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A fully-mixed finite element method for the steady state Oberbeck–Boussinesq system 稳态Oberbeck-Boussinesq系统的全混合有限元法
Pub Date : 2020-06-04 DOI: 10.5802/smai-jcm.64
Eligio Colmenares, G. Gatica, S. Moraga, R. Ruiz-Baier
A new fully-mixed formulation is advanced for the stationary Oberbeck–Boussinesq problem when viscosity depends on both temperature and concentration of a solute. Following recent ideas in the context of mixed methods for Boussinesq and Navier–Stokes systems, the velocity gradient and the Bernoulli stress tensor are taken as additional field variables in the momentum and mass equilibrium equations. Similarly, the gradients of temperature and concentration together with a Bernoulli vector are considered as unknowns in the heat and mass transfer equations. Consequently, a dual-mixed approach with Dirichlet data is defined in each sub-system, and the well-known Banach and Brouwer theorems are combined with Babuška–Brezzi’s theory in each independent set of equations, yielding the solvability of the continuous and discrete schemes. We show that our development also applies to the case where the equations of thermal energy and solute transport are coupled through cross-diffusion. Appropriate finite element subspaces are specified, and optimal a priori error estimates are derived. Furthermore, a reliable and efficient residual-based a posteriori error estimator is proposed. Several numerical examples illustrate the performance of the fully-mixed scheme and of the adaptive refinement algorithm driven by the error estimator. 2020 Mathematics Subject Classification. 65N30, 65N12, 65N15, 35Q79, 80A20, 76D05, 76R10.
当粘度取决于温度和溶质浓度时,提出了一种新的完全混合公式,用于固定的Oberbeck-Boussinesq问题。在Boussinesq和Navier-Stokes系统混合方法的背景下,将速度梯度和伯努利应力张量作为动量和质量平衡方程中的附加场变量。同样,温度梯度和浓度梯度以及伯努利矢量在传热传质方程中被认为是未知数。因此,在每个子系统中定义了Dirichlet数据的双混合方法,并将著名的Banach和browwer定理与Babuška-Brezzi的理论结合在每个独立的方程组中,得到了连续和离散格式的可解性。我们表明,我们的发展也适用于热能和溶质输运方程通过交叉扩散耦合的情况。给出了合适的有限元子空间,得到了最优的先验误差估计。在此基础上,提出了一种可靠、高效的基于残差的后验误差估计方法。数值算例说明了全混合方案和由误差估计器驱动的自适应改进算法的性能。2020数学学科分类。65N30, 65N12, 65N15, 35Q79, 80A20, 76D05, 76R10。
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引用次数: 9
A Reynolds-robust preconditioner for the Scott-Vogelius discretization of the stationary incompressible Navier-Stokes equations 平稳不可压缩Navier-Stokes方程的Scott-Vogelius离散化的reynolds -鲁棒预条件
Pub Date : 2020-04-20 DOI: 10.5802/smai-jcm.72
P. Farrell, L. Mitchell, L. R. Scott, F. Wechsung
Augmented Lagrangian preconditioners have successfully yielded Reynolds-robust preconditioners for the stationary incompressible Navier-Stokes equations, but only for specific discretizations. The discretizations for which these preconditioners have been designed possess error estimates which depend on the Reynolds number, with the discretization error deteriorating as the Reynolds number is increased. In this paper we present an augmented Lagrangian preconditioner for the Scott-Vogelius discretization on barycentrically-refined meshes. This achieves both Reynolds-robust performance and Reynolds-robust error estimates. A key consideration is the design of a suitable space decomposition that captures the kernel of the grad-div term added to control the Schur complement; the same barycentric refinement that guarantees inf-sup stability also provides a local decomposition of the kernel of the divergence. The robustness of the scheme is confirmed by numerical experiments in two and three dimensions.
增广拉格朗日预条件已经成功地为稳态不可压缩Navier-Stokes方程生成了reynolds -鲁棒预条件,但仅适用于特定的离散化。这些预调节器所设计的离散化具有依赖于雷诺数的误差估计,且离散化误差随着雷诺数的增加而恶化。本文给出了重心精细化网格上Scott-Vogelius离散化的增广拉格朗日预条件。这既实现了雷诺鲁棒性能,又实现了雷诺鲁棒误差估计。一个关键的考虑因素是设计一个合适的空间分解,以捕获添加到控制Schur补的grad-div项的内核;同样的以重心为中心的细化保证了内支撑的稳定性,也提供了散度核的局部分解。通过二维和三维数值实验验证了该方案的鲁棒性。
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引用次数: 25
Stable IMEX schemes for a Nitsche-based approximation of elastodynamic contact problems. Selective mass scaling interpretation 基于nitsche的弹性动力学接触问题近似的稳定IMEX格式。选择性质量标度解释
Pub Date : 2020-02-19 DOI: 10.5802/SMAI-JCM.65
É. Bretin, Y. Renard
We introduce some IMEX schemes (implicit-explicit schemes with an implicit term being linear) for approximating elastodynamic contact problems when the contact condition is taken into account with a Nitsche method. We develop a theoretical and numerical study of the properties of the schemes, especially in terms of stability, provide some numerical comparisons with standard explicit and implicit scheme and propose some improvements to obtain a more reliable approximation of motion for large time steps. We also show how selective mass scaling techniques can be interpreted as IMEX schemes.
