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28 August 2021, Volume 47 Issue 4 Previous Issue    Next Issue

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Materials Science and Engineering

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Microstructure and properties of K4169 superalloy with nano polycrystalline reinforcement LI Ya-min, ZHOU Sheng-rui, HU Wei 2021, 47 (4):  1-5.  Abstract ( 419 )   PDF (2010KB) ( 462 )   Save A manual electric arc furnace andwater-cooled copper mould were used to prepare superalloy K4169. The microstructure of the alloy as-cast and standard heat treatment was examined by XRD, SEM, TEM, and the mechanical properties of the standard heat treated alloy were tested. The results show that as-cast K4169 alloy is amorphous-nanocrystalline material, the precipitation in grain is very fine and smaller than 10nm. The γ″ and γ′ phase are precipitated as nano polycrystalline after standard heat treatment the alloy. Because of the reinforcement by nano polycrystalline, the fracture strength σb of alloy can reach 1 203.91 MPa, and the yield strength σ0.2 is 818.93 MPa, while the elongationδ is 16.8%, and the hardness reaches 112.4 HRB, and the tensile fracture characteristics conform to the ductile fracture mechanism. References | Related Articles | Metrics

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First-principles calculation of optical properties of Cu/Al co-doped ZnO LI Wei-xue, GAO Shan-shan, DAI Jian-feng, SUO Zhong-qiang, WANG Qing 2021, 47 (4):  6-12.  Abstract ( 360 )   PDF (5141KB) ( 405 )   Save Using CASTEP module based on density functional theory in Material Studio 2017 software, the simulation of ZnO supercell (2×2×2) was established, Zn atoms in supercell were replaced by different proportions of Cu/Al (Cu-Al, 2Cu-Al and Cu-2Al) in the same case, a Zn1－x－yCuxAlyO system was obtained, and the electronic structure and optical properties of pure ZnO and ZnO codoped with Cu-Al were calculated by the first-principles. The results show that the light absorption of the above-mentioned doped systems is red-shifted in the low energy zone, and the system is degenerate semiconductor. For different purposes of ZnO, the optical absorption or light transmission of the system in visible light can be improved by controlling Cu/Al doping ratio. In visible light, the light absorption of Zn0.812 5Cu0.125Al0.062 5O system is the strongest, which can be used to make photoelectrode materials for solar panels. The high transmittance of the Zn0.812 5Cu0.062 5Al0.125O system can be used to make high transmittance ZnO semiconductor thin films. References | Related Articles | Metrics

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Microstructure, mechanical and corrosion properties of an as-extruded Mg-Dy-Ni alloy modified by sliding friction treatment BI Guang-li , CHEN Si-qi, JIANG Jing, LI Yuan-dong ZHANG Yu-sheng, JIANG Chun-hong 2021, 47 (4):  13-21.  Abstract ( 223 )   PDF (7416KB) ( 67 )   Save The effects of the sliding friction treatment (SFT) on the microstructure, mechanical and corrosion properties of as-extruded Mg-12Dy-1.1 Ni (wt.%) alloy were investigated.The results shows that the SFT refined the surface grain size of the as-extruded alloy, the LPSO phase and Mg24Dy5 granular phase were crushed, and promoting their uniformly distributed. The SFT improved the mechanical and corrosion properties of the extruded alloy. The SFT alloy exhibited the higher maximum tensile strength (UTS=356 MPa) and elongation (ε=25%). The high tensile properties of the SFT alloy mainly originated from grain refinement, the dispersion strengthening of 18R-LPSO phase andphase precipitation strengthening of 14H-LPSO. Additionally,the weight loss rate of the SFT alloy immersed in 0.1 mol NaCl for 1 h decreased from 3.02 mg/cm2/h to 1.86 mg/cm2/h compared with as-extruded alloy. The corrosion current density of the SFT alloy decreased to 2.98 mA/cm2. The good corrosion property of the SFT alloy was related to the uniform distribution of alloying elements and the second phase particles. References | Related Articles | Metrics

