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28 August 2020, Volume 46 Issue 4 Previous Issue    Next Issue

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Materials Science and Engineering

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Effect of hot rolling deformation on microstructure and mechanical properties of 2507 duplex stainless steel prepared via the aluminothermic reaction LA Pei-qing, SHI Yu, WANG Ke-liang, SHENG Jie, LI Zheng-ning, ZHOU Xue-yuan 2020, 46 (4):  1-5.  Abstract ( 293 )   PDF (3179KB) ( 355 )   Save The 2507 duplex stainless steel with nano/micro-crystalline structure prepared by the aluminothermic reaction was subjected to a rolling treatment at 1 000 ℃ with 40%, 60% and 80% deformation. The microstructure of the as-rolled state was investigated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The mechanical properties were measured by using a universal tensile testing machine and a Brook field optical hardness measuring instrument respectively. All measured results show that the rolling process makes austenite and ferrite phases elongated along the rolling direction and the transformation of austenite to ferrite happens in the steel as a result. With increase of rolling deformation, the nanocrystalline size does not change too much, while volume fraction of the nanocrystalline decreases. The yield strength of the steel is about 232, 284, 456 MPa, tensile strength is about 533, 577, 582 MPa, hardness is 325, 330, 337 HV, elongation takes 12.5%, 11.1% and 11.5% when the steel was rolled at 1 000 ℃ with 40%, 60% and 80% deformation, respectively. References | Related Articles | Metrics

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Energy consumption and corrosion resistance of MAO coatings with same thicknesses fabricated under different voltages MA Ying, LIANG Zhi-long, AN Ling-yun, SUN Le, WANG Sheng, WANG Zhan-ying 2020, 46 (4):  6-9.  Abstract ( 272 )   PDF (1517KB) ( 363 )   Save AZ91D magnesium alloy was treated by micro-arc oxidation (MAO) technique in the silicate-containing electrolyte, and two groups of MAO coatings that have same thickness of 25 μm and same thickness of 40 μm were prepared respectively by adjusting voltage. The time for treatment, energy consumption, mass to thickness ratio and corrosion resistance of the two groups of equal thickness coatings were investigated in the case of increase of voltage, and compared further with each other trying to find out latent regularity. The results show that with the increase of voltage, the time for treatment as well as the energy consumption of the two groups of equal thickness coatings are both shortened and reduced respectively. At the same time, in contrast to coatings with thickness of 25 μm, those with thickness of 40 μm need longer time for treatment and consume more energy. Meanwhile, due to the low density of 40 μm coating, its corrosion resistance in sodium chloride medium is poorer, but its thicker thickness makes coatings exhibiting more excellent corrosion resistance in HNO3 corrosive medium. References | Related Articles | Metrics

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Effect of laser power on microstructure and properties of laser nitriding layer of TC4 alloy GU Yu-fen, GENG Pei-biao, SHI Yu, LI Guang, GUO Jin-chang 2020, 46 (4):  10-14.  Abstract ( 389 )   PDF (3625KB) ( 390 )   Save The nitrided layer of TC4 titanium alloy was prepared by using IPG high-power fiber laser in nitrogen atmosphere in this study. Effects of optical fiber laser power on surface morphology, microstructure and microhardness of the TC4 titanium alloy nitrided layer were investigated. Obtained results have demonstrated that the surface of the nitrided layer takes rough and smooth of two types. The microstructure of nitrided layer is dendritic, and that of HAZ is needle-like. When scanning speed takes 10 mm/s, the nitrogen flow rate is 10 L/min, the distance of the nozzle is 3 mm and the defocus reaches 0 mm, the penetration depth and width of the nitrided layer increase with the increase of laser power. In addition, the microhardness at the same depth from the surface of the nitrided layer increases with the increase of laser power. References | Related Articles | Metrics

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Effect of Sn-xTi/Al2O3 wettability with Ti addition SUI Ran, JU Chun-yan, JIA Jin-long, ZHAO Dan 2020, 46 (4):  15-21.  Abstract ( 238 )   PDF (3340KB) ( 251 )   Save In order to solve a problem that addition of active element Ti is beneficial to improve wettability of metal/Al2O3 system, but the wettability mechanism is still unclear, the wettability of molten Sn-(0%,2%,5%) Ti alloy on Al2O3 surface in high vacuum at 973~1 273 K was studied by improved sessile drop method. The results show that increase of Ti content significantly improves the wettability ofSn-xTi/Al2O3 system. The reason for wettability improvement is that the adsorption of Ti at the interface reduces free energy of the solid/liquid interface, rather than the reaction product precipitated at the interface. For this conclusion, conducted experimental results are verified by a statistical thermodynamic model of adsorption, and it is proved that the spreading kinetics of Sn-xTi Al2O3 system is well controlled by the adsorption kinetics to a great extent. References | Related Articles | Metrics

