Search Results (4,780)

This study numerically investigates the hydrothermal behaviour of a Jeffrey nanofluid with relevance to maritime thermal systems. The coupled nonlinear governing equations for momentum, heat, and mass transport are solved using a shooting technique that accounts for magnetohydrodynamic effects, Darcy porous-media resistance, viscous dissipation, and spatially varying internal heat generation. Variable thermophysical properties, including temperature-dependent viscosity and density, are also considered. The results reveal that porous resistance, fluid elasticity, and thermophysical variations significantly influence velocity, temperature, and concentration fields. The combined effects of porous drag and variable properties markedly alter the characteristics of heat and mass transfer. These findings provide insights into thermal and mass-transport performance, including skin friction, heat transfer, and concentration distributions, which are critical metrics for porous heat exchangers and nanofluid-based maritime coatings. Here, maritime relevance is represented via a generalised porous nanofluid model rather than a specific material. Among the key findings, increasing the slip velocity factor can reduce the surface skin-friction coefficient by approximately 48.7%, while the heat-transfer rate increases by nearly 27.1%, accompanied by a decrease of about 18.9% in the Sherwood number. Conversely, raising the density factor enhances the skin friction coefficient by roughly 103.8% and also augments the heat and mass transfer rates by about 61.3% and 106.1%, respectively. Likewise, at zero relaxation–retardation ratio, the flow reduces to the Newtonian case. Increasing this factor reduces the local Nusselt number by about 1.45%, indicating a slight weakening of heat transfer due to elastic effects. Furthermore, the reliability of the current numerical framework is established through a dual-validation approach, including an analytical assessment of limiting cases and a rigorous comparison with established data from the literature. Full article

The primary objective of this research was to systematically investigate how bond–slip behavior affects the flexural behavior of alkali-activated slag concrete (AASC) beams reinforced with steel fibers. To this end, a finite element model incorporating the steel–concrete interface bond–slip effect was formulated in Abaqus using a separated modeling approach, grounded in a thorough analysis of established bond–slip constitutive models. Numerical simulations were conducted on both reinforcing bar pull-out specimens and beam members to examine the bond–slip interaction between steel reinforcement and steel fiber-reinforced alkali-activated slag concrete (SFR-AASC), as well as its influence on the flexural behavior of the beams. The results indicate that the bond–slip interaction at the steel–concrete interface can be effectively captured using nonlinear spring elements. The proposed modeling approach is simple to implement and demonstrates stable numerical convergence. For the pull-out specimens, the numerically obtained stress contours along the loading direction, together with the corresponding load–displacement curves, show good agreement with experimental observations. Further comparisons between numerical predictions and experimental results for beam specimens reveal that the prediction errors of the fully bonded model range from 0.2% to 9.7%, whereas those of the model accounting for bond–slip effects are reduced to 0.1–4.7%. The bond–slip model provides more accurate predictions of cracking load, ultimate load, and overall load–displacement behavior, thereby verifying the validity and accuracy of the developed finite element modeling strategy. Full article

