Search Results (4,182)

Under high-Mach-number flight conditions, the combustion chambers of hypersonic vehicles encounter extreme thermal environments marked by unilateral heating, high-heat-flux density, and supercritical pressure. Traditional hydrocarbon fuel cooling often suffers from insufficient heat sinks, high-temperature cracking and coking blockages, making it difficult to meet long-endurance thermal protection requirements. Liquid metal, due to its extremely high thermal conductivity, wide liquid phase temperature range, low Prandtl number and electromagnetic pump driving capability, has become a key technology for breaking through the bottleneck of high-heat-flux thermal protection. Apart from the magnitude of heat flux, the heat-transfer time scale (such as the characteristic thermal response time of the wall and the fluid) is also crucial. During hypersonic flight, transient thermal loads can change within milliseconds, requiring rapid thermal response. Liquid metals, due to their high thermal diffusivity, have a shorter thermal diffusion time compared to hydrocarbon fuels. This review employs a systematic literature review of approaches using gallium-indium-tin alloy, GaInSn, focusing on three core directions: the flow and heat-transfer characteristics of liquid metals, the optimization of cooling micro-channels, and the application of thermal protection systems. It summarizes the research progress at home and abroad, compares and analyzes the performance differences and applicable scenarios of typical liquid-metal working fluids, and summarizes the advantages and disadvantages of existing models, structural designs, and system schemes. The research shows that liquid metals can significantly alleviate thermal stratification and eliminate coking, and deep, narrow, tree-shaped, and biomimetic micro-channels can effectively enhance heat transfer. The liquid-metal-fuel dual-channel waste heat recovery and thermoelectric power generation system has demonstrated engineering application potential. Currently, the field still faces key challenges, such as unclear heat-transfer mechanisms under extreme conditions, the lack of general heat-transfer correlation formulas, insufficient compatibility with high-temperature materials, poor miniaturization and vibration resistance of electromagnetic pumps, and low system integration. In the future, efforts should be focused on developing multi-field coupled heat-transfer models under extreme thermal environments using engineered micro-channel structures, corrosion-resistant materials, and lightweight electromagnetic pumps, promoting the research and development of integrated thermal protection, heating and power generation systems, and providing support for the development of advanced thermal management systems for hypersonic aircraft and aviation engines. Full article

Biomimetic surface texturing provides a promising strategy for regulating the vibration behavior of rolling bearings under starved lubrication. In this study, vein-like, elliptical, semi-elliptical, and composite textures inspired by Monstera deliciosa leaves were fabricated on the shaft-washer raceways of thrust cylindrical roller bearings at depths of 4 μm, 8 μm, and 12 μm. Tangential and normal vibration signals were analyzed using time-domain parameters, frequency spectra, power spectral density, and time–frequency maps. The results showed that both texture morphology and depth strongly affected vibration stability. Most textured bearings exhibited lower vibration responses than the smooth bearing after prolonged operation. Among the tested depths, 8 μm produced the most stable response, characterized by lower peak values, smoother root mean square curves, reduced power spectral density levels, and more uniform time–frequency energy distributions. The 8 μm semi-elliptical texture exhibited the best overall performance by suppressing transient impacts and high-frequency energy concentration. These findings indicate that vibration regulation in textured rolling bearings depends primarily on the synergistic matching between texture morphology and depth rather than texture complexity alone. Full article

Mountain biking over rough terrain exposes riders to vibrations that may affect comfort, health, bicycle control, and performance. This study analyzed the effect of wheel diameter on vibration transmission and performance during a short uphill and downhill test over rocky terrain. Forty-nine highly trained male mountain bikers completed repeated trials using two equivalent hardtail mountain bikes with 26- and 29-inch wheels. Vibrations were recorded with eight triaxial accelerometers placed on the bicycle and rider, and performance was assessed using an electronic photocell timing system. Both wheel sizes showed a similar vibration pattern, with lower root mean square (RMS) acceleration values at the helmet and coccyx and higher values at the wrists and ankles. However, wheel diameter significantly influenced vibration transmission. During the uphill test, the 26-inch bicycle produced higher accelerations at the coccyx and rear hub, whereas during the downhill test, the 29-inch bicycle transmitted greater vibrations to the rider’s wrists and ankles. No significant differences were observed between wheel sizes in the time required to complete either the uphill or downhill tests. These findings suggest that, in short and highly irregular uphill and downhill sections, 29-inch wheels do not necessarily improve performance over 26-inch wheels, although they modify the distribution of vibrations transmitted to the rider. Full article