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Study on arc and pool characteristics of DP-TIG welding with additional transverse alternating magnetic field QU Huai-yu, LIU Fen-xia, LIU Wen-lan, FENG Xiao-chun YU Jiang-rui, FU Xiao-yue 2021, 47 (4):  22-25.  Abstract ( 257 )   PDF (2004KB) ( 503 )   Save The defects of weld profiles in large-current and high-speed welding can be improved by adding alternating magnetic field. In order to obtain the influence of different magnetic excitation parameters on the arc and pool characteristics of DP-TIG (deep penetration TIG) welding, the DP-TIG welding experiment of 12 mm Q345B plate was carried out with additional transverse alternating magnetic field. The arc shapes were observed by a high-speed camera system, the arc pressures were measured through the small hole method, and the weld pool section profiles were analyzed based on the metallographic corrosion method. The results show that, compared with DP-TIG welding without magnetic field, the arc shape of DP-TIG welding with additional transverse alternating magnetic field changes obviously, the peak value of arc pressure first decreases and then increases with the increase of alternating frequency, and the weld pool section profile transits from finger-shape to pot-bottom-shape. In addition, the iron content in the weld surface of Ni-based overlay welding is less than 5%, and the dilution degree of welding material is low. References | Related Articles | Metrics

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Study on fretting wear mechanism of TC4 alloy in different media SONG Wei, LI Wan-jia, YU Shu-rong, MA Rong-rong 2021, 47 (4):  26-32.  Abstract ( 369 )   PDF (4283KB) ( 340 )   Save The fretting wear characteristics of GCr15/TC4 alloy pairs under mixed slip state in air medium and pure water environment were investigated by SRV-IV fretting wear tester. Three-dimensional morphology, wear volume, wear surface morphology, friction coefficient curve and fretting diagram were characterized by laser confocal microscope and scanning electron microscope to explore the fretting wear mechanism of TC4 alloy under mixed slip state in different environmental media. The results show that the change trend of friction coefficient curve in three media is basically the same. Under the condition of dry friction, the friction coefficient of air environment at 25 ℃ is high and fluctuates greatly, the wear volume is the largest, and the wear mechanism is mainly adhesive wear and slight oxidation wear. In 300 ℃ atmosphere environment, the friction coefficient and fluctuation degree are the smallest. High temperature and friction heat accelerate the oxidation of abrasive particles. The formation of the third body reveals that TC4 alloy has high temperature wear resistance, and the wear mechanism is adhesive wear and oxidation wear. Compared with dry friction, the friction coefficient, fluctuation degree and wear rate in water-covered environment are between them. Water medium plays a role in lubrication and antifriction, and the wear mechanism is abrasive wear. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Fault diagnosis method for rolling bearing based on cloud model and ensemble extreme learning machine ZHAO Rong-zhen, MA Sen-cai, WU Yao-chun 2021, 47 (4):  33-39.  Abstract ( 276 )   PDF (3066KB) ( 258 )   Save Aiming at the uncertainty and non-stationarity of bearing vibration signal as well as the slow convergence rate and poor stability of BP neural network learning algorithm, a rolling bearing fault pattern recognition method based on cloud theory and ensemble extreme learning machine was proposed. The pre-processed signal was cloudized to generate the signal cloud under different states of rolling bearing. Three parameters that can determine the signal cloud distribution were as follows: expectation, entropy and hyper entropy. These three parameters were taken as the characteristic quantities that characterize the bearing state and the original bearing state data set was constructed. Then, the fault feature data set that was normalized sent to the ensemble extreme learning machine for identification. The results showed that the cloud-ensemble extreme learning machine method could effectively realize bearing fault pattern recognition. Compared with the traditional neural network recognition method, the method had higher recognition rate and stability, and the ensemble extreme learning machine had a better performance in anti-noise. References | Related Articles | Metrics

