Search Results (618)

Fused silica–aluminum alloy dissimilar connections are in urgent demand in fields such as aerospace optoelectronic packaging, vacuum optical windows, and micro-electro-mechanical systems, yet the dramatic mismatch in thermal-expansion coefficient and thermophysical properties between the two materials has long been a bottleneck for reliable joining. Current ultrafast laser welding of such heterogeneous systems still suffers from prominent problems, including stringent optical contact requirements, high crack sensitivity on the fused silica side, and unclear coupling mechanism between clamping conditions and joint defects. This work systematically studies the joining process of femtosecond laser welding of fused silica and 6061 aluminum alloy dissimilar materials, focusing on the effects of scanning speed, pulse energy, scanning spacing, and fixture preload on the shear strength, microstructure, and elemental diffusion behavior of the joints. The results confirm that scanning speed and scanning spacing have a synergistic effect on heat input density; the magnitude of the fixture preload is a key factor determining the interfacial residual stress and crack sensitivity. By optimizing the scanning speed (6 mm/s) and combining it with a low preload and 140 μm scanning spacing, a high-strength heterogeneous joint with uniform elemental transition and no macroscopic cracks can be obtained. This study provides a detailed process-optimization approach for high-quality laser welding of dissimilar brittle/ductile materials. Full article

MEMS resonators vibrate about equilibria deflected by whatever combination of temperature, pressure, and bias voltage is present—not about the flat, unloaded plate—raising a basic design question: does the resulting natural frequency depend on the specific loads that produced the deflection, or mainly on the deflection itself? We address this for annular and circular plates through a self-contained derivation of the governing multi-load equations and the linearized vibration eigenvalue problem about an arbitrary thermal, mechanical, and electrostatic equilibrium, validated against two classical benchmarks and applied to a parametric study spanning radius ratio, Poisson’s ratio, and five load combinations at matched deflection. The spread in squared frequency, ${\omega }_1^2$, across combinations shrinks monotonically from $29\%$ at $w/h=0.4$ to $6\%$ at $w/h=2.4$, a dynamic counterpart to a known static result in which the large-deflection boundary layer at a clamped edge depends only on the local membrane stress, not on which loads produced it. Going beyond the linear eigenfrequency, a single-mode Duffing-type reduction, compared against four independent classical benchmarks, reproduces the same asymmetry direction and hardening-to-softening crossover reported in the literature. For the one annular geometry and axisymmetric motion studied here, the results suggest that once deflection exceeds about twice the plate thickness, resonator frequency can be tabulated against deflection amplitude alone, rather than the full space of operating conditions. Full article

This paper introduces a non-invasive ultrasonic sensing system for two-phase refrigerant flow characterization in heat pump circuits used in building energy systems, validated through machine learning (ML)-based regression of the acquired signals. Heat pumps play a crucial role in energy-efficient buildings. However, the absence of a low-cost, non-invasive instrument capable of measuring mass flow rate, mixture density, and vapor quality without disrupting the thermodynamics of a refrigerant circuit remains a gap for smart HVAC systems. A carbon dioxide (CO₂) refrigerant circuit was designed to calibrate such a sensing system under representative operating heat pump conditions. Ultrasonic measurements were conducted using piezoelectric transducers clamped onto the refrigerant pipeline. A calibration framework was structured with ground-truth flowmeter labels, establishing a thermodynamic envelope across 10–20 bar and down to −25 °C, and achieving R² = 0.901 for flow rate, 0.997 for density, and 0.971 for quality, with an overall R² = 0.956. The proposed measurement system is a plug-and-play kit enabling more efficient next-generation heat pumps, supporting building energy management and performance monitoring. The labeled dataset and calibration methodology provide a basis for training and validating ML regression models for real-time flow property inference in operational HVAC systems. Full article

