Search Results (20,558)

The widely applied empirical Darcy’s law in geotechnical engineering faces significant challenges in describing low-velocity flow processes in low-permeability porous media such as tight sandstones containing irreducible water. A deep understanding of low-velocity non-Darcy two-phase flow behavior in low-permeability porous media is essential for evaluating the development of ultra-low-permeability reservoirs. In this study, seven low-permeability three-dimensional digital cores with distinct pore structures were constructed based on realistic ultra-low-permeability sandstones. Using the lattice Boltzmann method, pore-scale investigations of water displacing oil were conducted. Low-velocity two-phase flow behavior under varying wettability conditions, pore structures, and fluid viscosities was simulated. The underlying mechanisms of low-velocity non-Darcy flow in ultra-low-permeability sandstones were examined, leading to a modified low-velocity non-Darcy flow equation. This improved model was subsequently applied to numerical simulations of ultra-low-permeability reservoirs. The results demonstrate that non-Darcy effects manifest primarily as nonlinearities in seepage curves, representing a marked departure from conventional Darcy’s law. Low-velocity non-Darcy (LVND) flow is predominantly constrained by the influence of complex pore-throat structures and capillary forces on fluid distribution. The dynamic equilibrium among capillary forces arising from residual water saturation, viscous forces, and pressure gradients constitutes the fundamental mechanism governing the onset of LVND flow. Enhanced nonlinear behavior is observed with increasing viscosity of the invading phase and elevated capillary forces. Substantial discrepancies in reservoir production dynamics are identified between LVND and classical Darcian regimes. Through pore-scale numerical simulations, this study systematically elucidates LVND behavior during bi-phasic flow in low-permeability porous media, while identifying critical controlling factors. These findings provide scientific rationale and technical support for addressing geological engineering challenges in tight sandstone formations. Full article

Hydraulic rock drill exhibits outstanding attributes of high power and high frequency, but there are some issues including unclear mechanisms governing impact dynamic behaviors and inaccurate evaluation of impact performance. In this study, a dynamic test platform for the hydraulic rock drill was established by employing the terminal velocity method, utilizing a high-frequency non-contact laser displacement sensor to precisely capture the transient kinematics of the impact piston. The quantitative results indicate that as the input pressure rises from 10 MPa to 23 MPa, the impact frequency increases from 50 Hz to 76.9 Hz, and the impact energy increases from 89.9 J to 275 J. A hydraulic rock drill AMESim simulation model incorporating the impact system, collision medium and buffer system was developed and validated. This reveals the operating mechanism of impact piston driven by the equivalent pressure difference between the front and rear chambers. And the stroke reversal interval governs the duration between the deceleration onset and collision of the impact piston. As a result, both excessively large and small stroke reversal intervals will lower the impact power. The 12 mm stroke reversal interval has been identified as the optimal setting for maximizing impact power, at which the impact power reaches 17,561.3 W, which presents an increase of 4.70% and 3.12% compared to the intervals of 7 mm and 17 mm, respectively. This study contributes a reliable theoretical basis and direct data support to the performance evaluation and optimized design of hydraulic shock systems. Full article

Background: Tile C1.2 pelvic ring injuries are characterized by combined rotational and vertical instability and require reliable posterior stabilization. The aim of this exploratory biomechanical study was to compare the construct-level mechanical behavior of three posterior pelvic ring fixation strategies in a standardized Tile C1.2 injury model while maintaining identical anterior symphyseal fixation in all specimens. Methods: Nine fourth-generation composite pelvic specimens with a simulated Tile C1.2 injury pattern were allocated to three groups (n = 3 per group) according to posterior fixation method: anterior sacroiliac plating, sacroiliac screw fixation, and ilioiliac plate fixation. All specimens received the same anterior symphyseal plate. Mechanical testing was performed under monotonic axial compression using a universal testing machine and a custom acetabular support designed to ensure reproducible load transmission. A preload of 50 N was applied before data acquisition, after which displacement was zeroed. Loading was then continued up to a predefined maximum load of 1.9 kN. Axial displacement was obtained from actuator travel, and apparent axial secant stiffness was evaluated at predefined load levels. Results: Across the tested loading range, sacroiliac screw fixation demonstrated the lowest axial displacement and the highest apparent axial secant stiffness, whereas ilioiliac plate fixation showed the greatest displacement and the lowest stiffness values. Anterior sacroiliac plate fixation showed intermediate mechanical behavior. No structural failure occurred within the tested load range. Conclusions: Within the limits of this small synthetic biomechanical study, the investigated posterior fixation strategies showed different construct-level displacement and stiffness profiles under monotonic axial compression when anterior fixation was kept constant. Among the tested posterior constructs, sacroiliac screw fixation was associated with lower displacement and higher apparent stiffness within this experimental model. Full article

