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20 October 2019, Volume 41 Issue 5
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    Review
    REVIEW ON OPTIMIZATION OF ASTEROID CAPTURE ORBITS
    BAOYIN Hexi, BAO Changchun
    2019, 41(5):  511-519.  doi:10.6052/1000-0879-19-106
    Abstract ( 203 )   HTML( 285 )   PDF (283KB) ( 285 )  

    The asteroid is of great significance for studying the formation of planets, the origin of life on the Earth, the defense against the collision of asteroids to the Earth and the mining on asteroids. Due to the insufficient capacity of the existing propulsion technology, the velocity increment needed to optimize the asteroid capture is the key for a successful capture mission. This paper reviews the capture orbit optimization method for asteroid and the extended capture period with the impulse thrust and lowthrust propulsions, including the strategy to capture asteroids by the gravity assisted and resonant orbital techniques, the continuous low thrust and temporary asteroid capture, and the scheme of extending the capture period.

    Applied Research
    2019, 41(5):  520-525.  doi:10.6052/1000-0879-19-246
    Abstract ( 260 )   HTML( 88 )   PDF (344KB) ( 88 )  

    The vibration isolation system with cubic stiffness and Bouc-Wen type hysteresis shows complex nonlinear dynamic characteristics. An undamped response model is established based on an anhysteretic restoring force. An approximate analytical solution is derived by the harmonic balance method (HBM) and the Taylor expansion. An analytical/numerical method is proposed to calculate the damped response of the vibration isolation system, based on the HBM and Levenberg-Marquardt algorithm. For the multi-value non-smooth function terms, the harmonic term coefficients are obtained by applying the fast Fourier Transform for the calculated time-domain response. The proposed methods are applied to a nonlinear vibration isolation system with horizontal wire ropes. It is verified that the vibration isolation system has a softening-hardening stiffness with cubic stiffness and Bouc-Wen type hysteresis. Both hysteretic damping and linear damping can effectively suppress the resonance, while with the hysteretic damping, better vibration isolation performance is shown at high frequencies.

