Search Results (228)

To analyze the wear performance induced by rotor–stator rubbing in an aero-engine sealing structure under authentic operating conditions, a transonic rotor system with double bearing is constructed. This system incorporates the disk, shaft, blades, joint bolts, and auxiliary support structure. The system was evaluated in terms of its critical speed, vibration characteristics, component strength under operational conditions, and response characteristics in abnormal extreme scenarios. A ball screw-type feeding system is employed to achieve precise rotor–stator rubbing during rotation by controlling the coating feed. Additionally, a quartz lamp heating system is used to apply thermal loads to coating specimens, and the appropriate heat insulation and cooling measures are implemented. Furthermore, a high-frequency rubbing force test platform is developed to capture the key characteristics caused by rubbing. The test rig can conduct response tests of the system with rotor–stator rubbing and abrasion tests with tip speeds reaching 425 m/s, feed rates ranging from 2 to 2000 μm/s, and heating temperatures up to 1200 °C. Test debugging has confirmed these specifications and successfully executed rubbing tests, which demonstrate stability throughout the process and provide reliable rubbing force test results. This designed test rig and analysis methodology offers valuable insights for developing high-speed rotating machinery. Full article

It is well known that aqueous solutions can emit electromagnetic waves in the radio frequency range. However, the physical nature of this process is not yet fully understood. In this work, the possible role of gas nanobubbles formed in the bulk liquid is considered. We develop a theoretical model based on the concept of gas bubbles stabilized by ions, or “bubstons”. The role of bicarbonate and hydronium ions in the formation and stabilization of bubstons is explained through the use of quantum chemical simulations. A new model of oscillating bubstons, which takes into account the double electric layer formed around their gas core, is proposed. Theoretical estimates of the frequencies and intensities of oscillations of such compound species are obtained. It was determined that oscillations of negatively charged bubstons can occur in the GHz frequency range, and should be accompanied by the emission of electromagnetic waves. To validate the theoretical assumptions, we used dynamic light scattering (DLS) and showed that, after subjecting aqueous solutions to vigorous shaking with a force of 4 or 8 N (kg·m/s²) and a frequency of 4–5 Hz, the volume number density of bubstons increased by about two orders of magnitude. Radiometric measurements in the frequency range of 50 MHz to 3.5 GHz revealed an increase in the intensity of radiation emitted by water samples upon the vibrational treatment. It is argued that, according to our new theoretical model, this radiation can be caused by oscillating bubstons. Full article

Purpose: The aim of this study is to achieve automated energy capture and charging for the ADXL355 accelerometer, enhance the vibration energy collection efficiency, and widen the energy trapping frequency band of a system in a working environment for bridge health state detection. Methods: A vibration energy harvester based on a magnetic coupling cantilever beam in an orthogonal direction was proposed. The harvester works by adjusting the angle and magnetic spacing between the two cantilever-beam piezoelectric oscillators, enabling the oscillators to produce large-scale and stable vibrations when excited by an external broadband vibration source. Results: Sinusoidal frequency sweep experiments showed that, under an excitation amplitude of 0.2 g, the proposed broadband vibration energy harvester based on orthogonal magnetic coupling double cantilever beams achieved the best energy harvesting performance when the magnetic angle of the double cantilever beam system was 130°, and the radius was 16 mm. In the frequency range of 5–20 Hz, the system can effectively capture higher effective voltages across all frequency bands, with a total captured voltage value of approximately 15.3 V. Compared with the control group, the system’s energy harvesting capacity under this working condition increases by 770%. Additionally, the effective frequency band of the system was broadened by 3.7 Hz. Conclusions: Unlike previous studies, which often limited the angles of the magnetic fields generated by the magnets at the ends of piezoelectric beams to specific values, this study explores the influence of rotating these magnetic fields to general angles on the working frequency band of the structure. The findings provide a new perspective and theoretical basis for the optimal design of broadband vibration energy harvesters. Full article

With the continuous development of maglev transportation technology, medium–low-speed maglev trains have been widely implemented in many countries. However, due to the limitations of existing specifications, the stiffness limit values of the large-span main girders used in medium–low-speed maglev trains have not been unified. To address this issue, this study takes a specific bridge on a dedicated maglev line as an example and uses self-developed software to model the vehicle–bridge dynamic system. The natural vibration characteristics and vehicle–bridge coupling vibration response of the bridge are calculated and analyzed. Based on this, the influence of pier top stiffness on the dynamic characteristics of a typical medium–low-speed maglev train–bridge system under different working conditions is investigated, with a focus on the lateral line stiffness at the pier top. The results show that vehicle speed has no significant effect on the lateral displacement of the main girder, the lateral displacement of the pier top, the lateral acceleration of the pier top, and the transverse and longitudinal angles of the beam end, and no obvious regularity is observed. However, in the double-track operating condition, the vertical deflection of the main girder is significantly higher than that in the single-track operating condition. As the lateral linear stiffness at the pier top increases, the fundamental frequency of the bridge’s lateral bending vibration gradually increases, while the fundamental frequency of longitudinal floating gradually decreases. The lateral displacements, including those of the main girder, pier top, and beam ends, all decrease, whereas the lateral and vertical vibration accelerations of the main girder and the train are less affected by the lateral stiffness at the pier top. Full article