Building upon our previous research in which we derived two formulations of the governing equations expressed in terms of $\left(\rho ,\mathit{B},\mathit{v}\right)$ and the perturbation displacement $\mathit{\xi }$, we extend our analysis to investigate the dispersion relation of linear magnetohydrodynamic (MHD) waves in a one-dimensional flux-sheet magneto-lattice. The convergence of the dispersion relations is examined by increasing the truncation order of the reciprocal lattice vectors from 3 to 10, for the central equations expressed in terms of $\left(\rho ,\mathit{B},\mathit{v}\right)$, and for modulation amplitudes of $B_m=0.01$, $0.02$, $0.1$, $0.2$, $0.3$ and $0.4$. The dispersion relations obtained at different truncation orders exhibit rapid convergence for small modulation amplitudes $B_m$, with only minor discrepancies emerging as $B_m$ increases, indicating overall satisfactory convergence of the plane wave expansion (PWE) method within the investigated parameter range. A comparative analysis with the previously studied sinusoidal magneto-lattice reveals that, while the overall dispersion structure remains qualitatively similar, the flux-sheet magneto-lattice yields wider bandgaps at equivalent modulation amplitudes. This is shown to result from the distinct Fourier spectra of the two periodic structures, which differ in both the magnitude and the harmonic content of their reciprocal lattice components. Full article

A large number of low-resistivity and low-permeability reservoirs have been discovered in the deep Paleogene strata of the Wenchang Sag. These reservoirs are characterized by complex porosity–permeability relationships and difficulties in fluid property identification, which restrict the progress of exploration and development operations. However, existing reservoir studies mostly focus on either low-permeability or low-resistivity reservoirs, with relatively few investigations targeting this specific type. Using petrological analysis and physical property testing as the main methods, combined with sedimentary and diagenetic studies, this paper examines the characteristics and genesis of low-resistivity and low-permeability reservoirs in the Paleogene of the Wenchang Sag. The results show that the Paleogene reservoirs are dominated by lithic quartz sandstones, with secondary pores as the main reservoir space, consisting of medium–small pores and fine throats. Samples of the same grain size exhibit a favorable porosity–permeability correlation. Based on capillary pressure curve morphology, the reservoirs can be classified into three types: high mercury intrusion saturation with low displacement pressure, medium mercury intrusion saturation with medium displacement pressure, and medium mercury intrusion saturation with medium–high displacement pressure. The low porosity and permeability are mainly attributed to the fact that the reservoir rocks are primarily deposited in near-source braided fluvial delta underwater distributary channels, resulting in low compositional and textural maturity of sandstones. Strong compaction resistance leads to a significant reduction in primary pores during burial, and intergranular cement filling further deteriorates physical properties. On the other hand, rapid lithological changes and complex pore structures give rise to abundant isolated pores and poor connectivity, leading to high irreducible water saturation. Coupled with high formation water salinity, these factors collectively give rise to low-resistivity reservoirs in the study area. This study clarifies the formation mechanism of low-permeability and low-resistivity reservoirs in the Paleogene of the Wenchang Sag, providing guidance for reservoir evaluation in subsequent oil and gas exploration and serving as a reference for analogous areas. Full article

As mining operations progressively advance to greater depths to meet increasing mineral demand, there is a growing need to develop new or improved rockbolts capable of effectively dissipating energy under dynamic loading conditions. Impact laboratory tests provide valuable insights into the dynamic performance of rockbolts; however, such tests require considerable time and cost associated with specimen preparation and experimental validation. Numerical modeling represents a robust alternative which, when properly calibrated with laboratory results, can accurately simulate the deformation process and energy dissipation mechanisms of support elements. This paper presents the implementation and results of a numerical model developed to simulate the dynamic behavior of a threadbar subjected to impact loading. The model explicitly represents all components of a full-scale impact test configuration, including the impact mass, reaction frame, threadbar geometry, grout, and steel tube. The numerical model enables real-time analysis of the dynamic response and interaction among the test components (steel tube, grout, and bolt). The implemented numerical codes were calibrated and validated against published laboratory results of threadbar dynamic behavior. Subsequently, a comprehensive parametric analysis was conducted to evaluate the response of each component in terms of load, displacement, and dissipated energy. The results allowed identification of the primary factors governing the dynamic response of the rockbolt system. The proposed methodology can be extended to other reinforcement systems and provides relevant insights into the design of bolts under dynamic loading conditions. Full article

