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28 February 2021, Volume 47 Issue 1 Previous Issue    Next Issue

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Materials Science and Engineering

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The effect of hot isostatic pressing temperature on the microstructure and tensile properties of TC4 alloy CHENG Jian-hong, XIAO Le, CHEN Yong-qing, YAN Ying-jie, CAO Rui 2021, 47 (1):  1-4.  Abstract ( 548 )   PDF (9525KB) ( 368 )   Save The preparation of TC4 alloy by powder NNS-HIP has received widespread attentions in recent years due to its unique advantages. In this research, effects of hot isostatic pressing temperature on the microstructure and tensile properties of TC4 alloy were systematically investigated. The experimental results show that the alloy is completely densified when the holding temperature reaches 800 ℃ under the holding pressure condition of 120 MPa for 2 hours; As the holding temperature increases from 800 ℃ to 920 ℃, the tensile strength of the alloy decreases from 942 MPa to 920 MPa, and the tensile strain increased from 13.7% to 18.1%; The volume fraction of β phase in the alloy microstructure increases with the rise of the holding temperature, and the distribution of β phase tends to be uniform as a result. The addition in β phase is a key factor for the decline in strength and ascent in plasticity of the alloy. References | Related Articles | Metrics

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Effect of silver on texture formation of Ni-7at.%W alloy substrates GAO Mang-mang, SU Sheng-yao, ZHANG Fang-yuan, ZHAO Xu, MA Lin, SUO Hong-li 2021, 47 (1):  5-6.  Abstract ( 293 )   PDF (3563KB) ( 364 )   Save The Ag element can make grains in the substrates of Ni and Ni-5at.%W alloy elongated so as to improve the current transmission ability of superconducting layer. The mechanism of Ag effect on texture of NiW substrates with high W content (>5at.%W) may be the basis for subsequent control of grain structure morphology. The results show that the presence of Ag decreases volume fraction of S-orientation in substrate, which further affects the formation of cubic crystal texture in the baseband after recrystallization. By introducing intermediate heat treatment at 550 ℃ for 2 h as the rolling deformation reaches about 90%, the deformation factor R of cold rolled baseband can be increased from 0.72 to 1.05, thus increasing the volume fraction of copper texture and increasing the orientation of deformed cubic crystals in the baseband by 65%. Finally, the alloy baseband with a volume fraction of 96.8% Ni-7at.%W-0.01at.%Ag with cubic crystal texture on the surface can be obtained after recrystallization in the heat treatment. References | Related Articles | Metrics

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Effect of rare earth yttrium addition on the microstructure and properties of Al-8%Mn alloy LIU Jian-jun, LÜ Shu-yue, ZENG Bao-gen, LAN Ye-feng, LI Qing-lin 2021, 47 (1):  11-15.  Abstract ( 251 )   PDF (13020KB) ( 124 )   Save The optical microscope, SEM, electron probe and XRD were used respectively in this research to investigate the dominant mechanism of rare earth Y added in Al-8%Mn alloy melt on microstructure of the alloy. The effect of amount of rare earth Y on the mechanical properties and corrosion resistance of the alloy was analyzed as well. Our results show clearly that the addition of rare earth Y can refine Al6Mn compounds and α-Al phases in Al-8%Mn alloy during alloy solidification. Moreover, after adding 3wt.% Y to Al-8%Mn alloy melt, the refining efficiency caused by Al6Mn and α-Al phases is most significant. The morphology of Al6Mn phases changes from coarse lath to small piece and blocky, and the average size of Al6Mn reduces from 67.4 μm to 36.5 μm. Hence, the morphology of α-Al phase transfers from coarse columnar crystal to equiaxed crystal, and the average size decreases to 48 μm when 3wt.%Y is added to Al-8%Mn alloy melt. Both the ultimate tensile strength and elongation of Al-8Mn-3wt.%Y alloy are improved up to 141.37 MPa and 2.26% respectively. In the end, the addition of rare earth reduces the intergranular corrosion resistance of the alloy in etching solution (30 g NaCl+10 mL HCl+1 L H2O). References | Related Articles | Metrics

