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The nonconforming virtual element method for Oseen’s equation using a stream-function formulation 用流函数公式求解Oseen方程的非协调虚元法
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-09-11 DOI: 10.1051/m2an/2023075
D. Adak, G. Manzini
We approximate the solution of the stream function formulation of the Oseen equations on general domains by designing a nonconforming Morley-type virtual element method. Under a suitable assumption on the continuous problem’s coefficients, the discrete scheme is well-posed. By introducing an enriching operator , we derive an a priori estimate of the error in a discrete H 2 norm. By post-processing the discrete stream function, we compute the discrete velocity and vorticity fields. Furthermore, we recover an approximate pressure field by solving a Stokes-like problem in a nonconforming Crouzeix-Raviart -type virtual element space that is in a Stokes-complex relation with the Morley-type space of the virtual element approximation. Finally, we confirm our theoretical estimates by solving benchmark problems that include a convex and a nonconvex domain.
通过设计一种非协调morley型虚元法,在一般域上近似求解了Oseen方程的流函数表达式。在对连续问题系数的适当假设下,离散格式是适定的。通过引入充实算子,我们得到了离散h2范数误差的先验估计。通过对离散流函数的后处理,计算出离散的速度场和涡度场。进一步,我们通过求解与虚元逼近的莫利型空间呈stokes复关系的非协调Crouzeix-Raviart型虚元空间中的一个类stokes问题,恢复了近似压力场。最后,我们通过解决包括凸域和非凸域的基准问题来确认我们的理论估计。
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引用次数: 2
On the convergence of an IEQ-based first-order semi-discrete scheme for the Beris-Edwards system Beris-Edwards系统一阶半离散格式的收敛性
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-09-06 DOI: 10.1051/m2an/2023071
Yukun Yue, Franziska Weber
We present a convergence analysis of an unconditionally energy-stable first-order semi-discrete numerical scheme designed for a hydrodynamic Q-tensor model, the so-called Beris-Edwards system, based on the Invariant Energy Quadratization Method (IEQ). The model consists of the Navier-Stokes equations for the fluid flow, coupled to the Q-tensor gradient flow describing the liquid crystal molecule alignment. By using the Invariant Energy Quadratization Method, we obtain a linearly implicit scheme, accelerating the computational speed. However, this introduces an auxiliary variable to replace the bulk potential energy and it is a priori unclear whether the reformulated system is equivalent to the Beris-Edward system. In this work, we prove stability properties of the scheme and show its convergence to a weak solution of the coupled liquid crystal system. We also demonstrate the equivalence of the reformulated and original systems in the weak sense.
本文给出了基于不变能量二次化方法(IEQ)的水动力q -张量模型Beris-Edwards系统的无条件能量稳定一阶半离散数值格式的收敛性分析。该模型由流体流动的Navier-Stokes方程和描述液晶分子排列的q -张量梯度流组成。采用不变能量二次化方法,得到线性隐式格式,加快了计算速度。然而,这引入了一个辅助变量来代替体势能,并且先验地不清楚重新表述的系统是否等同于Beris-Edward系统。在这项工作中,我们证明了该方案的稳定性,并证明了它收敛于耦合液晶系统的弱解。我们还证明了在弱意义上重新表述的系统与原始系统的等价性。
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引用次数: 0
A second-order absorbing boundary condition for two-dimensional peridynamics 二维周动力学的二阶吸收边界条件
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-09-06 DOI: 10.1051/m2an/2023072
Gang Pang, Songsong Ji, Leiyu Chao
The aim of this paper is to develop numerical analysis for the two-dimensional peridynamics which depicts nonlocal phenomena with artificial boundary conditions (ABCs). To this end, the artificial boundary conditions for the fully discretized peridynamcis are proposed. Then, the numerical analysis of the fully discretized scheme is developed such that the artificial boundary conditions solve the corner reflection problem with second-order accuracy. Finally numerical examples are given to verify theoretical results.