This work analyzes the non-Newtonian electromagnetohydrodynamic (EMHD) flow in an irregular circular porous microchannel while incorporating the consequences of surface charge-dependent slip boundary conditions. The Jeffrey fluid is employed to examine the non-Newtonian behavior, such as elasticity. The boundary walls of the channel are considered in the form of periodic sinusoidal wave function. The mathematical formulation is developed using the momentum equation, modified Darcy’s law, the continuity equation, and Ohm’s law. The perturbation method is used to derive the solutions up to second-order approximation. The analytical expression for the velocity field and volumetric flow rate are explicitly presented. At the zeroth-order, a nonhomogeneous partial differential equation is solved, and the solutions are presented in terms of Bessel functions. The first-order problem defined by a homogeneous partial differential equation is solved using the method of separation of variables. At the second-order, a homogeneous partial differential equation is obtained, and the solution form is prescribed by the boundary conditions, consisting of a radially varying mean component and a second-harmonic angular contribution. Two- and three-dimensional plots are used to analyze and discuss the impacts of key parameters, namely the Reynolds, Darcy, and Hartmann numbers, channel corrugation amplitude and wave number, surface charge density, and the relaxation and retardation times on the velocity field and flow rate. It is found that elastic memory causes a proportional growth between the flow rate and the relaxation time, emphasizing the consequences of surface charge application in conjunction with corrugations. Conversely, maintaining a short retardation time mitigates changes in wave amplitude and surface charge. While prolonging it lessens the flow rate and diminishes corrugations and surface charge effects. The Darcy number dampens the velocity and the flow rate, while its enhancement reduces the impact of surface charge density and corrugations amplitude. For high Reynolds number, a ring phenomenon emerges which is attenuated by increased Darcy number, preventing the formation of trapped boluses close to the border. Ignoring surface charge amplifies the flow rate while its consideration diminishes the latter with reinforced impacts of surface charge and wall corrugations at higher Reynolds number. Full article

Shear slip along structural planes in jointed rock masses is the primary trigger for rock slope instability, threatening geotechnical engineering safety. Direct shear tests were conducted on prefabricated granite specimens with regular sawtooth structural planes (undulation angles: 15°, 30°, 45°; tooth spacing: 10 mm) under 2, 4 and 6 MPa normal stresses, with synchronous acquisition of acoustic emission (AE) and infrasonic signals to explore shear failure characteristics, acoustic spectral features and instability precursors. Results show (1) peak shear stress and stiffness rise significantly with increasing undulation angle and normal stress, and failure modes evolve from sliding friction-dominated to asperity shearing-dominated, finally to composite asperity shearing and compressive crushing. (2) The spectral characteristics of both acoustic emission (AE) and infrasonic signals are closely related to the shear fracture mechanism. (3) Approaching peak shear stress, dominant frequency ratio correlation dimension drops to a minimum and the ib-value rises to a pre-sudden-drop critical point; higher undulation angles align these values with stress closer to the peak, valid as instability precursors. (4) A two-level early warning model (early to imminent warning) is proposed via cross-frequency band AE-infrasonic monitoring, providing a fundamental basis for rock slope stability monitoring using these signals. Full article

As the lightest metallic structural material, magnesium alloys face a fundamental trade-off between strength and ductility, limiting their broader application. This study investigates a processing approach to overcome this limitation by systematically comparing the effects of direct extrusion and a multi-directional forging (MDF) combined extrusion process on a Mg-8Gd-4Y-1Nd-0.5Zr alloy. The results demonstrate that MDF pretreatment effectively refines grains and enhances dynamic precipitation. It also significantly weakens the texture, reducing the intensity from 11.14 to 3.98 and tilting the {0001} basal planes by approximately 30° from the extrusion direction. This texture weakening is attributed to the combined effects of particle-stimulated nucleation (PSN) and the orientation diversity introduced by pre-forging, which promote orientation randomization during recrystallization. The alloy processed by the combined route exhibits an excellent strength–ductility synergy in the as-extruded state, with ultimate tensile strength, tensile yield strength, and elongation reaching 315 MPa, 228 MPa, and 13.1%, respectively. After peak aging, the strength further increases to 429 MPa and 323 MPa while maintaining a ductility of 7.3%. Schmid factor analysis confirms that the combined process facilitates the activation of non-basal slip and improves strain compatibility through multi-slip activity, providing an effective pathway for developing high-performance wrought magnesium alloys. Full article