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Defect detection and recognition of graphite electrode based on radiography ZHANG Peng-lin, YAO Ji, NIU Xian-ming, CHEN Kai-wang, ZHANG Wei-ping 2021, 47 (1):  16-21.  Abstract ( 319 )   PDF (4164KB) ( 424 )   Save In order to solve an existing problem in non-destructive testing of defects in graphite electrode, an electrode defect detection method based on the combination of X-ray detection and deep belief network is proposed in this paper. For this reason, an exposure curve of graphite electrode is made for the graphite electrode, and the exposure curve is used to select reasonable process parameters for prefabricated electrode blocks with different defects, and X-ray inspection is also carried out for the graphite electrode. The de-noising enhancement method is then utilized to improve the weak contrast and low signal-to-noise ratio of the electrode ray image, and the improved Canny operator edge detection method is also adopted to extract the edge of the electrode ray image, then the defect features can be selected and calculated easily. This is due to application of the deep belief network to identify intelligently electrode defects. All results from this research make us believing that it is feasible to apply the radiographic technology to detect graphite electrode defects. The improved Canny operator may be used to extract defect edges. The quality of the extraction has been improved greatly, and the accurate calculation of the characteristic parameters may be realized as a result. The deep belief network can be employed to identify electrode defects with an accuracy of 96.67%, which is a higher accuracy rate indeed. References | Related Articles | Metrics

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Influence of external axial magnetic field on metal argon arc welding short circuit transition FAN Ding, MA Xin, WU Li-jian, HUANG Jian-kang, XIAO Lei 2021, 47 (1):  22-27.  Abstract ( 289 )   PDF (7916KB) ( 107 )   Save In order to increase the short-circuit transfer frequency and reduce the welding spatter, the influence of axial magnetic field on short-circuit transfer was investigated by applying DC and alternating axial magnetic field respectively. The high-speed camera, current and voltage signals and the short-circuit transfer force of droplets under the action of magnetic field were analyzed as well. All results show that the short circuit transition frequency reaches the maximum when the DC magnetic field excitation current takes 4 A. When the AC magnetic field excitation current becomes 9A and the magnetic field frequency reaches 100 Hz, the short circuit transition frequency reaches the maximum, which is basically consistent with the fluctuation frequency of the current-voltage waveform. Appropriate application of magnetic field parameters can effectively promote the necking and disconnection of the liquid bridge, increase the short circuit transition frequency and reduce the spatter. References | Related Articles | Metrics

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The effect of Ag nanoparticles modification on photocatalytic properties of La-doped ZnO nanorods YU Fu-cheng, NAN Dong-mei, WANG Bo-long, LI Yuan-meng, LIU Zheng-yan, HE Ling 2021, 47 (1):  28-35.  Abstract ( 268 )   PDF (13895KB) ( 142 )   Save Ag nanoparticles decorated by La-doped ZnO nanorods were prepared in this study by hydrothermal method followed by a photo-deposition process. Effects of La-doping content and Ag modification on the photocatalytic performance of ZnO nanorods were investigated by photocatalytic degradation of methyl orange (MO) solution. The experiment results show that the photocatalytic performance of ZnO nanorods is much enhanced by La-doping and the decoration of Ag nanoparticles. La-doping changes the crystal quality, and the formed La—O bond makes the intrinsic absorption edge red-shift and increases the absorption intensity. Simultaneously, La-doping improves the electron concentration and impurity level of ZnO crystal. The decoration of Ag nanoparticles on the surface of La-doped ZnO nanorods inhibits the recombination of photo-generated electrons and holes, and the exciton life is thereby prolonged. Ag decorated La-doped ZnO nanorods show more effective photocatalytic performance than that of pure ZnO nanorods. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Research on the method of dimension reduction of rotor fault data set by fusing KPCA and LTSA ZHAO Rong-zhen, CHEN Yu-ji 2021, 47 (1):  36-40.  Abstract ( 235 )   PDF (1928KB) ( 440 )   Save In order to solve the problem that kernel principal component analysis (KPCA) and local tangent space alignment (LTSA) algorithm can not keep both the global and local structure characteristics of data in the process of dimensionality reduction, this paper uses linear superposition of kernel function to derive a nonlinear dimensionality reduction algorithm which combines KPCA algorithm with LTSA algorithm. The dimensionality reduction algorithm can make a fault dataset maintaining both global distance relationship and local neighborhood relationship between data samples after dimensionality reduction. Computational experiments show that this algorithm can accurately extract the global and local structural characteristics contained in the fault dataset, and make the results of fault classification clearer and more accurate as well as more effective. References | Related Articles | Metrics

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Analysis on mixed transport characteristics of oil-gas pump HAN Wei, YUAN Shi-fang, QUAN Hui 2021, 47 (1):  41-46.  Abstract ( 414 )   PDF (7286KB) ( 209 )   Save In order to reveal internal flow and mixing transport characteristics of an oil-gas pump, the steady gas-liquid two-phase flow simulation, which is based on the standard k-ε turbulence model and the Mixtere multiphase flow model, for the oil-gas pump is carried out by using computer simulation technology. And the distribution of internal pressure field, velocity field as well as gas volume ratio are obtained. Simulation results show that, from the impeller inlet to the impeller outlet, the degree of gas-liquid two-phase separation becomes more and more serious, the relevant pressure increases gradually, and the flow state tends to be turbulent. From the inlet of the guide vane to the exit of the guide vane, the bubble cluster moves gradually from the hub to the middle of the channel, and the relevant pressure decreases gradually also, forming a low pressure zone, which leads to eddy flow phenomenon in the low pressure zone. References | Related Articles | Metrics

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Study on turbulence effects on the wake and torque characteristics of horizontal axis wind turbine LI De-shun, SU Jin-cheng, LI Yin-ran, GUO Tao 2021, 47 (1):  47-53.  Abstract ( 562 )   PDF (5089KB) ( 418 )   Save Based on a horizontal axis wind turbine of 33 kW, the wake flow field of thewind turbine under condition of uniform flow or turbulent flow of different intensities is simulated by using the method of large eddy current to simulate coupled actuator line, and the effect of turbulence on the wake and torque characteristics of horizontal axis wind turbine is also investigated. Simulated results indicate that: the energy exchange between the wake and the surrounding flow field of the wind turbine in the turbulent flow is stronger than that in the uniform flow. The turbulent velocity is faster therefore, so that velocity recovery in the wake area becomes faster as a result. The greater the turbulence is, the faster the velocity recovery may be. Compared with the uniform flow, the maximum loss rate of the wake velocity of the wind turbine decreases during turbulent flowing, but the degree of turbulence has less effect on the maximum loss rate of the wake velocity. The expanding rate of wake radius decreases gradually in the range from the plane of the wind turbine to twice the diameter of the wind turbine, and remains basically unchanged after twice the diameter. Turbulence will increase expansion of the wake, and the greater the turbulence is, the stronger the expansion will be. Under the condition of 11 m/s wind speed, the increase of turbulence leads to not only the decrease of mean value of the wind turbine torque, and the increase of fluctuation amplitude, but also the increase of energy consumption of the wind turbine torque in high frequency and low frequency ranges. The increase of energy consumption in the range of low frequency is faster. References | Related Articles | Metrics

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Characteristic analysis of flow-dead-zone in pressure building of variable speed pump control system QIANG Yan, WANG Ya-qiang, ZHAO Chun-li, LI Wei, LUO Xiao-mei, WEI Lie-jiang 2021, 47 (1):  54-60.  Abstract ( 288 )   PDF (1556KB) ( 618 )   Save In order to reveal dominant mechanism of the flow-dead-zone of a hydraulic pump in pump control system, a mathematical model of the hydraulic pump, including the flow-dead-zone, is established in this paper. The model takes into account the leakage in the hydraulic pump caused by differential pressure flow and shear flow as well as the compressibility of oil. Through analyses of the mathematical model, it is concluded that the width of the flow-dead-zone of the hydraulic pump increases with increase of the outlet cavity, load pressure, oil temperature and start-up acceleration of the hydraulic pump, and decreases with increase of displacement of the hydraulic pump. For this reason, taking a gear pump as an example, a Simulink-Amesim joint simulation model is established to study further effects of different load pressure, oil temperature and start-up acceleration on the dead zone width, and verify the results from theoretical analyses. The results show that the dead zone width of hydraulic pump flow has a linear relationship with load pressure and start-up acceleration, and is close to an exponential relationship with oil temperature. References | Related Articles | Metrics