Cantilever roadheaders are widely used in medium-soft rock tunneling. However, conventional pick cutters suffer from high rock-breaking load, excessive energy consumption, and severe abrasion, which restrict the performance of roadheader vehicle-end intelligent control systems. Existing ultrasonic rock-breaking studies mainly focus on drilling and polycrystalline diamond compact (PDC) cutters, while calibrated EDEM simulation and experimental studies of synchronous ultrasonic-vibration-assisted pick cutter cutting remain limited. This study investigates the rock-breaking behavior of synchronous ultrasonic vibration coupled with pick cutter cutting using 21 MPa artificial rock-like specimens. A calibrated EDEM simulation model was developed based on the Hertz–Mindlin with Bonding contact model and validated by uniaxial compression and Brazilian splitting tests. Meta-particle technology was applied to analyze fragmentation characteristics. The effects of ultrasonic frequency, cutting angle, and cone angle on rock-breaking load, debris production, and specific energy consumption were investigated through simulations and experiments. An ultrasonic-assisted cutting test system equipped with force sensors was established for validation. Results show that 30 kHz ultrasonic vibration effectively reduces rock-breaking load under the investigated operating conditions. A relatively favorable parameter combination obtained from the numerical simulations consists of an ultrasonic frequency of 30 kHz, a cutting angle of 40°, and a cone angle of 60°. Compared with conventional cutting, the optimized scheme reduces average cutting load by 74.69%, increases debris yield by 54.71%, and decreases mass-specific mechanical cutting energy consumption by 83.63%. This study provides quantitative data support for roadheader vehicle-end intelligent control systems. Full article

Geomagnetically induced current (GIC) flowing through power transformers causes core saturation, leading to local hot-spot overheating, abnormal vibration, increased noise, and even irreversible transformer damage and forced outage. To prevent catastrophic GIC-induced failures, relay protection must isolate transformers in a timely and reliable manner, yet GIC has long been a critical challenge interfering with the correct operation of conventional transformer protection systems. This paper studies transformer excitation current characteristics under GIC impact, establishes a transformer model with extreme GIC injection, analyzes differential protection performance under varying GIC magnitudes, proposes a modified differential protection method, and verifies its effectiveness via simulations and experiments. Results demonstrate that GIC distorts transformer excitation current, introducing a second harmonic into differential current to trigger differential tripping blocking. The distinct second-harmonic features between magnetizing inrush and GIC injection enable reliable selective unblocking of harmonic restraint. To enable the differential protection to operate correctly under different GIC injection conditions, the operating threshold shall be adjusted according to the transformer parameters after the harmonic blocking is deactivated. The proposed strategy can potentially disable the harmonic blocker during GIC events, allowing relays to trip on demand, which is critical for ensuring transformer safety under extreme conditions. Full article

This review paper systematically investigates the surface modification technology of wooden table tennis blades, with a particular focus on the inherent conflict between coating-induced protection and the preservation of acoustic performance—a critical yet underexplored aspect of blade design. While protective coatings are essential for enhancing durability against moisture, wear, and impact, they inevitably alter the blade’s vibrational characteristics and acoustic feedback, compromising the tactile–auditory perception that elite players rely upon. The current literature predominantly treats protection and acoustics as separate design objectives, lacking an integrated framework to resolve their inherent trade-off. To address this gap, this review establishes a material–structure–function integrated design paradigm that elucidates the synergistic optimization of coating protection and acoustic response. We systematically analyze the regulatory mechanisms of key coating parameters—specifically elastic modulus, density, and damping coefficient—on blade vibration modes and impact sound characteristics, demonstrating that conventional singular optimization inevitably leads to undesirable frequency shifts and diminished tactile feedback. Our synthesis of materials science, acoustic analysis, and biomechanics reveals that the key to synergy lies in constructing a mechanical impedance-matching transition system through material selection and thickness gradient design. Notably, we show that a multi-layer gradient coating architecture, guided by finite element simulation, can enhance protective performance by 40% while restricting acoustic deviation to within 5%, validating a rational “design–simulation–verification” closed-loop methodology. Furthermore, this review identifies critical research frontiers, including smart adaptive coatings and sustainable bio-based materials, and proposes a multi-objective optimization framework to bridge the gap between laboratory innovation and manufacturable, high-performance sporting equipment. This work provides a foundational theoretical roadmap for the next-generation design of competition-grade table tennis blades, balancing durability with the nuanced sensory demands of elite athletes. Full article