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Effect of stress ratio on stress intensity factor of mode-Ⅰ crack at interface of composite plate LI You-tang, YANG Long 2021, 47 (4):  40-44.  Abstract ( 249 )   PDF (1534KB) ( 330 )   Save Taking mode-Ⅰ interface crack of aluminum-steel composite material as the research object, the node displacement extrapolation method is used to solve the stress intensity factor ofmode-Ⅰ interface crack of the composite material. The obtained stress intensity factor was expressed by the node displacement. The finite element numerical simulation was carried out to study the relationship of stress ratio and stress intensity factor. The results show that under the same stress ratio condition, the stress intensity factor increases with the increase of crack size ratio. Under the same crack size ratio, the stress intensity factor increases with the increase of stress ratio. References | Related Articles | Metrics

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Analysis of thickness of damping layer of large wind turbine blades and study on flutter suppression YANG Rui, YANG Wei, CHEN Zhi-long 2021, 47 (4):  45-51.  Abstract ( 273 )   PDF (2574KB) ( 439 )   Save In order to enhance the vibration suppression effect of large wind turbine blades, from the perspective of increasing the structural damping of the blades, the 8 MW wind turbine blades are taken as the object of study, and the design of the damping layer and the position of the damping layer are used to provide the basis for establishing the finite element model of the damping blade. SHELL181 and SOLID185 elements are used to simulate the upper and lower skins and damping layers of the blades, modal analysis are performed on the two models of undamped blades and damped blades, and the effect of the thickness change of the damping layer on the overall quality, natural frequency and structural loss factor of the original blades are discussed. The optimal laying thickness of the damping layer of the damping blade of the 8MW wind turbine is determined. Finally, based on the optimal damping layer thickness, the two types of blade vibration suppression effects are compared and analyzed. Combined with the structural loss factor, it is found that the thickness of the damping layer is not as large as possible. The optimum thickness of damping layer on the original blade can improve the ability of vibration suppression with little mass increase. References | Related Articles | Metrics

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Unsteady analysis of hydraulic performance of reactor coolant pump based on detached eddy simulation WANG Xiu-yong, DU Yong-feng, WANG Dong-shan, LÜ Xue, LI Yi-bin 2021, 47 (4):  52-58.  Abstract ( 257 )   PDF (6258KB) ( 451 )   Save In order to study the unsteady characteristics of hydraulic performance of reactor coolant pump under design conditions, based on the DDES(delay detached eddy simulation) turbulence model, the unsteady flow field of a reactor coolant pump was calculated, and the vortex structure captured by Q criterion was analyzed. The results show that, in a rotating period, the transient external characteristics of the pump have irregular periodic characteristics under the action of static and dynamic interference. The vortex structure in the passage of impeller and guide vane presents the unsteady phenomenon of periodic splitting and fusion, while the vortex structure in the pressurized water chamber is the change process of development and diffusion. The change of the vortex structure at the inlet of the guide vane will cause different degrees of blockage, thus, the fluctuation of the outlet pressure causes the pulsation effect of the hydraulic performance of the pump and intensifies the vibration of the pump. References | Related Articles | Metrics

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Research on product evolutionary design based on constraint network SU Jian-ning , BAI Rui-sheng , LI Xiong , BAI Xing-yi 2021, 47 (4):  59-65.  Abstract ( 243 )   PDF (2434KB) ( 317 )   Save In order to solve the problem of product design under constraints, a product innovative design model based on constraint network was established under the guidance of complex network theory and graph theory. Firstly, relevant factors were selected from the design constraint database as constraint variables to construct the design constraint network. Secondly, the centrality indexes of constraint network were calculated through dual graph to achieve the rank of node importance, and then the problem of design constraints were summed up and solved. Finally, a constraint-based evolutionary design system of product was established. By analyzing of constructed network, taking luminous jade cup as an example, key nodes were obtained, and concrete problems of design constraints were summed up. The methods such as dynamic simulation and interval constraint of control points were used to solve these problems. An evolutionary design system for luminous jade cup was developed, the form evolution was carried out on the representative samples of traditional luminous cup, and a series of design schemes satisfying the constraint conditions were generated. The results show that product design under the guidance of constraint network could be effectively realized. References | Related Articles | Metrics