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Effect of sphericity of nanoparticles on forced convection heat transfer of Al2O3- water nanofluid in a parallel-plate channel WANG Gang, ZHANG Qian, MA Bing-shan 2021, 47 (1):  61-65.  Abstract ( 182 )   PDF (1991KB) ( 523 )   Save A numerical calculation method was used to study the laminar forced convective heat transfer of water-based nanofluid with cubic, spherical or cylindrical Al2O3 nanoparticles in a flat plate channel. The effects of nanoparticle sphericity, nanoparticle volume fraction and Reynolds number on the forced convective heat transfer of Al2O3-water nanofluid in the flat plate channel were also analyzed. The results show that when nanoparticle volume fraction and Reynolds number keep constant, both the average Nusselt number on the channel wall and the intensity of convective heat transfer increase with the decrease of the sphericity of nanoparticles. With the increase of nanoparticle volume fraction and Reynolds number, the average Nusselt number on the channel wall becomes increasing when nanoparticle sphericity keeps constant and the corresponding intensity of the convective heat transfer increases also as a result. References | Related Articles | Metrics

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Simulation analysis on rigid-flexible coupling model for scroll compressor rotor system considering clearance ZHAO Man, ZHANG Qiang 2021, 47 (1):  66-71.  Abstract ( 317 )   PDF (4549KB) ( 519 )   Save In order to improve the accuracy and reliability of the scroll compressor rotor system, the multi-rigid body and rigid-flexible coupling model of rotor for scroll compressor with joint clearances were established by means of software ADAMS and ANSYS. Effects of the flexible drive bearing and joint clearances on the dynamic performance of the rotor system with overturn of orbiting scroll was simulated and analyzed, and on the basis of which the bearing eccentric worn area is analyzed by finite element method. Results from the finite element analyses show that under the clearance of the moving pair, the flexibility of the bearing has little influence on the displacement and speed of the bearing, but has a great influence on the acceleration and collision force of the bearing. The maximum acceleration is about 13.34 times that of the multi-rigid body model, and the maximum collision force increases by 2.9 times. The bearing has partial wear area in the range of 31.29° behind the exhaust angle, and the maximum stress occurs at 2/7 of the needle roller. The simulation results provide analytical method and theoretical guidance for design and dynamic behavior prediction of scroll compressor. References | Related Articles | Metrics

Chemical Industry and Light Industry

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Simulation of the critical condition of pressurization for high sulfur wet gas gathering and transportation system MA Hong-qiang, JIA Ji-wei, MA Weng, WANG Li, GAO Ji-feng, HAN Xi-lian 2021, 47 (1):  72-77.  Abstract ( 203 )   PDF (4247KB) ( 374 )   Save A numerical model of pressurized gathering and transportation model for wet gas field with high sulfur content are established in this paper. The influence of terminal station pressure on slug flow risk, pipe flow velocity and pipe transportation capacity is simulated and analyzed in terms of the thermos-mechanical coupling method. All simulated results show: that the error for reliability of the pressurized gas gathering and transportation mode maintains within 9%. When the gas well distribution keeps unchanged, the lower the total station pressure is, the smaller the liquid holding rate of the pipe is. The decrease of the pipe network operating pressure is conducive to avoid the formation of slug flow in the later stage of exploitation. When the total station pressure is 5.0 MPa, some pipe sections, namely 1#, 3# and 4#, have flow rate of too high, which exceeds predetermined design requirements. Therefore, the corresponding pipe sections need to be pressurized for gathering and transportation to reach the safety value. When the gathering and transportation pipe network meets the transportation capacity of 9 billion square / year, the operation pressure of the main station shall not be lower than 6.9 MPa. It is determined that the critical condition for pressurized operation of high sulfur wet gas gathering and transportation system is not to be lower than 7.0 MPa. References | Related Articles | Metrics

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Synthesis of N,N'-dicyclohexyl-diazen-N,N'-dioxide ZHANG Zhen-ming, XIA Tian, HUANG Wen-jing, PENG Xiao-han, CHEN Da, LI Shu-an 2021, 47 (1):  78-82.  Abstract ( 206 )   PDF (2502KB) ( 327 )   Save N,N'-dicyclohexyldiazene-N,N'-dioxide was prepared by oxidation of cyclohexylamine with the combined oxidant of sodium percarbonate-hydrogen peroxide-tetraacetylethylenediamine. Effects of the ratio of oxidant, pH, reaction temperature, reaction time and aging time after reaction on the yield were investigated by either orthogonal or single-factor experiments. The optimized process conditions are as follows: n(cyclohexylamine): n(sodium percarbonate): n(hydrogen peroxide): n(tetraacetylethylenediamine)=1:3.0:3.0:1.75, in water/ethyl acetate mixed solution (rotio of amount of substance=5.3:1.0) with pH =9 at 33 ℃ reaction for 3 h, and aging for 12 h, the yield reaches as high as 98.3%. The structure of the product was characterized by IR, 1H NMR, 13C NMR and MS. References | Related Articles | Metrics

Automation Technique and Computer Technology

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Dynamic output feedback control of networked system with communication constraints ZHU Chao-qun, LI Liu-yang, JIN Hui 2021, 47 (1):  83-90.  Abstract ( 242 )   PDF (1124KB) ( 713 )   Save In this paper, the design of dynamic output feedback controller in networked control systems is studied for a class of networked control systems with access constraints and time-varying delays. Considering that the media access constraint obeys Markov distribution and the upper bound of time-varying delay is less than one sampling period, the networked control system should be built into a kind of uncertain time-discrete Markov jump system in modeling of the system. According to the Lyapunov stability theory and the state augmentation method, the sufficient conditions for the asymptotic stability of the closed-loop networked control system are therefore given, and a dynamic output feedback controller may be designed to make the closed-loop system asymptotically stable. Finally, a numerical example is provided to demonstrate the correctness and effectiveness of the proposed modeling method. References | Related Articles | Metrics

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Measures of combinatorial centrality based on network local and global characteristics LU Peng-li, ZHOU Geng 2021, 47 (1):  91-96.  Abstract ( 310 )   PDF (3238KB) ( 505 )   Save This paper describes the significant influence of node centrality (i.e., the importance of nodes) on network robustness in complex networks, and elaborates also advantages as well as limitations of various importance methods for evaluating nodes. Combining inverse sum index(ISI), degree centrality(DC)and betweenness centrality(BC), a measurement method of combinatorial centrality(IDB)is proposed based on two kinds of artificial networks and two real networks. Simulation experiments are carried out to characterize the importance of nodes by differences of the maximum connected sub-graph of the network before and after the nodes are deleted. The feasibility and effectiveness of this method are verified by the simulation. The simulation results show that the performance of the combined centrality measurement method proposed is better than that of a single node in the aspect of ranking of node importance. References | Related Articles | Metrics

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Short-term load forecasting based on linear regression under MapReduce framework WU Li-zhen, KONG Chun, CHEN Wei 2021, 47 (1):  97-104.  Abstract ( 275 )   PDF (2853KB) ( 634 )   Save In order to solve problems of slow calculation speed and low prediction accuracy caused by large amount of data and various kinds of data in load forecasting, a linear regression model based on small batch random gradient descent method is proposed in this paper under the framework of MapReduce parallel programming. First of all, in order to clean up repetitive data and bad data generated by the intelligent distribution terminal, the adaptive nearest neighbor sorting algorithm is proposed to remove the repeated data, and accordingly the K-means clustering method is used to eliminate abnormal data and incomplete data. The F-test method is then employed to test whether a data set can represent the load linearly. The T-test method is further adopted to test the significance of linear relationship between the characteristic vector and the load. Finally, any characteristic vector with weak linear relationship with the load is accordingly eliminated as a result. According to the above methods, a short-term load forecasting model is established and applied to the short-term load forecasting of distribution network in Wuwei, Gansu Province. Results from the prediction show that the average absolute percentage error of the proposed short-term load forecasting model is about 2.043%, and the root mean square error takes about 3 112.62. These forecasted errors meet the requirements of load forecasting, and not all improve greatly the speed of load calculation but also shorten the time for load forecasting. References | Related Articles | Metrics