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Numerical simulation of stress and deformation for Al/steel sheet welding by trailing cooling of argon gas FAN Ding, HAN Miao-miao, ZHAO Jin-long, YU Xiao-quan, GAO Ming-jiang 2020, 46 (4):  22-26.  Abstract ( 289 )   PDF (3548KB) ( 716 )   Save The numerical simulation of butt brazing process of Al/steel dissimilar metal sheet under different welding conditions was carried out by using finite element analysis software ANSYS. Two models are established for TIG arc heat source and cold source respectively. Comparative analyses of residual stress and deformation reveal that the argon quenching at low temperature in the process of welding can effectively reduce longitudinal residual stress and deformation in the weld, resulting in apparent reduction by 32.8% and 48.1%, respectively. In order to verify the validity and prove the accuracy of our finite element simulation results, a welding test of Al/steel dissimilar metal sheet was carried out. Through analytical comparisons of the predicted results of temperature field and stress field and with tested ones, it is verified the effectiveness of the numerical model. It has been shown that the residual stress and deformation in Al/steel sheet welds can be effectively controlled by argon quenching technology. References | Related Articles | Metrics

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Prediction on flux bands constrained arc welding process based on a hybrid heating source model QIAO Ji-sen, RUI Zheng-lei, GAO Zhen-yun, YANG Yuan-zhuang 2020, 46 (4):  27-32.  Abstract ( 239 )   PDF (4321KB) ( 344 )   Save By means of software ABAQUS, a hybrid heating model coupled by a Gaussian face heat source and cylindrical volume heat source is established to analysis characteristics of welding-induced temperature distribution during the process of the flux band constrained arc T-joint welding. The thermal contact conductance between the fixture and work piece has been taken into account emphatically in the model during simulation. By comparing results from simulation with those from experiments, it is found that weld morphology and thermal cycle curves of each testing point in welding are basically consistent with experimental results. Thus, it is verified that the hybrid heat source model utilized in finite element analyses is feasible and effective to predict the temperature field of the flux band constrained arc T-joint welding. In the study of temperature field distribution of the T-joint, it is also found that the temperature distribution in panel plate and core plate of the simulated T-joint becomes uniform in direction of plate thickness. In the analysis of the thermal cycle curves, it is further found that the fixture plays an apparent role in cooling stage of the workpiece. The range of welding HAZ is then predicted numerically further in this case. The predicted results are consistent with our experimental ones. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Design of centrifugal chemical pump vibration test system based on LabVIEW ZHAO Rong-zhen, HUWen-gang 2020, 46 (4):  33-37.  Abstract ( 361 )   PDF (918KB) ( 495 )   Save Due to the disadvantages of traditional centrifugal pump vibration test, such as more instruments, poor reliability and high test cost etc., this research adopts virtual instrument technology, using LabVIEW graphical and modular programming language to code a program for data acquisition, processing, preservation and fault diagnosis, and meantime utilizing closed-circuit test device, vibration acceleration sensor and data acquisition card as well to build up a system of virtual vibration test system for centrifugal pump. The hardware structure, software frame, design ideas and relevant theoretical basis all associated with the virtual instrument system are elaborated one by one in detail in this project. The vibration test system is oriented to centrifugal pump and can realize claimed functions, such as multi-channel data acquisition, real-time data analysis and data preservation. Vibration acceleration signal of tested centrifugal pump can be collected by thistesting system. The obtained signal can be analyzed by axle center track analysis plus FFT spectrum analysis. Therefore it has realized fault diagnosis of centrifugal pump. Finally, effectiveness of the virtual instrument system in actual vibration monitoring is verified on a centrifugal pump test bench. The system exhibits a good human-machine interface, and is easy to maintain and be expanded. References | Related Articles | Metrics

