Abstract:Extreme environments such as low temperature, high humidity, high wind speed, high salinity, extreme daytime, and extreme nighttime can easily lead to icing on the surface of ships, low-altitude vehicles and other near-sea equipment, which seriously affects the normal operation of such equipment. To cope with the ice hazards brought by the complex environments, scholars both domestically and internationally have conducted numerous comparative experiments and mathematical modeling studies on icing detection and prediction methods, as well as anti-icing, de-icing, and ice-breaking technologies. This paper provides an analysis and summary of the existing research progress in the field of ice-related studies. Results show that icing prediction methods primarily rely on empirical, theoretical and numerical models, with theoretical models having an accuracy below 50% while numerical models achieve an accuracy above 60%. Ice detection mainly adopts two methods of observation and detection, in which the measurement accuracy of the average ice thickness of the observation method and detection method can reach ±0.038 mm and ±0.05 mm, respectively. Ice cover on the surface of polar equipment originates from wave droplets, rain droplets and the atmosphere, with wave droplets accounting for up to 90%. Ice prevention technologies include passive and active methods, with the former having low energy consumption and short service life,and the latter being more efficient but with complex device setups. The combination of both remains a future development trend. In polar regions, ice-breaking for waterborne vessels primarily involves ramming, crushing, and pressure ridging techniques, while ice-breaking for submarines beneath the ice utilizes mechanical squeezing, torpedo blasting, laser ice melting, and other direct ice-breaking methods or coupled techniques such as "weak ice first, then ice-breaking" coupling techniques. Based on the analysis of icing prediction and detection methods, and anti-icing, de-icing and ice-breaking technologies in polar low-temperature environments, further optimization directions for existing methods and technologies are proposed. These insights aim to provide references for the development of ice disaster protection and control technology for the carrier equipment and engineering equipment in complex low-temperature environments.

Abstract:Gas-solid bubbling fluidization system exhibits non-equilibrium, non-linear, and multiscale characteristics. In order to study the complex flow behavior inside the fluidized bed with clouded bubbles, this paper conducts numerical simulations on a three-dimensional bubbling fluidized bed using the clouded bubble-based multi-scale drag model. The variations of particle velocity and concentration at different positions are obtained. The time fluctuation sequences of particle concentration are processed by wavelet transformations. The particle fluctuation and bubble oscillation at the axial and radial positions are compared. The results indicate that the clouded bubble-based multiscale drag model can provide good predictions of flow behaviors in the bed. A core-annulus flow pattern where the particles rise in the center and fall along the walls is shown in the bed. Compared to the fluctuation of particle velocity, the fluctuation of particle volume fraction appears a higher frequency, which becomes more difficult to discern. The wavelet analysis reveals that the fluctuation intensities of both particle phase and bubble phase increase with bed height but gradually weaken towards the wall. The stronger fragmentation and aggregation behaviors of bubbles in a bubbling fluidized bed with Geldart A particles results in more uniform distribution of bubbles in the radial direction and smaller radial difference of energy fraction. Furthermore, increasing the inlet gas velocity enhances the non-uniformity of particle radial distribution and the energy fraction of particle and bubble fluctuation signals.

Abstract:In dynamic thermal management of multi-heat source systems, full-domain thermal analysis and real-time assessment are core elements. However, conventional discrete measurements and reconstruction techniques struggle to capture dynamic evolution of the temperature field in real time. Therefore, a full-domain temperature field reconstruction strategy based on discrete measurements is described. The eigenbasis functions of the temperature field are extracted by singular value decomposition (SVD), and the Gray Wolf Optimization (GWO) is introduced to optimize the layout of discrete sensors. A coefficient matrix for the full-domain temperature field reconstruction is computed by combining the eigenbasis with the discrete measurements. The reliability of this approach is validated based on numerical reconstruction experiments of four heat source systems. The results indicate that after sensor placement optimization, the level of theoretical reconstruction error for the four heat source systems is significantly reduced by at least three orders of magnitude. Moreover, in the temperature field reconstruction of a typical PCB multi-heat source system, comparison with numerical experiment results shows an average error of 0.12 ℃ and a root-mean-square percentage error below 1%. The reliability of the strategy in practical applications is validated, providing a reference for thermal analysis and control of electronic equipment.