在Nitsche方法考虑接触条件时,我们引入了一些近似弹性动力学接触问题的IMEX格式(隐式项为线性的隐式-显式格式)。我们对这些格式的性质进行了理论和数值研究,特别是在稳定性方面,提供了一些与标准显式和隐式格式的数值比较,并提出了一些改进,以获得更可靠的大时间步长的运动近似。我们还展示了如何将选择性大规模缩放技术解释为IMEX方案。
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引用次数: 1
Hyperparameter Estimation in Bayesian MAP Estimation: Parameterizations and Consistency 贝叶斯MAP估计中的超参数估计:参数化和一致性
Pub Date : 2019-05-10 DOI: 10.5802/smai-jcm.62
Matthew M. Dunlop, T. Helin, A. Stuart
The Bayesian formulation of inverse problems is attractive for three primary reasons: it provides a clear modelling framework; means for uncertainty quantification; and it allows for principled learning of hyperparameters. The posterior distribution may be explored by sampling methods, but for many problems it is computationally infeasible to do so. In this situation maximum a posteriori (MAP) estimators are often sought. Whilst these are relatively cheap to compute, and have an attractive variational formulation, a key drawback is their lack of invariance under change of parameterization. This is a particularly significant issue when hierarchical priors are employed to learn hyperparameters. In this paper we study the effect of the choice of parameterization on MAP estimators when a conditionally Gaussian hierarchical prior distribution is employed. Specifically we consider the centred parameterization, the natural parameterization in which the unknown state is solved for directly, and the noncentred parameterization, which works with a whitened Gaussian as the unknown state variable, and arises when considering dimension-robust MCMC algorithms; MAP estimation is well-defined in the nonparametric setting only for the noncentred parameterization. However, we show that MAP estimates based on the noncentred parameterization are not consistent as estimators of hyperparameters; conversely, we show that limits of finite-dimensional centred MAP estimators are consistent as the dimension tends to infinity. We also consider empirical Bayesian hyperparameter estimation, show consistency of these estimates, and demonstrate that they are more robust with respect to noise than centred MAP estimates. An underpinning concept throughout is that hyperparameters may only be recovered up to measure equivalence, a well-known phenomenon in the context of the Ornstein-Uhlenbeck process.
反问题的贝叶斯公式之所以吸引人,主要有三个原因:它提供了一个清晰的建模框架;不确定度量化方法;它允许有原则地学习超参数。后验分布可以通过抽样方法来探索,但对于许多问题,这样做在计算上是不可行的。在这种情况下,通常寻求最大后验估计量。虽然它们的计算成本相对较低,并且具有吸引人的变分公式,但一个关键的缺点是它们在参数化变化时缺乏不变性。当使用分层先验来学习超参数时,这是一个特别重要的问题。本文研究了在条件高斯分层先验分布下参数化选择对MAP估计量的影响。具体来说,我们考虑了中心参数化,即直接求解未知状态的自然参数化,以及在考虑维鲁棒MCMC算法时出现的以白化高斯作为未知状态变量的非中心参数化;MAP估计在非参数设置下只有在非中心参数化情况下才有良好的定义。然而,我们发现基于非中心参数化的MAP估计与超参数估计不一致;相反,我们证明了有限维中心MAP估计量的极限在维数趋于无穷时是一致的。我们还考虑了经验贝叶斯超参数估计,显示了这些估计的一致性,并证明它们相对于噪声比中心MAP估计更稳健。贯穿始终的一个基本概念是,超参数可能只能恢复到测量等效,这是Ornstein-Uhlenbeck过程中众所周知的现象。
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引用次数: 15
A combined first and second order model for a junction with ramp buffer 带匝道缓冲器的交叉口一、二阶联合模型
Pub Date : 2019-03-12 DOI: 10.5802/smai-jcm.90
J. Weißen, O. Kolb, Simone Gottlich
Second order macroscopic traffic flow models are able to reproduce the so-called capacity drop effect, i.e., the phenomenon that the outflow of a congested region is substantially lower than the maximum achievable flow. Within this work, we propose a first order model for a junction with ramp buffer that is solely modified at the intersection so that the capacity drop is captured. Theoretical investigations motivate the new choice of coupling conditions and illustrate the difference to purely first and second order models. The numerical example considering the optimal control of the onramp merging into a main road highlights that the combined model generates similar results as the second order model. AMS subject classifications: 65M08, 90C30
二阶宏观交通流模型能够再现所谓的容量下降效应,即拥堵区域的流出流量大大低于可达到的最大流量。在这项工作中,我们提出了一个具有匝道缓冲的交叉口的一阶模型,该模型仅在交叉口进行修改,以便捕获容量下降。理论研究激发了耦合条件的新选择,并说明了与纯一阶和二阶模型的区别。考虑匝道并入主干道最优控制的数值算例表明,该组合模型的结果与二阶模型相似。AMS学科分类:65M08、90C30
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引用次数: 0
On the Scalability of the Schwarz Method 论Schwarz方法的可扩展性
Pub Date : 2019-02-10 DOI: 10.5802/smai-jcm.61
