Search Results (541)

This study comprehensively investigates the dynamic vibration behavior of multilayer carbon nanotubes with stepped cross-sectional geometries under various boundary conditions, which is crucial for their advanced engineering applications. The methodology integrates classical molecular dynamics simulations to determine the bending stiffness of single-walled and multi-walled atomistic structures, which are subsequently utilized in the Euler–Bernoulli beam theory based on nonlocal elasticity for vibration analysis. The research focuses on elucidating the influence of the μ/L ratio (a key length parameter) and different support conditions on the natural frequencies and mode shapes of these nanostructures. Key findings reveal that the cross-sectional geometry significantly impacts the vibrational characteristics. A consistent trend observed across all examined boundary conditions is a decrease in natural frequencies as the μ/L ratio increases, indicating that increased free length or reduced fixed length leads to lower stiffness and, consequently, reduced natural frequencies. The study presents Frequency Response Functions (FRFs) and the first four mode shapes, which visually confirm these dynamic characteristics. Graphical representations further reinforce the sensitivity of natural frequencies to both the μ/L ratio and support conditions. The systematic analysis presented in this work provides vital data for predicting resonance phenomena, optimizing structural stability, and enabling precise control over the vibrational response of these advanced nanomaterials in diverse engineering applications. Full article

As a pivotal component of the single-gear reducer, the casing of the miniature car reducer not only safeguards the internal transmission system but also interfaces seamlessly with the external structure. Currently, the structural design of domestic single-stage reducers primarily leans on experience and standardized specifications. To guarantee the reliable and stable operation of the casing, a high safety factor is often incorporated, which inevitably results in increased weight and necessitates secure bolting connections. This study presents an innovative scheme to design the flange with the box and realize the lightweight nature of the box by finite element analysis to reduce the manufacturing cost. Based on the working state of maximum torque and maximum speed, this study obtains the stress distribution of each bearing seat under different working conditions and carries out static and dynamic analysis combined with other coupling constraints. The analysis results show that the structure has high stiffness and strength, which is suitable for lightweight design, and that the first ten spontaneous vibration frequencies are far away from the excitation frequency of the inner and outer boundary, avoiding the resonance phenomenon. Moreover, this study proposes a new structure design method, which effectively improves the stiffness of the structure. Through the calculation of volume ratio before and after three optimizations, the optimal volume ratio of 30% is selected, unnecessary materials around the bearing seat are removed, and the layout of ribs is determined. After structural optimization, the weight of the shell is reduced by 10.2%, and both the static and dynamic characteristics meet the design requirements. Full article

To address low-frequency vibration and noise issues in ship grating structures, this study proposes a novel acoustic optimization design method based on modulating flexural wave bandgap characteristics. By establishing an equivalent periodic spring-mass coupled beam model to predict bandgap properties, its effectiveness is validated through numerical simulations and experimental testing. By selectively enhancing longitudinal stiffness while weakening transverse components, the bandgap characteristics are effectively tuned to target frequency bands. This approach achieves an 8.2 dB noise reduction at the 31.4 Hz natural frequency. The results demonstrate that bandgap-based design provides a numerically and experimentally validated solution for low-noise ship structures. Full article

This article presents an extensive experimental investigation of the dynamic characteristics of three-arch historical masonry bridges, using Operational Modal Analysis (OMA). The research thoroughly characterizes the dynamic behavior of four representative masonry bridges from the Apulia Region in Southern Italy through detailed experimental campaigns. These campaigns employed calibrated and optimally implemented accelerometric monitoring systems to acquire high-quality dynamic data under controlled excitation and environmental conditions. The selected bridges include the Santa Teresa Bridge in Bitonto, the Roman Bridge in Bovino, the Roman Bridge in Ascoli Satriano and a moderner road bridge on the Provincial Road SP123 in Troia; they span almost two millennia of construction history. The experimental framework incorporated several non-invasive excitation methods, including controlled vehicle passes, instrumented hammer impacts and ambient vibration tests, strategically chosen for optimal signal quality and heritage preservation. This investigation demonstrates the feasibility of capturing the dynamic behavior of these complex and specific historic structures through customized sensor configurations and various excitation methods. The resulting natural frequencies and mode shapes are accurate, robust, and reliable considering the extended data set used, and have allowed a rigorous seismic assessment. Eventually, this comprehensive data set establishes a fundamental basis for understanding and predicting the seismic response of several three-span masonry bridges to accurately identify their long-term resilience and effective conservation planning of these valuable and vulnerable heritage structures. In conclusion, the data comparison enabled the formulation of a predictive equation for the identification of the first natural frequency of bridges from geometric characteristics. Full article

