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1.
针对流固耦合问题,发展了基于浸入边界-多松弛时间格子玻尔兹曼通量求解法(immersed boundary method multi-relaxation-time lattice Boltzmann flux solver,IB-MRT-LBFS)的弱耦合算法.依据多尺度Chapman-Enskog展开,建立不可压宏观方程状态变量和通量与格子玻尔兹曼方程中粒子密度分布函数之间的关系;采用强制浸入边界法处理流固界面使固壁表面满足无滑移边界条件,根据修正的速度求解动量方程力源项;结构运动方程采用四阶龙格-库塔法求解.格子模型与浸入边界法的引入使流固耦合计算可以在笛卡尔网格下进行,无需生成贴体网格及运用动网格技术,简化了计算过程.数值模拟了单圆柱横向涡激振动、单圆柱及串列双圆柱双自由度涡激振动问题.结果表明,IB-MRT-LBFS能够准确预测圆柱涡激振动的锁定区间、振动响应、受力情况以及捕捉尾流场结构形态,验证了该算法在求解流固耦合问题的有效性和可行性. 相似文献
2.
A Boundary Condition-Implemented Immersed Boundary-Lattice Boltzmann Method and Its Application for Simulation of Flows Around a Circular Cylinder 下载免费PDF全文
A boundary condition-implemented immersed boundary-lattice Boltzmann method (IB-LBM)
is presented in this work. The present approach is an improvement to the conventional
IB-LBM. In the conventional IB-LBM, the no-slip boundary condition is only approximately
satisfied. As a result, there is flow penetration to the solid boundary. Another drawback
of conventional IB-LBM is the use of Dirac delta function interpolation, which only has
the first order of accuracy. In this work, the no-slip boundary condition is directly
implemented, and used to correct the velocity at two adjacent mesh points from both
sides of the boundary point. The velocity correction is made through the second-order
polynomial interpolation rather than the first-order delta function interpolation.
Obviously, the two drawbacks of conventional IB-LBM are removed in the present study.
Another important contribution of this paper is to present a simple way to compute the
hydrodynamic forces on the boundary from Newton's second law. To validate the proposed
method, the two-dimensional vortex decaying problem and incompressible flow over a
circular cylinder are simulated. As shown in the present results, the flow penetration
problem is eliminated, and the obtained results compare very well with available data
in the literature. 相似文献
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基于虚粒子概念,提出进出口数值边界条件处理方法.在进口边界外设置进口区域,并赋予进口虚粒子相应的物理量;出口边界外设置出口和缓冲区域,出口虚粒子的物理量由计算获得,缓冲区的虚粒子初始物理量是指定的;根据每个时间步的流动情况,改变粒子的区域属性,添加/删除相应的粒子.利用拉格朗日形式的SPH方法,通过管内流动问题验证数值进出口边界方法的适用性,研究进出口边界条件在激波管、绕流问题中的应用.提出的进出口边界处理方法,避免了边界附近流体粒子积分截断问题,保证流体粒子能够流出边界,激波能够透射边界. 相似文献
5.
A local domain-free discretization-immersed boundary method (DFD-IBM)
is presented in this paper to solve incompressible Navier-Stokes equations
in the primitive variable form. Like the conventional immersed boundary method
(IBM), the local DFD-IBM solves the governing equations in the whole domain including
exterior and interior of the immersed object. The effect of immersed boundary
to the surrounding fluids is through the evaluation of velocity at interior and
exterior dependent points. To be specific, the velocity at interior dependent points
is computed by approximate forms of solution and the velocity at exterior dependent
points is set to the wall velocity. As compared to the conventional IBM, the
present approach accurately implements the non-slip boundary condition. As a result,
there is no flow penetration, which is often appeared in the conventional IBM
results. The present approach is validated by its application to simulate incompressible
viscous flows around a circular cylinder. The obtained numerical results
agree very well with the data in the literature. 相似文献
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一类各项异性半线性椭圆方程自然边界元与有限元耦合法 总被引:1,自引:0,他引:1
将冯康和余德浩提出的自然边界归化方法用于研究一类半线性椭圆方程外区域问题,提出一种自然边界元与有限元的耦合算法、针对某一类半线性椭圆方程,应用变分原理,研究其弱解性及Galerkin逼近,得到有限元解的误差估计及收敛阶O(h^n),最后给出相应数值例子。 相似文献
8.