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New fractional chaotic system circuit design and synchronization control YAN Min-xiu, XU Hui 2021, 47 (1):  105-112.  Abstract ( 308 )   PDF (2069KB) ( 567 )   Save For a new three-dimensional fractional chaotic system with only one nonlinear term, chaotic characteristics of the system are verified firstly by analyzing phase trajectory, Lyapunov exponent spectrum, power spectrum and Poincare section. Secondly, the stability of the equilibrium point of the system and the bifurcation diagram of the system with respect to fractional order and parameters are studied. The bifurcation diagram shows that the system has abundant chaotic characteristics. Then, a fractional-order chaotic circuit of the system is designed and simulated in software Multisim. The simulation results verify the possibility of realizing the new fractional chaotic system. Finally, the synchronization problem of fractional order systems with disturbances and uncertain parameters is studied. A sliding mode controller based on adaptive control is then designed, and the adaptive laws of unknown disturbances and uncertain parameters are explained reasonably. The synchronization of the system can be realized in the case of both unknown upper bound of the disturbances and parameter uncertainty. References | Related Articles | Metrics

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Cost optimization of wind-CSP combined power generation system based on simulated annealing SONG Wen-qin, ZHANG Wen-lian, LÜ Jin-li, LI Jin-jian, WANG Xing-gui, YANG Wei-man 2021, 47 (1):  113-117.  Abstract ( 190 )   PDF (1090KB) ( 370 )   Save Taking a wind-solar-thermal bundled power generation system as a research object, the full use of wind power as research background, the minimum unit power generation cost of the interconnected systems as a goal, the normal operation of the system as a constraint, and the optimization of output of the wind-solar-thermal power station as a way, an optimal control strategy based on simulated annealing algorithm is proposed in this paper. Simulation results show that, under permissible conditions, the proposed optimal control strategy can effectively reduce the unit power generation cost of the interconnected power generation systems. References | Related Articles | Metrics

Architectural Sciences

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Effect of freeze-thaw on compressibility of compacted sand in Yinchuan Plain LIU Yan, CUI Zi-zhi, HAN Li 2021, 47 (1):  118-121.  Abstract ( 229 )   PDF (1109KB) ( 438 )   Save In order to provide basic data for settlement analysis of compacted sandy soil foundation after freeze-thaw deformation stabilization, the compressibility of compacted sandy soil in Yinchuan Plain after 20 cycles of freeze-thaw was studied, with saturation of 30%, 50% and 70% and compactness of 0.88, 0.93 and 0.98 respectively. All results from our researches show that cyclic freeze-thaw increases the compressibility of compacted sand. The compressibility increment under the condition of supplementary freeze-thaw is obviously larger than that under the condition of non-supplementary freeze-thaw. Water supplementary condition is an important influencing factor. Water insulation is an effective measure to reduce the influence of freeze-thaw on compressibility. With the increase of compactness, the effect of freeze-thaw on compressibility decreases under no-water supplementary condition, but increases under water supplementary condition. Compactness and saturation have significant effects on the compressibility of compacted sand after freeze-thaw, both of which are the dominant factors. There is a good linear correlation between compressibility increment and freeze-thaw volumetric deformation rate. The compressibility increment can be estimated by freeze-thaw volumetric deformation rate to reduce test workload. All coming out of our research results have practical significance for evaluation and prevention of frost damage of compacted sand engineering in Yinchuan Plain. References | Related Articles | Metrics

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Screw pile to deal with collapsible loess foundation experiment analysis and evaluation HUANG Xue-feng, WEI Lin-hui, ZHANG Ji-lu, ZHANG Pei-ran 2021, 47 (1):  122-128.  Abstract ( 347 )   PDF (4781KB) ( 441 )   Save Because of its special pile technology and compaction effect, screw pile can effectively improve the mechanical properties of soil between piles and eliminate the collapsible of loess. In order to study the effect of screw pile on eliminating the collapsibility of loess foundation, the compaction effect of screw pile on loess under the condition of different pile center distance is studied and analyzed systematically. Test results show that the loess composite foundation treated with screw pile has a better compaction effect between pile and soil, and the collapsibility of loess is eliminated obviously. The dry density decreases with increase of the horizontal distance of the pile side due to particularity of the pile forming technology, and further the smaller the pile core distance is, the more obvious the compaction effect is. The collapsible coefficient decreases with the increase of depth and saturation. It is suggested therefore that the volumetric water content of soil instead of mass water content should be used as the influence factor of screw pile in the evaluation of collapsible loess compaction effect. Among those factors affecting the compaction effect of the screw pile in collapsible loess, the saturation focuses on the influence of soil pressure, and the liquid index mainly considers the influence of voids in the soil. References | Related Articles | Metrics

