致密微孔壁复合冷却对流换热系数研究

本文采用数值模拟的方法研究了吹风比M和孔阵排列偏转角γ对致密微孔壁复合冷却热侧壁面上对流换热系数的影响。分析比较了在M=0.50-2.0、γ=10°-35°几种情况下的对流换热系数。结果表明:M越大,对流换热系数越低。在气膜孔区内的上游部分γ对斜排对流换热系数影响不很明显,在中下游部分斜排模型的对流换热系数比常规错排模型低。     

三维透平叶片扭转颤振问题的流固耦合数值研究

颤振,尤其是失速颤振是引起叶轮机械安全事故的重要原因之一。由于叶片颤振的复杂性,过去人们一直采用半经验的方法研究叶片的颤振。本文发展了一套更精确的流固耦合计算方法,并用这种算法研究了三维透平叶片的扭转颤振。在模拟大负攻角下的颤振时发现,传播失速响应频率向固有频率靠近是振动发散的一个重要判据。通过计算得出了压比和攻角对颤振影响的特性曲线,它不但可用于判断流体激振的稳定性,而且可以研究颤振的强度。     

角钢插入式基础抗拔试验与分析

通过对 １１ 组 １９ 个角钢插入式基础试件的抗拔试验,得到了角钢在不同埋置长度、不同锚固形式下的抗拔承载力、角钢与混凝土间的粘结应力分布、平均粘结应力以及角钢插入式基础的破坏形式、最大试验荷载等。为工程设计提供了基础数据。     

环形含内钝缺口试件在斜加载作用下弹塑性场的分布特征

运用有限元数值计算方法,对含内缺口的环形试件在受到与缺口对称面成不同角度的载荷作用下,缺口前端附近的弹塑性场分布特征进行了研究,得到了缺口前端应力和应变场以及塑性区的变化情况,此外,选取缺口弧度不同的模型,探讨了缺口顶端钝化程度对弹生场的影响,为了对计算结果的可靠性进行评价,运用高精度云纹干涉实验力学方法进行了验证性试验,试验得到的位移,应变分布情况与计算结果基本吻合。文中得到的结果为钝口试件的材     

边坡倾倒变形的形成机制与影响因素分析

本文从边坡倾倒的变形特点出发,分析了倾倒变形的力学机制。在此基础上研究了结构面间距及力学参数对变形的影响。通过含有结构面的岩体的应力,位移以及屈服区的分布特点,讨论了反倾边坡的稳定性问题。     

Robust Stability Test for Dynamic Systems with Short Delays by Using Padé Approximation

The paper presents a simple approach to testifying the asymptotic stability and interval stability (robust stability against the change of system parameters in given intervals) for linear dynamic systems involving short time delays. The stability analysis starts with the study of the characteristic roots of a transcendental equation having exponential functions. By means of the Padé approximation to the exponential functions, the transcendental characteristic equation is approximated as an algebraic equation. Then, the test of asymptotic stability and interval stability of the system is completed in a very simple way. The stability analysis of a vibration system with short time delays in the feedback paths of displacement and velocity, taken as an example, is given in detail. The analysis and numerical examples indicate that the approach gives excellent accuracy for linear dynamic systems with short time delays.     

一种基于区间过程模型的时变可靠性分析方法

本文提出了一种基于区间过程模型的时变可靠性分析方法来处理涉及区间变量和区间过程的问题.首先,定义一种基于极值响应的可靠性指标来度量区间变量和区间过程不确定性下结构的可靠性.其次,建立并求解一双层优化模型以获得可靠性指标.在内层中,使用EGO方法计算功能函数关于时间的极值响应;在外层中,对极值响应关于原始区间变量和区间过程级数展开获得的区间变量进行优化,以得到其上边界和下边界.最后,通过两个例子以验证本文方法的有效性.     

单机上带有可变前瞻区间的分批在线排序问题

本文研究单台无界平行批处理机上带有可变前瞻区间的在线排序问题。工件按时在线到达,目标是最小化时间表长。在时刻$t$,在线算法能够预见到$（t,t+\Delta（t）]$内到达工件的信息,这里前瞻区间的长度$\Delta（t）=\beta p_{\max}（t）$并非定长,其中$p_{\max}（t）$表示在$t$时刻及之前到达工件的最大加工时长,$\beta\in（0,1）$是常数。本文对于工件加工时长的一般情形,给出了当 0<β≤1/6 时最好可能的在线算法;对于工件加工时长被限制在一个区间的情形,给出了当 0<β<1 时最好可能的在线算法。     

Risk models for the Prize Collecting Steiner Tree problems with interval data

Given a connected graph G=(V,E)with a nonnegative cost on each edge in E,a nonnegative prize at each vertex in V,and a target set V′V,the Prize Collecting Steiner Tree(PCST)problem is to find a tree T in G interconnecting all vertices of V′such that the total cost on edges in T minus the total prize at vertices in T is minimized.The PCST problem appears frequently in practice of operations research.While the problem is NP-hard in general,it is polynomial-time solvable when graphs G are restricted to series-parallel graphs.In this paper,we study the PCST problem with interval costs and prizes,where edge e could be included in T by paying cost xe∈[c e,c+e]while taking risk(c+e xe)/(c+e c e)of malfunction at e,and vertex v could be asked for giving a prize yv∈[p v,p+v]for its inclusion in T while taking risk(yv p v)/(p+v p v)of refusal by v.We establish two risk models for the PCST problem with interval data.Under given budget upper bound on constructing tree T,one model aims at minimizing the maximum risk over edges and vertices in T and the other aims at minimizing the sum of risks over edges and vertices in T.We propose strongly polynomial-time algorithms solving these problems on series-parallel graphs to optimality.Our study shows that the risk models proposed have advantages over the existing robust optimization model,which often yields NP-hard problems even if the original optimization problems are polynomial-time solvable.     

A fast and efficient mesh segmentation method based on improved region growing

Mesh segmentation is one of the important issues in digital geometry processing. Region growing method has been proven to be a efficient method for 3D mesh segmentation. However, in mesh segmentation, feature line extraction algorithm is computationally costly, and the over-segmentation problem still exists during region merging processing. In order to tackle these problems, a fast and efficient mesh segmentation method based on improved region growing is proposed in this paper. Firstly, the dihedral angle of each non-boundary edge is defined and computed simply, then the sharp edges are detected and feature lines are extracted. After region growing process is finished, an improved region merging method will be performed in two steps by considering some geometric criteria. The experiment results show the feature line extraction algorithm can obtain the same geometric information fast with less computational costs and the improved region merging method can solve over-segmentation well.