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28 February 2022, Volume 48 Issue 1 Previous Issue    Next Issue

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Materials Science and Engineering

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Preparation,characterization and pyroelectric properties of 0.94(Bi0.5Na0.5)TiO3-0.06Ba(Zr0.25Ti0.75)O3 ceramics ZHANG Hui, ZHANG Lu-yin, KONG Ling-bin, ZHAO Kun 2022, 48 (1):  1-7.  Abstract ( 319 )   PDF (5495KB) ( 319 )   Save The ferroelectric powder 0.96(Bi0.5Na0.5)TiO3-0.04Ba(Zr,Ti)O3(BNT-BZT) was synthesized by the solid-phase reaction method using BaCO3, Na2CO3, TiO2, ZrO2 and Bi2O3 as raw materials, and the BNT-BZT ceramic plate was prepared by the atmospheric sintering method. The effects of pressure and sintering temperature on the compactness of ceramics were investigated, and the structure, morphology and composition of BNT-BZT powder and ceramic plate were characterized.A pyroelectric nanogenerator based on BNT-BZT ceramicwas designedand its performance was studied. The results showed that the ceramic plate has the best compactness prepared under the conditions of a pressure of 7 MPa and a sintering temperature of 1 210 ℃. Under periodic cooling and heating conditions, the output peak current/voltage of the device reaches －18.5 nA/－0.9 V and 16.7 nA/0.8 V, respectively, which has excellent pyroelectric performance. References | Related Articles | Metrics

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Tribological properties of Ni-Al-Mo composite coating on Al alloy surface preparation by mechanical milling CHEN Ling-ling, YAN Cheng-qi 2022, 48 (1):  8-13.  Abstract ( 241 )   PDF (4830KB) ( 206 )   Save Ni-Al-Mo composite coating was prepared on surface of aluminum alloy by the method of mechanical milling. And the microstructure of coating,composition and tribological properties of the coating were analyzed. The result show that the elements in the Ni-Al-Mo composite coating are evenly distributed after 7 h mechanical ball milling. After annealing at 550 ℃,new phases of Al3Ni intermetallic were formed in the coating. The presence of Al3Ni and Mo in the composite coating makes the coating hardness higher than that of aluminum alloy substrate and Ni-Al coating, the coating hardness increases with the increase of Mo content, and that is respectively about 105 HV, 125 HV and 167 HV at the addition amount of10%, 20% and 30%; The increase of coating hardness effectively reduces the wear rate,and the wear rate of the coating is about0.4×10－3～0.6×10－3mm3/(N·m); The excellent friction coefficient and wear rate of the composite coating effectively protect the aluminum alloy matrix. References | Related Articles | Metrics

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Influence of the morphology of intermetallic compound layer in the soldering joint on diffusion concentration and stress LIU Wen-bin, LI Hong-ping, ZHANG Xu-dong, SUN Xue-min, REN Jun-qiang 2022, 48 (1):  14-19.  Abstract ( 226 )   PDF (4143KB) ( 396 )   Save Combining the experimental results, the intermetallic compound (IMC) interface model of welded joint in chip packaging technology was established. The diffusion process of Cu atoms during the formation of IMC layer between Sn solder and Cu substrate was calculated by finite element method, including the diffusion-induced stress and stress distribution. The results show that the interface morphology of IMC layer can significantly affect the behavior of Cu atoms diffusion and diffusion-induced stress. The concave-convex morphology of interface seriously obstructs the diffusion of Cu atoms, and the effect is more significant near the interface. The scallop morphology interface reaches diffusion stabilization faster than the flat morphology interface. The Cu atom concentration in the scallop interface is smaller than that in the flat interface, which makes the diffusion stress-affected region in the scallop interface smaller than that in the flat interface model. References | Related Articles | Metrics

