on the flutter behavior is also evaluated in this paper. At the end, potential challenges for future studies are addressed and discussed.

Exceptional properties of emerging of unconventional metamaterials including phononic/sonic crystals such as bandgap frequency have made them pertinent in various applications. In this paper, a novel single-phase optimized unit cell is proposed via genetic algorithm interfaced with the FE method. The unit cell parameters are fine-tuned according to two different objective functions over the low-frequency range of 2[Formula: see text]kHz to achieve the widest and maximum bandgaps summation for the in-plane and out-of-plane modes. For the in-plane propagation, almost 1681[Formula: see text]Hz bandgaps summation and a wide 635[Formula: see text]Hz frequency bandgap are obtained. Besides, there have been 1311[Formula: see text]Hz and 368[Formula: see text]Hz bandgap for the other case. Then, the meta-plates acquired through the investigations with finite arrangements are computed numerically and experimentally to mitigate longitudinal and bending wave propagation. It is found that the structures have high-performance capability to suppress the low-frequency vibrations inside the specified area and can substantially attenuate the propagation of elastic waves.

In the present paper, an auxetic tape composed of modified star-shaped unit cells is used to filter the propagation of elastic waves in two-dimensional structures. The pattern of the designed bandgaps and their capability to mitigate wave propagation is experimentally and numerically studied. First, the architecture of the conventional star-shaped unit cell is introduced, and according to the Bloch’s theorem the phononic bandgaps are calculated for the one unit cell. The unit cells' dimensions are designed to provide a wide phononic bandgap over the low-frequency range of 400–1700 Hz. The geometry of the conventional star unit cell is modified toward two modified stars to enhance low-frequency bandgaps. These unit cells are then used as a filter tool in a two-dimensional panel, and they are numerically simulated using the finite element method. Excitation is locally applied to the panel, and a layer of phononic crystal surrounds its location. It is shown that the lattice band is capable of trapping waves inside the bounded area and can remarkably suppress the propagation of waves. Numerical results and the bandgap formation obtained from Bloch’s theorem are verified with the results measured from an experiment.

The wheel squeal noise of a train is often made when it passes a tight curve. The noise annoys the passengers and the people living close to railway tracks. According to the research background, wheel vibration, as a result of unstable contact force, is the main source of wheel squeal noise. This study presents a novel method to reduce wheel squeal noise based on the active vibration control of wheels and the use of piezoelectric actuators attached to wheel treads. The proposed method is implemented in an experimentally validated time model involving the linear dynamics of wheel and track and nonlinear contact forces. Then, the model is modified to enhance the effect of the piezoelectric actuators. The relationship between the momentum and the voltage applied to the piezoelectric patch is also considered in modeling. To determine the amplitude and the direction of the applied voltage, a feedback controller is designed based on the fuzzy self-tuning PID controller scheme. This controller is similar to the conventional PID controller, but its coefficients are tuned by the fuzzy tuning mechanism according to the wheel response. The results show that the proposed method is capable of suppressing wheel squeal noise, especially in high frequencies. Furthermore, it is as applicable to worn wheels as to new ones.