Mechanics in Engineeringfirst published in 1979. It is administrated by the Chinese Academy of Sciences, with the Chinese Society of Theoretical and Applied Mechanics and the Institute of Mechanics, Chinese, Academy of Sciences jointly as the responsible institutions. It covers general fields of mechanics, with the widest circulation among journals devoted to mechanics in China. Its focuses are on progresses of mechanics and its interdisciplinary fields, applications in engineering, teaching notes on mechanics, profiles of scientists of mechanics, history of mechanics, interesting anecdotes, book reviews and others. With its unique features as distinguished from similar journals in China, keeps the following regular columns... More>>
08 August 2022, Volume 44 Issue 4
Hydrogen Entering Myriad Homes
RESEARCH PROGRESS OF NATURAL GAS FOLLOW-UP HYDROGEN MIXING TECHNOLOGY
ZHANG Liye, DENG Haitao, SUN Guijun, NING Chen, SUN Gang, LIU Wei, SUN Chen, LAN Xueying, LU Yanghui, JIA Guanwei, AN Yongwei, JI Shouhu, XU Weiqing
2022, 44(4):  755-766.  DOI: 10.6052/1000-0879-22-056
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Hydrogen is a secondary energy with zero emission, one of the most important energy sources to achieve the goal of “double carbon”. Using in-service natural gas pipeline or network to transport hydrogen blended to natural gas is an effective way to realize large scale transport of hydrogen. It is important to accurately control the proportion of hydrogen in the natural gas pipelines transport system. The structure and principle of electric type and mechanical type with following up hydrogen blended to natural gas system are introduced. The concentration sensors of mechanism and application with infrared absorption type, heat conduction type, semiconductor type are introduced. Then, their comprehensive measurement system in dynamic adjustment and measurement of hydrogen blended to natural gas ratio are analyzed. Three important in-service hydrogen blended to natural gas demonstration projects are introduced from the composition and operation results. Based on the engineering practice experience, the development trend of hydrogen blending to natural gas technology is projected.

HYDROGEN CONCENTRATION DISTRIBUTION IN FLOW OF HYDROGEN BLENDED TO NATURAL GAS IN PIPELINE
AN Yongwei, SUN Chen, JI Shouhu, JIA Guanwei, XU Weiqing, LIU Wei, ZHOU Liang, CAI Maolin
2022, 44(4):  767-775.  DOI: 10.6052/1000-0879-22-381
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Blending hydrogen into natural gas is the primary method to solve the mismatch between the origin and use of hydrogen and realize the large-scale and long-distance transportation for hydrogen. Hydrogen can lead to hydrogen embrittlement in natural gas pipelines and cause safety accidents. Therefore, it is necessary to investigate the regularity analysis of hydrogen composition, velocity, and accumulation in in-service natural gas pipelines. A T-type and a variable diameter type blending pipeline model have been constructed and researched for blending hydrogen in natural gas. The T-type results show that the pipe length of obvious layering and width are 35 times and 1/3 of pipe diameter, respectively. The results of variable diameter have been illustrated that the closer the blending center, the narrower of width and the lower of height with variable diameter can lead to hydrogen enrichment easily. Hydrogen embrittlement has been facile with a maximum hydrogen mole fraction of 50%~60% in blending nature gas pipelines. The results can provide a reference for the blending effect of natural gas with hydrogen and the selection of pipeline diameter.

EXPERIMENTAL STUDY ON HYDROGEN DIFFUSION AND HYDROGEN CORROSION IN STEEL PIPE
QIU Wenjie, LI Guomin, XIONG Haiyan, YU Wentao, LAN Xueying, SUN Chen, LI Bing
2022, 44(4):  776-785.  DOI: 10.6052/1000-0879-22-146
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The steel pipe transporting hydrogen-containing atmosphere will suffer from hydrogen corrosion slowly and its performance downgrades. In this study, by analyzing the mechanism of atomic hydrogen permeation and diffusion, three commonly used steel pipes (20#, 16Mn and X52) were selected for Devanathane-Stachurski hydrogen permeation experiment. The morphology of steel after hydrogen permeation was analyzed by scanning electron microscope, and the changes of self corrosion potential and current before and after hydrogen permeation were compared by potentiodynamic polarization curve. The results show that the hydrogen diffusion coefficient of 20# steel is the largest and X52 is the smallest. With the increase of hydrogen charging current density and hydrogen charging time, the corrosion degree of steel also intensifies. The potentiodynamic polarization curve test shows that the self corrosion current of 16Mn increases by two orders of magnitude and the performance decreases obviously; X52 steel has good corrosion resistance and the performance degradation is the least.