The dynamic performance of medium- and low-speed maglev vehicle–track coupling systems, as well as the dynamic response of the vehicle body and suspension frame under suspension electromagnet failure, is of great significance for the safe operation of maglev tracks. Based on vehicle–track coupling dynamics theory, and considering the spatial dynamic magnetic rail relationship in combination with the suspension control system, a dynamic vehicle–track model incorporating suspension electromagnet failure is established. The effect of such failures on electromagnet suspension force and overall vehicle performance are analyzed. The results indicate that the theoretically calculated electromagnetic force differs significantly from the actual force. Under four electromagnet operating conditions, lateral displacement has the greatest influence on suspension force. By considering the magnetic saturation of ferromagnetic materials and the leakage effect of suspension gaps, a spatial dynamic magnetic orbit relationship is established. A single-pole suspension electromagnet fault has little effect on overall vehicle performance. When the suspension electromagnet on one side fails, the suspension frame tilts toward that side and is supported and operated by a sled. When three suspension points fail, the entire suspension frame loses its suspension state and operates fully under sled support. When a suspension frame electromagnet becomes stuck, severe fluctuations in suspension force and vehicle vibration acceleration occur. These fluctuations increase with vehicle operating speed, seriously endangering operational performance. The findings provide a fundamental theoretical basis for the safe operation and maintenance of medium- and low-speed maglev vehicles under fault conditions. Full article

Background: Ultrasonography (US) has emerged as a non-invasive method for anatomical and functional evaluation of upper airway structures in adult obstructive sleep apnea (OSA). However, its role in severity stratification, dynamic assessment, elastographic characterization, and therapeutic monitoring remain to be investigated. Background/Objectives: The goal herein is thus to systematically review and synthesize available evidence on US assessment in adults with OSA, including structural parameters, dynamic measurements, correlation with the apnea–hypopnea index (AHI), integration with artificial intelligence, and evaluation of myofunctional therapy outcomes. Methods: A PRISMA-compliant systematic review of 19 studies (2007–2025) was conducted, evaluating US in adult patients with polysomnography-diagnosed OSA. Observational, pilot, case–control, and exploratory studies were included. Risk of bias was assessed using the National Institutes of Health Quality Assessment Tool for observational studies. Due to methodological heterogeneity, a structured qualitative meta-analytic synthesis was performed. Results: The tongue base was the most frequently studied structure. Increased tongue thickness, area, and stiffness were consistently associated with higher AHI. Elastography revealed increased intrinsic rigidity in patients with OSA. Dynamic US correlated with drug-induced sleep endoscopy findings and hyoid displacement. Machine learning integration improved severity prediction. A single study evaluated anatomical changes following myofunctional therapy, representing a nascent research area. US may become a complementary, non-invasive tool for anatomical and functional assessment of upper airway structures in adult OSA. Conclusions: Further standardization of acquisition protocols and well-designed longitudinal studies are needed to clarify the clinical role of US in phenotyping and therapeutic monitoring. Full article

On 6 February 2023, Türkiye was struck by two devastating earthquakes with moment magnitudes of 7.8 and 7.6, causing severe damage to numerous tall reinforced concrete buildings and emphasizing the need for improved seismic design strategies. This study investigates the seismic response of a representative high-rise reinforced concrete building by systematically varying the shear wall area-to-floor area ratio, a key parameter directly influencing lateral stiffness and overall stability. Utilizing a solid modeling approach and incorporating three-directional seismic records, this research provides detailed insights into displacement behavior beyond conventional frame-based analyses. Focusing on Adana, a major urban center with a significant concentration of tall buildings and notable seismic risk, three design scenarios with shear wall ratios of 1.14%, 1.54%, and 2.1% were examined. The results demonstrate that increasing the shear wall cross-sectional area compared to the building plan area significantly reduces lateral and vertical displacements, with the most pronounced improvement observed when moving from 1.14% to 1.54%. Further increase to 2.1% provides additional enhancement in seismic performance. This study suggests that adopting a minimum shear wall area-to-floor area ratio of at least 2% along each principal direction (resulting in a total combined ratio of approximately 4% for the building) can substantially improve seismic resilience and mitigate collapse risk in tall structures. Importantly, the shear wall ratios were considered separately for each principal direction, with the total combined ratio doubling, highlighting the need for balanced wall distribution in both directions. Full article

