基于镜像法提取多层介质中3D电容参数的研究

提出了一种适用于任意多层电介质分层结构中的3D互连电容参数提取的新方法--反射镜像法.该方法无需对格林函数进行推导,而是根据自由电荷反射原理计算反射镜像的位置和镜像电荷系数从而获得各级镜像分布,继而计算任意多层电介质环境下的3D电容,包括底层或顶层介质接地情况下的3D电容.该方法可克服级数形式的格林函数因受限于电介质分层数目而难以适应大规模集成电路中复杂多变电介质环境下的3D电容参数提取问题.通过对导体面元建立层次式数据结构,这一方法可以利用层次式算法(hierarchical method)实现计算加速.实验证明,该方法能在保证可靠精度的情况下达到迅速收敛,与层次式加速算法结合后,计算效率可达到FastCap法的数倍.     

A finite-element method for computing three-dimensional electromagnetic fields in inhomogeneous media

A finite-element method is presented that is particularly suited for the computer modeling of three-dimensional electromagnetic fields in inhomogeneous media. It employs a new type of linear vectorial expansion functions. Across an interface where the constitutive coefficients are discontinuous, they have the following properties: (1) the continuity of the tangential components of the electric and the magnetic field strengths is exactly preserved, (2) the normal component of the electric and the magnetic field strengths are allowed to jump and (3) the electric and the magnetic fluxes are continuous within the pertaining degree of approximation. The system of equations from which the expansion coefficients are obtained is generated by applying a Galerkin-type weighted-residual method. Numerical experiments are described that illustrate the efficiency of our elements, and the computational costs of the method.     

二维非均质材料应力场的数值化计算方法

等效夹杂方法是求解含杂质材料弹性应力场的一种有效方法,但是其解析求解只适用于椭球/椭圆类杂质问题。本文提出一种基于等效夹杂方法的数值化计算方法,介绍了其基本理论,并引入共轭梯度法求解该方法的一致性条件线性方程组。该方法通过计算区域的数值离散,能够实现对二维任意形状杂质弹性场的求解。将该方法得到的结果与解析解进行比较,验证了该方法的有效性。讨论了数值化等效夹杂方法在效率以及收敛性上的表现。通过对比证明,利用共轭梯度法实现该方法,能在保持精度的同时,相较于高斯消元法具有较大的效率优势。最后通过半椭圆杂质和氧化锆/氧化铝共挤复合材料算例验证了该方法处理任意形状杂质的能力。     

Numerical simulation of substation grounding grids buried in both horizontal and vertical multilayer earth model

In the simulation of quasi‐static electromagnetic fields produced by a point source located in both horizontal and vertical multilayer media, the conventional image method requires an infinite number of images to get an accurate solution, while the method of quasi‐static complex images needs only a few ones. Based on the method of quasi‐static complex images, the closed form of Green's function of a point source in both horizontal and vertical multilayer earth model is derived through matrix pencil (MP) approach. The fast convergent Galerkin's type of boundary element method (BEM) is taken to simulate and analyse a grounding system including floating electrode with any complicated structure, which can be located anywhere in horizontal or vertical multilayer earth model. Copyright © 2006 John Wiley & Sons, Ltd.     

Exposure to inhomogeneous static magnetic field beneficially affects allergic inflammation in a murine model

Previous observations suggest that static magnetic field (SMF)-exposure acts on living organisms partly through reactive oxygen species (ROS) reactions. In this study, we aimed to define the impact of SMF-exposure on ragweed pollen extract (RWPE)-induced allergic inflammation closely associated with oxidative stress. Inhomogeneous SMF was generated with an apparatus validated previously providing a peak-to-peak magnetic induction of the dominant SMF component 389 mT by 39 T m⁻¹ lateral gradient in the in vivo and in vitro experiments, and 192 mT by 19 T m⁻¹ in the human study at the 3 mm target distance. Effects of SMF-exposure were studied in a murine model of allergic inflammation and also in human provoked skin allergy. We found that even a single 30-min exposure of mice to SMF immediately following intranasal RWPE challenge significantly lowered the increase in the total antioxidant capacity of the airways and decreased allergic inflammation. Repeated (on 3 consecutive days) or prolonged (60 min) exposure to SMF after RWPE challenge decreased the severity of allergic responses more efficiently than a single 30-min treatment. SMF-exposure did not alter ROS production by RWPE under cell-free conditions, while diminished RWPE-induced increase in the ROS levels in A549 epithelial cells. Results of the human skin prick tests indicated that SMF-exposure had no significant direct effect on provoked mast cell degranulation. The observed beneficial effects of SMF are likely owing to the mobilization of cellular ROS-eliminating mechanisms rather than direct modulation of ROS production by pollen NAD(P)H oxidases.     

金属塑性成形三维有限元模拟软件3D - PFS的开发

金属塑性成形过程的三维有限元模拟仿真是否有效的关键在于快速适用的算法和有效的模拟系统.介绍了自主开发的三维刚塑性/刚粘塑性有限元模拟分析软件3D-PFs的组成及关键技术问题的处理,并给出了计算实例.结果表明:利用该系统可实现对体积和板料成形过程的模拟分析,获得成形过程中材料在模腔中的流动情况及成形规律,该系统是研究金属塑性成形的有效工具.     

