Search Results (4,164)

Seismic wave analysis is crucial for identifying subsurface formations and geological hazards. In this study, a seismic wave laser remote sensing system based on a Shack–Hartmann wavefront sensor was established by exploiting its high spatial resolution, array-based detection capability, and independent microlens spot centroid measurement. This method was employed to analyze the correlation characteristics among vibration-related physical variables. Experiments were conducted to assess the quantitative correlation between vibration amplitude and spot centroid shift by the Shack–Hartmann wavefront sensor across a range of 0.06–5.94 mm. Accordingly, based on the measured centroid shift, vibration velocity was derived and validated through comparison with reference vibrometer measurements. In addition, the correlation between vibration amplitude and vibration velocity was systematically analyzed. The experimental results demonstrate strong linear correlation between amplitude and both spot centroid shift and vibration velocity, with coefficients of determination $R^2$ exceeding 0.98. The vibration velocity obtained by the proposed system shows strong agreement with vibrometer data, confirming its effectiveness for low-frequency vibration detection. Measurement accuracy can be further improved by reducing noise. These results indicate that the proposed approach provides a promising laser remote sensing solution for seismic wave detection. Full article

This study investigates the vibration response and energy transfer characteristics of walnut trees in mechanical vibration harvesting, aiming to improve fruit detachment efficiency and reduce structural damage. Three walnut tree architectures were classified based on branching height, trunk stiffness, canopy size, and geometric regularity. A dynamic model of the trunk was established, modeled as an equivalent conical beam with Rayleigh damping, and the clamping point was simplified to a single-degree-of-freedom system. To quantify energy transfer, three indicators were introduced: energy transfer coefficient, energy attenuation rate, and trunk overload index (OLI). Sweep-frequency experiments (9–17 Hz) were conducted at a clamping height of 80 cm. Triaxial acceleration responses were measured, and branch kinetic energy was calculated. The model-predicted natural frequencies matched the experimental acceleration peaks well, identifying a frequency-sensitive band between 15 and 17 Hz. Significant differences in energy distribution were observed among the three tree architectures. Tree 1 exhibits intense energy concentration near the trunk, with rapid energy decay along branches and the highest canopy vibration index (OLI: 6.13), indicating the highest trunk overload risk. Tree 2 demonstrates whole-tree coordinated vibration and the lowest OLI value (2.10). Tree 3 possesses two sensitive frequency bands with relatively uniform energy distribution and an OLI of 2.89. Trunk stiffness, branching height, canopy structure, and geometric irregularities collectively determine energy distribution within resonance bands and overload risk. The proposed energy metrics and OLI provide quantitative guidance for selecting excitation frequencies and controlling operational duration during walnut vibration harvesting. Full article

Bacterial cellulose (BC) is highly valued for biomedical and industrial applications due to its exceptional biocompatibility, strength, and biodegradability. Polyvinyl alcohol (PVA) exhibits favorable characteristics, making it an ideal candidate for hydrogel formulation. In this study, BC–PVA composite hydrogels were synthesized by dissolving 1% w/w BC in ZnCl₂ 3H₂O and 10% w/w PVA in ZnCl₂nH₂O, n = 6, 9, 12, and 15. These solutions were combined at BC:PVA weight ratios of 3:1, 1:1, and 1:3, then crosslinking using a glutaraldehyde–acetone solution before immersion in deionized water. The resulting hydrogels exhibited a dense, tightly packed structure with mild to moderate porosity. FTIR analysis confirmed molecular interactions via a broad, reduced O–H stretching band and the appearance of C-H bending vibrations. The water content and swelling ratio ranged from 88.13% to 94.67% and 437.93% to 997.22%, respectively. At a compressive strain of 30%, the compressive strength ranged from 62.28 kPa to 93.16 kPa. This work introduces a novel and efficient method for preparing BC-PVA hydrogels using ZnCl₂ hydrate solvents. Both the ZnCl₂ hydration level and the BC:PVA ratio significantly influenced the structural, water content, swelling, and mechanical properties, offering tunable materials for biomedical or industrial applications. Full article

