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Finite–element analysis of the effect of material properties and fibre shape on stresses in an elastic fibre embedded in an elastic matrix in a fibre–composite material 材料性能和纤维形状对纤维复合材料中嵌入弹性基体的弹性纤维应力影响的有限元分析
Kheng Lim Goh, Richard M. Aspden, K. Mathias, D. Hukins
The finite–element method was used to calculate the axial stress in an elastic fibre embedded in an elastic matrix to model a fibre–composite material. Axisymmetric models were created for cylindrical, ellipsoidal, paraboloidal and conical fibres embedded in a matrix and characterized by a fibre axial ratio, q. The effects of varying q, from 200 to 1000, and the ratio of the Young moduli of the fibre and the matrix, Ef/Em, from 50 to 104, were investigated. For a cylindrical fibre, the axial stress distribution along the fibre axis was similar for all values of q and Ef/Em; it was greatest at the centre, decreased steadily over most of the fibre length and fell rapidly to zero near the fibre end. For fixed q, the magnitude of this stress increased with increasing Ef/Em, whereas for fixed Ef/Em the variation with q was small. There was good qualitative agreement between these data and previous analytical models. The axial stress in the conical fibre was a minimum at the fibre centre and rose gradually to a maximum close to the fibre end. This was most pronounced for small values of q and at large values of Ef/Em. Stress distributions for the paraboloid and ellipsoid lay between those for the cylinder and the cone. For small values of Ef/Em, both the magnitudes and the axial distributions of axial stress were almost indistinguishable for all shapes of fibre and all values of q studied.
采用有限元法计算嵌入弹性基体中的弹性纤维的轴向应力,对纤维复合材料进行建模。为嵌入在基体中的圆柱形、椭球形、抛物面和锥形纤维建立了轴对称模型,并以纤维轴向比q为特征。研究了q从200到1000的变化以及纤维与基体的杨氏模量Ef/Em的比值从50到104的变化对模型的影响。对于圆柱形纤维,所有q值和Ef/Em值沿纤维轴的轴向应力分布相似;它在中心处最大,在纤维长度的大部分稳步下降,在纤维末端附近迅速下降到零。对于固定q,应力的大小随Ef/Em的增加而增加,而对于固定Ef/Em,随q的变化很小。这些数据与以前的分析模型有很好的定性一致性。锥形纤维的轴向应力在纤维中心处最小,靠近纤维末端处逐渐增大至最大值。这在q值较小和Ef/Em值较大时最为明显。抛物面和椭球面的应力分布介于柱面和锥面之间。对于较小的Ef/Em值,所有形状的纤维和所有q值的轴向应力的大小和轴向分布几乎无法区分。
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引用次数: 39
Evans function stability of non-adiabatic combustion waves 非绝热燃烧波的Evans函数稳定性
V. Gubernov, G. Mercer, H. Sidhu, R. Weber
In this paper we investigate the linear stability and properties of the planar travelling non–adiabatic combustion front for the cases of zero and non–zero ambient temperature. The speed of the front is estimated numerically using the shooting and relaxation methods. It is shown that for given parameter values the solution either does not exist or there are two solutions with different values of the front speed, which are referred to as ‘fast’ and ‘slow’. The Evans function approach extended by the compound–matrix method is employed to numerically solve the linear–stability problem for the travelling–wave solution. We demonstrate that the ‘slow’ branch of the solutions is unstable, whereas the ‘fast’ branch can be stable or exhibits Hopf or Bogdanov–Takens instability, depending on the parameter values.
