一种有限元并行计算前处理方法

本文研究一种有限元并行计算前处理方法,只需将各子结构的超单元信息发送给各处理机,就可并行自动剖分各子结构和并行优化各子结构单元编号,以达到极小最大波宽和波宽的均主根,算例表明,该方法可大大减少有限元并行计算前处理时间。     

A multigrid pseudospectral method for steady flow computation

In this work two‐dimensional steady flow problems are cast into a fixed‐point formulation, Q = F(Q). The non‐linear operator, F, is an approximate pseudospectral solver to the Navier–Stokes equations. To search the solution we employ Picard iteration together with a one‐dimensional error minimization and a random perturbation in case of getting stuck. A monotone convergence is brought out, and is greatly improved by using a multigrid strategy. The efficacy of this approach is demonstrated by computing flow between eccentric rotating cylinders, and the regularized lid‐driven cavity flow with Reynolds number up to 1000. Copyright © 2003 John Wiley & Sons, Ltd.     

识别求解路径上奇异点的一个计算方法

提出一个在路径跟踪计算中识别分支点和极值点的实用方法，给出了算例。     

一种易于并行求解Euler方程组的分区技术

在具有复杂边界的计算区域内,求解偏微分方程组时,经常需要分区和并行计算,分区方法直接关系到数值计算的并行化程度,本文在应用时间算子分裂方法求解Euler方程组的过程中,提出了一种非常容易实现并行化计算的分区技术。     

A Godunov method for the computation of erosional shallow water transients

A Godunov method is proposed for the computation of open‐channel flows in conditions of rapid bed erosion and intense sediment transport. Generalized shallow water equations govern the evolution of three distinct interfaces: the water free‐surface, the boundary between pure water and a sediment transport layer, and the morphodynamic bottom profile. Based on the HLL scheme of Harten, Lax and Van Leer (1983), a finite volume numerical solver is constructed, then extended to second‐order accuracy using Strang splitting and MUSCL extrapolation. Lateralisation of the momentum flux is adopted to handle the non‐conservative product associated with bottom slope. Computational results for erosional dam‐break waves are compared with experimental measurements and semi‐analytical Riemann solutions. Copyright © 2003 John Wiley & Sons, Ltd.     

A numerical method for the computation of bifurcation points in fluid mechanics

Two original algorithms are proposed for the computation of bifurcation points in fluid mechanics. These algorithms consist of finding the zero values of a specific indicator. To compute this indicator a perturbation method is used which leads to an analytical expression of this indicator. Two kinds of instability are considered: stationary and Hopf bifurcations. To prove the efficiency and advantages of such numerical methods several numerical tests are discussed.     

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某些超静定结构, 当弯矩图确立后, 应用静力平衡条件无法绘出轴力图. 分析该类结构的基本特征和受力特点,利用某些刚架在结点集中力作用下无弯矩、只有轴力的特点和力法的思想, 提出解算已知弯矩图轴力超静定结构的计算方法. 算例表明该方法简化了力法的计算过程,将其应用于教学, 有利于学生对力法的深入理解.     

A simple postrocess procedure for Galerkin method

A kind simple postprocess procedure for classical Galerkin method for steady Navier-Stokes equations with stream function form was presented in this paper. The main ideal was to construct an approximate interactive rule between lower frequency components and higher frequency components by using the conception of Approximate Inertial Manifold (AIM) and a kind of new decomposition of the true solution. It is demonstrated in this paper that this kind of postprocess Galerkin method could derive a higher accuracy solution with lower computing efforts. Communicated by Zhang Hongqing Foundation item: the National Natural Science Foundation of China (19671067) Biography: Hou Yanren(1970-)     

A simple method for photographing transparent objects

Summary Expansion waves and shocks in a supersonic jet are photographed, using a simple optical device. The method is less sensitive but more robust than schlieren photography.     