Thin-walled components used in aerospace manufacturing are highly susceptible to machining-induced deformation due to their low structural stiffness and dynamic cutting instability. Although signal-based modeling approaches have been reported for machining process monitoring and performance evaluation, deformation prediction of thin-walled structures requires explicit consideration of structural flexibility. To address this challenge, a deformation error prediction framework integrating multi-source dynamic machining signals with static structural flexibility characteristics is proposed, enabling simultaneous representation of process dynamics and structural response. Kernel principal component analysis (KPCA) is employed to reduce the feature dimensionality, and the extracted low-dimensional features are subsequently used as inputs for a kernel-based support vector regression (KSVR) model to establish the prediction framework. The proposed method was validated through 25 milling experiments conducted on Al7075-T6 thin-walled workpieces, where deformation error was measured at predefined monitoring points under varying process conditions. The results indicate that the proposed model achieves high predictive accuracy for machining-induced deformation, with RMSE values below 13 μm and R² exceeding 0.89 on both validation and testing datasets, demonstrating strong agreement between predicted and experimental results. In addition, machining vibration amplitude exhibits a consistent correlation with deformation error, confirming that increased energy input and cutting instability significantly exacerbate thin-walled workpiece deformation. Full article

The precise prediction of vibration response is crucial for optimizing the assembly quality of multi-stage rotors. Existing models possess two key limitations: they neglect the geometric displacement excitation from spigot eccentricity error and oversimplify rotor behavior by not accounting for the excitation redistribution caused by significant dynamic deflection at high speeds, particularly near critical speeds. To overcome these shortcomings, this study establishes a novel dynamic model based on the synchronous excitation of both mass and spigot eccentricity errors, which simultaneously incorporates the coupling mechanism of dynamic deflection. System dynamics equations are developed using a finite element approach combined with Timoshenko beam theory and solved via the Newmark-β method. Simulations and experiments on a four-stage rotor demonstrate that the proposed model provides significantly improved accuracy. At sub-critical, first, and second critical speeds, it reduces the maximum prediction error for nodal displacement amplitudes by 6.1%, 9.2%, and 36.4%, respectively, compared to a model neglecting dynamic deflection. Furthermore, analysis confirms that the targeted assembly error excitation exists solely at the fundamental frequency. The developed model, which uniquely integrates dual eccentricity sources with dynamic deflection coupling, is essential for reliable high-speed vibration prediction and assembly optimization, especially for flexible rotors operating near critical speeds. Full article

A Lyapunov-based hybrid model predictive control (LHMPC) method is proposed for the control of a vehicle hybrid logic dynamic system (MLD) that regulates vehicle height through asymmetric damping forces. This method addresses the limitations of traditional hybrid model predictive control (HMPC), including its inability to guarantee closed-loop stability, long prediction horizons, and excessive computational burden. The method incorporates the decreasing condition of the Lyapunov function as a contraction constraint mechanism, ensuring asymptotic stability throughout the control process. Additionally, by following the terminal constraint principle, the Lyapunov function is introduced as an inequality constraint set, replacing the terminal equality constraints typically used in traditional stability frameworks. This further guarantees the recursive feasibility and closed-loop stability of the MLD system optimization. Simulation results based on a seven-degree-of-freedom vehicle model demonstrate that the proposed LHMPC significantly outperforms conventional HMPC in terms of height tracking accuracy, convergence rate, vibration suppression, and real-time controller performance. Furthermore, the method can effectively harness the vehicle body’s vibrational energy while achieving coordinated control of vehicle height and posture, thereby reducing energy consumption during the height adjustment process. Full article

