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Numerical modelling of hydro-mechanical behaviour of collapsible soils 湿陷性土壤水力学特性的数值模拟
Pub Date : 2007-11-29 DOI: 10.1002/CNM.1071
L. Costa, I. Pontes, L. Guimarães, S. R. M. Ferreira
This paper presents a numerical simulation of the response of unsaturated soil under different loads, with special attention devoted to the phenomenon of pore collapse during wetting. A coupled hydro-mechanical formulation, implemented in the computational code CODE_BRIGHT, is first presented. Then the model is applied to assess material parameter from laboratory tests and to simulate, as boundary value problems, new and appealing in situ tests designed in the Federal University of Pernambuco. The soil considered is a collapsible soil located in the semi-arid region of the northeast of Brazil. Two situations are analysed: (i) the soil is initially at its natural water content and then flooded at some determined stress level, (ii) the soil is previously flooded and then loaded. Comparison between output results of numerical simulations and experimental data shows a very good agreement, which validate to some extent the proposed experimental procedure and the model formulation. Copyright © 2007 John Wiley & Sons, Ltd.
本文对非饱和土在不同荷载作用下的响应进行了数值模拟,重点研究了润湿过程中孔隙坍塌现象。首先提出了一个耦合的水-力公式,在计算代码CODE_BRIGHT中实现。然后将该模型应用于评估实验室试验的材料参数,并模拟在伯南布哥联邦大学设计的新的和有吸引力的原位试验的边界值问题。所考虑的土壤是位于巴西东北部半干旱地区的可折叠土壤。分析了两种情况:(i)土壤最初处于其自然含水量,然后在某个确定的应力水平下被淹没;(ii)土壤先前被淹没,然后被加载。数值模拟输出结果与实验数据的比较表明,两者吻合较好,在一定程度上验证了所提出的实验步骤和模型公式。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 18
Hydraulic conductivity estimation in partially saturated soils using a full-Newton method 用全牛顿法估算部分饱和土的导流系数
Pub Date : 2007-11-29 DOI: 10.1002/CNM.1064
L. Guarracino, J. Santos
An iterative algorithm based on a full-Newton method for the estimation of the saturated hydraulic conductivity k from drainage experiments is presented. The water flow in the unsaturated zone is assumed to be described by Richards equation and the well-known van Genuchten constitutive model. The cost functional used for the parameter optimization is defined as the L2-error between the calculated pressure head values and the observed data at discrete points in the soil profile during the drainage process. The derivative of pressure head with respect to the parameter k is obtained as the solution of a differential equation with appropriate boundary and initial conditions. A Galerkin finite element procedure is used to obtain approximated solutions of the two differential problems involved in each iteration: the direct problem and the derivative of the functional. The algorithm was implemented in one-dimensional domains and used to estimate k in layered soils using both synthetically generated data and observed data from an experimental plot in the Azul River basin (Buenos Aires, Argentina). Numerical examples show that the proposed algorithm yields very good estimations of the saturated hydraulic conductivity and becomes a promising method for in situ estimation of this parameter. Copyright © 2007 John Wiley & Sons, Ltd.
提出了一种基于全牛顿法的排水试验饱和导电性k的迭代估计算法。假定非饱和区水流由Richards方程和著名的van Genuchten本构模型描述。用于参数优化的代价函数定义为排水过程中计算压力水头值与土壤剖面离散点观测数据之间的l2误差。得到压头对参数k的导数为具有适当边界和初始条件的微分方程的解。采用伽辽金有限元法求解每次迭代中涉及的两个微分问题:直接问题和泛函导数问题的近似解。该算法在一维域中实现,并使用Azul河流域(阿根廷布宜诺斯艾利斯)的一个实验地块的合成生成数据和观测数据来估计层状土壤中的k。数值算例表明,该算法能很好地估计饱和导水率,是一种很有前途的原位估计饱和导水率的方法。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 2
Algorithm for analysis of periodic oscillations of structural systems with geometric nonlinearity 几何非线性结构系统周期振动分析算法
Pub Date : 2007-11-19 DOI: 10.1002/CNM.1073
M. Ragulskis, K. Ragulskis
An algorithm for analysis of periodic oscillations of forced elastic systems with geometric nonlinearity is presented in this paper. Modal decomposition of the solution, computation of periodic oscillations for every eigenmode and estimation of geometric nonlinearities using the method of initial deformations enable to construct a computational technique that can be very effective in computation of steady-state periodic motions of slightly damped structures under periodic forcing. It is shown that the developed algorithm can be successfully exploited for the calculation of structural response of a micromechanical cantilever. Copyright © 2007 John Wiley & Sons, Ltd.