This study investigates the dynamic response of non-circular gear planetary trains in transplanting mechanisms, focusing on variable transmission effects. A time-varying mesh stiffness model was developed for non-circular gears using pitch curve parameters, incorporating pressure angle, contract ratio, and equivalent teeth number as dynamic variables. A dynamic model of the planetary gear train was established to analyze component vibration characteristics. Comparative analysis reveals that non-circular gears’ variable-speed transmission significantly amplifies gear train vibrations compared to that of circular gears. Structural angle effects were examined, demonstrating the structural angle’s critical role in modulating vibration energy distribution between sun and planet gears. Frequency-domain analysis identified optimal structural angle ranges that minimize resonance risks by controlling component center vibrations. This work clarifies the coupling mechanisms between geometric parameters and transmission characteristics in non-circular gear systems. A design criterion based on frequency–energy distribution is proposed to optimize high-speed transplanting mechanisms. These findings advance the understanding of vibration modulation in variable-ratio gear trains and provide theoretical guidance for enhancing operational stability in agricultural machinery. Full article

Subsurface faults in sediment-covered basins often lack clear surface expressions, necessitating integrated geophysical reconnaissance to identify structural complexities. The eastern margin of the Sofia Basin contains normal faults, with the geometry and activity of unmapped structures near Lozen Mountain being poorly understood. This study examines a presumed subsurface discontinuity using a ~216.2 m passive seismic profile across the Lozen Fault zone. Ambient vibrations from twelve point stations and a fixed reference station were analyzed to map structural anisotropy and wavefield variations using relative vertical-component spectral amplitudes, polarization parameters, and horizontal-to-vertical (H/V) spectral ratios. The spectral amplitude profiling revealed a significant lateral contrast of 6.21 dB across a depth interval of 0–140 m (p = 0.0043), suggesting a potential fault boundary. A two-level step model identified a horizontal transition at 109.0 m, with analyses indicating a zonal wavefield response. Southern stations recorded a more stable polarization axis (mean direction 37.32°) compared to the dispersed northern records (mean direction 60.43°, p = 0.097), while directional shifts in H/V distributions were significant (p = 0.0022). While these observations provide a clear structural indicator rather than direct proof of faulting, they effectively demonstrate that non-tectonic lithological and hydrological variations generate these identical spectral signatures. The results establish a well-constrained spatial target for future multi-profile surveys, electrical resistivity tomography, active-source seismic imaging, and paleoseismological trenches required to conclusively verify the geometry, age, and present-day activity of the fault structure. Full article

Carbon fiber reinforced plastic (CFRP) composites have been widely adopted in the aerospace industry due to their excellent mechanical and physical properties. However, their anisotropy and weak interlaminar bonding make them prone to defects such as delamination and fiber pull-out during conventional drilling (CD). Longitudinal-torsional coupled ultrasonic vibration-assisted drilling (LTC-UAD) integrates axial and circumferential vibrations to suppress hole defects and is considered a promising machining method for improving the quality of holes drilled in CFRP. Based on kinematic analysis, a model for the working rake angle of the main cutting edge is established to obtain the variation law of the maximum working rake angle along the cutting edge. Compared with CD and longitudinal ultrasonic vibration-assisted drilling (L-UAD), LTC-UAD significantly increases and homogenizes the maximum working rake angle of the main cutting edge, which helps optimize its cutting performance. A three-dimensional finite element model of CFRP is constructed to analyze the dynamic fiber removal process under typical fiber orientations. Finally, drilling experiments are performed to observe the hole wall micro-morphology at various fiber angles. The simulation results indicate that ultrasonic vibration causes periodic changes in the fiber cutting angle, subjecting the fibers to a directional shear state and making them more prone to shear fracture. Two-dimensional ultrasonic vibration cutting enhances the directional shear effect, promotes fiber fracture, accelerates chip removal, and improves the quality of the machined surface. Experimental observations confirm LTC-UAD alleviates fiber crushing, bare fibers, and surface cavities with uniform resin coverage. Furthermore, ultrasonic vibration suppresses thrust force. L-UAD and LTC-UAD yield 10.6% and 17.1% reductions via periodic cutting depth variation and facilitated carbon fiber shear fracture. Full article