EFFECT OF METHANE ADDITION ON HYDROGEN COMBUSITON AND EXPLOSION CHARACTERISTICS
WAN Xiaogang, LIU Wei, FANG Tan, DAI Hongchao, CAI Xiao, LI Qianqian, WANG Jinhua, HUANG Zuohua, LAN Xueying, CHANG Xuelun
2022, 44(4):  786-793.  DOI: 10.6052/1000-0879-22-158
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Hydrogen application can be carried out with the heat value of combustion maintained and the risk of explosion reduced, which is a feasible technical solution. In this paper, the effects of methane addition on the flammability limit and explosion characteristics of hydrogen are studied by using a constant volume combustion bomb. A comparative study of the explosion characteristics of hydrogen-enriched/methane/air and hydrogen/air is conducted under a wide equivalence ratio. Results show that the flammability range decreases exponentially with the increase of methane addition. The upper flammability limit can be reduced by 22.9% only by adding 10% methane. However, with 10% methane addition, its laminar burning velocity decreases, its explosion time under stoichiometric ratio increases by 20 times, and the heat loss also rises, which resulted in a slight drop of its maximum explosion pressure and a significantly lower value of maximum pressure rise rate. Combined with the analysis of the flame schlieren images, it can be seen that the addition of methane could reduce the risk of combustible gas explosion, which is not only affected by the reduction of laminar burning velocity, but also related to the weakening of flame surface cracks and cellular structure.

APPLICABILITY EVALUATION AND DEMONSTRATION OF DOMESTIC GAS APPLIANCE USING NATURAL GAS–HYDROGEN MIXTURE
YANG Mucun, LIU Wei, SUN Chen, YU Wentao, LU Yanghui, LIU Hongfang, AN Zhenhua, WANG Jinhua, LAN Xueying, SHI Tingting, CHANG Xuelun
2022, 44(4):  794-800.  DOI: 10.6052/1000-0879-22-183
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Hydrogen as one of the most potential clean energy has the advantageous characters of fast combustion rate and high conversion efficiency. It can be mixed with natural gas used as industrial, commercial or domestic fuel. Many countries in the world have developed plans to apply natural gas–hydrogen mixture for residential users and carried out demonstration verification. Based on theoretical analysis and calculation of combustion characteristic parameters of natural gas–hydrogen mixture, this work investigated the adaptability and safety of domestic gas appliances using natural gas–hydrogen mixture by referring to the corresponding national standards, so as to analyze the proportion of domestic gas appliances hydrogen blending that can bear without any adjustment through experimental tests.

RESEARCH ON STANDARD DEVICE MEASURING LIQUID HYDROGEN FLOW RATE BY STATIC MASS METHOD
WANG Jiaxiang, TU Chengxu, BAO Fubing, CHEN Weijie, ZHUO Yinjie, LI Xiang, XU Haohao, WU Shuqin, XIONG Maotao
2022, 44(4):  801-808.  DOI: 10.6052/1000-0879-22-139
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Liquid hydrogen is a cryogenic fluid of ultralow-viscosity and ultralow-density. The error introduced by the replacement with other fluids such as water in flowmeter verification is large. Therefore, it is necessary to develop a liquid hydrogen flow standard device used for the actual flow verification of liquid-hydrogen flowmeters. This paper summarizes the measurement principle, structural composition and functional characteristics of the few low-temperature flow standard devices around the world. A set of standard liquid hydrogen flow rate device is designed based on the static mass method, and its technological process and feasibility are discussed. This review can be helpful to build liquid hydrogen mass flow standards and improve hydrogen flow measurement system providing technical support.

