Search Results (1,334)

Accurate trajectory tracking is challenging for tracked agricultural vehicles in orchards. Uneven terrain, track slip, and vehicle posture variations are the main causes, often leading to model mismatch and degraded control performance. To address these issues, this paper proposes an improved nonlinear model predictive control (NMPC) strategy integrated with curvature feedforward compensation for trajectory tracking of tracked agricultural vehicles under uneven terrain conditions. An enhanced kinematic model based on the instantaneous center of rotation is developed by incorporating vehicle roll and pitch angles, and track slip parameters are estimated online using a Levenberg–Marquardt optimization method to improve prediction accuracy. Furthermore, curvature feedforward information derived from the reference trajectory is embedded into the NMPC objective function to provide anticipatory control inputs and reduce computational burden. Simulation results demonstrate that compared to conventional NMPC, the proposed method reduces the mean and standard deviation of tracking error by 30.28% and 32.46% respectively, while decreasing the mean and standard deviation of heading error by 37.27% and 35.05%. Concurrently, the maximum of optimize solution time is significantly reduced, effectively resolving tracking accuracy degradation caused by system solution timeouts. Field experiments conducted under different load conditions further validate that the proposed control strategy significantly reduces lateral, longitudinal, and heading tracking errors compared with conventional NMPC, confirming its effectiveness and robustness for tracked agricultural vehicle trajectory tracking in complex orchard environments. Full article

On 4 December 2025, nearly two years after the 2024 Mw 7.0 Wushi earthquake, an Mw 5.8 event struck the nearby county of Aheqi, southwestern Tianshan. Owing to the subparallel strikes of both nodal planes and the interspersed hypocenter locations among regional structures in the reported focal mechanisms, the exact fault geometry of this event remains unresolved, impeding a better understanding of regional tectonic activity and the associated seismic hazards. To resolve this, we applied Interferometric Synthetic Aperture Radar (InSAR) technique to map the coseismic deformation and invert for the fault geometry and slip pattern. Significant tropospheric delays are mitigated using a moving-window linear model and a multi-interferogram weighted averaging strategy. The result shows significant uplift (~5.0 cm for ascending track and ~6.0 cm for descending track), indicating thrust-dominated mechanism. Bayesian inversion reveals two possible fault models: a 31.6° north-dipping blind thrust or a 54.4° south-dipping back-thrust. While both fault planes fit the InSAR observations, integrated evidence from the absence of back-thrust development conditions, the surface deformation pattern, and regional topography indicates that the north-dipping Aheqi fault is the causative structure. Together with the steeper Maidan fault to the north, it forms the Orogen Basin boundary along the southern Tianshan piedmont. Our findings highlight that resolving moderate blind-thrust seismogenic structures using InSAR requires integration with pre-existing structural and geomorphic evidence. Furthermore, Coulomb stress calculations indicate a rupture-promoting effect from the Wushi earthquake, which occurred on a reactivated fault, onto the Aheqi event, with stress loading exceeding 2 bar at the hypocenter. Thus, the potential for stress-driven sequential rupture between reactivated and present-day active structures necessitates an updated seismic hazard assessment in the southern Tianshan. Full article

The selection of deformation mechanisms in hexagonal close-packed (HCP) metals is strongly influenced by both crystallographic orientation and macroscopic deformation constraints. In commercially pure titanium, plastic deformation under constrained loading conditions involves a complex interplay between dislocation slip and deformation twinning, whose respective activation cannot be fully described by classical stress-based criteria. In this study, the mechanical origin of slip and twinning variant selection in commercially pure titanium subjected to plane strain compression is investigated experimentally. Plane strain compression is used as a canonical loading condition representative of constrained deformation paths encountered in sheet metal forming. Interrupted in-situ electron backscatter diffraction is combined with slip trace and twin variant analyses to identify the active deformation mechanisms at the grain scale. Resolved shear stress calculations show that stress-based criteria provide a necessary first-order condition for the activation of both slip and twinning systems. While the Schmid factor reasonably predicts part of the observed slip activity, it fails to uniquely determine the selection of active twinning variants. A kinematic analysis reveals that twinning variant selection is governed by the compatibility between the deformation induced by twinning and the macroscopic strain constraints imposed by plane strain compression. Only variants whose deformation accommodates compression along the loading axis, extension along the free in-plane direction, and minimal strain along the constrained in-plane direction are preferentially activated. These results demonstrate that deformation mechanism selection in HCP titanium under constrained loading conditions results from a combined effect of resolved shear stress and kinematic compatibility. The proposed framework provides a physically grounded basis for interpreting deformation-induced texture evolution and offers clear perspectives for the development of crystal plasticity models incorporating twinning under complex strain paths. Full article

Unlined pressure tunnels and shafts are widely employed in hydropower projects where the surrounding rock mass is required to sustain the internal water pressure. Their hydraulic stability is governed by complex interactions among the three-dimensional in situ stress state, discontinuity geometry, rock mass properties, and operational water pressure. Conventional deterministic design approaches address these factors implicitly and provide limited information on the likelihood of hydraulic failure mechanisms, such as hydraulic jacking, hydraulic fracturing, and shear slip of discontinuities. This paper presents a probabilistic framework for assessing the hydraulic stability of unlined pressure tunnels and shafts, in which the governing failure mechanisms are explicitly formulated as limit states and key sources of uncertainty are systematically represented. The full three-dimensional stress tensor is rotated onto potential discontinuity planes to evaluate effective normal and shear stresses, and reliability-based methods are employed to quantify probabilities of failure. The methodology is demonstrated through a representative case study of a failed unlined pressure tunnel reflecting typical geological and stress conditions encountered in hydropower projects. The results show that variability in stress orientation and discontinuity characteristics has a strong influence on hydraulic stability and that commonly used deterministic criteria may not fully capture the associated failure risk. Full article

The construction of suspension bridges in mountainous expressways often involves tunnel-type anchorages in close proximity to shallow-buried bifurcated tunnels, particularly in soft rock strata with dense overlying structures. This proximity poses significant challenges to construction safety and stability. This study aims to investigate the influence of tunnel-type anchorage construction on the ground surface, surrounding rock, and adjacent bifurcated tunnels under such complex conditions. It was hypothesized that the anchorage load transfer and deformation mechanisms would significantly affect the adjacent tunnel, with potential cumulative effects due to the twin-anchor configuration. To address this, a combined approach of in situ scaled model testing (1:10 scale) and three-dimensional numerical simulation was employed. The model test incorporated monitoring of deformation and stress at key locations (anchor plug, rock mass, and anchor–rock interface) under incremental cable loads. Quantitative results from the model test indicate that at the design load (1P, equivalent to 2016.84 kN per anchor), deformations were minimal (e.g., maximum anchor displacement 0.35 mm). The anchor–rock interface exhibited limited slip (max 0.06 mm at 1P), and contact stresses were highest in the rear part of the anchor plug, indicating a non-uniform load transfer. Under overload conditions, the system reached yield at 7P and peak strength at 10.5P, with measured ground surface cracks up to 5 mm. Numerical simulations, calibrated against the experimental data, revealed that under increasing load (up to 10P), the plastic zones around the two anchors progressively expanded and eventually coalesced, leading to a characteristic “inverted trapezoid” failure pattern propagating to the surface, accompanied by shear failure along the 14° bedding plane. The combined results quantify the progressive interaction between the twin anchorages and the surrounding rock, highlighting the critical role of the anchor–rock interface and the cumulative effect of twin anchors on ground deformation and potential failure mechanisms. This research provides a scientific basis for the design and construction of tunnel-type anchorages in similar challenging geological and spatial settings. Full article

The mechanical performance of Zr–Nb dual-phase alloys is strongly influenced by the metastable β (body-centered cubic, BCC) phase and its crystallographic orientation, yet the underlying deformation mechanisms remain unclear. In this work, molecular dynamics (MD) simulations were conducted to investigate the compressive behavior of nanolayered Zr–Nb alloys with varying loading directions and BCC layer thickness (T_BCC). The results reveal that interfacial coordinated strain governs the activation of various deformation modes. When the loading conditions promote strain compatibility at the interface between the hexagonal close-packed (HCP) and BCC phases, significant plasticity in the BCC phase assists the nucleation of stacking faults (SFs) and the activation of high critical resolved shear stress (CRSS) <c + a> slip systems in the HCP phase, leading to enhanced strength–ductility synergy of the material. In addition, T_BCC induces a non-monotonic peak stress response, with a transition thickness of ~10.96 nm. Below this threshold, stress-induced phase transformation in the BCC phase is the dominant mechanism for strengthening. Above this thickness, increased interlayer spacing enhances dislocation interactions and spatial effects, resulting in improved strain hardening and plastic stability. These findings clarify the competition between transformation-induced and dislocation-mediated strengthening and provide atomic-scale guidance for the microstructural design of high-performance Zr–Nb alloys. Full article

