Transmitting boundary and radiation conditions at infinity

Relationship between the radiation conditions at infinity and the transmitting boundary for numerical simulation of the near-field wave motion has been studied in this paper. The conclusion is that the transmitting boundary is approximately equivalent to the radiation conditions at infinity for a large class of infinite media. And the errors of the approximation are of the same order of magnitude as those of the finite elements or finite differences in numerical simulation of wave motion. This result provides a sound theoretical basis for the transmitting boundary used in the numerical simulation of the near-field wave motion and gives a complete explanation for the major experiences accumulated in applications of the transmitting boundary to the numerical simulation.     

A generalized theory on the penetrating boundary conditions

A generalized formula for penetrating boundary conditions is derived based on the Z-transform. The well-known absorbing boundary conditions (ABCs), such as the Mur's ABC, and Liao's ABC, can be deduced from the formula. Furthermore, some new ABCs can also be deduced from it. The stability of these ABCs are demonstrated via Von Neumann method and their validity is verified by numerical examples.     

带有分数阶边界条件的一类Caputo差分方程边值问题

运用分数阶的基本定义和引理,讨论了一类带有分数阶边界条件的离散Caputo分数阶差分方程边值问题的格林函数,并给出了v=2时格林函数的几个重要性质.     

隐身桅杆计算边界条件的研究

以舰船筒形结构的全封闭形隐身桅杆为研究对象，利用有限元方法，考虑在两种不同的边界条件下，使用美国的大型有限元计算软件ANSYS对桅杆进行结构振动分析．并且根据舰船在风浪中航行时，作用在桅杆上的计算载荷，对桅杆进行结构强度计算．将得到的结果进行比较分析，发现由以往的方法设置边界条件计算得来的结果和由本文提出的简化的边界条件计算得来的结果，两者之间并无太大的差异，但工作量前者要大的多．因此建议今后在类似的短粗形桅杆计算中，可采用简化的边界条件来分析结构振动和强度性能．     

IAPWS-IF97计算模型中区域边界条件的确定

1997年国际水和水蒸汽协会(IAPWS)提出的工业用水和水蒸汽热力性质模型(IAPWS-IF97),具有适用范围较大、区域划分简洁、计算方程形式简单及精度高等优点,已被广泛接受。但在诸多文献中当由参数h,s求其他参数时,对其相关边界条件却很少提及。通过分析和研究,确定了相关边界条件,由参数h,s编程计算,保证了各区域内的其他参数的准确性。计算结果表明,能够通过所获得的边界条件,根据参数h,s准确地确定所要计算的区域并得出正确的结果,因此为开发各区域水蒸汽热力性质计算程序提供了保障。     

无网格法强制边界条件处理的一种新方法

针对无网格法位移边界条件处理困难和计算效率低的问题,提出了一种简洁实用的边界条件处理方法.在构造试探函数中,通过修改节点的权函数使试探函数穿过预施加位移边界条件的节点.采用有限元法中的位移边界条件处理方法使试探函数预先满足位移边界条件.该方法的计算量小,可解决大多数无网格法的位移边界条件问题和有限元耦合问题.以移动最小二乘法为例,通过算例证明了该方法的精确性与实用性.     

一种基于单向波方程的频域二阶吸收边界条件

文中推导了直角坐标系和圆柱坐标系中的频域二阶单向波方程,对他们进行了适当的离散化处理,分别得出了直角坐标系和圆柱坐标系中的二维二阶吸收边界条件。计算表明,这些吸收边界条件具有二阶精度,文中给出了一个计算实例,结果是令人满意的。     

时域有限差分法的优化吸收边界条件

基于单向波算子,给出了一个形式简洁的Ｎ阶优化吸收边界条件,给出了确定其参量的方法．数值结果表明,对于特定电磁问题,适当选择参量,优化吸收边界条件优于同阶Ｍｕｒ吸收边界条件．     

基于波动理论的粘弹性人工边界内源波动有限元分析

在地震激励作用下,当地基为无限介质时能量将逸散到无穷远处而耗散.目前广泛采用的无质量固定边界模型引入了不真实的反射地震波,无法模拟地震波的真实传播过程.基于波动理论采用粘弹性人工边界模拟地震波内源波动的远域能量逸散效应,并将计算结果与固定边界模型进行比较.计算结果表明粘弹性人工边界削弱了固定边界引起的荷载放大效应,能更...     

具双曲动力边界的拟线性椭圆方程解的爆破

讨论了一类拟线性椭圆方程具双曲动力边界的初边值问题,利用凸性方法给出了该拟线性椭圆方程具双曲动力边界非线性源项时解爆破的充分条件.     

