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The impact of confinement on the deformation of an elastic particle under axisymmetric tube flow 封闭对轴对称管流条件下弹性粒子变形的影响
IF 1.2 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-09-18 DOI: 10.1093/imamat/hxae022
Simon M Finney, Matthew G Hennessy, Andreas Münch, Sarah L Waters
We study an elastic particle translating axially along the centre-line of a rigid cylindrical tube filled with a Newtonian viscous fluid. The flow is pressure-driven and an axial body force is applied to the particle. We consider the regime in which the ratio of typical viscous fluid stress to elastic stiffness is small, leading to small elastic strains in the particle. In this case, there is a one-way decoupling of the fluid-structure interaction problem. The leading-order fluid problem is shown to be pressure-driven Stokes flow past a rigid sphere, and is solved using the semi-analytical method of reflections. The traction exerted by the fluid on the particle can be computed and used to formulate a pure solid-mechanics problem for the deformation of the particle, which can be solved analytically. This framework is used to investigate the role of the background flow, an axial body force, and the tube wall on the particle’s leading-order translational velocity, resulting deformation, and induced solid stress. By considering the first-order fluid problem the next-order correction to the translational velocity of the particle is shown to be zero. Depending on the magnitude of the ratio of applied body force to viscous forces, the particle can either have a bullet-like shape, an anti-bullet shape, or retain its original spherical shape. A non-linear arbitrary Lagrangian-Eulerian finite element implementation is used, in conjunction with various existing results from the literature, to validate the method of reflections solutions and interrogate their range of validity.
我们研究了一个沿充满牛顿粘性流体的刚性圆柱管中心线轴向平移的弹性粒子。流动由压力驱动,粒子受到轴向体力的作用。我们考虑的情况是,典型粘性流体应力与弹性刚度之比很小,从而导致粒子产生很小的弹性应变。在这种情况下,流固耦合问题是单向的。前序流体问题被证明是经过刚性球体的压力驱动斯托克斯流,并使用半解析反射法求解。流体对颗粒施加的牵引力可以计算出来,并用于制定颗粒变形的纯固体力学问题,该问题可以分析求解。该框架用于研究背景流、轴向体力和管壁对粒子前阶平移速度、产生的变形和诱导固体应力的作用。通过考虑一阶流体问题,粒子平移速度的下一阶修正为零。根据外加体力与粘性力之比的大小,质点可以是子弹状,也可以是反子弹状,或者保持原来的球形。使用非线性任意拉格朗日-欧拉有限元实现,结合文献中的各种现有结果,验证了反射解法,并询问了其有效性范围。
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引用次数: 0
On the P-Irreducibility of Quintic Positive Polynomials 论五次正多项式的 P-Irreducibility
IF 1.2 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-08-18 DOI: 10.1093/imamat/hxae021
Takeo Kamizawa, Andrzej Jamiołkowski, Takashi Matsuoka, Noboru Watanabe
In this paper we will discuss the p-reducibility/irreducibility of positive polynomials, and we will give some sufficient conditions for quintic polynomials to be p-reducible/irreducible. This research is closely related to some problems in bio-chemistry, especially to the cooperativity in bio-systems. We will study some applications of our results to these problems.
