混凝土中爆炸模拟的数值方法比较

应用AUTODYN商业软件对装药在混凝土靶介质中的爆炸过程进行数值模拟,对比了混凝土中爆炸模拟的不同方法。将各数值方法模拟得到的混凝土毁伤特征尺寸与相关实验数据进行比较,研究了各数值方法的准确性及描述混凝土毁伤特征的可靠性参数。结果发现：Euler算法计算的压力最大,SPH和Lagrange耦合算法计算的压力最小;Euler算法和SPH算法计算的压力衰减过程会发生比较显著的扰动。以不同的平均网格尺寸对数值模拟结果的影响分析了各种数值方法的稳定性。比较靶体上同一测点的压力时间历程表明网格变化对测点处压力影响不大。通过应用各种数值方法模拟再现混凝土中的爆炸过程,揭示了各种方法的优缺点,明确了现有商业软件模拟混凝土中爆炸的适用性。     

水电站压力钢管外压稳定问题的数值仿真研究

水电站压力钢管因失稳屈曲破坏过程的复杂性及影响失稳因素的多样性,导致对该问题的研究很难进行.目前该问题的传统计算方法存在一定的局限性,有时甚至计算结果相差较大.本文用神经网络模型结合模拟退火算法对该问题进行数值仿真求解,并通过测试样本验证了算法的可行性,为压力钢管外压稳定问题的分析方法开拓了一条新的研究思路.     

非正交同位网格下压力与速度耦合算法

发展了一种在非正交同位网格下以笛卡儿速度分量作为动量方程的独立变量、压力与速度耦合的S IM-PLER算法。该算法的特点是显式处理界面速度中的压力交叉导数项,得出压力与压力修正方程,使得压力及压力修正值与界面逆变速度直接耦合。通过对分汊通道内的流动问题进行验证计算,结果表明该算法可以有效而准确地模拟复杂区域内的流动与换热问题。     

浅地表地下质量异常重力与磁探测数值模拟方法

提出一种重磁观测值数值模拟方法,用于地下空穴测量数据的解释和反演算法研究。采用更具结构灵活性的旋转椭球体作为地下空穴模型,在重力异常和重力梯度异常计算表达式的基础上,推导其磁异常计算表达式,实现空穴重磁异常信号的分析计算;借助扰动位的功率谱密度函数实现重力异常谱和重力梯度异常谱的计算,经傅立叶逆变换到空间域实现背景场统计学模拟;采用高斯白噪声模拟测量仪器或其它随机噪声信号。将三部分数据叠加并进行数值仿真,证明该方法合理有效。     

不确定凸模型近似算法的一种改进

将非概率凸模型理论与摄动理论相结合，通过有界不确定参数结构的特征值问题，对凸模型理论的一次近似算法作出一种改进．改进后的算法由于在计算中不用特征值导数，与Ｅｌｉｓｈａｋｏｆ的算法相比，不仅拓广了凸模型理论的应用范围，而且还可提高算法的计算效率．     

一种无条件稳定的结构动力学显式算法

利用离散控制理论, 针对结构动力学方程时间积分提出了一种新的无条件稳定的显式算法. 新算法采用CR 算法的速度和位移递推格式, 同时利用Z变换获得算法对应的传递函数, 进而根据极点条件推导了递推格式系数的具体表达式. 然后, 在其系数中引入了一个控制周期延长率的变量s, 从而调节新算法的精度. 理论分析表明无条件稳定显式新算法具有二阶精度、零振幅衰减率、无超调和自起步特性, 且周期延长率可以用变量s控制, 而CR 算法只是本文新算法的特例. 最后, 确定了非线性刚度硬化系统的稳定性界限, 并给出了使新算法精度达到较高的变量s的区间. 算例分析表明, 在此变量区间内取值时, 新算法的精度要优于纽马克常平均加速度算法和CR 算法.      

不同网格扭曲率下压力修正全隐算法——IDEAL求解性能研究

2008年,本文作者和陶文铨等提出了一种用于速度和压力耦合求解的高效稳定压力修正全隐算法IDEAL,该算法通过在每个迭代层次上对压力方程进行两次内迭代计算,完全克服了SIMPLE算法的两个假设,充分满足了速度和压力之间的耦合,从而大大提高了计算的收敛性和健壮性。为了进一步实现IDEAL算法的推广应用,本文基于三维倾斜方腔顶盖驱动流动,研究了IDEAL算法在不同网格扭曲率下的求解特性。研究发现,在不同网格扭曲率下,IDEAL算法的健壮性和收敛性均优于SIMPLE算法,特别在高网格扭曲率情况下,IDEAL算法求解性能更加优于SIMPLE算法。在不同网格扭曲率下,IDEAL算法健壮性保持不变,几乎可以在任意速度亚松弛因子下获得收敛的解,同时IDEAL算法最短计算耗时较SIMPLE算法减少了56%~89%,验证了IDEAL算法的优越性。     

