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 2021, Volume 43 Issue 4
Review
THE MECHANISM OF ELECTROSPINNING DEVICE1)
YIN Jing, GAO Lulu, XU Lan
2021, 43(4):  489-505.  DOI: 10.6052/1000-0879-20-444
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Nanofibers have great application prospects in the fields of energy, environment, aerospace, biology, medicine, and others, because of their high specific surface, high surface energy and high surface activity. Electrospinning technology is one of the most convenient, direct as well as economical methods to produce nanofibers, and its mechanism was widely studied in recent years, as the key to solve the bottleneck problem of electrospinning nanofibers. This paper reviews the research progress of various kinds of electrospinning devices and their mechanisms. The mechanism of the jet in the electrospinning process and the related bottleneck problems are discussed. The development of the mechanical models of the jet and the numerical simulations of the electrospinning process are highlighted, as well as the future development of the numerical method in the electrospinning field.

Applied Research
EXPERIMENTAL INVESTIGATION OF THE INFLUENCES OF THE SPHERICAL PARTICLE ON THE JET FORMATION OF THE CAVITATION BUBBLE NEAR THE SOLID BOUNDARY1)
ZHANG Xiangqing, ZHANG Yuning
2021, 43(4):  506-511.  DOI: 10.6052/1000-0879-21-026
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Based on a high-speed camera system, this paper investigates the jet formation of the cavitation bubble during its collapse between the solid boundary and the spherical particle. During the experiment, the two parameters (the non-dimensional distance between the bubble and the particle, and the non-dimensional distance between the bubble and the solid boundary) are carefully controlled. Through the analysis of the photos and the data collected during the cavitation dynamic oscillations by the high-speed camera, it is found that the non-dimensional parameter $\alpha$ (the ratio between the aforementioned two distances, representing the relative position of the bubble near the solid boundary and the particle) is a key influencing factor determining the phenomenon, in the quantitative and qualitative analyses. Our analysis reveals that: (1) unlike the case without the particle, the presence of the particle could alter the jet direction significantly during the bubble collapse and the alternation of the jet increases with the decrease of $\alpha$; (2) for small $\alpha$, the bubble makes a significant movement along the particle interfaces.

NUMERICAL SIMULATION OF WIND TURBINE WITH THE IMMERSED BOUNDARY METHOD1)
LI Yanling, HU Jin, ZHOU Kun
2021, 43(4):  512-520.  DOI: 10.6052/1000-0879-21-155
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The aerodynamic performance of a wind turbine largely determines the safety and the efficiency. An efficient and accurate numerical simulation for the aerodynamics is a challenging task owing to its complexity. This paper presents a wind turbine modeling method based on immersion boundary method, including the whole process of the wind turbine modeling, the grid dispersion and the numerical simulation. The homotopy transform is used to generate a smooth blade model; the affine transform is used to deal with the taper and the twist of the airfoil. The numerical accuracy of the algorithm is tested for the lift and the drag of the two-dimensional airfoil. Based on the numerical results, the Richardson linear extrapolation is proposed to improve the numerical prediction of the drag substantially with only a mild increase of the computational complexity. The influence of the arch curvature and the thickness on the lift and drag forces of the two-dimensional airfoil is investigated. The power coefficients of a single wind turbine (including the tower) with different tip speed ratios are studied, along with the aerodynamic interaction between the tower and the blades. Finally, the aerodynamic interference of two wind turbines in-tandem with various separation distances in the wind field is studied. The feasibility of the integrated framework proposed here is verified and it can be used for future research projects of the automatic optimization and the selection of airfoils under prescribed constraints.

