Search Results (1,593)

Autonomous drifting requires coordinated steering and driving actuation near the tire friction limit, where strong tire nonlinearity and rapidly changing constraints challenge control accuracy and real-time solvability. This article proposes an equilibrium-free successive convexification (SCvx) nonlinear model predictive control framework for drift tracking under constant and varying curvature conditions. The front steering angle and rear-axle longitudinal force are optimized jointly subject to actuator, state, and tire-force constraints. A physics-guided MLP residual tire model is introduced to improve rear-tire-force prediction. Online reference generation determines the heading error, yaw rate, and rear longitudinal force targets from path curvature, lateral error, sideslip variation, and rear slip ratio error, eliminating the need for precomputed drift equilibria. SCvx converts the nonlinear predictive control problem into convex subproblems using virtual control, slack variables, and trust regions. Hardware-in-the-loop experiments confirm stable actuator coordination under both test conditions. Under varying curvature drifting, the proposed method reduces lateral error, velocity error, and yaw rate error by 39.2%, 53.7%, and 24.9%, respectively, compared with the Fiala tire model using the same solver. The results demonstrate improved tracking accuracy and numerical robustness for constrained autonomous drift control. Full article

High-speed railway track–bridge systems (HSRTBSs) in near-fault high-seismicity regions face combined threats from pulse-type seismic excitations, vertical earthquake components and track defects, which may trigger structural damage and deterioration of track regularity. This paper establishes refined OpenSEES coupled numerical models for a typical 32 m simply supported girder bridge equipped with CRTS II slab ballastless track, considering both conventional spherical steel bearings and friction pendulum bearings (FPBs). Nonlinear time-history analyses are performed with near-fault pulse-like and far-field non-pulse ground motions to explore the influences of peak ground acceleration (PGA), vertical-to-horizontal acceleration ratio (αVH), and CA mortar void length. The results demonstrate hierarchical controlling effects of these parameters. PGA dominates the overall seismic response; sliding layer damage follows the sensitivity sequence PGA > αVH > CA mortar void, whereas post-earthquake traffic capacity degradation obeys PGA > CA mortar void > αVH. Near-fault pulse-like ground motions produce more severe structural damage compared with far-field inputs. FPB isolation yields a maximum pier-top seismic reduction ratio of 86.73% and effectively mitigates structural deformation, but cannot eliminate track irregularity originating from CA mortar void defects. Conditional on the 0.2 g seismic level and the given structural configuration adopted in this study, αVH = 0.65 and the 1.95 m critical CA mortar void length for longitudinal track constraint failure can serve as reference values, though they are not universally applicable for all track–bridge systems. This work provides insights for seismic design, CA mortar defect remediation and post-earthquake traffic assessment of near-fault isolated HSRTBSs. Full article

Desert highways have long been subjected to aeolian sand hazards, and sand accumulation on the pavement significantly weakens the surface texture and deteriorates skid resistance, which has become one of the core contributing factors to traffic accidents on desert road sections. Current research predominantly focuses on the attenuation law of the macroscopic friction coefficient of sand-covered pavements; however, the quantitative correlation mechanism between three-dimensional micro-texture characteristics and skid resistance has not been sufficiently revealed, and there is a lack of high-precision skid resistance prediction methods under multi-condition coupling scenarios. To address the above research deficiencies, this paper takes the asphalt pavement in the Tengger Desert region as the research object. A handheld three-dimensional texture scanning system was employed to acquire the three-dimensional pavement morphology parameters under different sand coverages, and the sideway force coefficient (SFC) was synchronously measured under the corresponding conditions. Through Pearson correlation analysis and dual multiple comparison correction using the FDR-BH and Bonferroni methods, the core influencing indicators were identified. Subsequently, a skid resistance prediction model based on a BP neural network optimized by the particle swarm optimization (PSO) algorithm was constructed and horizontally compared and validated with LSTM and PSO-SVM models. The research results show the following: ① under dry conditions, the root mean square height ($S_q$), peak density ($S_{pd}$), arithmetic mean peak curvature ($S_{pc}$), valley void volume ($V_{vv}$), root mean square slope ($S_{dq}$), and developed interfacial area ratio ($S_{dr}$) are significantly linearly correlated with the SFC, among which $S_q$, $S_{pd}$, $S_{pc}$, and $V_{vv}$ are the core controlling indicators, with the absolute values of their correlation coefficients all exceeding 0.73, and ② the constructed PSO-BP prediction model achieved a coefficient of determination $R^2$ of 0.86093 on the test set, and its prediction accuracy and generalization ability are both superior to those of the LSTM and PSO-SVM models, enabling it to effectively characterize the nonlinear mapping relationship between multiple texture parameters and skid resistance. This study can provide theoretical support and a technical basis for skid resistance evaluation, sand accumulation disaster warning, and scientific maintenance decision-making for desert highways. Full article