A variational formulation and variationally consistent boundary conditions were derived for a coupled system of two boron nitride nanotubes (BNNTs), with the piezoelectric and surface effects taken into account in the formulation. The coupling between the nanotubes was defined in terms of Winkler and Pasternak interlayers. The equations governing the vibrations of the coupled system were expressed as a system of four partial differential equations based on nonlocal elastic theory. After deriving the variational principle for the double BNNT system, Hamilton’s principle was expressed in terms of potential and kinetic energies. Next, the differential equations for the free vibration case were presented and the variational form for this case was derived. The Rayleigh quotient was formulated for the vibration frequency, which indicated that piezoelectric and surface effects led to higher vibration frequencies. Next, the variationally consistent boundary conditions were formulated in terms of moment and shear force expressions. It was observed that the presence of the Pasternak interlayer between the nanotubes led to coupled boundary conditions when a shear force and/or a moment was specified at the boundaries. Full article

The application of double-layer shell structure is very common in some situations that require complex loads and vibrations, such as key components such as the shell and wings of aerospace engines, and the shell of underwater vehicles. Many authors have conducted research on the vibration and acoustic radiation characteristics of double-layer cylindrical shells. By adding reinforcement and ribs between the double-layer cylindrical shells and optimizing structural design, passive vibration control techniques can effectively solve high frequency vibration problems, but the impact on mid to low frequency vibrations is still limited. Therefore, this article conducts theoretical research on a novel active vibration control method that inserts an active actuator between a double-layer cylindrical shell to achieve better mid low frequency vibration control effects. Firstly, the substructure admittance method is applied to analytically and dynamically model a double-layer cylindrical thin shell structure with active support, and the vibration power flow of the system is theoretically derived to evaluate the vibration reduction effect. Then, numerical simulation analysis was conducted on the influence of different configurations of six feedback control parameters, time delays, and other factors on the vibration power flow. Finally, based on the image, the conclusion is drawn that all six feedback control parameters can improve the vibration control effect of the coupled system to a certain extent, but not every feedback control parameter has a prominent effect, and the effective range of some parameters is relatively narrow. Full article

During the tunneling process of a double-shield TBM, vibrations generated by rock–machine interaction can affect its safe, efficient, and stable operation. This study was based on the Eping Water Diversion TBM Project. By deploying a vibration monitoring system, the original vibration signals of the double-shield TBM were acquired. A denoising method combining Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (ICEEMDAN) and Multi-scale Permutation Entropy (MPE) was applied for signals reconstruct. The time-domain and frequency-domain characteristics of the reconstructed signals were extracted, and the three-directional vibration characteristics of the cutterhead were analyzed. The influence of surrounding rock classes and tunneling parameters on the vibration characteristics of the double-shield TBM cutterhead was investigated. The results indicate that cutterhead vibration exhibits anisotropy, with the tangential vibration amplitude being the largest, followed by the axial and radial components. The vibration energy is primarily concentrated in the high-frequency range. As the surrounding rock changes from Class II to Class V, the vibration intensity gradually decreases. During the transition from Class II to Class IV rock, the axial vibration frequency decreases while the tangential vibration frequency increases due to changes in rock-breaking patterns. In Class V rock, lower thrust leads to uneven load distribution at the cutterhead-fragmented rock interface, which increases axial vibration frequency. Meanwhile, lower rotational speed results in smoother cutting and reduces tangential vibration frequency. Increasing cutterhead rotational speed or thrust amplifies vibration intensity. Higher rotational speed shifts vibration energy toward lower frequencies, whereas increased thrust introduces more high-frequency components. The findings of this study provide valuable insights for the structural design, tunneling parameter optimization, geological condition perception, fault diagnosis and prediction of double-shield TBMs, thereby promoting green and intelligent tunneling construction. Full article