Model correction factor method for reliability problems involving integrals of non-Gaussian random fields

The model correction factor method (MCFM) is used in conjunction with the first-order reliability method (FORM) to solve structural reliability problems involving integrals of non-Gaussian random fields. The approach replaces the limit-state function with an idealized one, in which the integrals are considered to be Gaussian. Conventional FORM analysis yields the linearization point of the idealized limit-state surface. A model correction factor is then introduced to push the idealized limit-state surface onto the actual limit-state surface. A few iterations yield a good approximation of the reliability index for the original problem. This method has application to many civil engineering problems that involve random fields of material properties or loads. An application to reliability analysis of foundation piles illustrates the proposed method.     

An upscale theory of particle simulation for two‐dimensional quasi‐static problems

An upscale theory of the particle simulation, which is based on the distinct element method, is presented for two‐dimensional quasi‐static problems. Since the present upscale theory is comprised of four similarity criteria between different length‐scale particle‐simulation models, it reveals the intrinsic relationship between the particle‐simulation solution obtained from a small length‐scale (e.g. a laboratory length‐scale) model and that obtained from a large length‐scale (e.g. a geological length‐scale) one. The present upscale theory is of significant theoretical value in the particle simulation of two‐dimensional systems, at least from the following two points of view. (1) If the mechanical response of a particle model of a small length‐scale is used to indirectly investigate that of a large length‐scale, then the present upscale theory provides the necessary conditions, under which the particle model of the small length‐scale needs to be satisfied so that a similarity between the mechanical responses of two different length‐scale particle models can be maintained. (2) If a particle model of a large length‐scale is used to directly investigate the mechanical response of the model, then the present upscale theory can be used to determine the necessary particle‐scale mechanical properties from the macroscopic mechanical properties that are obtained from either a laboratory test or an in situ measurement. The related simulation results from two typical examples of significantly different length‐scales (i.e. a metre‐scale and a kilometre‐scale) have demonstrated the usefulness and correctness of the proposed upscale theory for simulating different length‐scale problems in quasi‐static geological systems. Copyright © 2007 John Wiley & Sons, Ltd.     

蒸汽喷射泵超音速流体三维模拟研究

利用大型流体力学软件FLUENT，对不同结构尺寸和边界条件的蒸汽喷射泵喷嘴内超音速流场进行了3D模拟。探讨了流场内压力和速度的相互作用及其分布规律；讨论了热力学参数和几何参数对流场特性的影响规律；并分析了喷嘴内影响喷射器性能的激波产生的因素。基本上与Dayton和石井博的研究结果一致。     

Toward a multifrequency quasi‐static Ritz vector method for frequency‐dependent acoustic system application

Computational issues concerning the calculation of acoustic responses of a complex finite element (FE) model for various noise and vibration inputs have become prevalent. Such a model requires a significant amount of computation time because of repeated inversions of dynamic stiffness matrices. Thus, even state‐of‐the‐art computer hardware and software often face limitations where a model order reduction (MOR) scheme can help. The established MOR schemes such as Ritz vector or quasi‐static Ritz vector methods are efficient for general engineering systems, but these MOR methods become inaccurate for frequency response analyses in some acoustic systems with frequency‐dependent mass and stiffness matrices and force vectors (hereinafter frequency‐dependent acoustic systems). To cope with the inaccurate prediction by these methods for frequency‐dependent acoustic systems, this research presents and applies the multifrequency quasi‐static Ritz vector method. Unlike the Ritz vector or quasi‐static Ritz vector methods, the present multifrequency quasi‐static Ritz vector method employs direct Krylov subspace bases without an orthonormal procedure at multiple center frequencies. In comparison with the existing MOR scheme, a significant gain in computational efficiency is achieved, as well as enhanced accuracy. A comparison of these methods based on criteria such as efficiency, accuracy, and reliability was also conducted. Copyright © 2011 John Wiley & Sons, Ltd.     

端部霍尔离子源的磁场设计与数值模拟

首先简单介绍了用于离子束辅助沉积的端部霍尔离子源的工作原理，然后分析了其性能对磁场的要求，据此介绍了磁路组件的设计。最后,采用ANSYS大型有限元分析软件对一个条形的端部霍尔离子源的磁场进行了模拟计算，并与实验结果进行了比较，获得了满意的结果。通过对模拟结果的分析，获得了对该离子源磁场分布的直观深入的认识，为具体的端部霍尔离子源的改进设计提供了理论指导。     

3D symplectic expansion for piezoelectric media

The symplectic series expansion method is extended to three‐dimensional problem for transversely isotropic piezoelectric media. The governing equations are first derived in Hamiltonian form, and symplectic eigensolutions are directly obtained through analytical method. All solutions of the problem are reduced to finding eigenvalues and eigensolutions. The classical St Venant solutions are described by zero‐eigensolutions, and the localized solutions are depicted by non‐zero‐eigensolutions. Symplectic relationships of the ortho‐normalization are used, end conditions are rewritten by eigensolutions, and a numerical scheme is formed analytically. Some numerical examples are given. Copyright © 2007 John Wiley & Sons, Ltd.     