Pipeline integrity is crucial for ensuring the safe and efficient transportation of hydrocarbons. One of the essential methods for maintaining pipeline integrity is periodic inspection using Pipeline Inspection Gauges (PIGs). These PIGs traverse extensive pipeline networks, collecting critical data related to inertial navigation and inspection technologies, such as geometric, ultrasonic, or magnetic flux inspection. Following an inspection, data is downloaded for post-processing to identify and accurately locate pipeline anomalies. Accurate positioning of indications is crucial for effective repair or maintenance of the identified pipeline section. Thus, ongoing efforts aim to improve the precision of indication positioning. This study introduces an innovative method and model for deriving pipeline trajectory characteristics to enhance positioning accuracy. The method is based on distance sampling of odometers, improving the PIG displacement measurement by implementing multiple odometries. Using the method described in this work can compensate for odometer slip, since the distance measurement error was reduced from 15.67% to 1.38%. The model simulates (three and four) odometer trajectories in curvature and calculates the curvature along the pipeline based on odometer data. The curvature model is evaluated with real data obtained from a test circuit, demonstrating that the proposed method and model technique can yield trajectory characteristics such as curvature detection; we can differentiate linear sections from bend sections in the test circuit. However, the curvature measurement error remains considerable due to odometer slippage. Therefore, future work proposes using additional odometers to improve measurement accuracy. Full article

The rapid development of renewable energy requires the support of large-scale energy storage technologies to maintain system balance. Salt cavern compressed air energy storage (CAES) is regarded as one of the key technological pathways for large-scale energy storage. In such systems, the wellbore serves as a critical structure connecting surface facilities and the underground salt cavern, while the cement sheath—formed between the casing and formation during well cementing—acts as the primary barrier ensuring the overall sealing integrity of the wellbore. Through cyclic loading–unloading tests on cement slurries under different temperatures, this study yields the following main conclusions: (1) Increasing temperature aggravates the accumulation of fatigue damage in cement specimens. Taking cumulative plastic strain as an example, it rises from 0.45% to 0.99% as the temperature increases from 25 °C to 115 °C. (2) Elevated temperature promotes greater irreversible energy dissipation under fixed cyclic stress limits. When the temperature rises from 25 °C to 115 °C, the dissipated energy density increases from 0.0033 mJ/m³ to 0.0046 mJ/m³, and its proportion relative to the input energy also increases from 5.52% to 7.13%. (3) Temperature rise leads to notable deterioration of the internal pore structure. At 115 °C, the NMR T₂ distribution peak shifts rightward by 0.49 ms, the total pore volume increases by 150.53 mm³, and the corresponding permeability rises by 1.398 × 10⁻³ μm². (4) Elevated temperature (up to 115 °C) weakens material performance through a dual mechanism: it accelerates dehydration of the cementitious system, reducing interparticle bond strength, while also promoting plastic slip. It is recommended to optimize the cement slurry formulation (e.g., by incorporating thermal stabilizers) to enhance its long-term sealing performance under service conditions. Full article

The Support System with Vertical Retractable Mechanism (SSVRS) is an advancement in telescopic technology that replaces continuous threaded or fluid-dependent interfaces with an internal stepped mechanism based on geometric mechanical interference. This coaxial design uses an integrated pin that engages with discrete grooves, enabling rapid height adjustments and positioning speeds that are significantly faster than those of traditional mechanisms. Unlike friction-based systems that are prone to slipping under dynamic loads, the SSVRS provides millimeter-level precision and exceptional stability, even in vibrational environments. The SSVRS’s versatility stems from its parametric modular design, which scales from lightweight domestic fixtures to heavy-duty industrial machinery by customizing material selection—ranging from high-strength steel to glass fiber-reinforced nylon—and slot configuration. Specifically, vertical slot arrangements facilitate rapid movement, and spiral geometries allow for high-precision alignment. Furthermore, the SSVRS optimizes long-term operational efficiency and sustainability through low maintenance requirements, minimal moving parts, and the use of recyclable materials. By combining high-speed positioning, robust structural integrity, and adaptive modularity, the SSVRS provides a high-performance, concrete alternative to current mainstream linear modules and traditional support structures. Full article

