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稀薄流热化学非平衡效应的DSMC研究 总被引:2,自引:0,他引:2
以钝体绕流驻点线流场为例,应用直接仿真蒙特卡罗法,模拟了五组元混合气体(N2,O2,N,O,NO)中的碰撞能松弛,离散反应,交换反应及复合反应,给出了碰撞分子各自由度间的能量交换模式及各类化学反应的选择模式。DSMC仿真结果与宏观粘性激波层方程计算结果,在飞行高度较低时基本相符,表明采用的热化学非平衡非模式是令人满意的,随着飞行高度增高稀薄气体效应增大,二者在激波附近有显著差异,表明高空飞行必须考 相似文献
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Willy Benz 《Space Science Reviews》2000,92(1-2):279-294
The physics of low velocity collisions (5 m/s to 40 m/s) between basalt bodies ranging in size from 1 m to 10 km is studied
in an effort to investigate the early phases of planetesimal accretions. To assess the importance of the internal structure
of planetesimals on the outcome of the collisions, we model them either as solid spheres or as rubble piles with a filling
factor of 0.5.
The collisions are simulated using a three dimensional Smooth Particle Hydrodynamics (SPH) code that incorporates the combined
effects of material strength and a brittle fragmentation model. This approach allows the determination not only of the mass
of the largest fragments surviving the collisions but also their dynamical characteristics.
We find that low velocity collisions are for equal incoming kinetic energy per gram of target material considerably more efficient
in destroying and dispersing bodies than their high velocity counterparts. Furthermore, planetesimals modeled as rubble piles
are found to be characterized by a disruption threshold about 5 times smaller than solid bodies. Both results are a consequence
of a more efficient momentum transfer between projectile and fragments in collisions involving bodies of comparable sizes.
Size and shape dependent gas drag is shown to provide relative collision velocities between similar meter-sized objects well
in excess of the critical disruption threshold of either rubble piles or solid bodies. Unless accretion can proceed avoiding
collisions between bodies of similar masses, the relative weakness of bodies in this size range creates a serious bottleneck
for planetesimal growth.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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矢通量分裂显式格式及二元喷管射流模拟 总被引:1,自引:0,他引:1
本文在较常用的显式两步格式的基础上,采用 Steger- Warming形式的矢通量分裂 (简称矢分或 FVS)的原理,提出了一种矢分二阶精度显式两步格式。在分析了格式的各种特性后,与Mac Cormack格式进行了实算对比。又给出了某二元喷管射流问题的模拟实例。计算结果表明,矢分与该显式格式的配合具有矢分法的基本优点和计算稳定、速度较快的优点。 相似文献
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基于复杂网络的无人机飞行冲突解脱算法 总被引:1,自引:0,他引:1
为解决局部空域内的无人机(UAV)群相撞和可能发生连锁碰撞问题,创新地以复杂网络理论为基础,将无人机群的飞行冲突解脱分为关键节点选择和避撞方向选择2个步骤实施,最大限度地保证无人机群受威胁时的安全性。通过分析无人机群的状态信息,选择最重要无人机(关键节点)进行避撞,同时遵循鲁棒性最小原则进行避撞方向选择。通过2个典型无人机飞行案例的仿真实验,验证该策略不仅可以有效解决当前无人机的冲突问题,而且可以防止连锁碰撞,实现整体的最优化。大量仿真实验验证了所提算法的可行性和可扩展性,以及与随机选择方向避撞算法进行比较,结果表明该算法能够提升无人机群的安全性。 相似文献
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The forecast of the terrestrial ring current as a major contributor to the stormtime Dst index and a predictor of geomagnetic storms is of central interest to ‘space weather’ programs. We thus discuss the dynamical
coupling of the solar wind to the Earth's magnetosphere during several geomagnetic storms using our ring current-atmosphere
interactions model and coordinated space-borne data sets. Our model calculates the temporal and spatial evolution of H+, O+, and He+ ion distribution functions considering time-dependent inflow from the magnetotail, adiabatic drifts, and outflow from the
dayside magnetopause. Losses due to charge exchange, Coulomb collisions, and scattering by EMIC waves are included as well.