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Study on heat storage performance of MgCl2·6H2O/MgSO4·7H2O complex phase-change system LIU Jian-jun, SHEN Liang-yu, YANG Xiao-tian, WANG Cai-long 2022, 48 (1):  20-24.  Abstract ( 293 )   PDF (2565KB) ( 281 )   Save The supercooling and phase separation of hydrated salt phase-change heat storage materials are two key issues that affect thermal stability and heat-storage performance of hydrated salt phase change heat storage materials. Using MgCl2·6H2O (MCH) as the main material and MgSO4·7H2O (MSH) as the nucleating agent, the composite phase change system MCH/MSH is prepared by the melt blending method. The effects of MSH on the phase change enthalpy, phase-change temperature, supercooling degree and phase separation phenomenon of composite phase-change materials are studied. The results show that the phase-change heat storage performance of MCH/MSH system constructed with appropriate amount of MSH is significantly higher than that of MCH. The system show the smallest supercooling, the best phase separation inhibition effect and the best heat storage performance when the MSH content is 5%. Its initial enthalpy change value can reach 330.91 kJ/kg, and the stable value can reach 254.43 kJ/kg after the cycle test, showing the prepared MCH/MSH composite material has good heat storage performance and cycle performance. References | Related Articles | Metrics

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Prediction model and optimization design of concrete mix ratio based on double mixing technology LI Chao, YANG Qiang-bin, ZHANG Hai-yu 2022, 48 (1):  25-29.  Abstract ( 304 )   PDF (1073KB) ( 392 )   Save With the speeding up of urbanization process, high-rise and super high-rise buildings continue to spring up, concrete materials are innovating and developing constantly. To improve durability and strength grade of concrete, reduce production cost and environmental pollution, and save energy consumption, a mathematical model for predicting the influence of admixtures on concrete strength was established based on the double mixing technology of concrete and experimental research. The results show that the content of fly ash and mineral has an important impact on the strength of concrete. The mathematical model can be used to predict the influence of admixtures on strength of concrete, control the content of admixtures and ensure the strength of concrete. Under the premise of not affecting the performance of concrete, the use of admixtures should be maximized to replace cement, so as to effectively reduce the amount of cement. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Study on simulation of near- and on- edge low-velocity impact damage of GFRP laminates XU Yao-xing, WEI Yao-bing, LIU Jian-hui 2022, 48 (1):  30-38.  Abstract ( 209 )   PDF (11573KB) ( 106 )   Save The near-edge and on-edge impact have a great influence on the residual strength of the composite material. Based on the three-dimensional Hashin failure criterion with stress description, combined with the improved Camanho degradation scheme, considering the impact damage of the test piece by the impact contact time, with the aid of ABAQUS to simulate the near-and on-edge impact damage of the glass fiber reinforced epoxy resin matrix composite (GFRP) laminate. At the same time, the Cohesive element is adopted to simulate the interlayer interface, and the impact process is simulated through the improved Vumat subroutine. The simulation results and the test results are compared and analyzed to verify the correctness of the model and the adapted subroutine. The results show that the non-linear reduction Vumat subroutine can predict the main characteristics of the laminate the near-edge, the on-edge impact damage, and the time-contact force curve more effectively compared with the direct reduction scheme. The near-edge and on-edge impact damage characteristics are quite different from the dynamic response. References | Related Articles | Metrics

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A small sample reliability assessment method based on Bootstrap ZHANG Zhen, LIU Jian-hui, ZHAO Cheng, YAN Chang-feng 2022, 48 (1):  39-44.  Abstract ( 497 )   PDF (2389KB) ( 475 )   Save In order to solve the problem that the maximum likelihood estimation method (Mle) may produce large errors in solving the distributed parameters in the case of small data samples, the B-MLE method is proposed based on Bootstrap data expansion. Firstly, the Bootstrap method was used to resample the small sample data to generate multiple groups of regenerated samples, so as to expand the data sample. Secondly, the maximum likelihood estimation is used to solve the distribution parameters of the regenerated samples, and the maximum likelihood estimation of multiple parameters is obtained. The probability density function is obtained directly from the parameter estimation by using the kernel density estimation method. Finally, at a given confidence level, the confidence interval of parameters is determined to obtain the confidence interval of reliability. The feasibility and credibility of the proposed method are verified by Monte Carlo method. The results show that the proposed method can reduce the error of maximum likelihood estimation. References | Related Articles | Metrics

