Search Results (763)

Despite the rapid proliferation of unmanned aerial vehicles (UAVs) across industrial, agricultural, and scientific domains, their deployment remains constrained by limited endurance, aerodynamic inefficiency, and acoustic emissions, all mediated by a shared onboard energy budget. Existing biomimetic UAV reviews have generally treated aerodynamics, structures, sensing, control, and energy systems as parallel topics rather than as interacting components of a unified aerial architecture. Drawing primarily on literature published between 2015 and June 2026 and identified through searches of Web of Science, Scopus, and Google Scholar, this review addresses this gap by examining bio-inspired technologies across six principal domains: aeroacoustic and passive flow control, aerodynamic efficiency, multifunctional structural composites, neuromorphic sensing and control, ionic energy storage, and energy harvesting. Its principal contribution is a cross-domain synergy analysis identifying five performance couplings and one structural enabling architecture through which these domains interact physically and functionally. Representative examples include serration-based propeller geometries that can simultaneously reduce noise and power demand; morphing wing surfaces that serve as both aerodynamic structures and triboelectric harvesting substrates; and neuromorphic spiking neural networks that have been reported, in specific event-vision inference benchmarks, to reduce inference energy by three to four orders of magnitude relative to embedded graphics processing unit (GPU)-based implementations. Mechanical harvesting outputs nonetheless remain orders of magnitude below propulsion requirements and are thus positioned as supplementary. Four systemic barriers (unquantified mass–energy balance, undocumented durability, aeroelastic co-design gaps, and heterogeneous metrics) are evaluated, and the resulting synthesis indicates that advancing bio-inspired UAVs requires a transition from structural imitation to functional, system-level biomimetics. Full article

To elucidate the mechanisms responsible for the low strength, pronounced variability, and long-term deformation of carnallitite, and to provide a basis for stope parameter design in deep potash mines, two carnallitite seams from a potash mine were investigated. Group C carnallitite and Group D halite-dominated rock salt were subjected to short-term compression tests and multiscale comparative analyses, while Groups A and B carnallitite specimens were tested under multistage creep loading. Particle Flow Code (PFC) simulations were conducted to evaluate the influence of particle size distribution. The results indicate the following: (1) The representative Group C specimens exhibited an average uniaxial compressive strength of 7.83 MPa, which was substantially lower than that of Group D. The acoustic emission (AE), scanning electron microscopy (SEM), and computed tomography (CT) analyses revealed greater heterogeneity in damage evolution and failure behavior, mainly associated with polymineralic composition, weak particle–matrix interfaces, local pores, and insufficient particle connectivity. (2) Particle-scale heterogeneity influenced the load-bearing capacity of carnallitite. In the PFC sensitivity analysis, narrowing the prescribed particle-size-distribution range from 0.4–8.0 mm to 4.0–4.0 mm at a mean particle size of 4.0 mm was associated with an increase in simulated strength from 7.82 to 10.40 MPa. Because quantitative contact-network descriptors were not extracted, the corresponding contact-network interpretation is treated as mechanistic rather than direct quantitative evidence. (3) The long-term uniaxial strengths of Groups A and B were estimated as 3.3 MPa and 4.8 MPa, respectively, using the adopted specific-failure-energy method. The modified Burgers model provided a good fit to the creep data within the tested stress levels, yielding coefficients of determination of 0.957 and 0.964 and root-mean-square error (RMSE) values of 0.0803 and 0.0552 percentage points. Based on the long-term strength constraints and the site-specific design assumptions adopted in this study, the calculated inter-room pillar widths were 6 m for Group A and 4 m for Group B. These findings provide insights into the multiscale damage mechanisms and long-term stability assessment of carnallitite stopes in deep potash mines. Full article

Fiber-reinforced high-water-resistance concrete backfill (FHWCB) is a rapid-setting cementitious backfill system used for underground support and backfilling, but its stability is strongly affected by mixture water content and fiber dispersion. This study investigated the fresh-state behavior, mechanical performance, acoustic emission (AE) fractal characteristics, b-value response, and energy evolution of FHWCB. Mixtures with water-to-cement ratios (w/c) of 1.0–1.8 and fiber volume fractions (Vf) of 0–0.5% were prepared and tested using fresh property measurements, unconfined compression, thermogravimetry, AE monitoring, correlation dimension analysis, b-value analysis, and strain energy partitioning. Increasing w/c improved flowability and delayed setting, but weakened the hydration skeleton and reduced early-age compressive strength by approximately 56–61%. Fiber reinforcement showed a non-monotonic effect: Vf = 0.3% increased compressive strength by approximately 16–26%, whereas excessive fiber addition reduced strength because of fiber clustering and weak local zones. AE amplitude sequences exhibited measurable fractal characteristics. A higher correlation dimension indicated distributed microdamage, while decreasing correlation dimension and b-value reflected the transition toward localized macrocrack growth. Energy analysis showed that the peak elastic strain energy density decreased from approximately 0.60 to 0.39 MJ/m³ as w/c increased. The proposed AE fractal–b-value–energy framework provides a quantitative basis for tracking damage progression and optimizing FHWCB for underground engineering. Full article

