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20 June 2020, Volume 42 Issue 3
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    Review
    2020, 42(3):  267-276.  doi:10.6052/1000-0879-20-077
    Abstract ( 64 )   HTML( 47 )   PDF (406KB) ( 47 )  
    The aircraft dynamics and control has achieved a significant progress, but also faces a series of problems that need to be dealt with. Deep learning provides a new solution for these problems, and it is good in many aspects, such as the working model of the experience storage, the intelligent accumulation and the off-line training. In this study, around the subject of the autonomy and the intelligence enhancement for the flight control, the applications of the deep learning in aircraft dynamics and control are reviewed in three aspects: (1) applications of deep learning in dynamic modeling to improve the computational efficiency and accuracy of modeling, or to solve the problem of inverse dynamics; (2) applications of deep learning in optimal control to improve the speed of trajectory planning or the real-time performance and autonomy of flight control; (3) applications of deep learning in mission design to improve optimization speed and decision-making intelligence. Furthermore, the advantages and the disadvantages are analyzed and representative papers are introduced. Finally, four suggestions to apply the deep learning in aircraft dynamics and control are given.
    Applied Research
    2020, 42(3):  277-281.  doi:10.6052/1000-0879-19-458
    Abstract ( 29 )   HTML( 20 )   PDF (323KB) ( 20 )  
    Strictly speaking, all conservation laws in hydrodynamics are for a material system (or a fluid system), such as the conservation laws of mass, momentum, momentum moment and energy. The Lagrange method is used to describe and characterize the motion behavior of the fluid particle system. If the motion and the conservation laws of the material system are put into the space coordinate system, the Euler method is often used. Therefore, for the observed (followed) fluid material system, each conservation law makes a transformation from the material system to the control volume, which is the famous Reynolds transport equation. In this paper, the Reynolds transport equations for different velocity control volumes are derived based on the boundary calculus. The physical significance of various transport equations is also discussed.
    2020, 42(3):  282-288.  doi:10.6052/1000-0879-19-450
    Abstract ( 38 )   HTML( 17 )   PDF (2504KB) ( 17 )  
    The mechanism of the bubble subsidence is studied based on hydrodynamics, focusing on the bubble subsidence behavior in vertically vibrating cylindrical vessels. With the consideration of additional mass and bubble compressibility, a mathematical model of the compressible bubble with subsidence effect is established, and the critical displacement and velocity of the bubble subsidence are obtained by the separating variable method. The results show that the amplitude and the frequency of the sinusoidal excitation are the important factors affecting the bubble subsidence, and they are closely related with the critical displacement and velocity, and the larger the amplitude and the frequency, the smaller the critical displacement, the easier the bubble sinks.
    OPTIMIZATION OF FUSELAGE OPENING ZONE OF CIVIL AIRCRAFT
    YIN Kaijun, SU Yanfei, ZHANG Yinli
    2020, 42(3):  289-373.  doi:10.6052/1000-0879-19-342
    Abstract ( 35 )   HTML( 20 )   PDF (1761KB) ( 20 )  
    The cabin door openings are usually arranged in the fuselage for civil aircraft, resulting in fuselage stiffness discontinuity. In view of the structural stiffness and the transmission of the load, the paper studies the opening structure of the fuselage: clarifying the factors affecting the stiffness of the opening structure and optimizing the opening angle and the size of the reinforcing structure. The above research shows the direction and the method of the design and the reinforcement of the opening structure in the preliminary design stage of the opening structure of the aircraft fuselage.
    Review
    2020, 42(3):  294-299.  doi:10.6052/1000-0879-19-320
    Abstract ( 64 )   PDF (375KB) ( 29 )  
    When a partially-filled tanker truck is turning, the center of gravity of the liquid shifts, which negatively influences the roll stability of the tanker truck. An elliptical-shaped tanker truck with partially-filled liquid is taken as an example and its rollover mechanism in the course of turning is analyzed. With the liquid level change being approximately represented by a quasi-static process, the pressure on the internal wall of the tank is calculated to locate the pressure center and a quasi-static equivalent mechanical model for the roll stability of partially-filled tanker trucks under turning conditions is established. This model provides a theoretical basis for developing the rollover-warning system of tanker trucks. It is shown that the roll stability of the tank car is related to the cross-sectional shape of the tank body and the filling rate of the liquid, and the results can be used for improving the roll stability of the tank car.
