共查询到20条相似文献,搜索用时 171 毫秒
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采用多粒子模拟方法,分析了北京正负电子对撞机(BEPC)储存环纵向不稳定性,给出了BEPC储存环束团长度与单束流强的关系,得出了阈值流强.模拟结果与BEPC95年4月实测结果符合较好. 相似文献
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BEPCⅡ直线注入器中的强流、短束团的尾场效应将损害束流的性能.用分析解和数值模拟计算的方法,系统地研究了尾场对纵向和径向束流动力学的影响,包括单束团的短程尾场和多束团的长程尾场对束流能量、能散、发射度、轨道和初级电子束在正电子产生靶上束斑尺寸的影响等.研究了有效抑制这些尾场效应的措施. 相似文献
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建立了Selkov模型中间反应物具有不同扩散和不同流速条件下的反应 扩散 流动方程 ,理论分析了非Turing不稳定形成的条件 ,求得其参数区间 ,对Andresen的结论作了拓展 .研究还发现 ,在振荡Hopf区域之外 ,静止波动 (空间周期结构FDS)仍然可以存在 .因而 ,此结构存在的参数空间大于Andresen的结果 .同时 ,还将此种不稳定参数区间与Turing不稳定和差速流动引起不稳定 (DIFI)的结果进行了比较 ,结果发现静态FDS值总是处于DIFI临界曲线相应的最小值之上 ,这表明动力学机制是由DIFI不稳定造成的 ,DIFI不稳定区是产生静止波FDS不稳定结构的必要条件 相似文献
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Summary The possible bifurcations of a convective instability in viscoelastic fluid are studied. The viscoelastic behaviour is modelized
by means of the Oldroyd type fluid whose parameters can be adjusted to suit a large class of polymeric fluids. We analyse
in some detail bifurcations of codimension one (stationary or oscillatory convection) and codimension two for such kind of
fluids. By a weak nonlinear analysis, the coefficients of the amplitude equations corresponding to the different bifurcations
are also determined. It has been found that the nature of the convective solution depends crucially on both the viscoelastic
parameters and the constitutive equation used to describe the fluid. 相似文献
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We comment on recently proposed dissipative inflationary models. It is shown that the strength of the inflationary expansion is related to a specific combination of thermodynamic variables which is known to measure the instability of self-gravitating dissipative systems. 相似文献
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Summary The onset of instability, due to the combined effects of thermal and mass concentration gradients, is investigated in the
hydrodynamic stability regime. It is found that the critical Rayleigh number, which determines the onset of instability, increases
as the chemical reaction rate constant increases hyperbolically over a wide range of values at both moderate and high permeabilities.
In addition, the instability grows with increase in porosity. Previous results show that the critical Rayleigh number rises
linearly when only the mass concentration gradient is considered. 相似文献
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通过数值模拟研究了非线性腔的横向效应,非线性表现在光场通过放大介质时所引起的相位变化与强度有关,模拟结果显示,随着非线性系数的变化,腔中的光场分布表现丰富的时空不稳定行为,其中包括横模跳变,时空周期行为以及光学涡旋的出现。 相似文献
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激光烧蚀瑞利泰勒不稳定性数值研究 总被引:5,自引:4,他引:1
介绍了激光烧蚀流体不稳定性计算程序EUL3D,其计算结果与Takabe 公式、FAST2D程序和LASNEX程序的结果以及日本大阪大学激光烧蚀瑞利—泰勒(RT)不稳定性实验,都较好符合,发现了横向电子热传导烧蚀在长波长扰动的非线性瑞利—泰勒不稳定性演变中起重要作用。在合理近似下,得到了烧蚀RT不稳定性线性增长率的预热致稳公式,此公式除包含了烧蚀对流致稳和密度梯度致稳因素外,还包含了Atwood数变小致稳因素,因此与各种情况的二维计算值都很好符合。 相似文献
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Summary We report an analysis of the selected wave vector, as a function of the Rayleigh number, in thermal convection in annular
geometry. The patterns have been studied by means of shadowgraph and, more quantitatively, with a sweeping laser beam. The
selection processes have been investigated in cells of different sizes. We find that the wavevector increases for radial aspect
ratios less than 2, whereas it decreases for larger aspect ratios. The thresholds for time-dependent regimes have also been
measured. 相似文献
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The paper is devoted to a new phenomenon of self-sustained oscillations triggered in a round free homogeneous-density jet. It was shown by the experimental investigations supported by the numerical approach based on extensive-Large Eddy Simulations studies that such a self-sustained regime can be established in a homogeneous-density jet, provided that the boundary layer at the nozzle exit is sufficiently thin and the perturbation level sufficiently low. The growth rate of the naturally amplified unstable modes is high enough to induce backflow leading to self-excited oscillations. 相似文献