PREDICTION AND TESTING TECHNOLOGY OF VIBRATION LOAD FOR SCALED-MODEL OF CARRIER BASED AIRCRAFT1)
JIN Xin, LIU Yu, TANG Changhong, ZHANG Yujie, ZHANG Jiangang
2021, 43(4):  521-528.  DOI: 10.6052/1000-0879-20-472
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The whole aircraft drop test for a carrier based aircraft aims to examine the bearing capacity of the aircraft body structure, the landing gear and the airborne equipment. However, it is difficult to carry out the whole aircraft drop test, as a large-scale dynamic test, because of the cost and the long preparation period required. This paper proposes a test method for prediction and analysis of the dynamic load of carrier based aircraft, based on the principle of scaling the prototype aircraft on the premise of ensuring the dynamic similarity. At the same time, a set of the full aircraft drop test methods is designed, derived from the dynamic similarity theory. The drop test results of the scaled model can be restored to the prototype ones. This method can be used to predict the whole aircraft drop test results of the prototype aircraft with a low cost. The test results of the prototype aircraft show that the prediction accuracy of the test is satisfactory, and the dynamic load on the ship surface can be predicted by the test method.

RESEARCH ON THE DESIGN AND VIBRATION ISOLATION PERFORMANCE OF A NEW LIGHTWEIGHT DAMPING BASE
LIU Ruixia, PEI Dongliang, WANG Yuren
2021, 43(4):  529-535.  DOI: 10.6052/1000-0879-21-016
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In order to achieve the purpose of reducing hull vibration and radiated noise, a new lightweight damping base has been designed by using phononic glass and arc connection structure in this paper. After the above procedures of design and preparation, we used the vibration level drop and vibration isolation test method to characterize and test the performance of vibration isolation for the damping base. The results show that the damping base has a significant vibration isolation effect in the frequency range of 20$\sim$10 000 Hz, and compared with the steel base with the same size, the total vibration drop can reach 12.93 dB. Finally, a clear conclusion is given that the lightweight damping base designed in this paper has the characteristics of high strength, high damping and wide frequency vibration isolation, so it has a wide range of potential applications in vibration isolation of equipment for marine machinery, vibration and noise reduction of vehicles, etc.

VIBRATION ANALYSIS OF FUNCTIONALLY GRADED POROUS CONICAL SHELLS RESTED ON ELASTIC FOUNDATIONS1)
HUANG Xiaolin, LIU Siqi, XIAO Weiwei, WU Di
2021, 43(4):  536-543.  DOI: 10.6052/1000-0879-21-039
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To study the vibration characteristics of porous functionally graded conical shells on elastic foundations, the vibration equations for the functionally graded conical shells with evenly and unevenly distributed pores are derived based on the classical shell theory. The solutions of the free vibrations and the dynamic responses for the shells are obtained by using the Galerkin method. The effects of pores, elastic foundation parameters, semi-vertex angle and other factors on the natural frequencies and the dynamic responses are investigated. The results show that the natural frequencies rise with the increase of the elastic foundation parameters. However, the dynamic responses are significantly reduced. The results also demonstrate that the dynamic responses are increased significantly by increasing semi-vertex angle. Compared with unevenly distributed pores, the effects of evenly distributed pores on the natural frequencies and the dynamic responses are more evident.

A NOVEL SLIDING MODE CONTROL OF ELASTIC-JOINT SPACE ROBOT BASED ON NONLINEAR CASCADE SYSTEMS1)
LIANG Jie, QIN Kaiyu, CHEN Li
2021, 43(4):  544-554.  DOI: 10.6052/1000-0879-20-439
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This paper discusses the design of an improved nonlinear disturbance observer (NDO), a novel adaptive dynamic terminal sliding mode control, and the elastic vibration suppression problem of the dual-arm elastic-joint space robot. Firstly, assuming that the joint of the space robot is elastic, an elastic joint space robot model is established based on the structure of the nonlinear cascade system. The model can be divided into an outer loop manipulator dynamic model and an inner loop joint dynamic model with asymptotic stability. Then, for the dynamic model of the outer loop manipulator, a novel adaptive dynamic terminal sliding mode control algorithm is designed based on the improved NDO. For the inner loop joint dynamic model, the torque feedback control algorithm is designed to suppress the elastic vibration of the flexible joints. The adaptive dynamic terminal sliding mode control algorithm is designed based on the nonlinear cascading system proposed in this paper with good dynamic characteristics and robustness. It can quickly suppress the vibration of the elastic joints under the condition of small flexible stiffness of joints, and achieve the accurate trajectory tracking of the space robots. The system simulation comparison test shows the effectiveness of the control algorithm.

