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Lin Q.,Nanjing University of Aeronautics and Astronautics | Nie H.,Nanjing University of Aeronautics and Astronautics | Xu L.,Shanghai Institute of Aerospace System Engineering | Chen J.,Nanjing University of Aeronautics and Astronautics
Nanjing Hangkong Hangtian Daxue Xuebao/Journal of Nanjing University of Aeronautics and Astronautics | Year: 2012

A kinetic model of the soft-landing is built to obtain the soft-landing stability criterion of lunar lander with four suspension legs and improve its soft-landing stabiliby. On this basis, the soft-landing stability criterion of lunar lander is derived. The parametric models of lunar lander and lunar soil are built by the ADAMS software. The influences of landing velocity, inclination of lunar surface and yaw angle of lunar lander on the soft-landing stability are analyzed mainly by the process simulation of soft-landing. Investigation results show that lunar lander symmetrically landing, and the vertical and horizontal landing velocities are not more than 4 m/s and 1 m/s make the landing safe and stable. If landing on the slope of lunar surface, the level velocity of lunar lander should be along the uphill direction, and the degree of the slope gradient cannot be greater than 10°.

Zhou X.,Shanghai Institute of Aerospace System Engineering | Chen C.,Tsinghua University
Computational Materials Science | Year: 2016

Metallic glasses (MGs) can have high fracture toughness by carefully choosing chemical compositions. However, their intrinsic toughening mechanism is vital but mysterious. In this paper, large scale molecular dynamic simulations are conducted to study the fracture behavior and underlying mechanism of MGs from atomistic points of view. By changing the composition ratios, the fracture behavior of the MGs transits from void nucleation and coalescence to shear bands toughening. Uniformed local atomic number density is found to be responsible for the high toughness while highly fluctuated local atomic number density result in cavitation governed brittle fracture. The strength of the ductile MGs is more sensitive to the initial void compared with the brittle ones due to the different fluctuations in atomic structures. In the simulations, it is also found that the ductile MGs have a higher Poisson's ratio which may also improve the toughness. The obtained results shed light on the effect of chemical compositions upon the toughness of MGs. © 2016 Elsevier B.V. All rights reserved.

Hu Y.,Shanghai JiaoTong University | Chen W.,Shanghai JiaoTong University | Li R.,Shanghai JiaoTong University | Fang G.,Shanghai Institute of Aerospace System Engineering
Composite Structures | Year: 2016

In this paper, modal behaviors of composite thin-walled lenticular tubes (CTLTs) in free vibration and cantilever vibration are performed by comparing experimental with numerical outcome. Then, a linear and nonlinear buckling analysis of CTLTs subjected to axial compression are proposed to compare their numerical critical buckling loads with corresponding experimental results. The numerical method to simulate buckling behaviors of CTLTs under axial compressions is also verified. As the flattened and wrapped CTLTs need to be deployed completely in space engineering application, the flattening and wrapping process of CTLTs should be studied by using numerical simulation method due to complexity of composite materials. To explore the change rules of mechanical characteristics of CTLTs and facilitate design of CTLTs, the design parameters of CTLTs in vibration analysis, buckling analysis and flattening and wrapping process are all evaluated. © 2016 Elsevier Ltd

Zhou X.,Tsinghua University | Zhou X.,Shanghai Institute of Aerospace System Engineering | Chen C.,Tsinghua University
International Journal of Plasticity | Year: 2016

Bulk amorphous alloys are in general strong, but brittle. Properly introduced interfaces can effectively improve their ductility. In this paper, the tensile behavior of amorphous/amorphous (A/A) nanolaminates is investigated by atomistic simulations. Upon loading, multiple shear bands transmit through the A/A interfaces and interact with each other. As a result, plastic plateaus are presented in the simulated tensile stress-strain curves of the nanolaminates with small layer thickness. Moreover, the strength of the A/A nanolaminates increases with the layer thickness decreasing, due to the interface obstruction to the shear band motion. It is also found that the plastic deformation mechanisms transit from localized shearing in the soft amorphous layers to multiple shear band interactions in the whole sample at a critical size. An analytical model considering shear band motion is proposed to predict the critical layer thickness for the localized to homogenous deformation transition in A/A nanolaminates. © 2016 Elsevier Ltd. All rights reserved.

Li W.,Beihang University | Huang H.,Beihang University | Peng F.,Shanghai Institute of Aerospace System Engineering
Advances in Space Research | Year: 2015

In the circular restricted three-body problem (CR3BP), transit orbit is a class of orbit which can pass through the bottleneck region of the zero velocity curve and escapes from the vicinity of the primary or the secondary. This kind of orbit plays a very important role in the design of space exploration missions. A kind of low-energy interplanetary transfer, which is called Interplanetary Superhighway (IPS), can be realized by utilizing transit orbits. To use the transit orbit in actual mission design, a key issue is to find an algorithm which can separate the states corresponding to transit orbits from the states corresponding to other types of orbits rapidly. In fact, the distribution of transit orbit in the phase space has been investigated by numerical method, and a Fourier series approximation method has been introduced to describe the boundary of transit orbits. However, the Fourier series approximation method needs several hundred sets of Fourier series. The coefficients of these Fourier series are neither easy to be computed nor convenient to be stored, which makes the method can hardly be used in actual mission design. In this paper, the support vector machine (SVM) is used to classify the trajectories in the CR3BP. Using the Gaussian kernel, the 6-dimensional states in the CR3BP are mapped into an infinite-dimensional space, and the bound of the transit orbits is described by a hyperplane. A training data generation method is introduced, which reduces the size of training data by generating the states near the hyperplane. The numerical results show that the proposed algorithm gives the good correct rate of classification, and its computing speed is much faster than that of the Fourier series approximation method. © 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.

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