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Analysis of a fully-discrete, non-conforming approximation of evolution equations and applications 演化方程的全离散非一致性近似分析及其应用
Pub Date : 2023-05-17 DOI: 10.1142/s0218202523500197
A. Kaltenbach, M. Ruzicka
In this paper, we consider a fully-discrete approximation of an abstract evolution equation deploying a non-conforming spatial approximation and finite differences in time (Rothe–Galerkin method). The main result is the convergence of the discrete solutions to a weak solution of the continuous problem. Therefore, the result can be interpreted either as a justification of the numerical method or as an alternative way of constructing weak solutions. We formulate the problem in the very general and abstract setting of so-called non-conforming Bochner pseudo-monotone operators, which allows for a unified treatment of several evolution problems. Our abstract results for non-conforming Bochner pseudo-monotone operators allow to establish (weak) convergence just by verifying a few natural assumptions on the operators time-by-time and on the discretization spaces. Hence, applications and extensions to several other evolution problems can be performed easily. We exemplify the applicability of our approach on several DG schemes for the unsteady [Formula: see text]-Navier–Stokes problem. The results of some numerical experiments are reported in the final section.
在本文中,我们考虑了一个抽象演化方程的全离散逼近,它采用非协调空间逼近和有限时间差分(Rothe-Galerkin方法)。主要结果是离散解对连续问题弱解的收敛性。因此,结果既可以解释为数值方法的证明,也可以解释为构造弱解的另一种方法。我们在所谓的非一致性Bochner伪单调算子的非常一般和抽象的设置中表述问题,它允许对几个演化问题进行统一处理。我们关于非一致性Bochner伪单调算子的抽象结果允许通过验证算子在时间和离散空间上的几个自然假设来建立(弱)收敛性。因此,可以很容易地执行针对其他几个演化问题的应用程序和扩展。我们举例说明了我们的方法对非定常[公式:见文本]-Navier-Stokes问题的几种DG格式的适用性。最后一节报告了一些数值实验的结果。
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引用次数: 1
A nonlinear bending theory for nematic LCE plates 向列LCE板的非线性弯曲理论
Pub Date : 2023-05-04 DOI: 10.1142/s0218202523500331
Soren Bartels, Max Griehl, Stefan Neukamm, David Padilla-Garza, Christian Palus
In this paper, we study an elastic bilayer plate composed of a nematic liquid crystal elastomer in the top layer and a nonlinearly elastic material in the bottom layer. While the bottom layer is assumed to be stress-free in the flat reference configuration, the top layer features an eigenstrain that depends on the local liquid crystal orientation. As a consequence, the plate shows non-flat deformations in equilibrium with a geometry that non-trivially depends on the relative thickness and shape of the plate, material parameters, boundary conditions for the deformation, and anchorings of the liquid crystal orientation. We focus on thin plates in the bending regime and derive a two-dimensional bending model that combines a nonlinear bending energy for the deformation, with a surface Oseen–Frank energy for the director field that describes the local orientation of the liquid crystal elastomer. Both energies are nonlinearly coupled by means of a spontaneous curvature term that effectively describes the nematic-elastic coupling. We rigorously derive this model as a [Formula: see text]-limit from three-dimensional, nonlinear elasticity. We also devise a new numerical algorithm to compute stationary points of the two-dimensional model. We conduct numerical experiments and present simulation results that illustrate the practical properties of the proposed scheme as well as the rich mechanical behavior of the system.
本文研究了一种由表层向列液晶弹性体和底层非线性弹性材料组成的弹性双层板。在平面参考结构中,假设底层是无应力的,而顶层的特征应变取决于局部液晶的取向。因此,平板显示出非平面的平衡变形,其几何形状非平凡地取决于平板的相对厚度和形状、材料参数、变形的边界条件和液晶取向的锚定。我们将重点放在弯曲状态下的薄板上,并推导出一个二维弯曲模型,该模型将非线性弯曲能量与描述液晶弹性体局部方向的指向场的表面osee - frank能量结合起来。这两种能量通过一个有效描述向列-弹性耦合的自发曲率项非线性耦合。我们从三维非线性弹性中严格推导出这个模型[公式:见文本]-极限。我们还设计了一种新的数值算法来计算二维模型的平稳点。我们进行了数值实验并给出了仿真结果,以说明所提出方案的实用特性以及系统的丰富力学行为。
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引用次数: 1
Multilevel domain uncertainty quantification in computational electromagnetics 计算电磁学中的多水平域不确定性量化
Pub Date : 2023-03-30 DOI: 10.1142/s0218202523500264
Ruben Aylwin, Carlos Jerez-Hanckes, Christoph Schwab, Jakob Zech
We continue our study [R. Aylwin, C. Jerez-Hanckes, C. Schwab and J. Zech, Domain uncertainty quantification in computational electromagnetics, SIAM/ASA J. Uncertain. Quant. 8 (2020) 301–341] of the numerical approximation of time-harmonic electromagnetic fields for the Maxwell lossy cavity problem for uncertain geometries. We adopt the same affine-parametric shape parametrization framework, mapping the physical domains to a nominal polygonal domain with piecewise smooth maps. The regularity of the pullback solutions on the nominal domain is characterized in piecewise Sobolev spaces. We prove error convergence rates and optimize the algorithmic steering of parameters for edge-element discretizations in the nominal domain combined with: (a) multilevel Monte Carlo sampling, and (b) multilevel, sparse-grid quadrature for computing the expectation of the solutions with respect to uncertain domain ensembles. In addition, we analyze sparse-grid interpolation to compute surrogates of the domain-to-solution mappings. All calculations are performed on the polyhedral nominal domain, which enables the use of standard simplicial finite element meshes. We provide a rigorous fully discrete error analysis and show, in all cases, that dimension-independent algebraic convergence is achieved. For the multilevel sparse-grid quadrature methods, we prove higher order convergence rates free from the so-called curse of dimensionality. Numerical experiments confirm our theoretical results and verify the superiority of the sparse-grid methods.
我们继续学习[R]。艾尔文,C. jerez - hankes, C. Schwab和J. Zech,计算电磁学领域不确定性量化,SIAM/ASA J. uncertainty。不确定几何的Maxwell损耗腔问题时谐电磁场的数值逼近[j] .量子学报,8(2020)301-341。我们采用相同的仿射参数形状参数化框架,用分段光滑映射将物理域映射到标称多边形域。在分段Sobolev空间中描述了标称域上的回拉解的正则性。我们证明了在标称域的边元离散化的误差收敛率,并优化了参数的算法导向,结合:(a)多层蒙特卡罗采样,以及(b)用于计算不确定域集成解的期望的多层稀疏网格正交。此外,我们分析了稀疏网格插值来计算域到解映射的代理。所有的计算都是在多面体标称域上进行的,这使得使用标准的简单有限元网格成为可能。我们提供了一个严格的完全离散误差分析,并表明,在所有情况下,维无关的代数收敛是实现的。对于多层稀疏网格正交方法,我们证明了高阶收敛速率,并且没有所谓的维数诅咒。数值实验证实了我们的理论结果,验证了稀疏网格方法的优越性。
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引用次数: 0
Bound-preserving finite element approximations of the Keller–Segel equations Keller-Segel方程的保界有限元逼近
Pub Date : 2023-03-01 DOI: 10.1142/s0218202523500148
Santiago Badia, Jesus Bonilla, Juan Vicente Gutierrez-Santacreu
This paper aims to develop numerical approximations of the Keller–Segel equations that mimic at the discrete level the lower bounds and the energy law of the continuous problem. We solve these equations for two unknowns: the organism (or cell) density, which is a positive variable, and the chemoattractant density, which is a non-negative variable. We propose two algorithms, which combine a stabilized finite element method and a semi-implicit time integration. The stabilization consists of a nonlinear artificial diffusion that employs a graph-Laplacian operator and a shock detector that localizes local extrema. As a result, both algorithms turn out to be nonlinear and can generate cell and chemoattractant numerical densities fulfilling lower bounds. However, the first algorithm requires a suitable constraint between the space and time discrete parameters, whereas the second one does not. We design the latter to attain a discrete energy law on acute meshes. We report some numerical experiments to validate the theoretical results on blowup and nonblowup phenomena. In the blowup setting, we identify a locking phenomenon that relates the [Formula: see text]-norm to the [Formula: see text]-norm limiting the growth of the singularity when supported on a macroelement.
本文旨在建立在离散水平上模拟连续问题下界和能量定律的Keller-Segel方程的数值近似。我们用两个未知数来解这些方程:生物体(或细胞)密度,这是一个正变量,而化学引诱剂密度,这是一个非负变量。我们提出了两种算法,结合稳定有限元法和半隐式时间积分法。该方法包括一个非线性人工扩散算法,该算法采用了一个图拉普拉斯算子和一个局部极值定位的冲击检测器。结果表明,这两种算法都是非线性的,可以生成满足下界的细胞和化学引诱物数值密度。然而,第一种算法需要在空间和时间离散参数之间有合适的约束,而第二种算法则不需要。我们设计后者以获得急性网格上的离散能量律。我们报道了一些数值实验来验证爆炸和不爆炸现象的理论结果。在放大设置中,我们确定了一种锁定现象,该现象将[公式:见文本]规范与[公式:见文本]规范联系起来,当在宏元素上支持时,限制奇点的增长。
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引用次数: 2
Non-mean-field Vicsek-type models for collective behavior 集体行为的非平均场vicsek型模型
Pub Date : 2023-02-02 DOI: 10.1142/s0218202522500646
Paolo Buttà, Ben Goddard, Thomas M. Hodgson, Michela Ottobre, Kevin J. Painter

We consider interacting particle dynamics with Vicsek-type interactions, and their macroscopic Partial Differential Equation (PDE) limit, in the non-mean-field regime; that is, we consider the case in which each particle/agent in the system interacts only with a prescribed subset of the particles in the system (for example, those within a certain distance). In this non-mean-field regime the influence between agents (i.e. the interaction term) can be normalized either by the total number of agents in the system (global scaling) or by the number of agents with which the particle is effectively interacting (local scaling). We compare the behavior of the globally scaled and the locally scaled systems in many respects, considering for each scaling both the PDE and the corresponding particle model. In particular, we observe that both the locally and globally scaled particle system exhibit pattern formation (i.e. formation of traveling-wave-like solutions) within certain parameter regimes, and generally display similar dynamics. The same is not true of the corresponding PDE models. Indeed, while both PDE models have multiple stationary states, for the globally scaled PDE such (space-homogeneous) equilibria are unstable for certain parameter regimes, with the instability leading to traveling wave solutions, while they are always stable for the locally scaled one, which never produces traveling waves. This observation is based on a careful numerical study of the model, supported by further analysis.

在非平均场条件下,考虑具有vicsek型相互作用的粒子动力学及其宏观偏微分方程(PDE)极限;也就是说,我们考虑的情况是,系统中的每个粒子/智能体只与系统中规定的粒子子集相互作用(例如,在一定距离内的粒子)。在这种非平均场状态下,代理之间的影响(即相互作用项)可以通过系统中代理的总数(全局缩放)或通过与粒子有效交互的代理的数量(局部缩放)进行归一化。我们在许多方面比较了全局尺度和局部尺度系统的行为,考虑了每一个尺度的PDE和相应的粒子模型。特别是,我们观察到局部和全局尺度的粒子系统在某些参数范围内都表现出模式形成(即行波解的形成),并且通常表现出相似的动力学。对于相应的PDE模型,情况并非如此。事实上,虽然两种PDE模型都有多个稳态,但对于全局尺度的PDE,这种(空间齐次)平衡对于某些参数域是不稳定的,这种不稳定导致行波解,而对于局部尺度的PDE,它们总是稳定的,永远不会产生行波。这一观察结果是基于对该模型的仔细数值研究,并得到进一步分析的支持。
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引用次数: 0
A diffuse-domain-based numerical method for a chemotaxis-fluid model 基于扩散域的趋化流体模型数值计算方法
Pub Date : 2023-02-01 DOI: 10.1142/s0218202523500094
Chenxi Wang, Alina Chertock, Shumo Cui, Alexander Kurganov, Zhen Zhang
In this paper, we consider a coupled chemotaxis-fluid system that models self-organized collective behavior of oxytactic bacteria in a sessile drop. This model describes the biological chemotaxis phenomenon in the fluid environment and couples a convective chemotaxis system for the oxygen-consuming and oxytactic bacteria with the incompressible Navier–Stokes equations subject to a gravitational force, which is proportional to the relative surplus of the cell density compared to the water density. We develop a new positivity preserving and high-resolution method for the studied chemotaxis-fluid system. Our method is based on the diffuse-domain approach, which we use to derive a new chemotaxis-fluid diffuse-domain (cf-DD) model for simulating bioconvection in complex geometries. The drop domain is imbedded into a larger rectangular domain, and the original boundary is replaced by a diffuse interface with finite thickness. The original chemotaxis-fluid system is reformulated on the larger domain with additional source terms that approximate the boundary conditions on the physical interface. We show that the cf-DD model converges to the chemotaxis-fluid model asymptotically as the width of the diffuse interface shrinks to zero. We numerically solve the resulting cf-DD system by a second-order hybrid finite-volume finite-difference method and demonstrate the performance of the proposed approach on a number of numerical experiments that showcase several interesting chemotactic phenomena in sessile drops of different shapes, where the bacterial patterns depend on the droplet geometries.
在本文中,我们考虑了一个耦合的趋化-流体系统,该系统模拟了氧合细菌在无根滴中的自组织集体行为。该模型描述了流体环境中的生物趋化现象,并将耗氧细菌和氧趋化细菌的对流趋化系统与重力作用下的不可压缩Navier-Stokes方程耦合在一起,重力作用与细胞密度相对于水密度的相对盈余成正比。我们为研究的趋化-流体系统开发了一种新的正极保持和高分辨率的方法。我们的方法是基于扩散域方法,我们用它来推导一个新的化学趋化-流体扩散域(cf-DD)模型,用于模拟复杂几何形状中的生物对流。跌落域被嵌入到一个更大的矩形域中,原始边界被一个有限厚度的漫射界面所取代。原始的趋化流体系统在更大的域上重新制定了附加的源项,这些源项近似于物理界面上的边界条件。当扩散界面的宽度缩小到零时,cf-DD模型渐近收敛于趋化-流体模型。我们通过二阶混合有限体积有限差分方法对所得到的cf-DD系统进行了数值求解,并在许多数值实验中证明了所提出方法的性能,这些实验展示了不同形状的固定液滴中几种有趣的化学趋化现象,其中细菌模式取决于液滴的几何形状。
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引用次数: 0
On the convergence of residual distribution schemes for the compressible Euler equations via dissipative weak solutions 利用耗散弱解研究可压缩欧拉方程剩余分布格式的收敛性
Pub Date : 2023-01-01 DOI: 10.1142/s0218202523500057
Remi Abgrall, Maria Lukacova-Medvid'ova, Philipp Offner
In this work, we prove the convergence of residual distribution (RD) schemes to dissipative weak solutions of the Euler equations. We need to guarantee that the RD schemes are fulfilling the underlying structure preserving methods properties such as positivity of density and internal energy. Consequently, the RD schemes lead to a consistent and stable approximation of the Euler equations. Our result can be seen as a generalization of the Lax–Richtmyer equivalence theorem to nonlinear problems that consistency plus stability is equivalent to convergence.
本文证明了残差分布格式对欧拉方程的耗散弱解的收敛性。我们需要保证RD方案满足底层结构保留方法的性质,如密度和内能的正性。因此,RD格式导致欧拉方程的一致和稳定的近似。我们的结果可以看作是拉克斯-里奇迈耶等价定理在非线性问题上的推广,即一致性加稳定性等价于收敛性。
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引用次数: 3
Responding to Open Access: How German Museums use Digital Content 回应开放获取:德国博物馆如何使用数字内容
Pub Date : 2019-07-18 DOI: 10.29311/MAS.V17I2.2756
Julia Wiedemann, Susanne B. Schmitt, E. Patzschke
Museums are expected to safeguard society’s cultural heritage while also making it publicly available to all. Recently, the digital transformation increased political and societal claims on museums to make their digital content openly available. This paper explores museums’ reactions to this claim and looks at how museums currently utilize their digital content. By analysing qualitative interviews with German museum officials we have found museums to follow four different types of strategies which are ‘Societal engagement’, ‘Safeguarding of heritage related knowledge’, ‘Scientific infrastructure’ and ‘marketing ends’. These were embedded in museums’ organizational identity and the prioritising of some of their tasks.
博物馆被期望保护社会的文化遗产,同时也向所有人开放。最近,数字化转型增加了对博物馆开放数字内容的政治和社会要求。本文探讨了博物馆对这一说法的反应,并探讨了博物馆目前如何利用其数字内容。通过分析对德国博物馆官员的定性访谈,我们发现博物馆遵循四种不同类型的策略,即“社会参与”、“遗产相关知识的保护”、“科学基础设施”和“营销目的”。这些都植根于博物馆的组织身份和他们的一些任务的优先级。
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引用次数: 3
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Mathematical Models and Methods in Applied Sciences
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