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20 April 2019, Volume 41 Issue 2
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    Review
    DYNAMICS AND CONTROL OF SPACECRAFT FORMATION FLYING IN EARTH ORBIT1)
    SUN Jun, HUANG Jing, ZHANG Xianliang, HUANG Tingxuan
    2019, 41(2):  117-136.  doi:10.6052/1000-0879-18-409
    Abstract ( 253 )   PDF (520KB) ( 192 )  
    The spacecraft formation flying is defined as the tracking or the maintenance of a desired relative separation, orientation or position between or among several spacecraft. This paper reviews the dynamics and the control of the spacecraft formation flying in Earth orbit, including the modelling methods and the control design techniques of the conventional propulsion system and the novel propellant-less system. The conventional propulsion system, where the spacecraft is actuated by thrusters using chemical fuels or plasma, can achieve a high accuracy and variable formation constellations with a relatively large power consumption. By contrast, the novel propellant-less system, where the spacecraft is actuated by novel means of actuation such as the atmospheric drag effect, the non-contacting internal forces, the geomagnetic Lorentz force, the momentum exchange, would greatly extend the lifetime of the formation and effectively avoid the plume contamination with new control characteristics. This paper summarizes the research methods and achievements in the dynamics and the control of these fields, and puts forward some issues worthy of further study in related fields and the direction of future development.
    Applied Research
    2019, 41(2):  137-144.  doi:10.6052/1000-0879-18-384
    Abstract ( 213 )   PDF (444KB) ( 63 )  
    The fracture behavior of a fluid-structure piezoelectric laminated column is studied under the condition of the axial shear vibration. The problem is solved by the variable separation method, the infinite trigonometric series, the Cauchy singular integral equation, the Bessel function and the Lobatto-Chebyshev collocation. The numerical results of the stress intensity factor (SIF) against the frequency are obtained, as well as the effects of the crack angle, the elastic modulus, the piezoelectric coefficient, the dielectric coefficient and the density on the first order resonance behavior of the stress intensity factor.
    2019, 41(2):  145-151.  doi:10.6052/1000-0879-18-434
    Abstract ( 180 )   PDF (2361KB) ( 39 )  
    This paper proposes an innovative composite wall, named the section steel-steel plate concrete composite shear wall. The seismic behavior of the composite walls is examined and the results of the quasi-static cyclic tests on the walls designed and machined are presented. The failure mechanism, the hysteretic behavior, the stiffness degradation and the energy dissipating capacity are investigated under various axial load ratios and shear span ratios.The test results indicate that the specimens fail in a flexural mode, the steel tubes are torn on the front and the side, characterized by the local buckling of the boundary steel plates and the compressive crushing of the concrete at the wall base.For the composite walls, the plastic deformation ability and the energy dissipation capacity are improved with the increase of the axial load ratios, while the shear span ratio has less effect.
    2019, 41(2):  152-156.  doi:10.6052/1000-0879-18-337
    Abstract ( 384 )   PDF (442KB) ( 72 )  
    Compared with the traditional metal materials, the composite materials have high specific strength, large modulus, good fatigue and corrosion resistance, and good thermal and electrical properties. In this paper, the composite materials are selected to carry out a layer-layer design for simply supported beams. Starting from the stress analysis of simply supported beams, the mathematical model of simply supported beams is established, according to the classical theory of composite material mechanics and the basic equation of elasticity. Then, the optimum design of the simply supported beam is carried out to determine the angle and the number of the layers of the simply supported beam, and the composite structure is constructed, the static analysis of the simply supported composite beam is carried out. Finally, the Tsai-Wu tensor criterion is used for the strength check.
    DESIGN OF LATERAL SOIL PRESSURE MODEL TEST SCHEME FOR ADJACENT COMPOSITE FOUNDATION1)
    LI Mingyu, QIAN Yuben, GUO Yuancheng, WEI Yanqing, ZHAO Shiyong, CUI Xinlei
    2019, 41(2):  157-163.  doi:10.6052/1000-0879-18-418
    Abstract ( 126 )   PDF (460KB) ( 47 )  
    In order to study the influence of the rigid pile composite foundation on the lateral soil pressure of adjacent supporting structures, prior to the design of the indoor model test scheme, the models of the adjacent natural foundation and the composite foundation are built by the finite element software for the numerical simulation, and the soil pressure distribution on the static retaining wall side under different foundation forms is estimated. The comparison of the numerical simulation results of the two groups shows that the soil pressure distribution of the composite foundation is different from that of the natural foundation. When the soil stress between the piles under the composite foundation cushion is the same as that of the natural foundation soil, the additional effect of the natural foundation on the wall side soil pressure at the same position of the retaining wall is significantly greater than that of the composite foundation, but as the "load transfer effect", the influence of the composite foundation on the lateral earth pressure of the retaining wall is gradually transmitted to the deeper soil as the load increases. It can be clearly seen that compared with the natural foundation, the effect of the composite foundation on the lateral earth pressure of the retaining wall is relatively weaker in the shallow soil layer, but stronger in the deep soil layer, and the stress concentration at the pile end has a significant effect on the lateral soil pressure at the bottom of the retaining wall.
