注射充模过程的压力求解方法及其比较

提出了一个LU局部分解方法来求解注射充模过程的压力方程,并与其他迭代方法进行了比较。LU局部分解法是当矩阵在逐渐变大时,保留已经分解的部分,只对新增加的部分进行分解,因此相当于只对最后的稀疏矩阵进行了分解。计算表明,LU局部分解法比预条件共轭梯度法快大约1个量级,而预条件共轭梯度方法又比超松弛迭代法快大约1个量级。     

Interaction of a shock pulse with a contact discontinuity

Passing of a triangular moderate-intensity pulse through a constant discontinuity is considered. Decay of the shock wave that passed into the second gas is analyzed. Damping of the detonation wave after burnout of the combustible mixture is discussed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 102–107, July–August, 2007.     

An algorithm and observability research of autonomous navigation and joint attitude determination in asteroid exploration descent stage

In this paper, an autonomous relative navigation and joint attitude determination algorithm in asteroid exploration descent stage is researched based on feature point information of perpendicular asteroid surface image observed by optical navigation camera, distance vectors from spacecraft to asteroid measured by three angled installed lidars and relative velocity increment measured by accelerometer when the relative distance vector to the centroid of asteroid can not be obtained. The inertial attitude of spacecraft is determined by sun vector, star vectors and inertial angular velocity respectively measured by sun sensor, star trackers and inertial reference unit. Also, in order to obtain measurement error model transferred from sensor noise, a covariance matrix solver considering error correlation is presented via the error model of normalized vector to first order. Numerical simulation and improved observability evaluation of filtering are undertaken to discuss the results of complete sensor observation and weak observation of lidars, and verify the effectiveness of the presented relative navigation and attitude determination algorithm.     

利用EXCEL工具率定典型流量数学模型方法探讨

介绍EXCEL【规划求解】功能拟合流量数学模型的操作方法和步骤,并与EXCEL内置图形函数拟合的流量数学模型进行对比分析,说明该功能拟合流量数学模型的优越性。分别以天然河道、水库堰闸、水电站实测流量系列资料为实例,应用该功能拟合不同类型的流量数学模型,结果表明【规划求解】功能拟合流量数学模型均能满足水文资料整编规范要求。     

基于动态符号执行的C代码缓冲区溢出检测

缓冲区溢出是C程序中众多安全隐患的根源之一,以C程序代码为目标对象,提出了一个基于底层虚拟机中间代码的缓冲区溢出检测工具PathChecker.该工具基于动态符号执行方法,使用无量词谓词公式刻画缓冲区操作的安全性质,并利用可满足模型理论求解器技术检验缓冲区操作的安全性.实验结果表明,该工具能有效检测C代码中的缓冲区溢出漏洞,且易于推广至其他高级程序语言代码和其他类型安全漏洞的检测.     

特征线坐标系下柱对称超音速流膨胀波计算方法研究

在静压圆盘止推气体轴承柱对称超音速流膨胀波系的计算中,借鉴Liepmann的特征线坐标系与自然坐标系变换理论和Liepmann引入两个黎曼不变量的方法,使得边界条件的处理更为直观和简便。采用特征线坐标系下的特征线法,推导计算该膨胀波系所用到的基本计算公式,将其应用于 P-M 流动并与 P-M 流动理论解进行比较。结果表明,数值计算结果与P-M流动理论解吻合,该计算方法可行。     

Total-FETI domain decomposition method for solution of elasto-plastic problems

In this paper we present an algorithm for the parallel solution of the rate-independent elasto-plastic problems with kinematic hardening. We assume the von Mises plastic criterion and the associated plastic flow rule. The time discretization is based on the implicit Euler method. The corresponding one-time-step problem is formulated in the incremental form with respect to the unknown displacement and discretized spatially by the finite element method. We use an ‘external’ algorithm based on a linearization of the elasto-plastic stress–strain relation by the corresponding tangential operator and we parallelize the arising linearized problem by the Total-FETI method. The numerical experiments were carried out using our novel C/C++ library FLLOP (FETI Light Layer On top of PETSc) at HECToR supercomputer located at EPCC, UK.     

Accurate evaluation of Green’s functions in a layered medium by SDP-FLAM

Based on local Taylor expansions on the complex plane, a method for fast locating all modes (FLAM) of spectral-domain Green’s Functions in a planar layered medium is developed in this paper. SDP-FLAM, a combination of FLAM with the steepest descent path algorithm (SDP), is employed to accurately evaluate the spatial-domain Green’s functions in a layered medium. According to the theory of complex analysis, the relationship among the poles, branch points and Riemann sheets is also analyzed rigorously. To inverse the Green’s functions from spectral to spatial domain, SDP-FLAM method and discrete complex image method (DCIM) are applied to the non-near field region and the near filed region, respectively. The significant advantage of SDP-FLAM lies in its capability of calculating Green’s functions in a layered medium of moderate thickness with loss or without loss. Some numerical examples are presented to validate SDP-FLAM method. Supported by the National Natural Science Foundation of China (Grant No. 60621002), and the State Key Development Program for Basic Research of China (Grant No. 2009CB320200)     

Level‐set topology optimization with many linear buckling constraints using an efficient and robust eigensolver

Linear buckling constraints are important in structural topology optimization for obtaining designs that can support the required loads without failure. During the optimization process, the critical buckling eigenmode can change; this poses a challenge to gradient‐based optimization and can require the computation of a large number of linear buckling eigenmodes. This is potentially both computationally difficult to achieve and prohibitively expensive. In this paper, we motivate the need for a large number of linear buckling modes and show how several features of the block Jacobi conjugate gradient (BJCG) eigenvalue method, including optimal shift estimates, the reuse of eigenvectors, adaptive eigenvector tolerances and multiple shifts, can be used to efficiently and robustly compute a large number of buckling eigenmodes. This paper also introduces linear buckling constraints for level‐set topology optimization. In our approach, the velocity function is defined as a weighted sum of the shape sensitivities for the objective and constraint functions. The weights are found by solving an optimization sub‐problem to reduce the mass while maintaining feasibility of the buckling constraints. The effectiveness of this approach in combination with the BJCG method is demonstrated using a 3D optimization problem. Copyright © 2016 John Wiley & Sons, Ltd.