提出了一种具有几何非线性的强迫弹性系统周期振动分析算法。通过对解的模态分解、每个特征模态的周期振动计算和初始变形法的几何非线性估计,构建了一种可以非常有效地计算周期强迫下微阻尼结构稳态周期运动的计算技术。结果表明,所开发的算法可以成功地用于微机械悬臂梁的结构响应计算。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 1
Computation of stress intensity factors for through cracks in plates using p-version finite element method 用p型有限元法计算板内贯通裂纹的应力强度因子
Pub Date : 2007-11-19 DOI: 10.1002/CNM.1065
K. Munaswamy, Ramalakshmi Pullela
The present study concerns the analysis of bending of plates and shells subjected to various boundary conditions and load. Bending stress intensity factors for plates containing through-thickness crack under edge bending load are evaluated. To accomplish this task, hierarchical degenerated plate/shell and crack-tip singular plate/shell elements were developed. The hierarchical degenerated plate shell element has four corner nodes, four mid-side nodes and one central node on the mid-surface of the shell geometry with five degrees of freedom at each node. p-Version shape functions up to order seven were used for defining the displacement field. Enriching the displacement field with the asymptotic displacement field near the crack tip, a crack-tip singular plate/shell element was developed. Some benchmark problems were analyzed and compared. Analyses were performed to obtain the stress intensity factors of plate with through-thickness crack using singular hierarchical degenerated plate/shell element around the crack tip. Numerical results obtained from the present element formulations are compared with analytical/numerical solutions available from literature. It is inferred that numerical results are in good agreement with the benchmark plate and shell problems. Copyright © 2007 John Wiley & Sons, Ltd.
本文研究了板壳在各种边界条件和载荷作用下的弯曲问题。对含透厚裂纹板在边缘弯曲载荷作用下的弯曲应力强度因子进行了计算。为此,建立了分层退化板壳单元和裂纹尖端奇异板壳单元。分层退化板壳单元在壳几何的中表面具有4个角节点、4个中侧节点和1个中心节点,每个节点有5个自由度。采用最高七阶的p-版本形状函数来定义位移场。利用裂纹尖端附近的渐近位移场来丰富位移场,建立了裂纹尖端奇异板壳单元。对一些基准问题进行了分析和比较。采用裂纹尖端周围奇异阶跃退化板壳单元,对含透厚裂纹的板进行了应力强度因子分析。数值结果得到了由目前的元素公式与解析/数值解从文献中可用的比较。计算结果与基准板壳问题吻合较好。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 7
A diagonal offset algorithm for the polynomial point interpolation method 一种对角偏移算法的多项式点插值方法
Pub Date : 2007-11-19 DOI: 10.1002/CNM.1076
B. Kanber, Ö. Bozkurt
A diagonal offset algorithm is presented to overcome the singular moment matrix problem in the polynomial point interpolation method. The value of terms in the diagonal line of moment matrix is changed with different offsets. The effects of the offsets on the Kronecker delta function and partition of unity properties are investigated and an optimum offset range is proposed. The algorithm is validated solving some patch tests and various elasticity problems in 2-D domain. Their results demonstrate that the proposed algorithm is very easy to implement and completely solves the singular moment matrix problem. The accuracy of the method with proposed algorithm is investigated for regular and irregular local domains. Copyright © 2007 John Wiley & Sons, Ltd.
