嫦娥二号任务地面应用系统实时业务仿真关键技术研究

通过分析探月工程二期嫦娥二号(Chang’E-2,CE-2)任务地面应用系统的结构和功能,提出了实时业务系统的仿真模型。根据实时业务的功能特点进行了关键技术分析及仿真系统设计和实现。最后针对关键技术问题进行了仿真试验及结果分析,提出了解决问题的思路和方法。论文为嫦娥二号任务地面应用系统数据仿真系统的建立提供了基础。     

More Emission Cones: Multi-frequency Simulation of the Pulse Profiles of PSR J0437-4715

Pulsar radio emission beams have been studied observationally for a long time, and the suggestion is that they consist of the so-called core and conal components. To reproduce these components is a challenge for any emission model, and that the pulse profile of pulsars changes with frequency presents even a greater challenge. Assuming a local surface magnetic structure (to produce the core or central beam) and a global dipole magnetic field (to produce the conal beams), Gil & Krawczyk (1997) applied curvature radiation to the pulse profile simulation of PSR J0437-4715 (hereafter the GK model). Here we present an alternative multi-frequency simulation of the same profiles within the framework of the Inverse Compton Scattering (ICS) model. It is obtained from our simulation (1) that besides the core, the inner cone and the outer cone, there is an outer-outer cone; (2) that the emission components of the core and cones evolve strongly with frequency. Some important differences between the ICS model and the     

Theoretical plasma distributions consistent with Ulysses magnetic field observations in a solar wind tangential discontinuity

The overall multi-layer structure of the magnetic field profile observed by Ulysses across a broad solar wind tangential discontinuity can be reproduced fairly well by means of a kinetic model. Such a simulation provides complementary information about the velocity distribution functions, which are not always available from the plasma experiment due to the low time resolution inherent in plasma measurements. The success of such a simulation proves that the kinetic model can be used as a realistic basis for further studies of the structure and stability of solar wind tangential discontinuities.     

On the deflection of asteroids with mirrors

This paper presents an analysis of an asteroid deflection method based on multiple solar concentrators. A model of the deflection through the sublimation of the surface material of an asteroid is presented, with simulation results showing the achievable impact parameter with, and without, accounting for the effects of mirror contamination due to the ejected debris plume. A second model with simulation results is presented analyzing an enhancement of the Yarkovsky effect, which provides a significant deflection even when the surface temperature is not high enough to sublimate. Finally the dynamical model of solar concentrators in the proximity of an irregular celestial body are discussed, together with a Lyapunov-based controller to maintain the spacecraft concentrators at a required distance from the asteroid.     

Computer simulation of three-dimensional stellar systems in cylindrical coordinates

TheN-body problem does not have an exact and analytic solution, and computer technique or computer simulation can be a good candidate to solve it. Computing speed in computer simulation is very important. There are many algorithms and computational methods in computer simulation which reduce computer time.In this report a computer simulation model in a cylindrical coordinate, in which the FACR (Fourier Analysis and Cyclic Reduction) method is used, has been proposed and demonstrated the presence of spiral, barred, and ringed galaxy. The method using a cylindrical grid has good symmetrical properties specially for rotating stellar systems.     

N-Body Simulations of Late Stage Planetary Formation with a Simple Fragmentation Model

We present results of two-dimensional gravitationalN-body simulations of the late stage of planetary formation. This stage is characterized by the direct accretion of hundreds of lunar-sized planetesimals into planetary bodies. Our simulation code is based on the Hermite Individual Timestep integration algorithm, and gravitational interactions among all bodies are included throughout the simulations. We compare our simulation with earlier works that do not include all interactions, and we find very good agreement. A previously published collisional fragmentation model is included in our simulation to study the effects of the production of fragments on the subsequent evolution of the larger planetary bodies. It is found that for realistic two-body collisions that, according to this model, both bodies will suffer fragmentation, and that the outcome of the collision will be a relatively large core containing most of the mass and a few small fragments. We present the results of simulations that include this simple fragmentation model. They indicate that the presence of small fragments have only a small effect on the growth or orbital evolution of the large planet-sized bodies.     

GEO空间碎片光度测量标定方法的研究

基于GEO卫星、太阳和观测站的空间几何关系,建立了消除太阳赤纬角对地球同步轨道( Geostationary Orbit,GEO)卫星光学特性的影响的方法.以三轴稳定GEO盒状卫星缩比模型为研究样本,在不同太阳赤纬角下进行仿真实验光度测量,研究太阳赤纬角和相位角的空间几何关系,得出消除太阳赤纬角对其辐亮度值以及以相位角...     

