The precast concrete (PC) pile reinforced with cemented soil (PCCS) is a novel composite pile system, formed by installing a PC pile into the centre of a deep mixing (DM) column. This technology has been extensively applied to support highways, railways and buildings constructed on soft soil foundation. However, PCCSs with short cores often struggle to penetrate deep enough to reach stronger bearing strata within thick soft subsoil layers, leading to inadequate reinforcement and poor settlement control. To address these limitations, this study proposes the use of a PCCS with long-core as a promising solution for reinforcing deep soft soil subgrades. Based on the field tests results, the bearing mechanism and performance of the long-core PCCS composite foundation under embankment loads were investigated through numerical analysis. Additionally, the soil arching effect in embankments supported by the PCCS with long-core, along with variations in vertical stress and horizontal soil pressure coefficients along the height of the embankment were elucidated. The results indicate that the stabilized stresses at the pile top and in the surrounding soil are 266.2 kPa and 33 kPa, respectively, yielding a stabilized pile-to-soil stress ratio of 8.1. The critical height of the embankment corresponds to 1.15 times the net pile spacing. Maximum settlements observed at the pile tops and the surrounding soil were 15.2mm and 47.5mm, respectively. The tensile stress within the geocell exhibited a symmetric, repetitive pattern along the horizontal direction, with the peak tensile force occurring near the embankment shoulder. These findings underscore the effectiveness of long-core PCCSs in enhancing load-bearing capacity and controlling settlement over soft soil foundations.

Optical fiber Fabry-Perot (F-P) sensor is a high-sensitivity sensor based on fiber-optic sensing and interference principle, which can be used in sensing of displacement, stress, strain, temperature, and so on. In this article, we propose an optical fiber F-P displacement sensor based on a flexible hinge structure, and develop a compact microsized displacement sensor with high sensitivity to measure microdisplacement, with a size of 15x10x2.4 mm(3). On the basis of mathematical model, we used an optimization algorithm to globally optimize the displacement sensitivity and obtained the optimal dimensional parameters of the sensor structure. We used ANSYS to simulate and analyze our sensor, and the results were basically consistent with the theoretical results. Then, we encapsulated and pasted the F-P cavity with a small-diameter glass capillary, and the F-P was fabricated with an optical fiber at one end and a fiber Bragg grating (FBG) for temperature measurement at the other end. The final experimental tests showed that the sensor had good linearity and displacement sensitivity can reach up to 64 100 pm/mm. The temperature sensitivity is 10.04 pm/degrees C for FBG and 33.04 pm/degrees C for F-P.

Precast concrete pile reinforced by cemented soil (PCCS) is a novel composite pile widely used for soft soil improvement, particularly in supporting embankments. This technique involves installing a PC pile (inner core) at the center of a deep mixing (DM) column (outer core), effectively combining the advantages of both technologies. However, there remains a lack of feasible methods for calculating the settlement of the PCCS with long-core-supported embankment, especially in deep soft soils. This study develops an analytical model designed to calculate the settlement of the PCCS with a long-core composite foundation under embankment loads. The proposed analytical model simplifies the embankment load to a uniformly distributed load acting on a composite foundation and then analyzes a pile body and underlying soft soil unit within the influence range of a single pile. The model then divides the unit into three regions-composite section, noncomposite section, and firm soil layer-and calculates the total settlement separately for each region. The models specifically treat the inner-core, outer-core, and the surrounding soil as isotropic linear elastic materials. By employing the Coulomb friction model, the distribution of lateral friction resistance between the inner and outer core, as well as the pile-soil interface, is analyzed, with the cemented soil and the surrounding soil in the composite section considered composite materials. The effectiveness of the analytical model is validated through comparison, with results from numerical analysis with the discrepancy being within 13%. Based on the analytical model, a sensitivity analysis explores the impacts of the key parameters of the DM column on the settlement of the PCCS with a long-core-supported embankment. The findings can be used for engineering design and optimization of this type of embankment.

