补偿Lévy流的实践稳定性

本文的目的是讨论补偿Ｌéｖｙ流的实践稳定性问题．我们推广了一些微分不等式,并通过Ｌｙａｐｕｎｏｖ函数与比较原理,得到补偿Ｌéｖｙ流的实践稳定性的若干判据．     

具有丢包补偿网络化控制系统的量化反馈稳定性分析

针对受丢包和量化反馈问题约束的网络化控制系统,研究了零输入补偿策略和保持输入补偿策略与系统稳定性的关系.丢包补偿策略是决定网络控制系统性能的关键因素之一,量化效应的存在使两种补偿策略对系统的影响与以往的结果产生一些区别.文章采用以连续丢包数作为切换信号的切换量化器,量化密度根据网络负荷情况动态调节,利用受限切换系统方法得到了网络控制系统分别使用零输入策略和保持输入补偿策略时的稳定性分析方法.所得到的稳定性判据具有更小的保守性.进一步比较了两种丢包补偿策略在不同情形下对系统稳定性的影响.从理论分析及仿真结果可知,这两种丢包补偿策略各有优劣,分别适用于两种不同的情况.     

经过修正的平面Couette流的非线性稳定性研究

本文讨论了经过修正的平面Couette流在二维扰动下的非线性稳定性性质,并同经过修正的平面Poiseuille流的非线性稳定性性质进行了比较.计算结果表明,对于有限振幅的扰动,平面Couette流比平面Poiseulle流更不稳定.     

一类三阶梯度流方程弱解的稳定性[英文]

本文研究R~3上的一类三阶梯度流方程弱解的稳定性问题.我们分别证明弱解的一个全局稳定性结果和一个渐近稳定性结果.所得结果改进了已有文献中的一些关于三阶梯度流方程弱解的稳定性结果.     

基于拟常曲率度量的拟DeTurck流的稳定性

C.Guenther利用中心流形以及极大正规性原理,讨论了常曲率空间中DeTurck流的稳定性问题.将常曲率空间推广为拟常曲率空间并讨论"拟"DeTurck流的稳定性问题,得到类似于C.Guenther所得的结果.     

经过修正的层流流动的流动稳定性问题(Ⅰ)——基本概念和理论

本文提出了经过修正的层流流动的流动稳定性理论,并在文中给出平行剪切流中平均速度的一类修正剖面,使这种理论可用于研究平行剪切流的流动稳定性,指出了流动失稳的一条新的可能途径.     

经过修正的层流流动的流动稳定性问题(Ⅲ)——经过修正的平行剪切流的非线性稳定性研究

本文根据文[1]给出的经过修正的层流流动的流动稳定性理论及平行剪切流中平均速度的一类修正剖面,研究了平行剪切流的非线性稳定性性质,并在本文的假设下,把背景湍流噪声的干扰引入了流动稳定性计算,对于平面Poiseuille流动和圆管Poiseuille流动,得到了与实验趋势相一致的结果.     

无限阶段网络博弈中合作解的策略稳定性

合作博弈的经典合作解不满足时间一致性, 并缺乏策略稳定性. 本文研究无限阶段网络博弈合作解的策略稳定性理论. 首先建立时间一致的分配补偿程序实现合作解的动态分配, 然后建立针对联盟的惩罚策略, 给出合作解能够被强Nash均衡策略支撑的充分性条件, 最后证明了博弈中的惩罚策略局势是强Nash均衡, 从而保证了合作解的策略稳定性. 作为应用, 考察了重复囚徒困境网络博弈中Shapley值的策略稳定性.     

K－ε模型在复杂管流中的模拟计算

本文对复杂管流中的湍流问题采用了k-ε模型进行模拟计算.对于复杂边界问题采用了阶梯型网格近似,取得了较好的结果.文中给出了两例复杂管流的计算算例,说明了K-ε模型具有很强的适应性和稳定性.     

电流互感器误差补偿原理和零磁通电流互感器检定系统

本文介绍了我国自行设计研制的、采用新补偿方法的高精度电流互感器和零磁通电流互感器检定系统。文中对电流互感器误差补偿原理进行了全面分析,把各种补偿方法归纳为磁势补偿和电势补偿两大类,从中找出了多种新补偿方法。并据此提出了磁势补偿和电势补偿两类零磁通电流互感器,分析了它们的稳定性。说明由电势补偿零磁通电流互感器分级分段组成的零磁通电流互感器检定系统,具有稳定性好、检定数据准确和线路简单等优点,是至今比较完整的电流比例检定标准。     

Observations on the Role of Vorticity in the Stability Theory of Wall Bounded Flows

The linearized equations for the evolution of disturbances to four wall bounded flows are treated. The flows are plane Couette flow and plane Poiseuille flow, Hagen-Poiseuille pipe flow, and the asymptotic suction profile. By looking at the vorticity it is proved simply that plane Couette flow and Hagen-Poiseuille flow are linearly stable. Further study is made of the structure of the disturbance equation by the introduction of a special vorticity adjoint.     