针对多项式点插值法中的奇异矩矩阵问题,提出了一种对角偏移算法。矩矩阵对角线上的项的值随着偏移量的不同而变化。研究了偏移量对Kronecker函数和单位性质划分的影响,提出了最优偏移量范围。通过对一些补丁测试和二维弹性问题的求解,验证了该算法的有效性。结果表明,该算法易于实现,完全解决了奇异矩矩阵问题。研究了该方法在规则局部域和不规则局部域的精度。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 3
Analysis of rubber‐like materials using meshless local Petrov–Galerkin (MLPG) method 用无网格局部Petrov-Galerkin (MLPG)方法分析类橡胶材料
Pub Date : 2007-11-19 DOI: 10.1002/CNM.1066
R. Batra, M. Porfiri
Large deformations of rubber-like materials are analyzed by the meshless local Petrov–Galerkin (MLPG) method. The method does not require shadow elements or a background mesh and therefore avoids mesh distortion difficulties in large deformation problems. Basis functions for approximating the trial solution and test functions are generated by the moving least-squares (MLS) method. A local mixed total Lagrangian weak formulation of non-linear elastic problems is presented. The deformation gradient is split into deviatoric and dilatational parts. The strain energy density is expressed as the sum of two functions: one is a function of deviatoric strains and the other is a function of dilatational strains. The incompressibility or near incompressibility constraint is accounted for by introducing the pressure field and penalizing the part of the strain energy density depending upon the dilatational strains. Unlike in the mixed finite element formulation, in the MLPG method there is no need for different sets of basis functions for displacement and pressure fields. Results computed with the MLPG method for a few sample problems are found to compare very well with the corresponding analytical solutions. Copyright © 2007 John Wiley & Sons, Ltd.
采用无网格局部Petrov-Galerkin (MLPG)方法分析了类橡胶材料的大变形。该方法不需要阴影元素或背景网格,因此避免了在大变形问题中网格失真的困难。利用移动最小二乘法生成近似试验解和测试函数的基函数。给出了非线性弹性问题的局部混合全拉格朗日弱公式。变形梯度分为偏变形和膨胀变形两部分。应变能密度表示为两个函数的和:一个是偏应变的函数,另一个是膨胀应变的函数。不可压缩性或近不可压缩性约束是通过引入压力场和惩罚依赖于膨胀应变的应变能密度部分来解释的。与混合有限元公式不同,MLPG方法不需要为位移场和压力场设置不同的基函数集。用MLPG方法计算的结果与相应的解析解非常吻合。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 6
A layer‐integrated approach for shallow water free‐surface flow computation 浅水自由表面流计算的分层集成方法
Pub Date : 2007-11-16 DOI: 10.1002/CNM.1061
M. Hung, T. Hsieh, T. Tsai, Jinn‐Chuang Yang
A novel semi-three-dimensional (semi-3D) layer-integrated approach was proposed in this study for the shallow water free-surface flow computation. A quadratic shape function proposed to approximate the velocity distribution in the layer ensures the continuity of velocities and shear stresses at interfaces. To discretize the governing equations, the finite volume formulation with staggered grid is used. As the two-dimensional (2D) sub-model for locating the free surface is not needed in this approach, the computational time consumption has been dramatically reduced. The model was verified through the wind-induced circulation in a closed basin by comparing the velocity profiles to the analytical solution. The formation of the velocity profiles due to change of viscosity distribution and the evolution process of water surface slope were also investigated. Further, the eddy viscosity is estimated by a function related to discharge, water depth, and Manning's n under the assumption of parabolic distribution of longitudinal velocity along the vertical direction for open channel flows. Two designed hypothetical cases were conducted to examine the proposed eddy viscosity relation and to demonstrate the capabilities of the proposed model. Copyright © 2007 John Wiley & Sons, Ltd.
