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.
With its great national strategic importance and socio-economic benefits, the high-speed vehicle always plays a specific role in the field of aerospace. In this paper, the structural optimization technique and its application in the aircraft design are reviewed firstly. Then, the specific applications of structural optimization techniques in the high-speed vehicle design are then discussed in the context of the typical service environment and the design requirement. We show typical cases subsequently with applications in the concept design of the high-speed vehicle and in the innovative and improved design of their parts over the last years. In view of the solid theoretical foundations as well as the numerous successful engineering practices of the structural optimization, it not only provides an effective tool, but also brings about revolutionary changes for the design of high-speed vehicle structures. It is anticipated that the structural optimization supplemented by the empirical design will surely be a standard procedure for the aircraft design, and the practice-oriented research will undoubtedly enhance the core competitiveness of the aerospace industry in China
This is the question asked in class: is it possible to obtain the covariant derivative of natural base vectors? To answer this question, the idea of axiomazitaion is introduced, the concepts of the generalized component and the generalized covariant derivative are defined. Based on these new concepts, the classical covariance is developed into the generalized covariance, and the classical covariant differentiation is developed into the generalized covariant differentiation. This paper summarizes the main difficulties and the important points of the above explorations, and shows the abstractions of the generalized covariant derivatives and the advances of the generalized covaraibilities.
The influence of the locked-in stress on the rock mechanical properties cannot be ignored. Since Chen Zongji proposed the definition of the locked-in stress in rocks, there were very few related studies. Starting from the definition, combined with the current development of the rock mechanics, this paper expands the concept of the locked-in stress，in a new definition of the locked-in stress in rocks. The forms of the stress in accordance with the new definition of the locked-in stress in the rock mechanics research are classified. The variation law of various kinds of locked-in stress and its empirical formula are summarized. The correlation between the locked-in stress and the excavation of the underground engineering and its influence are discussed. This paper provides a new way to explain the special phenomenon of deep rock mechanics.
The flexible stress sensitive conductive polymer composites (CPCs) have a wide application prospect in the fields of the wearable human machine interaction, the medical monitoring, the portable sports equipment and the bionic robot, and others. The conductive percolation theory, the response mechanisms and the sensitivity of the stress sensitive CPCs are discussed in this paper. The response characteristics of different types of stress sensitive CPCs are reviewed, including the numerical predications. Finally, the future development is commented.
The compression boundary layer transition and separation caused by the interference of the shock and the boundary layer directly affect the drag, surface thermal protection and the flight performance of flying vehicles. This paper first reviews the past work on the interference between the shock wave and the boundary layer. And then, the effects of the forward shock, the oblique shock and the head shock on the laminar flow and the turbulent boundary layer of supersonic and transonic flows are studied and compared. The shock waves of different intensities have different effects on the boundary layer.A strong interference is more likely to cause the separation and the airfoil stall.
Some fundamental concepts and problems in the research field of the structural topology optimization are introduced briefly. The essential characteristics of the truss-like and its discretization are analyzed. The classical analytical solutions as the benchmarks are listed in the references. The optimization strategies and the characteristics of various numerical methods for the structural topology optimization are reviewed. The numerical instabilities, such as the mesh-dependencies, the singular optima, the checkerboards and the local constraints, commonly in the structural topology optimization, are explained. The fundamental principles of the optimality criteria, the sequential programming and the heuristic methods are discussed.
The techniques for the drag reduction of large transport aircraft are reviewed in this paper. The techniques intended to reduce the friction drag, the induced drag and the wave drag are reviewed specifically. Techniques like the suction control for delay boundary layer transition, the riblets for reducing turbulent friction drag, and the winglet are relatively mature for practical application. Distributed roughness, plasma actuators and the contour bump are most like to be used in the newly designed large transport aircraft. These newly developed techniques might be useful in further improving the drag characteristic of the next generation aircraft.
Since the hypersonic vehicle is acted by a serious aerodynamic thermal load caused by the flight through the atmosphere, it is necessary to consider the effect of the high temperature in the ground test of the vehicle structures. But the structural modal experiment in a high temperature environment is far more complex than the normal modal experiment with many technical difficulties to be solved. In this paper, the advance of the thermal modal test technology is reviewed. The characteristics and the applicability of the excitation and measurement techniques to be used in the high temperature environment are discussed in detail. The development direction and the research focus of the structural modal test technology in the high temperature environment are suggested.