Modular multilevel converter is an attractive solution in medium or high voltage applications, and voltage balancing is one of the most significant technical problems especially for CPS-PWM based MMCs. To solve this problem, in this article, an inherent switching reallocated CPS-PWM is proposed for MMC. Based on arm current directions, switching states of submodules (SMs), voltage sorting and carrier sorting results, proposed method divides SMs and carriers into inserting and bypassing groups for each, enabling switching reallocation within these four cooptimized groups to inherently balance capacitor voltages. This effectively prevents additional switchings. Besides, most computations of the proposed CPS-PWM are logical operations implemented in FPGA, so proposed method can achieve reallocation frequency equal to sampling frequency. Unlike other CPS-PWM based methods for voltage balancing, the inherent switching reallocated CPS-PWM not only has superior converge speed in dynamic processes which accommodate a wide power range, but also has excellent balancing accuracy especially considering capacitance differences. Owing to appropriate reallocation principles, the proposed CPS-PWM has lower switching loss compared to existing carrier reallocation methods. Finally, the feasibility and superiority of the proposed method are validated by simulation and experiment results.

The development of innovative and cost-effective pile-supported embankment technologies is an intrinsic demand driving the advancement of soft ground improvement techniques. A significant innovation within this approach is the penetrated precast concrete pile reinforced with cemented soil (PCCS) combined with partially penetrated deep mixing (DM) columns for layered ground treatment, in which the PCCS is created by embedding a precast concrete (cored) pile within a DM column. This study aims to develop a numerical unit model for this type of pile-supported embankment, denoted as a PCCS multi-pile composite foundation-supported embankment, providing insights into the soil arching effect within the embankment and elucidating the variation patterns of vertical stress and the horizontal earth pressure coefficient along the embankment height. Based on Hewlett’s hemispherical arch model, a refined composite soil-arching analytical model is proposed specifically for the multi-pile composite foundation-supported embankment. The findings reveal that the critical height of the embankment is 1.05 times the net pile spacing, with embankment height showing minimal influence on the height of internal and external arches. In contrast, an increase in the embankment filling modulus significantly affects the fan-shaped arches between adjacent piles, while its impact on spherical arches remains limited. The stress ratios between the PCCS-soil and DM column-soil derived from the three-dimensional composite arch model differ from the measured results by 7.3 % and 8.5 %, respectively, confirming the model’s accuracy.

Corrugated steel structures have been found to have outstanding blast resistance and enable rapid attenuation of blast waves in tunnels. The propagation of blast waves is influenced by the structural parameters and duration of blast waves at the entrance in tunnels, forming various blast loadings. To investigate the effect of duration at the entrance in corrugated steel-lined tunnels, trinitrotoluene (TNT) and aluminized explosives were used to obtain various durations of blast waves at the entrance in testing. A series of simulations was designed and verified, in which the effect of duration at the entrance was analyzed under the same scaled distance. The variation caused by duration and linings on loading curves was analyzed, and the influence mechanisms of the duration at the entrance and the linings on blast waves were discussed using pressure nephograms. Meanwhile, the distribution of blast loadings under different conditions was obtained. A prediction model for the distribution of peak blast loading in corrugated steel-lined tunnels (CSLTs) was established, considering the duration at the entrance. The results showed that corrugated steel linings destroyed the reflection conditions on a flat wall surface, resulting in longer periods of loading fluctuations. A longer duration of blast waves at the entrance extended the distribution of blast loadings and even resulted in a significantly higher peak loading appearing after the first peak near the entrance, altering the characteristics of loadings.

Two-dimensional transition metal carbide/nitride MXenes have become a hot topic in the field of lithium-ion energy storage due to their unique surface chemistry and excellent electronic conductivity. However, electrodes made of multilayer MXenes suffer from low capacity, poor cycling performance, and slow lithiation kinetics. In this paper, the MoP2@Ti3C2T x composite was prepared by adsorbing Mo cations on the surface of Ti3C2T x followed by phosphatization. The uniformly distributed MoP2 nanostructure effectively increases the layer spacing, enlarges the specific surface area, and improves the structural stability of the material. At the same time, MoP2 and Ti3C2T x are connected by a P-O bond, which accelerates the diffusion and migration of lithium ions and the charge transfer, and the strong covalent Ti-O-P bond can cause rapid charge transfer and stabilize the structure of the material. The electrochemical activity of MoP2 nanostructures also provides more active sites for lithium ions. The presence of the lamellar structure of Ti3C2T x also inhibits to some extent the expansion of the transition metal phosphide volume with the cycling process, thus realizing more excellent lithium storage capacity. 1/2 MoP2@Ti3C2T x material has a high reversible capacity of 165.7 mAh g-1 (172% improvement over the original material) at a current density of 3000 mA g-1. The assembled 1/2 MoP2@Ti3C2T x //AC Li-ion hybrid capacitor LIC has 85.5% capacity retention after cycling at a current density of 1500 mA g-1. The ability of the assembled full battery to illuminate light-emitting diode (LED) light bulbs further confirms that the electrochemical reliability of the device meets the requirements of real-world applications. The results demonstrate that the strategy of constructing in situ-grown MoP2 nanostructures can effectively improve MXene high-energy-density applications in lithium-ion energy storage.