    2019, 41(5):  526-533.  doi:10.6052/1000-0879-19-138
    Abstract ( 198 )   PDF (1184KB) ( 94 )  
    A slender rod string in a vertical cylinder is subjected to an alternating tension-compression axial load. When the axial pressure at the bottom of the rod is greater than the buckling critical load, in the slender rod, a helical buckling deformation will be generated, and the transverse vibration of the rod will be stimulated by the buckling deformation. Taking the instantaneous buckling configuration of the slender rod in the cylinder as the displacement excitation of the transverse vibration, a simulation model for the collision between the slender rod and the inner wall of the cylinder under the instantaneous buckling displacement excitation is established. To solve the mathematical problem, the finite difference method is used to discretize the rod, and the Newmark method is used to discretize the time. The transverse vibration mathematical model is implemented in the numerical simulation, with the collision conditions between the slender rod and the cylinder satisfied by the method of the restitution coefficient. It is shown that the collision occurs mainly after the rod string is buckled, and the collision almost occurs along the whole cylinder with the collision force increasing gradually from the top of the cylinder to the bottom. But when the bottom load is a tensile force, few collision occurs and the collision force is also very small.
    CHARACTERISTICS OF AZIMUTHAL-RADIAL PENDULUM MOTION BASED ON ANALYTICAL MECHANICS1)
    LI Jiaxun, DENG Banglin, HU Zhigang, SU Kaiqi, ZHU Zuolei, ZHENG Linli
    2019, 41(5):  534-542.  doi:10.6052/1000-0879-19-097
    Abstract ( 465 )   PDF (433KB) ( 189 )  
    The study of the azimuthal-radial pendulum is useful in the application of the mechanical engineering. This paper presents theoretical and experimental studies of the factors that affect the azimuthal-radial pendulum trajectory. The differential equations of the system are obtained and solved by the numerical method after establishing the Lagrangian function. On the other side, the actual motion trajectory of the azimuthal-radial pendulum is obtained by the software Tracker. The influences of the length of the rod and the rope as well as the initial position of the azimuthal-radial pendulum trajectory are revealed, and it is found that the theoretical results are in good agreement with the experimental results.
    SIMILARITY LAWS OF HYPERVELOCITY PENETRATION EFFECTS OF CONCRETE1)
    CHENG Yihao, LI Gan, YUE Songlin, ZHANG Zhongwei, SONG Chunming, QIU Yanyu
    2019, 41(5):  543-549.  doi:10.6052/1000-0879-19-192
    Abstract ( 205 )   PDF (601KB) ( 87 )  
    To study the similarity laws of the hypervelocity penetration effects of concrete, the basic theories of similarity laws are firstly reviewed briefly, and the hypervelocity penetration experiments of concrete are conducted in the velocity range from 1.4 km/s to 3.9 km/s. According to the experimental results of this study and those in the related literature, the principal similarity criterions are obtained, and the normalized penetration depth is determined by data fitting. It is shown that the normalized penetration depth mainly depends on the Johnson number, the mass density ratio of the projectile to the target and the length-diameter ratio of the projectile, while weakly depends on the strength ratio of the projectile to the target and the nose-shape coefficient of the projectile. The normalized penetration depth firstly increases and then decreases with the increase of the normalized impact velocity, with a sudden drop when the impact velocity is close to the P-wave velocity of concrete, which is named as the “transonic speed effect”.
    2019, 41(5):  550-553.  doi:10.6052/1000-0879-19-109
    Abstract ( 169 )   PDF (285KB) ( 60 )  
    The arresting of a carrier-based aircraft in an attitude of yawing and off-center, will cause the lateral swing motion of the arresting hook along the arresting cable. Using the method of the simulation and the theoretical analysis, by adjusting the vibration frequency range of the lateral dynamic loads on the arresting hook, the dynamic load characteristics of the aircraft fuselage is studied. The results show that the severe loads on the fuselage can be caused at the vibration frequency of 2 Hz, 10 Hz and 20 Hz. The conclusions can be used for the optimal design of the structural stiffness and for reducing the hook head swing.
    EXPERIMENTAL RESEARCH ON FAILURE AND ENERGY DISSIPATION CHRACTERISTICS OF THE SANDSTONE1)
    GUO Yongcheng, WANG Kehui, HU Peng, LIU Xinyu, CHEN Zuogui, YAN Bin
    2019, 41(5):  554-558.  doi:10.6052/1000-0879-19-124
    Abstract ( 134 )   PDF (300KB) ( 61 )  
    The effects of unloading rate under different paths on the mechanical properties of sandstone and the energy dissipation in the failure process have been analyzed by the triaxial unloading test The results are as follows: the axial deformation plays a leading role in the elastic phase of the whole process stress-strain curve. And in the elastoplastic stage, the increase of the hoop strain is greater than the axial strain’s In the confining pressure unloading stage, the smaller the unloading rate, the greater the flexibility of the strain. At the same time, the deformation of the rock sample is insufficient, which is an obvious brittle failure characteristic. The dissipative energy under the constant principal stress difference path is 1.35 times than it is under the constant axial pressure path The larger the unloading rate, the smaller the elastic strain energy of the rock sample.
    2019, 41(5):  559-564.  doi:10.6052/1000-0879-19-129
    Abstract ( 180 )   PDF (226KB) ( 64 )  
    According to the theory of the “three zones” of failure and movement of the overlying strata in the longwall mining face, the subsidence deformation of the surface is controlled by the bending subsidence zone, and the maximum subsidence of the surface is far less than the thickness of the bending zone strata, therefore, the deformation of the bending zone strata conforms to the small deflection bending of a plate. On this basis, according to the characteristics of the mountain topography and the landform and the relationship between the slope direction and the coal seam tendency, the surface mountainous body is simplified into four cases: that with a forward slope, that with a reverse slope, the trench and the mountain ridge. The surface subsidence basin models in the four cases are established by a semi-inverse method of the thin plate theory. Despite some simplified assumptions in the model, the main factors affecting the mining subsidence are considered, such as the coal seam dip, the burial depth, the physical and mechanical properties of the strata, and the geomorphological shape.
    ON INITIATION OF GULLY DEBRIS FLOW BY LIMIT EQUILIBRIUM ANALYSIS1)
    Zhang Guoshuai, Wang Xiaoliang, Xia Jianxin
    2019, 41(5):  565-570.  doi:10.6052/1000-0879-19-161
    Abstract ( 109 )   PDF (359KB) ( 74 )  
    The key mechanism of debris flow initiation in a channel is the process of shear force over-coming bed friction. In this paper, the critical equilibrium condition of particle deposit is established by limit equilibrium analysis, which shows the stability of deposit depends on slope angle, internal friction, deposit height and water discharge. Then through series analysis of experimental data in literature, a critical velocity criterion for initiation of gully debris flow is obtained. The criterion is in good agreement with two typical series of experimental results of debris flow, which might provide a useful tool for gully debris flow initiation.
    A MODAL TESTING METHOD FOR CANTILEVER BEAM1)
    Liu Yongchun, Zhao Yanying
    2019, 41(5):  571-578.  doi:10.6052/1000-0879-19-136
    Abstract ( 232 )   PDF (968KB) ( 92 )  
    Based on the Euler-Bernoulli beam theory, the modal function of the free vibration of the cantilever beam is obtained. The node position of the first five modes of the cantilever beam and its ratio to the length of the beam are obtained by the numerical calculation. With the consideration of the influence of the sensor on the natural frequency of the cantilever beam, a beam-sensor model is established to simulate and analyze the first five natural frequencies of the cantilever beam. Based on the locations of the nodes and the measuring points, the excitation points are selected in the experiment. The experimental results are compared with the results of the beam-sensor simulation model. Through the error analysis of the first five natural frequencies, it is found that the maximum error between the simulation results and the experimental results is 1.3%. The details of the modal testing process of the cantilever beam are described in this paper.
    Research on Education
    TEACHING SYSTEMS AND TEXTBOOKS OF ELEMENTARY MECHANICS (II)—TEACHING SYSTEMS AND TEXTBOOKS OF THEORETICAL MECHANICS IN FOREIGN COUNTRIES 1)
    YE Zhiming,LI Junfeng,WANG Shibin,WU Zhiqiang,CHEN Liqun,YANG Xiao,WU Jianhua,HUANG Yi
    2019, 41(5):  579-587.  doi:10.6052/1000-0879-19-048
    Abstract ( 366 )   HTML( 377 )   PDF (3190KB) ( 377 )  