Acoustic emission (AE) monitoring is widely used to characterize coal failure, but specimens with different burst tendencies cannot be distinguished reliably using a single count, energy, b-value, or fractal indicator. This study reanalyzed archived Vallen AE data from uniaxial-compression tests on five strong-burst, five weak-burst, and three specimen-matched non-burst coal specimens. Thirteen VisualAE event tables were verified against independently decoded primary-data files; hit counts were identical and cumulative-energy differences were below 1%. Vallen C and c records were identified as transmitted and received calibration pulses and were excluded consistently from the physical-AE analysis. Calibration records contributed mean energy shares of 11.1%, 4.3%, and 92.5% in the strong-, weak-, and non-burst groups, respectively. After exclusion, the top 1% of retained events contributed 96.6%, 97.9%, and 66.6% of the AE energy; mean b-values at Ht + 5 dB were 0.788, 0.793, and 1.650; and raw-energy multifractal widths were 1.933, 1.729, and 1.219. The correlation dimension depended strongly on embedding, delay, and scaling-range choices and did not show a universal late-sequence decrease. An exploratory six-component AE multi-parameter index yielded group means of 0.659, 0.798, and 0.150. The results support complementary, explicitly parameterized AE sequence descriptors, while the non-burst sample size (n = 3), absence of strict machine-AE time synchronization, and field-scale transfer requirements limit generalization. Full article

This study investigates the damage evolution mechanism affecting the fracture-bearing performance of fly ash cement paste under low-temperature curing conditions. Pre-cut cement paste specimens with fly ash contents of 0%, 15%, and 25% were prepared and subjected to both standard curing and low-temperature curing at 5 °C for 28 days. Three-point bending tests combined with acoustic emission (AE) monitoring were conducted to analyze peak flexural load, AE ring count, cumulative energy, RA-AF crack classification, and b-value evolution. Additionally, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were employed to characterize micromorphology and relative changes in hydration product content. The results indicate that both fly ash incorporation and low-temperature curing significantly reduce the flexural bearing capacity of pre-notched specimens. Under low-temperature curing, the peak loads of LF15 and LF25 decrease by 34.83% and 47.19%, respectively, compared to LF0. At the same fly ash replacement level, all low-temperature-cured specimens exhibited lower peak loads than those cured under standard conditions. Overall AE activity was reduced in low-temperature-cured specimens, with crack propagation instability occurring at lower load levels. The addition of fly ash shifted the fracture mode toward a tensile-dominated type, whereas low-temperature curing increased the proportion of shear-type AE events. Fly ash incorporation increased the relative content of calcium silicate hydrate (C-S-H) gel and decreased that of calcium hydroxide (CH); however, this did not result in improved peak flexural load. This outcome is attributed to the insufficient reactivity of fly ash at low temperatures, leading to residual unreacted spherical particles, dilution of clinker, and inadequate interfacial bonding, which collectively weaken the continuous load-bearing skeleton of the matrix. This paper establishes a multi-scale interpretation of the damage mechanisms affecting the low-temperature fracture-bearing performance of fly ash cement paste by correlating macroscopic bearing response, AE damage evolution, crack types, and hydration product composition. Full article