Carbon-fiber-reinforced polymer (CFRP) composites possess outstanding specific stiffness and strength but typically exhibit low intrinsic damping, which limits vibration attenuation in lightweight dynamic structures. Herein, a hybrid toughening strategy combining carboxyl-terminated butadiene nitrile rubber (CTBN) and hexagonal boron nitride (h-BN) is developed to enhance the damping of CFRP laminates while preserving cure feasibility and thermomechanical stability. An E51/DICY/accelerator epoxy system (100:6.5:1.2, mass ratio) is used as the baseline matrix. Differential scanning calorimetry shows that both CTBN and h-BN shift the cure peak temperature upward (Tp: 160.6 → 170.3 °C) and reduce the reaction enthalpy (ΔH: 386.5 → 255.1 J/g), indicating dilution/transport effects and altered cure kinetics. Dynamic mechanical analysis (DMA) reveals that CTBN exhibits an optimum damping enhancement at 25 phr (tan δ_max = 0.300), whereas h-BN provides a stronger monotonic increase up to 25 phr (tan δ_max = 0.437). Notably, the CTBN/h-BN hybrid (25/25 phr) delivers a high tan δ_max of 0.468 together with the broadest effective damping window (ΔT_half = 28.6 °C), exceeding 85% of the linear additivity criterion proposed herein. When the materials are transferred into CFRP laminates, free-vibration tests (using the logarithmic decrement method) demonstrate a clear structural damping improvement (ζ: 0.021 → 0.035; δ: 0.132 → 0.221; t₁/₂: 0.48 → 0.27 s). Overall, the results suggest that the damping enhancement arises from a combination of EPBN-mediated ductile energy dissipation and h-BN-related interfacial/interlayer frictional losses, which can be jointly tuned to balance processability, thermal response, and damping performance in CFRPs. Full article

Given the increasing environmental degradation, this study investigates advanced zinc oxide (ZnO)-based materials for the mineralization of toxic compounds through the combined action of photo- and piezocatalysis. Two complementary strategies were employed to enhance catalytic efficiency. First, ZnO_1−xN_x thin films were deposited by reactive high-power impulse magnetron sputtering (R-HiPIMS) to reduce the band gap energy. Second, flower-like ZnO nanostructures were synthesized using the pulsed thermionic vacuum arc (p-TVA) technique to increase the specific surface area. Both systems were further modified by decoration with Ag₂O nanoparticles to improve charge separation. The R-HiPIMS technique offers significant advantages in terms of precise control over processing parameters, enabling accurate tuning of film properties, including microstructure, chemical composition, and electronic structure. However, films produced via R-HiPIMS generally exhibit lower photo-piezocatalytic activity compared to nanostructured counterparts, primarily due to their comparatively reduced effective surface area and limited charge separation efficiency. In contrast, the p-TVA technique enables the synthesis of nanostructured thin films with substantially enhanced photo-piezocatalytic performance. This improvement is attributed to the increased effective surface area and the promotion of more efficient electron–hole pair separation. The materials were comprehensively characterized in terms of optical properties (UV–Vis spectroscopy), chemical composition and bonding (XPS), crystalline structure (XRD), surface morphology (FE-SEM), and photo-piezocatalytic performance. Catalytic activity was evaluated via the degradation of methylene blue (MB) under visible light irradiation and mechanical vibrations. Nitrogen incorporation in ZnO_1−xN_x thin films led to an increase in photocatalytic efficiency from 20% to 28.7%, while the simultaneous application of light and mechanical stimulation increased efficiency to approximately 50%. Under identical irradiation conditions, Ag₂O-decorated ZnO and Ag₂O-decorated ZnO_1−xN_x exhibited photo-degradation reaction rate constants up to 65% higher than bare counterparts, attributed to reduced electron–hole recombination. ZnO nanostructures achieved degradation efficiencies of 59%, rising to 88.3% with Ag₂O decoration under solar illumination for 120 min. When combined with mechanical vibrations, after 60 min, the degradation efficiencies reached 93% for ZnO and 98% for Ag₂O/ZnO systems. A photodegradation mechanism of Ag₂O NPs-decorated ZnO heterostructures was proposed. Full article