Numerical Simulation of Air Flow in Model Room

Efficient, and appropriate indoor air environment is important issue in building design. Air flow patterns which are formed in the room are mainly depended on its geometrical parameters. Investigation of flow patterns are performed on a relatively simple geometry of model room, with a small obstacle (partition) in it. There are several interesting flow phenomena which are present in the model room: flow through sudden geometry expansion, stagnation flow with lateral boundaries, flow over the obstacle, etc. Since the air velocities are low, it is assumed that flow is incompressible. Numerical calculations of these patterns have been done using RANS modeling approach. For all calculations an extended version of open-source CFD software OpenFOAM was used. Several turbulence models have been used for RANS approach, with special attention on their performance in capturing unsteady flow phenomena. Comparison of obtained numerical results and available experimental results for mean velocities shown good agreement. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Factors Influencing the Disturbed Flow Patterns Downstream of Curved Atherosclerotic Arteries

Pulsatile blood flows in curved atherosclerotic arteries are studied by com- puter simulations.Computations are carried out with various values of physiological parameters to examine the effects of flow parameters on the disturbed flow patterns downstream of a curved artery with a stenosis at the inner wall.The numerical re- suits indicate a strong dependence of flow pattern on the blood viscosity and inlet flow rate,while the influence of the inlet flow profile to the flow pattem in downstream is negligible.     

Payne-Whitham型宏观交通流模型波动特性

宏观交通流模型将交通流比拟成流体流,通过整体变量如交通流量、平均车速以及交通密度来研究其整体性质,得到了越来越多的肯定.文章采用波前展开的方法,研究Payne-Whitham型宏观交通流模型描述扰动沿交通流波动的特性,同时给出了相应的稳定性条件.最后利用Padé逼近法进行数值仿真,得到的结果与理论分析相一致.     

血液动力学中血管流激波与驻波的相互作用

血液动力学问题是生物力学心血管系统中的重要研究课题.血管内斑块处,血管截面和血管壁的材质发生变化,对血液流动产生重要影响.血液流动中基本波及其相互作用对探究血液流动的规律、生理学意义及与疾病的关系有着重要的意义.本文研究血液动力学血液流动简化数学模型的基本波的相互作用.血管流模型是3×3非严格双曲型方程组.构造性地得到了初值为三段常状态时,血管流问题的解,即解决了激波与驻波的相互作用问题.特别地,给出四种后前激波与驻波的相互作用的结果.     

Numerical modeling of unsteady flow in steam turbine stage

This work deals with numerical solution of unsteady flow in turbine stage. We use models of compressible single-phase flow of air and two-phase flow of wet steam. Presented numerical methods are based on different stator-rotor matching algorithms, as well as different numerical schemes. Numerical results achieved by both methods and flow models are discussed.     

环空套管内粘弹性流的解析解

本文讨论了二阶流体和 Maxwell流体在环形套管内的轴向不定常旋转运动 ,给出了与文 [1 ]不同形式的解析解 ,修正了该文的结果 .     

Numerical Solution of Several Models of Internal Transonic Flow

The paper deals with numerical solution of internal flow problems. It mentions a long tradition of mathematical modeling of internal flow, especially transonic flow at our department. Several models of flow based on potential equation, Euler equations, Navier-Stokes and Reynolds averaged Navier-Stokes equations with proper closure are considered. Some mathematical and numerical properties of the model are mentioned and numerical results achieved by in-house developed methods are presented.     

Numerical simulation of pressure-driven startup laminar flows through a planar T-junction channel

A start-up flow of a viscous incompressible fluid in a T-junction channel is studied numerically. The flow starting from rest is driven by a constant pressure drops suddenly applied between the entries and exits of a planar T-junction channel. The Navier-Stokes equations in primitive variables are solved numerically using finite-volume techniques. Predicted variations with time of the volume flow rates and the flow patterns are presented for several values of pressure drops. It has been shown that a start-up flow can pass through different regimes (or different flow direction) before asymptotically reaching steady state distribution.