    2020, 42(3):  300-305.  doi:10.6052/1000-0879-19-367
    Abstract ( 27 )   PDF (375KB) ( 9 )  
    The coal mine impact ground pressure mainly occurs in the roadway. One of the main reasons is that a large amount of elastic energy is accumulated in the surrounding rock of the roadway. In order to obtain the characteristics of the elastic deformation energy accumulation of the surrounding rock of the rectangular roadway and to reduce the cost of the roadway support, the energy criterion of the roadway impact failure is established, and the calculation model of the surrounding rock energy accumulation of the rectangular roadway is built. The influence of the mining depth, the section size of the roadway and the thickness of the coal seam on the energy accumulation of the surrounding rock in the rectangular roadway is analyzed. It is concluded that for the rectangular roadway, the elastic energy increases with the increase of the depth of mining; the deeper the depth of the mining, the faster the growth rate of the elastic energy accumulated in the roadway; the energy accumulated in the surrounding rock of the roadway increases with the increase of the section size of the roadway; and when the thickness of the coal seam is less than the influence range of the roadway, the accumulation energy of the roadway increases as the thickness of the coal seam increases. In the actual project, the section size of the roadway should be reduced as much as possible, and the roadway is better arranged along the top and the bottom as far as possible. The research results provide a theoretical basis for the layout of the rockburst roadways and the reduction of the roadway support costs.
    A CONSOLIDATION MODEL OF GROUP WELLS ON COMPOSITE FOUNDATION1)
    ZHANG Yuguo, YANG Hanyue, DUAN Mengmeng, SHI Xiaojie, ZHANG Weijie
    2020, 42(3):  306-313.  doi:10.6052/1000-0879-19-461
    Abstract ( 22 )   PDF (524KB) ( 13 )  
    For the consolidation problem on the composite foundation, with consideration of the influence of the well resistance and the vertical seepage in the soil radial direction, a calculation model of composite foundation group wells with pile-soil-pile as a unit is established. By using the analytical method, the analytical solution of the composite foundation group well consolidation under an instantaneous load is derived, as well as the consolidation characteristics and the pore pressure variation of the composite foundation. The study shows that the consolidation model of the composite foundation group wells provides a new idea for the theoretical study of the consolidation of the composite foundation. When the borehole diameter ratio is greater than 5, based on the assumption that the flow rates in the central pile and the side pile are equal, the difference between the consolidation degree calculated by the group well consolidation theory of the composite foundation and that calculated by the traditional consolidation theory is very small and negligible. The consolidation rate of the composite foundation increases with the increase of the pile permeability coefficient, the radial permeability coefficient of the soil in the disturbed zone and the vertical permeability coefficient of the soil. The larger the load is, the larger the settlement and the vertical strain will be. The pore pressure dissipation rate and the vertical strain rate of the surface soil are higher than those of the underneath soil.
    2020, 42(3):  314-320.  doi:10.6052/1000-0879-19-399
    Abstract ( 20 )   PDF (4855KB) ( 23 )  
    In this paper, the relationship between stress and strain on the surface of brittle or quasi brittle materials is obtained by the high temperature Hertzian indentation method. According to the analysis of the indentation stress strain curve, the indentation modulus, the shear modulus and the hardness of the material can be determined and the deformation properties of the cement clinker are compared. Under the high temperature heat treatment of different temperatures (25 ${^\circ}\!$C$\sim $1400 ${^\circ}\!$C), the stress relaxation of the Hertzian indentation is observed. When the load peak value is 100 N, the load relaxation of the cement clinker is more obvious with the increase of the temperature. With the temperature increasing from 500 ${^\circ}\!$C to 1400 ${^\circ}\!$C, the load relaxation is very significant, especially at 1200 ${^\circ}\!$C. For the cement clinker samples within the C3S decomposition and the partial liquid phase, the stress relaxation is observed, most obviously at 1275 ${^\circ}\!$C, the clinker softened, and the relaxation load is 0 N. So 1275 ${^\circ}\!$C is the brittle ductile transition temperature of the clinker. The brittle plastic transition temperature of the cement clinker during the two heating processes can be determined by the high temperature Hertzian indentation relaxation test for the cement clinker. The temperature range for the sharp change of the elastic modulus and the compressive strength of the clinker can be determined. To study the mechanical behavior and the mechanical properties of the cement clinker at different temperatures, new ways to improve the grinding efficiency should be explored.
