Search Results (872)

To elucidate the influence of the extrusion-based 3D printing of concrete on the tensile performance of polyethylene fibre-based engineered cementitious composites (PE-ECC), quantitative analyses of reinforcing filament alignment and pore morphology were carried out using backscattered electron (BSE) imaging and X-ray computed tomography (X-CT). A micromechanics analytical model based on microstructural characteristics was further employed to predict the tensile response of additively manufactured PE-ECC. Due to the extrusion process, fibres in 3D-printed PE-ECC were predominantly oriented along the printing path, resulting in a smaller average inclination angle compared with the randomly distributed fibres in cast specimens. Internal pores exhibited elongated flattened ellipsoidal shapes, with more pronounced anisotropy in axial lengths across the three principal directions. Taking the major semi-axis of the equivalent ellipsoidal voids as a representative pore parameter, the analytical model accurately reproduced the cracking strength, stress-strain evolution, and crack pattern of the printed PE-ECC. This extrusion process enhanced multiple cracking capacity and strain-hardening performance by improving fibre orientation, strengthening interfacial bonding, and altering matrix fracture toughness. The integration of micromechanical modelling with experimentally measured microstructural parameters effectively revealed the intrinsic mechanisms underlying the enhanced tensile behaviour of 3D-printed PE-ECC and provides theoretical support for the optimized design of fibre-reinforced cementitious composites in 3D printing. Full article

“Miloschite”, a chromium-containing halloysite with intense blue hues, was first discovered in 1835 in Rudnjak, Serbia. Some of the collected “miloschite” samples remained in Serbia and are kept in the University Collection of Minerals and Rocks (Faculty of Mining and Geology, University of Belgrade) and in the Natural History Museum in Belgrade. During the 19th and 20th centuries, numerous studies examined this mineral. From the original samples collected at the type locality—initially described as “miloschite” and later confirmed to be varieties of halloysite enriched in chromium—subsequent interpretations of the authors on similar material from other localities worldwide led to a misinterpretation of “miloschite” as chromium-bearing kaolinite. This reinterpretation now requires revision. This investigation was carried out on an original sample employing techniques such as powder X-ray diffraction, thermal and various spectroscopic methods, along with assessments of cation exchange capacity, specific surface area, and color determination. Analyses reveal that “miloschite” primarily consists of chromium-bearing halloysite, where chromium is evenly distributed on the microscale and fills octahedral sites within the clay lattice. This research aims to reaffirm the status of “miloschite” as a significant geoheritage material from Serbia and to preserve its nomenclatural integrity as the chromium variety of halloysite. Full article

Polymer solutions play a crucial role in the polymer flooding process by influencing the flow characteristics of formation fluids and enhancing recovery efficiency. Their properties are influenced by the transient coupling of temperature, pressure, and viscosity, yet the underlying patterns remain unclear. This study establishes a non-steady-state coupling model of polymer temperature–pressure–viscosity in wellbores, solved numerically using a staggered-grid fully implicit scheme in Matlab. At a depth of 1000 m, the polymer viscosity is measured in the field as 102.12 mPa·s, while the simulated value is 107.46 mPa·s (4.97% error), indicating good agreement with the wellbore viscosity distribution. Wellbore temperature is the dominant factor, whereas injection pressure has minor effects. Injection flow rate governs heat exchange with the formation; low flow causes larger temperature and viscosity fluctuations, while high flow leads to insufficient heat transfer. With prolonged injection, wellbore temperature approaches dynamic equilibrium, viscosity decreases, and sand-carrying capacity weakens. These findings provide theoretical guidance for optimizing polymer flooding. Full article

This study presents a numerical investigation into the structural behavior of a pile-in-pile (PIP) slip joint utilizing square hollow section (SHS) members, with a comparative assessment against conventional circular hollow sections (CHSs). A comprehensive finite element model was developed and validated against published CHS experimental results to evaluate key performance indicators, including stress distribution, buckling behavior, and load-carrying capacity under pure bending, axial compression, and diagonal lateral loads. The analysis revealed that SHS joints demonstrated distinct stress concentration patterns and higher capacity under axial compression, whereas CHS joints provided superior performance under bending due to their geometric symmetry. However, SHS corners were more vulnerable under diagonal loading, exhibiting localized buckling at relatively lower loads. These structural weaknesses can be mitigated through design improvements, such as increased wall thickness or corner strengthening. The findings highlight that while SHSs introduce certain vulnerabilities compared to CHSs, they also offer advantages in axial load resistance, supporting their potential as a viable alternative for offshore wind foundation connections. Full article

