孔洞裂纹问题的一种数值方法

研究孔洞与裂纹的相互作用问题,通过把适于单一裂纹的Bueckner原理扩充到含有多孔洞多裂纹的一般体系,将原问题分解为承受远处载荷不含裂纹不含孔洞的均匀问题,和在远处不承受载荷但在裂纹面上和孔洞表面上承受面力的多孔洞多裂纹问题.于是,以应力强度因子作为参量的问题可以通过考虑后者来解决,而利用笔者提出的杂交位移不连续法,这种多孔洞多裂纹问题是容易数值求解的.算例说明该数值方法对分析平面弹性介质中孔洞与裂纹的相互作用既简单又有效.     

非均质问题中的无网格边界单元法

介绍了一种不需要内部网格计算非均匀介质问题的边界元算法.该算法是建立在一种能将任何区域积分转换成边界积分的径向积分转换法基础上,首先用对应各向同性问题的基本解来建立以正规化位移表示的非均质问题的积分方程,然后用径向积分转换法将出现在积分方程中的区域积分转换成边界积分,从而形成不需要使用内部网格来计算区域积分的纯边界元算法.与其它无网格法相比,此方法需要很少的内部点,有些问题甚至不需要内部点都能得到满意的结果,因此,可以计算大型的三维非均匀介质工程问题.由于此方法继承了边界元和无网格算法的优点,因而具有广阔的发展前景.     

基于拓扑描述函数的连续体结构拓扑优化方法

提出了一种利用拓扑描述函数(TDF)作为拓扑设计变量求解连续体结构拓扑优化问题 的新方法. 优化问题的目标函数是结构的整体柔顺性，约束条件为对于可利用材料的体积限 制. 这种方法不仅可以消除拓扑优化中经常出现的棋盘格式等数值不稳定现象，而且能够有 效地抑制传统算法处理此类优化问题时所引发的边界扩散效应. 与其它的基于水平集描述函 数的拓扑优化方法相比，所提出的算法不仅无需求解控制水平集函数演化的双曲守恒方 程，而且合理地考虑了目标函数的拓扑导数信息，因而使得算法的计算效率有了显著的提高.     

用于稠油输送的新蒸汽引射器

介绍一种自行研制的蒸汽引射器，蒸汽以自由射流形式注入到输油管中，利用蒸汽释放的热量提高稠油温度以降低黏度，从而达到低输送压降的目的。该引器具有加热效率高，防止稠油堵塞管线等优点，引射器已在辽河油田输油管线上进行了现场实验，取得了很好的效果。     

Application of a new fast multipole BEM for simulation of 2D elastic solid with large number of inclusions

A fast multipole method (FMM) is applied for BEM to reduce both the operation and memory requirement in dealing with very large scale problems. In this paper, a new version of fast multipole BEM for 2D elastostatics is presented and used for simulation of 2D elastic solid with a large number of randomly distributed inclusions combined with a similar subregion approach. Generalized minimum residual method (GMRES) is used as an iterative solver to solve the equation system formed by BEM iteratively. The numerical results show that the scheme presented is applicable to certain large scale problems. The project supported by the National Nature Science Foundation of China (10172053) and the Ministry of Education     

Numerical Modeling of the Development of a Streaky Structure in a Boundary Layer at a High Freestream Turbulence Level

The disturbances generated by external turbulence in the boundary layer on a flat plate set suddenly in motion are determined. A turbulent flow calculated by direct numerical simulation is taken as the initial conditions. The solution obtained simulates the initial stage of laminar-turbulent transition in the flat-plate boundary layer at a high turbulence level in the oncoming flow. The solution makes it possible to estimate the effects of different factors, such as nonstationarity, nonlinearity, and the parameters of the freestream velocity fluctuation spectrum, on disturbance enhancement in the boundary layer.     

单侧摩擦约束夹杂物的瞬态弹性波散射的时域边界元分析--反平面情况

应用时域边界元法研究了瞬态SH波对单侧摩擦约束夹杂物的散射问题，假设摩擦遵守库仑定量，当入射SH波足够强时界面会出现局部滑移，发现了一种有效的迭代技术以确定边界上的未知区域（滑移和粘着区）。算例计算了无限域中圆柱埋置夹杂物对瞬态SH波的散射问题。     

时域边界元法分析撞水响应

基于势流理论，考虑流场的可压缩性，首先利用积分变换导得了势流问题的一个动力学倒易定理，在此基础上，进而求得问题对应的时空边界积分方程，然后通过对边界和时间轴同时离散，建立了一组有递推形式的时间边界元方程最后结合液面条件和物体运动方程耦全求解得到了刚体的撞水响应。     

考虑晶界效应的多晶体有限变形分析

将晶界及其影响区综合考虑，建立了考虑晶界效应的力学模型，结合晶体塑性理论，利用有限变形有限元对多晶体进行数值模拟，数值结果显示了细观层次下晶粒变形场的特点，理论计算同实验定性一致。     

Boundary-layer relaxation after a separated region

With reference particularly to the work of Peter Bradshaw and his associates, some remarks are made about the recovery of previously distorted shear flows. It is emphasized that such recovery is usually extremely slow, and this is further illustrated by new measurements of the velocity field and turbulence structure in the relaxing flow downstream of a separated region. Data have been obtained for downstream distances (x) up to about 20 times the length of the separated region (x_r), or about 75 times the flow thickness at reattachment. This is a significantly more extensive region than has been previously studied, and the data are more comprehensive than any previously available.

It is shown that the recovery is even slower than previously surmized. Furthermore, the measurements demonstrate that the turbulence stresses eventually fall below standard boundary-layer values (at the same Reynolds number), although around reattachment they are very much higher, having values more akin to those in plane mixing layers. This undershoot is apparently a new finding and is argued to be a result of the influence of the outer part of the flow on the growing inner region. The usual log-law only begins to appear beyond x/x_r = 2.5. It effectively “sees” a turbulent outer region that recovers even more slowly than itself, and the response of the inner region therefore has similarities to the response of an ordinary boundary layer to free-stream turbulence.

It is concluded that even current second-order (i.e., Reynolds stress) models may not capture the exquisitely slow decay of the strong, large eddy motions in the outer part of the flow and the subtleties of their influence on the inner region.