The selection of materials for enhancing the energy performance of historic mosque structures, which form a significant part of Türkiye’s cultural heritage, should be based on scientifically supported methodologies and should also consider their architectural nature. In this work, an innovative Energy3D–MADA approach is developed for the comparative evaluation of thermal performance and sustainable selection of heritage natural stones. The proposed framework concentrates on the thermal aspect, while environmental, economic, mechanical, and material-related acoustic indicators are used as supplementary decision indicators. The study examined eight representative heritage natural stones using a representative Ottoman composite masonry wall. For the four climatic regions of Türkiye, the energy performance was predicted, and 32 scenarios were obtained. The annual heating and cooling energy requirements, total operational energy, operational CO₂ emissions, and costs of wall manufacturing were investigated through Energy3D. The results of the simulation indicated that the natural stones had a considerable impact on the performance of historic mosque buildings. Od Stone (Tuff) had the lowest heating and cooling annual energy demand, the minimum total operational energy consumption, and the fewest operational CO₂ emissions among all the alternatives considered, while Red Granite had the greatest energy demand. Compared to Red Granite, Od Stone achieved reductions in annual heating energy of 31%, in total operational energy consumption of 22–25%, and in operational CO₂ emissions of 22–25%, with only about a 1% increase in initial construction cost. Spearman’s rank correlation analysis (ρ) indicated the same ranking in all climate regions, which demonstrated the ranking consistency of the Energy3D-based comparative analysis. Ultimately, the Energy3D simulation outcomes were combined with the LODECI, MEREC, SPC, SIWEC-M, and ALPAS techniques to formulate a decision-support system for the comparative analysis and prioritization of heritage natural stones, to support sustainable mosque design and heritage conservation planning. Full article

This study proposes an approach based on an acousto-ultrasonic method and feature-based analysis to assess the condition of cables within their anchor bases. Experimental tests were performed on several model anchor configurations, including a healthy reference (REF-1) and different degraded configurations (namely DEF-1Z, DEF-2Z, DEF-W), in order to investigate the influence of the number of broken wires on the recorded signal. The acquired signals were characterised using acoustic emission features such as amplitude, energy, duration, counts, and centroid frequency. Z-score normalisation was applied according to two strategies—joint normalisation using a reference anchor base, and reference-free normalisation—in order to better reflect in situ inspection conditions. The objective is to discriminate between healthy and degraded cable states within anchor bases, first with a reference-based approach and then without any reference. The results show that several features have strong discriminative potential. In addition, the reference-free results show good agreement between sensor positions and degraded areas, confirming the localisation of the damage. Overall, this approach appears promising for future in situ applications. Full article

To investigate the evolution of acoustic emission (AE) parameters during the flexural failure of reinforced concrete (RC) beams subjected to freeze–thaw and corrosion, four RC beams were fabricated and assigned to four conditioning regimes: no deterioration, freeze–thaw only (75 cycles), corrosion only (4.8% mass loss), and combined. Three-point bending tests were conducted, combining AE and digital image correlation (DIC) techniques. The damage process was divided into four stages: micro-crack initiation, stable crack propagation, unstable crack propagation, and failure. The evolution of AE parameters including ring count, energy, amplitude, peak count, and duration was analyzed. Each parameter is positively correlated with load level and rises as the damage stage advances. The slope of cumulative parameters reflects crack development more reliably than instantaneous values. The effect of corrosion on these parameters is significantly greater than that of freeze–thaw. For corroded beams, AE parameter levels are higher during the micro-crack initiation stage but lower during the stable crack propagation stage. The overall AE activity decreases with increasing deterioration degree. High-amplitude events increase with damage progression, but fewer high-amplitude events are observed at the failure stage of severely deteriorated beams. This study reveals the correspondence between AE parameters and damage stages, providing an experimental basis for damage assessment using AE techniques. Full article

To investigate the effects of different moisture conditions and numbers of freeze–thaw cycles on the damage deterioration behavior of red sandstone, three freeze–thaw conditions were used in this study: GA (sealed water-retaining state after saturation), GB (semi-immersed state after saturation), and GC (full immersion state after saturation). The samples were subjected to 20, 40, and 60 freeze–thaw cycles, followed by uniaxial compression tests and acoustic emission (AE) monitoring. By analysing the stress–strain curves, tangent modulus–strain curves, crack-closure parameters, brittleness indices, AE counts, and energy dissipation characteristics, the freeze–thaw damage mechanism of red sandstone samples under disparate moisture boundary conditions was revealed. The results show that as the number of freeze–thaw cycles increases, the uniaxial compressive strength and tangential deformation modulus of red sandstone samples gradually decrease, whereas the peak strain and full compaction strain increase. The crack-closure stage is prolonged, and the failure process changes from sudden brittle failure to progressive damage failure. The degree of damage differed among the samples under different moisture conditions; overall, the GB group (semi-immersed state) exhibited the most pronounced deterioration, followed by the GC group (fully immersed state), whereas the GA group (sealed water-retaining state) experienced relatively weak deterioration. Energy analysis indicates that freeze–thaw cycling decreases the elastic energy storage capacity and increases the proportion of dissipated energy. The freeze–thaw damage variable established on the basis of the peak dissipated energy ratio can be used to characterize the strength attenuation and deformation growth processes effectively. Full article