Scaffolds are temporary structures that workers usually use during building or repair work. These structures can be built in different shapes and types depending on the type of joints to which the beams and columns of the scaffolds are connected. Due to their temporary nature, they are very sensitive to vibration under dynamic or static actions, and this causes many accidents and unstable behaviours in them. This unstable behaviour has different reasons, including bracing conditions and slenderness of the columns, stiffness of joints and anchors, imperfections in the construction, damage and corrosion due to climate change, etc. This article aims to reanalyse the mechanical properties of scaffold joints and anchors and obtain some critical factors in the overall stability of the mentioned structures, including load-bearing capacity, initial stiffness, energy absorption, and ductility. To this aim, some recent research on scaffolds has been summarised and discussed, and then the failure mode and mechanical behaviour of the scaffolds in different types of scaffold joints and anchors have been estimated and considered from previous studies. Moreover, some mechanical properties, including ductility, initial stiffness, and energy absorption, have been estimated and developed based on the force-displacement curves of previous studies. The results highlight the crucial importance of the mechanical properties and behaviour of anchors and joints in estimating the behaviour and stability of scaffolds. The results also revealed that determining the mechanical characteristics of the mentioned elements can have a significant influence on the optimisation and design of scaffolds more accurately and predictably. Moreover, determining the mechanical properties of the anchors and joints can enhance our insights and understanding of how the mentioned parameters can improve the behaviour, stability, and safety of the scaffold structures. Full article

The Wanning Bridge is a critical component of Beijing’s Central Axis World Heritage site and the only Yuan Dynasty heritage bridge in Beijing still in service. Investigating its structural response under complex traffic conditions is therefore essential for ensuring the longevity of this ancient structure and the safety of the urban transport system. However, the application of traditional research methods, such as direct sampling, is often constrained by the cultural relic characteristics of heritage bridges. This study first conducted a macroscopic on-site survey to document its current appearance and global geometry. Subsequently, more accurate geometric and material parameters of the bridge were acquired through non-destructive testing techniques including 3D laser scanning, ground-penetrating radar, and ultrasonic testing. Subsequently, using a combined approach of experimental and numerical simulation, this study reveals key structural responses and damage conditions of the bridge through static, dynamic, and metro-induced vibration tests. Dynamic tests show a maximum deformation of 0.26 mm and a natural frequency of 10.547 Hz, indicating shear strain accumulation as the primary damage driver. Subway-induced vibrations are well within the safety limits for stone relics, and the structure’s current load-bearing capacity complies with Class-II highway standards. Full article

To address the difficulty in eliminating low-frequency vibrations in the hydraulic pipelines of large marine vessels, this study first investigates the vibration characteristics of hydraulic pipelines. The research is conducted based on the stress states of pipelines under external excitations—specifically axial (X-direction), radial (Y-direction), and combined radial–axial (X + Y) excitations and integrates theoretical derivation, simulation, and experimental validation. Firstly, a multidimensional directional vibration equation for the pipeline was derived based on its stress distribution, yielding a more accurate vibration model for marine pipelines. Subsequently, simulations were performed to analyze the effects of fluid velocity, pipeline layout, and support distribution on the pipeline’s vibration characteristics. Finally, experiments were designed to verify the simulation results and examine the impact of external interference on pipeline vibration. The experimental results indicate the following: the influence of flow velocity variations on pipeline modes is generally negligible; increasing the number of pipeline circuits effectively reduces its natural frequencies; increasing the number of supports not only lowers the overall vibration intensity of the pipeline but also achieves peak shaving, thereby effectively reducing the maximum vibration amplitude; and the impact of external environmental interference on the pipeline’s vibration characteristics is complex, as it not only enhances vibration intensity but also weakens vibrations in specific directions. This study lays a theoretical foundation for subsequent vibration reduction efforts for marine hydraulic pipelines. Full article