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Single large wind turbine field experiment at high altitude WANG Dian, YANG Cong-xin, WANG Yin, ZHANG Gen-hao, WU Fa-ming, DING Bai-cen 2022, 48 (1):  45-52.  Abstract ( 174 )   PDF (5914KB) ( 258 )   Save In order to improve the performance of large-scale wind turbines in high-altitude areas, the 3.3 MW horizontal-axis wind turbine is taken as the research object. The inflow of wind turbines is measured by the Nacelle-type Lidar measures through the field experiment method. At the same time, the wind turbine wake is measured by the ground wind profile Lidar. Firstly, the inflow wind speed and wind direction measured by the Lidar in one day are compared with the wind speed and wind direction meter data on the nacelle, and the inflow wind speed measured by the Nacelle-type Lidar is extracted for a period of time. Secondly, the wake wind direction is compared with the inflow wind direction, the wake velocity profile and the inflow velocity profile. The results show that the inflow velocity measured by the Lidar has a strong correlation with the nacelle anemometer. The overall level of the wind deviation of the nacelle is slightly smaller than that of the anemometer, and the inflow wind speed will decrease with the distance from the rotor. The main wind direction distribution of the wake is consistent with the main wind direction of the inflow. With the increase of the position of the downstream measuring point from the wind wheel, the recovery of wake velocity loss is getting faster and faster. References | Related Articles | Metrics

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Effects of leading edge auxiliary airfoil on aerodynamic performance of wind turbine airfoil YANG Rui, ZHOU Nan-nan, WEN Wei-yue, YANG Wei, GU En-xin 2022, 48 (1):  53-58.  Abstract ( 185 )   PDF (4211KB) ( 281 )   Save S809 is used as the main airfoil and an auxiliary airfoil is added at its leading edge. Based on the SST k-ω model, the effect of the auxiliary airfoil on the aerodynamic characteristics of the main airfoil S809 at the angle of attack from 2°~22° are analyzed.The results show that when the leading edge auxiliary airfoil is added at the leading edge of the main airfoil, the lift force of the main airfoil is decreased and the drag force is increased at a small angle of attack of 2°~6°. However, when the angle of attack reaches 8°, the leading edge auxiliary airfoil increase the lift force of the main airfoil, the drag force is decreased and the lift-drag ratio is increased. The flow separation law and the lifting mechanism of the main airfoil at 10°, 14°, 18° and 22° are analyzed. The existence of leading edge auxiliary airfoil effectively inhibits and delays flow separation, and effectively inhibits separation bubbles at large angles of attack. As can be seen from vorticity cloud images of 10° and 18°, the vortex generated at the leading edge auxiliary small airfoil has an obvious inhibition effect on the main airfoil vortex. In the boundary layer, the x-direction velocity component at the same height is larger than that of the original airfoil, which indicates that the fluid along the x-direction of the airfoil surface has greater kinetic energy, which is helpful to improve the aerodynamic performance of the main airfoil at large angles of attack. References | Related Articles | Metrics

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Analysis of cavitation phenomenon on the surface of distributor of closed swash plate axial piston variable pump WANG Jian-sen, HE Xin-long, YANG Wei, CAO Wei-dong, YAO Yi-ming, WANG Zheng-rong 2022, 48 (1):  59-64.  Abstract ( 266 )   PDF (2668KB) ( 316 )   Save Taking the closed swash plate axial piston variable displacement pump with a port plate with positive opening and double damping grooves as the research object, the homogeneous multiphase transport equation, standard k-ε turbulence model and full cavitation model are used to study the time-space dynamic evolution process of cavitation flow field on the surface of port pair of piston pump considering the compressibility of medium. It is found that the location and extent of cavitation erosion on the surface of cylinder block are highly correlated with the location, duration and severity of cavitation on the surface of valve pair during the transition process of valve distribution. The main cause of cavitation damage on the valve surface of the cylinder block is the high pressure difference between the piston cavity and the oil suction cavity caused by the positive opening of the valve plate. The cavitation damage on the leading edge and the trailing edge of the cylinder block spacer is respectively related to the transient process of pressure rise and pressure relief of the piston cavity. References | Related Articles | Metrics