Phthalates (PAEs), commonly incorporated into materials such as polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC), are easily to migrate readily into the surrounding environment, which have become a matter of increasing concern. Traditional PAEs extraction methods have been prevented by long extraction times and high costs, requiring substitute to accelerate the extraction speed while reducing extraction costs. Ultrasonic-assisted extraction facilitates the release and dissolution of target compounds through the combined effects of acoustic cavitation and molecular vibration acceleration, which could be an effective means to overcome the limitations of traditional extraction methods. Herein, we have developed a four-frequency composite ultrasonic extraction technology for PAEs, with a recovery of 95.2%, approximately 38.2% higher than mode MU 20 kHz. Besides, an in-depth study on the mechanism of ultrasound-assisted extraction with sequential multi-frequency was conducted and we confirm that stepped-frequency ultrasound could achieve precise control of cavitation effects by dynamically adjusting frequency distribution, ensuring high extraction efficiency while maximally protecting the PVC matrix structure, providing a new technical path for efficient and green recovery of plasticizers. Full article

This paper investigates deflection deformation and premature bearing failure in deep-hole machining spindles with high length-to-diameter ratios under eccentric loading. A contact stiffness model for angular contact ball bearings was developed based on Hertz contact theory. Combined with the finite element method (FEM), a comprehensive mechanical analysis model of the spindle was established. The results show that spindles with high length-to-diameter ratios exhibit significant cantilever behavior, leading to considerable front-end deflection under eccentric loading. This deflection causes the inner and outer rings to incline, resulting in localized stress concentrations, which are the primary contributors to spindle fatigue failure. To improve the spindle’s stress distribution and dynamic performance, an optimized design replacing the metal housing with carbon fiber composite material is proposed. Static and modal analyses were performed using Abaqus and Romax. The analysis results demonstrate that the carbon fiber shell reduces self-weight deformation by 35.8%, decreases coupled deformation under self-weight and grinding loads by 28.6%, and increases modal fundamental frequencies by 20.88% to 47.41%. These improvements significantly enhance structural stiffness and dynamic stability. Experimental vibration monitoring during machine testing validated the accuracy of the modeling and simulation. Full article

An integrated nonlinear dynamic model was developed to investigate resonance in a four-cylinder engine mounted on a viscoelastic foundation. A coupled lumped-parameter formulation captures vertical and torsional responses under unbalanced inertial forces, combustion torque, and stochastic base excitation. Time-domain simulations show that at low rotational speeds the vertical displacement reaches transient amplitudes before converging to periodic oscillations, whereas higher excitation speeds reduce steady-state amplitudes. Torsional motion exhibits initial angles near 0.05 rad that decay below 0.01 rad in steady state, with further reduction at higher speeds. Frequency-domain analysis indicates that vibration energy is concentrated in engine-order harmonics between approximately 8 and 50 Hz, while components above 60 Hz are strongly attenuated, yielding a dynamic range exceeding 50 dB. Finite element modal analysis identifies the first four structural modes between 18 Hz and 666 Hz, revealing an increasingly dominant overall translational mode and a localized directional behavior at higher frequencies. A high-dimensional kernel density spectrogram integrates modal and spectral features to map resonance regions. Results indicate that increasing rotational excitation enhances inertial stiffening, systematically reduces displacement amplitudes, and preserves bounded periodic dynamics without instability. Full article

This study addresses the challenge of multi-order resonance in base structures within the low-frequency range (10~300 Hz), a common issue in shipbuilding and aerospace applications. Traditional vibration control methods, including those based on the Acoustic Black Hole (ABH) effect, often undermine base structural integrity, offer limited effective bandwidth, or pose practical implementation challenges. To overcome these limitations, this paper proposes a Gradient Variable-Thickness Composite (GVTC) damping plate for passive vibration control, integrating the ABH effect with anti-resonance theory. The key innovation is an engineering-oriented integrated design characterized by external mounting, multi-level stacking, and efficient shell-element modeling rather than a fundamental modification to the ABH principle itself. The composite plate comprises a uniform-thickness region, a gradient-thickness region, and a damping layer, with thickness variation defined by a power-law function. By tuning geometric and material parameters, the plate’s natural frequencies are matched to the base panel’s resonant peaks. Employing shell elements over solid elements significantly reduces computational cost while maintaining high accuracy (relative error of the first three natural frequencies < 0.6%). Finite element simulations and experimental tests have demonstrated significant vibration suppression: peak reductions of 10 dB, 12.1 dB, 9.7 dB, and 22.9 dB at 94 Hz, 188 Hz, 244 Hz, and 294 Hz, respectively, under simulation conditions, and 7.5 dB, 11.1 dB, 8.5 dB, and 7 dB at 82 Hz, 172 Hz, 234 Hz, and 286 Hz, respectively, in experiments. The additional mass of the damping plate accounts for only 1.53% of the base panel mass. This work provides a practical and efficient solution for low-frequency vibration control and facilitates the engineering application of ABH technology in high-end equipment. Full article