A simple method to compute standard two-fluid models

We describe in this paper, a tool to compute approximate solutions of standard two-fluid models with an equilibrium pressure assumption. The basic approach takes its grounds in the two-fluid two-pressure formalism, and takes advantage of the relaxation techniques. The method may be used to compute either the single- or the two-pressure model, depending on the size of mesh, which is used. It is also shown on the basis of a simple numerical experiment that the local equilibrium assumption may lead to a blow-up of the numerical solution on fine meshes, even if one accounts for drag stabilizing effects.     

简支梁中截面挠度计算的一种简易方法

介绍了一种首先利用简支梁的对称性找出等价悬臂梁, 然后利用叠加法求出等效悬臂梁自由端的挠度, 从而得到一般载荷作用下简支梁中间截面挠度的方法.     

A numerical method for the computation of the effects of an air vessel on the pressure surges in pumping systems with air entrainment

This paper describes an improved numerical method and computational procedure for the implementation of typical air vessel responses and their influence on the pressure transient for unsteady flow in a pipeline system with air entrainment. The proposed numerical method and computational procedure is without the necessity of an excessive iterative procedure as required previously by the conventional approach. The effects of air in the transient fluid system with the air vessel were then studied through the improved numerical computational method. Free and dissolved gases in the transported fluid, and cavitation at vapour pressure, are included. © 1998 John Wiley & Sons, Ltd.     

A simple method for calculating thermal expansion of crystals

Summary A simple method based on the classical statistical mechanics is suggested for the calculation of thermal expansion of crystals. The adequacy of the procedure is tested for alkali halide crystals in conjunction with the interatomic potential of the modified Born-Mayer Type.     

A simple method for the digital determination of the photoelastic fringe order

A new and simple approach to the digital determination of a photoelastic fringe order using two different loads is proposed. The relationships between the intensity values of light and the isochromatic fringe orders generated from two different loads are derived. The scheme used for the automated determination of the total fringe orders of a full-field photoelastic fringe pattern is described. The usefulness of this method is demonstrated using two isochromatic fringe patterns under two different loads. Extra filters are not needed in the proposed method as in the case of the two-wavelength method.     

A SYMBOLIC COMPUTATION METHOD TO DECIDE THE COMPLETENESS OF THE SOLUTIONS TO THE SYSTEM OF LINEAR PARTIAL DIFFERENTIAL EQUATIONS

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A new full discrete stabilized viscosity method for transient Navier-Stokes equations

A new full discrete stabilized viscosity method for the transient Navier-Stokes equations with the high Reynolds number （small viscosity coefficient） is proposed based on the pressure projection and the extrapolated trapezoidal rule. The transient Navier-Stokes equations are fully discretized by the continuous equal-order finite elements in space and the reduced Crank-Nicolson scheme in time. The new stabilized method is stable and has many attractive properties. First, the system is stable for the equal-order combination of discrete continuous velocity and pressure spaces because of adding a pres- sure projection term. Second, the artifical viscosity parameter is added to the viscosity coefficient as a stability factor, so the system is antidiffusive. Finally, the method requires only the solution to a linear system at every time step. Stability and convergence of the method is proved. The error estimation results show that the method has a second-order accuracy, and the constant in the estimation is independent of the viscosity coefficient. The numerical results are given, which demonstrate the advantages of the method presented.     

A simple method for compressible multiphase mixtures and interfaces

We develop a Godunov‐type scheme for a non‐conservative, unconditional hyperbolic multiphase model. It involves a set of seven partial differential equations and has the ability to solve interface problems between pure materials as well as compressible multiphase mixtures with two velocities and non‐equilibrium thermodynamics (two pressures, two temperatures, two densities, etc.).Its numerical resolution poses several difficulties. The model possesses a large number of acoustic and convective waves (seven waves) and it is not easy to upwind all these waves accurately and simply. Also, the system is non‐conservative, and the numerical approximations of the corresponding terms need to be provided. In this paper, we focus on a method, based on a characteristic decomposition which solves these problems in a simple way and with good accuracy. The robustness, accuracy and versatility of the method is clearly demonstrated on several test problems with exact solutions. Copyright © 2003 John Wiley & Sons, Ltd.