Chemical Industry and Light Industry

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Flame retardant property of Salen-metal complex polyphosphazenes in epoxy resin YANG Bao-ping, WANG Nian-nian, CUI Jin-feng, GUO Jun-hong, TIAN Li 2021, 47 (4):  66-75.  Abstract ( 224 )   PDF (5553KB) ( 365 )   Save In order to reduce the fire risk of epoxy resin (EP), three new types of Salen-metal complex polyphosphazene Salen-PZN-M(M = Ni, Zn, Cu) was prepared by condensation polymerization.The structure and morphology of Salen- PZN-M were characterized by infrared spectroscopy (FTIR), electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).Thermogravimetric analysis (TGA) and conical calorimeter (CCT) were used to characterize the thermal stability and combustion performance of the composite.The flame retardant mechanism of Salen-PZN-M/EP was analyzed by TG-FTIR, SEM, Raman test (LRS) and FTIR.TGA results showed that when Salen-PZN-M (mass fraction 5%)was added, different coordination metals had different effects on the composite.In the conical calorimetric test, the total heat release (PHRR) and total smoke release (TSP) of flame-retardant EP mixed with Salen-PZN-M(mass fraction 5%) were reduced by 20.41%, 37% and 16.93%, respectively, compared with the release of toxic CO gas.TG-FTIR results showed that Salen-PZN-M could reduce the formation of harmful gases.The flame retardant mechanism of Salen-PZN-M may be gas phase quenching, non-flammable gas release, synergistic catalytic carbonization effect and formation of extremely thermal stable components. References | Related Articles | Metrics

Automation Technique and Computer Technology

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Resonance suppression strategy of LLCL grid-connected inverter considering change of power network impedance WU Li-zhen, AN Li-feng, CHEN Wei, HAO Xiao-hong 2021, 47 (4):  76-82.  Abstract ( 450 )   PDF (4726KB) ( 432 )   Save Under the condition of weak grid, the normal operation of the grid-connected inverter will be affected by the background harmonics of the grid and the dynamic changes of the grid impedance, resulting harmonic resonance occurring in the grid-connected current. Therefore, a new resonant suppression strategy for LLCL grid-connected inverters is proposed. Based on the weighted average current control and grid voltage feedforward control, the strategy introduces the capacitive current feedback link, which preserves the advantages of eliminating the influence of grid voltage on the grid-connected current in the traditional grid voltage feedforward control method.By setting the feedback coefficient in the new feedback link, the resonance peak can be effectively suppressed, and at the same time, the stability of the grid-connected inverter is not affected by the grid impedance, which improves the stability of the LLCL grid-connected inverter and reduces the harmonic content of the grid-connected current. Finally, the effectiveness of the new strategy of resonance suppression is verified by building the simulation and experimental platform. References | Related Articles | Metrics

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Random forest regression model based on improved fruit fly optimization algorithm and its application in wind speed forecasting ZHU Chang-sheng, LI Sui-han 2021, 47 (4):  83-90.  Abstract ( 361 )   PDF (3146KB) ( 426 )   Save To solve the problem that it is difficult to determine the combination of parameters and obtain the precise forecasting results for the wind speed forecasting based on random forest (RF), an improved fruit fly optimization algorithm (IFOA) was used to optimize the parameters of RFR. Exponential function and trigonometric function were introduced into the fruit fly optimization algorithm (FOA) to realize the adaptive update of step size in search, which enhances the algorithm’s ability of global optimization and local exploration. Combining the advantages of RFR with a good tolerance for noise and abnormal values, IFOA was used to optimize the main parameters of RFR, and the optimized model was applied to wind speed forecasting. The experimental results show that the IFOA-RFR combined model has higher prediction accuracy compared with other models, and the feasibility of this method in wind speed prediction is verified. References | Related Articles | Metrics