LAYERED ELASTIC SYSTEM MECHANICS AND ITS APPLICATIONS
WANG Kai
2021, 43(4):  555-566.  DOI: 10.6052/1000-0879-21-018
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The mechanics of layered elastic system is a branch of elasticity. Firstly, the development history of layered elastic system mechanics is introduced. Secondly, the mechanical analysis and calculation of $N$-layer elastic system are introduced, including basic assumptions, expressions of stress and displacement components, definite solution conditions, establishment of linear algebraic equations for solving integral constants according to definite solution conditions, solution of integral constants by linear algebraic equations, calculation of Bessel function, integral calculation formula, numerical integration, subsequent mechanical calculation and calculation examples. Finally, the application of layered elastic system mechanics in scientific research and engineering design is introduced.

DETERMINATION OF THE BENDING OF RECTANGULAR PLATE UNDER HYDROSTATIC PRESSURE BASED ON HYBRID ENERGY PRINCIPLE
CHEN Yingjie, QUE Chunfa, GUO Dun
2021, 43(4):  567-575.  DOI: 10.6052/1000-0879-21-037
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In this paper, based on the principle of the minimum potential energy for mixed variables, the equations of the flexural surface of the rectangular plate in the elastic stage under the hydrostatic pressure are derived under three different boundary conditions: three sides simply supported and one side fixed, two adjacent sides simply supported and three sides simply supported,and by using the numerical analysis software, the obtained numerical solution and the finite element simulation values are obtained. The results show that the method adopted in this paper has good practicability for various related problems in engineering practice, and the calculation method provides a new way for solving engineering practical problems.

FURTHER ANALYSIS OF BENDING SHEAR STRESS ON THE FLANGE OF I-SHAPED THIN-WALLED BEAM1)
MA Zhimin, HUANG Kuntao, HUANG Zhiqiang, HU Bihua
2021, 43(4):  576-580.  DOI: 10.6052/1000-0879-21-051
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Based on the equilibrium conditions in the axial direction between two adjacent sections of the beam, the calculation formulas are derived for the shear stress perpendicular to the shear force at the junction of the flange and the web of the I-shaped thin-walled beam and the shear stress parallel to the shear force on the flange. It is shown that the obtained results completely satisfy the cross-section symmetry condition and the stress boundary condition. On this basis, a new shear stress distribution diagram on the section of the I-shaped thin-walled beam is obtained. The results of this research can be used as a sample for students to comprehensively study the bending shear stress on I-shaped thin-walled beams.

SETTLEMENT AND SEPARATION OF TAILINGS PARTICLES1)
HOU Yongli, HAO Zhe
2021, 43(4):  581-587.  DOI: 10.6052/1000-0879-20-388
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The settling and the separation of the tailings particles in fluid are studied. Firstly, the mechanical characteristics and the various force effects of the tailings particles in the fluid are analyzed. Secondly, the settling and the separation of the tailings particles in the Newtonian fluid are studied. Thirdly, the settling and separation of the tailings particles in the Bingham slurry are studied. Finally, the theoretical formula is derived and verified. The settling characteristics of the tailings particles in different fluids are determined, as well as the maximum size of the unsettled particles in the slurry flow, and the settling differential equation of spherical particles is deduced, as well as the formulas for the final settling velocity and the settling distance of particles, as well as the horizontal migration distance of particles. The theoretical formulas are verified.

Research on Education
THE CURRICULUM DESIGN FOR HIGHER ORDER THINKING TRAINING — TAKING TYPICAL EXAMPLES IN MECHANICS OF MATERIALS AS EXAMPLES
LI Min, LI Zhihan, CHEN Weimin
2021, 43(4):  588-592.  DOI: 10.6052/1000-0879-20-298
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To cultivate students' higher-order thinking mode is the goal of a course of the first-class, and the curriculum design of a challenging nature is the focus and the difficult point of the teaching work. This paper illustrates the characteristics of the design through examples and provides a reference for the implementation of related teaching work.

ENGINEERING IMPLICATION OF LOAD SAFETY FACTOR IN AIRCRAFT STRUCTURE DESIGN1)
CHENG Xiaoquan, ZHANG Jikui, LI Zhengneng
2021, 43(4):  599-602.  DOI: 10.6052/1000-0879-20-275
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In aircraft structure design, the safety factor is described with respect to the applied load, while the safety factor in the mechanics of materials is defined with respect to the material strength. It is difficult for beginners to distinguish the difference between them and to understand the connotation of the safety factor. In this paper, two definitions of the safety factor are compared and analyzed. The engineering implication of the load safety factor in the aircraft structure design is expounded. From analysis of the design value and the determination method of the safety factor for composite material structure, which are different from those for metal structure, the engineering significance of the load safety factor is made clear, which helps beginners to master the concept of the safety factor.

HOW WILL AN OBJECT RESTING ON AN INCLINED PLANE WITH A POINTED END MOVE?1)
QU Lijian, REN Qingqing
2021, 43(4):  603-608.  DOI: 10.6052/1000-0879-20-315
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An object with a pointed edge on an inclined plane at rest initially will have a variety of possible types of motion. The basic motions are sliding and rotation. There are 9 types of motion in total. The paper predicts what can actually happen, and presents the conditions for each type of motion. Our analyses show that the key factors influencing the dynamics of the object are the friction and the mass distribution. For objects with the center of mass locating on the top side of the inclined plane with respect to the pointed edge of the object, only the pure backward or forward rotation happens, sliding down combining with backward or forward rotation. If the center of mass is on the base side of the inclined plane, the object on the inclined plane will have a pure forward rotation or slide down as it rotates backward or forward. The problem can be used for teaching purposes to bring the students with the first taste of research.

A SIMPLE METHOD FOR CALCULATING THE VERTICAL FORCE OF RELATIVE EQUILIBRIUM LIQUID1)
GU Lei, NI Fusheng
2021, 43(4):  609-612.  DOI: 10.6052/1000-0879-20-332
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The calculation of the vertical component force of the relative equilibrium liquid on the wall by the integral method is very complicated, especially when it involves a parabolic equation. It is found that the pressure body method by geometric drawing is not only suitable for the static liquid, but also suitable for the relative equilibrium liquid. The theoretical basis and the basic method of calculation can be adjusted for both liquids. In this way, the integral calculation is transformed into the solution of the geometric volume, which can make the calculation of the relative equilibrium liquid as simple as for the pressure body.

INTERNAL FORCE CALCULATION OF PLANE SIDESWAY FRAME CONTAINING RIGID INCLINED BAR1)
WU Yaopeng, DENG Yuanhang, GUO Xin
2021, 43(4):  613-616.  DOI: 10.6052/1000-0879-20-353
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In order to simplify the calculations in structural analysis, it is often assumed that some members or their specific directions are rigid. The internal force calculations of the structure with rigid members are difficult points in teaching the structural mechanics. For the sidesway frame containing an inclined bar and a rigid bar, its node displacements will be limited, with the non-independent node displacements. This paper uses the constraint equations of the rigid bars to obtain the coefficient matrix. And based on the rank of the coefficient matrix, the basic unknown of the structure could be determined. Furthermore, the relationships between the independent node displacements and the non-independent node displacements of the structure are derived, so the internal force of the frame could be solved using the displacement method.

TEACHING OF EXPERIMENT BASED ON NEW PHOTOELASTIC EXPERIMENT TECHNOLOGY1)
HUANG Xing, MAO Shuangshuang, FENG Jiemin, WU Fenglin, WU Hong, ZHANG Dongsheng
2021, 43(4):  617-622.  DOI: 10.6052/1000-0879-20-384
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In order to solve the problem of complex and time-consuming data processing in the traditional photoelastic experiment teaching, the new photoelastic experimental technology is applied in the teaching of experiment. After a brief introduction of the basic method of the technology, this paper focuses on its applications in teaching of experiment with examples. The applications of this technology not only make the measurement in the photoelastic experiment go from the qualitative judgment to the quantitative one, but also expand students' vision and cultivate their innovative thinking abilities.