As power-electronic-interfaced renewable generation displaces synchronous machines, modern power systems face coupled day-ahead challenges: net-load variability demands peak shaving, while declining inertia necessitates explicit frequency-regulation scheduling. In sequential security-constrained unit commitment (SCUC) and Security-Constrained Economic Dispatch (SCED), the reserve procured in SCUC may lose deliverability after redispatch because the same storage bandwidth is reassigned to energy service. This paper proposes a two-stage day-ahead framework that addresses both challenges for low-inertia systems with high inverter-based resource (IBR) penetration. Stage I embeds Rate-of-Change of Frequency (RoCoF), frequency nadir, and quasi-steady-state (QSS) constraints in SCUC, with a piecewise-linear outer approximation for the non-convex nadir limit. Stage II strictly inherits the SCUC commitment and reserve reservation, and it applies bandwidth deduction to prevent peak-shaving redispatch from consuming committed frequency reserve. A technology-aware partition further assigns fast-response Lithium Iron Phosphate (LFP) batteries to sub-second frequency support and long-duration Vanadium Redox Flow Batteries (VRFBs) to energy shifting. Evaluated under the adopted reduced-order frequency-response framework and disturbance representation, tests on a modified IEEE 39-bus system under an extreme-wind scenario demonstrate that explicit frequency constraints eliminate all post-contingency violations, the inheritance mechanism closes a 23.85 MW reserve gap after redispatch, and heterogeneous storage partitioning preserves essentially the same disturbance sensitivity while increasing the peak-shaving ratio to 45.85%, lowering the day-ahead cost to CNY $10.483\times {10}^6$ and reducing the average system price to 209.33 CNY/MWh. Full article

Engineered wood products manufactured with the durability and density of a Pinus radiata D. Don species usually do not achieve the mechanical properties of a structural material for construction; hence, the reinforcement of this kind of product is recommended, but the use of commonly used hazardous adhesives is a problem. Therefore, the primary objective of this research was to investigate the enhancement of various properties of glulam beams made from radiata pine through the application of a high-performance reinforcing composite, based on carbon fiber, polyvinyl alcohol, and other nanomaterials, at a laboratory scale. For this purpose, thermal and mechanical tests were performed in different composite formulations to choose the best ones and to manufacture the glulam beams, in which bending properties were measured. Based on the results, the samples reinforced with graphene stood out, and the samples mixed with epoxy resin presented statistically the same values of flexural stiffness and strength as the control samples elaborated with commercial wood adhesives. It is also important to highlight the performance of the samples M7 (PVA (7.5%) + NL (0.01%) + GP (0.01%) + NSiO₂ (0.01%)) and M8 (PVA (7.5%) + NL (0.01%) + GP (0.01%) + NTiO₂ (0.01%)), which are not mixed with epoxy resin and showed statistically the same flexural performance as epoxy resin, in terms of maximum load and displacement. As a conclusion, it could be said that this new high-performance composite could be a comparable alternative to hazardous commercial adhesives, by obtaining lower values, but close to those of the control sample, which are the most used when reinforcing wood products with engineering fibers. Full article

Bees are essential pollinators for agricultural systems, making accurate, automated monitoring of their behavior critical for assessing colony health and ecosystem stability. Recent advances in computer vision and artificial intelligence have enabled large-scale bee traffic monitoring at hive entrances; however, most existing event classification methods focus exclusively on simple entrance and exit events. This simplification overlooks compound movements—such as U-turns and guarding behaviors—that represent a substantial portion of bee activity and can lead to inaccurate trajectory reconstruction and misleading behavioral interpretations. In this work, we systematically analyze existing event classification strategies used in automatic bee traffic monitoring, evaluating their performance on both simple and compound movements. We then propose extended classification methods that explicitly model compound events by incorporating bidirectional movement patterns derived from positional and angular cues. Using a manually annotated dataset of computer-vision-based hive entrance recordings, we compare threshold-based, displacement-based, and angle-based approaches under simple and mixed-event conditions. Our results demonstrate that compound events account for over one-third of all detected movements and that classification methods explicitly designed to handle bidirectional behavior substantially outperform traditional approaches in both accuracy and robustness. In particular, threshold-based bidirectional classification achieves near-perfect performance when full trajectories are available, while displacement-based methods provide a reliable alternative under partial observations. These findings highlight the importance of modeling compound behaviors in automated bee monitoring systems and contribute to more accurate flight reconstruction, behavioral analysis, and AI-driven decision support for precision agriculture and pollinator management. Full article