Rayleigh Scattering and Laser Spot Elongation Problems at ALFA

This article describes the qualitative effects of LGS spot elongation and Rayleigh scattering on ALFA wavefront sensor images.An analytical model of Rayleigh scattering and a numerical model of laser plume generation at the altitude of the Na-layer were developed. These models, integrated into ageneral AO simulation, provide the sensor sub-apertureimages. It is shown that the centroid measurement accuracyis affected by these phenomena. The simulation was made both for the ALFA system and for the VLT Nasmyth Adaptive Optics System (NAOS).     

核盘晕星系相互作用的模拟研究

用一个星系相互作用数值模拟的综合三体模型，研究椭圆星系是否由盘星系合并而成。结果表明，主要取决于星系的盘面和星系运行轨道面的夹角。如果夹角不等于零，盘星系的相互作用是可能形成椭圆星系的，否则还是盘星系。     

A hydrodynamic pulsation model under subharmonic resonance

We found a hydrodynamic pulsation model of yellow supergiants under subharmonic resonance. It is confirmed that the feature of pulsation by the resonance is long-lived in the model by performing the hydrodynamical simulation for a long time.     

The role of condensation and heat conduction in the formation of prominences: An MHD simulation

In this paper we investigate the effects of condensation and thermal conduction on the formation of Kippenhahn-Schlüter (K-S) type prominences in quiet regions (QP) due to symmetric mass injection. To implement this investigation, a self-consistent, two-dimensional, non-planar, time-dependent magneto-hydrodynamic (MHD) simulation model is developed. In the model, we use various values of the injection velocity, density, and magnetic field strength to determine the most favorable conditions for the QP formation. Based on these simulation results, we find that the formation of a K-S-type field configuration should be considered as a dynamic process, which needs both condensation and mass injection to supply enough mass to maintain such a configuration to complete the formation process of quiescent prominence.     

PARTICLE ACCELERATION AND TRANSPORT IN RECONNECTING PLASMAS

We model the behaviour of particles in and around X-type magnetic configurations, a possible solar flare reconnection geometry. Particles are accelerated by a time-varying electric field close to the neutral point, and followed by integrating the equations of motion. When their motion becomes adiabatic a stochastic simulation is used to model their further transport in a collisional magnetised medium.     

原子钟噪声的蒙特卡络模拟方法

讨论了原子钟噪声的蒙特卡络模拟方法．具体过程是：先产生模拟所需的正态分布随机数，从实际钟的阿仑方差估算出噪声电平，然后用１组递点函数产生高质量的模拟钟时差的随机序列．在对１台商品铯钟进行具体模拟后，给出了真实数据与模拟值的阿仑方差之问的相符程度，最后对实际问题进行了分析．     

A numerical model for isotopic patterns from thermal-extraction experiments

Abstract— A model based on volume diffusion is proposed to describe thermal extraction (progressive or stepped vacuum-pyrolysis or combustion) experimental results (yield and isotopic composition), reported against time or temperature. It accounts for the common asymmetrical shape of the release patterns, with peak-tails due to the extraction kinetics. By analogy to this model, a simulation function is introduced which allows calculation of the concentration and isotopic patterns resulting from component mixings during such experiments. In this calculation, each component's isotopic composition is assumed to be constant throughout its extraction. The simulation readily explains the shift between the isotopic composition peaks and the concentration peaks in the temperature release pattern commonly observed during pyrolysis or combustion of meteorite samples. Because of its simplicity, the principles of the simulation can be easily applied by the readers to real data. One example is taken from the meteoritic stable isotope literature: the progressive pyrolysis extraction of hydrogen from the Parnallee LL3 meteorite (Robert et al., 1987a). The simulation permits calculation of a range for the isotopic composition of a D-depleted reservoir in this meteorite: ?460 < δD < ?320‰ rel. SMOW.     

