A Study in Equipment Replacement

A Study in optimum replacement of fork lift trucks is described, using two models. The first is related to minimum average costs per truck per year, the second uses the approach of discounted cash flow. The parameters used in these models include the purchase price, the resale value and the maintenance costs of the equipment. The effect of capital allowances for tax purposes is included.     

An Equipment Replacement Problem

This paper describes a study undertaken to develop a model for the replacement of a particular type of machine. The dominant operating costs are identified, and existing replacement models reviewed. One of the most important factors is the cost of production stoppages which can sometimes result from the breakdown of these machines. In order to predict the effects of this in terms of the machines' age, a simulation model is developed.The results from the replacement model are investigated in terms of their sensitivity to the variability in the estimates of the parameters required by the model. In particular some interesting results relating the method used for calculating the resale values and the optimal replacement interval are presented.     

A Robust Replacement Model with Applications to Medical Equipment

Perceived shortcomings in the applicability of capital equipment replacement modelling, identified in a 1987 survey within the UK are addressed and a robust replacement model formulated. First, however, a comparison between the 1987 survey and a similar 1988 survey undertaken within the USA is made and explanations for apparent differences in conclusions are presented. A replacement model is then developed in the context of medical equipment where factors such as service and risk play a role in replacement decision-making. A mechanism for quantitatively allowing for qualitative and for political type factors within a short time horizon replacement model is introduced by means of a penalty factor. A case example is presented for medical ventilator equipment.     

一神非定常振荡流的稳定性分析

本文分析了一种非定常振荡的不稳定性问题.其特点是.应用偏微分方程特征理论以及O-S方程特征值的展开,求解扰动波的相函数而不是预先给定扰动波的波动形式.本文研究平面Poiseuille流与其垂向振荡流的组合流动系统.对于连续振荡源导致的波包演化,该系统存在不稳定性.     

Unsteady motion of a spheroid in an elastico-viscous liquid

In this paper we have considered the unsteady motion of a spheroid moving from rest in viscoelastic fluid. The paper has been divided into two sections. In Section A a general formula as well as approximate formula for the drag has been calculated. In Section B the expression for the velocity of the spheroid started from rest under the action of constant force has been investigated.     

Unsteady motion of a spheroid in an elastico-viscous liquid

In this paper we have considered the unsteady motion of a spheroid moving from rest in viscoelastic fluid. The paper has been divided into two sections. In Section A a general formula as well as approximate formula for the drag has been calculated. In Section B the expression for the velocity of the spheroid started from rest under the action of constant force has been investigated.

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Zusammenfassung In dieser Arbeit wird die nicht-stationäre Bewegung eines Spheroids von der Ruhe in einem viskoelastischen Fluid betrachtet. Die Arbeit ist in zwei Abschnitte geteilt. Im ersten Teil werden allgemeine Formeln sowie Näherungen für den Widerstand entwickelt. Im zweiten Abschnitt werden Ausdrücke für die Geschwindigkeit eines Speroids hergeleitet, welches von der Ruhe aus unter dem Einfluss einer konstanten Kraft sich bewegt.

     

Utilizing Weibull Failure Rates in Repair Limit Analysis for Equipment Replacement/Preventive Maintenance Decisions

Repair limit analysis was originally proposed as a methodology for determining whether to repair or to replace an operating unit. The approach structures the problem as a Markov or semi-Markov decision process in which state-dependent repair limits trigger the replacement decision. Such a basic framework can easily be applied to more general equipment repair/overhaul environments in which typical maintenance condition monitoring information can serve as the overhaul trigger. One unnecessary limitation of repair limit analysis found in the literature is the use of a constant force of mortality within each state of the model. The purpose of this paper is to extend the repair limit analysis by incorporating a changing force of mortality as the unit ages. In this way, the analysis is more flexible in the parameter estimation phase and it is argued here more appealing since a changing (and usually increasing) force of mortality is utilized in equipment maintenance environments.     

非牛顿流体在环管内的不定常旋转流

本文研究幂律非牛顿流体在环管内的不定常旋转流。该方程是一非线性方程,在部分因子的稳态近似假设之下,方程被线性化,用Laplace积分变换法我们获得了问题的解。文中给出了几组解曲线,它反映了角向速度的时间演化规律与空间分布特征。另外我们专门研究了幂律指数对流场的影响,该参数的敏感性具有一定的数值界限。这一结果,在有关的工程设计中具有重要的意义。     

On an Unconditionally Stable Scheme for the Unsteady Navier-Stokes Equations

Theoretical time step constraints of semi-implicit schemes are known to be more restrictive than should be in practice. We intend to alleviate the constraints with more smoothness assumptions on the solutions. By introducing a new scheme with modification on the treatment of the nonlinear term, we are able to prove that the scheme is unconditionally stable and convergent. Furthermore, we show that the modified scheme and the original semi-implicit one are equivalent under a weak condition on the time step and the number of space discretization points.     

Unsteady flow of an elastico-viscous fluid past a circular cylinder

Résumé Une solution numérique est obtenue pour l'écoulement initial d'un fluid élastique et visqueux autour d'un cylindre circulaire, à nombres de Reynolds 40 et 100. On emploi la méthode d'integration numérique de l'équation de tourbillon.     

突然开始旋转的圆盘上的三维非定常边界层

本文研究突然以常角速度ω开始旋转的圆盘上的三维非定常边界层.先求级数展开再用隐式差分把它延拓,得出了从ωt=0时的涡线扩散连续过渡到Kármán定常解的完整解答.最后给出了力矩系数c_M,来流速度w(∞),物面流线倾角随时间ωt的变化以及与实验点的比较.     

粘弹性流体流经作依赖时间运动伸展面的三维流动及其传质问题

研究粘弹性流体流经伸展面时的三维边界层流动．假定伸展面的运动速度依赖于时间．进一步考虑了更高阶次化学反应对传质的影响．应用同伦分析法(HAM)进行计算．精确地分析了所得级数解的收敛性．用图形讨论了各参数变化对速度和浓度的影响．还给出了面传质数值的计算,将所得结果与前人的数值解进行了比较．     

Unsteady Falkner-Skan flow

Zusammenfassung Mittels des Differenzenverfahrens wurden instationäre, laminare Grenzschichten längs eines Keiles (von verschiedenen Keilwinkeln ) gerechnet, der plötzlich aus der Ruhe herausbewegt wird. Es ist bemerkenswert, daß im Fall >0.6 die Grenzschicht an der betreffenden Stelle der Keilwand bereits vor der Ankunft der an der Vorderkante entstehenden Störungen fast stationär wird, und daß, wenn die -Zahl sich dem Wert –0.1988 nähert, es doch eine beträchtliche Zeit braucht vom Vorüberziehen dieser Störungen bis zum Erreichen des stationären Zustandes der Grenzschicht.