共查询到20条相似文献，搜索用时 31 毫秒
1.
Recurrent power series methods are particularly applicable to problems in celestial mechanics since the Taylor coefficients may be expressed by recurrence relations. However, as the number of Taylor coefficients increases as is often necessary because of accuracy requirements, the computing time grows prohibitively large. In order to avoid this unfavorable situation, Dr E. Fehlberg introduced in 1960 Runge-Kutta methods that use the firstm Taylor coefficients obtained by recursive relations, or some other technique.Optimalm-fold Runge-Kutta methods are introduced. Embedded methods of order (m+3)[m+4] and (m+4)[m+5] are presented which have coefficients that produce minimum local truncation errors for the higher order pair of solutions of the method, as well as providing a near maximum absolute stability region. It is emphasized that the methods are formulated such that the higher order pair of solutions is to be utilized. These optimal methods are compared to the existingm-fold methods for several test problems. The numerical comparisons show that the optimal methods are more efficient. It is stressed that these optimal methods are particularly efficient whenm is small. 相似文献
2.
We consider Sundman and Poincaré transformations for the long-time numerical integration of Hamiltonian systems whose evolution occurs at different time scales. The transformed systems are numerically integrated using explicit symplectic methods. The schemes we consider are explicit symplectic methods with adaptive time steps and they generalise other methods from the literature, while exhibiting a high performance. The Sundman transformation can also be used on non-Hamiltonian systems while the Poincaré transformation can be used, in some cases, with more efficient symplectic integrators. The performance of both transformations with different symplectic methods is analysed on several numerical examples. 相似文献
3.
A. P. Kornienko Yu. L. Zyskin Yu. I. Neshpor A. A. Stepanian 《Experimental Astronomy》1993,4(2):147-157
The detection efficiency of the atmospheric Cerenkov flashes in searching for very high energy (VHE) gamma-ray sources using the multichannel imaging cameras (MIC) are compared for various technique. Here the detection efficiency is regarded as the time needed for gamma-ray source detection with the preset flux at a certain confidence level. The shorter the time the higher the efficiency.The Monte Carlo simulation of the flashes detection process by MIC has been used for the comparison of various observational methods. The analysis has shown that the tracking of the source followed by the background tracking is the most efficient. Scanning and off-axis observations are 1.5–2.0 times less efficient. 相似文献
4.
We build high order numerical methods for solving differential equations by applying extrapolation techniques to a Symplectic
Integrator of order 2n. We show that, in general, the qualitative properties are preserved at least up to order 4n+1. This new procedure produces much more efficient methods than those obtained using the Yoshida composition technique.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
We study in some detail one-dimensional NLTE effects in solar Fei lines. The lines selected are frequently used in solar polarimetry, and also in studies of line asymmetries and for abundance determinations. Our model atom for Fei–Feii–Feiii is realistic: it takes account of multiplet structure and it includes over 200 bound–bound and bound–free transitions in detail. We use very efficient iterative methods for the self-consistent solution of the kinetic and radiative transfer equations (Auer, Fabiani Bendicho, and Trujillo Bueno, 1994). We have applied these fast methods of solution because they are suitable for the investigation of 2D and 3D NLTE transfer effects with multilevel atoms, which constitutes the next step of our ongoing research project on the iron line formation problem. 相似文献
6.
A comparison of three methods used for multi-temperature analysis of solar X-ray spectra is presented. The modified method of conjugate gradients appears to be very efficient for minimizing 2 subject to regularizing (smoothing) constraints. The Withbroe-Sylwester method also ensures good fits, particularly when computations are carried out in wide temperature intervals. Both methods are much faster than the Maximum Entropy method and yield models with an entropy close to that of the Maximum Entropy models. The reliability of revealing the shape of the differential emission measure is discussed. It is shown that the total emission measure and the plasma thermal energy content can be calculated to within a few percent. 相似文献
7.
D. Lee G. Xia C. Daley A. Dubey S. Gopal C. Graziani D. Lamb K. Weide 《Astrophysics and Space Science》2011,336(1):157-162
FLASH is a publicly available astrophysical community code designed to solve highly compressible multi-physics reactive flows.