本文研究了零和非零环境温度下平面行进非绝热燃烧锋面的线性稳定性和性质。采用射击法和松弛法对锋面速度进行了数值估计。结果表明,对于给定的参数值,解要么不存在,要么有两个解具有不同的前转速值,称为“快”和“慢”。采用复合矩阵法推广的Evans函数方法,对行波解的线性稳定性问题进行了数值求解。我们证明了解的“慢”分支是不稳定的,而“快”分支可以是稳定的或表现出Hopf或Bogdanov-Takens不稳定,这取决于参数值。
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引用次数: 30
Simulation of grain-boundary diffusion creep: analysis of some new numerical techniques 晶界扩散蠕变模拟:一些新的数值技术分析
J. Ford, N. Ford, J. Wheeler
We consider the simulation of deformation of polycrystalline materials by grain–boundary diffusion creep. For a given network of grain boundaries intersecting at nodes, with appropriate boundary conditions, we can calculate the rate at which material will be dissolved or deposited along each grain boundary and hence predict the rate at which each grain will move to accommodate this dissolution/deposition. We discuss two numerical methods for simulating the network changes over a finite time–interval, based on using the movement of adjacent grain boundaries over a small time–interval to estimate the velocities of the nodes. (The second of these methods has enabled us to speed up solution by 100 times in typical experiments compared with a naive forward–Euler approach.) We show that the accuracy with which the node velocities can be estimated is dependent only on the precision of the machine with which they are computed and deduce that, for all practical purposes, the lack of precise node velocity values does not detract from the quality of our solution. Finally, we consider the underlying stability of the problem under various different boundary conditions and conclude that our methods have the potential for providing useful insight into the effect of grain size and shape on deformation in polycrystalline materials.
本文考虑用晶界扩散蠕变法模拟多晶材料的变形。对于在节点处相交的给定晶界网络,在适当的边界条件下,我们可以计算材料沿每个晶界溶解或沉积的速率,从而预测每个晶粒为适应这种溶解/沉积而移动的速率。我们讨论了在有限时间间隔内模拟网络变化的两种数值方法,基于在小时间间隔内使用相邻晶界的运动来估计节点的速度。(在典型实验中,第二种方法使我们的求解速度比单纯的前向欧拉方法快100倍。)我们表明,估计节点速度的精度仅取决于计算节点速度的机器的精度,并推断出,对于所有实际目的,缺乏精确的节点速度值并不会降低我们解决方案的质量。最后,我们考虑了问题在各种不同边界条件下的潜在稳定性,并得出结论,我们的方法有可能为了解晶粒尺寸和形状对多晶材料变形的影响提供有用的见解。
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引用次数: 8
On boundary–layer separation and internal wave generation at the Knight Inlet sill 奈特入口基台边界层分离与内波产生研究
K. Lamb
This paper reports results of numerical simulations of stratified tidal flow over the Knight Inlet sill. A non–hydrostatic, two–dimensional model is used, which incorporates a no–slip bottom boundary condition through the use of a vertical eddy viscosity/diffusivity parametrization that is non–zero only near the bottom. In inviscid model runs, a large lee wave is rapidly formed, which quickly breaks, leading to the formation of a high–drag state and a strong downslope jet in the early stages of the ebb tide. The use of a no–slip bottom boundary condition results in boundary–layer separation from near the top of the sill. This significantly reduces the amplitude of the lee wave during the initial stages of the flow development. For most model runs, a large lee wave is ultimately formed and the separation point moves down the lee of the sill to a position immediately downstream of the lee wave. The transition to this high–drag state is significantly delayed compared with inviscid model runs. Weakened stratification immediately above the sill, inclusion of an eddy viscosity/diffusivity above the bottom and a pool of dense water on the downstream (seaward) side of the sill can all contribute to a delay in the transition to a high–drag state, and can eliminate it entirely. For one model run using a vertical eddy viscosity parametrization above the bottom, a reduction of the vertical diffusivity eliminated the formation of a high–drag state. This suggests that at least in some cases entrainment into the lee wave can cause its growth and result in the formation of a high–drag state.