Chemical Industry and Light Industry

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Effect of cooling rate on residual stress and equivalent thermal deformation of brazed plate-fin structures DAI Zhong-hua, LIUXin-wen, MA Hong-qiang, WANG Li, ZHANG Chun-e 2022, 48 (1):  65-70.  Abstract ( 184 )   PDF (3008KB) ( 226 )   Save In order to study the effect of different brazing cooling rate on the brazing residual stress and equivalent elastic thermal strain of plate-fin structure, a three-dimensional thermal stress analysis model of plate-fin structure is established, and the variation of brazing residual stress and equivalent elastic thermal strain under different brazing cooling rates are simulated and analyzed using the thermal-structural coupling method. The results show that the brazing residual stress of fin-structure is decreased with the decrease of the brazing cooling rate. The difference between the brazing residual stresses of the plate-fin structure is also different for different brazing cooling rates, and when the brazing cooling rate is less than a certain value, the brazing residual stress of the plate-fin structure will be approximately constant. The smaller the brazing cooling rate, the smaller the risk of fracture in the weak parts of the plate-fin structure. The brazing cooling rate has little effect on the equivalent elastic thermal strain of the plate-fin structure. References | Related Articles | Metrics

Automation Technique and Computer Technology

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Study on PV system virtual synchronization control with active power self-reserve ability MA Ming, BAO Guang-qing, LÜ Qing-quan, LIU Meng-xin, TAN Hong-tao, WANG Ning-bo 2022, 48 (1):  71-77.  Abstract ( 313 )   PDF (3077KB) ( 284 )   Save The virtual synchronous machine technology simulates the electromechanical transient characteristics of the traditional synchronous generator set, which makes the photovoltaic grid connected inverter have the inertia, damping, frequency and voltage adjustment of the synchronous unit. However, over-reliance on energy storage systems will inevitably affect traditional PV virtual synchronization technology applications in actual engineering, which will greatly increase the construction cost of PV system. In this paper, a reduced power virtual synchronous control strategy is proposed. By properly reducing the active power output of photovoltaic power supply making use of non-linear property of PV system output, the PV system can actively participate in the frequency response of power grid without additional energy storage unit. The simulation results verify the effectiveness and correctness of the proposed control strategy, which can provide a theoretical basis for large-scale PV connection and consumption. References | Related Articles | Metrics

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Improved genetic algorithm and its application in mine production scheduling WANG Zhi-wen, GONG Xu-peng, SUN Hong-tao, HU Ji-qiang 2022, 48 (1):  78-84.  Abstract ( 322 )   PDF (1073KB) ( 513 )   Save Based on the characteristics and shortcomings of multi-objective production scheduling, this paper constructs a multi-objective mine production scheduling model from the perspectives of mining and transportation costs and ore grade, considering factors such as ore types, shovel output and truck scheduling. Combining the advantages of genetic algorithm in solving multi-objective optimization problems, a mine production scheduling strategy based on an improved genetic algorithm and its implementation process are proposed, and the genetic algorithm before and after the improvement is compared to the solution of the model. The simulation experiment results show that the improved genetic algorithm is used to dispatch mine resources optimization is feasible and can promote better development of the mining industry. References | Related Articles | Metrics

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Domain adaptation based on adjustable discriminator ZHAO Xiao-qiang, JIANG Hong-mei 2022, 48 (1):  85-90.  Abstract ( 177 )   PDF (1612KB) ( 166 )   Save The current domain adaptation (DA) based on adversarial learning has poor adaptability to target samples, lower prediction accuracy of the target domain is caused. For this reason, this paper proposes a domain adaptation (A-DADA) algorithm based on an adjustable discriminator. First, the distance between the classification probabilities of the two discriminators is used as the weight to apply to the target domain confrontation training loss function, aiming to reduce the number of confrontation training times for aligned target samples and increase the number of confrontation training times for unaligned target samples. Secondly, square entropy loss function is used as the minimum entropy loss function to improve the class balance. Finally, the Office-31 datasetis used to compare the algorithm with JAN and other algorithms, the experimental results show that compared with the JAN algorithm, the average accuracy of the algorithm is increased by 2.5%. References | Related Articles | Metrics

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GPR image denoising based on bilateral filtering BM3D algorithm WANG Hui-qin, LÜ Jia-yun, ZHANG Wei 2022, 48 (1):  91-97.  Abstract ( 351 )   PDF (4081KB) ( 363 )   Save To enhance the image of ground penetrating radar (GPR), a joint denoising algorithm is proposed by combining bilateral filtering with 3D block matching algorithm (BM3D). At the same time, the peak signal-to-noise ratio under different variances is studied, and the image before and after denoising is evaluated objectively by maximizing the structural similarity between the real image and the estimated image. The experimental results show that, compared with the single denoising algorithm, the joint denoising algorithm can better maintain the integrity of the edge of the defective target in the ground penetrating radar image, and has a better denoising effect. References | Related Articles | Metrics

