Fluid-structure interaction simulation of three-dimensional flexible hydrofoil in water tunnel

The closely coupled approach combined with the finite volume method (FVM) solver and the finite element method (FEM) solver is used to investigate the fluid-structure interaction (FSI) of a three-dimensional cantilevered hydrofoil in the water tunnel. The FVM solver and the coupled approach are verified and validated by comparing the numerical predictions with the experimental measurements, and good agreement is obtained concerning both the lift on the foil and the tip displacement. In the noncavitating flow, the result indicates that the growth of the initial incidence angle and the Reynolds number improves the deformation of the foil, and the lift on the foil is increased by the twist deformation. The normalized twist angle and displacement along the span of the hydrofoil for different incidence angles and Reynolds numbers are almost uniform. For the cavitation flow, it is shown that the small amplitude vibration of the foil has limited influence on the developing process of the partial cavity, and the quasi two-dimensional cavity shedding does not change the deformation mode of the hydrofoil. However, the frequency spectrum of the lift on the foil contains the frequency which is associated with the first bend frequency of the hydrofoil.     

自由活塞压缩管ALE方法数值模拟

当前国际上实现高焓气体流动的实验手段之一是自由活塞驱动类脉冲设备,包括自由活塞激波风洞和自由活塞膨胀管.采用自由活塞压缩管作为激波风洞和膨胀管的驱动段时,其驱动能力在很大程度上决定了该类设备的性能.本文采用计算流体力学中任意拉格朗日——欧拉方法(arbitrary Lagrangian Eulerian)数值模拟了压缩管内部的自由活塞运动和气体流动特征.采用移动网格技术来适应活塞运动边界,耦合求解网格运动和气体流动过程,并通过双时间步长方法进行流体运动的时间积分.为了满足几何守恒律(geometric conservation law),对移动网格的法向矢量和表面面积计算进行了修正.不同时刻的活塞位置试验测量结果及欧拉方法预测结果,以及基于简单波理论获得的运动活塞底部气体压力、活塞速度与活塞位置都与当前的ALE方法十分一致.该工作为下一步数值模拟自由活塞激波风洞和自由活塞膨胀管中包括压缩管、激波管和喷管等不同部位的耦合流动提供了基础.      

Chen系统的非线性动力学究研

利用受控Chen系统，并基于镜像操作方法，发现Chen吸引子是由左、右两个吸引子所组成的复合结构，且左、右吸引子均可由极限环生成。采用一维时间序列相空间重构技术和系统混沌的定量判据准则，揭示出Chen系统从规则运动转化到混沌运动所具有的普适特征：Chen系统可通过Pomeau-Manneville途径走向混沌，且其间歇性与Hopf分岔和倍周期分岔有关、在这些途径上既可观察到锁相和准周期运动，也可观察到类Chen吸引子、Chen系统和Lorenz系统之间的过渡吸引子和类Lorenz吸引子。     

Matrix-fracture exchange in a fractured porous medium: stochastic upscalingCoefficient d'échange matrice-fracture en milieu poreux fracturé : changement d'échelle par approche stochastique

We present in this Note a stochastic approach to the matrix-fracture exchange in a heterogeneous fractured porous medium. We introduce an intermediate scale, called the unit-scale, between the local-scale (fracture-scale) and the large-scale characteristic of the reservoir mesh (reservoir block). This paper focuses on the problem of upscaling fluid exchange phenomena from the unit scale to the reservoir mesh or block scale. Simplifying the Darcian flow terms enables us to obtain a probabilistic solution of the dual continuum problem, in continuous time, in the case of a purely random exchange coefficient. This is then used to develop several upscaling approaches to the fluid exchange problem, and to analyze the so-called ‘effective’ exchange coefficient. The results are a first contribution to the more general problem of upscaling multidimensional flow-exchange processes in space and time, in randomly heterogeneous dual continua. To cite this article: M. Kfoury et al., C. R. Mecanique 332 (2004).     

