STOKES FLOW THROUGH A SYSTEM OF PARALLEL INFINITE CYLINDERS WITH AXES ORIENTED AT AN ANGLE TO THE DIRECTION Of MEAN FLOW

Theoretical models based on Stokes flow of air through a fibrous filter predict a significantly higher pressure drop than experimentally measured values. This discrepancy persists even when the interaction of the flow between) neighboring fibers is accounted for. Various authors have attributed this discrepancy to the inhomogeneity of the fiber distribution within the filter and to the possibility that some fibers are partially orientation in the directon of mean flow. It has been shown that fiber density inhomogeneity does indeed contribute to this discrepancy

In this paper, the effect on the flow and subsequent pressure drop when the fibers are oriented at an angle to the directon of mean flow is studied. The solution of the three dimensional equation for creeping, incompressible flow in a doubly periodic, infinite lattice of infinite circular cylinders when there is a constant mean flow whose direction makes an acute angle with the axes of the cylinders is given. If the volume fraction of fibers is small, the periodic boundary conditions can be replaced by requiring zero vorticity at the outer boundary of an imagined cylindrical cell of fluid surrounding one of the cylinders. The resulting parallel and transverse problems have known solutions and give an approximate solution to the flow through the periodic lattice. The resulting drag is used to compute the dimensionless pressure drop across a filter for several values of the volume fraction of fiber and is compared to the experimentally determined formula of Davies. It is shown that the average drag over a uniform distribution of fiber orientations yields a pressure drop which is significantly closer to the experimental values of Davies than that resulting from strictly transverse flow.     

一般支撑条件下横向流中弹性圆柱的响应

该文以横向流方形圆柱阵中的单根、两端带有一般支撑条件圆柱的流致振动现象进行研究。考虑圆柱的横向变形及其对轴力的影响,建立了系统动力学方程。分析了系统的稳定性及在不同流速条件下出现的复杂非线性行为,该文以分岔图、相平面图、庞加莱映射图来刻画流速变化对圆柱振动的影响。研究结果表明,系统的初始预应力,降低了圆柱的稳定性;当流速较小时,系统首先表现为周期运动;随着流速增大,系统进入概周期运动,该系统未发生混沌运动。     

小流量涡流管热端加湿制冷系统实验研究

本文针对一种小流量涡流管加湿制冷系统进行了实验研究,得出了涡流管制冷系统不同入口压力下无加湿系统和有加湿系统的绝热效率曲线,指出需要解决的关键技术问题.实验表明,有加湿系统可以大大提高涡流管的绝热效率.     

振动场作用下聚合物熔体在异型材挤出口模内的充填流动分析

利用ANSYS软件对受口模入口处周期性振动的压力驱动的非牛顿幂律聚合物熔体在“L”形异型材挤出口模内的充填流动进行了三维等温数值模拟,求得了压力和速度随时间和沿路径的变化曲线,并因此总结出了振动参数对充填流动的影响规律.结果表明,速度和压力的振动均沿挤出方向逐渐衰减,入口压力的低频高幅振动有利于充填过程的稳定.     

THE CRITERION FOR THE OPTIMAL SOLUTION OF AN INVENTORY SYSTEM WITH A NEGATIVE EXPONENTIAL CRASHING COST

In a recent paper, Ben-Daya and Raouf presented a continuous review inventory model in which they considered both lead time and order quantity as decision variables where the total crashing cost is denoted by a negative exponential function of the lead time. However, the solution procedure of Ben-Daya and Raouf has some drawbacks sometimes. The Newton-Raphson method with an appropriate starting point is used to improve that of Ben-Daya and Raouf. Numerical examples illustrate how the Newton-Raphson method works.     

A METHOD TO MEASURE ELECTROCHEMICAL POTENTIAL AT THE TIP OF A GROWING CRACK DURING AN ENVIRONMENTAL FATIGUE TEST

Abstract— Electrochemical potential at the tip of a fatigue crack was measured in a compact tension specimen, situated in demineralized, oxygen saturated water at 93°C.
Results show that the crack tip region is active with respect to the external specimen surface. Passivation occurs on the crack surfaces by the formation of an oxide layer. The oxygen concentration inside the crack is likely to be lower than in the bulk solution.     

A FINITE ELEMENT TECHNIQUE TO SIMULATE THE STABLE SHAPE EVOLUTION OF PLANAR CRACKS WITH AN APPLICATION TO A SEMI-ELLIPTICAL SURFACE CRACK IN A BIMATERIAL FINITE SOLID

This paper describes a numerical procedure to model the crack front evolution of initially arbitrary shaped planar cracks in a three-dimensional solid. The influence of a bimaterial interface on the fracture path of a semi-elliptical surface crack in a three-dimensional structure is examined. The analysis is based on the assumption that fracture is controlled by small-scale yielding and linear elastic fracture mechanics. The finite element method and the crack-tip contour J-integral in a volume domain representation are utilized to calculate the crack front energy release rate. The computed values of the energy release rate are used with a crack-tip velocity growth law to model crack growth increment. The progress of the crack growth evolution is brought forward by successive iterations. Examples of computed crack evolution are given for an embedded circular crack, a semi-elliptical surface crack in a finite plate, and a configuration that defines an isotropic homogeneous material layer with a surface crack located between two material layers. © 1997 by John Wiley & Sons, Ltd.