应用二维频移LDV测量多孔板管流的湍流特性

采用二维ＬＤＶ系统对圆管中装有四孔板和三孔板的湍流特性进行了实验研究．在孔板下游射流沿管轴逐渐混合．沿管壁可以观察到反向流区域．经足够长距离后，轴向和切向湍流度逐渐趋于相同数量级．实验结果表明，孔板结构和开孔度对湍流特性有重要影响．     

布孔方式对孔洞材料宏观力学性能影响的研究

运用材料破坏过程分析MFPA2D系统,从细观力学和损伤力学角度,研究了布孔方式对孔洞材料宏观力学性能以及破坏机理的影响。在研究中,分别建立了三种含双孔、四孔以及多孔的正方形数值模型。双孔以沿试件垂直中心线重叠布置,沿试件水平中心线并列布置和沿试件对角线倾斜布置三种方式进行布孔,四孔以正方形和菱形两种布孔方式置于试件中央区域,多孔成排布置并使其相邻四孔成正方形和菱形镶嵌于试件中。然后对这三种试件分别进行了标准的单轴压缩数值试验。通过对试验结果的讨论,阐明了布孔方式对孔洞材料宏观力学行为和细观损伤机理的影响。结果表明:孔洞的相互作用既可以增强应力集中程度,也可以减弱应力集中程度;正方形布孔方式比菱形布孔方式使孔洞材料具有更高的承载能力;多孔材料的延性断裂行为是孔洞应力屏蔽作用和材料损伤局部化行为共同作用的结果。     

室内空气流动数值模拟的N点风口动量模型

为适应工程应用中快速、准确模拟室内空气流动的需要，提出N点风口动量模型，以简化描述利用计算流体动力学CFD方法模拟室内空气流动时百叶、多孔板类送风口的入流边界条件。百叶和多孔板风口的等温自由射流算例以及HESCO孔板类散流器在室内送风的算例和实验数据对比表明，N点风口动量模型可以较好地解决数值模拟室内空气流动的风口入流边界条件描述问题。     

穿孔区域中双曲-抛物方程均匀化问题的一个注记

In this paper, we study a class of hyperbolic-parabolic problems in periodically perforated domains with a homogeneous Neumann condition on the boundary of holes. We focus on the homogenization of these equations, which generalizes those achieved by BensoussanLions-Papanicolau and Migorski. The proof is based on the periodic unfolding method in perforated domains.     

Numerical investigation on the position of holes for reducing stress concentration in composite plates with bolted and riveted joints

This paper studies the effects of fiber orientaion and holes position on stress concentration and the determination of weakened areas in the composite of glass fiber reinforced epoxy resin around the hole for joints by using the finite element method. In this study, for the observation of areas affected by stress concentration Tsai-Wu failure criterion is used to determine the failed elements and ANSYS Software is implemented for modeling. In order to compare the effect of geometric parameters on stress concentration around the holes, two types of hole position arrangement along with fibers orientation have been studied. Results show that the stress concentration coefficient is lower in the second type of holes arrangement in comparison with the first type for the same component dimensions. Increasing the distance from hole center to upper or lower edge of the sample and also decreasing the distance between holes, would result in an increase in the stress concentration.     

穿纤维微穿孔板吸声系数的有限元仿真

为拓宽微穿孔板的吸声频带,该文用有限元算法建立了典型微穿孔板和穿入不同数量金属纤维的微穿孔板模型,研究了两种微穿孔板的吸声系数、声阻抗和微孔内法向质点速度的空间分布,并进行了试验验证。有限元仿真和试验数据表明:穿入金属纤维可以拓宽微穿孔板的吸声频带,吸声系数也随纤维根数的增加而下降;吸声系数仿真结果与试验结果趋势一致,仿真模型可以有效模拟穿入纤维前后微穿孔板的吸声特性;穿入金属纤维导致黏滞效应引起的低质点速度区域增大,声阻增加,引起吸声系数的降低,而声抗变化不大。研究发现,有限元仿真方法适用于结构相对复杂的微穿孔结构的声学建模,能直观地体现微孔复杂结构的影响,值得继续深入研究和工程应用。     

微穿孔板吸声结构水下应用研究

马大猷教授提出的微穿孔板吸声结构在空气噪声降低和隔离方面得到了广泛的应用,但未见水下应用的相关研究和报道。本文将空气中微穿孔板理论应用到水中,得到了水下微穿孔板吸声结构的吸声公式。通过理论分析,得出了微穿孔板结构直接应用于水中无法获得宽频吸收的结论。提出了通过匹配液将微穿孔板间接应用到水下的设想。设计了单层板和双层板吸声结构,并对它们的吸声特性进行了理论分析与仿真。结果表明,本文设计的微穿孔板吸声结构在水中能够获得优于空气中的宽频带吸声效果。实验测量了自制的微穿孔板吸声结构,吸声系数的测量值与理论曲线基本吻合,从而验证了理论分析的正确性。     

Wave interaction with a new type perforated breakwater

In this study examined is the wave interaction with a new modified perforated breakwater, consisting of a perforated front wall, a solid back wall and a wave absorbing chamber between them with a two-layer rock-filled core. The fluid domain is divided into three sub-domains according to the components of the breakwater. Then by means of the matched eigenfunction expansion method, an analytical solution is obtained to assess the hydrodynamic performance of the new structure. An approach based on a step approach method is introduced to solve the complex dispersion equations for water wave motions within two-layer porous media. Numerical results of the present model are compared with previous limiting cases. The effects of rock fill on the reflection coefficient and the horizontal wave force are discussed. The project supported by the Program for Changjiang Scholars and Innovative Research Teams in Universities (IRT0420). The English text was polished by Keren Wang.     

空间屏打孔多层隔热材料热计算模型

分析了空间屏打孔多层隔热材料中导热和辐射的复合传热问题,在一定假设的基础上,根据反射屏能量平衡方程,建立了反射屏稳态温度计算模型和投射辐射数值分析模型。结合AD I法,对两个方程组进行迭代求解,得到材料屏间投射辐射热流和反射屏的温度。将文中模型的预测结果与文献中实验值进行比较,验证了模型在工程上应用的可行性。同时分析了当量导热系数、各种热流以及内部温度分布随层密度的变化规律,对材料的优化设计具有积极的指导意义。     

A mixed problem for the Laplace operator in a domain with moderately close holes

We investigate the behavior of the solution of a mixed problem in a domain with two moderately close holes. We introduce a positive parameter ε and we define a perforated domain Ω_ε obtained by making two small perforations in an open set. Both the size and the distance of the cavities tend to 0 as ε → 0. For ε small, we denote by u_ε the solution of a mixed problem for the Laplace equation in Ω_ε. We describe what happens to u_ε as ε → 0 in terms of real analytic maps and we compute an asymptotic expansion.