区间参数振动系统的动力优化

对具有区间参数的多自由度振动系统的不确定性优化问题，提出一种新的区间优化方法．利用泰勒展开和函数的区间扩张，将区间优化问题转化为近似的确定性优化问题．该方法应用于多自由度线性扭振系统，并把区间设计变量的中值和不确定性半径取作优化参数．算例表明该方法是有效的．     

缺口件疲劳特性研究方法

缺口件疲劳问题的研究日益引起各国学者的重视. 局部应力-应变法以其简单性在工程中得到了广泛应用, 该方法通常会得到偏于安全的结果. 引入疲劳缺口因子代替弹性应力集中因子针对缺口疲劳进行研究, 仍未能从本质上改善预测结果的准确性. 考虑到"热点应力" 附近的相对应力梯度, 提出了应力梯度法研究缺口件疲劳问题, 这一概念亦被用于应力场强度方法中, 如何准确确定损伤区域是应力场强度方法需要解决的问题. 临界距离理论可将Neuber 律、Peterson 方法及应力场强度方法进行有效统一, 同时有限元方法的发展进一步支持了该理论. 目前, 该方法在高周疲劳研究中取得了较好的效果, 但对低周疲劳寿命预测的有效性仍需进一步的验证.     

基于加权残量法的多变量等参元简明列式及其应用

根据作者提出的建立多变量有限元模型的系统化方法,应用加权残量法的基本原理,给出了建立多变量等参元模型的简明列式。然后应用该列式,构造了简明有效的平面四结点多变量等参元MQ4和MQ5前者不含内部自由度,后者含有内部自由度。文中结合若干典型算例对所构造的单元性能进行了考核,并与若干典型协调与非协调等参元的数值结果进行了比较。数值结果表明,无论是在规则网格还是在不规则网格情况下,本文构造的多变量等参元,不仅能通过分片检验的要求,而且表现出了良好的性能。     

概率功能度量求解的共轭梯度步长调节法

功能度量法(PMA)由于其稳定高效的特点,适用于概率结构优化设计中概率约束的评定。PMA中改进均值法常用于求解概率功能度量,针对其求解高度非线性功能函数时出现周期振荡和混沌等不收敛现象,提出了一种新的共轭梯度步长调节法(CGS)。该方法基于RMIL共轭搜索方向和自适应步长调节策略提出,新的共轭搜索方向在保证收敛性的前提下加速了迭代进程,而自适应步长调节策略无需了解功能函数凹凸性及非线性程度等先验信息,无需确定步长的合适取值。通过限定步长准则自动选取初始步长,并随迭代过程不断调节,直至最终收敛。多个算例表明,与其他求解方法相比,本文的共轭梯度步长调节法更加高效且稳健。     

Bingham流体与固壁、液面斜撞击的数值模拟

在交错网格中用MAC方法求解二维不可压N S方程 ,对圆截面液柱与固壁、液面斜撞击问题进行了数值模拟 ,得到了自由面随时间演化的图像。主要考察了 :(1)固壁和液面 ;(2 )牛顿、非牛顿流体 ;(3)碰撞入射角 ;(4 )Bingham流体近似本构式中参数q0 、K对计算结果的影响。结果表明 :液柱与液面碰撞形成的自由面更复杂。碰撞初期 ,Bingham流体和水的自由面相似 ;但碰撞后期 ,Bingham流体的自由面相对简单。对液柱与液面碰撞自由面的影响较大。本文条件下 ,当K 2 0时 ,K对自由面的影响不大 ;当q0 增大时 ,自由面变得相对简单。     

Research for the strain energy release rate of complex cracks by using point-by-point closed extrapolation approach

IntroductionTheresearchforcalculatingstrainenergyreleaserateisaveryimportanttaskforsolvingfracturemechanicsproblems.Inthepreviouscalculationforenergyreleaserate,externalforceworkwassubtractedbystrainenergy ,whichisthemethodoffreeenergy[1],thenodalforcesandnodaldisplacementsbetweentopandbottomsurfacesofcrackwasalsousedtocalculateenergyreleaserate[2 - 5 ].Theyarebothapproximatecalculations.Theformeriscomplex ,althoughtherearesomeadvisablefeaturesindefinition ,andawholecalculationforstrainenergy …