In response to the lubrication failure problem during spacecraft operation, new requirements have been put forward for micro, precise, and dynamically adjustable lubrication and oil-supply technology for its key moving components. This article charts the design of a micro fuel-supply device structure based on a piezoelectric oscillator. Through finite-element simulation, the influence of the vibration mode and excitation parameters (waveform, frequency, voltage amplitude) of the piezoelectric oscillator on the displacement response amplitude and period of the oscillator is analyzed in depth. Research on waveform characteristics shows that sine waves can maintain frequency and phase stability due to their single-frequency nature, with an amplitude of 0.21615 mm between the two; The study of frequency characteristics shows that the displacement response amplitude of the piezoelectric oscillator is the largest at a 4914.2 Hz resonant state, which is about 10 times that of the non-resonant state; the study on voltage amplitude characteristics shows that the vibration displacement amplitude is significantly positively correlated with the driving voltage. When the excitation voltage is 220 V, the displacement response amplitude is 0.21615 mm and the period is 3960 µs. This study provides important theoretical support for optimizing the performance of piezoelectric oscillators. Full article

Flying-wing aircraft based on high-aspect-ratio wings are a popular configuration for many aerospace engineering applications. Cracked (or cross) control surface structures can adjust the aerodynamic characteristics of flying-wing aircraft. Deep investigations into the effects of such a control surface can provide a helpful design foundation. This paper investigates the mass distribution influences of cracked control surfaces on gust responses of high-aspect-ratio flying wings. Validated finite element modelling, revised by detailed ground vibration test (GVT) with a frequency error of less than 10%, reveals that root boundary conditions significantly affect the natural modes and frequencies of present wings with cracked control surfaces. Changes in control surface (CS) mass have a critical impact on gust response: a 150 g increase in CS mass results in a 15–22% increase in peak response acceleration and a 25–30% increase in response duration, while redistributing mass to the outboard CS reduces the peak response by 18–26% while keeping the total mass consistent. The results can provide an effective suppression strategy for the gust responses of flying-wing configurations without redesigning the main structure. Full article

To study the vibration characteristics of viscoelastic slurry pipe structures under fluid–structure interaction (FSI), we constructed a three-dimensional FSI pipe model based on the finite element method to systematically investigate the effects of fluid effects, pipe length, and wall thickness on the vibrational characteristics of viscoelastic slurry pipes. A modal analysis demonstrated that fluid effects not only significantly reduced the natural frequency of the pipe but also disrupted the symmetry of the vibration modes and eliminated the phenomenon of frequency degeneracy. The frequency reduction caused by FSI reached 54%, which was dominant compared with the water-attached effects, and its impact intensified with the increasing vibration order. The water-attached effect exhibited differences between odd and even orders, attributed to the influence of vibration modes on the distribution of fluid inertial forces, with a contribution of 45.07% to 55.24% in the odd orders and of only 37.69% to 38.93% in the even orders. When the FSI and water-attached effects acted together, the frequency reduction was further aggravated, but the reduction ratio did not follow a simple linear superposition. The parametric analysis of the pipe showed that when the pipe length increased from 1 m to 3 m, the growth rate of its natural frequency was only 26.52% that of the shorter pipe, indicating that the longer the pipes, the slower the growth rate of frequency. When the wall thickness increased from 5 mm to 11 mm, the growth rate of the first-order natural frequency decreased from 15.43% to 7.44%, suggesting that the frequency improvement effect caused by the stiffness augmentation diminished with the increase in wall thickness. The research results hold significant guiding significance for the structural design of slurry pipe systems in practical engineering and the safe operation of pipe systems. Full article

The present work investigates the influence of natural rubber (NR) on the mechanical properties and free vibration characteristics of elastomer-embedded NR-filled GFRP laminates for anti-vibration (AV) mounts. The tensile, flexural, and impact strength values of the preferred hybrid laminates are evaluated as per ASTM standards. To estimate vibration characteristics such as the modal frequency and damping of the hybrid laminates, a free vibration study is carried out under the fixed-free boundary condition. Based on the experimental results, the effect of NR filling in an epoxy matrix of elastomer-centric GFRP laminates is thoroughly investigated for its application in AV mounts. Full article

