摘要:

AbstractThe distribution of the first‐passage time is of decisive importance in lift (elevator) design. It yields the easure of performance of the system, the expected number of stops, the interval (i. e. time elapsed between two successive departures from a given floor) and many other parameters and factors determining the required number of lifts in a building. The derivation is based on the transition probability matrix of the operation policy, and consists in solving a system of linear equation

ISSN:0029-5981    

DOI:10.1002/nme.1620150102

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractIt is sometimes convenient to express a numerical algorithm in terms of a network model. The physical picture given can often help the engineer to visualize the properties of the method. In field problems, a lumped network model corresponds to a space discrete field while a transmission‐line model corresponds to a field which is discrete in space and time. In this paper, the relationship is given between the lumped network models and transmission‐line network models used in the steady‐state solution of Maxwell's equations in two and three space dimensions. The use of dual networks is also discussed. An analysis is given for the velocity of waves travelling in any direction across the networks and this is used to compare the accuracy of the models. The use of diakoptics or substructures for the solution of large networks is outlined and this is illustrated by a compound two‐dimensional

ISSN:0029-5981    

DOI:10.1002/nme.1620150103

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractTransformation of dependent variables as, for example, the Kirchhoff transformation, is a classical tool for solving nonlinear partial differential equations. This approach is used here in connection with the finite element method and explained first in case of nonlinear heat conduction problems without phase change. The main applications of the method given in the paper concern a nonlinear degenerate parabolic equation for fluid flow through a porous medium and Stefan (moving boundary) problems.

ISSN:0029-5981    

DOI:10.1002/nme.1620150104

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA method is proposed for the study of growth, under normal internal pressure, of pre‐existing hydraulically induced planar cracks. The continuous growth process is approximated by a stepwise one, and during each growth step the volume of fluid within the crack cavity is assumed constant. The normal distance through which each point on the crack edge moves outwards is controlled by the level of stress intensity factorKIat each point, and the crack‐resistance characteristics of the material, which can be expressed by some critical level ofKI, denoted byKIC. For the present study, that distance was assumed proportional to (KI−KIC)4forKI>KIC. The evaluation ofKIat the crack edge is achieved by utilizing the method discussed by Mastrojanniset al.1The proposed method was applied to the study of the initial stage of growth of a circular crack under linearly varying normal pressure, and of an elliptical crack under uniform normal pre

ISSN:0029-5981    

DOI:10.1002/nme.1620150105

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractFourier analysis of numerical accuracy has traditionally concentrated on the propagation behaviour of various methods. When systems of equations in more than one unknown are involved, analysis of propagation accuracy alone is shown to be incomplete. A distribution factor is introduced to complement the Fourier analysis in these cases, and application of the concept to two problems commonly encountered in the water resources field is demonstrated. The distribution factor is shown to provide important information which cannot be obtained from the customary analysis of propagation accuracy.

ISSN:0029-5981    

DOI:10.1002/nme.1620150106

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractAn analysis of axisymmetric free jet impingement on to finite disks was performed using the finite element method. The method employed the velocity potential as the dependent variable and six‐node triangle elements to represent the region of flow. The analysis was divided into three parts corresponding to three distinct regions of the flow: (1) In the disk region, the free jet impinged on to a finite disk which was oriented normal to the flow. The jet was subjected to zero or normal gravity and to surface tension effects of varying degrees. (2) Upon leaving the disk region, the jet entered the plume region where it was acted upon internally by surface tension and externally by zero or normal gravity. (3) In the collision region, the flow from the plume region collided symmetrically at some downstream area about the axis of symmetry. The major result achieved from this investigation was the development of techniques to locate the free surface in all three regions for a range of conditions. The velocity profiles along selected lines of constant values of the potential were determined, and a successful comparison was made between the numerical results and existing experimental dat

ISSN:0029-5981    

DOI:10.1002/nme.1620150107

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThis paper presents a general procedure for calculating the buckling of stiffened skew plates by the Rayleigh‐Ritz method withB‐spline functions as co‐ordinate functions.Convergence of the solutions is investigated in a few typical cases and is found satisfactory. The results are compared with existing values based on other numerical methods and found to be in good agreement. Buckling characteristics of stiffened skew plates are also studies with varying stiffness parameters of stiffeners, skew angles and aspect r

ISSN:0029-5981    

DOI:10.1002/nme.1620150108

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractEfficient solution of boundary value problems for time‐dependent inelastic deformation in metallic structures is of great practical importance. These problems are generally solved by finite element methods and separate descriptions for time‐independent plasticity and time‐dependent creep are normally used. The boundary–integral equation method was recently applied for the first time to such problems. This paper presents a very efficient numerical implementation of the method with a linear description of the relevant variables over each boundary element and a newly developed Euler‐type time‐integration scheme with automatic time‐step control for time integration. Numerical results for plates in plane stress with and without cutouts, under different loading histories, are presented. A combined creep–plasticity constitutive theory with state variables is used to model material behaviour. The results are more accurate and are obtained with much less computational effort compared to a previous attempt with an uniform description of variables over each boundary element and a predictor–corrector scheme for time integration. The computer program developed is quite general and can handle plane stress problems for plates of arbitrary shapes subjected to arbitrary time‐histories of loadings. The numerical results presented in the paper are for certain il

ISSN:0029-5981    

DOI:10.1002/nme.1620150109

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThis paper describes the essential features of the program package MAGGY2. With MAGGY2, magnetostatic problems in two dimensions can be analysed. The co‐ordinate system may be Cartesian, cylindrical or polar. A finite element method with bilinear isoparametric quadrilaterals is used. Input must be given in the problem‐oriented language MAGLAN. This language is based on the idea that a user of MAGGY2 wants to describe his problem rather than give commands for its solution. The algorithm and the problem‐oriented language are described. Some examples showing the use of the package are

ISSN:0029-5981    

DOI:10.1002/nme.1620150110

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractUpwind and central difference schemes for laminar and turbulent flows over a step in a two‐dimensional channel are compared with each other and with experiment. Vorticity ω and stream function ψ are used as dependent variables and it is shown that an upwind difference method can give predictions which agree with experiment for high Reynolds number flows. The numerical implementation of the boundary conditions is found critically to determine the solutions obtained. Explicit prescription of ψ and ω at the inlet leads to incorrect values of the inlet velocity component perpendicular to the flow and a solution that does not agree with experiment. Experimental evidence is not available at low Reynolds numbers, but it is found that upwind differences give recirculation zones 8 per cent shorter and 8 per cent less intense than the more conventional conditionally stable central difference method.The distribution of the false diffusion effect in the upwind scheme is considered, and it is shown by use of a simple example that previous statements as to possible minimization of this effect are not generally true.The difficulty of determining the pressure distribution from the vorticity and stream function model is analysed and illustrated.Further, turbulent separated flows are seen to contain regions where two‐dimensional time‐dependent flow does not exist, and conventional theories do not give goo

ISSN:0029-5981    

DOI:10.1002/nme.1620150111

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY