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Table of Content
20 April 2020, Volume 42 Issue 2
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    JIN Hongbo, ZHANG Zhiqiang, SONG Liang
    2020, 42(2):  143-150.  doi:10.6052/1000-0879-20-010
    Abstract ( 229 )   HTML( 148 )   PDF (3870KB) ( 148 )  
    After the evolution of hundreds of millions of years, most turtles have developed excellent shells with high specific stiffness and toughness. Obviously, the multi-scale structural characteristics and the biological material mechanical behavior of these turtle shells can be used for promoting the bio-inspired design of safety protection structures. This paper reviews the research progress of the turtle shell relevant to its protective functions, including the macro and micro features of the carapace and the corresponding mechanical properties. In addition, some carapace-inspired designs that could be adopted in protection structures are summarized. Finally, the existing problems and the focus of the future research are discussed, to provide some food for thought in the bio-inspired design of safety protection systems in future.
    Applied Research
    YE Lijun, LIU Fucheng, BAOYIN Hexi
    2020, 42(2):  151-155.  doi:10.6052/1000-0879-19-321
    Abstract ( 100 )   HTML( 53 )   PDF (288KB) ( 53 )  
    The launch vehicle recycling technology has become a hot research topic. The Recovery Strategy of Launch Vehicle based on controllable network is proposed, the basic working principle and composition is introduced, and the preliminary design is given.
    2020, 42(2):  156-162.  doi:10.6052/1000-0879-20-044
    Abstract ( 129 )   HTML( 59 )   PDF (2086KB) ( 59 )  
    Many innovative enterprises, such as SpaceX and OneWeb, recently released plans building satellite mega-constellations at the low earth orbit, thus triggering a boom in the development of Satellite Internet. The public two-line element (TLE) is used in this paper to analyze the control strategy of the foreign constellations, including Iridium, OneWeb and StarLink. The mean semimajor axis difference of different satellites in the constellation is obtained by the relative phase difference analysis, to avoid the difficulty of estimating the maneuver of the satellite by the mean semimajor axis variation when the control value is small. Essential parameters like the orbital station keeping frequency and the control accuracy of foreign constellations are obtained. The conclusions obtained will provide a reference for the construction of the Internet constellation in our country.
    WANG Xiuhong, CUI Wen, LI Junfeng, HE Yufan, LI Haijing
    2020, 42(2):  163-169.  doi:10.6052/1000-0879-19-358
    Abstract ( 86 )   HTML( 25 )   PDF (333KB) ( 25 )  
    For the utilization space activities, the number of man-made space objects increases fast. Due to the limitation of the detect resource, the detected data of the mass space objects are less than what is adequate, which means a worse accuracy of the orbital calculated result. In this paper, the space objects are classified by the orbit altitude, and the influence on different perturbation factors are analyzed. It is indicated that with the perturbation model,the error of the atmospheric drag and the velocity of the initial radial direction is the major cause of the orbit propagation error, which is distributed along the track. By ignoring the error of the initial position, the values before and after the perturbation error caused by the orbit initial position error are approximately symmetric, which is confirmed in the simulation experiment. A method is then proposed to correct the catalog orbit determination velocity by reducing the position error propagated before the given point to improve the position precision propagated after the given point. In the experiment with the real observation data, the method works effectively in modifying the orbital result within the sparse data of the near-circular space object, and the accuracy of the self-catalogue space object is improved. The method improves the ability of the catalogue managing the space object.
    2020, 42(2):  170-176.  doi:10.6052/1000-0879-19-309
    Abstract ( 88 )   PDF (763KB) ( 50 )  
    Along with the continuous progress of science and technology, the vibration control of the intelligent structure is now widely used in the aerospace, the machinery manufacturing, the vehicles and the ships. Due to the diversity and the complexity of the multi-input multi-output, the stability of the system is a serious concern. To deal with this problem, an adaptive control strategy is proposed for the dual-drive intelligent cantilever beam system with two input spouts. First of all, based on the linear piezoelectric equation, the mechanical model of the dual-drive intelligent cantilever beam is established by assuming the modes, and the state equation based on the closed-loop control system is obtained. At the same time, the proportional--integral--derivative (PID) controller is designed to self-correct the PID by using the parameters of the online identification system by the recurrent least square method. The control effect of the self-correcting PID control is analyzed by comparing the vibration of the two-input single-output dual-drive intelligent cantilever beam system under PID control by the numerical simulation. The control effect of the self-correction PID control for the dual-drive intelligent cantilever beam system of the dual-input single output is verified by experiments, and two different sets of single-input single-output self-corrected PID control experiments are compared. The results show that the self-correcting PID control method can effectively suppress the free vibration of the intelligent cantilever beam, which is more effective than the two groups of the single input single output systems. The two input single output self-correction PID control is better and more effective.