条形药包岩石中爆炸的三维数值模拟

:对单自由面下岩石中条形药包的爆炸进行了三维数值模拟 ,对有效应力场、压力场及爆腔运动进行了比较全面的分析研究 ,得出了一些有意义的结论     

A dual BIE approach for large‐scale modelling of 3‐D electrostatic problems with the fast multipole boundary element method

A dual boundary integral equation (BIE) formulation is presented for the analysis of general 3‐D electrostatic problems, especially those involving thin structures. This dual BIE formulation uses a linear combination of the conventional BIE and hypersingular BIE on the entire boundary of a problem domain. Similar to crack problems in elasticity, the conventional BIE degenerates when the field outside a thin body is investigated, such as the electrostatic field around a thin conducting plate. The dual BIE formulation, however, does not degenerate in such cases. Most importantly, the dual BIE is found to have better conditioning for the equations using the boundary element method (BEM) compared with the conventional BIE, even for domains with regular shapes. Thus the dual BIE is well suited for implementation with the fast multipole BEM. The fast multipole BEM for the dual BIE formulation is developed based on an adaptive fast multiple approach for the conventional BIE. Several examples are studied with the fast multipole BEM code, including finite and infinite domain problems, bulky and thin plate structures, and simplified comb‐drive models having more than 440 thin beams with the total number of equations above 1.45 million and solved on a PC. The numerical results clearly demonstrate that the dual BIE is very effective in solving general 3‐D electrostatic problems, as well as special cases involving thin perfect conducting structures, and that the adaptive fast multipole BEM with the dual BIE formulation is very efficient and promising in solving large‐scale electrostatic problems. Copyright © 2007 John Wiley & Sons, Ltd.     

条形药包岩石中爆炸的三维数值模拟

:对单自由面下岩石中条形药包的爆炸进行了三维数值模拟 ,对有效应力场、压力场及爆腔运动进行了比较全面的分析研究 ,得出了一些有意义的结论     

基于单胞数字化模型的复合材料本构关系三维数值模拟

在渐进均匀化理论基础上, 建立了基于单胞数字化模型的复合材料宏观等效弹性性能的三维数值分析方法(DCB-FEA) 。该方法采用三维光栅化技术将三维单胞模型转化为三维光栅图形(数字化模型) , 并将光栅图形直接转化为三维有限元求解网格。产生的离散单元具有相同的几何尺寸和规则的形状, 单元刚度矩阵的数量将减少为单胞材料的个数。此外, 单胞数字化模型仅需记录每个离散单元的材料种类, 其他参数如单元节点编号、节点坐标等均可在求解过程中自动生成, 周期性边界条件也可以自动施加。随着分辨率的提高, 单胞数字化模型将产生更多数量的单元, 特别是对于三维单胞模型, 集成整体刚度矩阵时需要大量的计算机内存。采用基于Element-by-element 策略的预处理共轭梯度法( EBE- PCG) , 有限元方程的求解在单元级上进行, 避免了整体刚度矩阵的集成。通过对单向纤维增强复合材料的线弹性本构关系的数值模拟, 表明该方法可得到较为准确的复合材料等效模量。      

A boundary element method for the solution of a class of heat conduction problems for inhomogeneous media

A boundary element method is derived for solving the two-dimensional heat equation for an inhomogeneous body subject to suitably prescribed temperature and/or heat flux on the boundary of the solution domain. Numerical results for a specific test problem is given.     

A meshless method for solving 1D time-dependent heat source problem

A novel meshless numerical procedure based on the method of fundamental solutions (MFS) and the heat polynomials is proposed for recovering a time-dependent heat source and the boundary data simultaneously in an inverse heat conduction problem (IHCP). We will transform the problem into a homogeneous IHCP and initial value problems for the first-order ordinary differential equation. An improved method of MFS is used to solve the IHCP and a finite difference method is applied for solving the initial value problems. The advantage of applying the proposed meshless numerical scheme is producing the shape functions which provide the important delta function property to ensure that the essential conditions are fulfilled. Numerical experiments for some examples are provided to show the effectiveness of the proposed algorithm.     

双丝三电弧焊热源优化及数值模拟

为研究双丝三电弧焊焊接温度散布规律,根据其电弧形态和脉冲频率建立了适用于双丝三电弧焊接的体+面热源,并根据焊丝的倾角对其进行了旋转计算,利用有限元技术模拟了6 mm厚Q235碳素钢的双丝三电弧焊焊接温度场,通过遗传算法对其热源参数进行了迭代优化,提高了计算效率。计算结果表明：温度场呈长椭圆状分布,且最高温度和最大温度梯度都出现在R弧热源处,其原因是此处同时积累了R弧电弧热量和L弧焊后凝固时的热量;有限元模型温度场与实验温度场结果对比吻合度较高,其结果可为拓展双丝三电弧焊的应用和优化工艺参数提供仿真基础。