    INFLUENCE OF SEDIMENTARY DIRECTION ON SHEAR STRENGTH OF SATURATED DENSE SAND IN CONSOLIDATED DRAINED TRIAXIAL TEST1)
    LUO Qiang, TANG Zhen, WANG Zhongtao, MA Keshuan, JIANG Gengmin, XIE Xiaokang
    2019, 41(2):  164-170.  doi:10.6052/1000-0879-18-347
    Abstract ( 157 )   PDF (724KB) ( 71 )  
    Based on the capillary effect of the sand, a test technology is suggested to prepare the dense sand sample with different sedimentary directions. A series of triaxial tests are performed to study the influence of the sedimentary direction on the strength and the volume change of the sand sample, meanwhile, a fitting formula is suggested for the relation between the ultimate strength and the sedimentary direction. Main study results show that the sedimentary direction has a great influence on the ultimate strength and the deformation characteristics of the sand for the direction in the range between 0°~90°, but it has little influence on the residual strength of the sand. When the sedimentary direction is close to the failure plane direction, which is suggested as 45°+ ϕ/2, the test sample is easier to reach the failure stage and the ultimate strength is low. The suggested fitting formula could reflect the relation between the sedimentary direction and the ultimate strength reasonably, in which the confined pressure has an influence on the relation. Meanwhile, the formula could be used to predict the most unfavorable sedimentary direction.
    2019, 41(2):  171-177.  doi:10.6052/1000-0879-18-297
    Abstract ( 107 )   PDF (3550KB) ( 41 )  
    With the uniaxial and triaxial compression tests of the water-cooled granite samples under high temperature, the mechanical properties of the water-cooled granite under high temperature within 800°C against the temperature change and the confining pressure are determined. The experimental results indicate that: (1)The threshold for the effect of high temperature heating and rapid cooling with water on the mechanical properties of the granite is 400°C. (2)Under the same temperature condition, the peak deviator stress and the peak strain increase with the increase of the confining pressure. The elastic modulus increases first and then decreases with the increase of the confining pressure. (3)In uniaxial tests, when the temperature is lower than 400°C, the rock samples will be in a form of composite failure. With the increase of the temperature, the damage morphology changes to a tensile failure. While in the triaxial test, the rock samples all have the shear failure.
    2019, 41(2):  178-183.  doi:10.6052/1000-0879-18-420
    Abstract ( 256 )   PDF (411KB) ( 62 )  
    Because the soft clay soil usually has a significant rheological effect, the deformation of the soft clay is divided into two parts, i.e., that caused by the effective stress change and that caused by the secondary consolidation. A new stress-strain relationship is thus derived. Based on the Davis's consolidation theory, a one-dimensional nonlinear consolidation equation with consideration of the secondary consolidation is established. The newly proposed equation is solved analytically and its reliability is verified by comparing with the numerical results. The influence of the secondary-consolidation on the settlement of the soft ground is studied. The results show that both the dissipation rate and the consolidation rate obtained by the present method are reduced as compared with those obtained by the traditional method, and the neglect of the secondary consolidation will underestimate the post-construction settlement of the soft clay foundation.
    2019, 41(2):  184-187,183.  doi:10.6052/1000-0879-18-370
    Abstract ( 185 )   PDF (187KB) ( 46 )  
    The mathematical expression of the strength of the reinforced soil is theoretically deduced, and the influence of the soil cohesion and the soil-reinforcement interface parameters on the strength of reinforced soil is analyzed. It is shown that when the reinforced soil is subjected to the tensile load up to failure, the cohesive force is reduced to an extent as compared with the tensile force provided by the reinforcement, the strength of the reinforced soil will be less than that of the plain soil; when the reinforced soil is adhesively damaged, the strength of the reinforced soil is less than that of the plain soil when the cohesion are reduced to an extent as compared with the friction provided by the reinforcement. The degree of reduction of the strength of the reinforced soil is related closely to the degree of the interlayer formed by the reinforced material in the soil, the permeability of the soil-reinforcement interface, the spacing of the reinforcement and the indirect reinforcement range.