Identifying parameters of dynamical systems from sparse measurements is a core task in structural health monitoring and vibration engineering. For second-order oscillators, standard physics-informed neural networks (PINNs) struggle because different parameter values can produce nearly identical displacement records, making the inverse problem ill-posed. We propose the derivative-observation-augmented PINN (D-PINN), which incorporates velocity measurements into the training loss to resolve this degeneracy. Three theoretical results support the method: a Sobolev-type inequality proves that constraining the velocity error automatically bounds the displacement error; a Fisher information analysis shows that velocity observations increase the information available for parameter estimation; and a residual-based estimate bounds the parameter error in terms of the solution accuracy and its derivatives. Experiments on linear, forced near-resonance, and Duffing oscillators (10 random seeds, 20,000 epochs) show that D-PINN reduces the damping coefficient relative error from 40% to 11.7% without any parameter prior. With a weak prior (${\mu }_0=3.2$, a 20% deviation from the true value 4.0), the error drops further to 2.1%, a 19-fold improvement over standard PINN. We also analyze sensitivity to prior quality, derivative observation source, and measurement noise, and identify scenarios where derivative observations do not improve displacement fitting. Full article

The conformational composition and ultraviolet photochemistry of neutral valine isolated in solid parahydrogen were investigated using high-resolution infrared spectroscopy, ultraviolet photolysis, and density functional theory calculations. The observed infrared spectrum was analyzed by combining calculated vibrational frequencies, relative infrared intensities, and conformer-specific photolysis kinetics. Four distinct photolysis-rate categories were identified experimentally, providing direct evidence for the presence of at least four valine conformers in the parahydrogen matrix. The combined spectroscopic and kinetic analysis enabled assignment of the major absorption bands to the six lowest-energy conformers and revealed pronounced conformer-dependent photostability of valine. Upon irradiation at 213 nm, valine undergoes predominantly $\alpha$-carbonyl C–C bond cleavage, producing the hydrocarboxyl (HOCO) radical and 2-methylpropan-1-imine as the major photoproducts. The formation of HOCO is consistent with previous studies of amino acids isolated in solid parahydrogen and supports a common photodissociation pathway among aliphatic amino acids. The hydrogen-bonded Type II conformer exhibits significantly slower photodepletion than the Type I conformers, indicating that intramolecular hydrogen bonding enhances ultraviolet photostability of valine. These results establish a direct relationship between molecular conformation and photochemical stability in isolated amino acids while further demonstrating the unique capability of solid parahydrogen matrix isolation for conformer-specific photochemical investigations. Full article

The mechanical performance of CFRP/2024 Al alloy hybrid laminates joined by transverse ultrasonic vibration-assisted riveting (TUVAR) was investigated. The experiments were conducted on a self-developed ultrasonic riveting system with a power of 3000 W and a vibration frequency of 19.8 kHz, covering ultrasonic amplitudes from 0 to 24 μm. Test specimens were fabricated from T300/CFRP laminates, 2024 Al alloy sheets, and 2A10 Al alloy rivets. The influences of ultrasonic amplitudes (12 μm, 16 μm, 20 μm, and 24 μm) on riveting load, driven head geometry, interference, static tensile strength, and cyclic loading behavior were systematically analyzed. The results showed that TUVAR reduced the riveting force and promoted rivet deformation. As the amplitude increased, the driven head diameter increased, and the driven head height decreased, with a maximum reduction of 6.62%. The mean interference generally increased up to 20 μm and then decreased slightly at 24 μm; the relative interference variance coefficient ranged from 0.070 to 0.155 under TUVAR. Static tensile tests showed that the joint strength first increased and then decreased with increasing amplitude, with the highest mean static tensile load obtained at 20 μm. Cyclic tensile tests indicated that load-bearing capacity was improved with increasing amplitude, while the maximum deviation was maintained within 3.5%. These findings demonstrate that TUVAR can enhance both the forming quality and the mechanical performance of CFRP/2024 Al alloy riveted joints, and provide a useful reference for the high-performance joining of composite-metal hybrid structures in aerospace applications. Full article