The thermal vibration is the inherent vibration of nanostructures, which plays an important role in the dynamics of nanostructures. The quantum effects, the boundary effects and the van der Waals interaction have a significant influence on the thermal vibration of nanostructures. The carbon nanotubes and the graphene were extensively studied for their novel electronic properties and superior mechanical strength. This paper reviews some research methods for the thermal vibration of nanostructures, the thermal vibration of the carbon nanotube and the graphene in low temperatures and the nonlinear thermal vibration of the carbon nanotube.
The early-age concrete under the condition of restrained shrinkage is easy to crack, which would affect safety and durability of the structure, as well as the applicability. So it is very important to provide a simple and effective method to assess the crack resistance of the early-age concrete. In view of providing certain rigidity and the convenience of laboratory constraints, the restrained shrinkage ring test is widely used to evaluate the crack resistance of the concrete under restrained shrinkage conditions. This paper discusses the development of the restrained shrinkage ring test, the failure mechanism and the impact of three factors. The restrained shrinkage ring test is recommended as a standard test method by the American Association of State Highway and Transportation Officials (AASHTO) and the American Society for Testing and Materials (ASTM), and the test is conducted for different purposes, including the failure mechanism based on the maximum tensile stress fracture mechanics theory and the fracture energy to predict the concrete cracking. The annular test specimen geometry, the boundary conditions, the performance of the concrete materials and the pre-crack are considered as influencing factors. A test method of elliptical ring is adopted, which can effectively assess the crack resistance of the concrete under conditions of high degree of restraint.
The transfer orbit for the human lunar mission means that between the trans-lunar orbit and the trans-earth orbit, and it has the characteristics of long flight time, complex dynamics model, and strong nonlinear and variable coe-cients. The controllability of the inevitable deviation afiects the result of the task execution, even the success or the failure of the engineering task directly. This paper reviews the studies of the transfer orbit of human lunar mission, the analysis method of the deviation propagation, the mid-course correction optimal strategy and the mid-course correction aiming algorithm. At last, some suggestions are made or the mid-course correction of the Chinese human lunar mission in the future.
For the design and the safety assessment of wood structures, an adequate knowledge of wood fracture behavior is important. Due to the complexity in its structure, wood is naturally anisotropic in the macroscopic scale, which makes it more di-cult to study wood failure based on fracture mechanics than to study isotropic materials. Therefore, only fractures of pure mode I and pure mode Ⅱ were given a considerable attention. Wood structural members are, however, often subject to the mixed mode fracture in reality, and the mixed mode fracture is now one of hot topics in the fracture studies. This paper gives a literature review on the wood mixed fracture from two aspects:the fracture criterion and the testing method. After an introduction of some empirical and physical models to predict the mixed mode fracture failure of wood, a comparison is made among these models using the test data in the literature. Various test methods are reviewed, with focus on fractures of mode I and mode Ⅱ combined. Some issues for future studies are highlighted.
The studies on discrete Boltzmann modeling and simulation of phase separation are reviewed. According to the system component, the studies cover the single-component two-phase separation and the multi-component phase separation. According to the physical modeling, the studies cover the LBM (lattice Boltzmann method) simulations based on traditional hydrodynamic modeling and discrete kinetic modeling of the phase separation system. According to the main focus, the topic covers method/model studies and physical behavior investigations. The discrete kinetic modeling has brought some deeper insights into the phase separation process. The features of non-equilibriums obtained from discrete Boltzmann simulations can serve as some simple and effective physical criteria for dividing the two stages of phase separation, and can be used to discriminate and track various interfaces.
The prediction of high-frequency dynamic response of composite structures is one of key steps in the structural design of the aircraft and other vehicles. In order to make an accurate prediction, three methods are discussed. The energy finite element method is found to be suitable to obtain accurately the dynamic response of composite structures. In this paper, the energy finite element analysis and its applications for composite structures are reviewed. Some important issues for the further applications are suggested.