To address the limitations of poor adaptability and insufficient versatility of current surface capture technologies for autonomous underwater vehicles (AUVs) under high sea state conditions, this study proposes an ROV-based capture system equipped with guidance and clamping mechanisms for efficient and stable recovery of AUVs and similar floating targets in rough seas. This work is intended to provide technical support for solving AUV capture challenges in high sea states. Through a systematic investigation of capture methods and associated operational systems, the overall design of the dynamic surface AUV capture device is established. A three-dimensional model is developed to verify the feasibility of the overall operational sequence. Computational fluid dynamics (CFD) simulations are performed to analyze the hydrodynamic performance of the ROV carrier, with particular focus on the drag force and pressure distribution under flow velocities corresponding to Sea State 4 and below. The simulation results indicate that when the ROV inflow velocity reaches 3 m/s, the maximum drag force is approximately 5862 N and the maximum pressure on the frontal area is about 4570 Pa. Based on these data, the overall structural stability is verified, and the results confirm that the structure maintains adequate stability under the target operating conditions. Kinematic simulations are further conducted to investigate the collision force between the target AUV and the guidance/capture device under various initial attitudes and velocities in Sea State 4, thereby determining the overall capture tolerance envelope. Through design manual buffer parameter tuning and comparative improvement analysis, the collision force between the guidance device and the target is reduced by approximately 60%. Full article

The frequency-dependent impedance of electrical connectors, switchgear loops, and related contact structures can indicate degradation at electrical contact interfaces. Conventional contact measurements with a vector network analyzer require dedicated adapters and impedance matching, and the object under test usually has to be removed from the operating system. To simplify field measurements and avoid direct electrical contact, this study employs an established two-probe inductive-coupling/ABCD de-embedding framework in conjunction with a purpose-designed broadband current probe and calibration fixture. Commercial injection and receiving probes were first evaluated to identify practical limitations associated with probe resonance, magnetic-path air gaps, cable clamping, and probe-to-probe coupling. A parametric CST study on ferrite material, winding turns, and core geometry was then used to select a 3W800 NiZn ferrite core with six winding turns and dimensions of 5 mm inner diameter, 10 mm outer diameter, and 5 mm height. The prototype exhibited relatively flat S₁₂/S₂₁ responses from 1 to 400 MHz, with S₂₁ changing from approximately −13.5 dB at 1 MHz to −17.5 dB at 400 MHz and without a pronounced resonance. Quantitative impedance accuracy was validated only over 1–100 MHz: validation against an impedance analyzer using a 108 nH inductor and an 82 pF capacitor yielded mean relative magnitude errors of 4.00% and 4.5%, respectively. Field measurements on a 10 kV switchgear circuit were additionally conducted over 1–30 MHz to demonstrate non-invasive broadband impedance acquisition under practical contact conditions. Accordingly, the 1–400 MHz range in this work refers to probe-transfer characterization rather than experimentally validated impedance accuracy over the full band. Full article

Accurate and low-cost fault diagnosis is essential for improving the reliability of cascaded neutral-point-clamped (NPC) inverters. This paper proposes a single-sensor fault diagnosis method for a single-phase three-module cascaded NPC inverter. Only one DC-side current sensor is required for the diagnostic algorithm, while the voltage sensor used in the outer voltage-control loop is not involved in fault-feature extraction. The measured DC-side current is decomposed via Fourier analysis, and a low-dimensional feature vector is constructed using the amplitudes of the zeroth, 2nd, 3rd, and 4th harmonics together with the phases of the 1st and 3rd harmonics. The six Fourier features are normalized using feature-wise Min–max parameters determined exclusively from the training data. A back-propagation (BP) neural network is then adopted to identify and locate 24 single-switch open-circuit faults in the three-module system. The investigated inverter produces 13 output-voltage levels under healthy operation, and the BP network converges after 5835 training iterations to an error threshold of 1 × 10⁻⁶. An adaptive confirmation criterion based on consecutive diagnosis-code consistency and inter-window feature convergence is introduced. For the nominal 25-class simulation test set, the accuracy, macro-precision, macro-recall, and macro-F1-score are all 100%. In addition, 134 of the 136 dynamic-condition simulation runs are correctly diagnosed, corresponding to an overall robustness-test accuracy of 98.53%. One confirmed, but incorrect final code occurs under the load disturbance applied at 90° of the output-voltage fundamental, and another occurs at an SNR of 20 dB, while no unconfirmed run is observed. Under the severe RL-load condition with τ/T₀ = 1, the mean and maximum diagnostic delays are 41.7 ms and 52 ms, respectively. Full article