本文提出了一种新的浅水自由水面流计算的半三维(半三维)分层集成方法。提出了一种近似层内速度分布的二次形函数,保证了界面处速度和剪应力的连续性。为了使控制方程离散化,采用了交错网格的有限体积公式。由于该方法不需要二维子模型来定位自由曲面,因此大大减少了计算时间。通过封闭盆地风致环流试验,将风速剖面与解析解进行对比,验证了模型的正确性。研究了黏度分布变化导致的速度剖面的形成以及水面坡度的演化过程。此外,在明渠水流纵向速度沿垂直方向呈抛物线分布的假设下,通过与流量、水深和Manning’s n相关的函数来估计涡动粘度。设计了两个假设的案例来检验所提出的涡流粘度关系,并证明所提出的模型的能力。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 1
A Trefftz method for evaluating the T‐stress for cracks emanating from a hole in a rectangular plate 矩形板孔洞裂纹T应力的Trefftz方法
Pub Date : 2007-11-15 DOI: 10.1002/CNM.1072
Y. Chen, Z. X. Wang, X. Y. Lin
This paper proposes a Trefftz method for evaluating the T-stress for cracks emanating from a hole in a rectangular plate. In this method, the displacement and the stress field are an elasticity solution, which is derived from complex potentials. The complex potentials are assumed in a series form with undetermined coefficients. After using the minimum potential energy principle, an algebraic equation for the undetermined coefficients can be formulated. The coefficients can be obtained from the equation, and the whole stress field is determined. Stress intensity factor and T-stress can be evaluated immediately from the known solution. Merit of the suggested method is addressed. For three particular cases, R=0, R/w=0.25 and R/w=0.5, the computed results are tabulated. Copyright © 2007 John Wiley & Sons, Ltd.
本文提出了一种计算矩形板孔洞裂纹t应力的Trefftz方法。在该方法中,位移和应力场是由复势导出的弹性解。复势假定为带待定系数的级数形式。利用最小势能原理,可以得到待定系数的代数方程。由方程可求出各系数,并确定整个应力场。应力强度因子和t应力可由已知解立即求出。提出了该方法的优点。对于R=0、R/w=0.25和R/w=0.5三种特殊情况,计算结果制成表格。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 1
Polynomial basis functions on pyramidal elements 金字塔元上的多项式基函数
Pub Date : 2007-11-09 DOI: 10.1002/CNM.1070
M. Bluck, S. Walker
Pyramidal elements are necessary to effect the transition from tetrahedral to hexahedral elements, a common requirement in practical finite element applications. However, existing pyramidal transition elements suffer from degeneracy or other numerical difficulties, requiring, at the least, warnings and care in their use. This paper presents a general technique for the construction of nodal basis functions on pyramidal finite elements. General forms for basis functions of arbitrary order are presented. The basis functions so derived are fully conformal and free of degeneracy. Copyright © 2007 John Wiley & Sons, Ltd.
锥体单元是实现四面体向六面体单元过渡所必需的,这是实际有限元应用中常见的要求。然而,现有的金字塔过渡元存在退化或其他数值上的困难,至少在使用时需要警告和小心。本文给出了在锥体有限元上构造节点基函数的一般技术。给出了任意阶基函数的一般形式。由此导出的基函数是完全保角的,没有简并性。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 10
On the applicability of the pseudospectral Legendre method for edge detection 论伪谱勒让德方法在边缘检测中的适用性
Pub Date : 2007-11-09 DOI: 10.1002/CNM.1068
F. Ahmad, R. M. Castellane, E. L. Miller
The pseudospectral Legendre method is utilized to develop a gradient detector. This detector is proposed in this communication for the detection of edges in discrete images. The detector can be applied in both the horizontal and vertical directions. It is a separable detector where the smoothing orthogonal part resembles a one-dimensional notch filter. Discrete Canny's criteria values of the detector are similar to those of other known basic derivative filters. An example is given in which this detector is utilized and its applicability and validity are supported using comparison results from the use of the Sobel filter. Copyright © 2007 John Wiley & Sons, Ltd.
利用伪光谱勒让德方法研制了一种梯度检测器。该检测器在本次通信中被提出用于检测离散图像中的边缘。该探测器可应用于水平和垂直方向。它是一种可分离检测器,其平滑正交部分类似于一维陷波滤波器。该检测器的离散Canny准则值与其他已知的基本导数滤波器的准则值相似。给出了该检测器的应用实例,并通过与索贝尔滤波器的比较结果验证了该检测器的适用性和有效性。版权所有©2007 John Wiley & Sons, Ltd
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引用次数: 0
期刊
Communications in Numerical Methods in Engineering
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