    2020, 42(3):  321-330.  doi:10.6052/1000-0879-19-459
    Abstract ( 22 )   PDF (4476KB) ( 26 )  
    A general tire testing machine is used for the performance tests of the radial tires with radial stiffness. Orthogonal tests are used to analyze the grounding characteristics of the tires under different tire pressures and vertical loads. The simulation software ABAQUS is used for a simulation to compare with the tests. The results show that the Mooney-Rivli model for the rubber material can be applied in certain cases. The radial stiffness is linearly related with the tire pressure. As the area increases, the area of the tread marks decreases significantly. The pressure on the contact surface is mainly concentrated on the shoulders and that on the tread crown is also increased. When the tire pressure is constant and the vertical load is increased gradually, the stress on the entire footprint is in a symmetrical. distribution, and the distribution of the stress on the imprint surface changes gradually from high on the inner part and low on the outer part to high on the outer part and low on the inner part. A mathematical model is built and the finite element software is used to analyze the strain energy of the tire at the same time. It is found that the tire is prone to a slight lateral displacement and deformation at the same time when the tire is loaded at a low tire pressure of 150KPa. At this time, it is easy to cause a hysteresis loss and cause a sharp increase in the strain energy.
    NUMERICAL ANALYSIS OF ARC MOTION IN RAILGUN MUZZLE UNDER THE EFFECT OF BACKFLOW
    GAO Yuan, WANG Zhaoxin, XIAO Hongcheng, NI Yanjie, XU Yingtao, LI Baoming
    2020, 42(3):  331-336.  doi:10.6052/1000-0879-19-378
    Abstract ( 23 )   PDF (771KB) ( 11 )  
    During the launching process of the railgun, the high temperature air mass outside the muzzle moves to the interior at a speed far higher than the sound speed, which will change the arc shape of the muzzle and cause the arc displacement. This paper makes a numerical calculation of the movement process of the muzzle arc, based on the theory of magneto hydro dynamical (MHD), with a treatment method of potential boundary condition closely related to the electric conductivity of the arc plasma itself, and a three dimensional simulation model of the muzzle position arc is established. The arc motion under the backflow effect is analyzed, and the influence of the arc on the temperature distribution of the railgun inner bore flow field is studied. The simulation results show that the movement of the muzzle arc intensifies the temperature rise in the bore.
    A MECHANICAL MODEL OF CELL DURING INDENTATION BASED ON MEMBRANE THEORY
    WANG Yue, XU Xianzhong, LIU Ming, LIU Mengyun
    2020, 42(3):  337-343.  doi:10.6052/1000-0879-19-479
    Abstract ( 21 )   PDF (19927KB) ( 12 )  
    This paper proposes a mechanical model that can be used to analyze the deformation of the cell during indentation experiments based on the membrane theory. The mechanical model of the cell is validated through the macro-indentation tests on latex balls and PVC balls, the theoretical analysis and the comparison of the indentation testing curves of the different cells. At the same time, a specific mechanical analysis of the single chondrocytes is carried out by using the new model, and the mechanical parameters of the cell and the stress distribution on the surface of the cell membrane are obtained. A new idea is thus provided for the study of the mechanical properties of single cells.
    Research on Education
    PRACTICE OF SOFT ROBOTICS AND INNOVATION EDUCATION
    FENG Ruoyu, CHEN Lu, ZHANG Houzhen, DU Shuyuan
    2020, 42(3):  347-350.  doi:10.6052/1000-0879-19-351
    Abstract ( 28 )   PDF (685KB) ( 14 )  
    The course of practice can help cultivate students' skills of do-it-by-oneself and cooperation, and teach them the practical applications of theories. Recently the soft robotics becomes a nascent research field, which contains abundant mechanical principles. This paper explores an application of the soft robotics for teaching mechanics, including the methods of selecting subjects and organizing. As an implementation, in the soft robotics program of the 2019 aerospace technology science innovation and practice camp held by Tsinghua University, 14 undergraduate participants successfully developed 5 soft robots using different actuation mechanisms and locomotion gaits.
    DIFFERENCE BETWEEN ARTIFICIAL AND COMMERCIAL PIPES IN TRANSITION ZONE1)
    HUANG Shuxin, LI Yunlei, QU Dongyue, PAN Zheng
    2020, 42(3):  351-354.  doi:10.6052/1000-0879-19-364
    Abstract ( 20 )   PDF (145KB) ( 13 )  
    Pipe friction is a teaching content in the course of fluid mechanics, in which Darcy friction factors in transition zone obtained by using artificial and commercial pipes are different. The present work shows analyses on the difference at two aspects. One is according to the understanding of students on the problem, and another is from the definition of surface roughness. Both show the surface roughness effect on the phenomenon. It is still necessary to research the quantitative effect of surface roughness on the difference between artificial and commercial pipes in transition zone.
