偏微分方程求解的一种新颖方法-格子Boltzmann模型

介绍了一种偏微分方程求解的一种新颖方法格子Boltzmann模型,详细分析了它的基本理论和基本原理.并通过不可压Navier-Stokes方程组和二维含源项扩散方程的数值模拟计算实例,说明格子Boltzmann方法的有效性,展示了广阔的应用前景,为今后更深入的研究和广泛应用提供参考.     

一类含源Boussinesq系统解的数值分析及仿真

对于一类含源的高阶非线性波动方程Boussinesq方程的初边值问题,利用D1Q5模型的格子Boltzmann方程,通过选取不同的演化方程和局部平衡态分布函数及修正函数,应用ChapmanEnskog多尺度技术和Taylor展开技术,提出了具有五阶高精度带修正函数的非标准格子Boltzmann模型.应用所提出的模型,仿真模拟了几个具有精确解的Boussinesq方程初边值系统,并与传统的修正有限差分法(MFDM)进行了对比,结果表明该文模型所得的数值解与精确解吻合,其模误差小于MFDM.此外,还针对精确解未知的Boussinesq方程初边值系统进行了数值仿真,并与MFDM进行了对比.数值结果表明,两种计算格式的数值解比较吻合,进一步证明了文中所构造模型的有效性和稳定性.     

用格子Boltzmann方法模拟非线性热传导方程

对具有非线性源项和非线性扩散项的热传导方程建立格子Boltzmann求解模型.在演化方程中增加了两个关于源项分布函数的微分算子,对演化方程实施Chapman-Enskog展开.通过对演化方程的进一步改进,恢复出具有高阶截断误差的宏观方程.对不同参数选取下的非线性热传导方程进行了数值模拟,数值解与精确解吻合得很好.该模型也可以用于同类型的其他偏微分方程的数值计算中.     

求解Burgers方程的两层隐式紧致差分格式

<正>1引言Burgers方程是流体力学中扩散波最简单的非线性模型方程,它出现在许多物理问题当中,包括气体动力学问题、交通流问题和流体力学问题等.同时Burgers方程也可以作为流体动力学Navier-Stokes方程的简化模型方程.近年来,求解一维Burgers方程的计算方法受到科研工作者的广泛关注,有关的文献报道已有很多,如文献[1-5].这些方法在空间     

空间分数阶电报方程的格子Boltzmann方法

应用格子Boltzmann方法（LBM）对Riemann Liouville空间分数阶电报方程进行了数值模拟研究.首先,将分数阶算子中的积分项进行离散化处理,并进行了收敛阶分析.然后,构建了带修正函数项的一维三速度(D1Q3)的LBM演化模型.利用Chapman Enskog多尺度技术和Taylor展开技术,推导出各平衡态分布函数和修正函数的具体表达式,准确地从所建的演化模型恢复出宏观方程.最后,数值计算结果表明该模型是稳定、有效的.     

组合KdV方程带修正函数的格子Boltzmann模型

采用一种带修正函数的新格子Boltzmann模型模拟了组合Kdv方程,分析了由此得出的迭代格式的单调性和稳定性,并且得到了格式的单调性条件.在文中的单调性条件下,迭代格式是L∞稳定的.文中的数值模拟结果表明该格式是可行的.     

层射流的格子Boltzmann方法的数值模拟

通过引入一种格子Boltzmann方法的特殊边界处理,对对称和非对称的层射流进行有效的数值研究,模拟结果与已有的数值结果非常吻合.表明了格子Boltnnann方法解层射流问题的高效与稳定.     

BGK模型稳定性分析及其改进

<正>1引言格子Boltzmann方法相对于传统的计算流体力学,具有计算简单、节省内存、边界条件容易处理、适合并行计算等优点,在许多传统模拟方法难以胜任的领域,如多孔介质流[1]、多相流、电动力学[2]、磁流体[3]、非牛顿流体[4]、颗粒流、血液流[5]等,都可以进行有效的数值模拟.然而,Boltzmann方程中的碰撞算子非常复杂,阻碍了该方法的应用.     

