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INDENTATION OF THIN COATINGS: THEORETICAL AND EXPERIMENTAL INVESTIGATION 薄涂层的压痕:理论和实验研究
Pub Date : 2022-08-02 DOI: 10.2495/be450141
S. Aizikovich, A. Nikolaev, E. Sadyrin, L. Krenev, V. Irkha, A. Galybin
An effective mathematical model is proposed for describing the experiment on indentation of samples with layered or functionally graded coatings. It is based on the solution of the contact problem of the theory of elasticity of indentation of a punch into elastic half-space with a coating. The results of mathematical modelling and experiments on indentation of the ZnO coating manufactured by the method of pulsed laser deposition on a silicon substrate are compared. The microgeometrical characteristics, as well as the chemical composition of the coating, were studied.
提出了一种有效的数学模型来描述层状或功能梯度涂层样品的压痕实验。该方法是在求解带涂层弹性半空间冲床压痕弹性理论接触问题的基础上建立的。对脉冲激光沉积法制备ZnO薄膜压痕的数学模型和实验结果进行了比较。研究了涂层的微观几何特性和化学成分。
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引用次数: 0
FINITE LINE METHOD FOR SOLVING CONVECTION–DIFFUSION EQUATIONS 求解对流扩散方程的有限线法
Pub Date : 2022-08-02 DOI: 10.2495/be450041
Xiaowei Gao, Hua‐Yu Liu, Jingdong Ding
In this paper, a creative collocation-type numerical method, the Finite Line Method (FLM), is proposed for solving general convection–diffusion equations. The method is based on the use of a finite number of lines crossing each collocation point, and the Lagrange polynomial interpolation formulation to construct the shape functions over each line. The directional derivative technique is proposed to derive the first-order partial derivatives of any physical variables with respect to the global coordinates for the high-dimensional problems from the lines’ ones and the high-order derivatives are evaluated from a recurrence formulation. The derived spatial partial derivatives are directly substituted into the governing partial differential equations and related boundary conditions of the convection–diffusion equations to set up the system of equations. The finite number of lines crossing each collocation point is called the line set. To evaluate the convection and diffusion terms accurately, two different line sets are used for these two terms, which are called the convection line set and central line set, respectively. The former is formed according to the velocity direction and is used for performing the upwind scheme in the computation of the convection term, and the latter is formed by the crossed lines including the collocation point at the center. A numerical example will be given to verify the correctness and stability of the proposed method.
本文提出了求解一般对流扩散方程的一种创造性的配位型数值方法——有限线法(FLM)。该方法是基于使用有限数量的线穿过每个搭配点,并使用拉格朗日多项式插值公式来构造每条线上的形状函数。针对高维问题,提出了用直线的一阶偏导数求任意物理变量对全局坐标的一阶偏导数的方法,并用递推公式求出高阶导数。将导出的空间偏导数直接代入控制偏微分方程和对流扩散方程的相关边界条件,建立方程组。穿过每个搭配点的有限条线称为线集。为了准确地评估对流和扩散项,对这两项分别使用两个不同的线集,分别称为对流线集和中心线集。前者是根据速度方向形成的,在对流项的计算中用于执行逆风方案,后者是由包括中心搭配点在内的交叉线组成的。通过数值算例验证了所提方法的正确性和稳定性。
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引用次数: 0
LOCALIZED SINGULAR BOUNDARY METHOD FOR SOLVING THE CONVECTION–DIFFUSION EQUATION WITH VARIABLE VELOCITY FIELD 求解变速场对流扩散方程的局部奇异边界法
Pub Date : 2022-08-02 DOI: 10.2495/be450101
J. Mužík, R. Bulko
This paper focuses on deriving the local variant of the singular boundary method (SBM) to solve the convection–diffusion equation. Adopting the combination of an SBM and finite collocation, one obtains the localized variant of SBM. Unlike the global variant, local SBM leads to a sparse matrix of the resulting system of equations, making it much more efficient to solve large-scale tasks. It also allows solving velocity vector variable tasks, which is a problem with global SBM. The article presents the steady numerical example for the convection–diffusion problem with variable velocity field and examines the dependence of the accuracy of the solution on the nodal grid’s density and the subdomain’s size.
