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
In view of the fact that the Extend Kalman Filter (EKF) is prone to be divergent in the autonomous navigation by X-ray pulsars, this paper proposes an algorithm utilizing the fading memory filter. Based on the study of the error pattern of the EKF with the increase of iterations, some possible reasons for the divergency are analyzed. The fading memory filter can be used to reduce the peak of error, while delaying the divergence
When driving on a bend, due to the high gravity center and the heavy load, large trucks or lorries are easy to roll-over if their speed is high. This paper proposes a simplified theoretical model of the roll-over process of a truck during its turning, based on the dynamics analysis. Two critical velocities are defined to evaluate the state of the truck: the tilting critical velocity and the roll-over critical velocity. For a truck of given parameters, the main factors that affect the roll-over process are analyzed, including the weight of the truck, the height of the gravity center, and the turning radius of the road. Finally, some qualitative driving suggestions are given about how to avoid roll-over of large trucks.
This is the preface to Calculus II, a textbook to be published by Peking University Press. We explore the purpose and the pedagogy for teaching calculus in theoretical and applied mechanics curriculun.
The stress transformation formula, which is also called the Cauchy's formula for stresses on slanted surfaces, is widely used in solid mechanics. No explicit statement has been found on its limitations in application. The stresses at the sharp point of a V-shaped free-surface notch on a bar under axial loading at both ends are examined as an example. With the two intersecting surfaces being free, it is deduced from the transformation equations that the sharp point is stress free. This deduction is however contradictory to the fact that the stress concentrates near the sharp point. Clearly the stress transformation formula leads to incorrect results and thus is not valid at that sharp point. It is known that if the stress transformation formula is valid, the stress components constitute a stress tensor, but the stress at the sharp concave corner is shown to be discontinuous and double-valued. It is further pointed out that stress transformation formula is not applicable to any point where a stress component has discontinuity or lacks of uniqueness at a surface passing through that point. The tip of any crack is the case.
In the appreciation of the ancient poem for dragonflies, we discuss the magical hydrodynamic characteristics of dragonflies, which have evolved for hundreds of millions of years. The dragonfly's compound eye, the wings' ability of eliminating chatter, the superhydrophobicity of its epidermis, the drag reduction by its scales, and the mechanical characteristics of the water-jet propulsion of the dragonfly larvae; and their inspiration to the development of engineering technology are discussed. At the same time, the development status of the dragonfly robots is introduced as well.
In this paper, the paper folding problem is simplified to a three-point bending model of a simply supported beam with a rectangular cross section under the concentrated force acting on the middle position. The maximal folding times of a sheet of A4 printing paper and octavo newspaper under a normal human force are related with the maximum bending deflections and the minimum folding loads. The results show that for an ordinary A4 printing paper, an adult can only fold 6 times, or up to 7 times under extreme circumstances. For an octavo newspaper, an adult can easily fold 7 times, but not 8 times. The test results are in good agreement with the theoretical predictions.
The China Trajectory Optimization Competition (CTOCorganized by The Chinese Society of Theoretical and Applied Mechanics, has been successfully held for ten years since its initiation in 2009. With unremitting efforts during the past ten years, CTOC has become a communication platform for domestic universities and research institutions on space trajectory design and optimization research. It not only identifies research talents for space exploration, but also provides knowledge and ideas for this field. This article reviews the development history and achievements of CTOC following the timeline from 2009 to 2019, and summarizes the main features and innovations of the competition.
The 10th Global Trajectory Optimisation Competition hosted by Jet Propulsion Laboratory (JPL) came to an end in June 2019, and the Chinese team won the championship for the first time. For the first time in history, this competition is based on the sci-fi mission, designing the optimal orbit to settle in 100000 Milky Way stars. This paper introduces the tasks, gravity model and spacecraft maneuver model of the Galaxy settlement mission, and analyzes the merit function of this competition specifically. The tree structure is introduced to represent the settlement solution, and the design method of the initial settler distribution is described. Simultaneously, the forward and reverse tree generation strategies are introduced and compared. The methods of local optimization and topology reconstruction of settlement trees used in the competition are briefly introduced. In the galaxy-s stars map, the champion solution was presented in tree structures. The significance of this competition was summarized and some useful inspirations were obtained.