Table of Content

31 December 2021, Volume 27 Issue 6

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Invited Review

Numerical simulations of aero-engine turbine flow and noise

YAN Jia, CHAI Junsheng, REN Guozhe, WU Chenhan, TANG Xiaolong, YANG Xiaoquan, DING Jue, WENG Peifen

2021, 27(6):  993-1009.  doi:10.12066/j.issn.1007-2861.2349

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The development of reliable, efficient and low noise engine is an unremitting pursuit of aviation industry. Turbine is one of the core components of aero-engine, and its flow and heat transfer are always the top issues throughout the design and manufacture. As the noise from the engine fan and jet has been greatly controlled, turbine noise has become more important and has gained extensive concerns. To stimulate the industrial usage of proposed numerical methods in turbine simulations, numerical methods and investigations of the complex turbulence flow, heat transfer and noise in aero-engine turbines are reviewed. Firstly, focus is placed on the state-of-art of flow and heat transfer simulation in rotating cavities and rotating blades. Secondly, the research status of aeroengine turbine noise is analyzed, and the numerical methods of noise prediction are reviewed. Based on this, suggestions on further development of numerical methods and specialized software for the simulation of turbine flow, heat transfer and noise are proposed.



Research Articles

Design of shortcuts to adiabaticity for coupled harmonic oscillators

YANG Guanzhuo, CHEN Xi

2021, 27(6):  1010-1017.  doi:10.12066/j.issn.1007-2861.2226

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With the emergence of wide applications in atomic cooling and shuttling for quantum information processing, shortcuts to adiabaticity have been proposed to accelerate slow adiabatic processes. In this study, we consider a shortcut to adiabaticity for coupled harmonic oscillators and its application in a quantum heat engine. Based on the dynamical invariant of coupled harmonic oscillators, we first obtain an Ermakov equation and then design the frequency of a coupled harmonic oscillator using an inverse engineering method to speed up the adiabatic process without final excitation. Our results provide a theoretical basis for designing shortcuts to adiabatic state control of coupled harmonic oscillators and superadiabatic quantum heat engines.



Application of lightweight neural network and Hash tracking algorithm in embedded face capture system

XU Genglin, RAN Feng, DENG Liang, SHI Huakang, GUO Aiying

2021, 27(6):  1018-1028.  doi:10.12066/j.issn.1007-2861.2187

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To address the difficulty of balancing the speed and accuracy of face capture systems embedded in mobile devices, a fast and accurate embedded face capture system is designed based on the combination of a lightweight neural network and a Hash tracking algorithm. Firstly, an optimised face detection network is constructed based on the lightweight MobileNet solid state disk (SSD) object detector. After pruning and face alignment, a Hash algorithm is combined to track a face based on the average Hash (aHash) and a perceptual Hash (pHash) design, in which the key point distance and face size as well as the four-direction Sobel operator are used as the three standards to extract the best face image. Finally, MobileFaceNet is applied to identify the best face. The experimental results indicate that the speed of the proposed face detection algorithm is increased by 22.6% compared to using the standard MobileNet SSD. Furthermore, compared with using only the mean Hash or the pHash algorithm, the matching accuracy is improved by 21.7% and 10.1% when the combined Hash algorithm is applied, respectively. The face capture accuracy is greater than 95%, and the capture speed can reach 28 frame/s.



Kronecker tensor product representation of flexoelectric coefficients for various symmetries

YU Pengfei, PENG Limimg, LENG Weifeng, SUO Yaohong

2021, 27(6):  1029-1037.  doi:10.12066/j.issn.1007-2861.2335

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Kronecker tensor products play an important role in determining the symmetry of material coefficients. By constructing the orthogonal rotation tensor fourth-order Kronecker power, which conforms to the symmetry of the flexoelectric coefficient, for the first time, the matrix structure representation of the flexoelectric coefficient of seven crystal systems, 32 crystal point groups and isotropic is derived. These results confirm the number of independent flexoelectric coefficients and their specific component forms. The correctness of these results is verified by comparing with the findings of a previous work.



Effect of surface roughness on flow structures of turbulent Rayleigh-Bénard convection

YANG Jianlin, ZHANG Yizhao, ZHOU Quan

2021, 27(6):  1038-1046.  doi:10.12066/j.issn.1007-2861.2225

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Most thermal convection phenomena in nature have rough boundaries. Thus, the study of Rayleigh-Bénard (RB) turbulent thermal convection on rough surfaces is theoretically and practically significant in understanding turbulent heat transfer and flow structures. In this study, the effect of two-dimensional rough surfaces on flow structures of turbulent RB convection is investigated through numerical simulations. The main parameters, the Rayleigh number (Ra) and Prandtl number (Pr), were 10$^{7 }\le $ $Ra\le 10^{9}$ and $Pr = 0.7.$ An isosceles right-angle triangle of the rough element shape was used for calculations. The results showed that the inhibition of the rough element on the large-scale circulation and the enhancement of the rough element on the plume generation and secondary vortices led to the complexity of the Reynolds number (Re) variation and the abnormal scaling relationship between Ra and Re.