Z2—对称破缺音叉分歧点的分裂迭代算法

Ｗｒｒｎｅｒ和Ｓｐｅｎｃｅ在（５）中提出了一个正则的扩张系统，用以计算Ｚ２－对称破缺音叉分歧点。这种方法即是直接法。本文将用另一种方法－－分列迭代算法来计算Ｚ２－对称破缺音叉分歧点，分裂迭代算法超线性收敛，并明显地节约计算的工作量和计算所占用的内存。数值例子的计算成功地说明分裂迭代算法的有效笥。     

高超音速粘性流的快速算法

由 Lombard 等人提出的 CSCM-S 算法是求解 Euler 及 Navier-Stokes 方程的高效率方法。但是,由于该法在整个计算区域上采用总体迭代,实用上是不经济的。本文提出一种修正方案,即对超音速流为主的区域用一次推进解法与复杂流动区域用多次扫描,可大大节省 CPV 时间,更适于工程应用。     

弹塑性板壳结构非线性有限元分析

本文根据塑性流动理论的基本公式，由隐式积分导出了与路径无关的变量更新算法和一致切线模量。采用单元广义应力应变直接离散塑性流动定律，构造了杂交应力单元一致切线刚度矩阵的显式表达式，编制了结构有限元程序ＳＡＦＥ，数值算例表明：本文的计算方法和计算程序是正确可靠的，可用于弹塑性板壳结构的非线性分析，计算结果屈曲临界载荷和极限承载能力。     

基于PID方法的可倾瓦推力轴承分析

使用PID方法控制可倾瓦推力轴承流场求解中轴瓦倾角和支点膜厚的迭代,实现了力和力矩平衡同步收敛.以光滑及粗糙表面下可倾瓦推力轴承流场求解为例,对比PID方法和传统方法,PID法编程便捷,计算效率高,同时能够反映可倾瓦推理轴承的刚度特性.考虑表面粗糙度时,PID法能够求解传统方法不收敛的问题.     

船用燃气轮机进气滤清器惯性级内的流场计算和实验验证

本文提出了一套求解船用燃气轮机进气滤清器流道流场的数值方法,成功地计算了流道内流场的状态,给出了各种不同型号流道的气动特性,对指导滤清器的设计有较大的现实意义, 在这套方法中,我们应用上风差分来逼近二维、非定常、粘性、不可压缩流体非守恒型的N-S方程,提出了一种可计算雷诺数高达上万的粘性流的差分方程,考察了这种差分方程的稳定性,收敛性、精度和人工粘性,本文还提出了处理一些边界拐点处壁涡的计算方法,实际算例表明,使用本文提出的差分方程和壁涡处理方法给出的计算结果和实验吻合良好。     

Elastoplastic contact of rough surfaces: a line contact model for boundary regime of lubrication

This paper introduces an improved friction model accounting for elastoplastic behavior of interacting asperities along contiguous rough surfaces for a line contact solution. It is based on Greenwood and Tripp’s original boundary friction model and specifically tailored for a boundary regime of lubrication. The numerical solution of Reynolds’ equation is achieved by implementing Elrod’s cavitation algorithm for a one dimensional line contact. The transience in the numerical solution is retained by accounting for the squeeze film term in Reynolds’ equation under fixed loading conditions and varying sliding motion. A sliding bearing rig is used to measure friction and compare the results with the prediction made using the approach highlighted above. The numerical/experimental results show good agreement.     

局部狭窄血管中流动分离和临界雷诺数的判定

采用Karman-Pohlhausen方法,对过去轴对称局部狭窄血管内流动分离的理论计算进行修正,导出了确定流动分离位置轴向坐标的方程。对该方程数值求解的结果表明:(1)随着雷诺数或狭窄度的增加,在狭窄的舒张区(x>0)会出现分离和再附着现象,并且分离和再附着之间的区域会逐渐扩展;(2)分离和再附着点的坐标随雷诺数变化的理论曲线与以前的实验结果基本一致。     

A high‐order discontinuous Galerkin solver for low Mach number flows

In this work, we present a high‐order discontinuous Galerkin method (DGM) for simulating variable density flows at low Mach numbers. The corresponding low Mach number equations are an approximation of the compressible Navier–Stokes equations in the limit of zero Mach number. To the best of the authors'y knowledge, it is the first time that the DGM is applied to the low Mach number equations. The mixed‐order formulation is applied for spatial discretization. For steady cases, we apply the semi‐implicit method for pressure‐linked equation (SIMPLE) algorithm to solve the non‐linear system in a segregated manner. For unsteady cases, the solver is implicit in time using backward differentiation formulae, and the SIMPLE algorithm is applied to solve the non‐linear system in each time step. Numerical results for the following three test cases are shown: Couette flow with a vertical temperature gradient, natural convection in a square cavity, and unsteady natural convection in a tall cavity. Considering a fixed number of degrees of freedom, the results demonstrate the benefits of using higher approximation orders. Copyright © 2015 John Wiley & Sons, Ltd.     