本文报道了奈特湾海底分层潮流的数值模拟结果。采用非流体静力的二维模型,该模型通过使用垂直涡流粘度/扩散系数参数(仅在底部附近为非零),结合了无滑移的底部边界条件。在无粘模式运行中,快速形成较大的背风波,并迅速破裂,导致退潮初期形成高阻力状态和强下坡射流。无滑移底边界条件的使用导致边界层从基台顶部附近分离。这在气流发展的初始阶段显著降低了背风波的振幅。对于大多数模型运行,最终形成一个大的背风波,分离点沿着基岩的背风方向移动到背风波的下游位置。与非粘滞模型相比,过渡到这种高阻力状态的时间明显延迟。基台上方的分层减弱,底部上方的涡流粘度/扩散系数,以及基台下游(向海)一侧的致密水池,都有助于延迟过渡到高阻力状态,并可以完全消除这种状态。在一个使用底部上方垂直涡流粘度参数化的模型中,垂直扩散系数的降低消除了高阻力状态的形成。这表明,至少在某些情况下,夹带进入背风波会导致其增长,并导致形成高阻力状态。
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引用次数: 45
Analytical approximation of the percolation threshold for overlapping ellipsoids of revolution 重叠旋转椭球渗流阈值的解析近似
Y. Yi, A. Sastry
Analytic approximations for percolation points in two–dimensional and three–dimensional particulate arrays have been reported for only a very few, simple particle geometries. Here, an analytical approach is presented to determine the percolative properties (i.e. statistical cluster properties) of permeable ellipsoids of revolution. We generalize a series expansion technique, previously used by other authors to study arrays of spheres and cubes. Our analytic solutions are compared with Monte Carlo simulation results, and show good agreement at low particle aspect ratio. At higher aspect ratios, the analytic approximation becomes even more computationally intensive than direct simulation of a number of realizations. Additional simulation results, and simplified, closed–form bounding expressions for percolation thresholds are also presented. Limitations and applications of the asymptotic expressions are discussed in the context of materials design and design of sensor arrays.
二维和三维颗粒阵列中渗透点的解析近似只报道了很少的简单颗粒几何形状。本文提出了一种确定可渗透旋转椭球的渗透性质(即统计簇性质)的解析方法。我们推广了一种级数展开技术,这种技术以前被其他作者用于研究球体和立方体的阵列。将解析解与蒙特卡罗模拟结果进行了比较,发现在低粒子长径比条件下,解析解具有较好的一致性。在较高的纵横比下,解析近似比直接模拟许多实现变得更加计算密集。给出了附加的模拟结果,并给出了简化的、封闭的渗流阈值边界表达式。在材料设计和传感器阵列设计的背景下,讨论了渐近表达式的局限性和应用。
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引用次数: 120
On two-phase sediment transport: sheet flow of massive particles 论两相泥沙输运:大块颗粒的片状流
T. Hsu, J. Jenkins, P. Liu
A model is presented for concentrated sediment transport that is driven by strong, fully developed turbulent shear flows over a mobile bed. Balance equations for the average mass, momentum and energy for the two phases are phrased in terms of concentration–weighted (Favre averaged) velocities. Closures for the correlations between fluctuations in concentration and particle velocities are based on those for collisional grain flow. This is appropriate for particles that are so massive that their fall velocity exceeds the friction velocity of the turbulent fluid flow. Particular attention is given to the slow flow in the region of high concentration above the stationary bed. A failure criterion is introduced to determine the location of the stationary bed. The proposed model is solved numerically with a finite–difference algorithm in both steady and unsteady conditions. The predictions of sediment concentration and velocity are tested against experimental measurements that involve massive particles. The model is further employed to study several global features of sheet flow such as the total sediment transport rate in steady and unsteady conditions.
