共查询到20条相似文献,搜索用时 171 毫秒
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从Lagrange观点出发,采用分裂格式法求解一维辐射流体力学方程组中的三温方程,用于紧凑等离子体环与靶碰撞产生的X射线辐射的数值模拟研究。提出了求解电子、离子、辐射场三温相脱离的能量方程的隐式差分格式,介绍了能量交换项与压力做功及热传导项分开计算的分裂格式方法,数值模拟得到了其对温度变化的影响。 相似文献
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在三维三温辐射流体力学方程组求解过程中,为解决复杂的等离子体流场和难度大的三维网格计算,提出了用物理量迁移法求解方程组,并对三温能量方程采用了一种改进的显示算法。由此获得了较好的数值结果。 相似文献
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提出三种求解多模光纤非线性传输方程的误差估计准则—max,sum,ave准则,将多模误差向量转换为误差标量,基于对称分步傅里叶的局部误差法实现多模传输自适应步长统一变化.通过仿真高斯脉冲在渐变折射率多模光纤中的传输,验证了定变步长方法在不同准则下局部误差与全局误差的性能.实验结果表明三种准则的变步长算法都具有收敛性,且利用sum准则计算局部误差控制步长变化,在相同计算量的情况下能得到更高的数值精度,相同全局误差的情况下计算量相对更少,对进一步提高多模非线性传输方程的计算效率有参考意义. 相似文献
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提出二维可压缩流体力学问题的拉格朗日有限点方法,将求解区域离散为适当的点集.在每个时间步,每个离散点与其周围适当的五个邻点组成一个基本计算单元.在每个计算单元上,利用有限点方法中的典型微分算子的五点近似公式直接离散流体力学方程中的微分算子,并在每个方程中加上一个人为拉普拉斯粘性项,达到稳定格式的目的.给出时间步长的自动... 相似文献
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天然气-凝析液混输管线温降计算 总被引:1,自引:0,他引:1
基于普适的气液混合物流动能量方程,推导出了用于天然气-凝析液两相管流稳态计算的显式温降计算式,该式考虑了沿线换热,Joule-Thomson效应、地形起伏的影响.由此讨论了文献关于两相流温降计算的一些观点.取消了温度迭代循环,用两相流温降显式计算式替代焓平衡方程参与水力、热力耦合计算,提高了算法的效率.经与OLGA计算结果比较,本文提出的模氆和算法能够较准确地计算天然气-凝析液管流温度. 相似文献
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A previously described algorithm [T.A. Brunner, T.J. Urbatsch, T.M. Evans, N.A. Gentile, Comparison of four parallel algorithms for domain decomposed implicit Monte Carlo, Journal of Computational Physics 212 (2) (2006) 527–539] for doing domain decomposed particle Monte Carlo calculations in the context of thermal radiation transport has been improved. It has been extended to support cases where the number of particles in a time step are unknown at the beginning of the time step. This situation arises when various physical processes, such as neutron transport, can generate additional particles during the time step, or when particle splitting is used for variance reduction. Additionally, several race conditions that existed in the previous algorithm and could cause code hangs have been fixed. This new algorithm is believed to be robust against all race conditions. The parallel scalability of the new algorithm remains excellent. 相似文献
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基于声速分布,提出一种拉氏流体力学计算中大变形网格优化的数值技术.该方法不但可以优化网格的几何形状且可以提高拉氏流体计算的时间步长.介绍基于声速分布的网格松弛泛函、修正梯度流方程的推导、离散和求解方法,启动/终止网格优化过程的条件,及基于这种网格优化方法的ALE算法.给出Rayleigh-Taylor不稳定性问题等数值算例,用以证明该方法的有效性. 相似文献
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The as-deposited titanium film on silicon wafer was electrochemically treated in potential sweep and potential step modes in 0.1 M H2SO4 solution at 30 °C. Under the anodization conditions of potential sweep and properly modulated cyclic voltammetry (CV), nanoscale grains, step-terrace structure and atomic images were clearly observed on the surface of anodic oxide film on titanium. Under potential step conditions, if the anodization time was short (1 s), no grains could be found on the anodic oxide film surface, even though the potential was high up to 9000 mV. Moreover, whatever potential sweep or potential step mode was performed, sufficient time (low sweep rate means a prolonged anodization time) was needed for the formation of nanoscale grains, atomically flat surface and step-terrace structure on the anodized titanium film. 相似文献
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Zaïr A Holler M Guandalini A Schapper F Biegert J Gallmann L Keller U Wyatt AS Monmayrant A Walmsley IA Cormier E Auguste T Caumes JP Salières P 《Physical review letters》2008,100(14):143902