Abstract:Wastewater treatment is a significant contributor to greenhouse gas emissions, and the generation and emission of nitrous oxide (N₂O) in wastewater biochemical treatment have become a hot research topic. The production mechanism of N₂O generation is complex, and emission characteristics vary widely depending on the processes and operating conditions. While numerous studies have investigated N₂O generation and emission in wastewater biochemical treatment, there is a lack of research on N₂O emission reduction strategies based on the analysis of N₂O generation pathways. This paper systematically discusses the primary pathways of N₂O production in wastewater biochemical treatment process, including NH₂OH oxidation, nitrifier denitrification, heterotrophic denitrification, and abiotic pathways. The factors influencing N₂O production are described, including wastewater characteristics such as carbon source, nitrogen source, salinity, process parameters such as dissolved oxygen, reflux ratio, and the distribution of microbial communities. This paper summarizes corresponding mitigation strategies, highlighting the effective reduction of N₂O production and emission through process optimization, coupling different biochemical processes, and enriching microbial communities with low N₂O production levels. Current research challenges and future development directions are assessed, emphasizing that model construction remains an effective method to study N₂O production and emission biochemical treatment of wastewater, with broad prospect in N₂O recovery research.

Abstract:The issue of antibiotic pollution in aquatic environments has become one of the major challenges in the field of environmental protection. These pollutants not only cause serious ecological toxicity effects on aquatic organisms, disrupting the balance of aquatic ecosystems, but may also induce the production of resistance genes, posing serious risks and potential threats to ecological safety. Advanced oxidation technology has attracted much attention due to its efficient degradation ability of antibiotics. This technology generates strong oxidizing free radicals, rapidly oxidizes and decomposes antibiotic components, thereby achieving the goal of removing antibiotics. In recent years, this technology has been widely studied and gradually applied in practical application of antibiotic-containing wastewater treatment. However, in the process of advanced oxidative degradation, antibiotics produce a large number of intermediate products due to incomplete degradation and mineralization. The ecological toxicity of these intermediate products cannot be ignored, as they may also have negative impacts on aquatic ecosystems. The research on the ecotoxicity of intermediate products is a hot topic in this field, and it is also crucial for the safe application of advanced oxidation technologies in the future. This article systematically summarizes and categorizes the mechanisms and technical characteristics of various typical advanced oxidation technologies for degrading antibiotics.It focuses on introducing the research progress on the ecological toxicity of antibiotic advanced oxidation degradation products, and systematically analyzes the future development trends in this research direction.

Abstract:In response to issues of low efficiency, single purification capacity and potential secondary pollution associated with existing manned spacecraft air filtration and purification technology, an integrated technology route of man-machine coexistence based on YMn₂O₅ mullite catalyst synergized with ozone catalytic oxidation was proposed. The YMn₂O₅ catalyst prepared by citric acid gel-sol method was characterized by X-ray powder diffractometer and scanning electron microscope. The results revealed that the catalyst′s surface possesses abundant active sites, which are conducive to the production of a large number of reductive substances under the synergistic effect of ozone. This technology route enables efficient, green and low-energy consumption degradation and elimination of volatile organic compounds, viruses, bacteria and other microorganisms in the air through the highly active O* produced during the reaction process. Based on this technology route, a prototype equipment integrating air purification and virus elimination (Mcaton) was designed and produced by combining 3D modeling and 3D printing technologies. For different volatile organic pollutants and virus aerosols in the air, the purification and elimination effects of the prototype on gas pollutants and virus aerosols were tested in a sealed chamber, which validated the ability of the Mcaton technology to achieve rapid and efficient purification of various volatile organic pollutants and elimination of viruses and bacteria.

Abstract:Surface functional groups are important components of biochar, and their species and content have a great influence on the properties, performance and applications of biochar. Current quantitative analysis methods for surface functional groups in carbon materials is the Boehm titration method with large sample consumption, multiple operation steps and time-consuming procedures. To address these limitations, we developed a quantitative analysis method for mass molar concentration of trace surface functional groups content of biochar by constructing a proton depletion model, writing a Python program, carrying out acid-base titration experiments, and debugging model parameters. This method enables rapid measurement of the surface functional group content and their corresponding acid dissociation constant pK_afor trace amounts of biochar. By adjusting parameters and training the model, the mass range of biochar applicable to this method was analyzed. It was found that the E_MS of the model was less than 0.002 when the sample mass was 50 mg, and the E_MS of the model was less than 0.001 when the iteration number was set to 20 000. This indicates a high level of accuracy of the measurement results. The relative error between the total amount of surface functional groups on biochar determined by this method and the Boehm titration method was within 2%. In addition, this method reduces biochar used by 95%, shortens the measurement time by more than 10 hours, and greatly simplifies the experimental procedures. It meets the technical requirements for micro-trace and rapid quantitative analysis of surface functional groups on biochar.