Preparation and electrochemical properties of porous Sb$_{\mathbf 2}$O$_{\mathbf 3}$/Sb lithium-ion battery anode materials

ZHANG Haojie, HU Yemin

2021, 27(6):  1047-1055.  doi:10.12066/j.issn.1007-2861.2229

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An antimony (Sb) and Sb$_{2}$O$_{3}$ composite is prepared by mild oxidization of porous Sb. The oxidization temperature is determined through a gradient experiment, and the Sb$_{2}$O$_{3}$ content of the composite is controlled by controlling the oxidization duration. Results show that Sb contributes good conductivity and that the rate performance of the composite is enhanced, whereas Sb$_{2}$O$_{3 }$ contributes high capacity and the Li$_{2}$O produced during the conversion reaction can prevent agglomeration of Sb. As a result of the synergistic effect, the initial Coulombic efficiency of the Sb$_{2}$O$_{3}$/Sb composite is 78.2% and the retained capacity is 729.6 mAh$\cdot$g$^{-1}$ after 100 cycles at a current density of 200 mA$\cdot$g$^{-1}$. The Sb$_{2}$O$_{3}$/Sb composite sustains a capacity of 203 mAh$\cdot$g$^{-1}$ even at a current density of 10 000 mA$\cdot$g$^{-1}$. Compared with porous Sb, both the cyclic and rate performance of the Sb$_{2}$O$_{3}$/Sb composite is significantly enhanced.



Water quality of Dianshan Lake and its correlations with diffuse agricultural pollution from rice fields

ZHENG Yali, HU Xuefeng, LU Siwen, LI Jun, LUO Fan, LAN Guojun, ZHAO Jinglong, ZHANG Weijie

2021, 27(6):  1056-1064.  doi:10.12066/j.issn.1007-2861.2202

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The water quality of the inlets and outlets of Dianshan Lake was monitored annually. Likewise, a field experiment was conducted near Dianshan Lake to study the variations of nutrients in the surface water of experimental plots for various fertilizer treatments. The results indicated that the average contents of NH$_{3}$-Nandtotal P (TP) of the water in Dianshan Lake were 0.47 and 0.13 mg/L, respectively, which only met the Class Ⅴ level specified by the China Surface Water Environmental Quality Standard. The water quality of the inlets of Dianshan Lake varied from site to site and was generally worse than the water quality of the outlets. Further study found close correlations between the annual variations of nutrients in Dianshan Lake and the variations in the surface water of the rice fields. This suggests that the water quality of the lake was strongly influenced by diffuse agricultural pollution from the rice fields surrounding the lake. Therefore, to improve the water quality of Dianshan Lake further, it is highly important to reduce and control the diffuse agricultural pollution.



Molecular simulation of dislocation nucleation induced by nanosized helium bubbles in irradiated tungsten materials

HUANG Xinlong, Lü Chenyangtao, SUN Yuyao, CHU Haijian

2021, 27(6):  1065-1073.  doi:10.12066/j.issn.1007-2861.2222

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Based on molecular dynamics simulation, the effects of helium bubble pressure, bubble size, and bubble temperature on the mechanism of dislocation nucleation in irradiated tungsten materials are investigated. The nudged elastic band (NEB) method is applied to analyze the energy barrier of dislocation nucleation induced by a helium bubble for the first time. An ultimate value of the helium/vacancy ratio is determined. When the helium/vacancy ratio exceeds this ultimate value, a nanosized helium bubble is generated and a prismatic dislocation loop is formed and grows, through dislocation nucleation driven by high internal pressure, dislocation competition and reaction, and dislocation cross-slip. The ultimate internal pressure required for dislocation nucleation induced by the helium bubbles decreases with the increase in temperature and the growth of the helium bubbles. Increasing the helium/vacancy ratio can effectively reduce the energy barrier required for dislocation nucleation.