We have investigated the intensity dependence of high-order harmonic generation in argon when the two shortest quantum paths contribute to the harmonic emission. For the first time to our knowledge, experimental conditions were found to clearly observe interference between these two quantum paths that are in excellent agreement with theoretical predictions. This result is a first step towards the direct experimental characterization of the full single-atom dipole moment and demonstrates an unprecedented accuracy of quantum path control on an attosecond time scale. 相似文献
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It is shown that Lattice Boltzmann (LB) simulations using simple equilibrium boundary conditions at solid walls, provide quantitatively
accurate results for backward-facing step flows at moderate Reynolds numbers. The basic reason for such favorable behavior
is that well-resolved LB simulations operate in the so-called weak non-equilibrium regime, in which shear effects at the scale
of a single lattice spacing are weak, meaning by this that the cell-shear time scale is much longer than the molecular time
scales, so that the LB collisional relaxation takes place in a quasi-homogeneous velocity field. Due to their simplicity,
it is suggested that equilibrium boundary conditions may represent a viable option for the LB simulation of complex flows
with solid boundaries at moderate Reynolds numbers. 相似文献
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在保护液亚临界相变温度范围进行肾脏器官的低温延时保存,是一个不同于传统低温保存的新方法。为保持细胞活性必须从器官摘取的第一步展开研究,用保护液对离体肾脏进行冷灌注是移植器官保存的重要环节,研究冷灌注过程中器官温度随时间变化的传热特征,探求提供与传统生物保存方法所不同的传热传质条件非常重要。用高倍率红外热象仪、热电偶探针、超声血流计等,对猪整体肾脏冷灌注过程进行了实时测试,得出动脉血管作为冷源时的肾脏温度动态变化曲线。实验结果表明,在1℃冷却液匀速灌注过程中肾脏温度的降低表现为非均匀变化,究其原因是由于肾脏内特定的组织结构引起。实验研究将对肾脏器官的三维温度场数值计算提供宝贵的实验依据。 相似文献
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Joseph P. Wright 《Journal of computational physics》1998,140(2):263
Explicit central-difference time integration is frequently used to solve the wave equation, and the classical criterion for numerical stability is the Courant–Friedrichs–Lewy condition. Similarly, explicit integration of a spring-mass mechanical system has a stability condition. These conditions are derived under the assumption of constant time steps. This paper demonstrates the new and perhaps surprising result that numerical instability may occur when time steps vary, even though all steps are substantially less than the constant step criterion. 相似文献
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Comparison of conventional and ultrasound-assisted extraction of phenolics-rich heteroxylans from wheat bran 总被引:4,自引:0,他引:4
Various two-step extraction procedures with and without a short application of ultrasound in the first step at various reaction conditions (extracting agent, temperature and time), and constant conditions in the second step (5% NaOH, room temperature, 60 min) were used to isolate the hemicellulose component of industrial wheat bran. The polysaccharides recovered from the extracts were characterised by yield, chemical composition and radical scavenging activity. Similar total yields of polysaccharides were achieved by a short ultrasound-assisted extraction (up to 10 min) in the first step using 0.5% or 2% NaOH, when compared to the classical extraction lasting 60 min, what represents a shortening of the process by about 60% and lower consumption of the NaOH. The extracted polysaccharides comprised a complex of phenolics-rich heteroxylans contaminated to various extents with co-extracted amylose-rich starch as well as protein, which can be in part governed by the extraction conditions. The water-soluble fractions from both the classical and ultrasonics experiments were shown to exhibit significant radical scavenging activity in vitro, indicating their potential application as polysaccharide-based antioxidants. 相似文献