This research explores the use of industrial waste as an alternative to natural raw materials, promoting a circular economy in the construction sector. It specifically investigates the manufacturing of paving blocks using blast furnace slag and recycled aggregates. Paving blocks were produced without altering typical industry conditions, entirely replacing cement with alkaline-activated blast furnace slag. The study replaced natural aggregate in three proportions (20%, 50%, and 100%) with three types of recycled aggregates: concrete recycled aggregate (CA), masonry recycled aggregate (MA), and recycled mixed aggregate (RMA), in both coarse and fine fractions. The experimental procedure analysed the impact of recycled aggregates in an alkaline-activated slag matrix through three phases: characterising physical properties (mechanical properties, water absorption, density, abrasion resistance, and slip resistance), evaluating leaching behaviour, and conducting a life cycle analysis. The results of physical characterisation were statistically analysed using principal component analysis (PCA). The results obtained show the feasibility of manufacturing paving blocks with blast furnace slag by completely replacing the natural aggregate with the coarse fraction of the three recycled aggregates used and replacing up to 20% in the case of using the fine fraction. The properties of the paving blocks manufactured with slag depend mainly on the degree of substitution of natural aggregate with the recycled aggregate. All paving blocks can be considered environmentally safe from leaching according to the Dutch Soil Quality Decree. Paving blocks made from alkali-activated ground granulated blast furnace slag and recycled aggregates generate a lower carbon footprint compared to concrete paving blocks. Full article

Accurate prediction of surface rupture induced by seismogenic fault displacement is essential for the seismic safety assessment of major engineering projects. Most existing numerical simulations adopt quasi-static approaches, in which the effect of fault displacement is simplified as static loading. As a result, these methods cannot represent the dynamic characteristics of the fault rupture process, such as stress-wave propagation, soil inertial effects, and the influence of dynamic loading paths on rupture extension in soil layers. To address this issue, a full-process simulation method is established for simulating rupture of overlying soil subjected to dynamic fault displacement: Firstly, a non-uniform dynamic fault displacement loading is formulated for the two sides of the fault based on viscoelastic artificial boundaries, allowing the differential motion of the bedrock on both sides of the fault to be represented. Secondly, an improved dynamic skeleton curve constitutive model of soil is developed by introducing a minimum modulus constraint, providing an improved description of soil nonlinear dynamic behavior from small-strain hysteresis to large-strain shear failure. The reliability of the proposed method is verified through element-level tests and horizontal-site response simulation. As a benchmark, its ability to reproduce key rupture characteristics under quasi-static conditions is also assessed by comparison with classical quasi-static rupture studies. The method is then applied to simulate rupture extension and deformation response of overlying soil under strike-slip fault displacement. The results show that, compared to quasi-static analysis, dynamic fault displacement produces similar cumulative slip for surface rupture initiation and full connection, but induces transient amplification of peak surface displacement and a wider deformation zone with gentler displacement gradients. These findings demonstrate the necessity of considering dynamic fault dislocation of bedrock–overlying soil interaction in seismic assessments of engineering projects crossing active faults. Full article

Water saturation is a key factor influencing the mechanical behavior and stability of tunnel rock masses in water-bearing strata. However, current research based on physical model tests has yet to systematically reveal its intrinsic relationship with rock failure modes. To address this gap, this study systematically investigated the effects of water saturation levels (0%, 33%, 58%, and 100%) on the failure mechanisms of four typical tunnel cross-section models: wall-arch, horseshoe, circular, and square. The results indicate the following: (1) Water saturation exerts a significant deteriorating effect on the mechanical properties of tunnel models. As saturation increases, peak stresses generally decrease across all models, but the extent of deterioration varies markedly by tunnel shape: at low saturation (≤58%), peak stress follows the order Wall-Arch > Horseshoe > Circular > Square; at high saturation (>58%), this relationship reverses to Circular > Square > Wall-Arch > Horseshoe. (2) The failure mechanism is significantly controlled by saturation, exhibiting distinct transition characteristics: At low saturation, capillary effects dominate, with matrix suction enhancing material strength, resulting in brittle failure with crack concentration. At high saturation, pore water pressure effects prevail, reducing effective stress and leading to plastic failure dominated by distributed shear slip. Notably, square tunnels consistently exhibit pronounced flexural failure characteristics across all saturation levels. (3) Energy evolution analysis indicates the following: as saturation increases, the total energy U of specimens decreases, the dissipation rate of dissipated energy U_d accelerates, the energy inflection point advances, and failure precursors manifest earlier. The energy dissipation factor n of high-saturation specimens decreases more significantly with increasing strain, confirming that moisture accelerates energy dissipation and promotes premature material instability. (4) Significant differences exist in the response characteristics to moisture effects among tunnel types: Square tunnels consistently exhibit pronounced flexural failure; Circular tunnels demonstrate optimal stress distribution properties under high water content conditions; Wall-arch and horseshoe-shaped tunnels are most sensitive to saturation changes, with their failure modes transitioning from tensile-dominated to shear failure as water content increases. This study reveals the coupled mechanism between water saturation and tunnel cross-sectional shape in influencing rock mass stability. Full article

The corrosion of prestressed tendons in concrete structures remains a major durability concern, especially for post-tensioned members exposed to aggressive environments. High-strength aluminum alloy (AA) bars exhibit favorable characteristics such as corrosion resistance, low density, and high ductility and may therefore provide an alternative or supplementary prestressing material in durability-oriented structural design. In this study, a bonded post-tensioned T-shaped concrete beam with hybrid prestressing combining prestressed steel (PS) strands and 7075 AA bars was investigated. A refined finite element model was developed by considering the bond-slip relationship between the AA tendons and grout inside corrugated tubes. The flexural behavior of the beam was analyzed through a combination of finite element simulation and sectional theoretical analysis. In addition, a fatigue-life assessment framework was established based on vehicle fatigue loads and material fatigue constitutive models, and the fatigue performance of the proposed hybrid beams was compared with that of conventional prestressed concrete beams. The theoretical predictions agreed reasonably well with the numerical results. Results indicated that partial replacement of PS strands with corrosion-resistant AA bars could alter the governing fatigue failure mode and improve the fatigue durability of prestressed beams under corrosive conditions. These findings highlight the potential of hybrid AA–PS prestressing as a durability-oriented strategy for concrete beams in corrosive environments. Full article

This work investigated the influence of thickness-direction boundary conditions on the flow characteristics of granular material in a quasi-two-dimensional silo using the discrete element method (DEM). Two types of boundary conditions were considered in the thickness direction: wall conditions and periodic boundary conditions. The simulation results indicate that under wall conditions, velocity waves propagate upward, manifested by the formation of bubble-like sub-flow zones in the velocity field, and the particle motion in the upper bed region exhibits a clear stick–slip feature. In contrast, under periodic boundary conditions, particle motion displays a resonant mode. Further statistical analysis reveals that, despite the distinct macroscopic motion mode under the two boundary conditions, the probability distributions of particle vertical fluctuating velocities share similar characteristics: both exhibit fat-tailed and asymmetric features and deviate from Gaussian distribution. Additionally, under wall conditions, the horizontal distributions of particle vertical velocity conform to the kinematic model throughout the bed, whereas under periodic boundary conditions, the horizontal distributions in the upper bed region display plug flow characteristics. In summary, the results of this work demonstrate that thickness-direction boundary conditions play a crucial role in determining the flow characteristics of granular assembly in silos. Full article