本文的目的是对具有人工边界条件(abc)的非局部现象的二维周动力学进行数值分析。为此,提出了完全离散周动力的人工边界条件。然后,对完全离散格式进行了数值分析,使人工边界条件能以二阶精度解决角反射问题。最后给出数值算例对理论结果进行了验证。
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引用次数: 0
A virtual element method for overcoming locking phenomena in Biot's consolidation model 克服Biot固结模型锁紧现象的虚元法
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-09-05 DOI: 10.1051/m2an/2023073
Xin Liu, Zhangxin Chen
A novel algorithm for the three-field formulation of Biot's consolidation model based on mixed and divergence-free nonconforming virtual element methods is developed and analyzed. By establishing a discrete counterpart of Korn's inequality, we ensure the well-posedness of this algorithm without special constraints in the context of nonconforming methods. In addition, we also derive a unified error estimate for this fully discrete algorithm no matter whether the specific storage coefficient vanishes or not. Moreover, this algorithm has several features, including supporting general polygonal meshes and arbitrary space approximation orders, and without Poisson's locking and pressure oscillations. Numerical experiments are presented to validate the performance of this algorithm.
提出并分析了一种基于混合和无散度非协调虚拟元法的三场Biot固结模型的新算法。通过建立Korn不等式的离散对应物,保证了该算法在不符合方法的情况下不受特殊约束的适定性。此外,我们还导出了无论特定存储系数是否消失,该全离散算法的统一误差估计。此外,该算法还具有支持一般多边形网格和任意空间逼近阶数、无泊松锁定和压力振荡等特点。通过数值实验验证了该算法的有效性。
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引用次数: 0
On strictly convex entropy functions for the reactive Euler equations 反应性欧拉方程的严格凸熵函数
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-08-10 DOI: 10.1051/m2an/2023067
Weifeng Zhao
Abstract. This work is concerned with entropy functions of the reactive Euler equations describing inviscid compressible flow with chemical reactions. In our recent work [40] we point out that for these equations as a hyperbolic system, the classical entropy function associated with the thermodynamic entropy is no longer strictly convex under the equation of state (EoS) for the ideal gas. In this work, we propose two strategies to address this issue. The first one is to correct the entropy function. Namely, we present a class of strictly convex entropy functions by adding an extra term to the classical one. Such strictly entropy functions contain that constructed in [40] as a special case. The second strategy is to modify the EoS. We show that there exists a family of EoS (for the nonideal gas) such that the classical entropy function is strictly convex. Under these new EoS, the reactive Euler equations are proved to satisfy the conservation dissipation conditions for general hyperbolic relaxation systems, which guarantee the existence of zero relaxation limit. Additionally, an elegant eigen-system of the Jacobian matrix is derived for the reactive Euler equations under the proposed EoS. Numerical experiments demonstrate that the proposed EoS can also generate ZND detonations. Extension of the present results to high dimensions is direct.
摘要本文研究了具有化学反应的无粘可压缩流动的反应性欧拉方程的熵函数。在我们最近的工作[40]中,我们指出,对于这些方程作为双曲系统,在理想气体的状态方程(EoS)下,与热力学熵相关的经典熵函数不再是严格凸的。在这项工作中,我们提出了两个策略来解决这个问题。第一个是修正熵函数。也就是说,我们通过在经典熵的基础上增加一个额外的项,给出了一类严格凸熵函数。这种严格的熵函数包含[40]中构造的熵函数作为一种特殊情况。第二个策略是修改EoS。我们证明存在一组EoS(对于非理想气体),使得经典熵函数是严格凸的。在这些新的方程组下,证明了反应性欧拉方程满足一般双曲松弛系统的守恒耗散条件,从而保证了零松弛极限的存在。在此基础上,推导出反应性欧拉方程雅可比矩阵的优雅特征系。数值实验表明,该方法也能产生ZND爆轰。将所得结果直接推广到高维。
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引用次数: 0
A fully discrete finite element method for a constrained transport model of the incompressible MHD equations 不可压缩MHD方程约束输运模型的全离散有限元方法
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-08-04 DOI: 10.1051/m2an/2023061
Xiaodi Zhang, Haiyan Su, Xianzhu Li
In this paper, we propose and analyze a fully discrete finite element method for a constrained transport (CT) model of the incompressible magnetohydrodynamic (MHD) equations. The spatial discretization is based on mixed finite elements, where the hydrodynamic unknowns are approximated by stable finite element pairs, the magnetic field and magnetic vector potential are discretized by H(curl)-conforming edge element. The time marching is combining a backward Euler scheme and some subtle implicit-explicit treatments for nonlinear and coupling terms. With these treatments, the fully discrete scheme is linear and the computation of the magnetic vector potential is decoupled from the whole coupled system. The most attractive feature of this scheme that it can yield the exactly divergence-free magnetic field and current density on the discrete level. The unique solvability and unconditional stability of the scheme are also proved rigorously. By utilizing the energy argument, error estimates for the velocity, magnetic field and magnetic vector potential are further demonstrated under the low regularity hypothesis for the exact solutions. Numerical results are provided to verify the theoretical analysis and to show the effectiveness of the proposed scheme.