    2019, 41(2):  188-195.  doi:10.6052/1000-0879-18-330
    Abstract ( 149 )   PDF (6403KB) ( 45 )  
    In view of the restrictive requirement of the pressure port configuration for the flush air data sensing (FADS) system based on the classical triple algorithm, a modified triple algorithm is developed and verified. Firstly, the classical triple algorithm and the modified triple algorithm are described. Secondly, the feasibility of the FADS system based on the modified triple algorithm including the pressure port configuration and the solving accuracy is evaluated. Finally, the advantages and the disadvantages of these two different methods are compared. The following results are obtained: (1)The solving accuracy becomes much less sensitive to the pressure port configuration for the FADS system based on the modified classical triple algorithm than that based on the classical triple algorithm. Therefore, much more pressure configurations can be used to predict the flight parameters and the restrictive requirement of the pressure port configuration is not necessary. (2)The solving accuracy differences between these two different methods is small, and the pressure port configuration still need to be verified.
    Research on Education
    2019, 41(2):  196-201.  doi:10.6052/1000-0879-18-379
    Abstract ( 305 )   PDF (295KB) ( 114 )  
    This paper reviews some American textbooks of statics, including the history and the current situation, the origin and the developments, as well as the main contents and the technical details.
    2019, 41(2):  202-205.  doi:10.6052/1000-0879-18-487
    Abstract ( 157 )   PDF (159KB) ( 87 )  
    The teaching load of lecturers in Dept. of Mechanics of most Chinese universities is usually very heavy due to the arrangement that they have to teach fundamental mechanics courses for all other engineering majors. In view of the new requirements of reduced teaching hours with the contents and the level of knowledge unchanged, cramming teaching to large classes (often over 100 students) seems to be the only choice for most fundamental mechanics course lecturers. In addition, the lecturers may not necessarily understand well the engineering fields of the students of other majors, as their own major is normally mechanics and the communication with teachers at other engineering departments may not be easy, so that they normally teach same things to students of different engineering majors, lack of coherent and integration, lack of long-term retention, without appropriate concepts and ability of applications of fundamental mechanics to their engineering problems. Based on ten years of first-hand teaching experience and discussions with teachers and students from civil and mechanical engineering, the author has adopted a major-oriented teaching of fundamental mechanics courses and presented here in this paper the method and its application.
    2019, 41(2):  206-209.  doi:10.6052/1000-0879-18-322
    Abstract ( 225 )   PDF (6040KB) ( 55 )  
    A visual experimental teaching method for the material failure based on the digital image correlation technique is presented in this paper. Taking the concrete material as an example, this presented method is applied in the splitting tension and uniaxial compression tests. The splitting tensile and compressive failure processes are monitored, and the failure modes are analyzed to reveal the failure mechanisms of the concrete material in the splitting tension and compression. The strain distribution of the specimen is obtained using the digital image correlation method. The above results confirm the failure mechanisms of the concrete material and the applicable failure strength theory.
    2019, 41(2):  210-215.  doi:10.6052/1000-0879-18-386
    Abstract ( 274 )   PDF (226KB) ( 77 )  
    With the emerging technology of education, a teaching method, uniting the traditional classroom, the online classroom, the rain classroom and the flipped classroom, is discussed in this paper. This teaching method of the "Four-Classroom Integration" and assessment model are used in the course of theoretical mechanics in order to improve the classroom teaching effectiveness. Good teaching results are obtained according to the data of the final exam. This method provides a way of the teaching reform of the contemporary theoretical mechanics classroom.
    A NEW TEACHING METHOD OF ENGINEERING FLUID MECHANICS COURSE1)
    WANG Liang, XUE Rui, CAI Ning, SHANGGUAN Jianfeng, LIU Minghui, ZHOU Xin
    2019, 41(2):  216-221.  doi:10.6052/1000-0879-18-351
    Abstract ( 212 )   PDF (809KB) ( 95 )  
    In view of the teaching characteristics of the Engineering Fluid Mechanics course, the teaching mode of "Theoretical Deduction—Experimental Study—Numerical Simulation—Interactive Case" is proposed. This teaching mode links the related knowledge points, with a variety of methods for explanation. Taking the boundary layer separation phenomenon as an example, the theoretical deduction is used to analyze its mechanism, the experimental method is applied to show the separation phenomenon, the CFD numerical simulation method is used for improving the teaching effect and expanding the knowledge, and the network interaction method is used to improve the learning interest and deepen understanding. The traditional and the emerging technologies are combined and this mode can be used for the teaching of other courses.