With the shift of oil and gas exploitation to deep seas, the 35 kV high-voltage electric slip ring in Single-Point Mooring (SPM) systems faces critical challenges of insulation failure and thermal failure, threatening operational safety. This study aims to investigate its insulation strength and temperature rise characteristics. A three-dimensional electric field model and a magnetic–thermal coupling model considering the skin effect were established using the finite element method (FEM). Simulations were conducted under four high-voltage configurations and various high-current operating conditions, followed by AC breakdown tests and high-current temperature rise experiments for validation. The results show that the maximum electric field (up to 19.53 kV/mm) concentrates at the inlet polytetrafluoroethylene (PTFE) bushing, which is the insulation weak point. The maximum temperature rise at the center ring can be predicted by a power-law model. Moreover, simulation results agree well with experimental data, confirming the reliability of the computational studies. This work provides a theoretical and experimental basis for the optimal design and safe operation of high-voltage slip rings in offshore SPM systems. Full article

Advancing hydropower development is crucial for supporting China’s “Dual Carbon” strategy and ensuring energy security. A key safety challenge in this endeavor is the stability of arch dam abutments under the combined action of high in situ stress and reservoir water loads. This study addresses this issue by proposing an integrated methodology that links detailed geological characterization, in situ stress quantification, and mechanical stability analysis. Using the Guxue high-arch dam as a case study, we first established a three-dimensional geological model to identify controlling discontinuities and delineate potential sliding blocks. A finite difference model was then developed to simulate the in situ geo-stress field and operational water pressures. Through stress tensor transformation, the stress state on potential slip surfaces was accurately determined, and safety factors were calculated based on the Mohr–Coulomb strength criterion. The results show that the critical left and right abutment rock blocks exhibit safety factors of 1.30 and 1.24, respectively, meeting design specifications while indicating a relatively lower safety margin on the right bank. The proposed approach, grounded in precise stress analysis, provides a reliable framework for assessing abutment stability under complex loading conditions, offering practical support for the safety evaluation and targeted reinforcement of high-arch dam projects in similar geological settings. Full article

In order to design a new type of long-life and reliable casing hanger, this paper studied the failure mechanisms of the rubber sealing structures of the slip hanger and the mandrel hanger. Through tensile and compressive tests, the tests and analyses of different rubber structures were completed, data fitting was carried out, and the constitutive relationship of the rubber material was obtained. A superior constitutive model was applied to the sealing materials of the hanger. Numerical calculations were used to obtain the strength and sealing performance variation laws of the rubber sealing components with different structures, and the reasons for the failure of the conventional hanger were found. The results show that the rubber components and the ball-shaped metal sealing components will lose their elastic deformation under high-pressure and large-load conditions, and the reliability will decrease. Finally, a new type of metal sealing structure was designed. Compared with the previous metal sealing structures, this paper conducts a more in-depth and detailed study, and further presents the superiority of metal sealing in terms of structural dimensions and working principles. Experiments were conducted, and the results showed that this sealing structure can meet the usage requirements of the casing hanger with large loads and high pressure. The research results provide theoretical and application guidance for the design of long-life and reliable performance hanger sealing structures. Full article

This study investigates the transient wheel–rail contact mechanics of welded joints in heavy-haul rails via a validated 3D finite element model, and analyzes the stick-slip behavior, dynamic response and elastoplastic characteristics in the base material zone, heat-affected zone and weld bead zone. Results show a distinct contact state transition from stick-slip in the base material to predominant slip within the welded zones, indicating higher wear susceptibility. Dynamic response analysis reveals the highest and lowest contact-point acceleration amplitudes in the base material and heat-affected zone, respectively, due to material heterogeneity. Plastic deformation consistently initiates at the rail surface, where stress and strain concentrate, establishing it as the primary site for damage nucleation. A systematic parametric study shows that plastic deformation can be effectively mitigated by increasing the yield strength and elastic modulus of the welded joint material, or reducing the wheelset velocity, unsprung mass and wheel–rail friction coefficient. In contrast, adjusting the primary suspension and fastener parameters exerts a negligible influence on plastic deformation control. These findings provide a mechanistic basis for optimizing the performance and maintenance of welded joints in heavy-haul rail operations. This study reveals the coupling law of multiple mechanisms among contact behavior, dynamic response and material failure during the damage initiation process of rail welded joints from the mechanistic perspective, which provides a theoretical basis for the structural optimization, condition assessment and maintenance of rail welded joints in heavy-haul railways. Full article