Analysis of radial consolidation of unsaturated soil with vertical drains considering drain resistance and the smear effect

QIN Aifang, XU Weifang, JIANG Lianghua

2021, 27(6):  1074-1084.  doi:10.12066/j.issn.1007-2861.2231

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Based on the equal-strain hypothesis and Fredlund's consolidation theory of unsaturated soil mechanics, a semi-analytical solution to consolidation of unsaturated soil with vertical drains considering drain resistance and the smear effect is proposed. Firstly, the governing equations are transformed into easy-to-solve equivalent linear partial differential equations by introducing new variables and the Laplace transform, with both drain resistance and smear effect conditions in the solution derivation taken into account. By utilizing Crump's method, the inverse Laplace transform is then used to obtain the average excess pore-air and pore-water pressures and the average consolidation degree in the time domain. Moreover, the validity of the solution is verified by degenerating and comparing with the existing solution to the foundation with ideal boundary conditions of unsaturated soil based on the free-strain assumption. The results show that an increase in the drain resistance factor, smear coefficient, or smear zone radius ratio will extend the consolidation time. Drain resistance and the smear effect are considered useful for more reasonably predicting the consolidation degree of unsaturated soil with vertical drains.



Effect of an isolation trench on deformation and stress induced by dynamic compaction based on the discrete element method

LI Yuqi, YANG Fuan, ZHANG Wenjie

2021, 27(6):  1085-1093.  doi:10.12066/j.issn.1007-2861.2230

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To analyze the influence of an isolation trench on the foundation deformation and stress induced by dynamic compaction, based on two-dimensional discrete element theory and a previous centrifuge model test of a sand foundation under dynamic compaction, a foundation model under dynamic compaction was established. The influence of depth and location of the isolation trench on the upheaval of the ground surface was studied. The stress variation in the range of 3 m outside the trench was discussed at a grain level. The results show that an isolation trench can effectively reduce the upheaval deformation of the ground surface; however, the location and depth of the isolation trench have little effect on it. The influence of the isolation trench on the stress change gradually decreases with the increase of the depth of the monitoring point. At a depth of >4 m below the ground, the effect of the isolation trench on the stress change far from the center of the ramming pit is very small.



Stability mechanism of the excavation face for shield tunneling in soft and hard composite ground

ZHOU Liji, ZHANG Mengxi, WANG Wei, JIA Wurong, ZHANG Xiaoqing

2021, 27(6):  1094-1105.  doi:10.12066/j.issn.1007-2861.2228

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When the shield passes through composite strata, especially the upper soft and lower hard strata, instability of the excavation surface is variable and the stress mechanism is complex. Consequently, engineering disasters caused by instability of the excavation surface can occasionally occur. Based on the Fo-Guan intercity railway tunnel project, a three-dimensional finite element numerical model is constructed and a stratum composite ratio parameter is introduced to improve the wedge theory of earth pressure. The effects of different stratum composite ratios and soft soil internal friction angles on the stability of the excavation surface when the shield passes through the upper-soft and lower-hard strata are analyzed. The results indicate that the maximum deformation of the shield excavation face appears at a specific position in the soft soil area, which is related to the proportion of soft soil. The displacement of the excavation face can be divided into three stages: slow growth, sharp increase, and instability failure. When the support pressure ratio is close to the limit support pressure ratio, the excavation face deformation will increase sharply. The theoretical solution of the improved partial wedge model is consistent with the numerical simulation results, and the theory is reasonable. These research results can provide some theoretical guidance for shield construction of similar strata.



Method for detecting rotational stiffness of column-beam joints and timber elastic modulus of modern timber structures

LIU Jianhui, XU Chao, OUYANG Yu

2021, 27(6):  1106-1117.  doi:10.12066/j.issn.1007-2861.2149

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The mechanical properties and deformation characteristics of wooden column-beam structures are studied by using the wooden column-beam structures of a Xintai Warehouse as a prototype. The results show that the wooden column-beam joints have obvious semi-rigid connection characteristics, and the joint stiffness changes with the load. In addition, the upper and lower limits and the average value of the elastic modulus of the wood are determined relatively accurately by measuring the vertical displacement of the wooden beam and the lateral displacement of the middle of the wooden column, combined with the relevant calculation and analysis. The rotational stiffness of the column-beam joint and elastic modulus can be obtained by performing an on-site test on the wood structure to be tested using the proposed method. The results of this study have significance for the detection, identification and reinforcement design of historically protected buildings.