High-speed steel (HSS) substrates were coated with layers of CrC, NbC, TiC, and VC using thermo-reactive diffusion (TRD) at 900 and 1100 °C for 2 and 4 h. The experimental design was implemented according to the Taguchi L8 orthogonal array. Coating morphology was investigated using scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS), while phase composition was determined by X-ray diffraction (XRD). The contributions of coating type, temperature, and time to coating thickness, microhardness, coefficient of friction, and specific wear rate were evaluated using analysis of variance (ANOVA). SEM and EDS analyses showed that coatings produced at lower temperatures and shorter times exhibited irregular layer thickness, localized porosity, and irregular carbide formation, while coatings applied at higher temperatures and longer times were associated with smoother layers, more homogeneous element distribution, and improved surface morphology. XRD analyses confirmed that the coatings consisted of dense carbide phases and that the chemical composition of the substrate affected the resulting coating phases. Phase composition analysis revealed the presence of phases such as Cr₇C₃ and Cr₂₃C₆ in the coatings. It was observed that coating thickness and hardness generally increased with increasing temperature and coating time. Variance analysis showed that the highest additive ratios in terms of coating thickness belonged to coating type (45.13%) and temperature (42.34%), while in terms of microhardness, temperature (39.92%) and coating type (37.77%) had higher additive ratios. The highest additive ratio in terms of friction coefficient was obtained with coating type (87.98%), while temperature (34.99%) and coating type (33.37%) were determined as the parameters with the highest additive ratios in terms of specific wear rate. NbC coatings generally showed lower performance values compared to other coating types under the examined experimental conditions. Full article

Wearable assistive exoskeletons require lightweight, compact, and backdrivable transmission systems with low output impedance to ensure safe and comfortable human–robot interaction. These efficient, modular actuators benefit from reduction mechanisms that minimize axial bulk while providing high motion regularity. While existing transmissions perform well on some of these metrics, their practical implementation is often constrained by geometric complexity, low backdrivability, limited reduction ratios, or standard component sizes. This paper presents a novel combination of a Rolling Element Eccentric (REE) stage and a planetary gearbox, specifically designed for wearable exoskeleton actuation. The proposed architecture integrates a bearing-based REE drive concentrically within the sun gear of a planetary transmission, reducing mechanical complexity and friction and improving regularity. Moreover, the design exploits additively manufactured bearings, enabling substantial weight reduction, reduced encumbrance, and increased design freedom without reliance on standard bearing dimensions. A prototype reducer has been designed and fabricated using additive manufacturing techniques. It was experimentally evaluated and compared with state-of-the-art transmission designs. These investigations demonstrated low friction, minimal backlash, good torsional stiffness, and sufficient backdrivability, despite the high reduction ratio, while maintaining a compact, flat form factor. The experimental results indicate that the proposed rolling element eccentric planetary transmission is a viable and effective solution for lightweight, efficient, axially compact (independently of the implemented reduction ratio), and backdrivable actuators in assistive wearable robotics. Full article

Conventional cemented backfill used in narrow end-wall mining entries commonly suffers from shrinkage and insufficient roof contact, reducing its support effectiveness. In this study, a solid-waste-based expansive backfill was prepared from mine overburden, ordinary Portland cement, fly ash and hydrogen peroxide. Orthogonal tests were performed to evaluate the effects of fly ash dosage, aggregate-to-binder ratio and hydrogen peroxide dosage on slurry flowability, expansion ratio and compressive strength. The slurry exhibited a flowability of 17.9–24.7 cm and an expansion ratio of 11.23–46.52%, confirming the gas-generating expansion effect of hydrogen peroxide. The aggregate-to-binder ratio was the dominant factor influencing flowability, expansion and 28 d strength. Multi-index optimization identified an optimal mix of 40% fly ash, an aggregate-to-binder ratio of 4:1 and 10% hydrogen peroxide. The optimized backfill showed age-dependent increases in uniaxial compressive strength (UCS) and elastic modulus, with failure evolving from inclined shear to tensile and tensile–shear composite modes. Its shear behavior followed the Mohr–Coulomb criterion, with cohesion of 1.61 MPa and internal friction angle of 30.13°. SEM observations indicated that aggregate skeleton support, cementitious bonding and gas-generating expansion jointly controlled the material performance. Full article