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Analysis of dynamic characteristics of top drive system ZHANG Li, QIAO Mu, CHEN Yue-jun, ZHANG Li-hua 2020, 46 (4):  38-41.  Abstract ( 256 )   PDF (2670KB) ( 369 )   Save In order to solve well the problem of instable operation drive system in top drive device under special working condition, an LK500-type top drive is taken as research object to analyze the real-time dynamic characteristics of its drive system. A three-dimensional model of the transmission system and a finite element model of the major gear wheel on gear shaft are established, the modal analysis and harmonic response analysis of the major gear wheel on gear shaft is carried out with the help of analysis software Ansys-Workbench, and the influence of the flexibility of gear shaft on meshing force and meshing error of the gear pairs is analyzed by using ADAMS. The results show that the excitation frequency of the system should be as far as posible from the inherent frequency of the gears to make the operation of the drive system even more smooth. However, when the gear shaft is a flexible one, its influence on meshing force between gears will less and meshing error greater, so that making the system to vibrate and having influence on the smoothness of the system operation. The simulation result will provide reference for studying the dynamic performance and optimal design of the top drive gear transmission system. References | Related Articles | Metrics

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The study of flow pulsation of involute helical gear flowmeter with external gearing YANG Guo-lai, CHEN Chen, DONG Ji-cheng, GAO Wen-tao 2020, 46 (4):  42-46.  Abstract ( 238 )   PDF (1182KB) ( 420 )   Save When investigating flow pulsation of an involute helical gear flow-meter with external gear, the instantaneous flow can be regarded as superposition of countless instantaneous flow, staggering a fixed phase angle in turn along the width of the gear tooth, due to the effect of helical angle. Following this guideline, a mathematical expression of maximum variation of flow ripple of the involute external engagement helical gear flow-meter is deduced in this article by obeying the law of energy conservation and the principle of helical gear engagement. On above basis, taking the parameter relationships in the mathematical expression and the helical gear coincidence degree as the theoretical basis, the critical helical angle and the critical helical gear width without oil trapping were deduced in this research. The analysis shows that the level of flow ripple of the involute external engagement helical gear flow-meter is lower than that of the spur gear flow-meter in the case of same tooth capacity, and the flow pulsation will decreases with the increase of helical angle. References | Related Articles | Metrics

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Study on the influence of cavitation on the performance of reactor coolant pump CHENG Xiao-rui, ZHANG Shu-yan, FU Li 2020, 46 (4):  47-54.  Abstract ( 253 )   PDF (3181KB) ( 287 )   Save In order to study the effect of cavitation development on the external characteristics of a nuclear main pump and related internal flow region, this study, based on the continuous equation, the Reynolds time-average N-S equation and the RNG k-ε turbulence model, simulates cavitation behaviors occurred in full-flow region of a nuclear model pump under the design condition. Four cavitation conditions were selected in the study. By comparing simulation results with each other, the performance variation and the variation of internal flow region of the nuclear main pump were predicted when cavitation occurred. The simulation results show that when the nuclear main pump is cavitated, the external characteristics of the pump are sensitive differently to reduction of the effective airspace margin. As the degree of cavitation increases, the head decreases sharply and the power decreases more slowly. In cavitation state, the area of flow section is reduced and the relative velocity of fluid is increased due to the squeezing effect of air bubbles generated by cavitation on the flow path of impeller. In addition, because the bubbles generated by cavitation change the fluid state in the cavitation region and decrease the hydrodynamic viscosity, the turbulent dissipation rate and the turbulent dissipation loss in the cavitation region are reduced respectively. References | Related Articles | Metrics

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Multi-objective parameters optimization of low specific speed centrifugal pump based on NSGA-Ⅱ genetic algorithm ZHAO Wei-guo, XIA Tian, SHENG Yuan-zhi, LI Shang-sheng 2020, 46 (4):  55-61.  Abstract ( 287 )   PDF (2744KB) ( 547 )   Save In order to improve hydraulic efficiency and head of a low specific-speed centrifugal pump, a low specific-speed centrifugal pump with 30 specific-speed was selected as a research object in this study. By taking the maximum head and hydraulic efficiency of centrifugal pump as two optimization objectives, the basic equation of centrifugal pump and the Plackeet-Burman test are combined for screening parameters to be optimized. By doing so. the vane outlet placement angle of centrifugal pump impeller was selected, and the wrap angle and outlet width of the blades were selected too as variables for optimization in our study. In the optimization process, 30 groups of experiments were arranged using the optimal Latin super-cubic design method, and then an approximate model between the optimization target and the variables was fitted numerically by using the RBF neural network model. The multi-objective optimization was finally carried out in terms of NSGA-Ⅱ genetic algorithm. The optimization results show that the head of the optimized impeller basically remains unchanged, the hydraulic efficiency of the impeller is 5.82% higher than that before optimization. The optimization eliminates the hump on the flow-head curve of the impeller and makes the operation of the centrifugal pump more stable. The pressure gradient in the impeller flow channel is reduced after optimization, and the area as well as size of eddies are reduced apparently to some extent. The turbulence area in the impeller flow channel becomes uniformly distributed, and blades to work are enhanced as a result. Thus the hydraulic efficiency has been improved. References | Related Articles | Metrics