本文提出并分析了不可压缩磁流体动力学(MHD)方程的约束输运(CT)模型的全离散有限元方法。空间离散是基于混合有限元的,其中流体动力未知量由稳定有限元对近似,磁场和磁矢量位由H(旋度)一致的边缘单元离散。时间推进结合了向后欧拉格式和一些微妙的隐式显式处理非线性和耦合项。通过这些处理,完全离散格式是线性的,并且磁矢量势的计算与整个耦合系统解耦。该方案最吸引人的特点是可以在离散水平上得到完全无发散的磁场和电流密度。严格证明了该方案的唯一可解性和无条件稳定性。利用能量参数,进一步证明了在低正则性假设下精确解的速度、磁场和磁矢势的误差估计。数值结果验证了理论分析和所提方案的有效性。
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引用次数: 1
Time-explicit Hybrid High-Order method for the nonlinear acoustic wave equation 非线性声波方程的时间显式混合高阶方法
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-08-04 DOI: 10.1051/m2an/2023066
Morgane Steins, A. Ern, O. Jamond, Florence Drui
We devise a fully explicit scheme for the nonlinear acoustic wave equation in its second-order formulation in time, using the HHO method for space discretization and the leapfrog scheme for time integration. The key idea for the explicitation is an iterative procedure to approximate at each time step the static nonlinear coupling between the cell and face unknowns. This procedure is based on a splitting of the HHO stabilization operator and, in the linear case, is proved to converge for a large enough weight of the stabilization uniformly in the mesh size. Increasing the stabilization weight turns out to have a moderate impact on the CFL condition. The numerical experiments demonstrate the computational efficiency of the splitting procedure compared to a semi-implicit scheme for the static coupling between cell and face unknowns.
我们设计了非线性声波方程在时间上的二阶形式的完全显式格式,使用HHO方法进行空间离散,使用leapfrog格式进行时间积分。说明的关键思想是在每个时间步近似单元和面之间的静态非线性耦合的迭代过程。该过程基于HHO稳定算子的分裂,并且在线性情况下,证明了在足够大的稳定权重下均匀收敛于网格尺寸。结果表明,增加稳定重量对CFL条件的影响适中。数值实验表明,与半隐式分割方法相比,该分割方法对单元和面未知静态耦合的计算效率更高。
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引用次数: 0
Layer-averaged approximation of Navier-Stokes system with complex rheologies 具有复杂流变性的Navier-Stokes系统的层平均近似
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-07-30 DOI: 10.1051/m2an/2023065
E. Fernández-Nieto, J. Garres-Díaz
In this work, we present a family of layer-averaged models for the Navier-Stokes equations. For its derivation, we consider a layerwise linear vertical profile for the horizontal velocity component. As a particular case, we also obtain layer-averaged models with the common layerwise constant approximation of the  horizontal velocity. The approximation of the derivatives of the velocity components is set by following the theory of distributions to account for the discontinuities at the internal interfaces. Several models has been proposed, depending on the order of approximation of an asymptotic analysis respect to the shallowness parameter. Then, we obtain a hydrostatic model with vertical viscous effects, a hydrostatic model where the pressure depends on the stress tensor, and fully non-hydrostatic models, with a complex rheology. It is remarkable that the proposed models generalize plenty of previous models in the literature. Furthermore, all of them satisfy an exact dissipative energy balance. We also propose a model that is second-order accurate in the vertical direction thanks to a correction of the shear stress approximation. Finally, we show how effective the layerwise linear approach is to notably improve, with respect to the layerwise constant method, the approximation of the velocity profile for some geophysical flows. Namely, a Newtonian fluid and some complex viscoplastic (dry granular and Herschel-Bulkley) materials are considered.