We are adding capabilities to FLASH that will make it an open science code for the academic HEDP community. Among many important
numerical requirements, we consider the following features to be important components necessary to meet our goals for FLASH
as an HEDP open toolset. First, we are developing computationally efficient time-stepping integration methods that overcome
the stiffness that arises in the equations describing a physical problem when there are disparate time scales. To this end,
we are adding two different time-stepping schemes to FLASH that relax the time step limit when diffusive effects are present:
an explicit super-time-stepping algorithm (Alexiades et al. in Com. Num. Mech. Eng. 12:31–42, 1996) and a Jacobian-Free Newton-Krylov implicit formulation. These two methods will be integrated into a robust, efficient, and
high-order accurate Unsplit Staggered Mesh MHD (USM) solver (Lee and Deane in J. Comput. Phys. 227, 2009). Second, we have implemented an anisotropic Spitzer-Braginskii conductivity model to treat thermal heat conduction along
magnetic field lines. Finally, we are implementing the Biermann Battery term to account for spontaneous generation of magnetic
fields in the presence of non-parallel temperature and density gradients. 相似文献
8.
N. Hurlburt M. Cheung C. Schrijver L. Chang S. Freeland S. Green C. Heck A. Jaffey A. Kobashi D. Schiff J. Serafin R. Seguin G. Slater A. Somani R. Timmons 《Solar physics》2012,275(1-2):67-78
The immense volume of data generated by the suite of instruments on the Solar Dynamics Observatory (SDO) requires new tools for efficient identifying and accessing data that is most relevant for research. We have developed the Heliophysics Events Knowledgebase (HEK) to fill this need. The HEK system combines automated data mining using feature-detection methods and high-performance visualization systems for data markup. In addition, web services and clients are provided for searching the resulting metadata, reviewing results, and efficiently accessing the data. We review these components and present examples of their use with SDO data. 相似文献
9.
Scott A. Feinstein Craig A. McLaughlin 《Celestial Mechanics and Dynamical Astronomy》2006,96(1):49-62
Kepler’s equation needs to be solved many times for a variety of problems in Celestial Mechanics. Therefore, computing the
solution to Kepler’s equation in an efficient manner is of great importance to that community. There are some historical and
many modern methods that address this problem. Of the methods known to the authors, Fukushima’s discretization technique performs
the best. By taking more of a system approach and combining the use of discretization with the standard computer science technique
known as dynamic programming, we were able to achieve even better performance than Fukushima. We begin by defining Kepler’s
equation for the elliptical case and describe existing solution methods. We then present our dynamic discretization method
and show the results of a comparative analysis. This analysis will demonstrate that, for the conditions of our tests, dynamic
discretization performs the best. 相似文献
10.
A principle of restoration methods based on multichannel blind deconvolution (MBD) is introduced. The methods assume that
for every un-degraded unobservable image several degraded observed images are available. It is better conditioned than classical
single channel approach. The first algorithm represents a generalization of iterative deconvolution scheme introduced for
single images. The second MBD algorithm is based on so-called subspace technique. The subspace method is not iterative and
this possibly implies an implementation that can be computationally more efficient. Both methods are presented in applications
to artificial image data (computer-generated multichannel degraded data) with known ideal image to get a comparison with restored
one. Performance in a real situation on solar photosphere images is shown. 相似文献
11.
射频干扰(Radio Frequency Interference, RFI)是射电目标搜寻和精确分析研究的关键影响因素,因此RFI检测是相关数据处理中的一个重要环节.已有RFI检测方法可分为成分分解法、阈值分析法、机器学习类方法.从应用广泛性和可解释性方面考虑,阈值分析法最具代表性,特别是SumThreshold是近年备受关注的一个RFI检测方法.从SumThreshold方法的原理、算法设计、优化要点、适用性等方面进行介绍和探讨,以供同行参考. 相似文献
12.
《Chinese Astronomy and Astrophysics》2022,46(3):277-296
Radio frequency interference (RFI) is one of the main challenges in the search of radio targets and their accurate analysis. The efficient RFI detection and mitigation techniques are required in the radio data processing. Existing RFI mitigation algorithms typically fall into three categories: component decomposition methods, threshold-based methods, and machine learning methods. The threshold-based algorithms are widely used in real applications because of its clear principle, simple structure, and easily implementation. Especially, the SumThreshold method is becoming more concerned for its good performance in RFI detection. Therefore, this work investigates the principles and algorithm of SumThreshold, and discusses its characteristics and applicability. 相似文献
13.
In this paper we compare several Runge-Kutta type methods of fourth-order when they are applied in the Equatorial Magnetic-Binary Problem (EMBP) for which the analytical solutions are not known. The results of the comparison are presented with tables and diagrams, and the most efficient method is proposed according to the used criteria which are described.Section of Mechanics.Section of Mathematics. 相似文献
14.