An AZ31 magnesium (Mg) alloy sheet with a bimodal non-basal texture (BNT sample) exhibits significant potential for a lightweight component design in the aerospace field. However, its mechanical properties and microstructure characteristics during plastic deformation under service conditions when approaching cryogenic temperatures have not been thoroughly investigated. Aiming to elucidate this issue, cryogenic tensile experiments were conducted on a BNT sample and its control group (BT sample), which possesses the typical basal texture. Furthermore, relationships between the underlying deformation mechanisms and the deformation behavior of studied sheets were investigated through a synergistic approach combining a variety of characterization techniques with visco-plastic self-consistent (VPSC) simulations. The BNT sample shows 109.1% higher ductility (~0.23 fracture elongation, FE) but 40.2% lower 0.2% proof yield stress (YS) (~155 MPa) than its BT counterpart during cryogenic tensile deformation. As for the BNT sample, initial deformation is governed by a basal ⟨a⟩ slip and {10-12} extension twin (ET). The latter mainly contributes to accommodate intergranular plastic deformation, and this role cannot be captured in VPSC modeling. Subsequent activation of unusual {10-12}-{10-12} double twin (DT), instead of pyramidal <c+a> slip, enhances strain accommodation, boosting ductility. The discrepancy between simulation and experimental results also primarily stems from the lack of explicit incorporation of {10-12}-{10-12} DT. Full article

This study investigates the combustion and emission characteristics of a marine low-speed two-stroke engine using diesel-ignited ammonia dual direct injection. Using a validated 3D CFD model, the impact of ammonia blending ratios (R_a) was systematically explored. Results indicate that the strategy of shifting energy from early diesel injection to late ammonia injection physically repositions the combustion phasing. Rather than ammonia delaying the heat release, this late injection strategy avoids the overly early combustion observed at low ammonia concentrations, thereby lowering peak in-cylinder temperatures while maintaining robust work extraction. Consequently, indicated power at the N90 condition increases by 3.5% (to 1689 kW) over the diesel baseline, with a minimum EISFC of 165.5 g/kWh. High-ratio ammonia blending achieves deep decarbonization: at N90, peak CO and soot emissions are reduced by over 90% and 95%, respectively. Additionally, NO_x emissions decrease by approximately 70% at N90 compared to the N20 peak, attributed to the thermal DeNO_x mechanism. However, the low-temperature environment introduces trade-offs, leading to increased ammonia slip (4 ppm at N90) and elevated N₂O emissions (peaking at N70). These findings clarify the mechanisms governing ammonia combustion and provide theoretical support for optimizing zero-carbon marine propulsion systems. Full article

This study addresses the common challenges of complex soil behavior and the difficulties in achieving precise control during the construction of large open caissons. A centrifugal model test was conducted to investigate open caisson–fine sandy soil interaction, and the findings were further verified through field testing. Results indicated that during the sinking process, the open caisson–soil interface exhibited slip failure characteristics, while the soil at the cutting edge of the open caisson showed a tendency for inward shear slippage. The horizontal earth pressure along the open caisson sidewall was found to correspond to static earth pressure in the upper section and gradually approached active earth pressure in the lower section. The maximum earth pressure occurred at approximately three-quarters of the embedded depth of the open caisson wall. Furthermore, the friction angle at the soil-open caisson interface was approximately 0.63 times that of the soil friction angle. Based on the observed distribution patterns of earth pressure and skin friction, theoretical calculation formulas were developed. Their accuracy was confirmed through field tests, providing valuable references for the design and construction of large open caisson projects. Full article