在本文中,我们将讨论正多项式的可p性/不可p性,并给出五次多项式可p性/不可p性的一些充分条件。这项研究与生物化学中的一些问题密切相关,尤其是生物系统中的合作性问题。我们将研究我们的成果在这些问题上的一些应用。
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引用次数: 0
An explicit Maclaurin series solution to non-autonomous and non-homogeneous evolution equation, Omega Calculus, and associated applications 非自治和非均质演化方程的显式麦克劳林级数解、欧米茄微积分及相关应用
IF 1.2 4区 数学 Q2 MATHEMATICS, APPLIED Pub Date : 2024-07-11 DOI: 10.1093/imamat/hxae020
Antônio Francisco Neto
We give a new Omega Calculus (a.k.a MacMahon’s Partition Analysis) based integral-free representation for the solution of a non-autonomous and non-homogeneous evolution equation. Our new representation generalizes some of the main results of the recent work of Francisco Neto (2024, A basis- and integral-free representation of time-dependent perturbation theory via the Omega matrix calculus. Ann. Inst. Henri Poincaré D, 11, 383) and Bassom et al. (2023, An explicit Maclaurin series solution to a classic non-autonomous abstract evolution equation. Appl. Math. Lett., 139, 108537) and show that we can indeed compute the coefficients of the Maclaurin series solution associated with the evolution equation starting with the Peano-Baker series. Furthermore, we discuss in the context of our framework the inverse problem for homogeneous evolution equations in a Hilbert space answering a question left open by Bassom et al. in this case; that is, assuming the solution of the homogeneous evolution equation is a known analytic function the problem concerns the determination of the associated generator of the dynamics. Finally, in order to illustrate the versatility of our approach we explicitly determine the Maclaurin series solution related to the power series method in the context of the vibration problems for the non-uniform (tapered) Euler-Bernoulli beam and thus we explicitly solve the recursion relations considered by Adair and Jaeger (2018, A power series solution for rotating nonuniform Euler–Bernoulli cantilever beams. J. Vib. Control, 24, 3855-3864).
我们给出了一种新的基于欧米茄微积分(又称麦克马洪分区分析法)的无积分表示法,用于求解非自治和非均质演化方程。我们的新表示法概括了弗朗西斯科-内托(Francisco Neto,2024,A basis- and integral-free representation of time-dependent perturbation theory via the Omega matrix calculus.Ann.Henri Poincaré D, 11, 383)和 Bassom 等人(2023,经典非自治抽象演化方程的显式麦克劳林级数解。Appl.Lett., 139, 108537),并证明我们确实可以从皮诺-贝克级数开始计算与演化方程相关的麦克劳林级数解的系数。此外,我们还讨论了希尔伯特空间中同质演化方程的逆问题,回答了巴索姆等人在这种情况下提出的一个问题,即假设同质演化方程的解是一个已知的解析函数,那么问题就涉及如何确定相关的动力学发电机。最后,为了说明我们方法的多功能性,我们在非均匀(锥形)欧拉-伯努利梁的振动问题中明确确定了与幂级数方法相关的 Maclaurin 级数解,从而明确解决了 Adair 和 Jaeger(2018,A power series solution for rotating nonuniform Euler-Bernoulli cantilever beams.J. Vib.Control, 24, 3855-3864)。
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引用次数: 0
Stability analysis of viscous multi-layer shear flows with interfacial slip 具有界面滑移的粘性多层剪切流的稳定性分析
IF 1.2 4区 数学 Q3 Mathematics Pub Date : 2024-06-13 DOI: 10.1093/imamat/hxae012
A. Katsiavria, Demetrios T Papageorgiou
One of the most fundamental interfacial instabilities in ideal, immiscible, incompressible multifluid flows is the celebrated Kelvin-Helmholtz (KH) instability. It predicts short-wave instabilities that in the absence of other mollifying physical mechanisms (e.g. surface tension, viscosity) render the nonlinear problem ill-posed and lead to finite-time singularities. The crucial driving mechanism is the jump in tangential velocity across the liquid-liquid interface, i.e. interfacial slip, that can occur since viscosity is absent. The purpose of the present work is to analyse analogous instabilities for viscous flows at small or moderate Reynolds numbers as opposed to the infinite Reynolds numbers that underpin KH instabilities. The problem is physically motivated by both experiments and simulations. The fundamental model considered consists of two superposed viscous, incompressible, immiscible fluid layers sheared in a plane Couette flow configuration, with slip present at the deforming liquid-liquid interface. The origin of slip in viscous flows has been observed in experiments and molecular dynamics simulations, and can be modelled by employing a Navier-slip boundary condition at the liquid-liquid interface. The emerging novel instabilities are studied in detail here. The linear stability of the system is addressed asymptotically for long- and short-waves, and for arbitrary wavenumbers using a combination of analytical and numerical calculations. Slip is found to be capable of destabilising perturbations of all wavelengths. In regimes where the flow is stable to perturbations of all wavelengths in the absence of slip, its presence can induce a Turing-type instability by destabilisation of a small band of finite wavenumber perturbations. In the case where the underlying layer is asymptotically thin, the results are found to agree with the linear properties of a weakly non-linear asymptotic model that is also derived here. The weakly nonlinear model extends previous work by the authors that had a thin overlying layer that produces a different evolution equation.