G. Ciaramella, Muhammad Hassan, B. Stamm
In this article, we analyse the convergence behaviour and scalability properties of the one-level Parallel Schwarz method (PSM) for domain decomposition problems in which the boundaries of many subdomains lie in the interior of the global domain. Such problems arise, for instance, in solvation models in computational chemistry. Existing results on the scalability of the one-level PSM are limited to situations where each subdomain has access to the external boundary, and at most only two subdomains have a common overlap. We develop a systematic framework that allows us to bound the norm of the Schwarz iteration operator for domain decomposition problems in which subdomains may be completely embedded in the interior of the global domain and an arbitrary number of subdomains may have a common overlap.
本文分析了一阶并行Schwarz方法(PSM)对于多子域边界位于全局域内部的域分解问题的收敛性和可扩展性。例如,在计算化学的溶剂化模型中就会出现这样的问题。现有的关于一级PSM可扩展性的结果仅限于每个子域都可以访问外部边界,并且最多只有两个子域有公共重叠的情况。我们开发了一个系统框架,允许我们对域分解问题的Schwarz迭代算子的范数进行约束,其中子域可以完全嵌入到全局域的内部,并且任意数量的子域可以有共同的重叠。
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引用次数: 11
Uniform and pointwise shape preserving approximation (SPA) by algebraic polynomials: an update 代数多项式的均匀点形保持近似(SPA):更新
Pub Date : 2019-01-12 DOI: 10.5802/smai-jcm.54
K. Kopotun, D. Leviatan, I. Shevchuk
It is not surprising that one should expect that the degree of constrained (shape preserving) approximation be worse than the degree of unconstrained approximation. However, it turns out that, in certain cases, these degrees are the same. The main purpose of this paper is to provide an update to our 2011 survey paper. In particular, we discuss recent uniform estimates in comonotone approximation, mention recent developments and state several open problems in the (co)convex case, and reiterate that co-$q$-monotone approximation with $qge 3$ is completely different from comonotone and coconvex cases. Additionally, we show that, for each function $f$ from $Delta^{(1)}$, the set of all monotone functions on $[-1,1]$, and every $alpha>0$, we have [ limsup_{ntoinfty} inf_{P_ninmathbb P_ncapDelta^{(1)}} left| frac{n^alpha(f-P_n)}{varphi^alpha} right| le c(alpha) limsup_{ntoinfty} inf_{P_ninmathbb P_n} left| frac{n^alpha(f-P_n)}{varphi^alpha} right| ] where $mathbb P_n$ denotes the set of algebraic polynomials of degree $
人们应该期望约束近似的程度(保持形状)比无约束近似的程度更差,这并不奇怪。然而,事实证明,在某些情况下,这些程度是相同的。本文的主要目的是对我们2011年的调查报告进行更新。特别地,我们讨论了最近在共凸近似中的一致估计,提到了最近的发展,并说明了(co)凸情况下的几个开放问题,并重申了$q 3$的共$q$-单调近似与共凸和共凸情况完全不同。另外,我们证明了,对于$ $Delta^{(1)}$的每一个函数$f$, $[-1,1]$上的所有单调函数的集合,以及$ $alpha>0$,我们有[limsup_{n到infty} inf_{P_n mathbb P_ncapDelta^{(1)} 左| frc limsup_{n alpha(f-P_n)} varphi^ alpha 右| le c(alpha) limsup_{n到inf_{P_n mathbb P_n左| frac{n alpha(f-P_n)}{varphi^ alpha 右 ],其中$mathbb P_n$表示阶为$的代数多项式集
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引用次数: 5
Simulating 3D periodic structures at oblique incidences with discontinuous Galerkin time-domain methods: theoretical and practical considerations 用不连续伽辽金时域方法模拟三维斜入射周期结构:理论和实践考虑
Pub Date : 2019-01-11 DOI: 10.5802/SMAI-JCM.45
J. Viquerat, N. Schmitt, C. Scheid
In this work, we focus on the development of the use of Periodic Boundary Conditions (PBC) with sources at oblique incidence in a Discontinuous Galerkin Time Domain (DGTD) framework. Whereas in the context of the Finite Difference Time Domain (FDTD) methods, an abundant literature can be found, for DGTD, the amount of contributions reporting on such methods is remarkably low. In this paper, we supplement the existing references using the field transform technique with an analysis of the continuous system using the method of characteristics and provide an energy estimate. Furthermore, we also study the discrete stability of the resulting DGTD scheme. Additional details about sources, observables (reflectance, transmittance and diffraction efficiency), and the use of Complex Frequency-Shifted Perfectly-Matched Layers (CFS-PMLs) in this framework are also given. After numerical validations, two realistic test-cases are considered in the context of nanophotonics with the Diogenes DGTD solver (http://diogenes.inria.fr).