Crop leaves naturally exhibit a curved morphology and primarily display bending deformation and vibrational responses under wind load. The curved surface structure of leaves plays a critical role in the deposition and retention of pesticide droplets. In this study, wind tunnel experiments combined with high-speed photography and digital image analysis were conducted to systematically investigate the curvature and flexibility distributions of three typical crop leaves: walnut, peach, and pepper, across a range of wind speeds. The results indicate that with increasing wind speed, all three types of leaves gradually transition from smooth, uniform bending to a multi-peak pattern of pronounced local curvature, with increasingly prominent nonlinear deformation characteristics. Moreover, once the wind speed exceeds the critical threshold of 6 m/s, the primary deformation region generally shifts from the leaf base to the tip. For example, the maximum curvature of walnut leaves increased from 0.018 mm⁻¹ to 0.047 mm⁻¹, and that of pepper leaves from 0.031 mm⁻¹ to 0.101 mm⁻¹, both more than double their original values. In addition, all three types of leaves demonstrated a distinct structural gradient characterized by strong basal rigidity and high apical flexibility. The tip flexibility values exceeded 1.5 × 10⁻⁵, 4 × 10⁻⁴, and 5.6 × 10⁻⁴ mm⁻²·mN⁻¹ for walnut, peach, and pepper leaves, respectively. These findings elucidate the mechanical response mechanisms of non-uniform flexible crop leaves under wind-induced bending and provide a theoretical basis and data support for the optimization of air-assisted spraying parameters. Full article

This study explores the free vibration behavior of carbon fiber-reinforced sandwich open circular cylindrical shells featuring 3D reentrant auxetic cores (3D RSOCCSs). For theoretical predictions, a model integrating the Rayleigh–Ritz method (RRM) and Reddy’s third-order shear deformation theory (TOSDT) is adopted, whereas the finite element analysis approach is used for simulation predictions. All-composite 3D RSOCCSs specimens are produced via hot-press molding and interlocking assembly, and the modal characteristics of 3D RSOCCSs are obtained through hammer excitation modal tests. The predicted modal properties are in good agreement with the experimental results. In addition, the influences of fiber ply angles and geometric parameters on the natural frequency in the free vibration are thoroughly analyzed, which can offer insights for the vibration analysis of lightweight auxetic metamaterial cylindrical shells and promote their practical use in engineering scenarios focused on vibration mitigation. Full article

This study investigates the vibrational characteristics of multi-layered graphene sheets with variable thickness (VTGSs) by using molecular dynamics (MD) simulations. It is aimed to determine how the natural frequencies and vibration damping ratios of variable-thickness graphene change with respect to temperature. Atomistic models for six distinct geometries (1L, 3LT, 3LTB, 5LT, 5LTB, and 9LTB) were generated to analyze the influence of structural design and temperature on their natural frequencies. The simulations were performed using the Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) with an AIREBO potential to represent interatomic carbon interactions. Natural frequencies of all atomistic models were extracted by applying the Fast Fourier Transform (FFT) method to the Velocity Autocorrelation Function (VACF) data obtained from the simulations. In addition, the analysis was conducted at three different temperatures: 250 K, 300 K, and 350 K. Key findings reveal that an increase in the number of graphene layers results in a decrease in the fundamental natural frequency due to the increased mass of the structure. Moreover, it was noted that natural frequencies decrease with increasing temperature. It is attributed to the reduction in structural rigidity at higher thermal energies. These results provide critical insights into how geometric and thermal variations affect the dynamic behavior of complex multi-layered graphene structures. Full article

Ensuring the dynamic safety of buildings near open-pit mines during blasting is a critical concern for the normal conduct of mining operations. This study investigates the effects of blasting vibrations on brick–concrete structures by using deep-hole blasting tests conducted at the mine site, employing blasting vibration monitoring and numerical simulation techniques. The peak particle velocity and energy distribution characteristics of blasting waves in structural columns and brick walls were analyzed. Furthermore, a three-dimensional numerical model was developed to analyze the response characteristics of buildings to blasting vibrations. Considering the impact of a building’s natural frequency on blasting vibrations, harmonic response was utilized to identify the natural frequencies of different components. The relationship between these frequencies and a building’s natural frequency is discussed. Dangerous frequencies and components were identified. The findings of this study can serve as a theoretical foundation for understanding the damage mechanisms of buildings under blasting waves and for controlling the impact of blasting vibration effects. Full article