Hydrogen circulation pumps in industrial manufacturing equipment face typical sealing challenges at the shaft end. Due to the small molecular diameter and high diffusivity of hydrogen, a single improvement approach cannot adequately enhance sealing performance. While previous studies have largely focused on material modification, systematic investigations into the influence of structural parameters remain limited. Lip radius, lip thickness, and contact lip width are key structural parameters governing sealing performance; however, systematic investigations into modified PTFE lip seals under hydrogen operating conditions remain scarce. To address this gap, this paper presents an integrally structured aluminum alloy skeleton modified PTFE lip seal and develops a finite element analysis model. In this model, the mechanical behavior of the modified PTFE is described using the bilinear isotropic hardening model, while the contact nonlinearity between the lip and the shaft is solved using the Newton–Raphson iterative method. The effects of structural parameters on sealing performance indicators, including maximum contact pressure, maximum friction stress, and shaft clamping force and torque, are systematically analyzed. The results indicate that reducing the lip radius, increasing the lip thickness, and increasing the contact lip width can effectively improve the sealing-related contact characteristics of the seal ring. Full article

Dynamic inspection of hydropower-generator rotors is hindered by long imaging distances, metallic reflections, and motion-induced degradation of anti-loosening marking lines. We present a task-decoupled vision framework that first localizes bolts and then segments their marking lines within scale-normalized regions of interest. The YOLO-SE detector combines spatial-to-depth convolution with efficient multi-scale attention to preserve small-object features and suppress illumination interference. The segmentation stage integrates a MobileViT2 backbone, attention-enhanced atrous spatial pyramid pooling, and Dice cross-entropy loss to recover global context and sparse foreground boundaries. In laboratory experiments, YOLO-SE achieved 99.4% mean average precision at 0.5 intersection-over-union (mAP50) and 99.8% recall, exceeding YOLO26n by 3.2 and 3.4 percentage points, respectively. The complete segmenter achieved 98.67% mean intersection-over-union (mIoU) and 95.38% target-line IoU; across five seed-matched runs, YOLO-SE obtained 99.32 ± 0.10% mAP50 and the segmenter obtained 98.61 ± 0.09% mIoU. Site-specific validation on M12 rotor-clamp bolts supported field applicability under changes in scale, viewpoint, and illumination. The complete cascade required 53.1 million parameters, 207.7 GFLOPs, 2.38 GB peak GPU memory, and 31.8 ms per frame, meeting a 30 FPS GPU budget under the evaluated conditions. Full article

Conventional full-span movable weirs may require complete lowering for sediment or debris release, reducing upstream water-level control and limiting operational efficiency. This study evaluates a smart rubber and steel (SRS) movable weir that enables selective gate operation through a one-way coupled hydraulic–structural framework using the Environmental Fluid Dynamics Code (EFDC) and MIDAS Civil. Four gate-operation scenarios and gate heights of 0.5, 1.0, 1.5, and 2.0 m were analyzed to characterize flow redistribution, hydraulic loading, gate response, longitudinal-rib performance, and the safety of anchor bolts, clamping plates, and the airbag system. Selective lowering substantially altered flow distribution, with side-gate lowering producing the most critical condition and increasing maximum velocity by approximately 267% relative to the fully raised condition at a 2.0 m gate height. Hydraulic demand became strongly localized near the lowered and adjacent raised spans, although the governing static load remained dominated by hydrostatic loading. Rib comparisons showed that redistributing stiffness through additional longitudinal stiffeners reduced stress and deformation without relying solely on gate thickening, while all component-level static checks satisfied the adopted safety criteria. The results demonstrate that integrating span-specific hydraulic redistribution with structural response provides a practical basis for structurally safe and material-efficient river-infrastructure design. Full article