As initial and boundary conditions we use complementary data sets from spacecraft located at key regions in the inner magnetosphere,
Polar and the geosynchronous LANL satellites. We present recent model simulations of the stormtime ring current energization
due to the enhanced large-scale convection electric field, which show the transition from an asymmetric to a symmetric ring
current during the storm and challenge the standard theories of (a) substorm-driven, and (b) symmetric ring current. Near
minimum Dst there is a factor of ∼ 10 variation in the intensity of the dominant ring current ion specie with magnetic local time, its
energy density reaching maximum in the premidnight to postmidnight region. We find that the O+ content of the ring current increases after interplanetary shocks and reaches largest values near Dst minimum; ∼ 60% of the total ring current energy was carried by O+ during the main phase of the 15 July 2000 storm. The effects of magnetospheric convection and losses due to collisions and
wave-particle interactions on the global ring current energy balance are calculated during different storm phases and intercompared.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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本文首先将粒子云侵蚀条件下的驻点表面后退分解为无粒子烧蚀部分、粒子云引起的烧蚀增量部分和粒子撞击物面引起的直接侵蚀部分。然后研究了表面能量平衡关系,给出了粒子云引起的烧蚀增量表达式。最后分三类讨论粒子与飞行器的碰撞:(1)完全弹性碰撞(不符合实际);(2)完全非弹性碰撞;(3)部分弹性碰撞。对于后两种碰撞,本文分析了动能通量模拟适用的条件。 相似文献
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给出了利用灰色关联投影法解决武器系统多指标综合效能模糊评估问题的基本原理和步骤,并以6种具有典型代表意义的近程武器系统为例,按照给出的步骤,代入数据进行计算,得到的结论验证了方法的正确性和可行性。 相似文献
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There exists a large amount of man-made debris in low Earth orbit. The quantity of this debris is growing every year as a result of on-going activities in space. Much of the debris consists of particles which are too small to be tracked from the ground, but nevertheless pose a threat to spacecraft. This paper examines the possibility of an orbiting radar which, over a period of time, could measure debris positions and velocities and thereby build up a database of debris orbits. Spacecraft could use this database for advance warning of impending collisions and maneuver themselves out of the collision path, thereby mitigating the long-term risk of collision damage 相似文献
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本文提出了一种有限体积时间推进法,将其应用于均化N-S方程的求解,模拟跨音扩压器的湍流流场,并采用空间变时间步长和多重网格技术加快收敛速度。计算结果与有关文献的实验数据吻合良好。 相似文献
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弯管是粉末燃料冲压发动机燃料输送系统的重要组成部分,为了研究弯管内气固两相流的流场结构、颗粒碰撞以及压力损失的变化规律,基于连续相-离散元(CFD-DEM)耦合模型,考虑颗粒的碰撞受力和弹塑性形变,对铝粉在弯管内的流动状况进行数值仿真。研究结果表明:CFD-DEM算法相对于传统的双流体模型和轨道法,能更为准确地描述颗粒流的碰撞信息和两相流的流动状况。弯管内的总压损失随流化气流量的增加,呈先减少再增加的趋势,在本文研究的条件下,优选的流化气流量为6g/s~7g/s(流化气速度为3.0m/s~3.5m/s);在低流速下,颗粒间的碰撞次数远大于颗粒-壁面间的碰撞,随着流速的增高,颗粒与外侧壁面间的碰撞次数迅速增高,并导致颗粒-壁面间的碰撞次数超过颗粒间的碰撞。弯管的弯径越大,弯管内的总压损失越大,但颗粒-颗粒、颗粒-壁面的碰撞次数均减少。 相似文献
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A simple model has been developed that demonstrates that heliospheric X-ray emission can account for about 25%–50% of observed
soft X-ray background intensities. Similar to cometary soft X-ray emission, these X-rays are thought to be produced in the
heliosphere due to charge transfer collisions between heavy solar wind ions and interstellar neutrals. A more complex model
has now been developed to take into account temporal and spatial variations of the solar wind and interstellar neutrals. Measured
time histories of the solar wind proton flux are used in the model and the results are compared with the ‘long-term enhancements’
in the soft X-ray background measured by ROSAT for the same time period.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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M. E. Wiedenbeck W. R. Binns A. C. Cummings A. J. Davis G. A. de Nolfo M. H. Israel R. A. Leske R. A. Mewaldt E. C. Stone T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):415-429
The galactic cosmic rays arriving near Earth, which include both stable and long-lived nuclides from throughout the periodic
table, consist of a mix of stellar nucleosynthesis products accelerated by shocks in the interstellar medium (ISM) and fragmentation
products made by high-energy collisions during propagation through the ISM. Through the study of the composition and spectra
of a variety of elements and isotopes in this diverse sample, models have been developed for the origin, acceleration, and
transport of galactic cosmic rays. We present an overview of the current understanding of these topics emphasizing the insights
that have been gained through investigations in the charge and energy ranges Z≲30 and E/M≲1 GeV/nuc, and particularly those using data obtained from the Cosmic Ray Isotope Spectrometer on NASA’s Advanced Composition
Explorer mission. 相似文献
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The collisions between stationary satellites, and those between a stationary satellite and abandoned stationary satellites which have nearly synchronous orbits with relatively large inclination are discussed. A general formula is introduced for calculating the probability of collision, as a function of time, three-dimensional sizes, orbital bounds, and numbers of satellites. Numerical calculation shows that the probability of collision is negligible if the sizes and numbers are comparable to those of existing satellites, whereas collision is possible for larger size, e.g., for a huge hypothetical gigawatt solar power satellite. The possibility would become large if the satellites continued to increase in number and to be abandoned in the stationary orbit at the present rate over a century, even if the size is ordinary, such as several meters. 相似文献
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为了探究当量比对甲烷-空气连续旋转爆轰燃烧室(CRDC)特性的影响,利用二维可压缩欧拉方程对CRDC进行了数值研究,分析了爆轰波的发展过程和贫燃熄火过程,对比了不同工况下CRDC特性参数的变化情况。结果表明:CRDC起爆后燃烧场在由不稳定状态到相对稳定状态的过程中发生了2次碰撞,当进气当量比较低时,CRDC未能完全发生2次碰撞过程就已经熄爆。随着进气当量比的降低,爆轰波传播速度、轴向平均速度、出口平均温度、出口平均总压均呈下降趋势;增压比随当量比降低而减小的根本原因在于旋转爆轰燃烧过程和等压燃烧过程的熵增差减小,使吉布斯自由能增量差减小。CRDC的燃料驻留时间处于亚毫秒量级,燃烧热效率保持在99%以上。 相似文献