Vibrational double diffusion has gained increasing attention in recent studies due to its role in enhancing mixing, disrupting thermal boundary layers, and stabilizing convection structures, especially in nanofluids and porous media. This study focuses on the case of two-phase nanofluid flow in the presence of vibrational effects. The flow domain is a fined chamber that is filled with a non-Darcy porous medium. Two concentration formulations are proposed for the species concentration and nanoparticle concentration. The thermal radiation is in both the x- and y-directions, while the flow domain is considered to be inclined. The solution technique depends on an effective finite volume method. The periodic behaviors of the stream function, Nusselt numbers, and Sherwood numbers against the progressing time are presented and interpreted. From the major results, a significant reduction in harmonic behaviors of the stream function is obtained as the lengths of the fins are raised while the gradients of the temperature and concentration are improved. Also, a higher rate of heat and mass transfer is obtained when the vibration frequency is raised. Furthermore, for fixed values of the Rayleigh number and vibration frequency (Ra = 10⁴, σ = 500), the heat transfer coefficient improves by 27.2% as the fin length increases from 0.1 to 0.25. Full article

To investigate the mechanisms of unexpected failures in a multi-stage gear transmission system under a relatively low load, a rigid–flexible coupled multi-body dynamics model with 10 spur gears and 12 helical gears is established. The dynamic condensation theory is applied to improve computational efficiency. The construction of this model incorporates critical nonlinear factors, ensuring high precision and reliability. Based on the proposed model, four critical dynamic parameters, including acceleration, mesh stiffness, dynamic transmission error, and vibration displacement, are analyzed. This research systematically reveals the nonlinear dynamic mechanism under the multi-gear coupling effect. The spectrum of the gears exhibits prominent low-frequency peaks at 320 Hz and 750 Hz. Notably, alternate load-dominated gears show a shift in prominent low-frequency peaks. The phenomenon of marked oscillations in mesh stiffness suggests a potential risk of localized weakening in the system’s load-carrying capacity. Critically, alternating torques induce periodic double-tooth contact regions in the gear at specific time points (0.115 s and 0.137 s), which are identified as critical factors leading to gear transmission system failures. The variation characteristics of the dynamic transmission error (DTE) demonstrate that the DTE is strongly correlated with the meshing state. The analysis of vibration displacement further indicates that the alternating external loads are the dominant excitation source of vibrations, noise, and failures in the gear transmission system. Full article

The primary resonance responses of high-performance nanocomposite materials used in spacecraft components in complex electromagnetic field environments were investigated. Simultaneously considering the interfacial effect, agglomeration effect, and percolation threshold, a theoretical model that can predict Young’s modulus and electrical conductivity of graphene nanocomposites is developed by the effective medium theory (EMT), shear lag theory, and the Mori-Tanaka method. The magnetoelastic vibration equation for an axially moving graphene nanocomposite current-carrying beam was derived via the Hamilton principle. The amplitude-frequency response equations were obtained for different external loading conditions. The study reveals the significant role of graphene concentration, external force, and magnetic field on the system’s primary resonance, highlighting how electromagnetic forces play a critical role similar to external excitation forces. It is shown that the increase in graphene content could lead the system from period-doubling motion into chaotic behavior. Moreover, an enhanced magnetic field strength may lower the minimum graphene concentration needed for period-doubling motion. This work provides new insights into controlling nonlinear vibrations of such systems through applied electromagnetic fields, emphasizing the importance of designing multifunctional nanocomposites in multi-physics coupled environments. The concentration of graphene filler would significantly affect the primary resonance and bifurcation and chaos behaviors of the system. Full article

Although shear horizontal waves have advantages over longitudinal waves, including a higher resolution, less wave mode conversion, and much better reflection coefficients at void and crack interfaces in nondestructive detection, they require good contact surface flatness and efficient coupling agents. In this paper, we analyze and design the basic components of the dry-coupled ultrasonic shear wave probe through theoretical analyses and numerical simulations. The admittance characteristics, resonant frequency, and electromechanical coupling coefficients of the double-laminated vibrator under different size parameters in both 2D and 3D models are simulated, and the probe structures are optimized based on the simulation results and operational requirements. The simulation results of the wave field excited by the double-laminated vibrator show the effectiveness of the optimized probe models. Additionally, the dry coupling method of the probe is simulated to study the acoustic energy distribution under various dry-coupled structures. Finally, we compare the measured admittance with the simulated values, and they are in good agreement. Full article

