自适应多重网格法的应用

本文运用自应并行多重网格法求解了轴向大扰动,径向小扰动的跨音速方程。其计算结果表明该方法能够大大提高计算效率。     

Numerical simulation for separation of multi-phase immiscible fluids in porous media

Based on a lattice Boltzmann method and general principles of porous flow, a numerical technique is presented for analysing the separation of multi-phase immiscible fluids in porous media. The total body force acting on fluid particles is modified by axiding relative permeability in Nithiarasu＇s expression with an axiditional surface tension term. As a test of this model, we simulate the phase separation for the case of two immiscible fluids. The numerical results show that the two coupling relative permeability coefficients K12 and K21 have the same magnitude, so the linear flux-forcing relationships satisfy Onsager reciprocity. Phase separation phenomenon is shown with the time evolution of density distribution and bears a strong similarity to the results obtained from other numerical models and the flows in sands. At the same time, the dynamical rules in this model are local, therefore it can be run on massively parallel computers with well computational efficiency.     

利用(麥曲)霉淀粉酶测定粮食作物皮壳中淀粉含量的改进方法

一、前言粮食中淀粉之測定方法,随着含淀粉量多少的不同而一般采用如下两种方法: (1)酸分解法(即酸化法); (2)酶分解法(即酵素法)。前者适用于含淀粉量較高的原料,如玉米、高粱、谷子、糜子、荞麦、莜麦等粮食作物。后者适用于含淀粉量較低的原料,特别是粮食作物皮壳,如稻糠、高粱糠、谷糠和一些野生植物原料等。     

流动问题无网格Galerkin方法的稳定化方案研究

直接运用无网格Galerkin方法求解对流占优的非线性对流扩散方程及纯对流方程,会出现数值伪振荡现象。本文基于无网格Galerkin方法,构造了MFSUPG(Meshfree Streamline Upwind Petrov-Galerkin),MF-GLS(Meshfree Galerkin Least-Square),MFSGS(Meshfree Sub-Grid Scale)及MFLS(Meshfree Least-Square)四种稳定化方案。数值实验表明:四种稳定化方案中,MFLS的通用性最强。耦合MFLS的无网格Galerkin方法能很好地求解对流占优的非线性对流扩散方程及纯对流方程,具有计算精度高、稳定性好、前后处理方便、算法实施简单的优点,并能捕捉解的大梯度变化。     

PARAMETRIC SIMULTONS IN ONE-DIMENSIONAL NONLINEAR LATTICES

Parametric simultaneous solitary wave (simulton) excitations are shown to be possible in nonlinear lattices. Taking a one-dimensional diatomic lattice with a cubic potential as an example, we consider the nonlinear coupling between the upper cut-off mode of acoustic branch (as a fundamental wave) and the upper cut-off mode of optical branch (as a second harmonic wave). Based on a quasi-discreteness approach the Karamzin－Sukhorukov equations for two slowly varying amplitudes of the fundamental and the second harmonic waves in the lattice are derived when the condition of second harmonic generation is satisfied. The lattice simulton solutions are given explicitly and the results show that these lattice simultons can be nonpropagating when the wave vectors of the fundamental wave and the second harmonic waves are exactly at π/a (where a is the lattice constant) and zero, respectively.     

TEMPORAL OPTICAL SOLITONS VIA MULTISTEP χ(2) CASCADING

We consider a multistep χ⁽²⁾ cascading for light pulses with the dispersion of the system taken into account. Using the method of multiple scales we derive a set of coupled envelope equations governing the nonlinear evolution of the fundamental, second and third harmonic waves involved simultaneously in two nonlinear optical processes, i.e. second harmonic generation and sum frequency mixing. We show that three-wave temporal optical solitons are possible in three-and four-step cascading in the presence of a group-velocity mismatch between different pulses.     

Second harmonic generation of propagating collective excitations in Bose－Einstein condensates

We consider a possible second harmonic generation (SHG) of propagating collective excitations in a two-component Bose－Einstein condensate (BEC) with repulsive atom－atom interactions. We show that the phase-matching condition for the SHG can be fulfilled if the wave vectors and frequencies of the excitations are chosen adequately from different dispersion branches. We solve the nonlinear amplitude equations for the SHG derived using a method of multiple-scales and provide SHG solutions similar to those obtained for a SHG in nonlinear optical media. A possible experimental realization of the SHG for the propagating collective modes in a cigar-shaped two-component BEC is also discussed.     

参加全国周培源大学生力学竞赛的几点体会

结合力学课程的学习,着重介绍参加第七届全国周培源大学生力学竞赛团体赛的几点体会.