To address the technical challenges of difficult deduction, limited field measurement, and ambiguous instability determination of roof separation critical values in mining roadways within the weakly cemented coal-bearing strata of Xinjiang, this paper proposes a discrete element method that integrates the fracture of anchor bolt and anchor cable support materials with the damage degree of the surrounding rock. Taking a specific mine in the Hosh Tolgay coalfield as the research object, a systematic study was conducted. The research process was as follows. (1) Model parameter calibration was performed. Intact rock parameters were obtained through laboratory basic mechanical tests, and rock mass parameters were corrected based on reduction empirical formulas and the Hoek–Brown criterion. Numerical model verification showed that the errors between the simulated and theoretical values of the elastic modulus, compressive strength, and tensile strength of the rock mass were all less than 10%, indicating that the corrected parameters are reasonable. (2) The critical damage values of the rock mass considering a non-constant confining pressure environment were proposed. Through triaxial compression simulations, the differential evolution patterns of rapid damage increase in sandy mudstone under low confining pressure and stable damage accumulation in coal were revealed, thereby clarifying the damage thresholds for rock mass instability under different confining pressures. (3) A large-scale model was established to analyze the evolution laws of the fracture field, support field, and displacement field of the roadway surrounding rock. A comprehensive determination method for the instability of the roof anchored bearing structure was proposed. By comparing the damage thresholds of the scaled rock mass and the roadway surrounding rock and analyzing the fracture conditions of the roadway support system, a dual-criterion consisting of surrounding rock damage and support material fracture was constructed. Based on this criterion theory, the critical values for deep and shallow separation were obtained. The research results indicate that the evolution patterns of damage in coal and sandy mudstone differ with confining pressure. The sandy mudstone layers in the shallow part of the roof are more sensitive to mining-induced unloading disturbances. Consequently, the surrounding rock damage and support fracture of the mine roof exhibit distinct distribution characteristics: the dominant failure of the roadway is shear failure, with wide-range coalescence of shallow fractures and gradual development of deep fractures, alongside the concentrated failure of shallow anchor bolts and partial failure of deep anchor cables. Based on the instability state of the roof monitoring zones, the critical value for shallow separation was determined to be 90.7 mm, and the critical value for deep separation was 129.03 mm. These results are very close to the field measured values, verifying the engineering applicability of the method. This paper reveals the damage characteristics of the rock mass and surrounding rock in weakly cemented strata, as well as the mechanism of roof separation initiation and evolution. The proposed method for determining critical values provides a scientific and feasible practical reference for the support optimization and monitoring and early warning of roadway roofs in weakly cemented strata, possessing significant engineering value for ensuring safe and efficient mine production. Full article

Flapping-wing drones (FWDs), owing to their compact size and operation in cluttered and unsteady airflow environments, encounter significant aerodynamic and stability challenges. Studies of avian flight reveal that falcons and other raptors actively deflect their covert feathers to mitigate gusts and maintain stable flight. Drawing inspiration from this mechanism, this study presents a peregrine falcon-inspired Active Flow Control Unit (AFCU) integrated with a Deep Deterministic Policy Gradient (DDPG)-based deep reinforcement learning (DRL) controller for real-time disturbance attenuation. The AFCU employs mechanical covert feathers (MCFs) that actuate to dissipate gust loads during high wind conditions. A reduced-order bond graph model that encapsulates the nonlinear interaction between the primary wing and the feather-based active flow control surfaces is created which is used as a dynamic training environment for the DDPG agent. Utilizing closed-loop interactions, the successfully obtained learned policy produces optimal actuator forces to reduce feather-displacement error and aerodynamic load variations. The designed controller stabilizes the internally unstable open-loop AFCU, attaining near-zero steady-state error and settling times under 1.6 s for gust magnitudes ranging from 12.5 to 20 m/s. Simulations further illustrate a reduction of up to 50% in gust-induced loads compared to traditional approaches. This integration of bio-inspired design with learning-based active flow control offers a viable avenue for the development of highly adaptive and gust-resilient flapping-wing aerial systems. Full article

The mixing process is a critical factor influencing the performance of concrete. As an effective method for enhancing mixing, vibratory stirring relies on the propagation characteristics of mechanical vibration within the concrete matrix. To investigate the propagation behavior of mechanical vibration in fresh steel fiber-reinforced concrete, a custom-developed mechanical vibration source and testing system was established. The results show that the vibration intensity attenuates to 50% at a distance of 5 cm from the source, to approximately 10% at 10 cm, and to less than 3% at 20 cm. A lower water-to-binder ratio facilitates the transmission of the vibration wave, while the presence of fibers and 0–5 mm coarse aggregates hinders vibration propagation. Based on these findings, an input–output energy conservation equation was developed to describe the transmission behavior of vibration energy. The numerical results were compared with experimentally measured vibration power and particle velocity displacement integrals, validating the effectiveness of the proposed energy conservation equation. Full article