部分电极结构单极机的磁流体力学一维流动理论

本文提出了用待定电极壁边值并分区衔接的方法,完整地求解了环管中部分电极单极机的磁流体力学一维流动问题.做为两个特例,研究了环线电极和通常的全电极结构的单极机.对一些典型参数下的流场和感应磁场的分布进行了数值计算.与差分计算的结果比较,在数值和分布两方面都相当符合.着重研究了弥散效应及哈特曼边界层这些磁流体力学的特征现象,并用这些概念去讨论单极机的内部流动现象.结果表明,部分电极结构可以增加环管的流量,改善哈特曼边界层,控制二次流的发展.这些作用对具体的单极机应用有一定实用价值.     

高浓度氩气稀释气体爆轰波临界管径和临界间距关系

建立圆管及环形管道系统研究临近极限下爆轰波在管道内传播失效机理。选用C₂H₂+2.5O₂+70%Ar气体,采用光纤探针测量爆轰波在管道内传播速度,用烟迹法记录管道内爆轰波胞格结构。结果表明:初始压力远大于爆轰极限压力时,爆轰波在管道内以稳定速度传播;随着初始压力的减小,爆轰波速度逐渐降低;当初始压力一定时,爆轰波速度随着管道尺寸的减小而逐渐减小;当初始压力达到临界压力时,爆轰波在进入到管道内后其速度会逐渐衰减直至爆轰波完全失效。对于不同几何尺寸的圆管与环管,通过引入无量纲参数d/λ及w /λ(d为圆管管径,w为环管间距,λ为爆轰胞格尺寸)得出,爆轰波在管道内传播的临界圆管直径为环形间距的2倍,与理论模型结果相吻合,验证了稳态气体基于爆轰波波面曲率的失效机理。     

内管自转且公转时环管幂律流的受力分析

数值模拟了环管中内管偏心自转且公转时由轴向压力所驱动的幂律流体充分发展层流,分析了内管上的流体作用力。结果表明,内管偏心自转时流体作用力具有推动内管作和自转同向公转的效果。当只有外力矩驱动内管自转时,由于流体的作用,随内管线密度的不同,内管能达到的受力平衡态也不同:线密度较小时内管仅能在同心自转时达到受力平衡;线密度较大时内管能在作具有不变角速度和偏心率公转时达到受力平衡,且内管线密度越大,对应的受力平衡的公转的偏心率也越大。     

非均质油藏试井分析理论的研究进展

在明确了试井分析所用的油藏分类标准的基础上, 从油藏多孔介质的非均质性、油藏流体的非均质性、以及数学模型的解法和试井解释方法4个方面, 对非均质油藏的研究成果进行了概述, 归纳出了规则的非均质油藏和随机的非均质油藏的概念, 并分析了非均质油藏试井理论研究的发展趋势, 指出结合油田地质资料和油藏开发动态资料进行综合试井资料分析是试井理论发展的必然趋势, 数值试井方法是试井未来发展的方向.      

非完整系统力学的历史与现状

非完整系统力学是分析力学中的一个重要分支。"非完整"一词的法文是"non holonome",在我国也有人译为"不完整"、"非全定"。1788年法国学者Lagrange发表了名著《Mécanique Analytique》(分析力学),从而奠定了分析力学的基础。但在Lagrange时代,还不知道有独立坐标数目与坐标的独立变分数目不相同的系统--非完整约束系统的存在。直到1894年,德国学者Hertz...     

用无限相似单元法计算拱形试样的K_I和柔度

如图1所示的拱形三点弯曲试样易于从环管类构件上取样,试验也方便,因而是一种颇有实用意义的断裂韧度测试试样.陈篪等同志首先提出了这种试样,并用柔度法从实验标定获得了K_I 和BEC 数据.本工作报道拱形试样三点弯曲情况的K_I 和BEC及纯弯曲情况(图2)的K_I 计算结果.计算纯弯曲情况是为了用等效力系原理导出K_I 的一般表达式.文中K_I 均为无量纲形式K_I~*=(K_IBW~(3/2))/M,式中:B 为试样厚度;W=R_1-R_2为试样宽度;M 为裂纹平面上弯矩.     

梯度投影法的非概率可靠性应用研究

分析了现有结构可靠性设计中概率、非概率可靠性指标算法存在的问题,将概率可靠性中的梯度投影法运用到非概率可靠性中,提出了一种计算非概率可靠性指标的新方法并进行了数值实现,结果表明:该方法在变量较多、极限状态功能函数较复杂时,能够快速、准确地计算可靠性指标。在此基础上,将非概率可靠性指标与安全系数相结合,得出了两者之间的关系并进行了实例验证,结果表明:非概率可靠性指标与非概率安全系数用于评价结构可靠性时具有一致性,在结构的可靠性临界点处,非概率安全系数与非概率可靠性指标都近似等于1。     

喜读新著《非完整系统力学基础》

北京工业学院出版社出版的《非完整系统力学基础》(梅凤翔著)是一本系统的阐述分析力学的分支--非完整约束系统力学的好教材,读了这本书,受益不浅。一、是国内第一部《非完整系统力学》的教材。1788年拉格朗日发表了名著《分析力学》,从虚位移原理出发,用纯粹的数学分析方法处理力学问题,从...     