A method for reducing the spurious pressure oscillations observed when simulating moving boundary flow problems with sharp-interface immersed boundary methods (IBMs) is proposed. By first identifying the primary cause of these oscillations to be the violation of the geometric conservation law near the immersed boundary, we adopt a cut-cell based approach to strictly enforce geometric conservation. In order to limit the complexity associated with the cut-cell method, the cut-cell based discretization is limited only to the pressure Poisson and velocity correction equations in the fractional-step method and the small-cell problem tackled by introducing a virtual cell-merging technique. The method is shown to retain all the desirable properties of the original finite-difference based IBM while at the same time, reducing pressure oscillations for moving boundaries by roughly an order of magnitude. 相似文献
9.
针对非平衡态外推边界处理方法在某些条件下发生质量泄漏的问题,结合质量守恒定律对其进行修正,建立一种新的质量守恒型的边界处理格式.其基本思想是在边界处定义一个虚拟密度来修正平衡态分布函数,使得系统质量守恒.以重力作用下的密度场及磁流体模拟问题为例,利用该格式进行分析,讨论质量泄露问题的本质及各种因素的影响.通过对三种典型的流动:二维Poiseuille流、Couette流、Womersley流的模拟,验证该边界格式的计算精度和稳定性. 相似文献
10.
A new robust and accurate Cartesian-grid treatment for the immersion of solid bodies within a fluid with general boundary conditions is described. The new approach, the Boundary Data Immersion Method (BDIM), is derived based on a general integration kernel formulation which allows the field equations of each domain and the interfacial conditions to be combined analytically. The resulting governing equation for the complete domain preserves the behavior of the original system in an efficient Cartesian-grid method, including stable and accurate pressure values on the solid boundary. The kernel formulation allows a detailed analysis of the method, and it is demonstrated that BDIM is consistent, obtains second-order convergence relative to the kernel width, and is robust with respect to the grid and boundary alignment. Formulation for no-slip and free slip boundary conditions are derived and numerical results are obtained for the flow past a cylinder and the impact of blunt bodies through a free surface. The BDIM predictions are compared to analytic, experimental and previous numerical results confirming the properties, efficiency and efficacy of this new boundary treatment for Cartesian grid methods. 相似文献
11.
Wen Chen & Yan Gu 《advances in applied mathematics and mechanics.》2012,4(5):543-558
This study proposes a new formulation of singular boundary method (SBM)
to solve the 2D potential problems, while retaining its original merits
being free of integration and mesh, easy-to-program, accurate and
mathematically simple without the requirement of a fictitious boundary
as in the method of fundamental solutions (MFS). The key idea of the SBM
is to introduce the concept of the origin intensity factor to isolate the
singularity of fundamental solution so that the source points can be placed
directly on the physical boundary. This paper presents a new approach to
derive the analytical solution of the origin intensity factor based on the
proposed subtracting and adding-back techniques. And the troublesome sample
nodes in the ordinary SBM are avoided and the sample solution is also not
necessary for the Neumann boundary condition. Three benchmark problems are
tested to demonstrate the feasibility and accuracy of the new formulation
through detailed comparisons with the boundary element method (BEM), MFS,
regularized meshless method (RMM) and boundary distributed source (BDS)
method. 相似文献
12.
针对界面附近粒子光滑函数截断和非物理穿透问题,提出一种气-液界面边界条件的处理方法.当界面附近支持域出现不同材料粒子,每步计算可在支持域设置虚粒子,按照密度分配方法给虚粒子物理量赋值,并对界面附近粒子引入气-液两相阻力.采用SPH方法和Level-Set方法,计算运动激波对气-液界面作用问题,两者计算结果一致,初步验证了气-液界面边界条件处理的适用性.用SPH方法分别计算超声速气流中的圆截面液柱绕流和下落问题,界面两侧粒子压力和法向速度连续,给出弓形激波、回流区和下游回流区等定性合理结果.表明本文方法可适度避免界面附近流体粒子光滑截断和粒子非物理穿透现象、界面附近流场数值振荡. 相似文献
13.