在理想、不溶、不可压缩的多流体流动中,最基本的界面不稳定性之一是著名的开尔文-赫姆霍兹(KH)不稳定性。它预示了短波不稳定性,在没有其他物理机制(如表面张力、粘度)的情况下,短波不稳定性会使非线性问题难以解决,并导致有限时间奇点。关键的驱动机制是液-液界面切向速度的跃迁,即界面滑移,由于没有粘度,这种现象就会发生。本研究的目的是分析粘性流在小雷诺数或中等雷诺数下的类似不稳定性,而不是作为 KH 不稳定性基础的无限雷诺数。这个问题是通过实验和模拟得到的物理结果。所考虑的基本模型包括两个叠加的粘性、不可压缩、不溶性流体层,它们在平面库埃特流配置中被剪切,在变形的液-液界面上存在滑移。粘滞流中滑移的起源已在实验和分子动力学模拟中观察到,并可通过在液-液界面上采用纳维-滑移边界条件来模拟。本文详细研究了新出现的新型不稳定性。采用分析和数值计算相结合的方法,对长波和短波以及任意波数的系统线性稳定性进行了渐近分析。研究发现,滑移能够破坏所有波长扰动的稳定性。在没有滑移的情况下,流动对所有波长的扰动都是稳定的,但滑移的存在会破坏一小段有限波长扰动的稳定性,从而诱发图灵型不稳定性。在底层渐薄的情况下,结果与弱非线性渐近模型的线性特性相吻合。弱非线性模型扩展了作者以前的工作,即上覆薄层产生不同的演化方程。
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引用次数: 0
An iteration method to study nonlinear wave propagation for a non-Green elastic 1D bar 研究非格林弹性一维棒非线性波传播的迭代法
IF 1.2 4区 数学 Q3 Mathematics Pub Date : 2024-06-11 DOI: 10.1093/imamat/hxae017
R. Bustamante, P. Arrue, O. Orellana, R. Meneses
The problem of propagation of nonlinear waves in a 1D bar is studied, wherein the linearized strain tensor is considered as a function of the Cauchy stress tensor. Specifically, two constitutive equations for non-Green elastic solids are investigated, introducing a novel numerical iterative method capable to obtain approximate solutions of one nonlinear constitutive equation for rock, and one constitutive equation that shows a strain limiting behaviour. The numerical results are compared with exact solutions for the case of a linearized elastic solid.
研究了非线性波在一维棒材中的传播问题,其中线性化应变张量被视为考奇应力张量的函数。具体而言,研究了非格林弹性固体的两个构成方程,引入了一种新颖的数值迭代法,能够获得一个岩石非线性构成方程和一个显示应变限制行为的构成方程的近似解。数值结果与线性化弹性固体的精确解进行了比较。
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引用次数: 0
Global existence and steady states of the density-suppressed motility model with strong Allee effect 具有强阿利效应的密度抑制运动模型的全局存在和稳定状态
IF 1.2 4区 数学 Q3 Mathematics Pub Date : 2024-06-05 DOI: 10.1093/imamat/hxae013
Cui Song, Zhicheng Wang, Zhaosheng Feng
This paper considers a density-suppressed motility model with a strong Allee effect under the homogeneous Neumman boundary condition. We first establish the global existence of bounded classical solutions to a parabolic-parabolic system over a $N $-dimensional $mathbf{(Nle 3)}$ bounded domain $varOmega $, as well as the global existence of bounded classical solutions to a parabolic-elliptic system over the multidimensional bounded domain $varOmega $ with smooth boundary. We then investigate the linear stability at the positive equilibria for the full parabolic case and parabolic-elliptic case respectively, and find the influence of Allee effect on the local stability of the equilibria. By treating the Allee effect as a bifurcation parameter, we focus on the one-dimensional stationary problem and obtain the existence of non-constant positive steady states, which corresponds to small perturbations from the constant equilibrium $(1,1)$. Furthermore, we present some properties through theoretical analysis on pitchfork type and turning direction of the local bifurcations. The stability results provide a stable wave mode selection mechanism for the model considered in this paper. Finally, numerical simulations are performed to demonstrate our theoretical results.