This study addresses the inherently low damping and vibration susceptibility of carbon fiber reinforced polymer (CFRP) laminated cantilever plates by developing a comprehensive dynamic modeling and active vibration control framework. An electromechanical coupling model incorporating macro-fiber composite (MFC) actuators and sensors is established using the first-order shear deformation theory (FSDT) and the assumed mode method, with virtual springs introduced to account for non-ideal clamped boundary conditions. A reduced-order state-space model is then derived through model reduction, and a linear quadratic Gaussian (LQG) controller is designed for optimal state estimation and feedback control. The theoretical model is systematically validated via convergence analysis, ANSYS finite element simulations, and LMS impact hammer testing. The results demonstrate that, with the relative errors of the first four natural frequencies controlled within 2%, the theoretical mode shapes are highly consistent with those obtained from ANSYS simulations. An active vibration control experimental platform is established, and the effectiveness of the control strategy is verified under dual-spectrum harmonic and impact excitations. The results show that the designed LQG controller can effectively suppress multi-modal vibrations, substantially attenuating the response amplitudes of dominant modes and significantly accelerating the transient vibration convergence. This study addresses the challenge of precisely characterizing actual non-ideal clamped boundary conditions. Through model order reduction and closed-loop LQG control experiments, it provides a comprehensive set of theoretical methodologies, numerical solution strategies, and engineering-oriented experimental schemes for the electromechanical coupling dynamic modeling and optimal vibration suppression of CFRP thin-walled composite structures. Full article

Material conveying and collection are critical to harvesting efficiency, crop quality, energy consumption, and operational continuity in combine harvesters. However, existing studies mainly focus on individual technologies, while systematic criteria for technology comparison and selection remain insufficient. This review critically analyzes major conveying and collection technologies, mechanism-based simulation methods, and intelligent sensing and control strategies. Screw, clamping-flexible, chain/vibrating, and pneumatic conveying systems are compared in terms of conveying efficiency, crop damage and material loss, energy consumption, reliability, and adaptability. DEM, dynamic/vibro-acoustic analysis, and CFD–DEM are further evaluated according to their applicable mechanisms, physical fidelity, and computational cost. Recent advances in multi-source sensing, data-driven prediction, and feedforward–feedback control are summarized. Based on these comparisons, a system-level optimization framework is proposed, emphasizing efficiency, quality preservation, and energy efficiency while maintaining operational reliability and adaptability. The review indicates that no single technology is universally optimal; technology selection should be matched to crop properties, operating conditions, and dominant performance objectives. Future research should focus on material-property-informed technology selection, mechanism–data hybrid modeling, and adaptive closed-loop control for intelligent harvesting systems. Full article

Gas flowmeters are a key reference for natural gas trade settlement. To advance on-site verification technology, this paper presents air and natural gas flow test systems employing a clamp-on gas ultrasonic flowmeter, and systematically investigates the effects of pipeline parameters, pressure conditions, transducer usage, and noise reflection on measurement accuracy. Quantitative results show that measurement errors can be controlled within ±2% by selecting appropriate transducer types and installing them beyond 20D downstream of disturbances. Moreover, the proposed dual-transducer synchronous measurement—using two sets of transducers at the same location in different acoustic directions and averaging the results—effectively suppresses radial velocity effects, reducing installation and flow-related errors to within ±1.5%. Installing a single layer of acoustic damping material (≥30 mm beyond the transducer) further improves the coherent signal-to-noise ratio above 30 dB, ensuring reliable performance under noisy conditions. These quantitative findings offer practical guidelines for on-site calibration of natural gas flowmeters, contributing to improved fairness in gas trade measurement. Full article

The performance of ultra-high-performance fiber-reinforced concrete (UHPFRC) under repeated low-velocity impacts, particularly in the context of nominally fixed boundaries relevant to protective structures, remains underexplored. In practice, protective components made of UHPFRC, such as falling object barriers and vehicle parapet systems, are exposed to foreseeable repeated low-velocity impacts; however, no standardized design provisions or residual capacity assessment methods exist for such members, particularly under nominally fixed boundary conditions. This study presents an integrated experimental and numerical investigation into the progressive damage and failure mechanisms of a 50 mm thick UHPFRC plate with nominally fixed (bolted clamping) boundaries subjected to sequential low-velocity impacts. A custom drop-weight test setup was used for impact loading, while high-speed 3D digital image correlation (3D-DIC) captured the quarter-field transient kinematics, which were reconstructed back to the full field based on verified test symmetry and complemented by traditional accelerometer and strain gauge measurements. The results demonstrate a distinct progression of damage. Initial low-energy impacts (196 J/drop) caused negligible damage, highlighting the material’s tolerance. Subsequent higher-energy impacts induced a transition from flexural cracking to a combined flexural–punching shear failure mode. The model-assisted nominal secant stiffness indicator decreased by 5.3% over the repeated 0.5 m drops and fell by 50.8% after the 2.0 m drop, quantifying the transition in structural behavior. A finite element (FE) model, incorporating the concrete damaged plasticity (CDP) model with an energy-based degradation law, was developed and evaluated against the experimental data. This model replicated both the quantitative dynamic responses (with model-to-test ratios of peak acceleration, strain, and displacement between 0.86 and 1.30 across three energy levels) and the qualitative damage evolution. The model thus evaluated enabled a model-derived reconstruction of the critical impact force–time history, revealing the evolution of structural degradation toward the exhaustion of the plate’s global flexural resistance and the transition to a punching shear mechanism. Full article