提出了一个由强烈的、充分发展的湍流剪切流在移动床上驱动的集中泥沙输运模型。两相的平均质量、动量和能量的平衡方程用浓度加权(法夫尔平均)速度表示。浓度波动与粒子速度之间关系的闭包是基于碰撞颗粒流的闭包。这适用于质量大到其下落速度超过湍流流动的摩擦速度的粒子。特别注意的是固定床层上方高浓度区域的缓慢流动。引入了一种破坏准则来确定固定床的位置。在稳态和非稳态条件下,采用有限差分算法对模型进行了数值求解。泥沙浓度和流速的预测是根据涉及大质量颗粒的实验测量结果进行检验的。利用该模型进一步研究了稳定和非稳定条件下板流的总输沙率等全局特征。
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引用次数: 226
Absolute-stability results in infinite dimensions 绝对稳定性导致无限维度
R. Curtain, H. Logemann, O. Staffans
We derive absolute–stability results of Popov and circle–criterion type for infinite–dimensional systems in an input–output setting. Our results apply to feedback systems in which the linear part is the series interconnection of an input–output stable linear system and an integrator, and the nonlinearity satisfies a sector condition which, in particular, allows for saturation and deadzone effects. We use the input–output theory developed to derive state–space results on absolute stability applying to feedback systems in which the linear part is the series interconnection of an exponentially stable, well–posed infinite–dimensional system and an integrator.
我们得到了无限维系统在输入输出条件下的波波夫和圆准则型的绝对稳定性结果。我们的结果适用于反馈系统,其中线性部分是输入输出稳定线性系统和积分器的串联互连,非线性满足扇形条件,特别是允许饱和和死区效应。我们使用开发的输入-输出理论来推导绝对稳定性的状态空间结果,应用于反馈系统,其中线性部分是指数稳定的,适定的无限维系统和积分器的串联互连。
{"title":"Absolute-stability results in infinite dimensions","authors":"R. Curtain, H. Logemann, O. Staffans","doi":"10.1098/rspa.2003.1261","DOIUrl":"https://doi.org/10.1098/rspa.2003.1261","url":null,"abstract":"We derive absolute–stability results of Popov and circle–criterion type for infinite–dimensional systems in an input–output setting. Our results apply to feedback systems in which the linear part is the series interconnection of an input–output stable linear system and an integrator, and the nonlinearity satisfies a sector condition which, in particular, allows for saturation and deadzone effects. We use the input–output theory developed to derive state–space results on absolute stability applying to feedback systems in which the linear part is the series interconnection of an exponentially stable, well–posed infinite–dimensional system and an integrator.","PeriodicalId":20722,"journal":{"name":"Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2004-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79686181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 20
Mathematical formulation and analysis of a continuum model for tubulin-driven neurite elongation 微管蛋白驱动的神经突延伸连续模型的数学公式和分析
D. McLean, B. Graham
A partial–differential–equation model of neurite growth is developed. This model is the first of its kind and uses a continuum mechanical approach to model the effects of active transport, diffusion and species degradation of the oligomer tubulin, which is used in the elongation of a single neurite. The model problem is mathematically difficult since it must be solved on a dynamically growing domain. The development and implementation of a spatial transformation to a neurite length coordinate simplifies the problem. Existence and uniqueness of solutions to the steady–state problem are found and shown to be equivalent to solving a nonlinear equation for the steady–state length. This expression is not directly solvable except in certain degenerate cases. However, one system parameter is naturally small and permits solutions in terms of asymptotic series. We identify three growth regimes analytically and verify them numerically. It is then evident that a neuron may easily regulate the extent of its own neuritic growth by increasing or decreasing its tubulin production relative to the active transport/degradation fraction.