RESEARCH ON THE ISSUES AND SOLUTIONS OF LOW-TEMPERATURE ADSORPTION CHARACTERISTICS OF SMALL HYDROGEN STORAGE TANKS
CHENG Youliang, ZHANG Pan, HE Chuanjin
2022, 44(4):  809-817.  DOI: 10.6052/1000-0879-22-126
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In order to solve the problem of heat accumulation in the low temperature adsorption process of small hydrogen storage tanks, it first carried out the finite element numerical simulation of the charging and degassing characteristics of small hydrogen storage tanks equipped with different adsorption materials metal-organic frameworks MOF-177 and activated carbon AX-21-33. Studies have found that during the inflation process, the heat accumulation caused by thermal effects and compression work will seriously affect the adsorption of hydrogen. In this regard, this article proposes a solution to add heat exchange fins inside the hydrogen storage tank. By changing the position and spacing of the heat exchange fins, the effect on the temperature, pressure and adsorption capacity in the tank during the inflation process is analyzed. The simulation results show that this scheme can effectively reduce the temperature in the hydrogen storage tank, and at the same time solve the problem of heat accumulation at the bottom. The results of this study are of value for the application of hydrogen energy.

Simulation Research on Biomass Fluidized-Bed Thermochemical Conversion
NUMERICAL SIMULATION OF GAS-SOLID FLOW IN CHEMICAL LOOPING GRADED GASIFICATION FUEL REACTOR
GUO Yue, CUI Ying, SONG Tao, LU Ping, YIN Shangyi
2022, 44(4):  820-826.  DOI: 10.6052/1000-0879-22-196
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A numerical simulation of the gas-solid flow in a chemical looping gasification fuel reactor (the lower and upper part is designed as gasification and reforming reactor respectively) was carried out in this paper based on the multiphase particle-in-cell (MP-PIC) method. The sensitivity of the drag force model and the model parameters (normal-to-wall and tangent-to-wall momentum retention ewn and e) to the simulation results were verified, and appropriate models along with model parameters are determined. The effect of gas velocity and slit size at the interface between the two beds on the particle flux was investigated. The results show that the particle flux increases with gas velocity but decreases with slit size.

MODELING TAR EVOLUTION DURING BIOMASS PYROLYSIS IN A FLUIDIZED BED REACTOR BY USING A CFD–DEM METHOD
CHEN Tao, XIE Danmei, YUE Ya’nan, HOU Youmin
2022, 44(4):  827-833.  DOI: 10.6052/1000-0879-22-343
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Biomass gasification in fluidized bed reactors is one of the most important utilization methods through thermochemical conversion. Tar generation is the bottleneck of this technology. In this work, numerical simulations for biomass tar evolution under medium to high temperature pyrolysis conditions are carried out by combining a Euler–Lagrangian framework with a multistep pyrolysis model and a new tar cracking model. Comparison for the tar cracking under 600℃~800℃ operation conditions is studied and the corresponding effect on the light gas yield is also analyzed. Numerical results indicate that the established model can reasonably capture the influence of tar cracking on the pyrolysis yields. The current work provides a useful tool for the understanding of biomass pyrolysis in fluidized bed reactors.

CFD–DEM SIMULATION OF BIOMASS GASIFICAITON IN FLUIDIZED BED
KONG Dali, WANG Shuai, LUO Kun, FAN Jianren
2022, 44(4):  834-843.  DOI: 10.6052/1000-0879-22-078
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In this paper, the biomass gasification process in a bubbling fluidized bed (BFB) reactor was numerically simulated by using computational fluid dynamics–discrete element method (CFD–DEM) coupled with thermochemical and poly-dispersed drag model. After model validation, the effects of key operating parameters on particle-scale information (e.g., particle motion, mixing, heat transfer) and reactor performance were discussed. The results show that in the process of biomass gasification, convective heat transfer plays a leading role, followed by radiative heat transfer and reaction heat. The proportion of conductive heat transfer is the smallest and can be ignored. Increasing the operating temperature can enhance heat transfer and reaction, and increase the temperature of biomass particles. Increasing biomass/steam ratio promotes gasification reactions, consumes more heat and reduces biomass particle temperature. The decrease of biomass particle temperature will increase the temperature difference between biomass particles and bed material particles, so as to increase the conductive, convective and radiative heat transfer.