Accurate probabilistic analysis of wind-induced structural vibration is essential for accurately analyzing structural safety and serviceability. Though the FPK equation offers a tool for analysis, its application is challenged by the noise characteristics of wind spectra, such as the Davenport and Kaimal spectra. Using the conventional second-order linear filter model to fit Davenport and Kaimal spectra tends to underestimate their spectral energy in the mid-to-high-frequency range. To address this limitation, this paper proposes an improved second-order filter model that enhances fidelity without increasing filter dimensionality. This model is complemented by an optimization strategy based on the idea that the frequency range is partitioned, which generates three models specifically for low-, mid-, and high-frequency ranges. These models can better fit Davenport and Kaimal spectra in a much larger frequency range compared to the conventional model. The effectiveness of the proposed models is validated through numerically analyzing a linear SDOF stochastic oscillator and a nonlinear stochastic SDOF oscillator in various cases. The results demonstrate that the proposed models maintain exceptional accuracy across a wide range of structural natural frequencies. Full article

To address the challenges in understanding the raceway failure mechanisms of bearings under dynamic radial excitations, this study proposes a vibration evolution analysis method based on multi-source data fusion and a Granger causality test. Firstly, a vertical bearing vibration test bench that can simulate the dynamic excitation in engineering practice is built, and the bearing acceleration, inner ring displacement and cage data are collected at the same time. Subsequently, the evolution law and correlation relationship of bearing vibration signals during the expansion process of bearing raceway damage were studied. Based on this, a multi-source vibration data fusion method was proposed, and the effectiveness of different data fusion schemes in characterizing raceway damage expansion was compared. Finally, the Granger causality test was applied to analyze the causal relationship between the evolution of various vibration behaviors during the damage propagation process. Research results demonstrate that under complex loading conditions during sustained operation, the “False Brinelling” indentation gradually develops into raceway surface damage. The vibration behavior of bearings exhibits distinct stage-specific characteristics under dynamic radial excitations. Notably, variations in vibration behavior amplitude and transition timing between different operational phases demonstrate significant discrepancies. Significant alterations in causal relationships between vibration behaviors were observed throughout different degradation phases. The combined approach proposed in this paper, encompassing complex load simulation, multi-source data fusion, and causal analysis, offers a new understanding of the raceway failure mechanism of bearings under real-world operating conditions. Full article

Jacket foundations, with their excellent adaptability and economic efficiency, have been increasingly widely applied in medium-deep water areas. However, the scouring and erosion effects in the marine environment, coupled with complex wind-wave loads, have severely restricted the long-term safe service of jacket foundations. In this study, a structure-pile-soil coupled dynamic response model considering the effects of scour depth and changes in wind and wave directions for the jacket-type offshore wind turbine is developed by integrating the wind and wave load generation capability of OpenFAST and the nonlinear pile-soil interaction analysis function of OpenSees. By quantitatively analyzing key response parameters such as tower top displacement, nacelle acceleration, and internal forces of the foundation tower and pile shaft, this study reveals the significant influence of soil stiffness degradation induced by scour on structural dynamic characteristics, and verifies the effective suppression mechanism of the feathering shutdown strategy on structural responses under extreme loads. The research results indicate that scour has a negligible impact on the fundamental frequency of the jacket-type offshore wind turbine structure, while it significantly reduces the high-order frequencies and leads to a substantial increase in pile shaft internal forces; the effect of wind-wave angle intensifies the spatially coupled vibration response of the structure. The study provides important theoretical and technical support for the anti-scour design, multi-directional load assessment, and formulation of safety control strategies for jacket foundations in complex deep-sea environments. Full article