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Centrality algorithm of complex network based on neighborhood betweenness entropy and neighborhood degree entropy LU Peng-li, ZHOU Geng 2021, 47 (4):  91-98.  Abstract ( 326 )   PDF (2297KB) ( 632 )   Save Identifying the important nodes of complex network is always the key point of complex network research, and also the important theoretical basis of network stability determination. The commonly used central indicators to identify the important nodes include the centrality of the betweenness, the centrality of the degree, the centrality of the eigenvector and the centrality of K-core. These indicators have some limitations in identifying the important nodes. In order to solve the above problems, the neighbor node set is divided into two parts: the related neighbor node set (MR) and the unrelated neighbor node set (MUR). Based on the characteristics of graph entropy, a new information entropy NBE and NDE are proposed. Combined with NBE and NDE, new centrality RNC and URNC are proposed. In the experiment, dynamic attack is used to evaluate the efficiency of the new centrality index on one experimental network model and five real networks. By comparison, the new centrality is more efficient than the traditional centrality in identifying important nodes. References | Related Articles | Metrics

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Modeling and simulation of ionospheric range equation for high frequency surface radar YANG Yong-feng, YANG Xu-guang, SHANG Shang, YU Chang-jun 2021, 47 (4):  99-105.  Abstract ( 320 )   PDF (2047KB) ( 590 )   Save The distributed radar range equations of volume target and surface target are established, according to the unique distribution characteristics of ionosphere, and the scattering coefficient of the ionospheric RCS is estimated based on the principle of high frequency coherent scattering for irregularities. Thus, the generalized radar formula based on the physical mechanism of the ionosphere is derived, quantizing the impact of ionospheric characteristic parameters on HF radar system. Simulation results show that the near-vertical ionospheric echo conforms to the pulse-limited model, and the oblique ionospheric echo conforms to the beam-limited model, for the case of surface scattering with wide beam in HF surface wave radar. For volume scattering, the most important factor affecting the ionospheric clutter intensity is the amplitude of irregularities fluctuation. References | Related Articles | Metrics

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Radio signal classification based on deep learning LIU Jin-xia 2021, 47 (4):  106-110.  Abstract ( 466 )   PDF (2191KB) ( 538 )   Save The related technologies of radio signal classification are first studied, and then a novel deep learning network based on residual neural network and group convolutional neural network is proposed to realize radio signal classification. The neural network is trained based on sample composed of in-phase component signal and quadrature component signal. The experimental results show that the classification accuracy of 24 kinds of signals reaches 95.69% at 10 dB, and the effectiveness and practicability of the network architecture are revealed. References | Related Articles | Metrics

Architectural Sciences

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A optical fiber sensing monitoring device for reinforcement corrosion in concrete structures LI Zhong, CUI Hong, WANG Hong-xing, ZHANG Xi 2021, 47 (4):  111-115.  Abstract ( 253 )   PDF (1711KB) ( 699 )   Save Steel corrosion is becoming the main factor that affects the durability of reinforced concrete structures. The volume expansion of steel bar after corrosion causes the cover to crack gradually, which reduces structure performance and affects structural durability. Based on the corrosion expansion principle of steel bars in reinforced concrete structures and the principle of fiber grating strain sensing technology, a new corrosion monitoring device for steel bars is proposed and designed. According to the relationship between FBG wavelength and corrosion rate of steel bar, reinforced concrete specimens were made and accelerated test was carried out. Finally, ABAQUS finite element software is used to carry out numerical simulation with the experimental results, and the simulation results are in good agreement with the test results. The test results show that the new steel corrosion sensor can effectively monitor the corrosion degree of steel bars and realize the whole process monitoring of concrete cover cracking. References | Related Articles | Metrics