基于区间分析的结构非概率可靠性模型

本文用非概率的凸集模型模拟结构的不确定性,将结构的不确定参数描述为区间变量,基于区间分析,提出了一种新的非概率可靠性度量体系分析方法,从物理、几何意义等方面解释了文中理论的合理性,其计算方法简便,衫,给出了算例分析。     

结构的非概率安全系数方法和非概率可靠性方法的比较

对结构设计的非概率安全系数方法及非概率可靠性方法进行了比较研究,探讨了非概率安全系数与非概率可靠性指标的关系,从设计思想、度量方法及表现形式等方面分析了两种方法的区别,通过一个优化算例对两种方法进行了讨论.     

Transient viscoelastic helical flows in pipes of circular and annular cross-section

Start-up helical flows for Oldroyd-B and upper-convected Maxwell fluids are studied in straight pipes of circular and annular cross-section. The differential form of the constitutive equation leads to partial differential equations which are second-order in space and time. Apart from the condition that the fluid is initially at rest another initial condition is required to complete the solution process. By comparing results derived from the integral form of the constitutive equation we show that an appropriate initial condition may be found. Numerical results for start-up rotational flow in pipes of annular cross-section are presented.     

Analytical solution of flow of second-order non-Newtonian fluids through annular pipes

This paper presents an analytical solution to the unsteady flow of the second-order non-Newtonian fluids by the use of intergral transformation method.Based on the numerical results,the effect of non-Newtonian coefficient Hc and other parameters on the flow are analysed.It is shown that the annular flow has a shorter characteristic time than the general pipe flow while the correspondent velocity,average velocity have a(?)aller value for a given Hc.Else,when radii ratio keeps unchanged,the shear stress of inner wall of annular flow will change with the inner radius compared with the general pipe flow and is always smaller than that of the outer wall.     

Steady-state solutions for some simple flows of generalized Burgers fluids

The steady-state solutions for three types of unsteady oscillating flows of generalized Burgers fluids are determined by means of the Fourier sine transforms. These solutions are also presented in equivalent forms in terms of elementary functions exp, sine, cosine, hyperbolic sine and hyperbolic cosine. The similar solutions for Burgers, Oldroyd-B, Maxwell, Second grade and Navier-Stokes fluids can be also obtained as limiting cases of our solutions.     

Exact solutions for generalized Burgers’ fluid in an annular pipe

This paper deals with some unsteady unidirectional transient flows of generalized Burgers’ fluid in an annular pipe. Exact solutions of some unsteady flows of generalized Burgers’ fluid in an annular pipe are obtained by using Hankel transform and Laplace transform. The following two problems have been studied: (1) Poiseuille flow due to a constant pressure gradient; (2) axial Couette flow in a annulus. The well known solutions for Navier-Stokes fluid, as well as those corresponding to a Maxwell fluid, a second grade fluid and an Oldroyd-B fluid appear as limiting cases of our solutions.     

Analytical solutions for equations of unsteady flow of non-newtonian fluids in tube

This paper presents analytical solutions to the partial differential equations for unsteady flow of the second-order fluid and Maxwell fluid in tube by using the integral transform method. It can be used to analyse the behaviour of axial velocity and shear stress for unsteady flow of non-Newtonian visco-elastic fluids in tube, and to provide a theoretical base for the projection of pipe-line engineering.     

On viscoelastic effects in non-Newtonian steady flows through porous media

This paper presents a mathematical model for describing approximately the viscoelastic effects in non-Newtonian steady flows through a porous medium. The rheological behaviour of power law fluids is considered in the Maxwell model of elastic behaviour of the fluids. The equations governing the steady flow through porous media are derived and an analytical solution of these equations in the case of a simple flow system is obtained. The conditions for which the viscoelastic effects may become observable from the pressure distribution measurements are shown and expressed in terms of some dimensionless groups. These have been found to be relevant in the evaluation of viscoelastic effects in the steady flow through porous media.     

Analytic solutions of Newtonian and non-Newtonian pipe flows subject to a general time-dependent pressure gradient

This article is concerned with general analytic solutions of flows in cylindrical and annular pipes subject to an arbitrary time-dependent pressure gradient and arbitrary steady initial flow. The fluids considered are Newtonian, Maxwellian and Oldroyd B. Graphical results for (blood) flow in a dog’s femoral artery are presented.     

A note on the unsteady flow of a fractional Maxwell fluid through a circular cylinder

In this note the velocity field and the adequate shear stress corresponding to the unsteady flow of a fractional Maxwell fluid due to a constantly accelerating circular cylinder have been determined by means of the Laplace and finite Hankel transforms.The obtained solutions satisfy all imposed initial and boundary conditions.They can easily be reduced to give similar solutions for ordinary Maxwell and Newtonian fluids.Finally,the influence of pertinent parameters on the fluid motion,as well as a comparison between models,is underlined by graphical illustrations.     

A pressure-smoothing scheme for incompressible flow problems

A pressure-smoothing scheme for Stokes and Navier–Stokes flows of Newtonian fluids and for Stokes flow of Maxwell fluids is described. The stress deviator obtained from the calculated velocity field is substituted into the governing equilibrium equation. The resulting equation is then solved to obtain a new, smoothed pressure by a least square finite element method.     

Unsteady flow of viscoelastic fluid between two cylinders using fractional Maxwell model

The unsteady flow of an incompressible fractional Maxwell fluid between two infinite coaxial cylinders is studied by means of integral transforms.The motion of the fluid is due to the inner cylinder that applies a time dependent torsional shear to the fluid.The exact solutions for velocity and shear stress are presented in series form in terms of some generalized functions.They can easily be particularized to give similar solutions for Maxwell and Newtonian fluids.Finally,the influence of pertinent parameters on the fluid motion,as well as a comparison between models,is highlighted by graphical illustrations.