一类Burgers方程的孤立波解

Burgers方程在工程上有着重要的应用,它可以用来描述湍流、车队的交通流、氏族的随机迁移、化学工程中的分离等现象,对Burgers方程求解方法的研究有着重要的现实意义.对Burgers方程求解主要是应用差分和微分两方面的方法来展开求解的,1/G展开法是近年来发展起来的求解非线性偏微分方程的一种较为有效的微分解法.采用微分方程方面的方法,利用1/G展开法对一类Burgers方程进行求解,得到了此方程的一类孤立波解和扭曲波解,同时描绘出解的图像并分析解的结构和变化趋势.     

耦合Burgers方程的Painleve分析和相关性质

为研究耦合Burgers方程的可积性,利用WTC测试方法,给出了第一类Burgers方程的Painleve性质和第二类Burgers方程的条件Painleve性质．进而得到了第一类方程的变量分离解和第二类方程的（N2＋3N＋6/2）-参数Lie点对称群．     

Lattice Boltzmann solver of Rossler equation

We proposed a lattice Boltzmann model for the Rossler equation. Using a method of multiscales in the lattice Boltzmann model, we get the diffusion reaction as a special case. If the diffusion effect disappeared, we can obtain the lattice Boltzmann solution of the Rossler equation on the mesescopic scale. The numerical results show the method can be used to simulate Rossler equation.     

General propagation lattice Boltzmann model for variable-coefficient non-isospectral KdV equation

In this paper, a general propagation lattice Boltzmann model for variable-coefficient non-isospectral Korteweg–de Vries (vc-nKdV) equation, which can describe the interfacial waves in a two layer liquid and Alfvén waves in a collisionless plasma, is proposed by selecting appropriate equilibrium distribution function and adding the compensate function. The Chapman–Enskog analysis shows that the vc-nKdV equation can be recovered correctly from the present model. Numerical simulation for the non-propagating one soliton of this equation in different situations is conducted as validation. It is found that the numerical results match well with the analytical solutions, which demonstrates that the current general propagation lattice Boltzmann model is a satisfactory and efficient method, and could be more stable and accurate than the standard lattice Bhatnagar–Gross–Krook model.     

Lattice Boltzmann model for two-dimensional generalized sine-Gordon equation

The nonlinear sine-Gordon equation arises in various problems in science and engineering. In this paper, we propose a numerical model based on lattice Boltmann method to obtain the numerical solutions of two-dimensional generalized sine-Gordon equation, including damped and undamped sine-Gordon equation. By choosing properly the conservation condition between the macroscopic quantity $u_t$ and the distribution functions and applying the Chapman-Enskog expansion, the governing equation is recovered correctly from the lattice Boltzmann equation. Moreover, the local equilibrium distribution function is obtained. The numerical results of the first three examples agree well with the analytic solutions, which indicates the lattice Boltzmann model is satisfactory and efficient. Numerical solutions for cases involving the most known from the bibliography line and ring solitons are given. Numerical experiments also show that the present scheme has a good long-time numerical behavior for the generalized sine-Gordon equation. Moreover, the model can also be applied to other two-dimensional nonlinear wave equations, such as nonlinear hyperbolic telegraph equation and Klein-Gordon equation.     

Lattice Boltzmann model for two-dimensional unsteady Burgers’ equation

In this paper, a special lattice Boltzmann model is proposed to simulate two-dimensional unsteady Burgers’ equation. The maximum principle and the stability are proved. The model has been verified by several test examples. Excellent agreement is obtained between numerical predictions and exact solutions. The cases of steep oblique shock waves are solved and compared with the two-point compact scheme results. The study indicates that lattice Boltzmann model is highly stable and efficient even for the problems with severe gradients.     