CULTIVATION MODE OF MULTI-CIRCULAR MOSAIC “TECHNOLOGY” TYPE TALENTS UNDER THE BACKGROUND OF “INTERNET+”1)
MA Xinling
2021, 43(4):  623-627.  DOI: 10.6052/1000-0879-21-102
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The integration of the “Internet+” and the manufacturing technology promotes the rapid development of industry. Under the background of New Engineering, this paper proposes and refines the concept of the “technology” type talents, and the idea of the multi-cycle nested education, and how to train the outstanding engineering talents with both professional quality and skills, innovative ability and sense of responsibility by using the concept of the multi-cycle nested education. The teaching mode and the curriculum system of the “classroom-experiment-research” trinity are created. It is committed to provide skilled, comprehensive engineering and technical talents.

EXPERIMENTAL TEACHING REFORM OF MECHANICS OF MATERIALS BASED ON PROJECT MANAGEMENT MODE1)
WANG Yiping, YU Hualong, LI Changyun, YAO Yanbo
2021, 43(4):  628-631.  DOI: 10.6052/1000-0879-20-392
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Mechanics of materials is an important professional basic course for engineering students in colleges and universities. The experimental part of the course plays an irreplaceable role in cultivating students' ability of “combining theory with practice”. There is a common problem that the teaching of experiment in colleges and universities is not in harmony with the training requirements. Based on the project management mode, this paper proposes to reform the teaching content, the teaching methods and the teaching organization, and trains students' ability to solve practical engineering problems.

APPLICATION OF NUMERICAL SIMULATION SOFTWARE IN THE TEACHING OF VIBRATION MECHANICS1)
FENG Wenjie, LI Haiyan
2021, 43(4):  632-639.  DOI: 10.6052/1000-0879-20-413
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In the teaching of vibration mechanics, the emphasis is generally put on the explanation of concepts and theories, involving a great deal of formula derivation, which makes it difficult for students to understand the essence of the subject. In this paper, the numerical simulation is applied in the teaching of vibration mechanics. Firstly, the main problems of vibration mechanics are put forward, and several typical numerical simulation examples of vibration mechanics are presented. Thus, some phenomena and concepts in vibration mechanics are directly simulated by the finite element software. Through the questionnaire and the analysis of the related score distributions before and after the application, it is found that the teaching of vibration mechanics combined with numerical simulation can improve students' intuitive understanding of complicated problems of vibration mechanics, effectively stimulate students' learning enthusiasm, improve students' autonomous learning ability, and cultivate their ability to analyze and solve practical problems by means of numerical modeling and numerical analysis.

The Field of Mechanics:On mechanics around us
DYNAMIC ANALYSIS OF SCIENTIFIC TOY “MEMORY ALLOY ENGINE”
LI Can, XIONG Jufeng
2021, 43(4):  656-661.  DOI: 10.6052/1000-0879-20-503
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In this paper, the dynamics parameters of the science toy the “memory alloy engine” are analyzed quantitatively. Based on the bending principle of the elastomer, the physical model is built, and the effective rotational torque of the “memory alloy engine” is calculated. Based on the principle of the belt drive, the relationship between the angular velocity, the linear velocity, the power and the radius of the memory alloy wire, the radius of the driving wheel, the toggle angle and the inclination angle is obtained. It is shown that a certain effective torque is the first condition for the engine to rotate.

Featured ArticleMore>>   
  • Title: THE MECHANISM OF ELECTROSPINNING DEVICE 1) PDF
  • Author:YIN Jing, GAO Lulu, XU Lan
  • Abstract: Nanofibers have great application prospects in the fields of energy, environment, aerospace, biology, medicine, and others, because of their high specific surface, high surface energy and high surface activity. Electrospinning tec. . . More>>