Traffic engineering such as tunnels in various altitudinal gradient zone are at risk of accidental explosion, which can damage personnel and equipment. Accurate prediction of the distribution pattern of explosive loads and shock wave propagation process in semi-enclosed structures at various altitude environment is key research focus in the fields of explosion shock and fluid dynamics. The effect of altitude on the propagation of shock waves in tunnels was investigated by conducting explosion test and numerical simulation. Based on the experimental and numerical simulation results, a prediction model for the attenuation of the peak overpressure of tunnel shock waves at different altitudes was established. The results showed that the peak overpressure decreased at the same measurement points in the tunnel entrance under the high altitude condition. In contrast, an increase in altitude accelerated the propagation speed of the shock wave in the tunnel. The average error between the peak shock wave overpressure obtained using the overpressure prediction formula and the measured test data was less than 15%, the average error between the propagation velocity of shock waves predicted values and the test data is less than 10%. The method can effectively predict the overpressure attenuation of blast wave in tunnel at various altitudes.

Due to the wide application of modular multilevel converters (MMCs) in hybrid AC/DC distribution grids, enhancing the fault ride-through (FRT) capability of MMC is essential to improve the reliability of the hybrid AC/DC distribution grids. In this paper, an individual arm capacitor voltage control based comprehensive FRT strategy is presented. To balance the active power transmitted in each arm, an individual arm capacitor voltage control (IACVC) method is presented to regulate arm capacitor voltage stable to their reference. The decoupled control for positive pole and negative pole is achieved. Besides, an improved arm current references calculation (ACRC) method is proposed. During pole-to-ground (PTG) fault, the current of the fault pole is reduced to 0, and the healthy pole still transmit rated active power with rated voltage. In addition to, the adverse effects of AC side voltage imbalance are eliminated. The presented control strategy is verified by simulations and experiments on a MMC prototype.

The non-scaling effect on the penetration depth of rigid projectiles is an important issue that must be considered when extending the results of scaled experiments to prototype scenes. In this study, the evolution of the stress and strain of the target under penetration was analyzed. Expressions for the penetration resistance and penetration depth were obtained based on the conservation equation and continuity condition of the target. The penetration coefficients that characterize the nose shape, target resistance, and non-scaling effect were defined. Simplified calculation methods for the coefficients within the range of rigid projectile penetration were developed. Two methods for estimating the target parameters are proposed. The results show that the non-scaling effect is related to the failure process of the target and depends on the ratio of cavity radius to comminuted region radius. The nose shape coefficient can be approximated as a linear function of the length-to-diameter ratio of the nose. The nose-shape coefficient of a flat-nosed projectile is 0.57. The caliber coefficient is related to the projectile diameter and reflects the non-scaling effect, which increases with the projectile diameter. A practical formula for calculating the penetration depth of rigid projectiles considering the non-scaling effect is also proposed. This formula is in good agreement with penetration experiments on rock and concrete.