The cylindrical submerged linear motor with the primary core used in traditional welded stacked 50ww470 non-silicon steel sheets faces many shortcomings. These include its structure being complex and difficult to manufacture, the process requiring stages such as steel sheet blanking, stacking, and welding, and the iron core exhibiting large magnetic resistance and generating a lot of heat when the motor is working, reducing the motor efficiency. Therefore, an ultrasonic vibration-assisted (UVA) deep drawing process for multilayer sheets was proposed to replace the traditional process. The finite element analysis was carried out on single-layer sheet drawing. Using Abaqus software, we verified that UVA could improve the uniformity of the wall thickness of formed parts, and reduce wall thickness thinning and rebound; the core forming height is so low that there will be a larger rebound after forming. The “split ring” method was used to verify that ultrasonic vibration can suppress the rebound of the formed part. As the bottom of the core was made of six layers of silicon steel sheets, laminated and welded, the feasibility of different solutions was investigated by setting up a UVA deep drawing experimental platform to study single-, double-, three- and six-layer-sheets, and the forming quality and forming forces were analyzed. The final forming process was determined to require two deep-drawing three-layer sheets, and the forming part was successfully manufactured. Full article

Tuned liquid dampers (TLDs) are widely used in structural vibration mitigation, but they are limited by their damping frequency to use as passive damping equipment. To enhance the damping performance of the conventional TLD, a unique layered tuned liquid damper (LTLD) filled with water and diesel is proposed. The interfacial wave coupling mechanism for broadband energy dissipation has not been previously explored in sloshing-type dampers. A series of frequency-sweeping tests were carried out in the laboratory to compare the vibration suppression performance of the proposed LTLD against conventional TLD. The dampers were installed on an elastic supporting structural platform (SSP) with a height of one meter, and the bottom was horizontally excited with different amplitudes and frequencies using a hexapod motion simulator. The results indicate that the LTLD showed a better damping performance than the TLD under small-amplitude excitation and achieved optimization at two peaks. The separation surface movement dissipated the liquid motion’s energy and enhanced the hydrodynamic force in the horizontal direction. However, the damping effect of the LTLD weakened when the two liquids were no longer immiscible under large-amplitude excitation. Therefore, we recommend utilizing the LTLD to improve structural damping performance when $d_{max}/L$< 0.04984. In addition, the LTLD reduced the maximum wall pressure by about 25% in the transient state under large-amplitude excitation. This study presents experimental evidence that a water–diesel LTLD achieves broadband damping through interfacial wave coupling. The stable interfacial waves enhance energy dissipation and excite new vibration mitigation frequencies, offering a novel approach to overcoming the narrow-band limitation of conventional TLD. Full article

The study focuses on the results of the analysis of data recorded during Ambient Vibration Tests (AVT) conducted on a portion of the Medieval Walls of Verona (Northern Italy). Seismometric stations were installed both at the top and at the base of the walls, recording the free vibrations of the structure. Spectral analyses provide information about the principal modal frequencies, which are compared with the results obtained through Operational Modal Analysis (OMA) techniques. Numerical models were developed to describe the elastic behavior of the walls and to support the interpretation of the experimentally identified modes. Seismic noise measurements were also performed on the ground to characterize the spectral response of the soil and to estimate the soil–structure interaction. The combined use of AVT data, OMA procedures, and numerical modeling allowed for a robust identification of the fundamental dynamic properties of the walls, highlighting the predominance of out-of-plane modes and the limited dynamic coupling with the underlying soil. The study demonstrates the effectiveness of this non-invasive approach for improving the knowledge of structural assessment, reducing uncertainties in mechanical parameter calibration, and supporting informed conservation, maintenance, and risk-mitigation strategies for historic defensive masonry structures. Full article