    2020, 42(3):  355-358.  doi:10.6052/1000-0879-19-341
    Abstract ( 27 )   PDF (347KB) ( 15 )  
    Fluid mechanics is a basic course for undergraduates majoring in mechanics and mechanical engineering. As it involves many concepts of mathematics and physics, complex formulas, abstract theories and wide applications, fluid mechanics is regarded as one of the most difficult courses for teachers and students alike. This paper proposes a method of interdisciplinary teaching of fluid mechanics and other mechanics courses, such as theoretical mechanics, materials mechanics and electrodynamics. By making a full use of the links among these mechanics courses, students can review the knowledge of other mechanics courses while learning fluid mechanics, and deepen their understanding of fluid, solid, rigid body and electromagnetic field through comparisons. Thus they could obtain an overall vision of mechanics and the teaching effect would be improved.
    THE EXPLORATION AND THE PRACTICE OF CULTIVATING TALENTS IN PROFESSIONAL BASIC COURSES
    LÜ Xiaoyin, LÜ Jin, GUO Yiyuan, WANG Qi, JIA Yingjie
    2020, 42(3):  359-362.  doi:10.6052/1000-0879-20-082
    Abstract ( 26 )   PDF (8687KB) ( 113 )  
    Based on the modern information technology and the teaching resources, the curriculum education in professional courses of civil engineering, machinery, vehicles, and aerospace is explored. The elements of ideological and political courses and the cultivation of talents are combined in the teaching procedures of professional basic courses in order to realize the unification of cultivating morality and ability and to make students have both ability and virtue for realizing the great rejuvenation of the Chinese nation.
    DESIGN AND PRACTICE OF NEW FORM TEXTBOOK OF THEORETICAL MECHANICS BASED ON AUGMENTED REALITY TECHNOLOGY1)
    LI Yongqiang, ZHANG Yingjie, CHI Weichao, ZHAO Xiangdong, AN Li, LI Hongying
    2020, 42(3):  363-367.  doi:10.6052/1000-0879-19-308
    Abstract ( 15 )   PDF (1420KB) ( 14 )  
    Textbooks are the carrier of the educational ideas, the teaching contents, and the teaching methods. In this paper, the history and the current development of the textbooks of theoretical mechanics are analyzed, as well as the necessity of new form textbooks to integrate with internet technology, and the characteristics of the new form textbooks supplemented with digital course resources. The design of the new form textbook is proposed, and the development and the application of the new form textbook complied in Northeastern University are introduced.
    2020, 42(3):  368-371.  doi:10.6052/1000-0879-19-401
    Abstract ( 22 )   PDF (153KB) ( 22 )  
    According to the new engineering concept, the personnel training takes a combined learning mode, as an important trend of teaching reform in universities. The cloud teaching materials are the teaching resource, consisting with the combined learning mode. The preparation of cloud teaching materials of engineering mechanics is based on the OBE education concept, with the learning objectives, and integrating rich media digital publications, the cloud service and the mobile learning, to provide appropriate teaching resources for hybrid teaching of engineering mechanics. The practical application shows that the cloud teaching materials of engineering mechanics can arouse the students' interest in learning and enhance their autonomous learning.
    On mechanics around us
    2020, 42(3):  378-380.  doi:10.6052/1000-0879-19-395
    Abstract ( 17 )   HTML( 14 )   PDF (769KB) ( 14 )  
    This paper gives the dynamical explanation of a rainbow spring walking on a run-machine.
    BEWARE OF THE BEACH HIDDEN KILLER--RIP CURRENT
    TIAN Haiping, YI Xingrui, WANG Wei
    2020, 42(3):  381-387.  doi:10.6052/1000-0879-19-413
    Abstract ( 106 )   HTML( 66 )   PDF (6947KB) ( 66 )  
    The rip current is a strong current, perpendicular to the coastline and towards the open seas. It is very dangerous for people at the beach, and once carried away from the shoal by the rip current, inexperienced swimmers will find it difficult to swim back to the shore and will eventually be drowned due to the exhaustion. Most drowning accidents in the coastal area are associated with the rip current. The lack of public awareness about the rip current is one important cause. This paper reviews the damage, the development, the characteristics and the classification of the rip current from the perspective of hydrodynamics, and some suggestions are made of how to prevent the rip current and ensure the safety.
    National Zhou Peiyuan Competition on Mechanics
    DESIGN PRINCIPLES AND CASE ANALYSIS OF COLLEGE STUDENTS’ STRUCTURAL DESIGN COMPITITION
    SONG Xiaobing, WU Xiao'ang, YAN Bin, MENG Jingxi, CHEN Sijia
    2020, 42(3):  388-393.  doi:10.6052/1000-0879-19-237
    Abstract ( 35 )   PDF (485KB) ( 22 )  
    In the competition of structural design, the merits and the demerits of the structural scheme play an important role in the competition results, which is known as "the scheme is the king". Taking the work of Shanghai Jiaotong University team in the 11th National College Students' structural design competition as an example, this paper analyzes the general principles of the structural scheme design, and applies these principles in practical operations.