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Comparative analysis of seismic response of smart frame-rocking wall structure with dual energy dissipation elements LUO Wei-gang, LIU Ji-bin, ZHANG Yang, GUO Yi-ling, QI Pan, SONG Jiang-peng 2021, 47 (4):  116-124.  Abstract ( 200 )   PDF (4130KB) ( 326 )   Save Directed against the issues of frame-shear wall structure floor diaphragm were damaged or coupling beam failed, and the plastic hinges appeared at the bottom of shear wall under strong earthquake, a smart frame-shear wall dual structure system with BRB passive energy dissipation in between the frame and shear-wall was developed by the author's research group, and the shear wall is set as the rocking shear wall with metal damper at the bottom. A new frame-rocking shear wall structure system with dual energy dissipation elements is set up. In this paper, a six-story reinforced concrete frame-shear wall model are established using ABAQUS as prototype, the traditional frame-shear wall structure, the smart frame-shear wall dual structure, the frame-rocking wall structure with BRB in between rocking wall and frame, and the frame-rocking shear wall structure system with dual energy dissipation elements are compared. To obtain dynamic response of each structure, the non-linear dynamic time-history analysis is conducted. Results show that when the BRB yield strength ratio is 0.1~1, the seismic responses of the frame-rocking shear wall structure with dual energy dissipation elements are less than that of traditional structure. The frame inter-storey drift is also effectively controlled. It is further explained that, under the appropriate parameter value of the BRB and MD, the seismic response of the structure with dual energy dissipation elements is smaller than that of the single energy dissipation element. References | Related Articles | Metrics

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Numerical simulation of seismic performance of new type crimping PEC column-steel beam composite frame with partial self-centering BRS energy-dissipating connection JI Yun, FANG You-zhen, ZHANG Zhi-cheng, HUANG Zhi-hao 2021, 47 (4):  125-134.  Abstract ( 210 )   PDF (5722KB) ( 221 )   Save To study the seismic performance of new type crimping PEC column-steel beam composite frame with partial self-centering BRS energy-dissipating connection, several design parameters as layout of penetrating bolts, BRS plate hole size of T-stub, axial force of PEC column, connection style at bottom of PEC column, 5 specimens’ models with 1∶2 scale was established by use of the finite element software ABAQUS to simulate under the lateral cyclic loading. The seismic performance of the hysteretic behavior, lateral stiffness, energy-dissipation capacity and self-centering function were analyzed. Research results showed that arrangement of bolts for test could make mechanical developing process be postponed, while practical engineering arrangement of bolts could make performance-based design target be achieved effectively; performance-based design target of partial self-centering connection was primarily depended on the slotted hole size of T-stub; the axial force of PEC column has little effect on the initial stiffness and bearing capacity, but behavior of partial self-centering connection was developed fastly by the second-order effect; sound coordination of self-centering function, energy-dissipation capacity and safety redundancy was achieved for partial self-centering connection used in all specimens. References | Related Articles | Metrics

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Application of cavity expansion theory based on D-P revised criterion in fracturing grouting of loess WANG Teng, LI Ping, DING Yan-mei, SONG Yu 2021, 47 (4):  135-141.  Abstract ( 250 )   PDF (3434KB) ( 249 )   Save Based on the theory of plastic mechanics and large deformation, considering the hole expansion problem of Drucker-Prager modified criterion, an analysis model of loess splitting grouting pressure is established. The small deformation theory is adopted in the elastic zone and the large deformation theory is adopted in the plastic zone. The theoretical solutions of the stress field and displacement field of the elastic and plastic zone around the grouting bubble are derived. The analytical solutions of the radius of the plastic zone and the starting grouting pressure are studied. Finally, the engineering example is used to demonstrate. The results show that Based on the theoretical model of circular cavity expansion considering D-P correction criterion, the radial stress and circumferential stress show a nonlinear decreasing relationship with the increase of ru/rP. Under undrained condition, with the increase of soil material parameters (c、φ、E、ν), the splitting pressure increases nonlinearly when the slurry splits the soil vertically and horizontally. The theoretical calculation value is 514.2~693.7 kPa, which is close to the measured value of 430~780 kPa. It shows that the theoretical analysis method has a certain practical value in the splitting grouting project in loess area. References | Related Articles | Metrics