Relatively low-cost titanium carbide (TiC) materials and metal matrix composites (MMC) are proposed for waste-to-hydrogen conversion. Two types of steels are used as bases prepared from EN 10088 flat products, namely X2CrTi12 (1.4512, AISI 409) and X5CrNi18-10 (1.4301, AISI 304). TiC is mixed with TRIBALOY^® T-800 alloy in powder form and applied via laser-directed energy deposition (DED-LB) over the substrates. For the powder mixture, Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) are performed. The raw materials are investigated for the processes that occur in them under heating. After the solidification of the molten mixture, grinding and polishing are performed to achieve a thin layer. The studies of the obtained MMC include interface zone assessment, hardness and Young’s modulus distribution, microstructural analysis, and visual defect evaluation. Advanced sensors for acoustic emission (AE) and Electrical Contact Resistance (ECR) provided characterization together with micro-scratch testing. The use of photoluminescence spectroscopy is proposed for the new composite materials. The electron transfer pathway can be studied with time-resolved spectroscopy. Renewable energy production by breaking down waste into hydrogen-rich syngas can be achieved through pyrolysis, followed by steam reforming and purification. The obtained novel materials show promising application solutions with increased durability, corrosion, and wear resistance. Full article

This study investigates the texture of table olives by integrating mechanical, acoustic, and sensory approaches, with particular emphasis on the role of acoustic emission in the perception of crunchiness, a key quality attribute influencing consumer acceptance. Three Italian cultivars (Itrana Bianca, Nocellara del Belice, and Bella di Cerignola), processed using different debittering methods, were analyzed using needle and tip compression tests combined with simultaneous sound recording, as well as Texture Profile Analysis (TPA) and Kramer shear press, alongside sensory evaluation by a trained panel. Needle compression primarily characterized peel properties, identifying Itrana Bianca as having the firmest skin, while tip and Kramer tests, reflecting both peel and pulp, indicated that Bella di Cerignola was the hardest and most consistent sample. TPA revealed that Itrana Bianca exhibited higher elasticity and cohesiveness, whereas Bella di Cerignola showed greater firmness and chewiness. Nocellara del Belice consistently displayed the softest texture. Acoustic measurements suggested that sound emission was mainly associated with peel rupture rather than pulp characteristics and showed limited correlation with sensory crunchiness. Overall, the combined mechanical–acoustic approach provides a more comprehensive evaluation of olive texture and highlights the need for refined sensory descriptors, particularly for peel-related attributes, to better interpret acoustic responses. Full article

Conventional push-out tests detect bone–implant failure only at the point of macroscopic instability, leaving earlier damage stages unresolved. Here we present a proof-of-concept for a push-out test stand combined with acoustic emission (AE) monitoring, aimed at capturing crack initiation before the macroscopic load drop. To provide a controlled failure process, samples were fabricated from SLA resin with defined breaking points, serving as mechanical surrogates rather than biological models. Four sample types with varying strut number and thickness were tested while recording AE, and post-processing was applied to remove friction and noise signals. A four-stage fracture model—initial, pre-fracture, fracture, and post-fracture—was defined, with the pre-fracture stage showing AE activity prior to any macroscopic load response. Increasing strut thickness and contact area raised maximum load resistance and AE activity, and Principal Component Analysis confirmed a progressive, intensity-driven separation of stages. The results demonstrate that AE monitoring resolves a pre-fracture regime inaccessible to conventional load measurement, establishing a methodological basis for future application to bone–implant samples. Full article

Valve leakage in marine oil and gas pipelines is a critical failure mode that threatens operational safety, ecological integrity and production economic benefits, creating an urgent demand for accurate, real-time and robust fault diagnosis systems. Acoustic Emission (AE) technology captures transient acoustic signatures generated by leakage to enable non-intrusive online monitoring, while deep learning supports intelligent analysis through automatic signal feature extraction. Nevertheless, traditional AE-based leakage diagnosis methods rely heavily on manual feature engineering and fixed signal processing rules. Existing AE-driven deep learning methods fail to simultaneously deliver high detection accuracy, low inference latency and strong noise immunity, hindering their practical deployment on offshore platforms. To address these limitations, this paper proposes a Parameter-free Star-shaped Attention Fusion Network (SAFNet) for lightweight valve leakage localization using AE signals. Centered on the Temporal Pyramid Encoder (TPE) and Progressive Lightweight Star-shaped Attention (PLSA) module, SAFNet integrates Dual Bilinear Star Mapping (DBSM), Energy-Driven Feature Refiner (EDFR) and Multi-Scale Gated Attention Fusion (MS-GAF) modules. This architecture achieves efficient multi-scale temporal feature extraction, parameter-free nonlinear enhancement, noise-resistant refined feature processing and adaptive hierarchical feature fusion. The proposed method is applicable to valve leakage diagnosis of marine oil and gas pipelines under variable pressure and complex marine noise conditions. Comprehensive experiments are conducted on a dataset constructed by combining laboratory controlled leakage signals with real marine background noise recorded from the Liwan 3-1 offshore platform. The experimental results reveal that SAFNet balances high detection accuracy, compact model size and low inference latency simultaneously. Specifically, the network maintains a stable detection accuracy above 95% under pipeline pressures ranging from 2 MPa to 5 MPa, and exhibits excellent stability under extreme heavy noise environments. Ablation experiments further validate the synergistic performance gain brought by all core modules. The presented network delivers an efficient lightweight solution for valve leakage localization under simulated marine acoustic conditions, promotes the development of intelligent monitoring technologies for marine pipeline systems, and comprehensively improves offshore operational safety and marine ecological protection capacity. Full article