Sloshing of liquid propellant in microgravity and its influence on the attitude control system have been studied for several decades. Accurate modeling is necessary, especially, for modern spacecrafts carrying large amounts of liquid propellant. Research progress on this issue is reviewed, including a summary of analytical methods for both linear and nonlinear sloshing, an introduction of numerical techniques such as modal analysis and CFD (computational fluid dynamics) methods, and also a description of experimental approaches and advances. Finally, some critical problems concerning liquid sloshing in microgravity are proposed and discussed.
Earth penetration in geotechnical engineering is difficult to model, largely due to the transient, cou- pled nature of the impact event. The interaction between the penetrator and the target is inherent due to their vastly different material responses. The loading induced on the penetrator can lead to a significant deformation and potentially high shock levels on any onboard components. It is a challenging task to simulate such problems properly. This paper presents typical progresses, and the principles and features of each simulating method are elaborated. In addition, the rationale of the coupled Eulerian-Lagrangian method is discussed in detail. Two examples, the surface footing and the pile penetration, show that the coupled Eulerian-Lagrangian method is more accurate and convenient than other methods for the penetration analysis in geotechnical engineering. The numerical simulation methods of penetration in geotechnical engineering discussed in this paper can be used by related researchers.
Cables are widely used as tension structure members in engineering as they are light, flexible and of high strength. On one hand, the external excitations induce cable's complex dynamic responses with large amplitudes, which might cause structure's failure. On the other hand, the cable structure is a typical nonlinear system with both quadratic and cubic nonlinearities, which means extensive nonlinear dynamic behaviors. Therefore, the cable dynamics is an interesting research issue in both engineering and applied mechanics, and our knowledge about the cable dynamics is much enriched in the past few decades. This paper reviews the progress of cable dynamics, including cable's dynamic models, internally resonant dynamics, moving support induced cable dynamics, and complex excitation induced cable dynamics. And we also discuss the limitations of the present cable dynamics.
By comparing the characteristics of the frozen soil and the unfrozen soil, it is shown that the strength of the frozen soil is much stronger than that of the unfrozen soil, which increases the difficulty of the frozen soil excavation, as an issue in front of engineering operations in cold regions. There are several methods for the frozen soil excavation and the practicability and the feasibility of the methods are reviewed in this paper. It is shown that the mechanical method used to excavate the frozen soil is extremely effective. Secondly, the difficulty of the frozen soil excavation is related to the physic-mechanical properties of the frozen soil. In the process of excavation, the fracture mechanics and the damage mechanics of the frozen soil are more involved. This paper gives a brief overview of the dynamics of the permafrost to indicate the main factors that affect the mechanical properties of the frozen soil and the features of the damaged frozen soil, to help the permafrost mechanical excavation. A review of the previous experimental researches aims to help the studies of the permafrost cutting and impact performance, and a few suggestions are made for the further study of the frozen soil excavation.
In the numerical simulation of hydraulic fracturing in a shale gas reservoir, both the shale rock's properties and the multistage hydro-fracking technique of the horizontal well should be considered, which is a difficult problem of mechanics. In this paper, the mechanical characteristics of the shale rock and the multistage fracking technology of the horizontal well in the shale gas reservoir are discussed, as well as the applications of the extended finite element method, the boundary element method and the discrete element method in hydraulic fracturing and their advantages and limitations. It is indicated that the three dimensional displacement discontinuity method of the boundary element method is an effective approach to model the propagation of multistage fractures.
Mechanics, as the basic discipline of engineering sciences, plays a very important role in the design of the launch vehicle. Structure Dynamics, as an important part of mechanics, is especially important, and its developments reflect the level of the LV's (launch vehicle's) design in some extent. This paper discusses the interactions between structure dynamics and the launch vehicle technology, in the context of their development, and puts forward some proposals for the further development.