For polar ships, navigation in ice-covered regions can lead to high risk to structural safety. To study the structural risk induced by ice loads, a risk assessment framework is proposed based on a probabilistic analysis. The fatigue failure probability is derived with the first-order second-moment (FOSM) method. Typical ice load cases are extracted as a joint probability distribution of ice thickness and ship speed, based on shipboard measurements. Equivalent fatigue stresses for each case are calculated using a coupled discrete element method (DEM) and finite element method (FEM), and fatigue failure probabilities are obtained via linear cumulative damage theory. The ultimate strength failure probability is derived from the reliability theory. The probabilistic distribution of load-carrying capacity for the bow structure, determined by the moment estimation method, is used as the structural resistance, while the ice load distribution identified from shipboard monitoring is treated as the external load. Considering both the likelihood and consequence of failure, a risk matrix is constructed to assess structural failure risk. Inspection and maintenance intervals are then proposed according to the assessed risk levels. This approach offers a quantitative basis for structural risk management, supporting safe navigation and efficient maintenance planning for polar ships. Full article

Coastal water quality is crucial for ecosystem services, supporting biodiversity and tourism. However, high tourist influxes often overwhelm wastewater treatment plant (WWTP) capacities, leading to untreated discharge and eutrophication, which severely impacts bathing water. Water quality monitoring is currently limited to selected points at the beach and oceanographic sampling, which requires depths >20 m offshore, leaving a gap of measurements between 1 and 50 m from the beach. To resolve this gap, our study proposes a low cost-effective sampling and monitoring method by using a kayak with a submersible fluorometer FlowCAM, as well as fecal bacteria detection and quantification. The kayak sampling was carried out during high- and low-tourism seasons in coastal bathing waters surrounded by Marine Protected Areas. The results show a patchy phytoplankton distribution, with chlorophyll a concentration up to 5.5 μg/L, indicating local fertilization. The observed floating organic matter patches were fecal bacteria free, while effluents of the WWTP to the Jate river and shore exceeded the legal limits for bathing water. These results suggest that wastewater treatment was overwhelmed during the high-tourism season, likely discharging wastewater into the river that flows into the shore. These findings are discussed in a sustainable development and socioeconomical context. Full article

Water resources are fundamental to human survival, as well as critical to the sustainable progress of the economy and society. This study selects representative indicators and employs the TOPSIS model to evaluate the water resources carrying capacity (WRCC) in the Chang–Zhu–Tan region (2006–2022). Based on this, kernel density estimation and Moran’s I are applied to analyze the spatiotemporal distribution and evolution trends of WRCC. Additionally, the Lorenz curve, Gini coefficient, and imbalance index are utilized to examine the alignment between WRCC and socio-economic growth. Finally, a system dynamics model is used to simulate WRCC and matching dynamics under different scenarios. The findings reveal the following: (1) The overall WRCC is favorable but exhibits a declining temporal trend, with widening inter-district disparities and strong spatial agglomeration. (2) The match between WRCC and economic development is unbalanced, though alignment has gradually improved over time. (3) The WRCC varies across different scenarios. In current development scenario, WRCC declines significantly. In economic priority development and industrial restructuring scenarios, this reduction is slowed. Specifically, in water resource policy control scenario, WRCC can be enhanced. Aside from the industrial restructuring scenario, all other scenarios contribute to improving the coordination between WRCC and economic development. Full article

This study investigates hydrogen storage enhancement through adsorption in porous materials by coupling the Dubinin–Astakhov (D-A) adsorption model with H₂ conservation equations (mass, momentum, and energy). The resulting system of partial differential equations (PDEs) was solved numerically using the finite element method (FEM). Experimental work using activated carbon as an adsorbent was carried out to validate the model. The comparison showed good agreement in terms of temperature distribution, average pressure of the system, and the amount of adsorbed hydrogen (H₂). Further simulations with different adsorbents indicated that compact metal–organic framework 5 (MOF-5) is the most effective material in terms of H₂ adsorption. Additionally, the pair (273 K, 800 s) remains the optimal combination of injection temperature and time. The findings underscore the prospective advantages of optimized MOF-5-based systems for enhanced hydrogen storage. These systems offer increased capacity and safety compared to traditional adsorbents. Subsequent research should investigate multi-objective optimization of material properties and system geometry, along with evaluating dynamic cycling performance in practical operating conditions. Additionally, experimental validation on MOF-5-based storage prototypes would further reinforce the model’s predictive capabilities for industrial applications. Full article