Abstract:LiInSe₂ crystal is a semiconductor material used for thermal neutron detection at room temperature. In the paper, red and yellow LiInSe₂ crystals are successfully synthesized via the vertical Bridgman method after optimization of the synthesis process and the crucible material used. The crystal structural characteristics, relative content of elements, optical properties and macroscopic inclusion phase of the yellow crystals are studied. According to the results, the yellow LiInSe₂ polycrystalline material with controllable composition can be stably obtained by improving synthesis process and adding 3% of Li and 0.002 7 mol of Se as additional components. Meanwhile, it is found that utilizing a graphite crucible and implementing appropriate crucible rotation techniques, such as accelerated crucible rotation technique (ACRT), enables the production of high-quality LiInSe₂ crystals for neutron detection. Calculated by the transmission spectrum, the optical bandgap widths of the yellow crystals grown by different methods are approximately 2.8 eV. The density of the precipitates in the middle section of the yellow growing crystal is 3.50×10³/cm², and the size of the inclusion phase is about 510 μm.

Abstract:To investigate the effect of the near-surface mounted (NSM) technique using shape memory alloy (SMA) bars on the seismic performance of reinforced concrete columns, six reinforced concrete (RC) columns strengthened with near-surface mounted (NSM) shape memory alloy (SMA) bars were designed and fabricated to investigate the failure process and failure modes of SMA-reinforced concrete columns through low-cyclic reversed loading tests. The effect of SMA reinforcement ratios, axial compression ratio and CFRP wraps on the seismic performance of the columns, including hysteresis performance, displacement ductility, stiffness degradation, and energy dissipation capacity of those columns, were analyzed. Additionally, the curvature distribution of reinforced concrete columns strengthened with near-surface mounted SMA bars was analyzed based on the displacement field provided by the digital image correlation (DIC) method. Results indicated that the failure of concrete columns reinforced with SMA bars results from the yield of longitudinal tension reinforcement and concrete crushing at the column base, forming plastic hinges. This primarily exhibits a ductile failure mode. Under the same axial compression ratio, the load bearing capacity of the strengthened columns increased by 51.2% to 70.2% compared to ordinary RC column. Displacement ductility and the cumulative energy dissipation of the columns were also increased, significantly enhancing the seismic performance. As the amount of SMA reinforcement increased, the energy dissipation capacity, the length of the plastic hinges and the ultimate displacement of the strengthened columns greatly improved. The bearing capacity of the strengthened columns did not show a significant decrease before the drift ratio reached 1/50. As the axial compression ratio increased to 0.4, the peak load and energy dissipation capacity increased, while the ductility decreased significantly. The deformation performance and energy dissipation capacity of the columns wrapped with CFRP improved obviously. Additionally, based on the plane sections assumption, a theoretical calculation model that predicts the flexural bearing capacity of the SMA bar strengthened columns was established. The calculated results were in good agreement with the test results.

Abstract:In order to study the variation of mechanical properties of cold-formed thin-walled steel materials under the coupling effect of high temperature and corrosion, a series of experiments involving neutral salt spray corrosion, high-temperature calcination, cooling and tensile tests were conducted. The mechanical properties of 180 S280GD+Z cold-rolled steel sheets with thickness of 1.5 mm, which underwent accelerated corrosion for 0-60 d and high temperature calcination from 20 to 800 ℃, were studied under cooling in air and cooling in water. The results indicate that under the coupling effect of corrosion and high temperature, the surface characteristics and failure modes of the steel are greatly affected by the cooling methods. When the corrosion rate is less than 6%, the corrosion has little impact on the mechanical properties of S280GD+Z steel. When the fire temperature is below 600 ℃, the fire temperature and cooling methods have insignificant effects on the yield strength and ultimate strength of S280GD+Z steel. However, under the coupling effect of corrosion and high temperature, when the fire temperature exceeds 600 ℃, the strength degradation of steel becomes the dominant factor affecting the strength of steel. The cooling method has a significant impact on the elongation of the steel. Under natural cooling conditions, the elongation increases and then decreases with the increase in fire temperature. Under immersion cooling conditions, the elongation shows an overall decreasing trend with the increase in fire temperature. A mathematical model was established to quantify relationship between the mechanical parameters of S280GD+Z steel and the corrosion rate and temperature under the coupling effect of corrosion and high temperature. Based on a simplified secondary plastic flow model, a constitutive model for S280GD+Z steel under the coupling effect of corrosion and high temperature was established.