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Study on coupling model of prestress loss of anchor cable and soil creep of high slope in loess area WAN Nian-qing, DING Ying-xia, DING Ya-fei, HOU Xi-nan, ZHU Yan-peng 2021, 47 (4):  142-148.  Abstract ( 278 )   PDF (1811KB) ( 376 )   Save The prestressed anchor cable anchoring technology is widely used because it can effectively control the slope deformation, but at the same time, there are also a lot of engineering failure problems caused by the loss of anchoring force. Based on M-2K model, this model is established, which is suitable for M-B-B model for creep coupling of anchor cable and slope in Loess. Meanwhile, the corresponding constitutive equation, relaxation equation and creep equation are derived, which theoretically solves the relationship between the change of anchorage force and slope creep. Taking an unstable slope treatment project in Chengguan District of Lanzhou City as an example, the genetic algorithm is adopted, which can reversely calculate the creep parameters of the model soil. The results are compared with the existing M-K-B model. The results show that the M-B-B model is more suitable for high slope in loess area, and it can be used to predict the change of prestress in the long run. The project is divided into filling soil, which leads to large horizontal deformation of filling soil. There is a slow rise stage of prestress before the stable stage of prestress loss, and the M-B-B model can perfectly fit this change. The research results can be used as reference for the design, construction and safe operation of anchorage engineering. References | Related Articles | Metrics

Scientific

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X-Ding projective modules WU De-jun, SONG Meng-yu 2021, 47 (4):  149-156.  Abstract ( 281 )   PDF (712KB) ( 276 )   Save Let R be an associative ring with identity and X is a class that contains all flat R-modules, the definitions of X-Ding projective modules and X-Ding projective dimensions are introduced and the relative properties are studied. A right R-module M is called X-Ding projective if there exists an exact sequenceP=∶…→P1→P0→P0→P1→…of projective right R-modules such that M=Ker (P0→P1) andHomR(P,F) is exact whenever F∈X. It is proved that the class of all X-Ding projective modules is projectively resolving and is closed under direct sums and direct summands. In addition, it is proved that ifGX-Dpd(R)<∞,then (X-DP(R), (X-DP(R))⊥) is a complete here ditary cotorsion pair. References | Related Articles | Metrics

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Nonlinear large deflection analysis of the composite structure bellows diaphragm HAN Ming-jun, ZHOU Chao-yu, LI Hong-rui, MA Lian-sheng 2021, 47 (4):  157-164.  Abstract ( 478 )   PDF (2643KB) ( 347 )   Save Based on the theory of nonlinear large deflection theory, the continuous method is used to analyze the nonlinear large deformation of the bellows diaphragm of flat conical shell-circulararc-circular plate composite structure,which is widely used in the dry gas seal system.The numerical calculation is carried out by the method modified iteration method of theory of plates and shells, the nonlinear large deformation of a composite structure bellows diaphragm with one end fixed and another end free is solved. At the same time, the nonlinear bearing capacity of the different inclination angles of the bellows flat conical shell part diaphragm at the maximum deflection of the arc is analyzed by the quadratic approximation solution. And on the basis of the same waveform,the diaphragm bearing capacity of the parameters such as wave depth and arc radius at the maximum deflection of the arc is analyzed.With the increase of the inclined angle of the bellows diaphragm, the nonlinear deflection of the diaphragm increases. With the increase of the height of the bellows diaphragm, the nonlinear deflection of the diaphragm increases. With the increase of the arc wavelength of the bellows diaphragm, the nonlinear deflection of the diaphragm increases. References | Related Articles | Metrics

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Study on excitation characteristics of SiF2 molecule with external electric fields in different directions LIANG Dong-mei, HUANG Yi, CHEN Liang, ZENG Fan-ju, SUN Guang-yu, JING Tao 2021, 47 (4):  165-172.  Abstract ( 202 )   PDF (2809KB) ( 221 )   Save A density functional method(B3P86) with 6-31++g**(3df,3pd) basis sets has been used to study the geometric parameters, total energies, electronic structure and energy levels with the external electric field (－0.05~0.05 a.u.) along the y-and z-axe direction; On the basis of optimized configuration, the excitation properties of molecules are calculated by the configuration interaction singles(CIS-B3P86) method with external electric field. The results show that thegeometric parameters of molecules change obviously with the electric field. Such asexternal electric field in zdirection makes the bond length and dipole moment decrease, the total energy first decreases and then increases, and the energy gap decreases. The excitation energy and wavelength of the excited state change obviously with the size and direction of the external electric field, and the oscillator strength is affected by the direction of the electric field, which changes the transition performance of the molecule. References | Related Articles | Metrics