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The effect of particles on the separation flow around airfoil in dusty environment LI Ren-nian, ZHAO Zhen-xi, LI De-shun, LI Yin-ran, WANG Ya-e, GUO Xing-duo 2020, 46 (4):  62-66.  Abstract ( 221 )   PDF (2406KB) ( 506 )   Save A delayed detached eddy simulation method is employed for the numerical simulation of flows around NREL S809 3D airfoil in clean air and various dusty environment with particles of different diameters. The effect of particle on the flow separation of airfoil was studied. It is shown that at an attacking angle of 8°, DDES has demonstrated the eddy shedding on the suction surface of the airfoil, and addition of particles significantly changes the regularity of eddy shedding on the suction surface of the airfoil, thus enlarging the range of the rear eddy and dissipating it faster. However, with the increase of particle diameter, the tail eddy gradually returns to the state closer to that of clean air. When the attacking angle is less than 6°, there is no flow separation on the surface of the airfoil, and the particles have little effect on the flow region. When the attacking angle is greater than 12°, the particles have even more little effect on the flow around the airfoil. Particles at different attacking angles have different effects on lift factor of the wing. The analysis of the effect of particles on the flow separation on the airfoil surface at different attacking angles shows that the attacking angle most affected seriously by particles is between 7°to 10°. References | Related Articles | Metrics

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Experimental study of heat loss of heat storage tank in solar heating system of northwest region LI Jin-ping, LIU Run, CUI Wei-dong, HUANG Juan-juan, WANG Chuan-long 2020, 46 (4):  67-72.  Abstract ( 325 )   PDF (877KB) ( 735 )   Save Taking the solar heating system in an 117.07 m2 northwest China as investigation object and the day of December 15th as an example, it is concluded that the heat loss of heat storage tank occurs mainly during the natural cooling period, the total heat loss of the heat storage tank is 9.49 MJ when its daily total heat loss coefficient is 5.68 W/℃. Then the test data of other 11 typical days is chosen to carry out the fitting of several factors of influence on total heatloss coefficient and total heat loss of the heat storage tank. It is shown that the total heat loss of the heat storage tank will be influenced by the ambient temperature and outdoor wind speed, leading to the change of the temperature of the heat storage tank. Decrease of every 1 ℃ of average ambient temperature will increase the total heat loss of heat storage tank by 0.067 MJ and the increase of every 1 m/s of outdoor wind speed will increase the total heat loss of the heat storage tank by 0.042 MJ, The increase of temperature of 1 ℃ of heat storage tank will increase the total heat loss of heat storage tank by 0.068 MJ. The increase of the temperature of 1 ℃ of heat storage tank will increas the total heat loss of the heat storage tank by 1.641 MJ. Aimed at the analysis of heat loss of heat storage tank and the present situation of indoor thermal environment, it is presented that a suggestion on indoor location of heat storage tank can be taken into consideration to enhance the heat storage capacity of heat storage tank and improve the indoor comfortableness of the building. References | Related Articles | Metrics

Chemical Industry and Light Industry

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Environmental optimization of high-efficiency cultivation of Chlorella in domestic sewage WANG Yu, SHI Wen-qiang, GUO Ya-min, LU Shi-guo, LIU Juan-juan 2020, 46 (4):  73-78.  Abstract ( 363 )   PDF (1175KB) ( 458 )   Save In order to cultivate Chlorella effectively with domestic sewage in villages and towns in northern China, the growth environment (initial sewage concentration, ambient temperature, illumination intensity and illumination time) for Chlorella was studied by single factor and orthogonal experiments in this study. The results showed that the initial sewage concentration, ambient temperature, illumination intensity and illumination time of sewage have respectively a significant effect on the growth of Chlorella under single-factor environmental conditions. The optimum initial sewage concentration is two times dilution of raw sewage, an ambient temperature of 30 ℃, an illumination intensity of 12 000 Lux, and a illumination time of 20 h. The results of orthogonal experiments showed that the optimal culture conditions of Chlorella are not a simple overlay of environmental factors, but controlled by the coupling of environmental factors. The dominant environmental factors are the initial sewage concentration and illumination time. Two times dilution of the raw sewage, the ambient temperature of 30 ℃, the illumination intensity of10 000 Lux, the illumination time of 16 h, the sewage culture Chlorella reaches the highest efficiency at this time. References | Related Articles | Metrics