本文研究了在均质 Neumman 边界条件下具有强阿利效应的密度抑制运动模型。我们首先建立了在 $N $维 $mathbf{(Nle 3)}$ 有界域 $varOmega $ 上抛物-抛物线系统有界经典解的全局存在性,以及在具有光滑边界的多维有界域 $varOmega $ 上抛物-椭圆系统有界经典解的全局存在性。然后,我们分别研究了全抛物情况和抛物-椭圆情况下正平衡点的线性稳定性,并发现了阿利效应对平衡点局部稳定性的影响。通过将阿利效应视为分岔参数,我们重点研究了一维静止问题,并得到了非恒定正稳态的存在,这相当于从恒定平衡$(1,1)$出发的小扰动。此外,我们还通过对局部分叉的叉型和转向方向的理论分析,提出了一些特性。稳定性结果为本文所考虑的模型提供了一种稳定的波浪模式选择机制。最后,我们进行了数值模拟来证明我们的理论结果。
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引用次数: 0
Stratification in drying films: Diffusiophoresis driven by nanoparticles and their counterions 干燥薄膜的分层:由纳米粒子及其反离子驱动的扩散电泳
IF 1.2 4区 数学 Q3 Mathematics Pub Date : 2024-06-05 DOI: 10.1093/imamat/hxae015
Clare R. Rees-Zimmerman, Alexander F Routh
Recent experimental work has highlighted that electrolyte-driven diffusiophoresis is likely to be the most significant phoretic motion in a mixture of silica nanoparticles and relatively large latex particles, which are commonly used in coatings. In this present work, this diffusiophoretic effect, powered by gradients in the nanoparticles and their stabilising cations, is modelled in drying films. A continuum hydrodynamic model is derived, and the resulting partial differential equations solved numerically. An asymptotic solution is found for high evaporation rate. It is found that the final film structure is governed by the relative magnitudes of the diffusive and diffusiophoretic terms. Two methods are discovered to control the resulting stratification: (i) setting the surface charge on the particles, and (ii) setting the background salt concentration. Either of these can be used to select either small- or large-on-top stratification or a homogenous film. The diffusiophoretic term promotes small-on-top stratification, and so may account for experimental observations of accumulated small particles at the top surface of dried films.
最近的实验工作表明,电解质驱动的扩散泳动很可能是二氧化硅纳米粒子和相对较大的乳胶粒子混合物(常用于涂料)中最重要的幻影运动。在本研究中,这种由纳米粒子及其稳定阳离子的梯度驱动的扩散蠕动效应被模拟在干燥薄膜中。推导出了一个连续流体力学模型,并对由此产生的偏微分方程进行了数值求解。找到了高蒸发率下的渐近解。研究发现,最终的薄膜结构受扩散项和扩散蠕动项相对大小的制约。发现了两种控制分层结果的方法:(i) 设置颗粒表面电荷;(ii) 设置背景盐浓度。这两种方法中的任何一种都可用于选择顶部小分层或顶部大分层或均质膜。扩散项会促进顶部小颗粒分层,因此可以解释实验观察到的干燥薄膜顶部表面积聚小颗粒的原因。
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引用次数: 0
Exact and numerical solutions of a free boundary problem with a reciprocal growth law 具有倒数增长规律的自由边界问题的精确解和数值解
IF 1.2 4区 数学 Q3 Mathematics Pub Date : 2024-06-04 DOI: 10.1093/imamat/hxae014
N. R. McDonald, Samuel J Harris
A two-dimensional free boundary problem is formulated in which the normal velocity of the boundary is proportional to the inverse of the gradient of a harmonic function $T$. The field $T$ is defined in a simply connected region which includes the point at infinity where it has a logarithmic singularity. The growth problem in which the boundary expands outward is formulated both in terms of the Schwarz function of the boundary and a Polubarinova-Galin equation for the conformal map of the region from the exterior of the unit disk. An expanding free boundary is shown to be stable and explicit solutions for growing ellipses and a class of polynomial lemniscates are derived. Numerical solution of the Polubarinova-Galin equation is used to compute the evolution of the boundary having other initial shapes.