Water conservation, as a critical ecosystem service, plays a vital role in maintaining regional water resources balance. Against the backdrop of rapid urbanization, the expansion of construction land has intensified the encroachment on ecological spaces, posing significant challenges to water resource carrying capacity. From a supply–demand perspective, this study employs the InVEST model and integrates multi-source data including meteorological and socio-economic datasets to construct models of water conservation supply and demand. Furthermore, spatial analysis methods are applied to examine the evolution of water resource carrying capacity in Gansu Province—a key region within the Yellow River Basin—from 2000 to 2020. The results indicate the following: (1) through desertification control, unused land has been progressively restored to grassland, yet continuous urban expansion has substantially encroached upon surrounding plowland and grassland; (2) the spatial pattern of water conservation supply exhibits a “high in the south and west, low in the north and east” distribution, with the maximum value per pixel increasing from 7.89 × 10⁵ m³ to 8.15 × 10⁵ m³. Overall, water resource carrying capacity has generally declined, with intensified pressure in central cities such as Lanzhou, while some improvement is observed in forested areas of the south; and (3) cold spots in the western Qilian Mountains have expanded toward the Hexi Corridor, reflecting significant spatial changes and indicating ecological degradation. Urbanization has markedly exacerbated regional imbalances in water resource carrying capacity, providing a scientific basis for water–ecological risk management in arid regions. Full article

With the increasing demand for lightweight, high-strength, and ductile structural systems in modern infrastructure, the hybrid composite column has emerged as a promising solution to overcome the limitations of single-material members. This paper proposes an innovative variant of double-skin tubular columns (DSTCs), termed as square double-skin hybrid concrete bar columns (SDHCBCs), composed of one square-shaped outer steel tube, small-diameter concrete-infilled glass FRP tubes (SDCFs), interstitial mortar, and an inner circular steel tube. A series of axial compression tests were conducted on eight SDHCBCs and one reference DSTC to investigate the effects of key parameters, including the thicknesses of the outer steel tube and GFRP tube, the substitution ratio of SDCFs, and their distribution patterns. As a result, significantly enhanced performance is observed in the proposed SDHCBCs, including the following: ultimate axial bearing capacity improved by 79.6%, while the ductility is increased by 328.3%, respectively, compared to the conventional DSTC. A validated finite element model was established to simulate the mechanical behavior of SDHCBCs under axial compression. The model accurately captured the stress distribution and progressive failure modes of each component, offering insights into the complex interaction mechanisms within the hybrid columns. The findings suggest that incorporating SDCFs into hybrid columns is a promising strategy to achieve superior load-carrying performance, with strong potential for application in high-rise and infrastructure engineering. Full article

Inter-turn short-circuit faults in power transformers generate enormous short-circuit currents within the affected turns, making full-scale experimental investigations impractical. To address this issue, this study proposes an experimental method utilizing a third external short-circuit winding to simulate inter-turn faults through structural improvements in winding configuration and conductor current-carrying capacity. A simulation calculation model for transformer inter-turn short circuits was first established to investigate the equivalence between the proposed equivalent fault model and actual fault conditions under varying short-circuit positions and proportions. Simulation results demonstrate that both models exhibit consistent primary/secondary winding currents, short-circuit turn currents, and spatial radial leakage magnetic field distributions post-fault, with average errors less than 5%. Subsequently, an experimental platform for inter-turn short-circuit fault simulation was constructed. Current and leakage magnetic field measurements under different fault positions and proportions were validated against simulation data, confirming the proposed method’s equivalence. This approach provides an effective pathway for investigating fault characteristics and monitoring methodologies of transformer inter-turn short circuits. Full article

