检索结果-南通市图书馆

Direct Optimization of Low-thrust Many-revolution Earth-orbit Transfers

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Aeronautics 2009年第4期22卷 426-433页

作者： Gao Yang academy of Opto-Electronics,chinese academy of sciences,beijing 100190,China academy of Opto-Electronics Chinese Academy of Sciences Beijing 100190 China

Low-thrust Earth-orbit transfers with 10^- 5-order thrust-to-weight ratios involve a large number of orbital revolutions which poses a real challenge to trajectory optimization. This article develops a direct method to optimize minimum-time low-thrust many-revolution Earth-orbit transfers. A parameterized control law in each orbit, in the form of the true optimal control, is proposed, and the time history of the parameters governing the control law is interpolated through a finite number of nodal values. The orbital averaging method is used to significantly reduce the computational workload and the trajectory optimization is conducted based on the orbital averaging dynamics expressed by nonsingular equinoctial elements. Furthermore, Earth＇s shadowing and perturbation effects are taken into account. The optimal transfer problem is thus converted to the parameter optimization problem that can be solved by nonlinear programming. Taking advantage of the mapping between the parameterized control law and the Lyapunov control law, a technique is proposed to acquire good initial guesses for optimization variables, which results in enlarged convergence domain of the direct optimization method. Numerical examples of optimal Earth-orbit transfers are presented.

关键词： low thrust orbital transfer optimization direct method orbital averaging Lyapunov method

ON DISCRETE PROJECTION AND NUMERICAL BOUNDARY CONDITIONS FOR THE NUMERICAL SOLUTION OF THE UNSTEADY INCOMPRESSIBLE NAVIER-STOKESEQUATIONS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2002年第1期20卷 35-56页

作者： Lan Chieh Huang (ICMSEC, academy of Mathematics and System sciences, chinese academy of sciences, beijing 100080, China) ICMSEC Academy of Mathematics and System Sciences Chinese Academy of Sciences 北京 100080

Focuses on a study on the fully implicit Crank Nicholson (CN) schemes and three projection methods for approximate preservation of component-consistency under projection. Transformation from incompressible Navier-Stokes equations to differential algebraic equations CN schemes; Local errors of CN projection methods; Numerical boundary conditions.

关键词： differential algebraic equations discrete projection numerical boundary conditions

Investigation of a New Exsolved Cu-Fe-S Phase in“Abnormal Sphalerite”

在线全文

学校读者我要写书评

暂无评论

Acta Geologica Sinica(English Edition) 1991年第1期65卷 27-36,110-111页

作者： Li Jiuling Wang Su Institute of Mineral Deposits, chinese academy of Geolgical sciences,beijing beijing Laboratory of Electron Microscopy, chinese academy of sciences, beijing Institute of Mineral Deposits Chinese Academy of Geolgical Sciences Beijing China

A new exsolved copper-iron-sulfur phase in sphalerite has been found in the Dajing cassiterite- sulfidecopper-silver-tin deposit, Inner Mongolia, China. After investigating the optical properties, chemical composi-tion, crystal structure and exsolved Characters of the exsolved phase, the authors present important evidencefor its being a new exsolved copper-iron-sulfur phase mineral. Its formation mechenism is discussed in consider-ing heating experiments, phase equilibrium data and the geology of the deposit.

关键词： Ph Fe Abnormal Sphalerite Cu

THE DUAL MIXED METHOD FOR AN UNILATERAL PROBLEM

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2003年第6期21卷 733-746页

作者： Lie-heng Wang(LSEC, ICMSEC, academy of Mathematics and System sciences, chinese academy of sciences,beijing 100080, China) LSEC ICMSEC Academy of Mathematics and System Sciences Chinese Academy of Sciences Beijing 100080 China

In this paper, the dual mixed method for an unilateral problem, which is the simplified modelling of scalar function for the friction-free contact problem, is considered. The dual mixed problem is introduced, the existence and uniqeness of the solution of the problem are presented, and error bounds O(h3/4) and O(h3/2) are obtained for the dual mixed finite element approximations of Raviart-Thomas elements for k = 0 and k = 1 respectively.

关键词： Dual Mixed Method Unilateral Problem.