CFD–DEM SIMULATION OF HEAT TRANSFER DURING THE BIOMASS COMBUSTION PROCESS IN FLUIDIZED BEDS
XIE Jun, NIU Miaomiao
2022, 44(4):  844-851.  DOI: 10.6052/1000-0879-22-197
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In this paper, based on CFD–DEM, several heat transfer models were coupled with dense gas-solid flow and chemical reaction to simulate the heat transfer characteristics of biomass combustion in bubbling fluidized bed. The results show that for fuel particles, heat of reaction is dominated, and radiation and convection also play an important role, but heat conduction has little effect. With the increase of volatile content of fuel, the contributions of convection and particle-particle conduction increase, but the contribution of particle-wall conduction decreases. The local hot spot in the bed is mainly caused by the volatiles combustion, which is generated from the bed surface and rises to the freeboard. The biomass particle temperature generally increases with the decrease of local particle concentration.

Applied Research
DYNAMIC SIMULATION AND ANALYSIS OF “BRAKE FAILURE” OF TESLA ELECTRIC VEHICLE
WANG Yufan, CHEN Mengjing, ZHOU Lüwen
2022, 44(4):  852-856.  DOI: 10.6052/1000-0879-21-478
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The event of “Tesla brake failure” has sparked heated discussions in the society. In this paper, based on Ackerman steering technology and vehicle motion equations, a model is built to restore the driving state and the track before the accident according to Tesla's published data. The result is consistent with the qualitative description of the accident given by the owner. So, it can be judged that the data provided by Tesla is basically credible. This paper also discusses the three questions raised by netizens and car owners. It is proved that the braking system works normally and the possibility of overspeed driving exists.

BENDING DEFORMATION AND OPTIMAL DESIGN OF GRADIENT HONEYCOMB STIFFENED PANEL
ZHANG Chenfan, DENG Qingtian, LI Xinbo, SONG Xueli
2022, 44(4):  857-867.  DOI: 10.6052/1000-0879-21-516
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The multi-cell-wall honeycomb structure was introduced into the stiffened plate design. Based on the load-bearing method of the three-point bending experiment, the wall thickness and porosity of the honeycomb cells were designed in a gradient form. The specimens were manufactured by 3D printing technology, and the materials was polylactic acid. Through experimental testing and finite element analysis, the influence of gradient form, cell direction and bearing position on the structure's bearing performance was studied, and the stiffened layer was optimized based on the results. The results show that: the gradient form of wall thickness, the vertical direction of the cell and the closeness of the indenter axis to the horizontal direction can all improve the structural bearing performance; the optimization to stiffened layer can significantly improve the utilization rate of the materials. In addition, the specimens under different bearing positions have different destruction modes.

CRUSHING EXPERIMENT AND THEORETICAL AND NUMERICAL ANALYSIS OF RECTANGULAR THIN-WALLED ALUMINIUM ALLOY BEAM
XU Zhiqiang, HU Guoqiang, SONG Xiaoyu, REN Yibin, LIU Yungang, LI Yingdong
2022, 44(4):  868-874.  DOI: 10.6052/1000-0879-21-486
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The average crushing force determines the energy absorption capacity of the longitudinal beam in a passenger vehicle during the collision process. The longitudinal beam is usually in the form of rectangular thin-walled beam because of its high collapse and shrinkage energy absorption ratio. In this paper, the axial crushing experiment was carried out to study the crushing performance of rectangular thin-walled beams. The formula of the average crushing force of rectangular thin-walled beams was deduced by using the asymmetric super-folding element theory. The finite element numerical simulation of rectangular thin-walled beams was carried out to obtain the experimental, theoretical and simulated values of the average crushing force. By comparing the these results, it was concluded that the theoretical and numerical results of the average crushing force were consistent with the experimental results, which provided an effective theoretical guidance for the early structural design of rectangular thin-walled beams.

