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SiC/multi-walled carbon nanotube (MWCNT) composites are considered to be promising materials for high-temperature electromagnetic wave (EMW) absorption due to their strong thermal stability and tunable dielectric properties. However, the EMW absorption performance of these composites is limited by poor impedance matching. This study proposes a novel multiscale structure synergistic regulation approach to enhance EMW absorption performance, which involves constructing a heterointerface structure and a triple periodic minimal surface (TPMS) meta-structure. The addition of a SiO 2 shell as an impedance layer to the SiC/MWCNT core to improve the intrinsic impedance. Meanwhile, the heterointerface between the core-shell structure leads to multiple interface polarization, significantly enhancing EMW energy dissipation. Consequently, the effective absorption bandwidth (EAB) of SiO 2 –SiC/MWCNT composites increased from 0.88 to 4.56 GHz. Furthermore, a TPMS meta-structure, fabricated by three-dimensional (3D) printing and sol infiltration technology, is developed to further improve impedance matching with the equivalent electromagnetic effect. Simulation and experimental results demonstrate that the SiO 2 –SiC/MWCNT TPMS meta-structure exhibits broadband EMW absorption performance, with the EAB reaching 7.2 GHz. This improvement is attributed to the synergistic regulation of the heterointerface structure and TPMS meta-structure, which provides a good balance between the requirements of electromagnetic loss and impedance matching. Additionally, the composites exhibit excellent oxidation resistance, as their EAB remains almost unchanged after exposure to 1000 °C for 6 h. This research offers a new design paradigm for ultrabroadband design of the nonmagnetic high-temperature absorbing materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Bridge scouring is one of the factors affecting the safety of bridge. Considering the energy loss and sand-bed, a prediction model equation (PMEL) had been proposed to estimate the cylindrical bridge piers scour depth. The influence of energy loss on the accuracy of local scour depth prediction was discussed. The energy loss caused by the interaction between the flow field with the pier and the riverbed was introduced, and the reduction of effective peak velocity in a reciprocating flow was considered. This paper adopted eighteen data sets from cylindrical bridge piers scouring experiments that combined numerical simulation analysis. Then the relationship between the influence parameter H r (the non-dimensional effective fluid height) and V / V c (flow intensity) was established to guide the selection of calculated water depth. Finally, compared to directly using numerical simulation to solve the local scouring depth of bridge, the PMEL improved the solving efficiency. The accuracy of PMEL has been validated through physical experiments, standardized equations, and results from other researches. Compared with the local scour depth prediction model, without considering energy loss, it was found that the calculation accuracy had increased by 27%. • A local scour prediction model for Cylindrical bridge piers considering energy loss is established. • The relationship between effective water depth and flow intensity was proposed. • Compared to the standard equation and other prediction models, the new model has lower errors. [ABSTRACT FROM AUTHOR]

In recent years, precast segmental concrete bridge columns became prevalent because of the benefits of accelerated construction, low environmental impact, high quality and low life cycle costs. The lack of a detailed configuration and appropriate design procedure to ensure a comparable performance with monolithic construction has impeded this structural system from being widely used in areas of high seismicity. In this study, precast segmental bridge column cyclic loading tests were conducted to investigate the performance of unbonded post-tensioned segmental bridge columns. One monolithic and two precast segmental columns were tested. The precast segmental column exhibited minor damage and small residual displacement after the maximum 7% cyclic drift; energy dissipation (ED) can be enhanced byadding ED bars. The experimental results were modeled by a simplified pushover method (SPOM), as well as a fiber model (FIBM) finite element method. Forty-five cases of columns with different aspect ratios, axial load ratios and ED bar ratios were analyzed with the SPOM and FIBM, respectively. Using these parametric results, a simplified design method was suggested by regressive analysis. Satisfactory correlation was found between the experimental results and the simplified design method for precast segmental columns with different design parameters. [ABSTRACT FROM AUTHOR]

In this study, we carried out a series of physical experiments using a submersed flume model to investigate how sand/clay content influences the depositional mechanism of submarine debris flows. A three-dimensional biphasic numerical model, with a Herschel-Bulkley rheology, was used to back-analyze the physical experiments. The calibrated numerical model was then used in a back-calculation to investigate the effects of viscosity on the deposition process. The results show that as submarine debris flows mix with water during the deposition process, shear stress at the slurry-water interface generates a vortex that leads to a swirl-wedge front head. High-viscosity slurry flows with a swirl-wedge front head travel at a higher aspect ratio and with a greater radius of rotation. Hydroplaning was observed when the front head was lifted by water during flow. The lifting height increased with flow depth fluctuation. Higher viscosity slurry was found to lift more rapidly due to its larger vortex and the decrease in density at the front head over time, both of which promote fluctuation. Although a high-density slurry has a greater lifting height, the ratio of lifting height to front head height is lower, indicating a smaller lifting force influence. Lower density flows have higher kinetic energy as the transfer of potential energy into kinetic energy is more efficient. Kinetic energy dissipation comprises three stages: (1) gravity-dominated coherent flow and hydroplaning lead to a rapid increase in kinetic energy; (2) sharp reduction in kinetic energy as slurry mixes with water, coherence and hydroplaning are reduced, and the influence of the shear stress increases; (3) slurry mixed very well with water, turbidity current dominates the kinetic energy dissipation. High-density slurry dissipates quicker in the last two stages. In stage 3, which dominates the temporal evolution of the debris flow, the Froude number is lower than 1, the flow thins and elongates, and the deposition process of submarine debris flows is dominated by gravity, and the difference of morphology of the different cases become clear. [ABSTRACT FROM AUTHOR]