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Structural damage identification method based on local generalized curvature modal information entropy and BP neural network XIANG Chang-sheng, YUAN Zi, ZHOU Yu 2021, 47 (1):  129-135.  Abstract ( 261 )   PDF (5629KB) ( 324 )   Save In view of the fact that curvature mode is less sensitive to vibration mode nodes and can not estimate damage quantitatively, a formula of mode information entropy for generalized local curvature is deduced, based on generalized local information entropy and by introducing conception of the curvature model. The corresponding damage index is established therefore. A simple supported beam is analyzed by using the finite element software Midas civil. The dynamic parameters of the simply supported beam are extracted and processed. The first-order curvature mode and the local generalized curvature modal information entropy are used respectively as two input parameters for the neural network to identify the damage. The conclusion of two parameters having been identified are compared with each other so as to study the influence of the number of measure points on the identification accuracy of each index. The results show that the generalized local curvature mode information entropy as the input parameter of the neural network can locate and quantify the damage much better. The accuracy of indicators near the vibration mode node is higher than the result by the method of the curvature mode. When the number of measuring points takes 33, the identification accuracy becomes the highest. References | Related Articles | Metrics

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Dynamic response analysis of CFRP strengthened debris flow flexible cable net system WANG Xiu-li, ZHOU Lei 2021, 47 (1):  136-143.  Abstract ( 226 )   PDF (7132KB) ( 95 )   Save In order to improve the durability and impact resistance of debris flow flexible cable net system, a reinforced flexible cable net system combining lightweight, high strength and corrosion resistant carbon fiber reinforced polymer (CFRP) with cable net is proposed. Through nine groups of static tensile tests and numerical simulation with finite element software ANSYS/LS-DYNA, the influence of CFRP material on the static performance of reinforcements is analyzed. The dynamic responses of single cable, composite cable and cable net pasted with carbon fiber cloth under impact loading are also studied. The effect of carbon fiber cloth on impact resistance of the flexible cable net is discussed and compared with that of flexible cable without pasting carbon fiber cloth. Tested results show that in the tensile test, carbon fiber cloth can obviously improve the yield strength of reinforcement, but the improvement of tensile strength is not obvious. In the simulated impact process, the overall stiffness of the steel cable bonded with carbon fiber cloth may be improved to a certain extent, and the displacement is reduced under all levels of impact loads. Carbon fiber sheet can share part of stress of a steel cable without failure. The carbon fiber sheet near the impact point or at the fixed end of the cable is prone to failure, resulting in a “sudden change” in the stress of the cable. References | Related Articles | Metrics

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Study on performance of C50 mechanism sand concrete by high frequency vibration stirring QIN Ren-jie, ZHANG Ren, DENG Luo-bin, LIU Xue-peng 2021, 47 (1):  144-149.  Abstract ( 348 )   PDF (6477KB) ( 442 )   Save Based on the background of an expressway project in Guizhou province, an experimental investigation on mechanical sand C50 concrete prepared by high frequency vibration was carried out in the construction site laboratory. The main raw materials are selected in test and their performances are tested and optimized to determine the best mixing ratio of the C50 machine-made sand concrete. The compressive strength and durability of the C50 machine-made sand concretes prepared by different stirring methods are tested and compared with each other. The compressive strength and durability of C50 sand concretes prepared by different stirring methods were tested and compared further, and internal microstructures of C50 sand concretes prepared by different stirring methods were observed one by one by industrial CT scanning. Tested results indicate that the high-grade concrete of machine-made sand may be prepared by using the special high-frequency vibration mechanism. Compared with the ordinary self-falling machine-made sand concrete, it is found that the performance of the concrete prepared by high-frequency vibration is higher than that of the concrete prepared by ordinary stirring. The compressive strength and durability of the concrete are improved therefore. The internal structure of the machine-made sand concrete prepared by high-frequency vibration stirring becomes more compact and uniform, and the integrity of the concrete is better as a result. References | Related Articles | Metrics