MEASUREMENT OF LOCKED-IN STRESS IN QUARTZ VEIN SILICEOUS SLATE BASED ON X-Ray Diffraction
TONG Yemeng, WANG Tao, YE Weiwei, WANG Li
2022, 44(4):  875-883.  DOI: 10.6052/1000-0879-21-493
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In the process of rock cooling and long geological evolution, some stress are enclosed. The phenomenon of enclosed stress in rock is gradually recognized. In order to reveal the existence form of locked-in stress in rock, the quantity of locked-in stress is measured and calculated by the tilt solid ψ method with an X-ray diffractometer, and the principal of locked-in stress is determined. The results show that the quartz particle size is about 40μm in the target area of quartz vein slate samples. In the diffraction angle range of 152°~156°, the diffraction peak of (324) crystal plane obtained with different ψ is consistent, which proves the existence of sealing stress. The sealing stress of quartz vein measurement point is compressive stress. The maximum principal stress (22.71 MPa) is parallel to the vein body strike , and the minimum principal stress (12.97 MPa) is vertical to the vein body strike. The linear correlation law of 2θ–sin2ψ was not found in the matrix measurement points. The measurement method of confining stress proposed in this paper can provide reference for subsequent observations and related research of confining stress of different types of rocks.

OPTIMAL SUSPENSION POINTS BASED ON SYNCHRONOUS FAILURE PRINCIPLE FOR A NEW DOUBLE HOISTING RECLAIMING BOOM
MENG Peng, LIU Meng, YU Ming, GANG Xianyue
2022, 44(4):  884-889.  DOI: 10.6052/1000-0879-21-510
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The semi-portal scraper reclaimer is a continuous and efficient bulk material loading equipment, which is widely used in industry. Truss-type reclaiming boom hanging under the semi-portal frame is an important part of the scraper reclaimer. The hanging position of the reclaiming boom determines its bending moment and stress distribution, which directly affects safety. In this paper, a kind of reclaiming boom with dual equal-force hanging point is proposed, which shows better stress distribution than the reclaiming boom with a single hanging point. Based on the simultaneous mode of failure approach, a mathematical model is built for the hanging position design of reclaiming boom, and subsequently the optimal hanging position is determined. Finally, a numerical example demonstrates the superiority of the proposed model.

ANALYTICAL SOLUTIONS OF STEADY-STATE RESPONSES OF A VISCOELASTIC ROD WITH THE DAMPING EFFECT
CHEN Bo, LI Yinghui, LI Xiangyu, YUAN Jianghong
2022, 44(4):  890-894.  DOI: 10.6052/1000-0879-21-513
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In this paper, the analytical solutions of the steady-state responses of a viscoelastic rod in Kelvin’s model subjected to time-harmonic forces are derived based on Green’s function method and the superposition principle. Laplace transform method is employed to obtain Green’s function for the forced vibration of the viscoelastic rod with arbitrary boundary conditions. A unified strategy applied to various boundaries is proposed to determine unknown constants involved in the Green’s function. Computational results show that the dynamic deflection of the rod considering viscous damping of the material and external damping is not separable in time and space.