    LI Zhijun, LEI Haitao, YUAN Yuan, TANG Ruochen, WANG Sheliang
    2020, 42(2):  177-183.  doi:10.6052/1000-0879-19-306
    Abstract ( 65 )   PDF (737KB) ( 31 )  
    A new method for optimal distribution of electromagnetic inertial mass dampers (EIMDs) based on the genetic algorithm (GA) is proposed in this paper, to reduce the amplitudes of vibration responses of an eccentric high-rise building structure with EIMDs subjected to the earthquake wave. According to the mechanical mechanism of the EIMD, the dynamic equation of motion of the eccentric structural system with EIMDs is derived and some parameters of the structure are determined correspondingly. Moreover, the optimal quantities and the installation location of the EIMDs are determined by using the proposed GA with the feasible fitness function. Finally, a feasible semi-active control strategy is adopted for the eccentric high-rise building structure with EIMDs. A full-size eccentric high-rise building structure with 24 stories is used as an example to demonstrate the effectiveness of the proposed method. Simulation results show that the control performance of the proposed optimal strategy is superior to the one of the stochastic distribution strategy.
    2020, 42(2):  184-188.  doi:10.6052/1000-0879-19-369
    Abstract ( 106 )   PDF (545KB) ( 51 )  
    The distribution of the added water mass is investigated for an immersed cantilever cylinder through an analytical method. A non-dimensional coefficient for the mass distribution is derived. With a numerical fitting analysis of the mass distribution, the effect of the added water mass can be expressed as the equivalent mass density of the structure. The mass density of the immersed cylinder is replaced with the equivalent mass density in the vibration analyses. The wet frequencies of the immersed cylinders are experimentally studied. The wet frequencies obtained by the present simplified (added water mass) method agree well with the experimental results. It is shown that the mass effect of the around water can be well described by the present simplified formula.
    2020, 42(2):  189-195.  doi:10.6052/1000-0879-19-345
    Abstract ( 86 )   PDF (869KB) ( 23 )  
    For the expansive rock in the Nanning basin, its expansibility, shear strength and thermal characteristics are measured by using, respectively, the undisturbed samples and the remolded samples of different particle sizes in the laboratory test, and the differences of their values are studied. The results show that the free swelling ratio of the remolded expansive soil samples in different particle size ranges sees a significant increase, as compared with undisturbed ones, but the peak value of the principle stress difference, the shear strength and the thermal characteristic index are decreased. Therefore, the soil particles of appropriate sizes should be selected for remolding instead of undisturbed samples in the laboratory test. The free swelling ratio and the expansive force of the remolded samples take similar values as with the undisturbed samples when the soil particle size is in the range of 1 mm≤d<2 mm and the properties of samples in the minimum range of the soil particle size are close to those of the undisturbed samples, as shown in the triaxial test and the thermophysical experiment.
    2020, 42(2):  196-201.  doi:10.6052/1000-0879-19-301
    Abstract ( 77 )   PDF (536KB) ( 34 )  
    The Mohr-Coulomb strength criterion is used as the statistical distribution variable in the Weibull random distribution for the frozen soil micro-meter damage. The damage constitutive model of the frozen clay under uniaxial stress state is established by using the strain equivalence hypothesis. On this basis, the relationship between the model parameters and the elastic modulus and the freezing temperature is edetermined. The model parameters and the elastic modulus are corrected reasonably. The damage constitutive model of the frozen clay under the temperature influence is established and the results are compared with the experimental results. The analysis results show that the damage constitutive model with consideration of the temperature effect can be used to simulate the stress-strain full process of the frozen clay well, with a good adaptability.
    2020, 42(2):  202-208.  doi:10.6052/1000-0879-19-347
    Abstract ( 72 )   PDF (1162KB) ( 22 )  
    The particle flow discrete element software PFC2D is widely used in geotechnical engineering. The main problem is how to calibrate its mesoscopic parameters. At present, the "trial and error method" is mostly used. The disadvantage of this method is large amount of work and low efficiency. This paper proposes to replace this method with the back propagation (BP) neural network method, and use the PFC2D built-in FISH and Python language to re-develop a software, which then automatically runs to obtain 40 sets of macro mechanical parameter samples. The results show that the BP neural network method can quickly and accurately establish the macro and meso parameter mapping relationship, and the error is kept within 0.01. The simulated stress-strain curve is highly consistent with the indoor test curve, and the network can be created without large data samples. The efficiency is higher; and it is verified that the straight joint model selected in this paper can effectively determine the small UCS/TS value of the parallel bond model, indicating that the straight joint model can be used to better simulate the rock.
    Research on Education
    2020, 42(2):  209-213.  doi:10.6052/1000-0879-19-333
    Abstract ( 121 )   PDF (270KB) ( 89 )  
    The general equations of dynamics in theoretical mechanics are referred to as the principle of d'Alembert--Lagrange in analytical mechanics. The generality of these equations lies on the fact that from these equations not only can the general theorems of dynamics be proved, but also can the differential equations of motion for systems with the holomonic or inholomonic constraints be derived, as well as the related integral functional principles.