Scientific

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The (strong) complements of frames in Hilbert K-submodules DONG Fang-fang, PEI Rui-chang 2021, 47 (1):  150-154.  Abstract ( 169 )   PDF (1044KB) ( 297 )   Save The concepts of frame transform and orthogonal projection in Hilbert K-submodulesare are introduced in this paper. The Hilbert base, the (strong) complement of frames and the inner product of straight sum in Hilbert K-modules are redefined hereby. The (strong) complements of frames in Hilbert K-submodules are mainly studied from the aspect of orthogonal projection by the relationship between the frame transform and the orthogonal projection. Finally, some important results coming from the researches are obtained and generalized. References | Related Articles | Metrics

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Pseudo-parallel space-like hypersurfaces with three different eigenvalues in Mn(c)×R1 DAI Zhong-zhu, JIANG Yun-zhi, CHU Pei-pei 2021, 47 (1):  155-157.  Abstract ( 169 )   PDF (1009KB) ( 393 )   Save The pseudo-parallel space-like hypersurface in Lorentzian product space Mn(c)×R1 is studied, and the necessary and sufficient conditions for the hypersurfaces to be pseudo-parallel are hence obtained. This proves that the pseudo-parallel hypersurfaces are equivalent to H-parallel hypersurfaces, and proves further that the pseudo-parallel space-like hypersurfaces with three different eigenvalues are constantly-angled hypersurfaces. References | Related Articles | Metrics

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Analysis of statically indeterminate problem of shape memory alloy beam under thermal and mechanical loads YANG Jing-ning, WANG Yong-xiang, TANG Jian 2021, 47 (1):  158-163.  Abstract ( 216 )   PDF (2482KB) ( 232 )   Save Based on the bending deformation theory of beam and the stress-strain relationship of shape memory alloy, and further taking the relationship between critical stress and critical temperature of the shape memory alloy into account, the nonlinear mechanical behavior of statically indeterminate beam of shape memory alloy under the condition of impure bending is analyzed in this paper. In order to describe directly the asymmetry of phase transformation on both sides of the beam under tension or compression, a tension-compression asymmetry coefficient is hereby introduced. The stress distribution on cross section at each phase transformation stage is then analyzed. By solving the equilibrium equation, the displacement and curvature of neutral axis and the change of phase boundary along the axial direction are therefore obtained. References | Related Articles | Metrics

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Free vibration and buckling characteristics of four-sides compressed FGM rectangular plates resting on Winkler-Pasternak foundation TENG Zhao-chun, WANG Jun-lin 2021, 47 (1):  164-172.  Abstract ( 267 )   PDF (3937KB) ( 422 )   Save Based on the classical thin plate theory, a governing differential equation is derived by using the generalized Hamilton principle and the equation is treated to dimensionless. The differential transformation method (DTM) is then utilized to determine first three dimensionless natural frequencies and buckling loads of the equation under different boundary conditions. The solution of the equation is reduced further to two cases: functionally graded plate without foundation and common material plate with foundation. The DTM solution is compared with the solution published in literature, and both results are consistent indicating the applicability and accuracy of DTM. Finally, the effects of boundary conditions, gradient index, elastic stiffness coefficient of the foundation, shear stiffness coefficient as well as aspect ratio of the foundation on the dimensionless natural frequency and critical buckling load of the FGM rectangular plate are analyzed respectively. The results show that: under the boundary conditions studied, the stronger the boundary constraint is, the larger the dimensionless natural frequency is; the increase of elastic stiffness coefficient, shear stiffness coefficient as well as aspect ratio of the foundation will also lead to the increase of the dimensionless natural frequency; the increase of in-plane pressure load may lead to the decrease of the dimensionless natural frequency; the larger the aspect ratio, the smaller the critical buckling load; the larger the gradient index, the smaller the critical buckling load; the larger the gradient index, the smaller the critical buckling load. References | Related Articles | Metrics