Abstract:In order to study the seismic performance and deformation index limits of a new assembled shear wall, based on the seismic performance test of the new assembled shear wall made by the research group, a total of 216 wall models with different shear span ratio, axial compression ratios and longitudinal reinforcement ratios of edge members were designed using factor analysis method. The corresponding single push performance experiment was performed to investigate the structrual behavior. Based on the recognition of failure modes using finite element analysis, the failure modes were divided into three categories: bending failure, bending shear failure and shear failure. A criterion for classifying the failure modes of the shear wall was put forward. Referring to "Code for seismic design of buildings" (GB 50011—2010), six performance states were defined for flexural failure and flexural-shear failure, while two performance states were defined for shear failure. Based on the strain and bearing capacity of concrete and steel bars under the limit state of the component, the criterion of the performance state of the wall was determined. Finally, regression equations were derived through linear regression to determine the limit values of plastic displacement angles for componments under bending failure, bending shear failure and shear failure modes. Furthermore, deformation index limites with 90% guarantee rate were proposed for each failure mode, providing a reference for performance-based seismic design of new assembled shear walls.

Abstract:After the structural model is discretized by the finite element method, it may introduce false high-frequency components that can adversely affect the structural dynamic response of the structure. Therefore, it is necessary to introduce numerical damping into the integration algorithm to effectively suppress these false high-frequency componments. Based on a semi-explicit integration formulation, this paper proposes an unconditionally stable semi-explicit integration algorithm with controllable numerical damping by matching the characteristic equation coefficients of the amplification matrix of the implicit ρ∞-Bathe algorithm. The new semi-explicit (NSE)-ρ∞ algorithm controls the numerical damping of the integration algorithm by two free coefficients ρ∞ and γ, and does not require weighted equation of motion. The numerical characteristics of the new algorithm, such as stability, accuracy, period elongation and amplitude decay, are analyzed. It is found that the new algorithm is unconditionally stable for both linear elastic and nonlinear stiffness softening systems. Through representative numerical examples, the new algorithm is compared with two other unconditionally stable explicit integration algorithms with controllable numerical damping. The analytical results demonstrate that the new algorithm is more effective in suppressing the spurious high-frequency components.

Abstract:A slender steel frame system composed of steel members with a high width-to-thickness ratio was adopted to achieve lightweight steel residential structures. By carefully selecting the section configuration the system achieves a balance between load-carrying capacity and ductility. To study the seismic performance of the slender steel frame system, two full-scale frames are constructed. These frames include members with S1, S3 and S4 configurations, varying in their cross-section width-to-thickness ratios. The frames are subjected to cyclic tests to analyze their failure mechanisms, hysteresis curves, load-carrying capacity, ductility, and energy dissipation capacity. The test results indicate that both specimens were mainly damaged by local buckling deformation at the beam end and column bottom region, with the initial concentrated damage occurring at the beam ends, leading to the specimens reaching their ultimate bearing capacity state. In addition, the sequence and degree of buckling deformation significantly influence the seismic performance of the frames. The slender steel frame structure, when combined with components of different width-to-thickness ratios, can achieve lightweight design while maintaining satisfactory ductility and plastic energy dissipation capacity. Finally, based on the experimental results, finite element models of the specimens were established using ABAQUS. Parametric analysis was conducted to determine the failure mechanisms and corresponding internal force variations of the buckling sections under different section configurations.

Abstract:Aiming to address the challenge of simultaneously ensuring both level alignment and sufficient seismic performance in the case of wing flange in externally extended cantilever spliced full-bolted connection joint beam, a novel stepped full-bolted connection beam-column joint is proposed. Low-cycle reciprocating loading tests were conducted on cantilever-type joint specimens with two different end-plate connection forms. A detailed analysis of failure modes, hysteresis curves, skeleton curves, bearing capacity, ductility, and energy dissipation capacity of the specimens was carried out to investigate the seismic performance of this type of joint. Furthermore, the influence of the connection form between the thick end-plate and U-shaped buckle on the seismic performance was analyzed. The test results indicate that different connection forms have a minor impact on the elastic segment performance of the joint but a significant impact on the ultimate failure mode of the joint. The stepped joint with a thick end plate exhibits good bearing and deformation performance, while the U-shaped buckle joint shows poor seismic performance. A finite element model was established and validated using the thick end-plate specimen. By changing parameters in the finite element software, the influence of end-plate thickness on the seismic performance of the new joint was explored. It was found that as the end-plate thickness decreases, the initial stiffness, bearing capacity, and energy dissipation capacity of the joint decrease accordingly.