本文提出了一个二维自由边界问题,其中边界的法向速度与谐函数 $T$ 梯度的倒数成正比。场 $T$ 定义在一个简单连接的区域,该区域包括无穷远处的点,在该点有一个对数奇点。边界向外扩展的增长问题是根据边界的施瓦茨函数和该区域从单位盘外部的共形映射的 Polubarinova-Galin 方程提出的。结果表明膨胀的自由边界是稳定的,并推导出了增长椭圆和一类多项式∞的显式解法。Polubarinova-Galin 方程的数值解用于计算具有其他初始形状的边界的演变。
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引用次数: 0
Can physics-informed neural networks beat the finite element method? 物理信息神经网络能否战胜有限元法?
IF 1.2 4区 数学 Q3 Mathematics Pub Date : 2024-05-23 DOI: 10.1093/imamat/hxae011
Tamara G Grossmann, Urszula Julia Komorowska, Jonas Latz, Carola-Bibane Schönlieb
Partial differential equations play a fundamental role in the mathematical modelling of many processes and systems in physical, biological and other sciences. To simulate such processes and systems, the solutions of PDEs often need to be approximated numerically. The finite element method, for instance, is a usual standard methodology to do so. The recent success of deep neural networks at various approximation tasks has motivated their use in the numerical solution of PDEs. These so-called physics-informed neural networks and their variants have shown to be able to successfully approximate a large range of partial differential equations. So far, physics-informed neural networks and the finite element method have mainly been studied in isolation of each other. In this work, we compare the methodologies in a systematic computational study. Indeed, we employ both methods to numerically solve various linear and nonlinear partial differential equations: Poisson in 1D, 2D, and 3D, Allen–Cahn in 1D, semilinear Schrödinger in 1D and 2D. We then compare computational costs and approximation accuracies. In terms of solution time and accuracy, physics-informed neural networks have not been able to outperform the finite element method in our study. In some experiments, they were faster at evaluating the solved PDE.
偏微分方程在物理、生物和其他科学领域的许多过程和系统的数学建模中发挥着重要作用。为了模拟这些过程和系统,通常需要对偏微分方程的解进行数值近似。例如,有限元法就是一种常用的标准方法。最近,深度神经网络在各种近似任务中取得了成功,这促使它们被用于 PDE 的数值求解。这些所谓的物理信息神经网络及其变体已证明能够成功逼近大量偏微分方程。迄今为止,对物理信息神经网络和有限元法的研究主要是相互孤立的。在这项工作中,我们通过系统的计算研究对这两种方法进行了比较。事实上,我们采用这两种方法对各种线性和非线性偏微分方程进行数值求解:一维、二维和三维泊松方程,一维艾伦-卡恩方程,一维和二维半线性薛定谔方程。然后,我们比较了计算成本和近似精度。在我们的研究中,就求解时间和精度而言,物理信息神经网络无法超越有限元方法。在某些实验中,神经网络在评估求解的 PDE 时速度更快。
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引用次数: 0
Forward to the special issue on “The Applied Mathematics of Machine Learning” 机器学习的应用数学 "特刊前言
IF 1.2 4区 数学 Q3 Mathematics Pub Date : 2024-05-20 DOI: 10.1093/imamat/hxae010
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引用次数: 0
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IMA Journal of Applied Mathematics
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