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Simulation of gas-solid two-phase flow erosion in elbow LI Cang, SUN Bao-cai 2020, 46 (4):  79-83.  Abstract ( 417 )   PDF (1656KB) ( 507 )   Save On the basis of research background of a gas transmission process containing solid impurity particles, a E/CRC model for erosion-induced wear developed in ANSYS-FLUENT software is used in this paper to simulate the gas-solid two-phase flow in a 90°curved pipe in a gas pipeline. All effects such as different gas velocity, mass flow rate of solid impurity particles, and particle size of solid impurity particles on erosion-induced wear to 90° elbow of the curved pipe are discussed in detail. Our analytical results show that the larger the gas inlet velocity is, the greater the erosion rate of 90 °bend is, and the greater the mass flow rate of solid impurity particles is, the greater the erosion rate of 90°bend is. As if the particle size is less than a certain critical value, the larger the particle size is, the smaller the erosion rate is. When the particle size is larger than this critical value, the larger the particle size is, the greater the erosion rate is. The research result can be used in duty inspection of gas transportation pipeline by predicting the possibility of pipeline erosion, which can save the inspection cost and improve the safety of gas transportation in pipeline. References | Related Articles | Metrics

Automation Technique and Computer Technology

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Research on life prediction and life extension method of feedback control system under actuator degradation LI Wei, WANG Cheng-wen 2020, 46 (4):  84-90.  Abstract ( 351 )   PDF (2152KB) ( 677 )   Save During long-term operation, the control system may be affected by complex working environment, the actuator may be damaged to varying degrees and its performance will be degraded, which will cause the performance of the feedback control system to drop or even not work properly. Therefore, in view of the deterioration of system performance caused by actuator degradation, this paper establishes a degradation model for the actuator that works under combinative action of wear and shock. The working condition of the actuator is incorporated in the controller design, and the method based on the probability distribution of failure time is employed to predict remaining life of the system. By adjusting control constraints and modifying set points on line, a trade-off between system performance and actuator health index is found to delay actuator degradation and extend the life cycle of the control system. Finally, the effectiveness of the proposed method is verified by simulated examples. References | Related Articles | Metrics

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Research on adaptability for distributed PV generation connected to distribution network based risk evaluation with beyond limit WANG Zhou, YANG Chang-hai, PENG Jing, YANG Ting-ting, BAI Yong-li 2020, 46 (4):  91-95.  Abstract ( 363 )   PDF (2014KB) ( 554 )   Save In order to evaluate adaptability of distribution network with planned and distributed PV generation,aiming at questions of voltage and power flow beyond limit when distributed PV power supply connected to distribution network,typical distribution network topology structure and connection modes are both discussed in this paper. The standard node IEEE34 of distribution network system of distributed PV power model is established in Matlab/Simulink environment. Taking into account the risk brought by random output disturbance and load fluctuation of distributed PV power supply to the operation of distribution network, an index model of risk evaluation of node voltage and branch power flow beyond limit has been established. It is analyzed the capacity of the same node for different capacity power supply, and discussed mainly the access capacity of distributed PV power to distribution network, and carried out simulation experiments as well by taking the typical actual parameters of distribution network as an example. Our simulated results have verified validity of the evaluation adaptability of distribution network of the proposed method. References | Related Articles | Metrics