Brush seals using compliant bristle packs can reduce turbomachinery leakage more effectively than conventional labyrinth seals, but their coupled structural and flow behavior makes design difficult. Under large pressure loading, bristles can deflect, lose contact with the rotor, and generate clearance, causing the sharp leakage increase known as blow-out. This study develops a model linking nonlinear bristle deflection, rotor–bristle contact loss, and leakage response. The bristle is treated as an inextensible nonlinear elastic member subjected to distributed pressure loading, backing-plate support, and frictional rotor contact. Contact and separated states are solved iteratively using boundary-value and initial-value solvers. Leakage through the bristle pack is calculated using a random bristle-bed formulation, and leakage through generated clearance is evaluated with an orifice-flow model. The model agrees well with published bristle-deflection predictions. Increasing pressure load reduces normal contact force until lift-off occurs, producing clearance and a sharp rise in leakage. Increasing front-plate free height shifted lift-off from pressure ratio ≈4 to ≈2, while clearance flow contributed up to 36.5% after lift-off. Brush-seal blowout is therefore governed by the transition from rotor–bristle contact to separation. Lower back-plate height can delay blow-out, but hysteresis and durability tradeoffs must be considered. Full article

Enhanced circular tubes are widely employed in shell-and-tube heat exchangers, power-generation condensers, chemical reactors, refrigeration systems, and air-cooled heat exchangers, where improved convective performance can reduce the heat-transfer area required for a specified thermal duty. Helical screw tapes (HSTs) are passive inserts that promote sustained swirling motion and enhance convective heat transfer within such tubes. Although helical screw tapes and multiple-insert arrangements have been investigated previously, the combined thermohydraulic and second-law effects of increasing the number of co-rotating HSTs under fixed geometric ratios remain insufficiently quantified. In this investigation, turbulent airflow in a heated round tube was numerically investigated to examine the effect of tape number on heat transfer, pressure drop, thermal performance, total entropy generation (S_total), and exergy destruction (Ex_D). Six HST configurations containing one to six tapes were examined over a Reynolds-number range of Re = 5000–20,000 in a circular tube with an inner diameter of D_T = 31 mm, which was also adopted as the characteristic length for the Reynolds number, Nusselt number, and friction factor. The helical pitch P, screw diameter D_s, tape width W, and tape thickness t were 60 mm, 30 mm, 4.5 mm, and 0.2 mm, respectively, giving a pitch ratio of P/D_s = 2.0 and a width ratio of W/D_s = 0.15. A plain tube (PT) served as the baseline case. The results show that increasing the number of tapes intensifies swirl flow and enhances heat transfer but also leads to a continuous increase in pressure loss. For the optimum three-tape arrangement, the Nusselt number is increased by 126.0–158.8% and the thermal performance factor by 4.5–19.5% relative to the plain tube, while the total entropy generation and exergy destruction are simultaneously reduced by 7.9–61.0%. Among the configurations examined, HST-P2.0-W0.150-3, comprising three tapes at a pitch ratio of P/D_s = 2.0 and a width ratio of W/D_s = 0.15, achieved the best overall performance by delivering the highest thermal performance factor and the lowest total entropy generation and exergy destruction among the HST cases. Full article

The recycling of construction and demolition waste and the reduction of carbon emissions are important issues in sustainable construction. Recycled aggregate concrete (RAC) is promising for structural use, but the weak old mortar and multiple interfacial transition zones in recycled coarse aggregate (RCA) may reduce the load-transfer capacity at the steel–concrete interface. To address this problem, this study developed carbonated recycled aggregate concrete-filled flat steel tube (FST-CRAC) members and investigated their interfacial bond–slip behavior through material strength tests and push-out tests on nine specimens. The effects of RCA replacement ratio, carbonation treatment, section aspect ratio, and width-to-thickness ratio were examined. RCA was carbonated at 0.5 MPa for 24 h. The 28-day compressive strength increased from 32.6 to 44.3 MPa in the uncarbonated P series and from 36.2 to 46.2 MPa in the carbonated T series. However, because the two series were developed through separate preliminary mix-design trials, these differences should be interpreted as being jointly associated with carbonation treatment and mix-proportion adjustments rather than as evidence of an isolated causal effect of carbonation. Push-out failure was governed by interfacial debonding, local crushing near the corners, and post-peak frictional slip, with damage consistently concentrated at the short sides and corners of the flat section. Carbonation treatment increased the peak bond load by 2.85–26.23%, with the largest benefit observed at a moderate replacement ratio, while increasing the RCA replacement ratio from 50% to 100% increased the peak load by 27.90% for uncarbonated specimens but only 4.21% for carbonated specimens, indicating that carbonation reduces the sensitivity of bond capacity to replacement ratio. A moderate increase in section aspect ratio increased the peak load by 22.30–25.86%, and reducing the width-to-thickness ratio increased the peak load by 5.95–40.92%. A four-linear bond–slip constitutive model was proposed to describe the full interfacial response, from initial bonding through peak degradation to residual friction. These findings provide experimental support for the use of carbonated recycled aggregates in steel tube-confined composite members and a basis for subsequent nonlinear analysis. Full article