2D layered Ti3C2Tx materials attract great attention in lithium-ion energy storage field due to their unique surface chemistry properties. However, the low capacity accompanied by sluggish lithiation kinetics of electrodes made from multi-layer MXene has limited their further application for lithium ion storage. The key challenge to overcome the abovementioned issue is to increase the concentration of active sites in the MXene electrode for lithium storage and to reduce the lithium ion diffusion resistance. In this study, N,P-MXene composites were prepared by hydrothermal construction of N,P elemental functional groups in multilayer MXene. The uniformly distributed N,P elemental functional groups effectively enhance the interlayer spacing of the material and expand the specific surface area. The in situ EIS test shows that the N,P doping effectively reduces the SEI film formation resistance and improves the lithium ion diffusion coefficient. Meanwhile, DFT calculations demonstrate that P-doped functional groups can effectively improve MXene conductivity, reduce lithium adsorption energy, and provide more active sites for lithium storage. The electrochemical activity of P-containing functional groups provides additional lithium ion active sites for lithium storage. After N,P doping, the MXene material with increased layer spacing (N,P-MXene) exhibits a high reversible capacity of 126.7 mAh/g at 3000 mA/g (similar to 232 % of the original value) and an excellent outstanding cycling stability for 1700 cycles at 150 mA/g for lithium ion storage. By coupling the N,P-MXene negative electrode to the LiFePO4 positive electrode, the assembled lithium-ion batteries can provide a high specific capacity of over 300 mAh/g.

This is an article in the field of mineral processing engineering. A microfine-ultramicron refractory gold ore containing carbon and arsenic is a medium-high temperature hydrothermal altered rock type gold ore in the compressive structural fracture zone of mylonite in Qinghai Province. The main sulfide is pyrite (3.51% content), followed by arsenopyrite (1.10% content) and argillaceous mineral content 37%. Most of the gold is microscopically or ultramicroscopically dispersed in sulfide minerals such as pyrite and arsenopyrite. Gangue and limonite contain 14.43% and 8.20% of gold, respectively, and 81.04% of gold less than 0.005 mm. Based on the research of process mineralogy, this paper further optimized the flotation process parameters and reagent system, and carried out the research of the combined process of strong agitation and selective grinding, which alleviated the contradiction between fine grinding and slime of ore to a certain extent, and obtained the test indexes of gold grade of 33.06 g/t and gold recovery of 85.70%, achieving a great breakthrough in the original process index.

To achieve the fault ride through (FRT) operation of DFIG-based wind turbines, various improved control methods have been proposed. However, it is difficult to reveal their essential relations and quantitatively evaluate their performance differences, due to the wide assortment of solving ideas and control structures. To cope with this issue, this paper revisits the FRT control from a new perspective of rotor-port impedance characteristics (RPIC). First, a unified RPIC model of nine typical FRT controls is established and it is found that their RPIC are manifested as the pure inductance, but the inductance values are different in the phase sequence. Subsequently, the influence of RPIC on FRT performance is analyzed and some practical design guidelines for FRT control are given. On this basis, nine typical FRT control methods are quantitatively evaluated and compared in terms of six key performance dimensions. Moreover, the study contributes to the understanding, analysis and redesign of FRT control, and the RPIC perspective features the definite physical meaning and simple. Finally, the analysis is validated by the experiments.

Crowbar is the most widely used low voltage ride-through (LVRT) solution for doubly-fed variable speed pumped storage (VSPS) unit. However, the conventional crowbar solution suffers from excessive crowbar activation period when applied to large-scale VSPS unit, which leads to the disadvantages of high reactive power absorption and huge electromagnetic torque oscillation. To solve the issue, this article analyzes the condition of crowbar release from the perspective of system controllability. Based on it, a hybrid LVRT control strategy combining crowbar and dynamic demagnetizing control is proposed. In this strategy, the crowbar operational duration can be minimized by optimizing the demagnetizing coefficient dynamically. Moreover, the objective of reactive power support or electromagnetic torque oscillation suppression can be achieved to enhance the transient performance of VSPS unit. Finally, the proposed hybrid LVRT control method is validated by the experiments.

Dynamic compaction is a method of ground reinforcement that uses the huge impact energy of a free-falling hammer to compact the soil. This study presents a DC method for strengthening coral reef foundations in the reclamation area of remote sea islands. Pilot tests were performed to obtain the design parameters before official DC operation. The standard penetration test (SPT), shallow plate-load test (PLT), and deformation investigation were conducted in two improvement regions (A1 and A2) with varying tamping energies. During the deformation test, the depth of the tamping crater for the first two points’ tamping and the third full tamping was observed at two distinct sites. The allowable ground bearing capacity at two disparate field sites was at least 360 kPa. The reinforcement depths were 3.5 and 3.2 m in the A1 and A2 zones, respectively. The DC process was numerically analyzed by the two-dimensional particle flow code, PFC2D. It indicated that the reinforcement effect and effective reinforcement depth were consistent with the field data. The coral sand particles at the bottom of the crater were primarily broken down in the initial stage, and the particle-crushing zone gradually developed toward both sides of the crater. The force chain developed similarly at the three tamping energies (800, 1500, and 2000 kJ), and the impact stress wave propagated along the sand particles primarily in the vertical direction.