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Fault diagnosis of batch process based on DDNPE algorithm ZHAO Xiao-qiang, YAO Hong-juan 2020, 46 (4):  96-102.  Abstract ( 203 )   PDF (2576KB) ( 349 )   Save Traditionally, Euclidean distance determined only by neighborhood preserving embedding (NPE) algorithm is usually adopted to select the nearest neighbors for attracting characteristic features in fault diagnosis in industries. The troubleshooting effects in this way for the fault diagnosis are not effectively enough as well known. By employing a diffusion distance (DD) and combining it with NPE algorithm, a new fault diagnosis method based on the diffusion distance neighborhood preserving embedding (DDNPE) algorithm is proposed in this article by the author. The proposed new method explores the inherent popular structure embedded in the original high-dimensional data first, and reduces the data dimension, then extracts the characteristic information from the original data by learning the potential geometry information contained in the original data, while keeping local information structure in the original data popularity and unchanged. By doing so, it avoids the existing problem that the NPE algorithm selects the characteristics of the neighborhoods only by Euclidean distance. The problem of insufficient feature extraction can be avoided. It is now becoming possible to detect faults in fault diagnosis in industries by using T2 and SPE statistics and the fault variable can be also diagnosed by the variable contribution graph method. Simulation results of penicillin fermentation process coming out from this research demonstrate that the proposed method is effective indeed. References | Related Articles | Metrics

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Distributed WSN intrusion detection model based on deep forest algorithm DONG Rui-hong, YAN Hou-hua, ZHANG Qiu-yu, LI Xue-yong 2020, 46 (4):  103-109.  Abstract ( 412 )   PDF (1763KB) ( 425 )   Save In view of the poor performance, poor real-time detection along with higher model complexity of the existing feature selection algorithm and classification algorithm adopted in the wireless sensor network (WSN) intrusion detection system, a distributed WSN intrusion detection model based on the random forest algorithm and the deep forest algorithm is presented in this paper. The proposed model preprocesses traffic data passing through all sensor nodes first, and then allocates lightweight random forest classifier to sensor nodes and cluster head nodes respectively. Sensor nodes and cluster head nodes work up together to deal with the traffic data. Consequently, with the help of the deep forest algorithm emerged attacking behaviors can be seized at a base station from a large amount of traffic data. Intrusion detection can be thus carried out by means real-time classification of intrusion behaviors in WSN. In order to validate effectiveness of the proposed model, we use WSN-DS and NSL-KDD data sets to evaluate the reliability of the proposed model. The experimental results show that, comparing with the existing intrusion detection model, the proposed model does having better detection performance and better real-time performance. The weakness of over fitting in modeling can be avoided as a result. References | Related Articles | Metrics

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Image matching algorithm based on Agast-Adaboost XU Zhu-ye, ZHAO Xiao-qiang 2020, 46 (4):  110-115.  Abstract ( 390 )   PDF (4051KB) ( 359 )   Save In response to the problem of high mismatch rate and low match rate of traditional floating-point feature description algorithm,a algorithm of ALBFMA (Agast-Adaboost local binary feature matching algorithm, ALBFMA) based on AGAST and fast feature extraction is proposed in this paper. Firstly, this algorithm builds Gaussian scale space pyramid and integrates AGAST with scale space and extracts relevant feature points. Then it uses the improved Adaboost algorithm to conduct binary description for those feature points to generate the feature vector, thus providing a high matching rate and matching accuracy of the algorithm. Our experimental results show that compared with the existing algorithms, the proposed algorithm has advantages of high matching accuracy, and have good robustness for lighting, scale and rotation. References | Related Articles | Metrics

Architectural Sciences

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A comparative analysis of damping effect in small high-rise with different roof-TMD DING Yan-mei, WANG Teng, KOU Xing-ting, JIAO Zhen-yu, SONG Yu 2020, 46 (4):  116-121.  Abstract ( 402 )   PDF (2131KB) ( 388 )   Save According to the damping effect of roof water tank and thermal insulation layer on the overall structure of a house, this paper establishes three kinds of TMD control devices for different roofs with lead rubber bearings, i.e. TMD for single water tank roof, TMD for double water tank roof and TMD for roof thermal insulation layer. The seismic reduction effect of those control devices is predicted and compared then by means of finite element analyses and dynamic time-history analyses as well. The compared results indicate that these three kinds of roof-TMD have obviously vibration-suppressing effect. As the quality ratio is within 3% the greater the mass is, the more homogeneous distribution of load is, the batter the vibration-suppressing effect will be. Among which the thermal-insulating roof-TMD is the best, the double tank-TMD becomes the second, and the single tank-TMD takes the worst. Our research findings may provide a theoretical basis for the follow-up study and design of TMD. References | Related Articles | Metrics