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Hyperspectral image classification based on multi classifier fusion WANG Yan, LI Guo-chen, SUN Xiao-li 2022, 48 (1):  98-106.  Abstract ( 362 )   PDF (4459KB) ( 376 )   Save Aiming at the problem of huge amount of data, strong data correlation, and integration of maps and spectrum in hyperspectral images, which might cause difficulty to classify hyperspectral images, a hyperspectral image classification model based on multi-classifier fusion is constructed. The model first uses bilateral filtering algorithm for denoising, and then uses the combination of LDA algorithm and PCA algorithm, separate PCA algorithm, and Gabor filter and PCA algorithm to perform dimensionality reduction and feature extraction on the data respectively, and use SVM classifier, LightGBM classifier and AdaBoost classifier for classification. Finally, an AHP-voting method is designed to merge the classification results of the three classifiers. The results show that the effect of the fusion model is significantly increased, the overall accuracy (OA) up to 97.59%, the average accuracy (AA) up to 98.95%, Kappa coefficient can reach more than 97.32%, the OA, AA, and Kappa coefficients are improved by 2.30%, 1.13%, and 2.54% on average compared with a single model classifier. References | Related Articles | Metrics

Architectural Sciences

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Effect of external admixture on water stability of asphalt mixture under freeze-thaw cycle conditions LI Ping, MAO Yu, WANG Meng, DING Fan, ZHAI Xiao-cheng 2022, 48 (1):  107-113.  Abstract ( 251 )   PDF (4003KB) ( 428 )   Save In order to evaluate the effect of the external admixture on the water stability of the asphalt mixture, the cement, hydrated lime, rubber powder and high molecular polymer were incorporated into the AC-13 and AC-16 asphalt mixture, then the water stability performance were evaluated by the splitting strength under freeze-thaw cycles. Firstly, the optimum modification content of cement and hydrated lime was determined by high temperature stability, low temperature crack resistance and water stability test method. Secondly, the optimal blending amount of high molecular and rubber powder polymer was obtained by three major indicators of asphalt test methods, elastic recovery test and beam bending test. Finally, the two types of asphalt mixture containing the best blend of external admixtures were subjected to a splitting test under freeze-thaw conditions. The results show that the optimum modified contents of cement, hydrated lime, rubber powder and high molecular polymer are 3%, 2%, 20% and 0.3%, respectively. The four external admixtures can effectively improve the splitting strength of the asphalt mixture, among which the splitting strength with rubber powder increases the most. The gradation composition of asphalt mixture has a great influence on the splitting strength. Under the same conditions, the splitting strength of AC-13 is better than that of AC-16. With the increase of the number of freeze-thaw cycles, the splitting strength ratio of asphalt mixture shows a downward trend, and the rate of decline of rubber asphalt is relatively slow, and the anti-cracking effect is the best. References | Related Articles | Metrics

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Computational method of beam deflection curve under frame-external prestressing system SONG Yu, CHAI Ying 2022, 48 (1):  114-120.  Abstract ( 190 )   PDF (1237KB) ( 283 )   Save Taking the frame beam of frame structurefully reinforced by external prestressing technology as the research object, force characteristics were analyzed and the corresponding mechanical models wereestablished. The principles of force balance, point oblique solution andmoment-curvature relation were appliedto infer the expression of cable internal force and the curve expression afterdeformation, the load-deflection curve equation of the beam,which were compared with the previous experimental results. The results show that the internal force of cable changes with the vertical position of cable node and there is a non-linear relationship between the internal force of cable and the axial force of the web member.In the elastic stage, when the boundary condition of the beam deflection curve equation approaches infinitely the state of simply supported beam (or embedded beam), the maximum value of the deflection curve equation is basically consistent with that of the deflection of the beam in the middle span in the existing literature. While there is a great difference between the theoretical and experimental values of the deflection curve in the plastic stage. The analysis results in the elastic stage can provide a theoretical reference for engineering practice. References | Related Articles | Metrics