Thin liquid film flows of nanofluids over porous surfaces are central to applications ranging from microfluidic thermal management to precision coating technologies. This study investigates the hydrodynamic and thermal stability of a nanofluid flowing down a non-uniformly heated inclined porous plane subject to the Beavers-Joseph slip boundary condition. Using the long-wave approximation, a nonlinear evolution equation governing the film thickness is derived. The stability characteristics are systematically analyzed via linear stability theory, weakly nonlinear analysis, and fast Fourier transform (FFT) numerical simulations. Quantitative results indicate that the porous medium permeability, density difference, and Marangoni number act as destabilizing factors; specifically, increasing the porous parameter $\beta$ (from 0 to 0.3), the density ratio ${\zeta }_0$ (from 0 to 5), and the Marangoni number $Mn$ (from 0 to 0.3) significantly reduces the critical Reynolds number and accelerates the onset of interfacial instabilities. In contrast, increasing the nanoparticle volume fraction $\varphi$ from 0 to 0.3 exerts a dominant stabilizing effect by elevating the critical Reynolds number and shrinking the unstable wavenumber domain. Furthermore, nonlinear simulations confirm that higher nanoparticle concentrations effectively suppress the saturation amplitude of disturbances, promoting the eventual stabilization of the liquid film. Full article

Through room-temperature tensile testing, microstructural observation, and comparative analysis of dislocation configurations, this study investigates the deformation and damage behavior of a high-concentration Re/Ru single-crystal alloy. The results show that the alloy possesses excellent mechanical properties at room temperature, with a tensile strength of 875 MPa and a yield strength of 847 MPa. During tensile deformation, plastic strain primarily occurs through dislocation slip within the γ matrix and dislocation shear into the γ′ phase. Dislocations sheared into the γ′ phase exhibit distinct decomposition patterns. Microcracks initiate at γ′/γ interfaces where two slip systems intersect. As tensile loading continues, these microcracks coalesce, leading to increased local stress and unstable crack propagation along the γ/γ′ interfaces, ultimately resulting in fracture. This process constitutes the deformation and damage mechanism of the alloy during room-temperature tensile deformation. These findings suggest that high Re/Ru concentrations fundamentally alter low-temperature deformation pathways, which may improve resistance to brittle fracture during cold start or handling conditions. Full article

Factor graph optimization (FGO) has emerged as a powerful alternative to Kalman filtering for high-precision GNSS positioning, particularly under challenging conditions. Its modular structure allows for the seamless integration of motion constraints, ambiguity modeling, and multi-sensor data across diverse platforms and environments. This study reviews recent FGO architectures for high-precision GNSS methodologies (PPP, RTK), comparing ambiguity management strategies, measurement factor designs, and robust optimization techniques. We compare strategies for modeling ambiguities within the graph and evaluate how they interact with measurement factor design, cycle slip detection, and integer ambiguity resolution (IAR). Trade-offs in ambiguity management and optimization techniques are discussed to guide future design choices. Full article

Austenitic Fe-Mn-Al-C lightweight steels have attracted considerable interest for automotive applications due to their exceptional specific strength, where κ-carbides precipitation critically influences mechanical properties. This review systematically examines the crystal structure, classification, and precipitation kinetics of κ-carbides, emphasizing their spatial distribution-dependent effects: coarse κ-carbides at austenite grain boundaries induce embrittlement and degrade toughness, while nanoscale κ’-carbides within grains enhance strength and ductility through dislocation interactions (e.g., Orowan bypassing and shearing), activating deformation mechanisms such as Dynamic Slip Band Refinement (DSBR), Shear Band-Induced Plasticity (SIP), and Microband-Induced Plasticity (MBIP). Thermodynamic calculations guide alloy design to ensure a single-phase austenite structure at the typical hot-rolling finishing temperature (~900 °C), avoiding harmful phases while promoting beneficial precipitates. Mn suppresses κ-carbide formation, whereas Al and C act as promoters, with intragranular κ’-carbides favoring higher Al/C concentrations (e.g., >6.2% Al and >1.0% C). Heat treatment parameters critically influence κ-carbide distribution, where rapid cooling (e.g., water quenching) suppresses κ-carbides, and subsequent aging (500–700 °C) enables homogeneous precipitation of κ’-carbides. Pre-deformation prior to annealing further accelerates κ-carbide nucleation by introducing crystal defects. Optimal performance requires integrated composition-processing-microstructure optimization to achieve a nnanoscaleκ’-carbide-strengthened austenite matrix through controlled composition and thermo-mechanical processing to achieve an optimal strength-ductility balance. Full article