The paper presents an efficient algorithm for the study of satellite and space debris orbits on long time intervals. The averaged equations of motion are integrated by means of the implicit midpoint method. This approach is known as a symplectic mapping technique. The perturbing forces included in the mapping are: the geopotential, the atmospheric drag, lunisolar perturbations and the direct radiation pressure (without shadow effects). The influence of the atmosphere is approximated by simple methods for the estimation of integrals. The described mapping is valid for the wide range of orbits including the resonant and the eccentric ones; it can be helpful in practical and theoretical problems. The lifetime of GPS transfer orbits is discussed as an exemplary application. 相似文献
15.
16.
K. G. Hadjifotinou M. Gousidou-Koutita 《Celestial Mechanics and Dynamical Astronomy》1998,70(2):99-113
We present a new implementation of the recurrent power series (RPS) method which we have developed for the integration of
the system of N satellites orbiting a point-mass planet. This implementation is proved to be more efficient than previously
developed implementations of the same method. Furthermore, its comparison with two of the most popular numerical integration
methods: the 10th-order Gauss–Jackson backward difference method and the Runge–Kutta–NystrRKN12(10)17M shows that the RPS
method is more than one order of magnitude better in accuracy than the other two. Various test problems with one up to four
satellites are used, with initial conditions obtained from ephemerides of the saturnian satellite system. For each of the
three methods we find the values of the user-specified parameters (such as the method's step-size (h or tolerance (TOL)) that
minimize the global error in the satellites' coordinates while keeping the computer time within reasonable limits. While the
optimal values of the step-sizes for the methods GJ and RKN are all very small (less than T/100, the ones that are suitable
for the RPS method are within the range: T/13<h<T/6 (T being the period of the innermost satellite of the problem). Comparing
the results obtained by the three methods for these step-sizes and for the various test problems we observe the superiority
of the RPS method over GJ in terms of accuracy and over RKN both in accuracy and in speed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
We present a generalisation of the Levi-Civita and Kustaanheimo-Stiefel regularisation. This allows the use of more general time rescalings. In particular, it is possible to find a regularisation which removes the singularity of the equations and preserves scaling invariance. In addition, these equations can, in certain cases, be integrated with explicit symplectic Runge-Kutta-Nyström methods. The combination of both techniques gives an explicit adaptive symplectic (EASY) integrator. We apply those methods to some perturbations of the Kepler problem and illustrate, by means of some numerical examples, when scaling invariant regularisations are more efficient that the LC/KS regularisation. 相似文献
18.
Numerical methods are usually used for the computation of ephemerides with perturbations for the precise orbital determination of an artificial satellite. But their numerical stability will be encountered in a long arc. In this case the use the improved Encke special perturbation methods has been suggested. The results of this paper show that Encke's method does indeed have a certain effectiveness, but cannot yet completely resolve the numerical stability, and the more efficient method is to use the energy integral or its variational relation to control the growth of the along-track error in general numerical calculations so that the aim of stabilization can be achieved. 相似文献
19.
Numerical integration methods for orbital motion 总被引：1，自引：0，他引：1
O. Montenbruck 《Celestial Mechanics and Dynamical Astronomy》1992,53(1):59-69
The present report compares Runge-Kutta, multistep and extrapolation methods for the numerical integration of ordinary differential equations and assesses their usefulness for orbit computations of solar system bodies or artificial satellites. The scope of earlier studies is extended by including various methods that have been developed only recently. Several performance tests reveal that modern single- and multistep methods can be similarly efficient over a wide range of eccentricities. Multistep methods are still preferable, however, for ephemeris predictions with a large number of dense output points. 相似文献
20.
This paper investigates a method for optimizing multi-rendezvous low-thrust trajectories using indirect methods. An efficient technique, labeled costate transforming, is proposed to optimize multiple trajectory legs simultaneously rather than optimizing each trajectory leg individually. Complex inner-point constraints and a large number of free variables are one main challenge in optimizing multi-leg transfers via shooting algorithms. Such a difficulty is reduced by first optimizing each trajectory leg individually. The results may be, next, utilized as an initial guess in the simultaneous optimization of multiple trajectory legs. In this paper, the limitations of similar techniques in previous research is surpassed and a homotopic approach is employed to improve the convergence efficiency of the shooting process in multi-rendezvous low-thrust trajectory optimization. Numerical examples demonstrate that newly introduced techniques are valid and efficient. 相似文献