A Pseudo-Kinetic Approach for Helmholtz Equation

A lattice Boltzmann type pseudo-kinetic model for a non-homogeneous Helmholtz equation is derived in this paper. Numerical results for some model problems show the robustness and efficiency of this lattice Boltzmann type pseudo-kinetic scheme. The computation at each site is determined only by local parameters, and can be easily adapted to solve multiple scattering problems with many scatterers or wave propagation in non-homogeneous medium without increasing the computational cost.     

A new lattice Boltzmann model for the laplace equation

In this paper, a new lattice Boltzmann equation which is independent of time is proposed. Based on the new lattice Boltzmann equation, some steady problems can be modeled by the lattice Boltzmann method. In the further study, the Laplace equation is investigated with the method of the higher-order moment of equilibrium distribution functions and a series of partial differential equations in different space scales. The numerical results show that the new method is effective.     

Numerical solutions of two-dimensional Burgers’ equations by lattice Boltzmann method

In this paper, the two-dimensional Burgers’ equations with two variables are solved numerically by the lattice Boltzmann method. The lattice Bhatnagar–Gross–Krook model we used can recover the macroscopic equation with the second order accuracy. Numerical solutions for various values of Reynolds number, computational domain, initial and boundary conditions are calculated and validated against exact solutions or other published results. It is concluded that the proposed method performs well.     

General propagation lattice Boltzmann model for a variable-coefficient compound KdV-Burgers equation

In this paper, a general propagation lattice Boltzmann model for a variable-coefficient compound Korteweg-de Vries-Burgers (vc-cKdVB) equation is investigated through selecting equilibrium distribution function and adding a compensation function, which can provide some more realistic models than their constant-coefficient counterparts in fluids or plasmas. Chapman–Enskog analysis shows that the vc-gKdVB equation can be recovered correctly from the present model. Numerical simulations in different situations of this equation are conducted, including the propagation and interaction of the bell-type, kink-type and periodic-depression solitons and the evolution of the shock-wave solutions. It is found that the numerical results match well with the analytical solutions, which demonstrates that the current lattice Boltzmann model is a satisfactory and efficient algorithm. In addition, it is also shown the present model could be more stable and more accurate than the standard lattice Bhatnagar–Gross–Krook model through adjusting the two free parameters introduced into the propagation step.     

A higher-order moment method of the lattice Boltzmann model for the conservation law equation

In this paper, we proposed a higher-order moment method in the lattice Boltzmann model for the conservation law equation. In contrast to the lattice Bhatnagar–Gross–Krook (BGK) model, the higher-order moment method has a wide flexibility to select equilibrium distribution function. This method is based on so-called a series of partial differential equations obtained by using multi-scale technique and Chapman–Enskog expansion. According to Hirt’s heuristic stability theory, the stability of the scheme can be controlled by modulating some special moments to design the third-order dispersion term and the fourth-order dissipation term. As results, the conservation law equation is recovered with higher-order truncation error. The numerical examples show the higher-order moment method can be used to raise the accuracy of the truncation error of the lattice Boltzmann scheme for the conservation law equation.     

Lattice Boltzmann model for the bimolecular autocatalytic reaction–diffusion equation

A lattice Boltzmann model for the bimolecular autocatalytic reaction–diffusion equation is proposed. By using multi-scale technique and the Chapman–Enskog expansion on complex lattice Boltzmann equation, we obtain a series of complex partial differential equations, complex equilibrium distribution function and its complex moments. Then, the complex reaction–diffusion equation is recovered with higher-order accuracy of the truncation error. This equation can be used to describe the bimolecular autocatalytic reaction–diffusion systems, in which a rich variety of behaviors have been observed. Based on this model, the Fitzhugh–Nagumo model and the Gray–Scott model are simulated. The comparisons between the LBM results and the Alternative Direction Implicit results are given in detail. The numerical examples show that assumptions of source term can be used to raise the accuracy of the truncation error of the lattice Boltzmann scheme for the complex reaction–diffusion equation.