    YE Zhiming, WANG Dejiang, ZHAO Huiling
    2020, 42(2):  214-218.  doi:10.6052/1000-0879-20-024
    Abstract ( 176 )   PDF (181KB) ( 110 )  
    This paper discusses the course education, as well as the curriculum of science and engineering courses, including the idea, the method and the cases.
    LI Min, LI Yilun
    2020, 42(2):  219-222.  doi:10.6052/1000-0879-19-287
    Abstract ( 82 )   PDF (3863KB) ( 94 )  
    In this paper, the section design of the beam, with its development process in time is discussed, combined with an analysis of the related technologies and materials, to provide the classroom with an example for comprehensively understanding the ideas in materials mechanics.
    2020, 42(2):  223-225.  doi:10.6052/1000-0879-19-188
    Abstract ( 91 )   PDF (368KB) ( 89 )  
    The circular ring will experience a special kind of deformation under a uniformly distributed torsion and is apt to jump. The stability is an important factor not to be overlooked. In this paper, the equilibrium path is derived for the circular ring of circular cross-section under the uniformly distributed torsion based on the principle of the minimum potential energy. With the energy criterion for the system’s stability, the stability of the equilibrium, the deformation and the moving process of the circular ring are analyzed. Finally, the maximum value of the internal force on the circular ring's cross-section is obtained in the stable equilibrium state.
    2020, 42(2):  226-231.  doi:10.6052/1000-0879-19-172
    Abstract ( 121 )   PDF (333KB) ( 79 )  
    The controversy about "gold course" or "worthless course" in a university becomes a hot spot, and the course of materials mechanics in provincial universities faces with the same problem. In order to meet the needs of the emerging engineering education and the transformation and upgrading of provincial universities, a gold course of the materials mechanics is developed by reorganizing the knowledge module, the multi-dimensional material construction, the transformation of teaching and learning and the multi-index comprehensive evaluation, with a diversified teaching system including theory and practice, teaching and scientific research, design and competition, to stimulate the students' learning motivation and professional interest.
    2020, 42(2):  232-236.  doi:10.6052/1000-0879-19-280
    Abstract ( 86 )   PDF (1215KB) ( 60 )  
    The digital image correlation-based plane strain measurement technique is adopted in the teaching of mechanics in the materials laboratory. Students are asked to determine the mechanical properties and to have the visualized strain data of low carbon steel and Al--Mg alloy under the uniaxial tension. Students' comprehension of the theoretical knowledge is enhanced, they are motivated in the study and their scientific analysis ability is cultivated.
    2020, 42(2):  237-241.  doi:10.6052/1000-0879-19-289
    Abstract ( 116 )   PDF (284KB) ( 75 )  
    The case library construction of materials mechanics involves the knowledge points, the related situations and the problems as three elements of a case, and integrates various case resources, such as teacher's notes, the graduate recommendations and the selected student notes. The teaching design based on the case library aims to cultivate students' ability to find, analyze and solve problems, and to strengthen their practical awareness and safety awareness. With various professional backgrounds and disciplines, the Internet-based teaching, the "mechanics on the fingertips", is effectively put into practice through meticulously selected cases and interactive discussions in class and after class, to promote the sharing of online and offline resources, the interactions between teachers and students in and out of class, and the in-depth integration of problem analysis and problem solving.
    The Field of Mechanics
    2020, 42(2):  249-254.  doi:10.6052/1000-0879-20-119
    Abstract ( 66 )   HTML( 39 )   PDF (10364KB) ( 39 )  
    Based on the historical data, this paper briefly describes the establishment process of the International Union of Theoretical and Applied Mechanics (IUTAM) and some stories of the Chinese Society of Theoretical and Applied Mechanics (CSTAM) joining the International Union of Theoretical and Applied Mechanics in 1980 , which can be used as a reference for readers to study the history of mechanics.
    2020, 42(2):  258-264.  doi:10.6052/1000-0879-19-179
    Abstract ( 181 )   HTML( 116 )   PDF (2308KB) ( 116 )  
    The famous energy equation for the steady flow of ideal fluids, the Bernoulli equation, has contributed greatly to the fluid mechanics since its publication. Based on the connotation of Bernoulli equation, this paper discusses its successful application in hydrostatics, steady orifice outflow, pitot tube velocity measurement, venturi flow and airfoil flow. At the same time, the modeling of the local following fluid particles is suggested by Bernoulli equation. It is summarized by Euler as the flow field method describing the fluid motion, which is the basic basis for deriving the Euler equations and the NS equations. It also laid the foundation for the establishment of the later turbulence theory, boundary layer theory, aerodynamic noise and other theories.