弹性支撑及连接边界的多跨曲梁面内自由振动分析

针对弹性支撑边界曲梁的振动问题,采用一种改进的傅里叶级数方法对多跨曲梁面内自由振动特性进行了求解分析.将曲梁面内径向和切向位移函数表示成傅里叶级数形式,并引入辅助多项式函数用以解决弹性边界的不连续性.采用瑞利-里茨方法求解基于能量原理的哈密顿方程,得到关于未知位移幅值系数的标准特征值问题,求解得到多跨曲梁的固有频率和振型.通过单跨、两跨的自由、简支、固支等传统边界及弹性边界的曲梁模型结果与有限元法结果的对比验证了本文方法的正确性,并分析了两跨固支曲梁中间连接刚度对固有频率的影响.     

A theoretical study of asymptotic boundary conditions for the numerical solutions of open-boundary static electromagnetic-field problems

Based on the multipole expansion theory of the potential, a satisfactory interpretation is put forward of the exact nature of the approximations of asymptotic boundary condition (called the ABC) techniques for the numerical solutions of open-boundary static electromagnetic-field problems, and a definite physical meaning is bestowed on ABC, which provide a powerful theoretical background for laying down the operating rules and the key to the derivation of asymptotic boundary conditions. This paper is also intended to reveal the shortcomings of the conventional higher-order ABC, and at the same time to give the concept of a new type of higher-order ABC, and to present a somewhat different formulation of the new nth-order ABC. In order to test its feasibility, several simple problems of electrostatic potentials are analyzed. The results are found to be much better than those of conventional higher-order ABCs.     

锥形体电阻数值计算中边界条件的处理

讨论了用微分方程数值解法计算锥体电阻时,不适当的侧面边界条件差分格式所引入的附加误差问题,通过对不同差分格式的理论分析及实际计算效果对比发现,在侧面边界上,如忽略轴对称疰一维问题与二维问题的差异,则所用边界条件的差分格式会引入明显的附加误差。     

电磁场边界条件的一种新推导方法

对由不同煤质所组成的电磁场场域，当分界面上场的散度源和旋度源不为零时，场量将在分界面两侧发生突变，通常使用的单一煤质区域中的斯托克斯公式不再适用这种情况，推广了单一煤质中的斯托克斯公式，得到了适用于多媒质区域的多曲面斯托克斯公式，对于由不同煤质所组成的电磁场场域，利用所推广的多曲面斯托克斯公式，给出了电磁场边界条件的一种新的推导方法，所推导的公式对于由多种媒质组成的矢量场有广泛应用。     

激波与边界层干扰研究综述

综述了激波与边界层干扰的研究工作,其内容涉及定常激波－边界层干扰的一般特性、气动加热、理论研究、数值模拟以及非定常激波－边界层干扰的若干问题。     

吹除法对斜激波/边界层干扰控制数值模拟

为了对进气道内斜激波/边界层干扰进行控制,采用RSM模型,以二维平板/楔结构为基础,研究了斜激波冲击平板诱导边界层分离现象,探讨了吹除状态下流场波系结构和壁面参数分布,分析了吹除位置和总压对分离区及流场的影响.研究表明加入吹除控制之后,流场参数得到了有效改善,吹除喷嘴靠近分离区,吹除效果更好.吹除总压并不是越高吹除效果就越好,存在一个最佳吹除压力,该压力就是使吹除喷嘴出口气流达到近似音速,这一结论如进一步得到实验证实,对实际工程具有指导意义.     

A simple and robust method for essential boundary condition treatments in mesh-less methods

To improve the treatment efficiency of essential boundary condition in mesh-less methods,a simple and robust method is proposed in this paper.Rising weight of nodes in the construction of trail function,specified for essential boundary condition,can make the trail function pass through these nodes.And then,the trail function can satisfy the essential boundary condition previously by setting diagonal element to 1 or multiplying diagonal element by a big number in FEM.The MLS method is adopted to validate this method,and it is proved that this method is costless and robust in most of mesh-less methods.     

Application of generalized impedance boundary conditions to sommerfeld half-space problem

Generalized impedance boundary conditions are employed to simplify the solution of the Sommerfeld half-space problem. An analytical expression is derived for the Hertz potential of a vertical electric dipole over the earth’s surface, in which the earth is assumed to be a layered media or homogeneous dissipative half-space.A Sommerfeld type integral in the potential function is expressed as the sum of two parts: a zeroth order Hankel function and an absolutely convergent series of Bessel functions. In addition, two expressions in closed form are obtained as the far-field and near-field approximation of the present result.     

Characteristics of the boundary layer of magnetic clouds and a new definition of the cloud boundary

The concept of magnetic clouds is the combination of the frozen-in magnetic field and of the plasma clouds proposed in the 1950s or earlier[1—5]. The necessary conditions to identify a mag-netic cloud are[6]: (ⅰ) enhanced magnetic field strength, (ⅱ) a smooth rotation of the magnetic field direction through a large angle at the interval of an order of one day, and (ⅲ) low proton temperature and low plasma b. As an important and distinct subset of interplanetary large-scale transient struct…