    This paper analyzes the textbooks of mechanics, especially the textbooks and their teaching systems of theoretical mechanics and materials mechanics, including the national states of the mechanics courses, the textbooks, the achievements and problems of the teaching systems for elementary mechanics, the introduction of overseas elementary mechanics textbooks, focusing on the theoretical mechanics teaching and the teaching system in foreign countries.

    2019, 41(5):  588-590.  doi:10.6052/1000-0879-19-339
    Abstract ( 532 )   HTML( 166 )   PDF (131KB) ( 166 )  

    The paper introduces the basic situation, characteristics and problems of the 7th teaching competition of youth faculty of Fundamental Mechanics Courses, which was held by the teaching guidance committee of foundation mechanics courses in colleges and universities of the Ministry of Education. Some suggestions were given to improve in teaching abilities of teachers. Through this paper, the teachers in colleges and universities in China can know this teaching competition and the problems reflected in the competition. This paper is also a reference for improving the teaching level and quality of fundamental mechanics courses in China.

    FROM “TEACHERS TEACH” TO “STUDENTS LEARN”
    WU Aihui,ZHU Zhongliang,HUANG Daofeng
    2019, 41(5):  597-600.  doi:10.6052/1000-0879-18-488
    Abstract ( 237 )   HTML( 91 )   PDF (169KB) ( 91 )  

    Student-centered teaching and learning is now widely accepted in the modern higher education worldwide with active learning as its core. It is a big challenge for both the teachers and the students to turn successfully from the traditional teacher-centered teaching to the relatively new student-centered learning. This paper presents a discussion on the feasible and efficient ways from the traditional“teacher-centered teaching”to the “student-centered learning” organized by the Quality Assurance Office and the Center for Excellent Teaching of the Tongji University. Being used to the cramming teaching, some students lack the initiative of active learning, teachers should do their best to arouse students in class. Effective ways to encourage active learning include designing an appropriate quality evaluation system, focusing on student learning efficiency and ability improvement, with an effective teaching pedagogy such as the “peer instruction”, and the introductions of problems or projects without preset answers in class.