DYNAMIC SIMULATION OF REPLACEMENT PROCESS OF GAS PIPELINE NETWORK
WANG Anran, ZHANG Kai, ZHAO Yao, MIAO Qian, YANG Rongchao, ZENG Bo, ZHANG Qing, SHI Zhandong
2022, 44(4):  895-905.  DOI: 10.6052/1000-0879-21-487
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At present, the gas replacement process is difficult to monitor. Most of the parameters such as gas supply pressure and replacement time need to be calculated from personnel experience, which will cause a waste of resources and potential safety hazards. In this paper, a dynamic simulation model of gas pipeline network replacement process is established. Based on the one-dimensional topological network algorithm, the resistance coefficient in the pipeline network is accurately solved. Firstly, the horizontal straight pipe structure is established, and the correctness of the algorithm is verified by Fluent. Then the law of gas replacement process is analyzed and summarized. At the end of this paper, the model is applied to a gas pipeline network replacement project and compared with the actual measurement data. The calculation results show that the accuracy of the model proposed in this paper meets the requirements, and can provide an important guiding basis for the formulation of gas pipeline network replacement scheme.

DESIGN OF AN INNOVATIVE SOUTH-POINTING CHARIOT AND PROTOTYPE FUNCTIONS TESTING
DONG Yanzhang, CHEN Guangfei, LIU Qixin, LU Haibin, LI Ying
2022, 44(4):  906-913.  DOI: 10.6052/1000-0879-22-071
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The fixed-axle south-pointing chariot and the differential-type south-pointing chariot were compared and analyzed in this article. And it is found that although the fixed-axle south-pointing chariot is limited to plane straight and plane fixed-point turning, it has certain advantages in straight-driving over obstacle; the differential-type south-pointing chariot can drive or turn arbitrarily in the plane, it has obvious disadvantages in straight-driving over obstacle. Then combining the advantages of the two solutions of south-pointing chariot, based on the differential-type south-pointing chariot, supplemented by the concept on automatic clutch device from the fixed-axis south-pointing chariot, the design goal is to solve the inherent defect on straight-driving over obstacle from the differential-type south-pointing chariot. Afterwards a tooth-mounted clutch was designed for the control of the south-pointing mechanism under different working conditions in this article; and the design scheme of the external dimensions and internal mechanism parts of the innovative south-pointing chariot was completed based on the tooth-mounted clutch. Furthermore, the motion mechanism simulation of south-pointing chariot was completed through the three-dimensional modeling of the innovative south-pointing chariot. Finally, the preparation and functional testing of the prototype vehicle were completed; and the results show that the performance on south-pointing from the prototype vehicle satisfies the expectation under those working conditions.

Research on Education
EXPECTATIONS OF COURSE REFORM IN THEORETICAL MECHANICS
HU Haiyan
2022, 44(4):  914-917.  DOI: 10.6052/1000-0879-22-297
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According to the education requirements of both engineering scientists and research engineers, this article presents four suggestions for the course reform in theoretical mechanics. They cover how to improve the content of the course to meet the needs of engineering, how to update the teaching materials to respond to the call of the times, how to lead students to improve their academic taste and how to help them broaden their academic visions. Each suggestion includes some measures in detail.

COLLISION: A BLIND SPOT IN “PARTICLE AND RIGID-BODY DYNAMICS”
YU Tongxi
2022, 44(4):  918-924.  DOI: 10.6052/1000-0879-22-022
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Collision is a kind of mechanical phenomena which widely exist in nature, people’s live, sports and engineering. After a brief review of historical development, the article summarizes the fundamental laws of collinear collision between two particles/bodies, and points out that the particle dynamics only provides us the law of momentum conservation and the momentum-impulse theorem, with no information on the magnitude and pulse shape of colliding force, or on energy loss during collision. The mechanical models of collision based on linear elasticity, contact mechanics and elastoplastic theory are respectively illustrated, indicating that the coefficient of restitution (COR) is not a material constant. Finally, the article calls for making up the knowledge of collision dynamics in the teaching reform of basic mechanics, so as to help students to establish correct concepts.