COMPOSITE-STEP LIKE FILTER METHODS FOR EQUALITY CONSTRAINT PROBLEMS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2003年第5期21卷 613-624页

作者： Pu-yan Nie(LSEC, ICMSEC, academy of Mathematics and System sciences, chinese academy of sciences, beijing 100080, China) 中科院数学与系统科学院 LSEC ICMSEC CAS 北京 100080

In a composite-step approach, a step Sk is computed as the sum of two components Uk and hk. The normal component Vk, which is called the vertical step, aims to improve the linearized feasibility, while the tangential component hk, which is also called horizontal step, concentrates on reducing a model of the merit functions. As a filter method, it reduces both the infeasibility and the objective function. This is the same property of these two methods. In this paper, one concerns the composite-step like filter approach. That is, a step is tangential component hk if the infeasibility is reduced. Or else, Sk is a composite step composed of normal component Uk, and tangential component hk.

关键词： Composite-step like approaches Filter methods Equality constraints Sequen- tial quadratic programming(SQP) algorithms Normal component Tangential component Convergence.

MODELLING AND NUMERICAL SOLUTIONS OF A GAUGE PERIODIC TIME DEPENDENT GINZBURG-LANDAU MODEL FOR TYPE-Ⅱ SUPERCONDUCTORS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 1997年第4期15卷 365-384页

作者： Zhi-ming Chen (Institute of Mathematics, chinese academy of sciences, beijing, China) 中科院数学所北京

In this paper we seek the solutions of the time dependent Ginzburg-Landau model for type-Ⅱ superconductors such that the associated physical observables are spatially periodic with respect to some lattice whose basic lattice cell is not necessarily rectangular. After appropriately foring the gange, the model can be formulated as a system of nonlinear parabolic partial differential equations with quasi-periodic boundary conditions. We first give some results concerning the existence, uniqueness and regularity of solutions and then we propose a semiimplicit finite element scheme solving the system of nonlinear partial dmerential equations and show the optimal error estimates both in the L2 and energy *** also report on some numerical results at the end of the paper.

关键词： Math QT MODELLING AND NUMERICAL SOLUTIONS OF A GAUGE PERIODIC TIME DEPENDENT GINZBURG-LANDAU MODEL FOR TYPE SUPERCONDUCTORS

Subspace Search Method for Quadratic Programming With BoxConstraints

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 1999年第3期17卷 307-314页

作者： Zi-luan Wei(ICMSEC, chinese academy of sciences, beijing 100080, China) 中科院计算数学与科学工程计算所北京

A subspace search method for solving quadratic programming with box constraints is presented in this paper. The original problem is divided into many independent subproblem at an initial point, and a search direction is obtained by solving each of the subproblem, as well as a new iterative point is determined such that the value of objective function is decreasing. The convergence of the algorithm is proved under certain assumptions, and the numerical results are also given.

关键词： subspace search method quadratic programing matrix splitting

A CLASS OF NEW PARALLEL HYBRID ALGEBRAIC MULTILEVEL ITERATIONS

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 2001年第6期19卷 651-672页

作者： Zhong-zhi Bai (LSEC ICMSEC, academy of Mathematics and Systems sciences, chinese academy of sciences, beijing 100080, China) 中科院计算数学与科学工程计算所北京 100080

Presents preconditioning matrices having parallel computing function for the coefficient matrix and a class of parallel hybrid algebraic multilevel iteration methods for solving linear equations. Solution to elliptic ... 详细信息

关键词： elliptic boundary value problem system of linear equations symmetric positive definite matrix multilevel iteration parallel method

A Remark on Using Gravitational Lensing Probability as a Probe of the Central Regions of CDM Halos

在线全文

学校读者我要写书评

暂无评论

chinese Journal of Astronomy and Astrophysics 2002年第5期2卷 399-407页

作者： YunLiNational Astronomical Observatories, chinese academy of sciences, beijing 100012 National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

We calculate the gravitational lensing probabilities by cold dark matter (CDM) halos with different density profiles, and compare them with current observations from the Cosmic Lens All-Sky Survey (CLASS) and the Jodrell-Bank VLA Astrometric Survey (JVAS). We find that the lensing probability is dramatically sensitive to the clumping of the dark matter, or quantitatively, the concentration parameter. We also find that our predicted lensing probabilities in most cases show inconsistency with the observations. It is argued that high lensing probability may not be an effective tool for probing the statistical properties of inner structures of dark matter halos.

关键词： cosmology: dark matter - gravitational lensing - cosmology:theory - galaxies: halos