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Monitoring and numerical simulation analysis of red sandstone foundation pit excavation of Lanzhou subway ZHU Yan-peng, LI Feng-qi, YANG Xiao-hui,MA Xiao-rui, YIN Li-jie 2022, 48 (1):  121-127.  Abstract ( 251 )   PDF (3624KB) ( 302 )   Save Taking the red sandstone deep excavation at Dongfanghong square subway station in Lanzhou city as the research object, the displacement of the retaining piles and the ground settlement around the foundation pit during the excavation of the foundation pit are monitored on site, and the measured results are analyzed. Using the MIDAS GTS numerical simulation software, three-dimensional models for deep excavation support and seepage analysis were established respectively, and the displacement of the deep foundation pit during the excavation process was calculated. The results show that the horizontal displacement of the pile increases first and then decreases with the depth of the pile body emplacement, and the overall shape is “)”. The settlement of the surface of the pit is basically stable after the completion of the excavation. The maximum displacement occurs before the setting of the third reinforced concrete cross braces, and the displacement has an obvious spatial effect.The trend of displacement change of the two simulation is basically the same, but the displacement result of the numerical analysis considering the seepage effect is o larger. The numerical analysis result of the seepage shows: the seepage effect caused by the imbalance of pore water pressure reaches the maximum after the excavation of the foundation pit is completed. References | Related Articles | Metrics

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Study on construction control of twin curved shield tunnels LI Shao-hua 2022, 48 (1):  128-133.  Abstract ( 202 )   PDF (5912KB) ( 392 )   Save Using the countermeasures of the smooth implementation of the curved shield tunnel with micro curvature radius in Tokyo, Japan for reference, and relying on the inter-city railway in Zhuhai, China, this paper focuses on the analysis of the effect of the measures of shortening the shield length on the construction control for twin curved shield tunnels. 3D surface-to-surface contact is established to simulate the interaction between the segments by ABAQUS, and a specific constraint between the longitudinal bolt and the segments is established to simulate the installation of the inclined bolt. As a result, a refined simulation of the excavation of twin curved tunnels considering the characteristics of circumferential joints in the wedge-shaped segment is realized. On the basis of validated reliability of the refined numerical simulation method in this paper, a contrastive analysis of the construction control effects are completed. The results show that shortening the shield length can effectively reduce the ground settlement and the horizontal displacements of the soil at the inner and outer sides of the curved tunnels. Meanwhile, for the segment structure, the maximum bending moment is reduced and the safety factor is improved. Shortening the length of shield tunneling is a reliable measure to effectively control the soil deformation and to ensure the safety of the segment structure, which is worthy of popularization and application in engineering practice. References | Related Articles | Metrics

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Load monitoring of bolted spherical joint connection based on wavelet packet energy analysis XU Jing, GOU Kang-kang, LIU Ke, ZHANG Chun-wei 2022, 48 (1):  134-142.  Abstract ( 174 )   PDF (6653KB) ( 299 )   Save Aiming at the problem that the bolts, sleeves and other components will be damaged by the force change in the connection area during the installation and use of the bolt ball joint, and the joint failure will occur thereby, piezoelectric (PZT) ceramic sensor are used, based on wavelet packet energy analysis method to study the force monitoring of the bolt ball joint connection area. A scaled grid model composed of bolted ball nodes is designed and made. By applying different torques to the sleeves in the connection area of the bolt ball node, the connection area is in a different tightness state, and different connection areas are constructed. Two PZTs are sticked on the center bolt ball and the rod end close to the bolt ball, respectively, as an exciter and receiver. The wavelet packet analysis is performed on the received stress waves under different torques, and the corresponding stress wave energy is obtained. By calculating the risk index RMSD, the monitoring of the force on the connection area of the bolt ball joint is realized. The test results verify the effectiveness, anti-noise and anti-interference of the wavelet packet energy analysis method, and finally proved the feasibility of monitoring the force state of the bolted ball joint connection area based on the wavelet packet energy method. References | Related Articles | Metrics