INFLUENCE OF TRANSLATED RUSSIAN TEXTBOOKS ON CHINESE THEORETICAL MECHANICS TEXTBOOKS
CHEN Liqun
2022, 44(4):  925-934.  DOI: 10.6052/1000-0879-22-103
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The content comparison is performed among the early Chinese textbooks published from the late 1920s to the early 1950s, the Russian textbooks translated in the 1950s, and Chinese textbooks published in the 1960s. Therefore the influence of the translated Russian textbooks on the Chinese theoretical mechanics textbooks is analyzed. The investigation shows that the translated textbooks has a limited impact on the theoretical mechanics textbooks for the mathematics and physics majors, but has a significant impact on the theoretical mechanics textbooks for engineering majors. The influence includes formulating the teaching system consisting of statics, kinematics and dynamics, rigidifying the teaching treatments of kinematics, and expanding the teaching content of dynamics. In addition, a translated Russian textbook published in the 21st century is studied to understand its impacts.

DISCUSSION ON THE INFLUENCE OF STRUCTURAL PARAMETERS OF IMPACT PROBLEM IN MECHANICAL OF MATERIALS
LI Min, LI Yilun, CHEN Weimin
2022, 44(4):  935-940.  DOI: 10.6052/1000-0879-22-019
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It is the main teaching content of the dynamic response part in mechanics of materials that the structure is subjected to the drop impact of object without initial velocity. The diversity of structural forms, especially the difference between structure withstanding impact independently and with buffer structure, tends to cause confusion in conceptual understanding. This paper analyzes the function of each component through several classic examples, combined with the parameter analysis of the basic formula, to provide reference for explaining related problems in teaching activities.

HOW TO CULTIVATE STUDENTS’ THINKING AND ABILITY IN TEACHING (2): QUALITATIVE AND QUANTITATIVE ANALYSIS
GAO Yunfeng
2022, 44(4):  941-946.  DOI: 10.6052/1000-0879-22-250
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The indexes and values of the system will be obtained by quantitative analysis based on the data and model, and the nature, characteristics and change rules of the system will be judged by qualitative analysis based on intuition and experience. The premise of quantitative analysis is sufficient data and definite model, while qualitative analysis is suitable for the situation when the data is insufficient or the model is unclear. From the perspective of qualitative and quantitative analysis, this paper introduces the distance of the relative to vertical deviation of falling body, and how to draw four-leaf rose line, and the principle and design of a tilted container in ancient China. The preliminary results of these problems can be obtained by using the method of qualitative analysis, then the details information of these problems can be known by using the method of quantitative calculation, to make students to realize the complex problems can be solved simply and skillfully by the combination of qualitative and quantitative analysis.

RESEARCH ON TEACHING AND LEARNING OF THEORETICAL MECHANICS BASED ON CULTIVATION OF STEPPED MECHANICS THINKING
ZHANG Juan
2022, 44(4):  947-954.  DOI: 10.6052/1000-0879-22-031
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An output-oriented teaching and learning reform mode of theoretical mechanics is proposed based on the cultivation of stepped mechanics thinking. Firstly, the concept of stepped mechanics thinking is put forward, and mechanics thinking is divided into basic mechanics thinking, middle mechanics thinking and advanced mechanics thinking. Then the requirements of specific ability and the training mode of stepped mechanics thinking are given. Finally, an output-oriented teaching and learning mode with the training of mechanics thinking as the core is given, and the basic mechanics thinking is established through online and offline blended teaching. The middle mechanics thinking is established through the deep using of fusion case library. The modeling ability is cultivated through case library of video animation library, and the whole teaching process is integrated with the cultivation of advanced mechanics thinking. The results of teaching reform and mechanics competition in recent four years proved that this teaching and learning mode has achieved good teaching output.

PROVING OF YIELD CRITERION OF MISES GEOMETRIC SHAPE IN PLASTIC MECHANICS TEACHING
MEI Ruibin, BAO Li, LIU Xianghua
2022, 44(4):  955-959.  DOI: 10.6052/1000-0879-22-013
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It is difficult for students to understand the yield criterion in the plastic mechanics. The plane ellipse and spatial cylindrical trajectory of Mises yield criterion was proved based on the method of coordinate transformation and geometric projection. Furthermore, from the similarities and differences of mathematical expressions, the internal and external relations and geometric shape of Tresca and Mises yield criterions were investigated in the paper. The research is helpful for students to understand the yield criterion.