Evidence for Amazonian northern mid-latitude regional glacial landsystems on Mars: Glacial flow models using GCM-driven climate results and comparisons to geological observations

A fretted valley system on Mars located at the northern mid-latitude dichotomy boundary contains lineated valley fill (LVF) with extensive flow-like features interpreted to be glacial in origin. We have modeled this deposit using glacial flow models linked to atmospheric general circulation models (GCM) for conditions consistent with the deposition of snow and ice in amounts sufficient to explain the interpreted glaciation. In the first glacial flow model simulation, sources were modeled in the alcoves only and were found to be consistent with the alpine valley glaciation interpretation for various environments of flow in the system. These results supported the interpretation of the observed LVF deposits as resulting from initial ice accumulation in the alcoves, accompanied by debris cover that led to advancing alpine glacial landsystems to the extent observed today, with preservation of their flow texture and the underlying ice during downwasting in the waning stages of glaciation. In the second glacial flow model simulation, the regional accumulation patterns predicted by a GCM linked to simulation of a glacial period were used. This glacial flow model simulation produced a much wider region of thick ice accumulation, and significant glaciation on the plateaus and in the regional plains surrounding the dichotomy boundary. Deglaciation produced decreasing ice thicknesses, with flow centered on the fretted valleys. As plateaus lost ice, scarps and cliffs of the valley and dichotomy boundary walls were exposed, providing considerable potential for the production of a rock debris cover that could preserve the underlying ice and the surface flow patterns seen today. In this model, the lineated valley fill and lobate debris aprons were the product of final retreat and downwasting of a much larger, regional glacial landsystem, rather than representing the maximum extent of an alpine valley glacial landsystem. These results favor the interpretation that periods of mid-latitude glaciation were characterized by extensive plateau and plains ice cover, rather than being restricted to alcoves and adjacent valleys, and that the observed lineated valley fill and lobate debris aprons represent debris-covered residual remnants of a once more extensive glaciation.     

Forward modeling of the coronal response to reconnection in an X-ray bright point

We use MDI magnetic field observations and the theory of reconnection through a separator to constrain a numerical simulation of an X-ray bright point observed in EUV by TRACE. A gasdynamic model is employed to describe the corona and transition region in the bright point loop. Nonlocal effects such as opacity and ambipolar diffusion are important to the transition region; these effects are approximated locally by modification of the radiative loss and thermal conduction. A straightforward comparison of measured light curves versus those generated by the simulation shows that the reconnection model is unable to account for the observations. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005205807984     

Studying magneto‐convection by numerical simulation

Following a brief overview of the two main approaches to investigate the interaction between magnetic fields and convective flows near the solar surface layers by numerical simulation, namely idealized model problems and ‘realistic’ large‐eddy simulations, we present first results obtained with a newly developed MHD code. The first example concerns the realistic simulation of the magnetic field dynamics in a solar plage region while the second example demonstrates small‐scale dynamo action in idealized compressible convection.     

Formation of fast magnetosonic shock waves during a two-current-loop collision in solar flares

We present a numerical simulation of the fast magnetosonic shock wave formation during a two-current-loop collision by using a magnetohydrodynamical model. It is shown that the rarefaction waves are generated in the initial stage when the two current loops start to collide. After the rarefaction waves propagate away from the excited region, the fast magnetosonic waves with density enhancement can be produced for the simulation when the current strength of the loop is weak. As the current becomes strong enough, the magnetosonic shock waves can be generated in the direction perpendicular to that of the two-loop collision.     

The interaction of the spiral density wave and the Sun's galactic orbit

The galactocentric radial motion of the Sun introduces another periodicity to the encounters between the Sun and the spiral density wave. We describe a model simulation of the effect and present the associated periods.     

基于数值模拟的大口径高精度射电望远镜台址风障优化设计研究

随着射电望远镜口径增大、观测频率提高, 对其指向精度的要求也越来越高. 然而, 望远镜服役于野外台站, 台址风扰对天线指向精度的影响在高频段观测时已不能忽略. 由于风扰的时变性, 现有的抗风方法无法保障大口径高指向精度望远镜在高频段的有效观测时长. 因此, 提出了一种基于风障精确布置改善台址风环境的方法. 通过数值模拟构建了风障仿真模型, 并将仿真结果与风洞实测数据比较, 两种孔隙率风障的平均误差分别为3.7%和6.1%, 保证了风障模型的可靠性. 以新疆奇台射电望远镜(QiTai radio Telescope, QTT)台址为例, 基于QTT台址斜坡地形构建了计算域模型, 开展单风障不同高度、不同孔隙率的系列风场仿真试验, 得到了风障参量与下游挡风效果的关系. 基于单风障合理高度和最优孔隙率设置南北风障, 仿真结果表明在确定高度下最优孔隙率可以组合, 孔隙率0.1-0.1组合的风障挡风效果最优, 南方向来风在天线区域可以有效降低75%以上的风速.