船用气水分离器惯性级流场分析及阻力特性研究

采用二阶全展开ETG有限元与大涡模拟（LES）相结合的算法，对120－20－35－3型船用气水分离器惯性级在不同雷诺数条下的流动进行了模拟，通过其中一组雷诺数条件下计算所得该实验件阻力系数与物理实验所得阻力系数相比较，确定出该雷诺数条件下采用大涡模拟时所需的亚格子应力模型常数，将该常数带入其它各组雷诺数条件下的计算中，并将计算结果与相同条件下的物理实验结果相比较，证实了该常数的通用性。该常数一经确定，对各雷诺数条件下的流场进行分析，结果反映出采用二阶全展开ETG有限元与大涡模拟（LES）相结合的算法可以捕捉到非常丰富的涡系及涡动的时变过程。在流场分析的基础上本文计算了该实验件内的能耗场，计算结果表明实验件内的能耗主要集中在大涡丰富的区段内。     

The effect of the hydrodynamic interaction on the rheological properties of Hookean dumbbell suspensions in steady state shear flow

The diffusion equation for the configurational distribution function of Hookean dumbbell suspensions with the hydrodynamic interaction (HI) was solved, in terms of Galerkin’s method, in steady state shear flow; and viscosity,first and second normal-stress coefficients and molecular stretching were then calculated. The results indicate that the HI included in a microscopic model of molecules gives rise to a significant effect on the macroscopic properties of Hookean dumbbell suspensions. For example, the viscosity and the first normal stress coefficient, decreasing as shear rate increases, are no longer constant; the second normal-stress coefficient, being negative with small absolute value and shear-rate dependent, is no longer zero; and an additional stretching of dumbbells is yielded by the HI. The viscosity function and the first normal-stress coefficient calculated from this method are in agreement with those predicted from the self-consistent average method qualitatively, while the negative second normal-stress coefficient from the former seems to be more reasonable than the positive one from the latter.     

An iterative parallel algorithm of finite element method

In this paper, a parallel algorithm with iterative form for solving finite element equation is presented. Based on the iterative solution of linear algebra equations, the parallel computational steps are introduced in this method. Also by using the weighted residual method and choosing the appropriate weighting functions, the finite element basic form of parallel algorithm is deduced. The program of this algorithm has been realized on the ELXSI-6400 parallel computer of Xi'an Jiaotong University. The computational results show the operational speed will be raised and the CPU time will be cut down effectively. So this method is one kind of effective parallel algorithm for solving the finite element equations of large-scale structures.     

A preconditioned alternating inner-outer iterative solution method for the mixed finite element formulation of the Navier-Stokes equations

In the present work a new iterative method for solving the Navier-Stokes equations is designed. In a previous paper a coupled node fill-in preconditioner for iterative solution of the Navier-Stokes equations proved to increase the convergence rate considerably compared with traditional preconditioners. The further development of the present iterative method is based on the same storage scheme for the equation matrix as for the coupled node fill-in preconditioner. This storage scheme separates the velocity, the pressure and the coupling of pressure and velocity coefficients in the equation matrix. The separation storage scheme allows for an ILU factorization of both the velocity and pressure unknowns. With the inner-outer solution scheme the velocity unknowns are eliminated before the resulting equation system for the pressures is solved iteratively. After the pressure unknown has been found, the pressures are substituted into the original equation system and the velocities are also found iteratively. The behaviour of the inner-outer iterative solution algorithm is investigated in order to find optimal convergence criteria for the inner iterations and compared with the solution algorithm for the original equation system. The results show that the coupled node fill-in preconditioner of the original equation system is more efficient than the coupled node fill-in preconditioner of the reduced equation system. However, the solution technique of the reduced equation system revals properties which may be advantageous in future solution algorithms.     

一种动力响应混合快速分析方法及其在功能梯度材料板瞬态响应分析中的应用

提出了一种把减基法嵌套在Newmark法中快速求解动力问题的混合算法.这种算法把Newmark法作为动力问题的基本求解器.而在嵌套减基法时,把参数样本空间对应的解集做成一个训练空间,采用贪婪算法进行减基空间基向量的自适应选取,进而由减基空间得到减缩系统.通过求解减缩系统对应的Newmark增量式来达到快速求解动力问题的目的.最后采用了一个无限大的功能梯度材料板的瞬态响应分析来验证文中方法的高效性和精确性.