The integration of multifunctional modules into ultrathin, spatially constrained flexible electronics often leads to localized heat accumulation, challenging device reliability under conformal operation. Achieving precise heat-flux manipulation, mechanical flexibility, and scalable fabrication within a unified platform remains an open challenge. Here, we report a gradient-discretized design strategy for flexible thermal metamaterials that combines multiscale topology optimization with transformation thermotics. This framework links microstructural geometry, deformation-induced effects, and macroscopic thermal functionality, including thermal cloaking and thermal concentration. Using flexible printed-circuit fabrication, we fabricate gradient arrays containing 6×6 to 20×20 unit cells, with pitches ranging from 10 to 3 mm, within a fixed 60×60 mm² footprint. We also develop a coupled thermomechanical resistance model to quantify bending-induced perturbations. In the flat state, the thermal-cloaking function suppresses the temperature gradient within the protected region to approximately 1% of the surrounding background gradient, thereby enabling thermal concealment of embedded heterogeneous structures. The thermal-concentration function enhances local heat focusing by nearly one order of magnitude, increasing the temperature difference available to a thermoelectric module. Both functions remain effective under bending at a radius of 19 mm, with only moderate performance degradation. These results establish a scalable and mechanically compliant platform for programmable heat-flux control in next-generation conformal and wearable electronics.
Radiant heat flux serves as a direct indicator for assessing the spread of wildland fires and the extent of thermal injury. It is of primary importance for wildland managers and firefighters to estimate the thermal radiation from a flame front and the safety distances of persons and houses within the Wildland-Urban Interface. In the presence of ambient wind, wildland fires frequently develop flames with a tilted, triangular prism morphology. Hence the estimation of incident radiant heat flux and safety distance can be realized based on solid flame model by solving the view factor. This work presents an analytical model for both horizontal and vertical view factors from a tilted rectangular flame to a target at any position. The proposed model was validated by comparing its results with previous studies. The calculated view factors were applied in the determination of radiant heat fluxes for smallscale and large-scale wildland fires based on some assumptions. The distribution patterns of horizontal and vertical radiant heat fluxes along the central vertical section of the fire source were revealed. The safety distances respectively for persons without protection and firefighters with protection were determined as a function of the fire width or flame height. The maximum ignition distance of houses built with wood for a large wildland fire was determined as 70 m. Then some useful loss mitigation measures were proposed. This work helps enhance the understanding of wildland fire spread potential and radiation-induced ignition likelihood, while also contributing to wildland fire modeling and wildland area planning.
Traditional phase selection method is influenced by control strategy of double-side converters in Low-Frequency Transmission System of Offshore Wind Power, resulting in reduced reliability and difficulty in adaptation. Aiming at to the above issues, proposes a transient fault phase selection method suitable for LFTSOWP. Then, a reasonable frequency range for traveling wave analysis is selected, and a phase-selection method based on the Generalized S-Transform using the energy ratio of line voltage traveling waves is proposed. In addition, the positive and negative energy ratios of phase voltages are adopted as auxiliary criteria to solve the problem of identifying the faulty phase in phase-to-phase ground faults under a certain fault startup Angle. Finally, a typical LFTSOWP model is built in PSCAD/EMTDC. The verification results indicate that the proposed method can rapidly identify the fault phase, has good robustness.
Slurry shield tunnelling in pebble-rich strata often encounters difficulties in transporting large-sized pebbles. As a result, particle retention and blockage in the slurry circulation pipeline constitute major risks to excavation stability. In this study, free-settling experiments and slurry circulation system model experiments were conducted to investigate the settling behaviour, critical flow velocity, and transport velocity characteristics of large-sized pebbles in slurry media. Three types of pebbles were selected, namely ellipsoidal, rounded non-spherical, and spherical pebbles, with a maximum major-axis length not exceeding 100 mm. The carrier media included a 20 wt% sodium bentonite slurry with a density of 1.18 g/cm3 and a funnel viscosity of 25.6 s, as well as a CMC saline solution with comparable density and viscosity for visual observation. The critical flow velocities of the tested pebbles ranged from 0.278 to 0.982 m/s and were measured in horizontal, inclined, joint, and vertical pipeline sections. The results indicate that temporary retention, particle reorientation, and cyclic overturning occurred mainly at abrupt joint transitions for the ellipsoidal and rounded non-spherical pebbles, whereas no local stagnation or cyclic flipping was observed for the three spherical reference particles, whose highest critical velocities occurred during vertical lifting. Pebble transport velocity increased approximately linearly with solution flow velocity in the investigated pipeline sections. All fitted slopes were positive and statistically significant (p < 0.001), with slopes of 1.22–1.80 in the vertical section and 1.01–1.16 in the downstream section, indicating greater sensitivity of vertical transport to changes in flow velocity. Rank-correlation analysis indicated morphology-dependent and joint-dependent geometric associations. For the ellipsoidal pebbles, the width-to-length ratio showed the strongest apparent association with the upstream-joint response, whereas the thickness-to-length ratio showed the strongest apparent association with the downstream-joint response. For the rounded non-spherical pebbles, the thickness-to-length ratio exhibited the strongest apparent negative associations with the joint velocity differences. The findings provide an experimental basis for identifying vulnerable pipeline sections, selecting operating flow velocities, and mitigating blockage risks in slurry shield circulation systems.
Electric vertical take-off and landing vehicles (eVTOLs) can provide fast, potentially lower-carbon trunk services for long-distance urban commuting, but they require coordination with ground feeder modes because they cannot provide door-to-door service. Under fluctuating passenger arrivals, fixed timetables are easy to operate but inflexible, whereas load-based departure rules improve utilization but create unpredictable waiting. This study proposes an adaptive soft-target dispatch strategy that schedules eVTOL departures based on passenger accumulation, stranded demand, and vehicle availability. The integrated land-air dispatch problem is formulated as an event-driven, multi-line decision process and solved using multi-agent reinforcement learning. Numerical experiments show that the proposed strategy reduces average system cost by 22.57% relative to fixed timetables and 0.51% relative to full-match rules, with the largest gains under low-to-medium demand and medium-to-high values of time. A Chengdu airport case study further confirms its cost-saving potential.