Abstract:To investigate the seismic performance of reinforced concrete (RC) beams with corroded steel bars, artificial climate accelerated corrosion tests and quasi-static loading tests were conducted on eight RC beams. The influence of corrosion level and stirrup ratio on the failure process, load-carrying capacity, deformation capacity, and energy dissipation capacity of RC beams was analyzed. Additionally, SFI-MVLEM elements and zero length section elements were used in OpenSees to simulate the flexural-shear deformation and bond-slip deformation of the beams. Model parameters were calibrated based on the principles of optimal load-carrying capacity and energy dissipation capacity. The results show that as the corrosion rate of the longitudinal bars increase from 0 to 6.8%, the shear failure characteristics of the specimens become more severe, and the load-carrying capacity, ductility, and plastic rotational capacity decrease by 6.7%, 5.1%, and 11.5% respectively. As the stirrup ratio increases, the deformation capacity, ductility, and load-bearing capacity of the specimen gradually improve. For a unit increase in longitudinal bar corrosion rate, the peak load, ductility coefficient, and plastic rotation angle of specimen DL-4 decrease by 1.48%, 1.79%, and 3.04% respectively compared to specimen DL-3 with the same stirrup ratio. Similarly, for specimen DL-8, the peak load, ductility coefficient, and plastic rotation angle decrease by 1.77%, 3.20%, and 6.97% respectively compared to specimen DL-7 with the same stirrup ratio, indicating a coupling effect between the corrosion rate and stirrup ratio parameters. The average errors in load-carrying capacity and cumulative energy dissipation capacity between simulation and testing are 8.95% and 9.82% respectively, indicating that the proposed numerical model has good accuracy and could be used for assessing the seismic performance of corroded RC beams.

Abstract:To address the construction difficulties of steel reinforced concrete structures and fully leverage material performance, the rebar cage was discretized into randomly distributed steel fibers. Steel fiber reinforced concrete was concentrated in the compression zone to form the locally composite steel and steel fiber reinforced concrete structure. Four-point bending tests were carried out on 18 beam specimens with different steel fiber volume fractions (ρ_sf), shear span ratios (λ), concrete protective layer thicknesses for upper and lower parts of steel compression flange (C_ss and C_sv), and shaped steel specifications (I_s). The effects of these test parameters on failure modes, load-deflection curves, and failure symmetry of specimens were analyzed. The results show that increasing ρ_sf had a positive effect on improving the interface bonding performance for specimens with smaller λ (1.5 or 1.7), and the failure mode changed from interface failure to bending-torsion failure. To ensure that the concrete protective layer provides sufficient "grip-wrap effect" on the shaped steel and avoid or weaken the adverse effects of bending and torsion deformation, C_ss and C_sv should increase simultaneously with I_s. The deflection degradation coefficient was obtained by Gaussian distribution fitting, and the deflection when the specimen′s overall performance began to seriously degrade was predicted.

Abstract:In order to study the variation in bonding performance of carbon fiber reinforced plastic (CFRP) sheet bonded shale bricks under freeze-thaw and high-temperature conditions, the material properties of shale bricks, CFRP sheet, and epoxy resin adhesive were tested under individual freeze-thaw environments, high-temperature (60 ℃) environments, freeze-thaw and high-temperature cycling environments. The single shear experiment was also conducted to explore the effect of bonding performance of CFRP sheet bonded shale bricks under different conditions. The test results show that the material properties of shale bricks, CFRP sheet, and epoxy resin are significantly affected by the cycles of freeze-thaw and high-temperature conditions. After three major cycles, the compressive strength of shale bricks decreased by 31.62%, the tensile strength and elastic modulus of CFRP sheet decreased by 44.38% and 42.28%, respectively. The tensile strength and elastic modulus of epoxy resin decreased by 32.45% and 35.36%, respectively. The freeze-thaw and high-temperature cycling effects have the most significant effect on the single shear performance of CFRP sheet bonded shale bricks, followed by the effect of freeze-thaw, and the effect of high-temperature being the least. The proposed calculation formula can accurately calculate the single shear bearing capacity of CFRP sheet bonded shale bricks under different environments.