L p-Perturbations of Invariant Subbundles for Linear Systems

We use Riccati's equations and the ordinary and exponential dichotomies to get simple recurrent formulae for the asymptotic integration of linear systems subjected to L _p -perturbations with arbitrary p 1. Moreover, we establish conditions which are necessary and sufficient for the persistence of one-dimensional invariant subbundles for the linear system under L _p -perturbations. In this way, we prove the sharp nature of the well known Levinson and Hartman–Wintner asymptotic theorems.     

跨声速激波边界层相互作用的被动控制

运用激波管风洞在Ｒ＿（ｅ∞／ｍ＝３×１０￣７，Ｍ＿∞＝０．７３２－０．８１７范围内，在厚度比为１２％的圆弧翼型半模型和厚度比为１４％的超临界翼型半模型上，对被动控制现象及其若干规律进行了实验研究。结果表明，不同空腔深度的开孔壁和导管连通壁均可对壁面激波与边界层的相互作用实现被动控制，使得沿以上两种模型表面的马赫数峰值、逆压力梯度和激波强度明显减小。这对于飞行器将起到减阻作用，如将这一原理和方法用于超、跨声速压气机内激波与边界层相互作用的控制，将提高压气机的效率和工作的稳定性。     

The effect of pore-structure on hysteresis in relative permeability and capillary pressure: Pore-level modeling

The effect of pore-structure upon two-phase relative permeability and capillary pressure of strongly-wetting systems at low capillary number is simulated. A pore-level model consisting of a network of pore-bodies interconnected by pore-throats is used to calculate scanning loops of hysteresis between primary drainage, imbibition and secondary drainage. The pore-body to pore-throat aspect ratio strongly influences the pattern of hysteresis. Changes in the patterns of hysteresis often attributed to consolidation can be understood in terms of changes in aspect ratio. Correlation between the sizes of neighboring pore-throats affects the shape of the relative permeability curves, while the width and shape of the pore-size distribution have only a minor influence.     

Slow Effects of Fast Harmonic Excitation for Elastic Structures

High-frequency excitation may affect the slow behavior of a dynamical system. For example, equilibria may move, disappear, or gain or loose stability. We consider such slow effects of fast excitation for a simple mechanical system that incorporates features of many engineering structures. The study is intended to contribute to the general understanding of periodically excited linear and nonlinear systems, as well as to the current attempts to utilize high-frequency excitation for altering the low-frequency properties of structures.     

Multiscale Structures to Describe Porous Media Part I: Theoretical Background and Invasion by Fluids

A porous medium with a broad pore-size distribution is described on the basis of the Multiscale Percolation System concept. The representative structure is the superposition of several constitutive elementary networks, of which mesh sizes are proportional to the diameter of the class of pores considered. To account for the contribution of each class to the connection of the medium, a recurrent building process, involving rescaling and superposition, is defined. This process leads to an equivalent monoscale network, involving elements representative of the various classes. Mercury intrusion at increasing pressure into a finite-size sample of this equivalent network is modelled. The inverse problem is solved, leading to the identification of the representative multiscale structure of a given material from the experimental intrusion curve.     

On Vaporizing Water Flow in Hot Sub-Vertical Rock Fractures

Water injection into unsaturated fractured rock at above-boiling temperatures gives rise to complex fluid flow and heat transfer processes. Examples include water injection into depleted vapor-dominated geothermal reservoirs, and emplacement of heat-generating nuclear wastes in unsaturated fractured rock. We conceptualize fractures as two-dimensional heterogeneous porous media, and use geostatistical techniques to generate synthetic permeability distributions in the fracture plane. Water flow in hot high-angle fractures is simulated numerically, taking into account the combined action of gravity, capillary, and pressure forces, and conductive heat transfer from the wall rocks which gives rise to strong vaporization. In heterogeneous fractures boiling plumes are found to have dendritic shapes, and to be subject to strong lateral flow effects. Fractures with spatially-averaged homogeneous permeabilities tend to give poor approximations for vaporization behavior and liquid migration patterns. Depending on water flow rates, rock temperature, and fracture permeability, liquid water can migrate considerable distances through fractured rock that is at above-boiling temperatures and be only partially vaporized.     

圆柱绕流尾迹中相干结构对湍流特性的影响

实验研究了圆柱尾迹中相干结构对湍流平均量的影响.用一个X热线在距离圆柱体y/d=4测量参考信号,用X热线和冷线相结合的三线探头测量从x/d=10～40的圆柱绕流尾迹中的速度和温度脉动,用条件平均的方法研充圆柱绕流近尾迹中的相干结构,并对相干结构对动量和热量的湍流输运过程的影响进行初步分析.结果表明:相干结构对尾迹中速度的横向脉动影响最大;相干结构对湍流参数的影响随x/d的变化明显.该工作还对相干结构引起的湍动能产生率变成负和逆温度梯度输运现象做了定性的解释.     

添加剂与铝合金的相互作用研究 Ⅰ.静态反应膜及油润滑下的摩擦学性能

静态下分别于２５℃，９０℃及１８０℃下进行硫化异丁烯（ＳＯ）、亚磷酸二正丁酯（ＤＢＰ）、ＳＯ＋ＤＢＰ的混合物（质量比２０∶１）、二烷基二硫代磷酸锌（ＺＤＤＰ）及十二酸（ＬＡ）５种添加剂均以质量分数为２％的比例添加到液体石蜡（ＬＰ）中与铝合金进行油浸试验．用动－静摩擦系数精密测定仪评价了在铝合金表面上所形成的静态反应膜的摩擦磨损行为，并考察了上述添加剂在ＬＰ中对铝合金－钢摩擦副的润滑作用．结果表明：静态反应膜的摩擦磨损行为与添加剂的化学活性密切相关，其中ＤＢＰ最易与铝合金发生反应，故其反应膜具有最低的摩擦系数和最长的耐磨寿命；ＺＤＤＰ在１８０℃下的静态反应膜具有较低的摩擦系数和较长的耐磨寿命；ＳＯ、ＳＯ与ＤＢＰ的混合物及ＬＡ的静态反应膜则不具有减摩抗磨性能，预示这些添加剂在ＬＰ中不与铝合金发生较强的化学作用．含上述添加剂的ＬＰ润滑下的摩擦磨损试验显示，ＤＢＰ与ＺＤＤＰ具有较好的摩擦学性能．这表明添加剂在铝合金表面静态反应膜的摩擦磨损试验结果与其在常规润滑下的具有较好的相关性．     

基于神经网络与光纤传感阵列的结构状态监测方法

以探测机敏复合材料与结构内应变、应力及损伤等物理状态的位置信息为目的．提出了一种新颖的可内埋于材料与结构内作为结构状态监测用的强度调制型光纤传感阵列网络，并采用人工神经网络来处理传感阵列输出的并行分布式传感信号，阐述了适用的Ｋｏｈｏｎｅｎ网模型及其变化形式，给出了仿真实验结果     

参数激励与强迫激励联合作用下非线性振动系统的余维2退化分叉

在本文里我们首先研究了具有Z_2-对称性的范式理论和退化向量场的普适开折理论。然后利用上述理论研究了参数激励与强迫激励联合作用下非线性振动系统的余维2退化分叉,从而解决了当解具有两个零特征值时解的稳定性问题。最后利用Melnikov方法求出了参数平面上的同宿分叉曲线,讨论了全局分叉的存在性。