INVESTIGATION AND ANALYSIS OF RECENT TEXTBOOKS ON VIBRATION ABROAD
HUANG Xiuchang, HUA Hongxing
2022, 44(4):  960-968.  DOI: 10.6052/1000-0879-21-529
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In order to better select and guide the compilation of mechanical vibration textbooks, this article investigates and analyzes mechanical vibration textbooks in European and American countries and other countries published during 2006 to 2021. The investigation is carried out in the aspects from the classic textbooks on mechanical vibration in European and American countries and their reprints, new textbooks on mechanical vibration in European and American countries, postgraduate textbooks and high-level vibration books (structure-borne noise, modal, vibration control), textbooks on vibration from other countries, and textbooks compiled by industrial consultants suitable for engineers. The analysis includes the main contents, characteristic contents, engineering cases, exercises, breadth and depth of the contents, and across of disciplines and industries. Finally, in combination with our current development, suggestions for the development of vibration textbooks are put forward.

APPLICATION OF MATLAB TO SOLVE COUETTE FLOW IN COMPUTATIONAL FLUID MECHANICS COURSE
LIU Yi, FU Xiaoli
2022, 44(4):  969-973.  DOI: 10.6052/1000-0879-21-553
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Computational fluid mechanics mainly studies how to solve the governing equations of fluid mechanics through numerical methods. In this paper, taking the incompressible Couette flow as an example, based on the theoretical analytical solution, the finite difference control equations of explicit method and implicit method are established, and the third method based on pressure correction method is proposed. The flow field distribution is solved by Matlab programming, and the effects of propulsion steps, equal fraction, time interval, and Reynolds number on the calculation error are studied. By studying the mechanical characteristics of classical flow phenomena, students can deepen their understanding of the basic methods and ideas of computational fluid mechanics, and cultivate the ability to integrate theory with practice.

BUILDING A BRIDGE BETWEEN MECHANICS AND PRACTICE—THE COURSE CONSTRUCTION OF “MECHANICS AND PRACTICE”
WEI Sha, SONG Yicheng, SONG Lifen, ZHENG Bingyue
2022, 44(4):  974-977.  DOI: 10.6052/1000-0879-22-009
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In order to explore the way to reform the course teaching by combining mechanics theory and innovative practice, this paper summarizes and investigates the teaching design and practice of the practical course “mechanics and practice”. This course is a practical course for students majoring in theoretical and applied mechanics at Shanghai University. It aims to bridge the gap between mechanics and practice for undergraduates. Students are trained to be able to use a combination of theoretical analysis, computational simulation and scientific experiments to investigate structural motion, vibration and other engineering problems related to their majors based on the basic knowledge of mechanics, and to communicate effectively. Teaching practice shows that the course “mechanics and practice” would strengthen the ability of students to think independently, apply their knowledge to solve problems and work in teams.

The Field of Mechanics: On mechanics around us
TALK ABOUT ANCIENT CLOCK “BEI-LOU” AND MAGNETIC PERPETUAL MOTION MACHINE
LIU Yanzhu
2022, 44(4):  997-999.  DOI: 10.6052/1000-0879-21-298
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The mechanics of the ancient clock “Bei-lou” is discussed in this paper, and the close connection with the magnetic perpetual motion machine is explained.

CAVITATION AND BUBBLE I: THE SECRET OF THE FAILED FIRST VOYAGE OF THE SHIP TURBINIA
ZHANG Yuning, ZHANG Xiaofei
2022, 44(4):  1000-1002.  DOI: 10.6052/1000-0879-21-502
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This paper briefly reviews the history of the failure of the first voyage of the ship Turbinia due to the cavitation phenomenon. Based on the historical facts, the main features and the background of Turbinia are introduced in the present paper. The reasons for the failure of the first voyage are analyzed. The basic concept of cavitation and its close relationship with propeller speed are described. Furthermore, the continuous improvement and further trials of Turbinia are summarized. Finally, this paper briefly summarizes the significance and the influence of the ship Turbinia together with the contributions of the scientist Charles Parsons on the cavitation phenomenon.

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