    2019, 41(5):  601-606.  doi:10.6052/1000-0879-19-037
    Abstract ( 206 )   PDF (254KB) ( 254 )  
    A particle on an inclined plane is under the action of a constant sliding force due to the gravity and a frictional force, with the direction of the frictional force varying with the velocity. When the ratio of the friction factor to the slope gradient of the inclined plane, i.e. the equivalent frictional factor, λ> 1, the particle will eventually stop on the slope; when 0:5 <λ≤1, the particle will not stop but with a limit in the horizontal direction; and when λ≤0:5, the particle can move to an infinite distance in the horizontal direction. The curves of the particle trajectories have an outer envelope for the same equivalent friction factor.
    2019, 41(5):  607-611.  doi:10.6052/1000-0879-18-437
    Abstract ( 194 )   PDF (209KB) ( 87 )  
    The Lagrange’s equation is widely used in solving complex dynamic problems. As soon as the kinetic energy of a system at a general position is known, the governing equation of the system can be easily obtained by the Lagrange’s equation. But to calculate the kinetic energy of a system at a general position is not easy in many cases, which is an obstacle to the application of the Lagrange’s equation. From a theoretical analysis, we find that to the dynamic problems of the velocity-free release, the Lagrange’s equation provides a simple way of solution.
    2019, 41(5):  612-614.  doi:10.6052/1000-0879-19-142
    Abstract ( 234 )   PDF (114KB) ( 93 )  
    This paper discusses the teaching of fluid mechanics with representations of fluid flow, based on the Lagrange picture and the Euler picture, as well as with the relation between these representations. The fluid flows will be shown in the vivid time-space views instead of just concepts.
    2019, 41(5):  615-619.  doi:10.6052/1000-0879-19-198
    Abstract ( 237 )   PDF (831KB) ( 68 )  
    In order to strengthen students’ mastery of theoretical knowledge of convection mechanics course and experimental teaching, this paper combines numerical simulation technology with experimental teaching of fluid mechanics, aiming at the problems limited by hardware facilities and models in traditional experimental teaching.With Bernoulli experiment as an example, the application of simulation software for physical modeling, meshing, variable parameter numerical simulation experiment content, etc. Through the stress nephogram and streamline simulation analyses the characteristics of energy conversion, to enhance the students’ knowledge of convection strength theory and the related parameters of the understanding of the physical meaning and characteristics, so that the students in the experiment the intense “engagement”, effectively improve the teaching level and teaching quality.
    2019, 41(5):  620-623.  doi:10.6052/1000-0879-19-078
    Abstract ( 309 )   PDF (592KB) ( 111 )  
    The concept of “the unity of leaning and doing” is deeply rooted in the educational world, but it is not easy to put it into practice earnestly. After nine years of effort, with the innovative practical course of the “Structural Model Design and Fabrication” developed by Shanghai Jiaotong University, the good integration of ”learning and doing” is preliminarily realized, with a remarkable effect. The present paper gives a summary of the course with some food for thought, hoping to provide a useful reference for the related engineering teaching reform in China.
    The Field of Mechanics
    2019, 41(5):  628-631.  doi:10.6052/1000-0879-18-413
    Abstract ( 342 )   HTML( 121 )   PDF (830KB) ( 121 )  

    The Noether’s theorem is one of footstones in modern physics and mechanics, due to the correlations it has established between the conservation laws and the symmetries. The origin, the content and the related anecdotes of the Noether’s theorem are reviewed, as well as the relations between the J-integral, the Eshelby tensor and the Noether’s theorem.

    LEONARDO DA VINCI AND FLUID MECHANICS 1)
    CHEN Guangyao, YANG Shaoqiong, JIANG Nan
    2019, 41(5):  634-639.  doi:10.6052/1000-0879-19-154
    Abstract ( 298 )   HTML( 112 )   PDF (7580KB) ( 112 )  

    Leonardo da Vinci, known as painter, sculptor, astronomer, inventor, musician, mathematician,anatomist, physiologist, geologist, botanist, writer, military engineer, architect and cartographer, is a representative figure of the Italian Renaissance humanism. This paper describes another aspect of Da Vinci:his research results of fluid mechanics and the contributions related with turbulence, flight, wave and storm, and it is concluded that he is the pioneer and founder of fluid mechanics science as well.