The magnetohydrodynamic technology becomes a research hotspot since the "AJAX" concept was proposed by Russia in the early 1990s. This paper reviews the advances of the studies of magenetohydrodynamic turbulence, mainly in two parts: the characteristics of magenetohydrodynamic turbulence and the numerical models of magenetohydrodynamic turbulence. Magnetohydrodynamic turbulence has some peculiar characteristics such as the anisotropy induced by the magnetic field, the Joule dissipation, the relaminarization of turbulence, which are different from common turbulence. This paper also discusses the effects of the magnetic field on the turbulence structures and the turbulence intensities. Two methods of numerical simulations are addressed for engineering applications: the Reynolds average Navier-Stokes equations and the large eddy simulation. Almost all studies are conducted for incompressible fluid, and it is not the case for aerospace applications since most of air vehicles operate in a medium of high Mach number, that is compressible.
At the beginning of this century, the lunar exploration programs Constellation, Aurora and Chang'e are proposed by NASA(National Aeronautics and Space Administration), ESA(European Space Agency) and CAST(China Academy of Space Technology), respectively. They open a new page for human being returning to space, and pose new requirements for the manned lunar mission. These requirements include more diversified detection scope, more accurate trajectory design and more strict safety measures for human crew. These make the program more complicated and sophisticated. This paper reviews in detail the developments of manned lunar mission's trajectory, Earth——Moon transfer trajectory, autonomous rendezvous guidance and lunar global coverage design, and presents the relevant hot topics in these fields. Finally, this paper outlines the tendency of future researches on this direction.
The fatigue accumulative damage theories for metal materials can be divided into the following three categories:(1) linear cumulative damage theories of invariable damage;(2) linear cumulative damage theories of variable damage;(3) periodical linear cumulative damage theories of invariable damage. They are reviewed in this paper with respect to their theoretical bases, material constants, parameters involved, engineering applications and major typical models. Besides, several sets of variable loading tests of metal materials under a two-level spectrum, a multiple-level spectrum and a random spectrum are used to verify the major typical models. Finally, the applicable scopes and applications of the above three kinds of accumulative damage rules are compared and discussed according to their theoretical basis and the accuracy rate.
The rockburst (rock burst) is a peculiar, abnormal, localized, isolated, delayed, sudden and damaging phenomenon associated with the underground rock excavation. Several hours after the completion of the excavation, some parts of the in-situ intact rock wall might be actively, suddenly and vigorously ejected, thrown and blown off from the original wall into the excavated open space, with high initial ejecting velocity and kinetic energy. It often causes fatality, injury and damage because its occurrence is usually unforeseeable and unpredictable. The rockburst is still a worldwide tough problem that puzzles the international communities of rock mechanics in spite of tremendous research efforts over the past 50 years. This paper puts forward a hypothesis of micro-fluid inclusions as the cause and mechanism of the rockburst. The fluid inclusions in the micro-voids of intact rocks may have a high initial pressure equaling to the average of the three in-situ principal stresses. The fluid inclusions with a high initial pressure can have a high expansion power. They can flow, migrate and turn from the liquid phase into the gas phase after the rock excavation. Their physical and chemical expansion power can cause the rockburst of the excavated intact rock wall. This hypothesis offers effective solutions for the rockburst problem to reduce and eliminate its damage.
This paper reviews the developments of the Timoshenko beam theory with consideration of the shear deformation, the calculations of the shear correction factors, the linear and geometrically nonlinear finite elements of the Timoshenko beam, the material nonlinerity analysis, the vibrating theories, the stability theories, the coupling theories of the shear lag and the shear deformation and the coupling theories of the distorsion and the shear deformation in a box beam, the shear deformation effect on the composite box girder with corrugated steel webs, the elastic foundation beam, and the applications in civil engineering.
The high-porosity cellular metals and the related sandwich structures are a new type of light-weight structural and functional material/structure. They are attractive for their high specific strength, high specific stiffness and excellent energy absorption capability. This paper reviews various processing techniques, the mechanical performance and the application fields of the sandwich structures with cellular metal cores. The mechanical behavior of metallic sandwich structures, including beams, plates and shells, subjected to quasistatic and dynamic loads is discussed, including theoretical predictions, numerical simulations and experimental results. The discussion also includes the deformation/failure, the dynamic response and the energy absorption of sandwich structures.
The load-unload response ratio theory has made a great progress in predicting the stability of a nonlinear system, as is reviewed in this paper, which focuses on the field of predictions of earthquakes and landslides, including its shortcomings. The development trend and applications are analyzed.