建立了神经突生长的偏微分方程模型。该模型是同类模型中的第一个,它使用连续力学方法来模拟微管蛋白的主动运输、扩散和物种降解的影响,微管蛋白用于单个神经突的伸长。模型问题在数学上是困难的,因为它必须在一个动态增长的域上求解。开发和实现到神经突长度坐标的空间变换简化了问题。发现了稳态问题解的存在唯一性,并证明了其等价于求解稳态长度的非线性方程。这个表达式不是直接可解的,除非在某些简并情况下。然而,有一个系统参数自然很小,并且允许解以渐近级数形式存在。我们通过分析确定了三种增长机制,并对其进行了数值验证。因此,很明显,神经元可以通过增加或减少相对于主动运输/降解部分的微管蛋白产生来容易地调节其自身的神经生长程度。
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引用次数: 20
On the higher–order Stokes phenomenon 关于高阶斯托克斯现象
C. Howls, P. J. Langman, A. Olde Daalhuis
During the course of a Stokes phenomenon, an asymptotic expansion can change its form as a further series, prefactored by an exponentially small term and a Stokes multiplier, appears in the representation. The initially exponentially small contribution may nevertheless grow to dominate the behaviour for other values of the asymptotic or associated parameters. In this paper we introduce the concept of a‘higher–order Stokes phenomeno’, at which a Stokes multiplier itself can change value. We show that the higher–order Stokes phenomenon can be used to explain the apparent sudden birth of Stokes lines at regular points and how it is indispensable to the proper derivation of expansions that involve three or more possible asymptotic contributions. We provide an example of how the higher–order Stokes phenomenon can have important effects on the large–time behaviour of partial differential equations.
在Stokes现象的过程中,渐近展开式可以改变其形式,因为在表示中出现了由指数小项和Stokes乘数预因式的进一步级数。然而,最初的指数级小贡献可能会逐渐主导渐近参数或相关参数的其他值的行为。本文引入了“高阶斯托克斯现象”的概念,在这种现象下,斯托克斯乘子本身可以改变值。我们证明了高阶Stokes现象可以用来解释Stokes线在正则点上的明显突然产生,以及它对于包含三个或更多可能渐近贡献的展开式的适当推导是如何不可或缺的。我们提供了一个例子,说明高阶Stokes现象如何对偏微分方程的大时间行为产生重要影响。
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引用次数: 47
Low–frequency decay conditions for a semi–infinite elastic strip 半无限弹性条的低频衰减条件
E. Babenkova, J. Kaplunov
In this paper we investigate in–plane harmonic vibrations of a semi–infinite elastic strip with prescribed edge stresses. Low–frequency decay conditions are established demonstrating the deviation from the classical Saint–Venant principle in quadratic terms in frequency. In the case of the symmetric motion (strip extension), the proposed correction is expressed explicitly in terms of given end data, whereas for the antisymmetric motion (strip bending) this also involves unknown edge displacements. Further applications are defined including those related to dynamic analysis of plates and shells excited by statically self–equilibrated edge loads. The derivation is based on a perturbation approach using the Laplace transform technique. We also address methodological aspects dealing with a continuous eigenspectrum and the two–parametric nature of the problem.
本文研究了具有规定边缘应力的半无限弹性条的面内谐波振动。建立了低频衰减条件,证明了频率二次项与经典圣维南原理的偏差。在对称运动(带材延伸)的情况下,提出的修正是明确地表示在给定的端数据,而对于反对称运动(带材弯曲),这也涉及未知的边缘位移。进一步的应用被定义,包括那些与受静态自平衡边缘载荷激励的板壳的动态分析有关的应用。推导是基于使用拉普拉斯变换技术的微扰方法。我们还讨论了处理连续特征谱和问题的双参数性质的方法方面。
{"title":"Low–frequency decay conditions for a semi–infinite elastic strip","authors":"E. Babenkova, J. Kaplunov","doi":"10.1098/rspa.2003.1275","DOIUrl":"https://doi.org/10.1098/rspa.2003.1275","url":null,"abstract":"In this paper we investigate in–plane harmonic vibrations of a semi–infinite elastic strip with prescribed edge stresses. Low–frequency decay conditions are established demonstrating the deviation from the classical Saint–Venant principle in quadratic terms in frequency. In the case of the symmetric motion (strip extension), the proposed correction is expressed explicitly in terms of given end data, whereas for the antisymmetric motion (strip bending) this also involves unknown edge displacements. Further applications are defined including those related to dynamic analysis of plates and shells excited by statically self–equilibrated edge loads. The derivation is based on a perturbation approach using the Laplace transform technique. We also address methodological aspects dealing with a continuous eigenspectrum and the two–parametric nature of the problem.","PeriodicalId":20722,"journal":{"name":"Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2004-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80181428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 25
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Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences
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