Application of DIC technology in soil displacement analyses around model piles

JIANG Yun, LU Ye, WANG Xiaoyong

2021, 27(6):  1118-1127.  doi:10.12066/j.issn.1007-2861.2227

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To study the extrusion effect of the press-in method on surrounding soil, the soil displacement field was determined using the semi-model pile test combined with digital image correlation (DIC) technology and horizontal soil stress was measured by mini pressure cells. Firstly, the cumulative displacement of soil was analyzed at different distances from the pile and the changing law of soil stress was recorded during the pile press-in process. Secondly, the final soil displacement was recorded and analyzed when piling was completed. Finally, the disturbance layer was recorded at the pile-soil interface using a local camera, and the thickness of the disturbance layer was measured. Cumulative displacement gradually reached a stable state, and the measure of displacement decreased with distance from the pile. The maximum value of horizontal soil displacement was at a depth of $16R$ ($R$ is the pile radius). The direction of vertical displacement varied with depth. The development of lateral soil stress was considered including the effects of horizontal and vertical displacement. A strong positive relationship was found between lateral soil stress and vertical as well as horizontal soil displacement during the pile press-in process. The results support the development of a squeezing effect caused by the pile press-in process and the mechanism between the pile and the soil.



Experiment on a diaphragm connection between U-shaped steel concrete composite beams and square steel tube concrete columns

ZHOU Jian, YANG Feng

2021, 27(6):  1128-1137.  doi:10.12066/j.issn.1007-2861.2205

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A new type of diaphragm connection between U-shaped steel reinforced concrete composite beams and concrete-filled steel tubular columns is introduced. An experimental study is conducted under low-cyclic repeated loading, and a finite element (FE) analysis of the test is performed using ABAQUS. The failure location, stress distribution, and a hysteresis curve of the joints obtained by finite element simulation are basically consistent with the experimental results. Based on the FE method, the effects of the wall thicknesses of the U-shaped steel beams, steel tube columns, and through partition on the seismic behavior of joints are investigated. Combined with test failures, the deficiencies of the joint structure are improved. Results showed that the wall thicknesses of the U-shaped steel beams had a significant effect on the seismic performance of the joints, whereas those of the steel tube columns and that of the through diaphragm had little impact on seismic performance. However, compared with the single increase in material size, reasonable construction measures could improve the seismic performance of the joints to a greater extent, take advantage of the superiority of composite materials, improve the efficiency of material utilization, and reduce engineering costs.



Bayesian inference of HIV transmission in MSM population in Beijing

CHENG Jinjin, JIN Xin, WANG Zhen, LOU Jie

2021, 27(6):  1138-1143.  doi:10.12066/j.issn.1007-2861.2195

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In this study, the Bayesian phylogenetic method was used to extract valuable information on epidemiological processes from 44 HIV$^{-1}$ (human immunodeficiency virus$^{-1}$) gene sequences of a young men who have sex with men (MSM) population sampled in Beijing, especially the transmission dynamic parameter, i.e., the effective reproductive number $R_{\rm e}$. These results reveal that the transmission of HIV/acquired immune deficiency syndrome (AIDS) increased rapidly during the period of 2006—2014, which may have a close relation to the growing acceptance of MSM in the past decade among young Chinese. The result reveals the HIV/AIDS transmission trend among the young MSM population over the past decade. Such information is meaningful and can help people understand and predict an epidemic, and establish intervention measures for the future.



The properties of complex centroid body

JIN Tian, LENG Gangsong

2021, 27(6):  1144-1148.  doi:10.12066/j.issn.1007-2861.2234

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We define a complex centroid body and the support function. We prove the linearity of the complex centroid operator. For any two non-empty complex convex bodies, we prove the inclusion relationship of the Minkowski addition on the complex centroid body and extend it to convex bodies.



Asymptotics and large time behavior of solutions to a type of time-space fractional wave equation

LI Zhiqiang

2021, 27(6):  1149-1161.  doi:10.12066/j.issn.1007-2861.2257

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This study investigates the asymptotic behaviors of a solution to time-space fractional partial differential equation with the fractional Laplacian, where the time fractional derivative is in the sense of Caputo, with the order $\alpha\in(1,2)$. By using the properties of the Fox $H$-function and Young's inequality, gradient estimates and large time behavior of the solution are obtained.



In vitro evaluation of the prebiotic properties for Lactobacillus fermentum B44

HAN Jin, WU Yanting, WAN Sibao, WU Zhengjun

2021, 27(6):  1162-1170.  doi:10.12066/j.issn.1007-2861.2207

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Lactobacillus fermentum B44 is a lactic acid strain isolated from Bulgarian homemade yoghurt. In vitro experiments showed that L. fermentum B44 has strong hydrophobicity (79.67%) and an electrostatic effect of low acid and high alkali; the strain could tolerate 1 mg/mL lysozyme and has a better adhesion and survival ability in oral cavities. In addition, it also has a high self-agglomeration rate (13.34%) and strong co-aggregation with Streptococcus mutans. When co-cultured with S. mutans, the formation of S. mutans biofilm was inhibited, and the inhibition rate was 63.43%. The above results showed that L. fermentum B44 could play a positive role in preventing and treating human dental caries; it is a potential oral probiotic and has a suitable application prospect in human oral health.