An ovoid is a common particle, which is usually formed by constant extrusion and friction during running water handling. However, there is still debate over how the form of ovoidal particles affects the tortuosity and water permeability of particle packing systems. The tortuosity and permeability of the particle packing system are examined in relation to the shape and volume fraction of the particles in this work. The ovoid particle packing system is built using the Monte Carlo approach, and the tortuosity is obtained numerically. Then, the accuracy of the tortuosity prediction model is evaluated by comparing the theoretical derived tortuosities with the simulated results in this work and other literature. By combining the widely used Kozeny–Carman (K-C) formula with the derived theoretical tortuosity prediction model, we develop a modified K-C formula to predict the permeability of ovoidal particle packing systems. By comparing the model outputs with published experimental data and self-conducted lattice Boltzmann method (LBM) numerical simulations, we verify that the modified K-C formula achieves high prediction accuracy. According to the findings, when the aspect ratio c/a rises, the tortuosity first decreases and then increases, and the permeability first increases and then decreases. Full article

CrAlN PVD coatings are frequently used to protect cutting tools because of their superior hardness and wear resistance. However, the influence of carbon addition to such coatings remains largely unexplored. Therefore, Cr-Al-C-N coatings were deposited by HiPIMS using a commercial PVD unit equipped with a segmented sputter target. The target consisted of an upper half of Cr and a lower half of Al. Carbon was added under reactive sputtering conditions with the aim of reducing internal stress and introducing a friction-reducing component. A range of different Al-Cr-C compositions could be efficiently explored by varying the acetylene reactive gas flow. Depending on the positioning of the samples, Cr/Al ratios could be varied between about 4/1 and 1/2 while three different levels of carbon concentration (0, 11, and 25 atomic % of total coating composition) were investigated. It was found that an intermediate carbon concentration effectively increased the hardness of Cr-rich coatings, achieving maximum plastic hardness values over 40 GPa. With increasing Al content, hardness drops to below 30 GPa. The cubic CrN phase with mostly 200-oriented grains was detected for most variants. With increasing Al and C contents, a rapid decrease in crystallite size is observed, accompanied by a reduced intensity of the (200) XRD reflection. A turning test on stainless steel showed decreasing flank wear with higher Al contents. However, no improvement associated with carbon addition could be confirmed within the investigated concentration range. Full article

This study investigates the macromolecular interaction mechanisms between linear-anionic xanthan gum (XG) and branched-nonionic guar gum (GG) biopolymers in three mineralogically distinct soils: Bentonite Clay (BC), Zeolite Silty Soil (ZS), and Red Clay (RC). Mıxtures were prepared by dry mixing of soil powders with biopolymer powders at designated ratios (0%, 1%, 2%, 3%, and 4% by dry weight). The prepared mixtures were characterized using X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), and standard compaction and shear strength tests. The results show that geotechnical macro-behavior is primarily influenced by polymer chain conformation and mineral interfacial reactions. In ZS-XG mixture, hydraulic conductivity increased approximately 26-fold (from 0.107 × 10⁻⁹ to 2.83 × 10⁻⁹ m/s), a phenomenon attributed to the Donnan electrostatic exclusion effect, where linear anionic XG chains repel zeolite surfaces and generate low-friction macro-flow paths. Conversely, the addition of GG to RC formed a strongly interconnected hydrogel network through hydrogen bonding with trivalent iron and magnesium oxides, resulting in a 20.8% increase in cohesion (up to 70.05 kPa). In contrast, GG addition decreased cohesion in BC and ZS. These findings confirm that sustainable biopolymer-based soil remediation depends on customizing the polymer morphology according to the properties of the soil. In engineering applications, ZS-XG mixtures should be evaluated for drainage projects requiring high permeability, whereas the RC-GG4 mixture should be considered a primary option for infiltration barriers (e.g., landfill liners) requiring low permeability and high cohesion. Full article

