Probability Distribution Function of Passive Scalars in Shell Models

被动分级的问题的一个壳模型版本被介绍，它被 K 的模型启发。Ohkitani 和 M。Yakhot [K。Ohkitani 和 M。Yakhot， Phys。加快。Lett。60 (1988 ) 983；K。Ohkitani 和 M。Yakhot，学监。Theor。Phys。81 (1988 ) 329 ] 。作为处于原来的问题，规定随机的速度地是 Gaussian， δ 及时相关。确定的微分方程被认为是非线性的 Langevin 方程。然后，为被动数量的 PDF 的佛克普朗克常数方程数字地被获得并且解决。在精力输入范围(n 【 5， n 是壳数字) ，被动数量的概率分发功能(PDF ) 在 Gaussian 分发附近。在惯性的范围(5 ≤ n ≤ 16 ) 并且驱散范围(n ≥ 17 ) ，被动数量的概率分发功能(PDF ) 有明显的间歇性。并且被动数量的可伸缩的力量是异常的。数字模拟的结果与试验性的大小相比。

Anomalous scaling in a non-Gaussian random shell model for passive scalars

In this paper, we have introduced a shell-model of Kraichnan＇s passive scalar problem. Different from the original problem, the prescribed random velocity field is non-Gaussian and σ correlated in time, and its introduction is inspired by She and Levveque （Phys. Rev. Lett. 72, 336 （1994））. For comparison, we also give the passive scalar advected by the Gaussian random velocity field. The anomalous scaling exponents H（p） of passive scalar advected by these two kinds of random velocities above are determined for structure function with values of p up to 15 by Monte Carlo simulations of the random shell model, with Gear methods used to solve the stochastic differential equations. We find that the H（p） advected by the non-Gaussian random velocity is not more anomalous than that advected by the Gaussian random velocity. Whether the advecting velocity is non-Gaussian or Gaussian, similar scaling exponents of passive scalar are obtained with the same molecular diffusivity.

Influence of Velocity Shell Correlations on Anomalous Scaling Exponents of Passive Scalars in Shell Models

We propose a new approach to the old-standing problem of the anomaly of the scaling exponents of passivescalars of turbulence.Different to the original problem,the distribution function of the prescribed random velocity fieldis multi-dimensional normal and delta-correlated in time.Here,our random velocity field is spatially correlative.Forcomparison,we also give the result obtained by the Gaussian random velocity field without spatial correlation.Theanomalous scaling exponents H (p) of passive scalar advected by two kinds of random velocity above are determined forstructure function up to p=15 by numerical simulations of the random shell model with Runge-Kutta methods to solvethe stochastic differential equations.We observed that the H(p) 's obtained by the multi-dimensional normal distributionrandom velocity are more anomalous than those obtained by the independent Gaussian random velocity.

Influence of velocity spatiotemporal correlations on the anomalous scaling exponents of passive scalars

In this paper, we consider spatial-temporal correlation functions of the turbulent velocities. With numerical simulations on the Gledzer-Ohkitani-Yamada （GOY） shell model, we show that the correlation function decays exponentially. The advecting velocity field is regarded as a colored noise field, which is spatially and temporally correlative. For comparison, we are also given the scaling exponents of passive scalars obtained by the Gaussian random velocity field, the multi-dimensional normal velocity field and the She-Leveque velocity field, introduced by She, et al. We observe that extended self-similarity sealing exponents H（p）/H（2） of passive scalar obtained by the colored noise field are more anomalous than those obtained by the other three velocity fields.

Searching for a_(0)(980)-meson parton distribution function

In this paper,we calculate the scalar a_(0)(980)-meson leading-twist wave function by using the light-cone harmonic oscillator model(LCHO),where the model parameters are determined by fitting theξ-moments■of its light-cone distribution amplitudes.Then,the a_(0)(980)-meson leading-twist light-cone distribution amplitudes with three different scalesζ=(1.0,2.0,5.2)Ge V are given.After constructing the relationship between the a_(0)(980)-meson leading-twist parton distribution functions/valence quark distribution function and its LCHO wave function,we exhibit the■(x,ζ)and■(x,ζ)with different scales.Furthermore,we also calculate the Mellin moments of the a_(0)(980)-meson’s valence quark distribution function■with n=(1,2,3),i.e.■=0.027,■=0.018 and■=0.013.Finally,the scale evolution for the ratio of the Mellin moments x■are presented.

板材冲压成形的晶体塑性有限元模拟

将率相关晶体塑性本构理论引入Mindlin曲壳单元模型与动力显式有限元法,采用切线系数法计算剪切应变率,根据晶体取向正态分布规律在单元积分点处分配晶体取向,按各晶体取向体积分数的加权平均计算多晶体应力,开发晶体塑性动力显式有限元程序,实现板材冲压成形过程模拟和晶体取向演化预示。以主要初始织构为铜织构和S织构的轧制铝板为对象,对方盒件冲压成形过程及织构演化进行数值模拟,计算结果与试验结果呈现出较好的一致性。通过晶体弹塑性有限元法不仅可以预示板材宏观成形构形变化,而且能够预测板材织构的演化情况。模拟结果显示在方盒件冲压成形过程中,铜织构和S织构为不稳定取向,变形后逐渐转到其他取向。

一种改进的非傍轴Beckmann-Kirchhoff随机表面散射模型研究

针对Beckmann-Kirchhoff(B-K)散射模型在非傍轴区域入射和散射存在非物理不连续问题,介绍了一种改进的B-K模型。该模型使用新因子替换原有几何因子,消除散射光辐射强度和辐射亮度在非傍轴区域的差异,在计算中使输入光能和输出光能满足能量守恒定理的要求。和实验数据比较,改进的B-K模型在大角度掠射时理论数据曲线表现出对实验数据良好的预测性能,较好解决了原有模型在非傍轴区域入射和散射非物理不连续这一问题。