    ANSYS AND TEACHING OF MECHANICS OF MATERIALS1)
    ZHOU Xiaomin, SUN Zheng
    2019, 41(2):  222-226.  doi:10.6052/1000-0879-18-368
    Abstract ( 236 )   PDF (462KB) ( 114 )  
    The traditional classroom teaching of Mechanics of Materials focuses on the theoretical derivation of formulas, with relatively boring effect. The experimental classes cannot coordinate with the theoretical course, and it is impossible to show the other information than the deformation of the specimen. In order to improve the teaching efficiency, ANSYS is introduced into the classroom of mechanics of materials. Through the animation and contour figures, the deformation and the stress of the basis problems of Mechanics of Materials are presented. With the theoretical formula, it can not only deepen the students' understanding of various mechanical concepts, knowledge points and formulas but also stimulate students' learning interest and innovative thinking. It is helpful for the cultivation of engineering talents.
    2019, 41(2):  227-232.  doi:10.6052/1000-0879-18-378
    Abstract ( 426 )   PDF (242KB) ( 92 )  
    When the regular diagram multiplication method is applied to compute the displacements of beam structures with variable cross-sections, many difficulties will be encountered, such as too much area blocks, excessive numbers of diagram multiplications, great amount of computation, and low computational efficiency. So a new stiffness-distribution diagram multiplication is proposed to solve these difficulties based on the structural stiffness. Basic formulas are derived with operation principles for their applications. The concept of the new method is very clear and can be understood easily, with the advantages of the diagram multiplication method taken fully. The application and the comparison of a numerical case show that the operation of the stiffness-distribution diagram multiplication method is very simple and reasonable. With the new method, small amount of computation is taken with high efficiency. So it is worth being recommended.
    The Field of Mechanics
    2019, 41(2):  237-238.  doi:10.6052/1000-0879-19-068
    Abstract ( 186 )   PDF (137KB) ( 103 )  
    This paper discusses the science fiction film "The Wandering Earth" from the point of view of mechanics, and the possibility of the future technology imagined in this film is discussed.
    2019, 41(2):  239-243.  doi:10.6052/1000-0879-18-263
    Abstract ( 230 )   PDF (3603KB) ( 58 )  
    The essence of Sonic-Boom-Cloud is the water vapour condensation cloud caused by the local acceleration and the temperature decreased to the dew point and below, as the flying aircraft passes the high humidity air. It is more appropriate to call it the Condensation Cloud instead of the Sonic-Boom-Cloud. According to the flight speed and their different features, the Condensation Clouds can be divided into three types: the Low Subsonic Speed Irregular Condensation Cloud, the High Subsonic Speed Cone Condensation Cloud and the Supersonic Speed Cone Condensation Cloud. The formation mechanisms of the three types of Condensation Clouds, their different features, their relationship with the shock wave and the Sonic-Boom are discussed in this paper. The first type has no relationship with the Sonic-Boom. The second type is accompanied by the local weak shock wave, it does not break through the Sound Barrier and it is basically irrelevant with the Sonic Boom. The third type is related with the supersonic shock wave and the Sonic Boom.
    RIGID EQUILIBRIUM AS EXEMPLIFIED BY BIRDS STANDING ON A BRANCH1)
    Zhang Weiwei, Xue Shuhang, Wang Zhihua
    2019, 41(2):  244-246,243.  doi:10.6052/1000-0879-18-011
    Abstract ( 442 )   PDF (1034KB) ( 241 )  
    To enhance the students' interest for studying Theoretical Mechanics, two teaching cases of static equilibrium are designed in this paper, as the static analysis for birds standing on a branch. Some knowledge points, such as the parallelogram of force, the transmissibility of force, the three-force balance intersecting principle and the conditions of rigid body equilibrium, are used to analyze the forces on the bird' legs on a branch; and the function of the woodpecker tail when it pecked the worm. It is a very enjoyable and educational experience for the students, and can raise students' interest in learning and improve teaching results.
    ON FLOW IN POROUS MEDIA
    LIU Junli
    2019, 41(2):  249-252.  doi:10.6052/1000-0879-19-051
    Abstract ( 90 )   PDF (413KB) ( 74 )  
    Flow in porous media (or porous flow) is the manner in which fluids behave when flowing through a porous media. There are many types of porous media, such as rocks (including various types of minerals), soils, biological materials, and artificial porous media materials. The porous flow phenomena widely exist in the natural world, engineering materials and inside the body of plant and animals. The porous flow theory is fundamentally important in exploiting underground resources, such as underground water, geothermal resource, petroleum, natural gas and coal. This article explains the basic concepts, classifications, influencing factors and key characteristics associated with porous flow. The research significance of porous flow is also discussed.