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451.
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453.
工业计量中的基本问题述评 总被引:1,自引:0,他引:1
提出并讨论了工业计量中的几个基本问题;分析了其特点及解决方向;结合现状和可持续发展,讨论了工业计量的目的、体系、范围、问题等几个方面的内容及对策;提出了工业计量可持续发展的一种解决方案。 相似文献
454.
给出了正定几何规划及对偶问题的有关定量证明,指出了原文献中凸数证明错误的地方,并补充了正确的证明。 相似文献
455.
Resonant quasi-periodic near-rectilinear Halo orbits in the Elliptic-Circular Earth-Moon-Sun Problem
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(1):336-354
Motivated by the near-future re-exploration of the cislunar space, this paper investigates dynamical substitutes of the Earth-Moon’s resonant Near-Rectilinear Halo Orbits (NRHOs) under the Elliptic-Circular Restricted Four-Body Problem formulation of the Earth-Moon-Sun system. This model considers that the Earth and Moon move in elliptical orbits about each other and that a third body, the Sun, moves in a circular orbit about the Earth-Moon barycenter. By making use of this higher-fidelity dynamical model, we are able to incorporate the Sun’s influence and the Moon’s eccentricity, two of the most significant perturbations of the cislunar environment. As a result of these perturbations, resonant periodic NRHOs of the Earth-Moon Circular Restricted Three-Body Problem (CR3BP) are hereby replaced by two-dimensional quasi-periodic tori that better represent the dynamical evolution of satellites near the vicinity of the Moon. We present the steps and algorithms needed to compute these dynamical structures in the Elliptic-Circular model and subsequently assess their utility for spacecraft missions. We focus on the planned orbit for the NASA-led Lunar Gateway mission, a 9:2 synodic resonant L2 southern NRHO, as well as on the 4:1 synodic and 4:1 sidereal resonances, due to the proximity to the nominal orbit and their advantageous dynamical properties. We verify that the dynamical equivalents of these orbits preserve key dynamical attributes such as eclipse avoidance and near-linear stability. Furthermore, we find that the higher dimensionality of quasi-periodic solutions offers interesting alternatives to mission designers in terms of phasing maneuvers and low-altitude scientific observations. 相似文献
456.
Yue Wang Shijie Xu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The J2 problem is an important problem in celestial mechanics, orbital dynamics and orbital design of spacecraft, as non-spherical mass distribution of the celestial body is taken into account. In this paper, the J2 problem is generalized to the motion of a rigid body in a J2 gravitational field. The relative equilibria are studied by using geometric mechanics. A Poisson reduction process is carried out by means of the symmetry. Non-canonical Hamiltonian structure and equations of motion of the reduced system are obtained. The basic geometrical properties of the relative equilibria are given through some analyses on the equilibrium conditions. Then we restrict to the zeroth and second-order approximations of the gravitational potential. Under these approximations, the existence and detailed properties of the relative equilibria are investigated. The orbit–rotation coupling of the rigid body is discussed. It is found that under the second-order approximation, there exists a classical type of relative equilibria except when the rigid body is near the surface of the central body and the central body is very elongated. Another non-classical type of relative equilibria can exist when the central body is elongated enough and has a low average density. The non-classical type of relative equilibria in our paper is distinct from the non-Lagrangian relative equilibria in the spherically-simplified Full Two Body Problem, which cannot exist under the second-order approximation. Our results also extend the previous results on the classical type of relative equilibria in the spherically-simplified Full Two Body Problem by taking into account the oblateness of the primary body. The results on relative equilibria are useful for studies on the motion of many natural satellites, whose motion are close to the relative equilibria. 相似文献
457.
Using the method of quasisolutions for inverse boundary-value problems of aerohydrodynamics, a problem of constructing an airfoil was solved by the specified velocity distribution along the sought airfoil contour when there is an irregularity in the flow such as a vorticity source. The cases of a source (sink) and vortex are obtained as particular ones. The airfoils are constructed numerically and analytically and conclusions are made about an influence of the irregularity position and type on the shape and aerodynamic characteristics of the airfoil. 相似文献
458.
运用平行算法,提出一种寻求广义均衡问题解及有限个严格伪压缩映像不动点集的公共元的新的迭代格式.在Hilbert空间中.证明了该算法的强收敛性。 相似文献
459.
460.
基于反问题的研究思路,探讨了阵风/ 叶栅干涉噪声的一种前馈式主动控制策略。具体研究思路是试图通过在静子叶栅表面引入附加的“二次级声源”,精确地消去所感兴趣区域的声音,二次级声源强度基于阵风/ 叶栅干涉气动声学反问题模型获得,并通过数值实验的方法探寻了二次级声源合理布放策略。研究结果不仅证实了在叶栅表面布放偶极子声源的可行性,而且提出了在尽量不影响气动性能前提下的前馈主动噪声控制方法。 相似文献