Steel is widely used in building structures, and the constitutive model that describes the steel's response to load is an essential component of structural mechanics analysis. This paper aims to investigate the thermoplastic behavior of steel at elevated temperatures. Based on the classical elastoplastic mechanics framework, this study introduces a generalized Mises yield criterion derived from energy theory, which takes into account the temperature effect. In conjunction with relevant assumptions, hardening condition, flow rule, the generalized Hooke's law, and consistency condition, we derive a novel incremental thermoplastic constitutive model for steel. And the new thermoplastic constitutive model's rationality is further verified by utilizing high-temperature steady-state tensile test data. It is encouraging that this new model can accurately describe the mechanical behavior of steel in high-temperature environment such as fire, which is of significant importance for fire safety design of building structures.

Two-dimensional titanium carbide (Ti3C2Tx) is a promising lithium storage anode material owing to high conductivity and larger redox sites. However, Ti3C2Tx exhibits lower specific capacitance in an organic system due to the passivation effect of surface terminals and also suffers from restacking issues with long-term cycles. Herein, the material composed of a molybdenum-phosphorus compound and Ti3C2Tx nanosheets is reported through thermal decomposition of polyoxometalate. The derived molybdenum phosphide provides greater free space to afford the volume change and facilitate lithium-ion transport. The unique diphosphorus centers are favorable to improving lithium storage capacity and electrochemical reaction. In addition, molybdenum oxide with abundant oxygen vacancies not only accelerates the electronic and ionic conductivity but also provides more active sites. The optimized 0.1PMA@Ti3C2Tx composite delivers a superior specific capacity of over 500 mAh g(-1) at 30 mA g(-1) and maintains the specific capacity of 155.6 mAh g(-1) at 750 mA g(-1) after 400 cycles. The lithium-ion capacitor based on the 0.1PMA@Ti3C2Tx anode material presents a wonderful energy density of 153.95 Wh kg(-1) at a higher power density of 4696.8 W kg(-1). This work provides a strategy for high-capacity lithium storage of MXene materials and opens up an idea for the application of polyoxometalates in lithium storage.

The AC line fault near the LCC-HVDC inverter station usually causes commutation failures (CFs). The accuracy of power frequency phasor extraction will be affected by the distortion of fault voltage and current waveform, resulting in deterioration of power frequency phasor distance protection performance. The adaptability of the traditional power frequency phasor distance protection is analyzed by simulation. Then, according to the AC line RL model, a time domain distance element based on the polarity comparison of the instantaneous voltage at the protection installation and the instantaneous voltage of the setting point compensation is proposed. The proposed time domain distance element is not affected by the nonlinear output characteristics of the inverter station. Finally, the effectiveness of the time domain distance protection is verified by simulation.

Dynamic mechanical performance tests were conducted on concrete materials cooled at different temperatures using Φ74mm large-diameter split Hopkinson pressure bar (SHPB). Through these tests, this paper investigates the stress strain relationship and fracture modes of concrete at different temperatures and strain rates. The dynamic compressive strength, damage variables, damage mechanism and damage evolution equation were analyzed. The results showed that excessive temperature would cause damage to concrete materials. In the range of 100℃-200℃, the dynamic compressive properties of concrete declined only to a limited extent. However, when the temperature reached 400℃ and above, its mechanical properties declined significantly and the broken shape serious. Excessive crack expansion also inhibited the growth of damage variables to a certain extent. The relationship between damage variables and plastic strain was given based on the above experimental data. The damage evolution equation was applied to the constitutive relationship of concrete. By comparing with the test results, the obtained damage evolution equation can accurately simulate the mechanical properties of concrete under different temperatures and different strain rates.