The dynamic behavior of three-layer composite beams, consisting of concrete slabs and steel beams, is influenced by the structural configuration of each layer as well as the shear connectors. The interlayer shear stiffness in three-layer composite beams governs their global dynamic behavior, while interlayer slippage-induced localized vibration effects represent a key limiting factor in practical applications. Based on the dynamic test results of steel–concrete double-layer composite beams, the feasibility of a finite element solid model for composite beams, which accounts for interlayer shear connectors and beam body characteristics, has been validated. Utilizing identical modeling parameters, an analytical model for the inherent vibration characteristics of three-layer steel–concrete composite beams has been developed. This study encompasses two types of composite beams: concrete–steel–concrete (CSC) and concrete–concrete–steel (CCS). Numerical simulations and theoretical analysis systematically investigated the effects of interface shear connector arrangements and structural geometric parameters on dynamic performance. Research indicates that the natural frequency of steel–concrete three-layer composite beams exhibits a distinct two-stage increasing trend with the enhancement in interlayer shear stiffness. For CSC-type simply supported composite beams, the fundamental vertical vibration frequency increases by 37.82% when achieving full shear connection at both interfaces compared to the unconnected state, while two-equal-span continuous beams show a 38.06% improvement. However, significant differences remain between the fully shear-connected state and theoretical rigid-bonding condition, with frequency discrepancies of 24.69% for simply supported beams and 24.07% for continuous beams. Notably, CCS-type simply supported beams display a 12.07% frequency increase with full concrete-to-concrete connection, exceeding even the theoretical rigid-bonding frequency value. Longitudinal connector arrangement non-uniformity significantly impacts dynamic characteristics, while the transverse arrangement has minimal influence. Among structural parameters, steel flange plate thickness has the most significant effect, followed by concrete slab width and thickness, with steel web thickness having the least impact. Based on the observation that the first-order vertical vibration frequency of three-layer composite beams exhibits a two-stage decreasing trend with an increase in the span-to-depth ratio, it is recommended that the span-to-depth ratio of three-layer steel–concrete composite beams should not be less than 10. Full article

Based on time-averaged digital holography, a vibration deformation measurement system was designed and a full process reconstruction and identification strategy was developed for detecting the micro-defects in optical materials. Through the double beam expansion setting and off-axis imaging adjustments, it is suitable for measuring optical materials with non-specular surfaces by double exposure shots. The scheme was applied to optical sandwich composites and 3D printed glass. Abnormal amplitudes occur at the defects due to different resonance frequencies, resulting in anomalous vibrations under excitation, and the differences in the amplitudes and phases before and after vibration can effectively characterize vibration amplitude and subsurface defects, proving that this method has a high detecting sensitivity. Full article

The measurement system proposed in this paper, based on double intensity modulation, can achieve the detection and recovery of vibration signals. The system uses a Mach–Zehnder modulator to modulate the intensity of the laser light before and after it is reflected from the target, and the modulated optical signal carries the vibration signal information. After photoelectric conversion and data processing, the system measures and recovers the amplitude and frequency of the vibration signal. For sinusoidal signals, amplitudes of $15\mathsf{\mu }$m, $25\mathsf{\mu }$m and $40\mathsf{\mu }$m and frequencies of 100 Hz, 500 Hz and 1000 Hz were measured, and the experimental results demonstrate that the rapid measurement and waveform recovery of such signals can be achieved using our proposed system. Specifically, the absolute deviation in amplitude measurement is less than $0.13\mathsf{\mu }$m, and the relative error does not exceed 0.35%; the absolute deviation in frequency measurement is less than 0.35 Hz, with a relative error below 0.01%; and a refresh rate of up to 4 kHz can be reached. Moreover, an aluminum plate is selected as the target object instead of the reflector in the system, providing a new method for vibration signal detection and expanding the scope of dynamic detection in industrial applications. Full article

This study presents a Multi-layer Quasi-Zero-Stiffness (ML-QZS) vibration isolation platform for variable loads in large-amplitude and low-frequency dynamic environments. In one isolation mount of the proposed ML-QZS isolation platform, Multi-layer permanent magnets are constructed to generate discontinuous Multi-layer negative-stiffness regions. The first design criterion is to achieve the low-frequency and wide-amplitude vibration isolation range for different loads. The second design criterion is carried out for the dynamic performances of transient and steady states. Since both structural design and damping determine vibration transient time and the displacement transmissibility, which often exhibit contradictions depending on system parameters, a bi-objective Pareto optimization criterion is proposed to balance the vibration transients between different layers while ensuring significant isolation effectiveness in one layer. Finally, the relevant experimental prototype is constructed, and the results verify the design principle of Multi-layer double magnetic ring construction and optimization criterions for structural parameters and damping coefficients. This study provides an advanced nonlinear isolation platform with a wide QZS range for different loads, and the optimization method to coordinate the vibration performances, which provides important theoretical and experimental guidance for the design and realization of isolation platforms in practical engineering applications for large-amplitude and low-frequency dynamic environments. Full article