本文重点推导了求解对流扩散方程的奇异边界法(SBM)的局部变体。将SBM与有限配置相结合,得到了SBM的局部化形式。与全局变量不同,局部SBM导致结果方程组的稀疏矩阵,使其更有效地解决大规模任务。它还允许求解速度矢量可变任务,这是全局SBM的一个问题。本文给出了变速场对流扩散问题的定常数值算例,并考察了解的精度与节点网格密度和子域大小的关系。
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引用次数: 0
SINGULAR AND HYPERSINGULAR INTEGRAL EQUATIONS IN FLUID–STRUCTURE INTERACTION ANALYSIS 流固耦合分析中的奇异和超奇异积分方程
Pub Date : 2022-08-02 DOI: 10.2495/be450061
V. Gnitko, Artem Karaiev, Kyryl Degtyariov, I. Vierushkin, E. Strelnikova
The paper presents new computational techniques based on coupled boundary and finite element methods to study fluid–structure interaction problems. Thin shells and plates are considered as structure elements interacting with an ideal and incompressible liquid. To describe the motion of both structural elements and the fluid, the basic relations of the continuous mechanics are incorporated. The liquid pressure is determined by applying the Laplace equation. Two kinds of boundary value problems are considered corresponding to one-sided and two-sided contact of structural elements with the liquid. Integral equations for numerical simulation of pressure are obtained. For a two-sided contact of the structural element with the liquid, hypersingular integral equations are received, whereas singular integral equations with logarithmic singularities describe the problems of one-sided contact. Considering the structure axial symmetry, the integral equations are reduced to one-dimensional ones. The finite element method for determining modes and frequencies of the elastic structure coupled with boundary element method for the hypersingular integral equation is implemented to find the fluid pressure on the structure element with two-sided contact with the liquid. The liquid pressure evaluation in axisymmetric problems is reduced to one-dimensional integral equations with kernels in the form of elliptic integrals. The effective technique is developed for numerical simulation of obtained singular integrals. The same technique is extended to hypersingular integral equations. The frequencies and modes of structure vibrations taking into account the added masses of the liquid are obtained. Thin circular plates and shells of revolution are considered as structure elements in numerical simulations. The accuracy and reliability of the proposed method are ascertained.
本文提出了基于耦合边界法和有限元法研究流固耦合问题的新计算技术。薄壳和薄板被认为是与理想的不可压缩液体相互作用的结构元件。为了描述结构单元和流体的运动,结合了连续力学的基本关系。液体压强是由拉普拉斯方程决定的。考虑了结构单元与液体的单面接触和双面接触的两类边值问题。得到了压力数值模拟的积分方程。对于结构单元与液体的双面接触问题,采用了超奇异积分方程,而单面接触问题采用了具有对数奇异性的奇异积分方程。考虑结构轴对称,将积分方程简化为一维积分方程。采用确定弹性结构模态和频率的有限元法,结合超奇异积分方程的边界元法,求出与液体双面接触的结构单元上的流体压力。将轴对称问题中液体压力的计算简化为具有椭圆积分形式核的一维积分方程。提出了一种有效的方法来对得到的奇异积分进行数值模拟。将同样的方法推广到超奇异积分方程。得到了考虑液体质量增加的结构振动频率和振型。在数值模拟中,将旋转薄板和圆壳作为结构单元。验证了该方法的准确性和可靠性。
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引用次数: 1
INTEGRAL EQUATIONS FOR MODELLING OF FRACTURE INITIATION AND DEVELOPMENT IN LAYERED POROELASTIC MEDIA 层状孔隙弹性介质中裂缝起裂与发育的积分方程模拟
Pub Date : 2022-08-02 DOI: 10.2495/be450081
A. Galybin, S. Aizikovich
In this study, we consider a special incorrectly posed boundary value problem of the theory of cracks, which arises when modelling the initiation and development of fracture on the interface between poroelastic materials. The main feature of the problem is the formulation of boundary conditions, which is different from the standard formulations. The problem is considered for a strip, where three conditions are set on one side of the strip and one on the other side, which makes it possible to classify this formulation as a semi-inverse one.
在本研究中,我们考虑了在模拟孔隙弹性材料界面上断裂的起裂和发展时出现的一个特殊的错误的裂纹理论边值问题。该问题的主要特点是边界条件的表述,不同于标准表述。考虑带的问题,其中带的一侧设置了三个条件,另一侧设置了一个条件,这使得将该公式分类为半逆公式成为可能。
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引用次数: 0
RECENT ADVANCES IN LOCALIZED COLLOCATION SOLVERS BASED ON SEMI-ANALYTICAL BASIS FUNCTIONS 基于半解析基函数的局部配置求解方法研究进展
Pub Date : 2022-08-02 DOI: 10.2495/be450121
Wenzhi Xu, Zhuojia Fu
This paper presents a brief overview of recently developed localized collocation solvers and their various engineering applications. The research progress of localized collocation solvers is discussed, and their basic mathematical formulations are summarized. Finally, applications for thermal analysis in functionally graded materials and steady-state convection-diffusion equation with nonhomogeneous term are given.
本文简要介绍了近年来发展起来的局部配置求解器及其各种工程应用。讨论了局部配点法的研究进展,总结了它们的基本数学表达式。最后给出了在功能梯度材料热分析和非齐次稳态对流扩散方程中的应用。
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引用次数: 0
IMPLICATIONS OF STOKES–CARTAN THEOREM TO TIME-HARMONIC ACOUSTIC BOUNDARY INTEGRAL EQUATION FORMULATIONS stokes-cartan定理对时谐声学边界积分方程的意义
Pub Date : 2022-08-02 DOI: 10.2495/be450071
P. Schafbuch
Direct boundary integral equation (BIE) formalisms for wave radiation and scattering have been stable and universally accepted for decades. Yet, the classic separation of variables (SOV) solutions for acoustic radiation and scattering from spheres do not always agree with BEM results. For certain conditions, the boundary acoustic field predicted by low-frequency SOV and BEM methods match exactly and for other situations predicted fields by the two methods are complex-conjugates of each other. While this difference is subtle, modern BEM literature has not cited the transfer of known mathematics to this engineering application. Tracing signs within BEM code is daunting. To create a lucid and reproducible record of the issue and its resolution, this paper presents an analytical BIE solution for spherical geometry based on a Legendre polynomial simplex element and a power series of the spatial phase term of the Helmholtz operator Fundamental Solution. Optical theorem reasoning suggests the traditional BIE approach is the method in error. The core of this issue is the application of the divergence theorem (strictly true only for real-valued functions) to time-harmonic (complex-valued) formulations. The conjugation of spatial derivatives of a complex-valued field can be understood from Wirtinger derivatives and Dolbeault operators. This issue manifests itself when the Sommerfeld radiation condition is applied for unbounded domains. Exterior calculus ideas properly unite, generalize and extend a variety of related classical theorems including divergence, Cauchy’s integral theorem from complex analysis, and Green’s identities used in constructing a BIE. The resulting Stokes–Cartan theorem is properly applied to acoustic scattering in 3D within this paper and invokes corrections which match BIE and SOV solutions for the low frequency problems investigated.
几十年来,波辐射和散射的直接边界积分方程(BIE)形式一直是稳定和普遍接受的。然而,经典的球声辐射和散射的分离变量(SOV)解并不总是与边界元计算结果一致。在某些条件下,低频SOV法和边界元法预测的边界声场是精确匹配的,而在其他情况下,两种方法预测的边界声场是复共轭的。虽然这种差异是微妙的,但现代BEM文献并没有将已知的数学转移到这种工程应用中。在BEM代码中跟踪符号是令人生畏的。为了创造一个清晰和可重复的问题及其解决方法的记录,本文提出了一个基于勒让德多项式单纯形元和亥姆霍兹算子基本解的空间相位项幂级数的球面几何解析BIE解。光学定理推理表明,传统的BIE方法是一种错误的方法。该问题的核心是将散度定理(仅对实值函数严格成立)应用于时调和(复值)公式。复值域空间导数的共轭可以用Wirtinger导数和Dolbeault算子来理解。当将Sommerfeld辐射条件应用于无界域时,这个问题就表现出来了。外部微积分思想恰当地统一、推广和扩展了各种相关的经典定理,包括散度定理、复数分析中的柯西积分定理和用于构造BIE的格林恒等式。所得的Stokes-Cartan定理在本文中适用于三维声散射,并对所研究的低频问题调用了与BIE和SOV解相匹配的修正。
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引用次数: 0
ACCURATE FAST MULTIPOLE SCHEME FOR THE BOUNDARY ELEMENT ANALYSIS OF THREE-DIMENSIONAL LINEAR POTENTIAL PROBLEMS 三维线性位势问题边界元分析的精确快速多极格式
Pub Date : 2022-08-02 DOI: 10.2495/be450011
N. Dumont, Hilton Marques SOUZA SANTANA
This paper is part of a research work to implement, test, and apply a novel numerical tool that can simulate on a personal computer and in just a few minutes a problem of potential or elasticity with up to tens of millions of degrees of freedom. The first author’s group has already developed their own version of the fast multipole method (FMM) for two-dimensional problems, which relies on a consistent construction of the single-layer potential matrix of the collocation boundary element method so that ultimately only polynomial terms (as for the double-layer potential matrix) are required to be integrated along generally curved segments related to a given field expansion pole. The core of the present paper is the mathematical assessment of the double expansions needed in the 3D FMM. The 3D implementation is combined with a particular formulation for linear triangle elements in which all integrations for adjacent source point and boundary element are carried out analytically. As a result, numerical approximations are due exclusively to the FMM series truncations. This allows isolating and testing truncation errors incurred in the series expansions and thus for the first time properly assessing the mathematical features of the FMM, as illustrated by means of two examples. Adaptive numerical quadratures as well as the complete solution of a mixed boundary problem using a GMRES solver, for instance, are just additional tasks and, although already implemented, are not reported herein.
本文是一项研究工作的一部分,旨在实现、测试和应用一种新颖的数值工具,该工具可以在个人计算机上模拟,并在短短几分钟内模拟出具有高达数千万自由度的潜在或弹性问题。第一作者的小组已经开发了他们自己的二维问题快速多极方法(FMM),它依赖于搭配边界元方法的单层势矩阵的一致构造,因此最终只需要沿与给定场展开极相关的一般弯曲段积分多项式项(对于双层势矩阵)。本文的核心是对三维FMM所需的双展开式的数学评价。三维实现与线性三角形元素的特定公式相结合,其中相邻源点和边界元素的所有积分都以解析方式进行。因此,数值近似完全是由于FMM系列截断。这允许隔离和测试序列展开中产生的截断错误,从而首次正确评估FMM的数学特征,如两个示例所示。例如,自适应数值积分以及使用GMRES解算器的混合边界问题的完整解只是附加任务,尽管已经实现,但本文未作报道。
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引用次数: 2
CERTAIN RELATIONS BETWEEN THE MAIN MATRIX CONDITION NUMBER AND MULTIQUADRIC SHAPE PARAMETER IN THE NON-SYMMETRIC KANSA METHOD 非对称kansa法中主矩阵条件数与多二次曲面形状参数之间存在一定的关系
Pub Date : 2022-08-02 DOI: 10.2495/be450111
O. Popczyk, G. Dziatkiewicz
The Kansa method is one of the most popular meshless methods today. Its ease of implementation, high order of interpolation and ease of application to problems with complex geometry constitute its advantage over many other methods for solving partial differential equation-based problems. However, the Kansa method has a significant disadvantage – the need to find the shape parameter value despite these undeniable advantages. There are dozens of algorithms for finding a good shape parameter value, but none of them is proven to be optimal. Therefore, there is still a great scientific need to research new algorithms and improve those already known. In this work, an algorithm based on the study of the oscillation of certain shape parameter functions concerning the problems of two-dimensional heat flow in a material with spatially variable thermophysical parameters was investigated. It has been shown that algorithms of this type allow this class of problems to achieve solutions with high accuracy. At the same time, it was indicated that this direction of development of algorithms for searching for a good value of the shape parameter is auspicious. It is because this algorithm can be extended to a wide range of functions whose oscillation is studied and, consequently, its application to a broader range of problems.
Kansa方法是当今最流行的无网格方法之一。它易于实现、高阶插值和易于应用于复杂几何问题构成了它比许多其他求解偏微分方程问题的方法的优势。然而,Kansa方法有一个明显的缺点——尽管有这些不可否认的优点,但需要找到形状参数值。有几十种算法用于寻找良好的形状参数值,但没有一种被证明是最优的。因此,仍然有很大的科学需要研究新的算法和改进那些已知的。本文研究了具有空间可变热物性参数的材料中二维热流问题的一种基于某些形状参数函数振荡研究的算法。已经证明,这种类型的算法允许这类问题获得高精度的解决方案。同时指出,这种寻找形状参数的良好值的算法的发展方向是吉祥的。这是因为该算法可以推广到更广泛的振荡函数的研究范围,从而使其应用于更广泛的问题。
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引用次数: 0
QUADRATURE RULE FOR SINGULAR INTEGRALS IN COMMON ENGINEERING PROBLEMS 一般工程问题中奇异积分的求积分规则
Pub Date : 2022-08-02 DOI: 10.2495/be450051
Rocío Velázquez Mata, Antonio Romero ORÕNEZ, Pedro GALIN Barrera
This paper describes a general method to compute the boundary integral equation for common engineering problems. The proposed procedure consists of a new quadrature rule to evaluate singular and weakly singular integrals. The methodology is based on the computation of the quadrature weights by solving an undetermined system of equations in the minimum norm sense. The B´ezier–Bernstein form of a polynomial is also implemented as an approximation basis to represent both geometry and field variables. Therefore, exact boundary geometry is considered, and arbitrary high-order elements are allowed. This procedure can be used for any element node distribution and shape function. The validity of the method is demonstrated by solving a two-and-a-half-dimensional elastodynamic benchmark problem.
本文介绍了计算常见工程问题边界积分方程的一般方法。提出了一种新的求奇异积分和弱奇异积分的求积分规则。该方法是通过在最小范数意义上求解待定方程组来计算正交权值。多项式的B´ezier-Bernstein形式也被实现为表示几何和场变量的近似基。因此,考虑了精确的边界几何,并允许任意高阶元素。本程序可用于任何元素的节点分布和形状函数。通过对一个二维半弹性动力基准问题的求解,验证了该方法的有效性。
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引用次数: 0
期刊
WIT transactions on engineering sciences
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