在这项工作中,我们提出了一组Navier-Stokes方程的层平均模型。对于其推导,我们考虑水平速度分量的分层线性垂直剖面。作为一种特殊情况,我们还得到了层平均模型,该模型具有常见的水平速度逐层常数近似。速度分量导数的近似是通过遵循分布理论来设定的,以解释内部界面的不连续。根据关于浅度参数的渐近分析的近似阶数,提出了几种模型。然后,我们得到了一个具有垂直粘性效应的流体静力模型,一个压力取决于应力张量的流体静力模型,以及一个具有复杂流变学的完全非流体静力模型。值得注意的是,所提出的模型推广了文献中大量以前的模型。此外,它们都满足精确的耗散能量平衡。我们还提出了一个在垂直方向上二阶精确的模型,这要感谢对剪应力近似的修正。最后,我们展示了分层线性方法是如何有效地显著改善,相对于分层常数法,一些地球物理流动的速度剖面的近似。即,牛顿流体和一些复杂的粘塑性(干颗粒和赫歇尔-巴克利)材料被考虑。
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引用次数: 0
Steady-state inhomogeneous diffusion with generalized oblique boundary conditions 广义斜边界条件下的稳态非齐次扩散
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-07-26 DOI: 10.1051/m2an/2023063
A. Bradji, D. Lesnic
We consider the elliptic diffusion (steady-state heat conduction) equation with space-dependent conductivity and inhomogeneous source subject to a generalized oblique boundary condition on a part of the boundary and Dirichlet or Neumann boundary conditions on the remaining part. The oblique boundary condition represents a linear combination between the dependent variable and its normal and tangential derivatives at the boundary. We first prove the well- posedness of the continuous problems. We then develop new finite volume schemes for these problems and prove rigorously the stability and convergence of these schemes. We also address an application to the inverse corrosion problem concerning the reconstruction of the coefficients present in the generalized oblique boundary condition that is prescribed over a portion $Gamma_{0}$ of the boundary $partial Omega$ from Cauchy data on the complementary portion $Gamma_{1} = partial Omega backslash Gamma_{0}$.
我们考虑具有空间相关电导率和非均匀源的椭圆扩散(稳态热传导)方程,该方程的一部分边界满足广义斜边界条件,其余部分满足狄利克雷或诺伊曼边界条件。斜边界条件表示因变量与其在边界处的法向导数和切向导数之间的线性组合。首先证明了连续问题的适定性。然后,我们为这些问题开发了新的有限体积格式,并严格证明了这些格式的稳定性和收敛性。我们还解决了反腐蚀问题的一个应用,该问题涉及广义斜边界条件中存在的系数的重建,该条件是根据柯西数据在互补部分$Gamma_{1} = partial Omega backslash Gamma_{0}$上规定的部分$Gamma_{0}$边界$partial Omega$。
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引用次数: 0
Convergence analysis of time-domain PMLs for 2D electromagnetic wave propagation in dispersive waveguides 二维电磁波在色散波导中传播的时域pml收敛性分析
IF 1.9 3区 数学 Q2 Mathematics Pub Date : 2023-07-13 DOI: 10.1051/m2an/2023060
É. Bécache, M. Kachanovska, M. Wess
This work is dedicated to the analysis of generalized perfectly matched layers (PMLs) for 2D electromagnetic wave propagation in dispersive waveguides. Under quite general assumptions on frequency-dependent dielectric permittivity and magnetic permeability we prove convergence estimates in homogeneous waveguides and show that the PML error decreases exponentially with respect to the absorption parameter and the length of the absorbing layer. The optimality of this error estimate is studied both numerically and analytically. Finally, we demonstrate that in the case when the waveguide contains a heterogeneity supported away from the absorbing layer, instabilities may occur, even in the case of the non-dispersive media. Our findings are illustrated by numerical experiments.
本文研究了二维电磁波在色散波导中传播的广义完美匹配层(pml)。在相当一般的频率相关介电常数和磁导率假设下,我们证明了均匀波导的收敛估计,并表明PML误差相对于吸收参数和吸收层长度呈指数减小。对该误差估计的最优性进行了数值和解析研究。最后,我们证明,当波导中含有远离吸收层的非均匀性时,即使在非色散介质的情况下,也可能发生不稳定。数值实验证明了我们的发现。
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引用次数: 0
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Esaim-Mathematical Modelling and Numerical Analysis-Modelisation Mathematique et Analyse Numerique
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