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Aerodynamic optimization of outdoor large-scale three-sided single column billboard YANG Wen-wei, LUO Jin-cai, Du Ya-nan 2022, 48 (1):  143-149.  Abstract ( 260 )   PDF (5585KB) ( 248 )   Save Outdoor large-scale single-column billboards are wind-damage vulnerable structures. In order to optimize their wind pressure distribution and wind-induced effect under the most unfavorable wind direction angle, based on the aerodynamic principle, the wind load characteristics of the billboard structure are numerically calculated using FLUENT. The simulation was compared with the wind tunnel test results to verify the reliability of the numerical simulation. On this basis, six kinds of single-column three-sided billboard shape optimization schemes were designed based on different sagittal span ratios for comparative analysis. The results show that the maximum negative wind pressure of each panel appears at the side and the edge of the panel, and the absolute value is twice the maximum positive wind pressure value. Comparing with the shape optimized model, it is found that the convex shape has obvious advantages in reducing wind pressure compared with the concave shape. When the structural sagittal span ratio S/L=1/9, the maximum positive wind pressure and the maximum negative wind pressure are both about 1000 Pa. Compared with the plane billboard, the pressure and suction of the structure are more balanced, the structural extreme wind pressure is greatly reduced, which is the optimal working condition. References | Related Articles | Metrics

Scientific

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Primitive exponents of a class of three-colored digraphs with two (n－1)-cycles LUO Mei-jin, LU Yu-song, WEI Yu-cheng 2022, 48 (1):  150-155.  Abstract ( 162 )   PDF (822KB) ( 166 )   Save In order to study the primitive exponent problem of nonnegative matrix pairs, the two-colored digraphs are extended to three-colored digraphs. Using the corresponding relation between a digraph and a matrix, a class of primitive three-colored digraphs whose uncolored digraphs has n vertices, consists of one n-cycle and two (n－1)-cycles is studied. Some primitive conditions, a tight upper bound of primitive exponents and the characterization of extremal three-colored digraphs are given. References | Related Articles | Metrics

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Properties of product of composition operators in L2-spaces ZHOU Ze-hua, LU Hui-qiang, ZHOU Hang 2022, 48 (1):  156-160.  Abstract ( 186 )   PDF (766KB) ( 284 )   Save Let (X,A,μ) be a σ-finite measure space. A transformation ø:X→X is non-singular if μ°ø－1 is absolutely continuous with respect to μ. For this non-singular transformation, the composition operatorCø:D(Cø)→L2(μ) is defined by Cøf=f°ø,f∈D(Cø). Properties of product of composition operators Cøn···Cø1in L2-Spaces are investigated. References | Related Articles | Metrics

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W⊥-Gorenstein injectivity under Frobenius extensions SONG Wei 2022, 48 (1):  161-167.  Abstract ( 220 )   PDF (812KB) ( 263 )   Save The notions of W⊥R-Gorenstein injective module and W⊥R-Gorenstein injective dimension respect to a generalized tilting moduleWR,and it is prove that the W⊥-Gorenstein injectivity is preserved under Frobenius extensions, that is, for a Frobenius extension S/R and an R-ModuleMR,MR is W⊥R-Gorenstein injective if and only ifMⓧRSS is (WⓧRSS)⊥S-Gorenstein injective. Some properties of W⊥R-Gorenstein injective dimension are obtained. Furtheremore,as an applications, some valuable corollaries about some classical homological dimension as applications. References | Related Articles | Metrics

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Effects of magnetic flux viscosity flow on dynamic stress intensity factor in high temperature superconductor ZHAO Yu-feng, ZHANG Miao 2022, 48 (1):  168-172.  Abstract ( 144 )   PDF (2254KB) ( 228 )   Save Establish a simple high-temperature superconducting material model: place a superconducting cylinder with a central crack in a falling external magnetic field. Using plane strain theory and other methods, the relationship of the Lorentz force in the superconducting cylinder with time is calculated, and the ABAQUES finite element analysis method is used to solve the time-varying dynamic stress intensity factor. By changing the viscous flow velocity of the magnetic flux, the length of the crack and the maximum applied magnetic field, the change process of the dynamic stress intensity factor under different conditions can be obtained. The results show that the existence of viscous flow of magnetic flux changes the distribution of the trapped magnetic field of the superconducting cylinder, significantly increases the peak value of the dynamic stress intensity factor of the superconducting cylinder, and increases the rate of increase of the dynamic stress intensity factor. In the study of various aspects of high-temperature superconductors, the viscous flow of magnetic flux should not be ignored. References | Related Articles | Metrics