在这项工作中,我们专注于在不连续伽辽金时域(DGTD)框架中发展斜入射源的周期边界条件(PBC)的使用。而在时域有限差分(FDTD)方法的背景下,可以找到大量的文献,对于DGTD,报道这种方法的贡献量非常低。本文利用特征分析方法对连续系统进行了分析,补充了已有的利用场变换技术的文献,并给出了能量估计。此外,我们还研究了所得到的DGTD格式的离散稳定性。此外,还详细介绍了光源、观测值(反射率、透射率和衍射效率)以及在该框架中使用复频移完美匹配层(cfs - pml)。经过数值验证后,在纳米光子学的背景下,用Diogenes DGTD求解器(http://diogenes.inria.fr)考虑了两个现实的测试用例。
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引用次数: 0
Connections between numerical integration, discrepancy, dispersion, and universal discretization 数值积分、差异、离散和普遍离散之间的联系
Pub Date : 2018-12-09 DOI: 10.5802/smai-jcm.58
V. Temlyakov
The main goal of this paper is to provide a brief survey of recent results which connect together results from different areas of research. It is well known that numerical integration of functions with mixed smoothness is closely related to the discrepancy theory. We discuss this connection in detail and provide a general view of this connection. It was established recently that the new concept of {it fixed volume discrepancy} is very useful in proving the upper bounds for the dispersion. Also, it was understood recently that point sets with small dispersion are very good for the universal discretization of the uniform norm of trigonometric polynomials.
本文的主要目的是提供一个简短的调查,最近的结果连接在一起的结果从不同的研究领域。众所周知,混合光滑函数的数值积分与差异理论密切相关。我们将详细讨论这种联系,并提供这种联系的一般视图。最近,{ 固定体积差异}的新概念在证明色散的上界方面是非常有用的。此外,最近人们认识到,具有小色散的点集对于三角多项式一致范数的普遍离散化是非常好的。
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引用次数: 4
Virtual Element approximations of the Vector Potential Formulation of Magnetostatic problems 静磁问题矢量势公式的虚元逼近
Pub Date : 2018-11-18 DOI: 10.5802/SMAI-JCM.40
L. B. D. Veiga, F. Brezzi, L. D. Marini, A. Russo
1 Dipartimento di Matematica e Applicazioni, Università di Milano Bicocca, Via Cozzi 55, I-20153, Milano, Italy and IMATI-CNR, Via Ferrata 1, I-27100 Pavia, Italy E-mail address: lourenco.beirao@unimib.it 2 IMATI-CNR, Via Ferrata 1, I-27100 Pavia, Italy E-mail address: brezzi@imati.cnr.it 3 Dipartimento di Matematica, Università di Pavia, Via Ferrata 5, I-27100 Pavia, Italy and IMATI-CNR, Via Ferrata 1, I-27100 Pavia, Italy E-mail address: marini@imati.cnr.it 4 Dipartimento di Matematica e Applicazioni, Università di Milano Bicocca, Via Cozzi 55, I-20153, Milano, Italy and IMATI-CNR, Via Ferrata 1, I-27100 Pavia, Italy E-mail address: alessandro.russo@unimib.it.
1、大学应用数学和米兰Bicocca、Cozzi 55 I-20153、米兰、意大利和IMATI-CNR、意大利帕维亚I-27100方面1、电子邮件为:lourenco beirao@unimib。it 2 IMATI-CNR,意大利帕维亚I-27100方面1、电子邮件为:数学brezzi@imati .中央人民广播电台3系、帕维亚大学、中法大学5、I-27100 Pavia, Italy and IMATI-CNR,中法1、意大利帕维亚I-27100,电子邮件为:marini@imati.cnr.it 4数学与应用系,米兰大学Bicocca, Via Cozzi 55, I-20153,米兰,意大利和意大利- cnr, Via Ferrata 1, I-27100 Pavia,意大利电子邮件address: alessandro.russo@unimib。
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引用次数: 3
期刊
The SMAI journal of computational mathematics
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