In traditional scheduling operations, dispatchers mainly rely on SCADA/EMS systems or personal experience. However, with access to a large number of new energy sources, the scale of the distribution network continues to expand, and its topology becomes increasingly complex, leading to potential security risks in scheduling operations. Therefore, it is very important to carry out risk assessments before scheduling operations. In this paper, risk theory is introduced into the field of distribution network scheduling operations, and a new risk assessment method is proposed considering various uncertain factors in the distribution network. In order to comprehensively analyze the influence of uncertainty factors in the operational process of a new distribution network, the output probability models of wind power, photovoltaic power, and load are first constructed in this study. Then, the improved Latin hypercube sampling method is used to extract the operating state of the distribution network system from the probability model, and the node voltage over-limit and line power flow overload are used as indicators to measure the severity of the consequences so as to establish a quantitative scheduling operation risk assessment system and analyze its framework in detail. Finally, simulation analysis is carried out in the improved IEEE-RTS79 test system: taking 15–25 lines from the operation state to the maintenance state as an example, this paper analyzes the influence of different locations and capacities of wind and solar access on the scheduling operation risk of distribution networks. The results can provide a reference for dispatchers to prevent risks before operation. Full article

Traditional single-layer water-lubricated rubber or plastic bearings suffer from water film rupture, excessive frictional losses, and insufficient load-carrying capacity, which limit performance and service life in marine propulsion and ocean engineering. To address these issues, this study introduces an innovative laminated bearing consisting of a rubber composite layer and an ultra-high-molecular-weight polyethylene (UHMWPE) layer. A three-dimensional dynamic model based on fluid–structure interaction theory is developed to evaluate the effects of eccentricity, rotational speed, and liner thickness on lubrication pressure, load capacity, deformation, stress–strain behavior, and frictional power consumption. The model also reveals how thickness matching governs load transfer and energy dissipation. Results indicate that eccentricity, speed, and thickness are key determinants of lubrication and structural response. Hydrodynamic pressure and load capacity rise with eccentricity above 0.8 or higher speeds, but frictional losses also intensify. The rubber layer performs optimally at a thickness of 5 mm, while excessive or insufficient thickness leads to stress concentration or reduced buffering. The UHMWPE layer exhibits optimal performance at 5–7 mm, with greater deviations resulting in increased stress and deformation. Proper thickness matching improves pressure distribution, reduces local stresses, and enhances energy dissipation, thereby strengthening bearing stability and durability. Full article

Travel safety and comfort depend on the design and maintenance of road and stormwater drainage systems. In low-lying areas, poor drainage systems can—especially near underpasses—lead to flooding and serious risks, such as reduced load-bearing capacity hydroplaning, where tires lose grip. This study focuses on the effect of granular material deposits on the surface roughness of roadside gutters, as expressed through the Gauckler–Strickler coefficient. The literature equations have pointed out that this coefficient is largely affected by the grain size distribution of granular material. To this end, a field study was carried out in six urban roads in San Nicola la Strada, Italy, with the objectives of the following: (1) identifying the grain size distribution of the material deposited in roadside gutters; (2) estimating how such material decreased in the cross-sectional area of the gutters, as well as increasing their flow resistance, ultimately resulting in decreased water conveyance. Considering gutters with deposited material rather than clean ones results in the failure of three out of six gutters to effectively drain stormwater. Full article

Reinforced composite prestressed concrete hollow square (RCPHS) piles, installed through pre-drilling, grouting, and static jacking, integrate the large lateral contact area of cement–soil casings with the high strength and stiffness of prestressed concrete cores. This study combines full-scale vertical static load tests and finite-element (FE) simulations to explore the interaction among the core pile, plain-concrete casing, and surrounding soil. Results show that, at 3600 kN, RCPHS piles exhibit 76% less pile-head settlement compared to PHS piles, and a 36.5% reduction in pile-material expenditure is achieved using the RCPHS scheme. At the same settlement of 23 mm, RCPHS piles carry 87% more load than PHS piles. A 3D FE model developed in ABAQUS reveals that the core pile carries approximately 94% of the applied load. When the load exceeds 4180 kN, the axial force in the casing sharply increases at depths of 7–10 m. The simulated P–s curves align well with field measurements, confirming model accuracy. The superior performance of RCPHS piles is attributed to the graded elastic modulus and coordinated stress distribution of the core–casing–soil system, which enhances interface friction and overall load capacity. These findings provide a foundation for the design optimization of RCPHS piles in dense sandy foundations. Full article