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Effects of dry-wet and freeze-thaw cycles on microstructure of soil based on SEM TIAN Hui, LI Li, ZHANG Kun, WANG Peng 2020, 46 (4):  122-127.  Abstract ( 373 )   PDF (3297KB) ( 466 )   Save In order to investigate the cause of surface spalling of highway slope, we extracted Q3 undisturbed loess at K700+200 of a highway. In the investigation, scanning electron microscope (SEM) was used to detect prepared samples after 0, 1, 5, 10 and 20 dry-wet cycles and freeze-thaw cycles respectively. Changes of SEM images after different dry-wet cycles and freeze-thaw cycles were compared and analyzed quantitatively. Soil skeleton as well as pore morphology are analyzed either by IPP image processing software in our research. Change rules of surface porosity, average pore diameter and pore size fractal dimension after different times of dry-wet cycle and freeze-thaw cycle are obtained therefore, and variations of soil microstructure after different dry-wet cycles and freeze-thaw cycles are quantitatively analyzed. Results coming from our investigations indicate that:Both dry-wet cycle and freeze-thaw cycle have great influence on soil microstructure. It is revealed further that the surface spalling of loess slope is closely related to dry-wet cycle and freeze-thaw cycle. References | Related Articles | Metrics

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The simplified design methods of four-bolt and eight-bolt extended end plate connections LIU Xiu-li, WANG Yan, GUO Chao 2020, 46 (4):  128-132.  Abstract ( 180 )   PDF (933KB) ( 343 )   Save In order to popularize the application of extended end-plate connections, this research work, based on the theory of plastic hinge distribution and the theory of equivalent T-shaped parts, employs a theoretical method to deduce and analyze equivalent T-shaped parts connected by four bolts and eight bolts. Consequently, a series of simplified design formulas are obtained, and coefficients associated with the simplified design formulas are fitted in terms of calculated examples. The comparison of the calculated examples has demonstrated that all results calculated in terms of the simplified design method are in good agreement with the American LRFD CODE and Chinese JGJ82 CODE, and furthermore the proposed simplified design method is convenient for engineering predictions and applications. The research results may provide references for popularization and applications of the extended end-plate connections. References | Related Articles | Metrics

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Effect of cross-section shape on the lateral response of steel piles LI Wei-chao, GE Bin, YANG Min 2020, 46 (4):  133-138.  Abstract ( 282 )   PDF (1031KB) ( 339 )   Save Current researches on pile withspecial-shaped sections mainly focus on the vertical bearing capacity of cast-in-place concrete piles, but there is little research on thelateral response of thin-walled steel piles with special-shaped sections. By means of numerical simulation, this paper presents an extensive study on the lateral response of steel piles with three different cross-section shapes (including the circular pipe pile, square hollow pile and X-section pile) and two different aspect ratios (the ratio of pile embedded length to the outer diameter or width). The results show that: for semi-rigid piles, compared with that of the pipe pile having the same displacement at the pile head, the bearing capacity of the square hollow pile increases about 9% and X-section pile increases up to 11%. for flexible piles, with a given pile head displacement, the bearing capacity of square hollow pile is about 15% higher than that of pipe pile and X-section pile. Furtherly, this paper discusses the merit and demerit ofthese three cross-section pile by comparing their displacement and bending moment, from which, the relationships betweem them are developed to aid the industrial design. References | Related Articles | Metrics

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Effect of hydraulic loading on percolation performance and porosity of bio-retention cell system WANG Ya-jun, GENG Chong-chong, CAI Wen-juan, LI Jin-shou 2020, 46 (4):  139-142.  Abstract ( 286 )   PDF (1448KB) ( 481 )   Save Bio-retention cell system is the main way to treat rain water runoff in the initial stage. It can not only retain water and save it, but also has a certain effect in reducing pollutants. Therefore, its applications in the field of water treatment are gradually expanding. The variation of permeability coefficient and average porosity of the bio-retention cell were investigated experimentally under four different influent loads. Results coming out from the investigation indicate that both the permeability coefficient and the average porosity decrease gradually with running time, and tend to be stable finally. When the influent load is less than 2.0 m3/(m2·d), there is a certain correlation between the permeability coefficient and the average porosity. The biological structure appearing in the bio-retention cell system reaches stable when it runs for about 25 days. When the influent load is greater than or equal to 4 m3/(m2·d), the hydraulic scouring effect has a great influence on the internal biological structure of the bio-retention cell system. Variations of the permeability coefficient and the average porosity are not distinct in this case as a result. References | Related Articles | Metrics