The propagation behavior of hydraulic fractures in deep hard roofs is governed by the multi-factor coupling of injection rate, in situ stress, and fluid viscosity. Taking the Cuimu coal mine as the engineering background, this study systematically investigates the effects of injection rate, lateral pressure coefficient, and fluid viscosity on fracture propagation through numerical simulation. Theoretical derivations based on the KGD (Kristianovich-Geertsma-de Klerk) model are further integrated and validated by field tests. The results indicate a critical injection rate of 6 × 10⁻⁸ m³/s, above which the marginal increase in acoustic emission events declines significantly. Increasing the lateral pressure coefficient from 1.0 to 3.5 shifts the fracture pattern from relatively simple to increasingly complex and interwoven, accompanied by a logarithmic increase in fractal dimension from 1.38 to 1.80. The total acoustic emission count rises to a peak of 125,910 as viscosity increases from 0.001 Pa·s to 0.5 Pa·s, then drops to 44,061 at 1.0 Pa·s, showing a unimodal trend. Theoretical analysis shows that during the propagation stage, the fracture length follows $L\propto Q^{1/2}$, and the maximum fracture opening follows $w_{\max }\propto Q^{1/3}$. The lateral pressure coefficient controls the complexity of the fracture network through the directional distribution of stress intensity factors. Field tests at the Cuimu coal mine adopted a combination of stepwise injection rate and low-viscosity fluid, together with borehole densification and interval-skipping fracturing sequences. The effective fracturing radius reached 25~30 m, roof convergence was reduced by 31%, and the proportion of high-energy microseismic events decreased from 12% to 4%. This study establishes a complete theoretical framework from initiation theory to propagation dynamics and then to multi-crack competition, providing both a theoretical basis and engineering example for optimizing fracturing parameters in hard roofs under high stress anisotropy. Full article

This study investigates the acoustic emission (AE) characteristics associated with the shear failure mode based on the principles of active waveguide monitoring for the bedding rock slopes. Physical simulation experiments were conducted to assess the AE response during the shear-induced failure process of active waveguide structures. The findings indicate that during the initial loading phase, the scatter points of the signals are concentrated within a relatively narrow range. As the shear stress exceeds 90% of the peak stress and approaches the failure stage, there is a significant increase in the AE count and a rise in the high-frequency signals. Additionally, the distribution range of signals in the parameter correlation plot expands progressively. With increasing shear stress, the AE count, amplitude, and energy also rise gradually. And the emergence of continuous high-frequency signals is noted. During the failure stage, numerous microcracks initiate and propagate within the specimen, with signal amplitudes ranging between 40 and 90 dB. The peak frequency range of the AE signals broadens, with high-frequency components mainly concentrated between 350 and 450 kHz. Loading tests conducted at shear displacement rates of 0.25–1.5 mm/min reveal a strong correlation between the AE count and the shear displacement rate. Furthermore, prior to the shear failure of the active waveguide structures, the AE count shows a positive correlation with shear displacement. After the shear failure of the waveguide structure specimens, the AE count gradually decreases from a higher level to a lower level, demonstrating a negative correlation with shear displacement. The active waveguide structure can monitor the internal deformation conditions of the bedding rock slope so as to provide some reference for the early warning research. In addition, quantitative statistical analysis and curve fitting are conducted on the relationship between AE statistical count and shear displacement under different loading rates. The measured data show good agreement with the fitted curves, and a distinct two-stage evolutionary pattern (positive correlation before peak and negative correlation after peak) is quantitatively identified. These results further enhance the reliability of using AE parameters for quantitative evaluation of shear failure characteristics and displacement rate effects in bedding rock slopes. Full article