The performance of a Proton Exchange Membrane Fuel Cell (PEMFC) stack is largely determined during assembly, where component materials, sealant selection, and clamping force jointly influence both sealing effectiveness and interfacial losses. These factors interact through coupled mechanical, thermal, and electrical phenomena. Although detailed multiphysics models can accurately capture these effects, their high computational cost limits their application in parametric analyses and optimisation studies. The Equivalent Stiffness Model (ESM) provides an efficient alternative, representing each stack component as a simplified stiffness formulation. Starting from an earlier ESM that reproduces the nonlinear compression of the Membrane Electrode Assembly (MEA) and sealants, this work adds the calculation of the electrical contact resistance at the Gas Diffusion Layer (GDL)–Bipolar Plate (BPP) interface and the resulting GDL porosity. Given the large number of input parameters, a Design of Experiments (DoE) approach systematically explores a wide range of stack configurations and operating conditions. The analysis shows that GDL type, sealant properties, and clamping force are the main drivers of assembly-related performance, whereas BPP material and thermo-hygrometric conditions become more influential during operation. These results provide quantitative guidance on which design and operating choices most strongly affect stack behaviour and under which conditions. Full article

Insulin resistance (IR) represents one of the most pressing problems in contemporary public health. Its estimated global prevalence ranges from approximately 15.5% to over 61%, depending on the population studied, the diagnostic criteria applied, and the method used for its assessment. Despite the scale of the problem, IR remains underrecognized and lacks formal definition as a distinct disease entity, even as a growing number of clinicians and researchers worldwide describe it as such. Its asymptomatic or mildly symptomatic course allows it to remain undetected for years, during which it makes a significant contribution to the development of type 2 diabetes, cardiovascular disease (CVD) and metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD), and has been increasingly linked to cellular senescence, certain cancers, neuropsychiatric disorders, and other metabolic conditions. The aim of this review was to summarize current knowledge on the pathophysiology, diagnosis, and clinical implications of insulin resistance, to discuss current challenges in its diagnosis, and to evaluate whether available scientific evidence supports its recognition as a distinct disease entity. This narrative review is based on clinical, epidemiological, and mechanistic data retrieved from PubMed and Google Scholar. Meta-analyses, systematic reviews, clinical and observational studies, clinical guidelines, and expert position statements were analyzed. Animal studies were excluded to maintain a focus on human public health implications. The diagnostic gold standard—the hyperinsulinemic-euglycemic clamp—was discussed, along with surrogate methods used in clinical practice (HOMA-IR, OGTT with insulin measurements, the TyG index, and the TG/HDL-C ratio). Factors potentially contributing to the pathogenesis of IR were examined, including hyperinsulinemia (HI), high-carbohydrate diets, inflammation, stress, and sleep disturbances, as well as conditions in which IR occurs physiologically. The findings indicate that current evidence supports the need for a clearer clinical and diagnostic framework for insulin resistance and suggest that its recognition as a distinct disease entity could facilitate earlier diagnosis, improve the standardization of clinical management, and enable earlier metabolic intervention. Given the steadily rising prevalence of metabolic disease, systemic efforts directed at the early identification and treatment of IR may be a key component of strategies aimed at reducing the population-level burden of metabolic disease and its negative consequences. Full article