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Study of deformation characteristics of compacted Q2、Q3 loess in Yan’an region QIAO Jun-yi, HAO Ming-yue, KONG Yang 2020, 46 (4):  143-149.  Abstract ( 252 )   PDF (4256KB) ( 344 )   Save Indoor confined consolidation tests of compacted Q2、Q3 loess in Yan’an region are carried out in this research work. Factors to influence deformation characteristics of the compacted loess are discussed either. A best fitting model is established to characterize stress-strain relationship of the compacted loess under lateral conditions. On this basis, this paper analyzes the relationship between secant modulus and vertical compressive stress and the relationship between secant modulus and compactness under the condition of optimal water content, and puts forward a generally applicable constitutive model for the compacted loess. The results show that: After the consolidation of compacted Q2 loess, the soil has high compactness, low gas content, low permeability and small additional deformation under applied load, so it is a good filling-material in the foundation. The Gunary model, with high fitting accuracy and good stability, is suitable for characterizing the stress-strain relationship of the compacted Q2 and Q3 loess under lateral conditions. The relationship between secant modulus and vertical compressive stress obtained from the transformation of Gunary model covers the linear relationship in the case of low pressure compactness and the nonlinear relationship in the case of high pressure compactness, which has better applicability. References | Related Articles | Metrics

Scientific

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The complete central Delannoy number YANG Sheng-liang, LIU Ting 2020, 46 (4):  150-153.  Abstract ( 372 )   PDF (737KB) ( 316 )   Save The complete central Delannoy number can be defined by Delannoy triangle or counting of lattice path. By using A-matrix of Riordan matrix, the Riordan matrix expressions of several lattice paths are derived. Several combinatorial explanations of the complete central Delannoy numbers are given and the relationship between these matrices and the complete central Delannoy number is also considered. References | Related Articles | Metrics

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D4-δ-covers and their applications WANG Yong-duo, WANG Ya-ting 2020, 46 (4):  154-156.  Abstract ( 168 )   PDF (675KB) ( 291 )   Save The concept of D4-δ-covers is introduced. A pair (F,g) is called a D4-δ-cover of a module M if F is a D4-δ-module, g an epimorphism of F onto M, and Ker(g)《δF. The properties of D4-δ-cover and their relations to projective δ-cover are studied and δ-perfect rings (semiperfect rings, semiregular rings) are characterized by using D4-δ-covers. References | Related Articles | Metrics

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Higher order Diethelm method for the time fractional diffusion equation YANG Yan, WANG Xi-yun 2020, 46 (4):  157-163.  Abstract ( 269 )   PDF (850KB) ( 385 )   Save A new implicit difference method is proposed for a time fractional diffusion equation, in which space derivatives are discretized by the central difference method. For a time fractional derivative, the Caputo fractional derivative is transformed into the Riemman-Liouville fractional derivative, and further forming it in the form of the Hadamard finite part integral. The finite part integral is then approximated by piecewise quadratic polynomials. A new 3-α order approximation scheme to the Riemman-Liouville fractional derivative can be derived as result of the approximation. Consequently, an implicit difference scheme for fractional diffusion equations, which is unconditionally stable and convergent, can be obtained. Our numerical experiments verify effectiveness of the implicit difference scheme. References | Related Articles | Metrics

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Some criteria with parameter for nonsingular H-matrices ZHANG Jun-li 2020, 46 (4):  164-168.  Abstract ( 193 )   PDF (710KB) ( 269 )   Save Some iterative criteriawith parameters for H-matrices are given according to the relations of α-diagonally dominant matrices and nonsingular H-matrices,which extend and improve some recent results.Effectiveness of the criteria is illustrated by some numerical examples. References | Related Articles | Metrics

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Dynamic load coefficient analysis of cantilever beam under the impact of heavy hammer WU Xiao 2020, 46 (4):  169-172.  Abstract ( 349 )   PDF (1294KB) ( 515 )   Save Impact phenomena of heavy hammer on cantilever beam are investigated. A motion equation for the hammer and a vibration control equation for the cantilever beam are both established therefore, and an impact force expression for the hammer acting on the cantilever beam is obtained by obeying the Galerkin principle. Obtained results point out that when mass of the hammer is grater than that of the cantilever, errors between the approximate solution of the impact force and experimental results, and those between the finite element approximation and the experimental results as well are obviously bigger without exception. When mass of the hammer is less than that of the cantilever, errors are less than 5% for above two cases. References | Related Articles | Metrics