The contradiction between high compliance and low load-bearing capacity of flexible manipulators limits their engineering applications. Meanwhile, the theoretical modeling of the deformation and variable stiffness characteristics of flexible joints still faces considerable challenges. This paper proposes a positive-pressure double-airbag gap-constrained particle-jamming variable stiffness method and develops a novel actively variable stiffness pneumatic flexible bending joint with an integrated configuration of actuator, variable stiffness device (VSD), and primary structure. Based on classical elasticity theory and Coulomb–Amontons’ law of friction, theoretical models for the bending angle and tangential stiffness are established and verified through prototype experiments. With VSD activation, the joint reaches a bending angle of 56.35° at 0.4 MPa. At 40° forward bending, VSD activation increases the tangential stiffness from 0.167 N/mm to 0.832 N/mm, with the stiffness ratio between 40° and 0° increasing from 1.56 without VSD to 4.80 with VSD activation. Model predictions agree well with experimental data, yielding mean relative errors of 6.77% for the bending-angle model with VSD and 6.76% for the forward tangential-stiffness model with VSD activation. A coupling effect between bending deformation and stiffness is observed. The results demonstrate that the proposed joint achieves substantial stiffness regulation, providing a basis for its application in flexible robotic systems. Full article

Due to their high strength-to-weight ratio and corrosion resistance, carbon fiber-reinforced polymers (CFRPs) are increasingly used as tension elements in bridge engineering. Their pronounced anisotropy, resulting from stiff carbon fibers and a weaker polymer matrix, is critical for fatigue behavior under multiaxial dynamic stress states, such as those occurring in stay cables over saddles of extradosed bridges or at clamps of suspension-bridge hangers. This multiaxial loading can cause progressive damage accumulation in the contact regions and lead to premature failure. To study this efficiently, an energy-based progressive damage analysis (PDA) model for CFRP tension elements under multiaxial fatigue loading was implemented as a vectorized user material in ABAQUS^® 6.14 (VUMAT in FORTRAN) and validated against tension-tension fatigue tests on pin-loaded CFRP straps. The model was then applied to two representative bridge applications, viz. a clamped CFRP rod and a CFRP cable bent over a saddle, where parameters such as clamping pressure, maximum stress level, and friction coefficient were varied to quantify their influence on fatigue life and to assess suitability in line with fib recommendations. The results indicate that clamping pressures inducing transverse compressive stresses above roughly 85% of the CFRP’s transversal compressive strength significantly reduce fatigue life, whereas keeping the maximum fatigue stress below about 40% of the mean longitudinal tensile strength, the stress amplitude below 200 MPa, and the friction coefficient near 0.2 yields fatigue lives exceeding 2 × 10⁶ load cycles, which is satisfactory under fib criteria. Full article

During vacuum induction melting (VIM) of superalloys, oxygen and nitrogen control involves interfacial processes at both the melt free surface and the crucible–melt interface, where melt flow is an important factor affecting reaction kinetics. A coupled electromagnetic and fluid flow model with a deformable free surface was developed and validated for a 3 t industrial VIM furnace with two electromagnetic excitation modes. The melt flow under the Heating and Stirring modes is compared, with particular attention to the role of free-surface deformation, and the effects of input power and filling ratio are further examined. The results show that at an input power of 190 kW and a filling ratio of 85%, the Heating mode produces two counter-rotating vortices separated by a low-velocity mid-region, while the Stirring mode generates a dominant upper vortex covering most of the melt volume with a smaller counter-rotating vortex at the bottom. The Stirring mode achieves approximately 1.3 times the surface velocity, 1.7 times the wall friction velocity, and half the mixing time of the Heating mode. Free-surface deformation significantly affects the predicted flow structure, particularly under the Heating mode. Parametric results further show that input power mainly changes the flow intensity without altering the flow structure under either mode. By contrast, the filling ratio strongly affects the flow structure under the Heating mode, while that under the Stirring mode is largely preserved. These findings provide insight into the melt flow conditions relevant to oxygen and nitrogen removal during VIM processing. Full article