Several kinds of waveguide components such as curved waveguide bends, arbitrary angle waveguide bends and T-junctions have been analyzed with boundary element method in this paper. A new discretization method for the boundary element method to solve the waveguide discontinuities has been given. The numerical results obtained agree well with the experimental results and numerical results in other literature. Especially, the scattering characteristics of Forded E-, H-plane T-junctions in 3mm band have been analyzed using boundary element method and the calculation results are presented. 相似文献
14.
This article addresses the resolution of the inverse problem for the parameter
identification in orthotropic materials with a number of measurements merely on
the boundaries. The inverse problem is formulated as an optimization problem of
a residual functional which evaluates the differences between the experimental and
predicted displacements. The singular boundary method, an integration-free, mathematically
simple and boundary-only meshless method, is employed to numerically
determine the predicted displacements. The residual functional is minimized by the
Levenberg-Marquardt method. Three numerical examples are carried out to illustrate
the robustness, efficiency, and accuracy of the proposed scheme. In addition, different
levels of noise are added into the boundary conditions to verify the stability of the
present methodology. 相似文献
15.
Iterative Method for Solving a Problem with Mixed Boundary Conditions for Biharmonic Equation 下载免费PDF全文
The solution of boundary value problems (BVP) for fourth order
differential equations by their reduction to BVP for second order
equations, with the aim to use the available efficient algorithms
for the latter ones, attracts attention from many researchers. In
this paper, using the technique developed by the authors in recent
works we construct iterative method for a problem with complicated
mixed boundary conditions for biharmonic equation which is
originated from nanofluidic physics. The convergence rate of the
method is proved and some numerical experiments are performed for
testing its dependence on a parameter appearing in boundary
conditions and on the position of the point where a transmission of
boundary conditions occurs. 相似文献
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The moving least-square approximation is discussed first. Sometimes the method can form an ill-conditioned equation system,
and thus the solution cannot be obtained correctly. A Hilbert space is presented on which an orthogonal function system mixed
a weight function is defined. Next the improved moving least-square approximation is discussed in detail. The improved method
has higher computational efficiency and precision than the old method, and cannot form an ill-conditioned equation system.
A boundary element-free method (BEFM) for elastodynamics problems is presented by combining the boundary integral equation
method for elastodynamics and the improved moving least-square approximation. The boundary element-free method is a meshless
method of boundary integral equation and is a direct numerical method compared with others, in which the basic unknowns are
the real solutions of the nodal variables and the boundary conditions can be applied easily. The boundary element-free method
has a higher computational efficiency and precision. In addition, the numerical procedure of the boundary element-free method
for elastodynamics problems is presented in this paper. Finally, some numerical examples are given. 相似文献
19.
The rarefied effect of gas flow in microchannel is significant and cannot be well described by traditional hydrodynamic models. It has been known that discrete Boltzmann model(DBM) has the potential to investigate flows in a relatively wider range of Knudsen number because of its intrinsic kinetic nature inherited from Boltzmann equation.It is crucial to have a proper kinetic boundary condition for DBM to capture the velocity slip and the flow characteristics in the Knudsen layer. In this paper, we present a DBM combined with Maxwell-type boundary condition model for slip flow. The tangential momentum accommodation coefficient is introduced to implement a gas-surface interaction model.Both the velocity slip and the Knudsen layer under various Knudsen numbers and accommodation coefficients can be well described. Two kinds of slip flows, including Couette flow and Poiseuille flow, are simulated to verify the model.To dynamically compare results from different models, the relation between the definition of Knudsen number in hard sphere model and that in BGK model is clarified. 相似文献
20.
Boundary element-free method for elastodynamics 总被引:3,自引:0,他引:3
CHENG Yumin & PENG Miaojuan . Shanghai Institute of Applied Mathematics Mechanics Shanghai University Shanghai China . Department of Civil Engineering Shanghai University Shanghai China 《中国科学G辑(英文版)》2005,48(6):641-657
1 Introduction In recent years, more and more attention has been paid to researches on the meshless (or meshfree) method, which makes it a hot direction of computational mechanics[1,2]. The meshless method is the approximation based on nodes, then the large deformation and crack growth problems can be simulated with the method without the re-meshing technique. And the meshless method has some advantages over the traditional computa- tional methods, such as finite element method (FEM) and boun… 相似文献